This PDF file contains the front matter associated with SPIE Proceedings Volume 7984, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

This work focuses on an analysis of wave propagation in isogrid structures as it relates to Structural Health Monitoring (SHM) methods. Assembly, integration, and testing (AI&T) of satellite structures in preparation for launch includes significant time for testing and reworking any issues that may arise. SHM methods are being investigated as a means to validate the structure during assembly and truncate the number of tests needed to qualify the structure for the launch environment. The most promising of these SHM methods uses an active wave-based method in which an actuator propagates a Lamb wave through the structure; the Lamb wave is then received by a sensor and evaluated over time to detect structural changes. To date this method has proven effective in locating structural defects in a complex satellite panel; however, the attributes associated with the first wave arrival change significantly as the wave travels through ribs and joining features. Previous studies have been conducted in simplified ribbed structures, giving initial insight into the complex wave propagation phenomena. In this work, the study has been extended numerically to the isogrid plate case. Wave propagation was modeled using commercial finite element analysis software. The results of the analyses offer further insight into the complexities of wave propagation in isogrid structures.

Aerospace structures contain multi-layered components connected by fasteners, where fatigue cracks and disbonds or localized lack of sealant can develop due to cyclic loading conditions and stress concentration. High frequency guided waves propagating along such a structure allow for the efficient non-destructive testing of large components, such as aircraft wings. The type of multi-layered model structure investigated in this contribution consists of two aluminium plates adhesively bonded with an epoxy based sealant layer. Using commercially available transducer equipment, specific high frequency guided ultrasonic wave modes that penetrate through the complete thickness of the structure were excited. The wave propagation along the structure was measured experimentally using a laser interferometer. Two types of hidden damage were considered: a localized lack of sealant and small surface defects in the metallic layer facing the sealant. The detection sensitivity using standard pulse-echo measurement equipment has been quantified and the detection of small hidden defects from significant stand-off distances has been shown. Fatigue experiments were carried out and the potential of high frequency guided waves for the monitoring of fatigue crack growth at a fastener hole during cyclic loading was discussed.

In this study, a new damage detection technique is developed so that delamination in a multilayer composite plate can be detected by comparing multi-path pitch-catch Lamb wave signals in a piezoelectric transducer network rather than by comparing each signal with its corresponding baseline signal obtained from the pristine condition. The development of the proposed technique is based on the premise that the fundamental anti-symmetric mode (A0) slows down when it passes through a delamination area while the speed of the fundamental symmetric mode (S0) is invariant. First, the delay of the A0 mode in each path is used as a delamination sensitive feature and extracted using a proposed mode extraction technique. This mode extraction technique uses dual piezoelectric transducers composed of a concentric ring and circular piezoelectric transducers, and it is capable of isolating the A0 mode in any desired frequency without frequency or transducer size tuning. Once the time delays of the A0 mode are computed for all pitch-catch paths in the transducer network, an instantaneous outlier analysis is performed on these features to identify wave propagation path(s) affected by the delaminated region(s). Because the time delays of the A0 mode are instantaneously computed from existing multiple paths, it has been demonstrated that robust delamination detection can be achieved even under varying temperature conditions.

In this paper, a Structural Health Monitoring (SHM) strategy is proposed in order to detect interlaminar delamination in a Carbon Fiber Reinforced Polymer (CFRP) structure using guided waves. The delamination is simulated by inserting a Teflon tape between two transverse plies and the guided wave generation and measurement is ensured by piezoceramic (PZT) elements. Theoretical propagation and through-the-thickness strain distribution are first studied in order to determine the optimal configuration of the final system in terms of mode and frequency selection and piezoceramic spacing for detection of cross-sectional delamination. Finite element simulation are then used to validate the assumptions and pitch and catch measurements are performed by comparing wave propagation for different frequencies and along damaged and undamaged paths and the analysis of results is performed using Reassigned Short-Time Fourier Transform (ReSTFT). It appears that in the low frequency range (below 300 kHz), A0 mode is sensitive to the damage while in the high frequency range, S 1 and A1 modes are both very sensitive to the damage while the propagation of the S 0 mode is not much affected.

Piezoelectric fiber composite (PFC) transducers can be used to transmit and receive ultrasonic guided waves for structural health monitoring. Comb-type surface mounted PFC transducer strips are used to excite planar Lamb waves that interact with cracks and corrosion in a plate. Both finite element simulations and experiments examine the wave/defect interaction within a square domain that could be bounded by four strip transducers. In addition to transmitted, reflected, and scattered wave energy, beam spreading is investigated. Boundary conditions are applied in the finite element simulation to eliminate artificial end wall reflections. The experiments use a Doppler laser vibrometer to visualize wave propagation. Parallel PFC strips at wavelength spacing comprise an actuator that generates a wave field that is imaged by the scanning vibrometer. The results of the finite element simulation are qualitatively confirmed by the experiments.

Structural Health Monitoring (SHM) based on Lamb waves, a type of ultrasonic guided waves, is a promising method for in-service inspection of composite structures. In this study mode selective actuators are developed to excite a particular Lamb wave mode in composite plates. Different manufacturing technologies based on monolithic piezoceramics with applied interdigitated electrodes and piezocomposites are described. A mode selective actuator is designed and optimized. Finite element modeling and experimental tests on quasi-isotropic composite plates are performed in order to characterize the mode selectivity of the actuators.

Plate-like aerospace engineering structures are prone to mechanical/residual load during flight operation. The mechanical/residual prestresses can cause significant changes in guided-wave (GW) propagation for structural health monitoring (SHM) systems. The paper focuses on the characterization of the GW propagation using surfacebonded piezoelectric wafer actuators in metallic spacecraft plates under prestresses. First, a new in-plane analytical model with coupled piezo-elastodynamics is proposed to quantitatively capture the dynamic load transfer between a thin piezoelectric actuator bonded onto an isotropic plate that is subject to prestresses. Based on the developed model, effects of prestresses on the GW propagation generated by piezoelectric actuators are then analyzed and demonstrated. It can be found that the both time-of-flight and amplitude of wave responses can be affected by the presence of prestresses in plates. The results hopefully provide useful information for the real-time SHM.

Piezoelectric sensors that are embedded in large structures and are inter-connected as a sensor network can provide critical information regarding the integrity of the structures being monitored. A viable data communication scheme for sensor networks is needed to ensure effective transmission of messages regarding the structural heath conditions from sensor nodes to the central processing unit. In this paper we develop a time reversal based data communication scheme that utilizes guided elastic waves for structural health monitoring applications. Unlike conventional data communication technologies that use electromagnetic radio waves or acoustical waves, the proposed method utilize elastic waves as message carriers and steel pipes as transmission channels. However, the multi-modal and dispersive characteristics of guided waves make it difficult to interpret the channel responses or to transfer correctly the structural information data along pipes. In this paper, we present the basic principles of the proposed time reversal based pulse position modulation and demonstrate by simulation that this method can effectively overcome channel dispersion, achieve synchronization, and delivery information bits through steels pipes or pipe-like structures correctly.

Embedded sensors in large civil structures for structural health monitoring applications require data communication capabilities between sensor nodes. Conventional communication modalities include electromagnetic waves or acoustical waves. However, ultrasonic guided elastic waves that can propagate on solid structures such as pipes for a great distance have rarely been studied for data communication purposes. The multi-modal and dispersive characteristics of guided waves make it difficult to interpret the channel responses and to transfer useful information along pipes. Time reversal is an adaptive transmission method that can improve the spatial and temporal wave focusing. Based on the focusing effect of time reversal, we have developed a data communication technique using guided waves in a highly dispersive pipe environment. In this paper, we experimentally demonstrate the data communication using time reversal pulse position modulation (TR-PPM). Three-step laboratory tests have been performed using piezoelectric transducers in a pitch-catch mode. We first measure the channel responses between the transmitter and the receiver on a pipe. We then carry out the time reversal transmission by reversing the sounding signal and feeding it back to the same channel. Finally, we perform the time reversal communication experiment by sending the modulated time reversal signals as a stream of binary bits at a given data rate. A series of experiments are conducted on steel pipes. Experimental results demonstrate that time reversal pulse position modulation for data communications can be achieved successfully using guided elastic waves.

With the vastness of existing railroad infrastructure, there exist numerous road crossings which are lacking warning light systems and/or crossing gates due to their remoteness from existing electrical infrastructure. Along with lacking warning light systems, these areas also tend to lack distributed sensor networks used for railroad track health monitoring applications. With the power consumption required by these systems being minimal, extending electrical infrastructure into these areas would not be an economical use of resources. This motivated the development of an energy harvesting solution for remote railroad deployment. This paper describes a computer simulation created to validate experimental on-track results for different mechanical prototypes designed for harvesting mechanical power from passing railcar traffic. Using the Winkler model for beam deflection as its basis, the simulation determines the maximum power potential for each type of prototype for various railcar loads and speeds. Along with calculating the maximum power potential of a single device, the simulation also calculates the optimal number and position of the devices needed to power a standard railroad crossing light signal. A control system was also designed to regulate power to a battery, monitor and record power production, and make adjustments to the duty cycle of the crossing lights accordingly. On-track test results are compared and contrasted with results from the simulation, discrepancies between the two are examined and explained, and conclusions are drawn regarding suitability of the device for powering high-efficiency LED lights at railroad crossings and powering track-health sensor networks.

This paper describes a method based on Guided Ultrasonic Waves for the structural health monitoring of sign support structures. The general framework presented in this paper is applied to ultrasonic data collected from an overhead sign structure removed from service, and tested at the University of Pittsburgh under varying environmental conditions. The probing hardware consisted of a National Instruments-PXI platform that controlled the generation and detection of the ultrasonic signals by means of piezoelectric transducers. The effectiveness of the proposed approach to detect damage under large temperature variations and dry/wet/snowy conditions is demonstrated. Finally, the same hardware / algorithm system was applied for the health monitoring of two structures deployed in the Pittsburgh (Pennsylvania) area.

In this study, the feasibility of monitoring the structural integrity of welded thick aluminum plates was experimentally tested using two widely used SHM methods: impedance and Lamb wave analyses. The test structure was fabricated from two 1/4 inch thick aluminum plates welded together, and various structural defects, such as holes and cuts, were applied. At each of these damage steps, data were collected for both the impedance and Lamb wave techniques. Results consistently revealed the impedance method to be sensitive to damage in and through the weld. The envelopes of the Lamb wave signals were calculated using the S-transformation of the time histories. There was significant change to the curves when different defects were added to the plate. Both of the SHM methods studied detected each of the cuts and holes acting to reduce the overall strength of the structure. Each technique also detected the hole damage on the opposite side of the weld as the sensor(s) used for damage detection. The study further verified that surface waves move across welds allowing SHM methods to detect the defects even if the sensors are located on neighboring plates or geometries.

In cylindrical structures such as pipelines, cracks are more likely to occur along the longitudinal (axial) direction and they are usually fatal to the serviceability of the structures. Unfortunately, the conventional ultrasonic crack detection methods are not very sensitive to this type of cracks. This paper focuses on using piezoelectric macro-fiber composite (MFC) to generate torsional wave for health monitoring of cylindrical structures. Numerical simulations are performed using ANSYS. Nodal release method is used to model the crack. Experimental verifications are also presented. Four pieces of MFC oriented at 45° against the axis of the specimen are used to generate both longitudinal wave and torsional wave. The numerical results and the experimental results show that the axial-direction crack propagation in cylindrical structures can be well monitored using the presented wave propagation approach.

In a structure, damage can occur at several scales from micro-cracking to corrosion or loose bolts. This makes the identification of damage difficult with one scale of sensing. Hence, a multi-scale actuated sensing system is proposed based on a self-sensing circuit using a piezoelectric sensor. In the self sensing-based multi-scale actuated sensing, one scale provides a wide frequency-band structural response from the self-sensed impedance measurement and the other scale provides a specific frequency-induced structural wavelet response from the self-sensed guided wave measurement. In this study, an experimental study using the pipeline system under a water flow-operation is carried out to verify the effectiveness and the robustness of the proposed structural health monitoring approach. Different types of structural damage are artificially inflicted on the pipeline system. To classify the multiple types of structural damage, a supervised learning-based statistical pattern recognition is implemented by composing a three-dimensional space using the damage indices extracted from the impedance and guided wave features as well as temperature variation. For more systematic damage classification, several control parameters to determine an optimal decision boundary for the supervised learningbased pattern recognition are optimized. Finally, further research issues will be discussed for real-world implementation of the proposed approach.

Guided wave imaging has shown great potential for structural health monitoring applications by providing a way to visualize and characterize structural damage. For successful implementation of delay-and-sum and other elliptical imaging algorithms employing guided ultrasonic waves, some degree of mode purity is required because echoes from undesired modes cause imaging artifacts that obscure damage. But it is also desirable to utilize multiple modes because different modes may exhibit increased sensitivity to different types and orientations of defects. The well-known modetuning effect can be employed to use the same PZT transducers for generating and receiving multiple modes by exciting the transducers with narrowband tone bursts at different frequencies. However, this process is inconvenient and timeconsuming, particularly if extensive signal averaging is required to achieve a satisfactory signal-to-noise ratio. In addition, both acquisition time and data storage requirements may be prohibitive if signals from many narrowband tone burst excitations are measured. In this paper, we utilize a chirp excitation to excite PZT transducers over a broad frequency range to acquire multi-modal data with a single transmission, which can significantly reduce both the measurement time and the quantity of data. Each received signal from a chirp excitation is post-processed to obtain multiple signals corresponding to different narrowband frequency ranges. Narrowband signals with the best mode purity and echo shape are selected and then used to generate multiple images of damage in a target structure. The efficacy of the proposed technique is demonstrated experimentally using an aluminum plate instrumented with a spatially distributed array of piezoelectric sensors and with simulated damage.

Guided waves are being considered for structural health monitoring (SHM) applications, and they can also be used to reduce subsequent inspection times once defects are detected. One proposed SHM method is to use an array of permanently attached piezoelectric transducers to generate and receive guided waves between the various transducer pairs. The interrogation can be done on a continuous or periodic basis to assess the health of the structure. Once defects are suspected in the structure, the traditional approach is to disassemble components for conventional nondestructive evaluation (NDE); however, this is an expensive and time consuming process. A less expensive alternative to conventional NDE is to record acoustic wavefield images of guided waves generated from the attached transducers. These images clearly show details of guided waves as they propagate outward from the source, reflect from structural discontinuities and specimen boundaries, and scatter from any damage sites within the structure. However, the recorded waves are typically narrowband to enable effective visualization of echoes that are relatively compact in time. In this paper, we consider wavefield images that are recorded from a chirp excitation, which offers the advantage of high quality broadband data from a single excitation. However, responses are not directly useful because the received echoes are too extended in time. Signals are post-processed to obtain multiple narrowband and broadband responses containing echoes that are more compact in time to enable visualization of guided waves interacting with structural features. This technique is demonstrated on an aluminum plate that contains attached stiffeners and glued-on piezoelectric disc transducers. Wavefield data are recorded using an air-coupled transducer scanned over the plate surface while one of the attached transducers acts as a guided wave source. Waves interacting with the stiffener and the inactive discs are analyzed via broadband and narrowband processing at multiple frequencies.

This research investigates the feasibility of measuring acoustic nonlinearity in aluminum with different ultrasonic guided wave modes. Acoustic nonlinearity is manifested by generation of a second harmonic component in an originally monochromatic ultrasonic wave signal, and previous research has shown this correlates to an intrinsic material property. This parameter has been shown to increase with accumulated material damage - specifically in low- and high-cycle fatigue - prior to crack initiation, whereas other ultrasonic nondestructive evaluation (NDE) techniques measuring linear parameters are unable to detect damage prior to crack initiation. In structural components such as jet engines and aircraft structures subjected to fatigue damage, crack initiation does not occur until ~80% of a component's life. Thus, there is a need for structural health monitoring (SHM) techniques that can characterize material damage state prior to crack initiation, and therefore nonlinear ultrasonic techniques have the potential to be powerful NDE and SHM tools. Experimental results using Rayleigh and Lamb guided wave modes to measure acoustic nonlinearity in undamaged aluminum 6061 samples are presented, and a comparison of the efficiency of these modes to measure acoustic nonlinearity is given.

Materials State Awareness (MSA) goes beyond traditional NDE and SHM in its challenge to characterize the current state of material damage before the onset of macro-damage such as cracks. A highly reliable, minimally invasive system for MSA of Aerospace Structures, Naval structures as well as next generation space systems is critically needed. Development of such a system will require a reliable SHM system that can detect the onset of damage well before the flaw grows to a critical size. Therefore, it is important to develop an integrated SHM system that not only detects macroscale damages in the structures but also provides an early indication of flaw precursors and microdamages. The early warning for flaw precursors and their evolution provided by an SHM system can then be used to define remedial strategies before the structural damage leads to failure, and significantly improve the safety and reliability of the structures. Thus, in this article a preliminary concept of developing the Hybrid Distributed Sensor Network Integrated with Self-learning Symbiotic Diagnostic Algorithms and Models to accurately and reliably detect the precursors to damages that occur to the structure are discussed. Experiments conducted in a laboratory environment shows potential of the proposed technique.

Pre-launch testing of space vehicles is a complex process taking weeks if not months to accomplish. An onboard structural health monitoring system is considered for reduction of testing time and component validation. The active elements of the system, embedded sensors, are used to transmit and receive elastic waves carrying information on component characteristics and structural integrity. Parameters of the elastic wave recorded with embedded sensors are investigated using several measurement methods coupled with temporal analysis of elastic wave signatures. In particular, attention is given to temporal distribution of signal phase and nonlinear effects. Specimens of simple and complex geometry incorporating defects typical to space structures are considered in experimental studies. Local measurements with a single sensor as well as global assessment of structural components with a sensor network were explored for damage detection, characterization, and location. Proposed diagnostic approaches were validated on a realistic satellite panel with isogrid reinforcement. Conclusions are presented on sensing capabilities of active sensors and effectiveness of the associated signal analysis.

Mode and frequency control always plays an important role in ultrasonic guided wave applications. In this paper, theoretical understanding of guided wave excitations of axisymmetric sources on plate structures is established. It is shown that a wave number spectrum can be used to investigate the guided wave excitations of an axisymmetric source. The wave number spectrum is calculated from a Hankel transform of the axial source loading profile. On the basis of the theoretical understanding, phased annular array transducers are developed as a powerful tool for guided wave mode and frequency control. By applying appropriate time delays to phase the multiple elements of an annular array transducer, guided wave mode and frequency tuning can be achieved fully electronically. The phased annular array transducers have been successfully used for various applications. Example applications presented in this paper include phased annular arrays for guided wave beamforming and a novel ultrasonic vibration modal analysis technique for damage detection.

Localized and distributed guided ultrasonic wave array systems allow for the efficient structural health monitoring of large structures, such as aircraft, ship hulls, or oil storage tanks. Permanently attached sensor arrays have been applied for the detection of corrosion and fatigue damage. A hybrid model has been developed for the efficient prediction of the sensitivity of guided waves array systems to detect through thickness and part-through fatigue cracks at different locations in plate structures. Using a point transmitter and receiver model for the wave propagation along the structure, the distances between sensor elements and potential defect locations are taken into account. The influence of the orientation of the crack relative to the transducer elements has been predicted from localized 3D Finite Element simulations. The directivity pattern of the scattered guided wave field has been shown to depend on the defect orientation and on the ratio of the characteristic defect size and depth to wavelength, and has been verified from experimental measurements. Good agreement was found and the localized amplitude and directivity patterns provide the basis for the quantification of the detection sensitivity for fatigue cracks. Using a hybrid model, the relative amplitudes of received pulses for different sensor array layouts can be calculated. From a comparison with the signal to noise ratio of the array system, detection capabilities can be predicted for various defect sizes and orientation. This provides a rapid tool for the development and optimization of guided wave array SHM systems.

In the present paper, a technique called Excitelet is presented for the imaging of damages in thin-walled structures using the correlation of the measured signals with dispersed versions of the excitation signal. Piezoceramic (PZT) actuators are used to generate burst Lamb waves which interact with defects in metallic structures and the measurement is taken using sparse and compact array configurations of PZT sensors. The sparse sensing configuration consists of individual circular PZT elements distributed over the plate while the compact array configuration consists of a linear arrangement of sensors micro-machined on a single piece of bulk PZT wafer. This approach is presented as an extension of the classical imaging techniques and takes advantage of the chirplet-based matching pursuit algorithm. The approach is investigated experimentally on a 1.54 mm thick aluminum plate and comparison with existing Embedded Ultrasonic Structural Radar (EUSR) algorithm is performed for A0 and S0 modes for two frequency ranges of interest (centered at 150 kHz and 550 kHz). Damages are simulated using stacked magnets at different locations on the plate. Significant improvement of imaging quality is demonstrated with respect to existing imaging techniques based on group velocity and Time-of-Flight (ToF), for both sparse and compact PZT array configurations. Multimodal imaging strategies are presented to improve the imaging results. Moreover, it is shown that the proposed imaging technique provide accurate results in the case of dispersive propagation, while existing imaging techniques are no longer applicable.

A novel hyper-elastic thin film nitinol (HE-TFN) covered stent has been developed to promote aneurysm quiescence by diminishing flow across the aneurysm's neck. Laboratory aneurysm models were used to assess the flow changes produced by stents covered with different patterns of HE-TFN. The flow diverters were constructed by covering Wingspan stents (Boston Scientific) with HE-TFNs (i.e., 82 and 77% porosity) and deployed in both in vitro wide-neck and fusiform glass aneurysm models. In wide-neck aneurysms, the 82% porous HE-TFN stent reduced mean flow velocity in the middle of the sac by 86.42±0.5%, while a 77% porous stent reduced the velocity by 93.44±4.99% (n=3). Local wall shear rates were also significantly reduced by about 98% in this model after device placement. Tests conducted on the fusiform aneurysm revealed smaller intra-aneurysmal flow velocity reduction to 48.96±2.9% for 82% porous and to 59.2±6.9% for 77% porous stent, respectively. The wall shear was reduced by approximately 50% by HE-TFN stents in fusiform models. These results suggest that HE-TFN covered stents have potential to promote thrombosis in both wide-necked and fusiform aneurysm sacs.

Standard techniques for the analysis of biological tissues like immunohistochemical staining are typically invasive and lead to mortification of cells. Non-invasive monitoring is an important element of regenerative medicine because implants and components of implants should be 100% quality-checked with non-invasive and therefore also marker-free methods. We report on a new bioreactor for the production of collagen scaffolds seeded with Mesenchymal Stem Cells (MSCs). It contains a computer controlled mechanical activation and ultrasonic online monitoring and has been constructed for the in situ determination of ultrasonic and rheological parameters. During the cultivation period of about two weeks the scaffold is periodically compressed by two movable pistons for improved differentiation of the MSCs. This periodic compression beneficially ensures the supply with nutrition even inside the sample. During the physiological stimuli, rheological properties are measured by means of highly sensitive load cells. In addition measurements of the speed of sound in the sample and in the culture medium, with frequencies up to 16 MHz, are performed continuously. Therefore piezoceramic transducers are attached to the pistons and emit and detect ultrasonic waves, travelling through the pistons, the sample and the culture medium. The time-of-flight (TOF) of the ultrasonic signals is determined in real time with the aid of chirped excitation and correlation procedures with a resolution of at least 10 ps. The implemented ultrasonic measurement scheme allows beside the speed of sound measurements the detection of the distance between the pistons with a resolution better than 100 nm. The developed monitoring delivers information on rigidity, fluid dynamics and velocity of sound in the sample and in the culture medium. The hermetically sealed bioreactor with its life support system provides a biocompatible environment for MSCs for long time cultivation.

The mechanical properties of blood vessel walls are important determinants of physiology and pathology of the cardiovascular system. Acoustic imaging (B mode) is routinely used in a clinical setting to determine blood flow and wall distensibility. In this study scanning acoustic microscopy in vitro is used to determine spatially resolved tissue elastic properties. Broadband excitation of 30 MHz has been applied through scanning acoustic microscopy (SAM) for topographical imaging of swine thoracic aorta in reflection mode. Three differently treated tissue samples were investigated with SAM: a) treated with elastase to remove elastin, b) autoclaving for 5 hours to remove collagen and c) fresh controlled untreated sample as control. Experimental investigations are conducted for studying the contribution of individual protein components (elastin and collagen) to the material characteristics of the aortic wall. Conventional tensile testing has been conducted on the tissue samples to study the mechanical behavior. The mechanical properties measured by SAM and tensile testing show qualitative agreement.

A full-scale foot pressure/shear sensor that has been developed to help diagnose the cause of ulcer formation in diabetic patients is presented. The design involves a tactile sensor array using intersecting optical fibers embedded in soft elastomer. The basic configuration incorporates a mesh that is comprised of two sets of parallel optical fiber plane; the planes are configured so the parallel rows of fiber of the top and bottom planes are perpendicular to each other. Threedimensional information is determined by measuring the loss of light from each of the waveguide to map the overall pressure distribution and the shifting of the layers relative to each other. In this paper we will present the latest development on the fiber optic plantar pressure/shear sensor which can measure normal force up from 19.09 kPa to 1000 kPa.

Mode selective excitation and detection together with chirped excitation and digital pulse compression is employed to study the variation of the time-of-flight (TOF) of Lamb waves. The acoustoelastic coefficients for the variation of TOF depend not only on the actual modes but also on the actual frequency or center frequency of the observed propagating wave. The modes are selected from dispersion relations obtained by appropriate modeling. To allow a continuous and monochromatic variation of the load, specially designed apparatus has been designed minimizing the disturbing influence of static and dynamic friction, generally a demerit in the standard force exerting hydraulic equipment. The possibility of delicate maneuverability of force application with minimal deviation with selective excitation and detection of Lamb wave modes lead us to the observation of positive and negative acoustoelastic coefficients and dependencies of these coefficients on applied stress with respect to central frequency are discussed.

The paper presents a method of quantifying the mode conversion of Lamb waves within a 1D structure from a notch-like asymmetric damage using both in-plane and out-of-plane velocity/displacement measurements. The method is applied to data recorded from a Scanning Laser Doppler Vibrometer, and likewise to numerical studies from a plane strain finite element model. A filtering procedure is implemented, and the reflected, converted, and transmitted waves are separated in the frequency/wavenumber domain, and then integrated spatially in the space/frequency domain. An accurate experimental technique for capturing the multiple components from a single laser head is verified. Based on an initial in-plane excitation, the spatially-integrated multiple component mode conversion coefficients are shown to mitigate experimental noise compared to single component mode conversion coefficients.

Critical challenges related to Guided Wave (GW) inspection for Structural Health Monitoring (SHM) include the size and proximity of damages that can be individually resolved as well as accessibility of the areas to be monitored. Effective damage imaging has been recently demonstrated through a Warped-Basis Pursuit (W-BP) approach that provides dispersion removal and high localization accuracy. Theoretical limits to the distance range resolution of this technique are discussed in this paper, and practical resolution capabilities of the W-BP are assessed in challenging situations. This is done by processing the wavefield recorded by a Scanning Laser Doppler Vibrometer outside of the damaged area of an aluminum plate. Considered scatterer configurations include a couple of masses whose mutual distance is progressively reduced and a series of holes of various dimensions and spacing. Potentials and limitations of W-BP are analyzed, along with its application for the inspection of remote/inaccessible areas in complex waveguides. Specifically, the case of an L-bent plate is considered. Mode conversion associated to the structural feature is studied and the ability of W-BP to handle multimodal propagation is exploited to separate relevant damage-induced scattering from reflections due to the bend.

In acoustics, Lamb waves are extremely useful for damage detection in sheet materials and tubular products. Among variety of techniques for the generation of lamb waves, lamb waves are detected using contact piezo electric transducers mounted on an aluminum sample. For this task, two pairs of transducers were introduced where each pair mounted on both surfaces of the sample. Mode selective excitation technique is used and two pre-amplifier circuits served as a part of the signal detection. For this application and more precisely with low frequency excitation signal, orthogonal zero order modes are observed in a high resolved fashion in aluminum sample of 1mm thickness. Principles of the developed method together with instrumental details are discussed.

A pair of identical piezoelectric (PZT) wafers collocated on a beam enable extraction of individual Lamb wave mode signals due to their polarization characteristics. Among these extracted Lamb wave mode signals, mode-converted ones proved to be promising for reference-free crack detection in a beam. This paper investigates the mode-converted Lamb wave signal induced by a notch on the beam in the frequency domain. Through the FFT of the mode-converted Lamb wave signals truncated by a series of time windows, the convergence of the temporal spectrums are demonstrated resulting in the resonance of the beam within the driving frequency range. The root mean squares (RMS) of the temporal spectrums indicate that the signal to noise ratio associated with damage is amplified as the time window size increases. Based this observation, it is concluded that the electro-mechanical (EM) impedance signal is more promising than the transient Lamb wave signals for reference-free damage diagnosis in an overall sense.

Acoustic bulk waves were excited by local electric field probe in an anisotropic piezo-electric crystal Lithium Niobate (X-cut). A narrow pulse with a width of 25 ns was used for excitation to obtain wide frequency content in the Fourier domain. A wide spectrum ensures metamorphosis of bulk waves into Lamb waves for scan lengths comparable to the involved wavelengths. The low frequency content experiences multiple reflections from the two surfaces of the plate and disperses along the propagation direction. Acoustic bulk wave's evolution and transformation to Lamb waves are illustrated and explained with the aid of the Lamb wave dispersion phenomenon. The holographic images in the Fourier domain exemplify the metamorphosis of waves during propagation following the excitation at an approximate point source.

This research work presents an in-situ imaging method for the localization of the impact point in complex anisotropic structures with diffuse field conditions, using only one passive transducer. The proposed technique is based on the time reversal approach applied to a number of waveforms stored into a database containing the experimental Green's function of the medium. The present method exploits the benefits of multiple scattering, mode conversion and boundaries reflections to achieve the focusing of the source with high resolution. The optimal re-focusing of the back propagated wave field at the impact point is accomplished through a "virtual" imaging process, which does not require any iterative algorithms and a priori knowledge of the mechanical properties of the structure. The robustness of the time reversal method is experimentally demonstrated on a stiffened composite panel and the source position can be retrieved with a high level of accuracy (error less than 3%). The simple configuration, minimal processing requirements and computational time (less than 1 sec) make this method a valid alternative to the conventional imaging structural health monitoring systems for the acoustic emission source localization.

The contents of the present report are focused on characterizing a thinly sectioned skin tissue with a mechanical scanning acoustic reflection microscope (tone-burst-wave mode) and describes the quantitative data acquisition technique with V(z) analysis. The reflectance function for the tissue located on a substrate was theoretically determined, and fitted into the mathematical model of the V(z) curve. The V(z) curves with frequency at 200 MHz for thinly sectioned normal and abnormal tissues located on soda-lime glasses were theoretically and experimentally formed. Their leaky surface acoustic wave velocities were obtained by the experimentally formed V(z) curves through FFT analyses. Finally, a computer simulation with a parameter-fitting technique (i.e., matching the distances of the periods of the theoretical and experimental V(z) curves by inputting different longitudinal wave velocities and densities of the tissue) was implemented to obtain the longitudinal wave velocities and densities of the tissues. The obtained longitudinal wave velocity may be used to simulate contrast analysis.

It is known that high dose X-ray irradiation increases the probability of cancer development in humans. Therefore, the dose decrease at every X-ray imaging event is a major goal, especially during CT tests, where the applied dose is generally a multiple of a few single radiographic imaging doses. Using narrow energy X-ray beams instead of wide energy X-rays has several advantages. First, it reduces the beam hardening effect, when the output beam (after the patient) is harder, i.e. it consists of a higher ratio of high energy X-ray photons than the input beam. Imaging with narrow energy X-rays also provides lower scatter noise than using wide energy X-rays. As a result we can obtain high signal to noise (S/N) ratio X-ray images while using much lower dose than with a regular x-ray beam. The paper points out how we can generate narrow energy X-ray beams by using special materials for which the K edge absorption peak falls into the diagnostic X-ray energy range. Furthermore, it will be shown that contrast agent materials such as Iodine are more effective when combined with the right K edge filter material.

A non-intrusive novel detection scheme has been implemented to detect the lateral muscle extension, force of the skeletal muscle and the motor action potential (EMG) synchronously. This allows the comparison of muscle dynamics and EMG signals as a basis for modeling and further studies to determine which architectural parameters are most sensitive to changes in muscle activity. For this purpose the transmission time for ultrasonic chirp signal in the frequency range of 100 kHz to 2.5 MHz passing through the muscle under observation and respective motor action potentials are recorded synchronously to monitor and quantify biomechanical parameters related to muscle performance. Additionally an ultrasonic force sensor has been employed for monitoring. Ultrasonic traducers are placed on the skin to monitor muscle expansion. Surface electrodes are placed suitably to pick up the potential for activation of the monitored muscle. Isometric contraction of the monitored muscle is ensured by restricting the joint motion with the ultrasonic force sensor. Synchronous monitoring was initiated by a software activated audio beep starting at zero time of the subsequent data acquisition interval. Computer controlled electronics are used to generate and detect the ultrasonic signals and monitor the EMG signals. Custom developed software and data analysis is employed to analyze and quantify the monitored data. Reaction time, nerve conduction speed, latent period between the on-set of EMG signals and muscle response, degree of muscle activation and muscle fatigue development, rate of energy expenditure and motor neuron recruitment rate in isometric contraction, and other relevant parameters relating to muscle performance have been quantified with high spatial and temporal resolution.

The adaptive neural network is a standard technique used in nonlinear system estimation and learning applications for dynamic models. In this paper, we introduced an adaptive sensor fusion algorithm for a helmet structure health monitoring system. The helmet structure health monitoring system is used to study the effects of ballistic/blast events on the helmet and human skull. Installed inside the helmet system, there is an optical fiber pressure sensors array. After implementing the adaptive estimation algorithm into helmet system, a dynamic model for the sensor array has been developed. The dynamic response characteristics of the sensor network are estimated from the pressure data by applying an adaptive control algorithm using artificial neural network. With the estimated parameters and position data from the dynamic model, the pressure distribution of the whole helmet can be calculated following the Bazier Surface interpolation method. The distribution pattern inside the helmet will be very helpful for improving helmet design to provide better protection to soldiers from head injuries.

In the present work, a reliable wireless healthcare monitoring network which is compatible with common platforms and operating systems is designed and implemented. The main advantages of our suggested wireless monitoring network are the ability to monitor any required quantity, the usage of an efficient programming environment to allow all features of monitoring, controlling, and data processing to be implemented, the ability to extend the number of monitored patients, and the ability to transfer measurement data over wired or wireless channels. In addition to all of the above mentioned features, the system is implemented with components which achieve the minimum costs without scarifying accuracy. The use of low cost wireless communication and internet network facilities makes our suggested monitoring system reliable for all capital projects with minimum costs and ensures upgradability to adapt additional wide user requirements.

In this paper an approach based on an array of macro-fiber composite (MFC) transducers arranged as rosettes is proposed for high-velocity impact location on isotropic and composite aircraft panels. Each rosette, using the directivity behavior of three MFC sensors, provides the direction of an incoming wave generated by the impact source as a principal strain angle. A minimum of two rosettes is sufficient to determine the impact location by intersecting the wave directions. The piezoelectric rosette approach is easier to implement than the well known time-of-flight based triangulation of acoustic emissions because it does not require knowledge of the wave speed in the material. Hence the technique does not have the drawbacks of time-of-flight triangulation associated to anisotropic materials or tapered sections. The experiments reported herein show the applicability of the technique to high-velocity impacts created with a gas-gun firing spherical ice projectiles. The experimental testing involved the following six specimens: an aluminum panel, a quasi-isotropic CFRP composite panel, a highly anisotropic CFRP composite panel, a stiffened aluminum panel, a stiffened quasi-isotropic CFRP composite panel, and a stiffened anisotropic CFRP composite panel.

This paper deals with monitoring impacts on aluminum and composite aerospace panels. The specific problems addressed are (1) the identification of the impact forces (force magnitude time history) and (2) the discrimination of "damaging impacts" from "non-damaging impacts." Ultrasonic guided waves generated by the impacts are used as the sensing mechanism. Flexible Macro-Fiber Composite (MFC) patches are used as the ultrasonic receivers. The impact force identification method is based on an optimization routine which minimizes the difference between the experimental impact waves and the numerical impact waves calculated by a Semi-Analytical Finite Element (SAFE) forced analysis. The differentiation of "damaging impacts" vs. "non-damaging impacts" is based on a frequency analysis of the impact waves. These techniques are demonstrated through an extensive experimental testing program involving the following six specimens: an aluminum panel, a quasi-isotropic CFRP composite panel, a highly anisotropic CFRP composite panel, a stiffened aluminum panel, a stiffened quasi-isotropic CFRP composite panel, and a stiffened anisotropic CFRP composite panel. These panels were subjected to low-velocity hammer impacts and to high-velocity gas-gun impacts by ice projectiles at speeds up to 170 m/sec using UCSD's gas-gun test facility. In all of these experiments, the techniques summarized above gave excellent results for both impact force identification and impact force discrimination.

This study presents a new impact localization technique that can pinpoint the location of an impact event within a complex aircraft fuselage using a time reversal concept and a scanning laser Doppler vibrometer (SLDV). First, an impulse response function (IRF) between an impact location and a sensing piezoelectric transducer is approximated by exciting the sensing piezoelectric transducer instead and measuring the response at the impact location using SLDV. Then, training IRFs are assembled by repeating this process for various potential impact locations and sensing piezoelectric transducers. Once an actual impact event occurs, the impact response is recorded and compared with the training IRFs. The correlations between the impact response and the IRFs in the training data are computed using a unique concept of time reversal. Finally, the training IRF, which gives the maximum correlation, is chosen from the training data set, and the impact location is identified. The proposed impact technique has the following advantages over the existing techniques: (1) it can be applied to isotropic/anisotropic plate structures with additional complex features such as stringers, stiffeners, spars and rivet connections; (2) only simple correlation calculation based on unique time reversal is required, making it attractive for real-time automated monitoring; (3) temperature variation barely affects the localization performance; and, (4) training is conducted using non-contact SLDV and the existing piezoelectric transducers which may already be installed for other structural health monitoring purposes. Impact events on an actual aluminum fuselage specimen are successfully identified using the proposed technique.

Structural buckling can lead to failure, but beyond the initial onset of buckling there exists a stable region within which there may be no material damage, the structure retains the load carrying capacity, and can recover fully elastically when unloaded. Reclaiming this region as valid design space requires the full understanding of changes in the structure that take place in this post buckled region that precede failure. In addition, there is also a critical need for a monitoring technique that can measure the extent of excursion of a given structural element into the post buckled region and ensure that there is sufficient margin of safety. Such a monitoring technique based on vibration characteristics of buckled structures is proposed in this paper. In this research, to determine the feasibility of such an approach, the natural frequencies and mode shapes of an aluminum shear panel were monitored while the panel was undergoing different levels of buckling under uniform edge shear. The changes seen in frequencies and mode shapes were found to a measure indicative of the level of buckling deformation.

This paper presents the application of a novel vibration based technique for detecting fatigue cracks in structures. The method utilizes the empirical mode decomposition method (EMD) to establish an effective energy-based damage index. To investigate the feasibility of the method, fatigue cracks of different sizes were introduced in an aluminum beam subjected to a cyclic load under three point bending configuration. The vibration signals corresponding to the healthy and the damaged states of the beam were acquired via piezoceramic sensors. The signals were then processed by the proposed methodology to obtain the damage indices. In addition, for the sake of comparison, the natural frequencies of the healthy and damaged states of the beam were obtained through the Fast Fourier Transform (FFT). The results of this study concluded in two major observations. Firstly, the method was highly successful in not only predicting the presence of the fatigue crack, but also in quantifying its progression. Secondly, the proposed energy-based damage index was proved to be superior over the frequency-based method in terms of sensitivity to the damage detection and quantification. Moreover, this technique could be regarded as an efficient non-destructive tool, since it is simple, cost effective, and does not rely on analytical modelling of the structure.

This paper proposes a vibration testing and health monitoring system based on an impulse response excited by a laser ablation. High power YAG pulse laser is used for producing an ideal impulse force on structural surface. It is possible to measure high frequency vibration responses in this system. A health monitoring system is constructed by this vibration testing system and a damage detecting algorithm. A microscopic damage of structures can be extracted by detecting fluctuations of high frequency vibration response with the present health monitoring system. In this study, loosening of bolt tightening torques is defined as the damage of the system. The damage is detected and identified by statistical evaluations with Recognition-Taguchi method.

Extending the number of functions and to improving the reliability of portable equipments is a current issue. Considering the recent progresses in ultralow-power electronics, powering complex systems on ambient energy is not chimerical anymore This paper addresses the problem of the mechanical to electrical energy conversion in electroactive materials (ferroelectrics and electrostrictive polymers) and underlines the similarities and differences between these two classes of materials in terms of energy conversion. These materials exhibit different conversion abilities and mechanical properties. The lightweight, flexible, conformable polymer properties are definitively a strong advantage for practical application like energy harvesters. The proposed energy conversion improvement is an extension, to polymer materials, of the so-called "SSHI "technique previously developed for ferroelectric materials. This non-linear voltage processing basically consists in switching the voltage, for a short period, when the voltage reaches a maximum or a minimum, resulting in a large enhancement of the conversion, up to 1000%, as well as the harvesting capability. Unlike ferroelectrics based energy harvesters, polymer harvesters require a bias electrical field to convert mechanical to electrical energy that forbids a direct extension of the SSHI technique. The needed adaptations will be discussed as well as the different trade-offs between the mechanical and electrical characteristics that the system must meet to maximize the converted energy. Increasing the polymer capacitance to enhance the conversion has been done by introducing nano-conductive particles in the polymer matrix. The paper will present and discuss experimental and theoretical data.

For practical use, the electrical field requirements of Electro Active Polymer (EAP) actuators have to be lowered down. Recently, we developed nano carbon filled polymeric films which can generate a large strain (30-50%) at moderate electrical field (less than 20 MV/m). Herein, the electrostrictive strain saturates versus electrical field and that the maximum strain depends strongly on the sample thickness. Combining polarization saturation effect and heterogeneities in the polymer thickness lead to a model that describes correctly the strain behavior versus electrical field, polymer thickness and frequency. A three-layer model was established which assumes that the polymer is not homogeneous along the thickness. Two outer and one inner layers exist, which must be formed during the polymer curing. It is considered that these layers have slightly different characteristics, such as permittivity. When the electrical field is input parallel to the polymer thickness, a different strain would take place in each layer according to the field distribution. Since the layers are attached together, the strain must be the same in each layer. Consequently stresses appear in the different layers. Introducing in this model a saturation of the polarization for high field leads to simulation results that fit well the experimental data.

This paper describes the design and fabrication of an optical sensor to sense vertical displacement of a diamagnetically stabilized levitating rotor. The planar rotor described in this paper rotates due to nine electromagnetic coils evenly spaced around the rotor. A driving circuit allows current to flow through the coils one phase at a time. This produces a magnetic field strong enough to spin the rotor. However, instability due to a number of factors is prevalent in the present system. This instability is observed as vertical and horizontal displacement of the levitating rotor. The purpose of an additional optical sensor is to measure and record this vertical displacement and combine it with topsensing optical measurements in order to create a three-dimensional optical sensing mechanism around the rotor.

The paper presents the concept and construction of a prototype self-configuring building block for potential application in smart dynamic structure. The design contains several modular self-configuring blocks with integrated controllers, gear trains, extending arms and magnetic latches. The structure could be reconfigured via the connection and disconnection of magnetic latch between the modules. Through the coordination of the individual cubes themselves, the entire structure can reassemble via pushing and pulling the individual components into almost any desired shape. Information as to the current location or the next necessary movement could be passed from cube to cube by a physical connection between the cubes or remotely through broadcast signals. To provide the hardware strategy, we present the mechanical design of the self-configure modules and their latch mechanism of Halbach array. In the end, we will discuss our proposed application in dynamic building structure and storage management.

A new damage detection technique is presented which can localize a breathing crack in a metallic rod-like structure. Biologically inspired by the combination tone phenomenon which occurs in the human auditory system, the nonlinear signal produced at the difference combination frequency of the two harmonic excitation frequencies ( f₁ - f₂ ) is used to detect and localize the breathing crack. An experimental investigation is performed to verify the proposed approach. Compared to previously introduced techniques for detection of breathing cracks based on super-harmonic or subharmonic nonlinear response signals, the proposed approach is much more robust and easier to implement.

In this work, a new chiral metacomposite is proposed by integrating two-dimensional periodic chiral lattice with elastic metamaterial inclusions for low-frequency wave applications. The plane harmonic wave propagation in the proposed metacomposite is investigated through the finite element technique and Bloch's theorem. From that, band diagrams, dispersion surfaces as well as phase and group velocities are obtained to illustrate wave properties of the chiral metacomposite. Effective dynamic properties of the chiral metacomposite are numerically calculated to explain lowfrequency bandgap behavior in the chiral metacomposite. Specifically, design of a metacomposite beam structure for the broadband low-frequency vibration suppression is demonstrated.

This paper discusses the reasons why we need to change our habit of developing quick software to validate our theoretical results. It is explained here how to create computer programs, to use high level functions and to have a team's common strategy. To achieve this goal, an innovative concept of software development is presented, called AIS (Application Interface Software). This concept is illustrated by developing DPSM (Distributed Point Source Method) programs which is used for 3D ultrasonic field modeling.

Lamb waves have been used with considerable success to detect and quantify damage in aerospace, mechanical and civil structures. The mathematical representation of these particular waves is well known and understood, and we build upon these results in an attempt to detect and quantify scattering due to the presence of a spherical corrosion pit on the surface of a layer. By using the usual superposition argument, the total field consists of the incident and scattered fields, where the latter is generated by tractions on the surface of the cavity, which are obtained from the stress fields of the incident Lamb wave. In the approximation advanced in this paper these tractions are then represented by body forces in the interior of the intact layer. The acoustic radiation from the resultants of these body forces approximates the scattered field. The resultant forces are decomposed in symmetric and anti-symmetric systems, which generate symmetric and anti-symmetric radiating modes. The time-harmonic elastodynamic form of the reciprocity theorem is employed in an elegant way to obtain an analytical solution to the scattered field amplitudes. As our damage metric we obtain the ratio of scattered to incident Lamb mode amplitudes, which in a closed form include material properties, geometry of the pit and layer, and angular frequency of the incident wave. Results of this study yield graphical representations for the magnitude of the out of plane scattered displacements with respect to pit geometry, and has the potential to lead to a unique solution of the inverse problem.

Several techniques are used to diagnose structural damages. In the ultrasonic technique structures are tested by analyzing ultrasonic signals scattered by damages. The interpretation of these signals requires a good understanding of the interaction between ultrasonic waves and structures. Therefore, researchers need analytical or numerical techniques to have a clear understanding of the interaction between ultrasonic waves and structural damage. However, modeling of wave scattering phenomenon by conventional numerical techniques such as finite element method requires very fine mesh at high frequencies necessitating heavy computational power. Distributed point source method (DPSM) is a newly developed robust mesh free technique to simulate ultrasonic, electrostatic and electromagnetic fields. In most of the previous studies the DPSM technique has been applied to model two dimensional surface geometries and simple three dimensional scatterer geometries. It was difficult to perform the analysis for complex three dimensional geometries. This technique has been extended to model wave scattering in an arbitrary geometry. In this paper a channel section idealized as a thin solid plate with several rivet holes is formulated. The simulation has been carried out with and without cracks near the rivet holes. Further, a comparison study has been also carried out to characterize the crack. A computer code has been developed in C for modeling the ultrasonic field in a solid plate with and without cracks near the rivet holes.

Composite structures are being extensively used in the modern industries because of their superior strength to weight ratio, high stiffness, and long fatigue life. The ability to tailor the material properties along different directions also increases the avenues of composites material application. The ever-increasing demand for composite structures and the need to ensure the structural integrity necessitates the development of sustainable and efficient structural health monitoring (SHM) systems. Guided wave (GW) methods offer an attractive solution for SHM due to their tunable sensitivity to different defects and their ability to interrogate large structural surfaces. Because of the anisotropy present in the composite materials, the development of the SHM methods is significantly more complex and challenging than in the case of isotropic materials. This paper presents numerical simulations based on the local interaction simulation approach (LISA) to characterize the propagation of GW in laminated composite plates.

Ultrasound damage detection using built-in piezoelectric transducers is a promising technique because it can automatically inspect and interrogate structural damage in hard to access areas. Although numerous efforts have been devoted to the application of the structural health monitoring (SHM) concepts to real world problems; there is a shortage in the modeling tools specifically tailored for rapid computer aided design of SHM applications. This is due to the fact that the finite element method, which is the dominant method in the simulation of the wave propagation problems due to its geometric versatility and the capability to simulate complex boundary conditions as well as coupling effects, lacks the required computational efficiency for the structural health monitoring applications. This is because of the high frequencies usually utilized is SHM, posing a huge burden on the mesh size to minimize the errors. Spectral element method (SEM), a variant of the p/FEM, combines the fast convergence rates associated with the spectral methods with the geometric flexibility of the finite element method, thus allowing for more computationally efficient simulation, leading to fast product design cycle. Recently, these advantages have drawn the attention of the different researchers in the field of the SHM. The advantage of the SEM as a high accuracy solution method enables the refinement and the testing of different concepts of SHM. One of these concepts is the main focus of the current paper. The presented work is a parametric study of the effect of the piezoceramic actuator thickness on the fundamental Lamb waves S ₀, and A₀ using a tailored SEM solver. In order to illustrate the reduction of the computational costs the running times of the SEM solver were compared with the running times for some of cases solved using commercial FEM solver (ANSYS), as well as the results are compared with analytical results based on a widely accepted model from the literature. Additionally, the cases were validated experimentally, showing a good agreement with the simulation results.

Lamb wave testing for SHM is complicated by multimodal propagation and by reflections. In this paper, the effectiveness of the decomposition inWarped Curvelet Frames for the analysis of guided ultrasonic waves is studied. The transformation acts by expanding the analyzed signal into a tight frame of basis functions named Curvelets. The curvelet transform may be effectively combined with warping procedures to analyze wave propagation in dispersive media. Experimental results show that, thanks to the spatial and temporal localization of curvelets, it is possible to decompose waves that are overlapped both in the time/space and in the frequency/wavenumber domain.

Wind turbine systems are attracting considerable attention due to concerns regarding global energy consumption as well as sustainability. Advances in wind turbine technology promote the tendency to improve efficiency in the structure that support and produce this renewable power source, tending toward more slender and larger towers, larger gear boxes, and larger, lighter blades. The structural design optimization process must account for uncertainties and nonlinear effects (such as wind-induced vibrations, unmeasured disturbances, and material and geometric variabilities). In this study, a probabilistic monitoring approach is developed that measures the response of the turbine tower to stochastic loading, estimates peak demand, and structural resistance (in terms of serviceability). The proposed monitoring system can provide a real-time estimate of the probability of exceedance of design serviceability conditions based on data collected in-situ. Special attention is paid to wind and aerodynamic characteristics that are intrinsically present (although sometimes neglected in health monitoring analysis) and derived from observations or experiments. In particular, little attention has been devoted to buffeting, usually non-catastrophic but directly impacting the serviceability of the operating wind turbine. As a result, modal-based analysis methods for the study and derivation of flutter instability, and buffeting response, have been successfully applied to the assessment of the susceptibility of high-rise slender structures, including wind turbine towers. A detailed finite element model has been developed to generate data (calibrated to published experimental and analytical results). Risk assessment is performed for the effects of along wind forces in a framework of quantitative risk analysis. Both structural resistance and wind load demands were considered probabilistic with the latter assessed by dynamic analyses.

An in-service health monitoring system is needed for steam pipes to track through their wall the condensation of water. The system is required to measure the height of the condensed water inside the pipe while operating at temperatures that are as high as 250^oC. The system needs to be able to make real time measurements while accounting for the effects of cavitation and wavy water surface. For this purpose, ultrasonic wave in pulse-echo configuration was used and reflected signals were acquired and auto-correlated to remove noise from the data and determine the water height. Transmitting and receiving the waves is done by piezoelectric transducers having Curie temperature that is significantly higher than 250^oC. Measurements were made at temperatures as high as 250^oC and have shown the feasibility of the test method. This manuscript reports the results of this feasibility study.

Continuous on-line monitoring of active and passive systems, structures and components in nuclear power plants will be critical to extending the lifetimes of nuclear power plants in the US beyond 60 years. Acoustic emission and guided ultrasonic waves are two tools for continuously monitoring passive systems, structures and components within nuclear power plants and are the focus of this study. These tools are used to monitor fatigue damage induced in a SA 312 TP304 stainless steel pipe specimen. The results of acoustic emission monitoring indicate that crack propagation signals were not directly detected. However, acoustic emission monitoring revealed crack formation prior to visual confirmation through the detection of signals caused by crack closure friction. The results of guided ultrasonic wave monitoring indicate that this technology is sensitive to the presence and size of cracks. The sensitivity and complexity of guided ultrasonic wave (GUW) signals is observed to vary with respect to signal frequency and path traveled by the GUW relative to the crack orientation.

One of the most important parameters in the area of structural inspections is nondestructive testing. In recent years, a new approach known as "ultrasound guided waves" has been developed in the field of ultrasonic testing. The main advantages of this method are ability of propagation along the structure and inspection of long distances, high speed and low cost. In this study, a sinusoidal input signal with three pulses has been used for excitation of guided waves. These waves have been propagated along the pipe and data capturing has been performed in three positions. Afterwards, a saw cut has been applied on the pipe as a crack and the receiving signals have been recorded in the same positions. Upon capturing, signals have been processed and compared via wavelet analysis. Variations in wave amplitudes due to passing the crack has been investigated and signals have been compared simultaneously in both time and frequency domain by means of wavelet analysis. Results indicate that even if the crack is not detected, presence of crack in the way of passing wave will affect the amplitude of propagating wave, yet it does not have any effect on the frequency and time contents of the signal.

Wireless sensor networks are increasingly adopted in many engineering applications such as environmental and structural monitoring. Having proven to be low-cost, easy to install and accurate, wireless sensor networks serve as a powerful alternative to traditional tethered monitoring systems. However, due to the limited resources of a wireless sensor node, critical problems are the power-consuming transmission of the collected sensor data and the usage of onboard memory of the sensor nodes. This paper presents a new approach towards resource-efficient wireless sensor networks based on a multi-agent paradigm. In order to efficiently use the restricted computing resources, software agents are embedded in the wireless sensor nodes. On-board agents are designed to autonomously collect, analyze and condense the data sets using relatively simple yet resource-efficient algorithms. If having detected (potential) anomalies in the observed structural system, the on-board agents explicitly request specialized software agents. These specialized agents physically migrate from connected computer systems, or adjacent nodes, to the respective sensor node in order to perform more complex damage detection analyses based on their inherent expert knowledge. A prototype system is designed and implemented, deploying multi-agent technology and dynamic code migration, in a wireless sensor network for structural health monitoring. Laboratory tests are conducted to validate the performance of the agent-based wireless structural health monitoring system and to verify its autonomous damage detection capabilities.

This study proposes a novel hierarchical sensing system for detecting impact damage in composite structures. In the hierarchical system, numerous three-dimensionally structured sensor devices are distributed throughout the whole structural area and connected with an optical fiber network through transducing mechanisms. The distributed devices detect damage, and the fiber optic network gathers the damage signals and transmits the information to a measuring instrument. This study began by discussing the basic concept of the hierarchical sensing system through comparison with existing fiber-optic-based systems and the impact damage detection system for the composite structure was then proposed. The sensor devices were developed based on Comparative Vacuum Monitoring (CVM) system and Brillouin based distributed strain sensing was utilized to gather the damage signals from the distributed devices. Finally a verification test was conducted using a carbon fiber reinforced plastic (CFRP) fuselage demonstrator. Occurrence of barely visible impact damage was successfully detected and it was clearly indicated that the hierarchical system has better repairability, higher robustness, and wider monitorable area compared to existing systems.

The purpose of this paper is to develop a novel ferromagnetic polymeric metal detector system by using a fiber-optic Mach-Zehnder interferometer with a newly developed ferromagnetic polymer as the magnetostrictive sensing device. This ferromagnetic polymeric metal detector system is simple to fabricate, small in size, and resistant to RF interference (which is common in typical electromagnetic type metal detectors). Metal detection is made possible by disrupting the magnetic flux density present on the magnetostrictive sensor. This paper discusses the magnetic properties of the ferromagnetic polymers. In addition, the preliminary results of successful sensing of different geometrical metal shapes will be discussed.

In recent years, it is becoming more common to use fiber optic sensors (FOS) in the structural health monitoring (SHM) sector, especially in the civil engineering field. A number of surface-mountable sensor system for FOS have been developed in the past years, the recent development of Brillouin Optical Time Domain Reflectometry (BOTDR) was a great evolution towards the SHM system development, it inspired the new edge of FOS SHM system. Different from the traditional monitoring instruments, it provides distributed, long distance, real-time, interference free and high accuracy/precision measurement data. It is now possible to achieve "continuous" measurement data and this SHM technique is applicable in area that is inaccessible. The research aims to solve the problems which exist in the convergence measurement using the conventional measuring methods, however, there is still a gap between the lab experiments and field applications. Limited research has been conducted on how to maximize its possible applications due to its brittle and fragile material nature. A number of additional considerations for a successful pairing of these two must be taken into account for successful field applications. This article provides a short review on underground monitoring techniques and FOS SHM systems. The focuses is on examine (i) the feasibility and effectiveness of different BOTDR sensors installation methods (ii) the suitable commercially-available o sensing cable for underground application (iii) the sensing performance of customized sensor protection package BOTDR sensor that manufactured involving layers of fiber reinforced composites. This research serves a bridge in between the technology advancement to the creation of a structure health monitoring system with practical application, numerical simulation and theoretical analysis aspects, and also to provide the insights into the mechanisms of BOTDR.

The fabrication and experimental investigation of a fiberoptic microphone is described. The sensing element is a silicon diaphragm with gold thin film coating that is positioned inside a silicone rubber mold at the end of a single mode optical fiber. Thus, a Fabry-Perot interferometer is formed between the inner fiber and the diaphragm. An acoustic pressure change is detected by using the developed microphone. The polymeric cavity and silicon diaphragm-based system exhibits excellent physicochemical properties with a small, simple, low cost, and lightweight design. The system is also electromagnetic interference / radio frequency interference immunity due to the use of fiberoptics.

The accuracy of the Born Approximation as a forward model of elastic wave scattering in the context of simulating Impact Echo tests of reinforced of concrete is investigated in this paper. The ability of a forward model to realistically simulate the physics of a system can be important when such a model is used as part of an inverse solution. Synthetic data of scattering by air void defects that are typically present in damaged civil engineering structures is generated by a two-dimensional Finite Difference in Time Domain (FDTD) model for elastic wave propagation in an infinite, homogeneous and isotropic concrete medium. Horizontal elongated cracks and air voids with compact shapes are considered in this study for comparison between the synthetic and the Born approximated data. It is observed that the Born Approximation simulates a compact air void better than a horizontal elongated one. This knowledge provides insight on Born Approximation as part of an inverse solution towards imaging of air voids of various shapes in a damaged civil engineering structure.

Current study is aiming at making an in-depth research about the characteristics of the acoustic emission (AE) signals produced during the steel corrosion of reinforced concrete. Basing on the simplified waveform parameter analysis, a more effective method-frequency spectrum analysis for each waveform in time-domain is carried out to get more comprehensive and detailed AE signals' characteristics. The research shows that the accelerated corrosion process can be divided into four stages: inaction, onset, acceleration and deterioration. The combination of simplified parameter analysis and frequency spectrum analysis is shown successful for the research about the characteristics of AE signals in each phase. From these results, a great promise for AE technique to monitor the corrosion process in reinforced concrete is clarified. And the combination of different methods for signal analysis especially spectrum analysis is more reliable to the study about the characteristics of the AE signals.

Transmissibility-related features are one class of indicators used to detect structural defects, especially because of their sensitivity to local changes. In this paper, we consider a SIMO identification model and regard the change in transmissibility as a feature indicating damage occurrence. Both inherent randomness in the system identification process and the noise contamination (or other types of measurement/sampling/quantization variabilities) are included as the sources of transmissibility uncertainty. The uncertainty quantification is necessary to group-classify the measurements into either undamaged or damaged (binary) conditions with a better understanding of Type I/II trade-offs. A sensitivity research is deployed in this paper, where Receiver Operating Characteristic (ROC) curves for individual frequency lines are given with different damage levels and extraneous noise levels, and Area Under Curve (AUC) will be evaluated as the key performance metric across the entire frequency domain. The paper concludes that regions near resonance will have the best hypothesis test performance in terms of sensitivity and specificity.

The rapid deployment of satellites is hindered by the need to flight-qualify their components and the resulting mechanical assembly. Conventional methods for qualification testing of satellite components are costly and time consuming. Furthermore, full-scale vehicles must be subjected to launch loads during testing. The focus of this research effort was to assess the performance of Structural Health Monitoring (SHM) techniques to replace the high-cost qualification procedure and to localize faults introduced by improper assembly. SHM techniques were applied on a small-scale structure representative of a responsive satellite. The test structure consisted of an extruded aluminum spaceframe covered with aluminum shear plates, which was assembled using bolted joints. Multiple piezoelectric patches were bonded to the test structure and acted as combined actuators and sensors. Piezoelectric Active-sensing based wave propagation and frequency response function techniques were used in conjunction with finite element modeling to capture the dynamic properties of the test structure. Areas improperly assembled were identified and localized. This effort primarily focused on determining whether or not bolted joints on the structure were properly tightened.

This paper presents a dynamics-based methodology for accurate damage inspection of thin-walled structures by combining a boundary-effect evaluation method (BEEM) for space-wavenumber analysis of measured operational deflection shapes (ODSs) and a conjugate-pair decomposition (CPD) method for time-frequency analysis of time traces of measured points. BEEM is for locating and estimating small structural damage by processing ODSs measured by a full-field measurement system (e.g., a scanning laser vibrometer or a camera-based motion measurement system). BEEM is a nondestructive spatial-domain method based on area-by-area processing of ODSs and it works without using any structural model or historical data for comparison. Similar to the short-time Fourier transform and wavelet transform, CPD uses adaptive windowed regular harmonics and function orthogonality to perform time-frequency analysis of time traces by extracting time-localized regular and/or distorted harmonics. Both BEEM and CPD are local spectral analysis based on local, adaptive curve fitting. The first estimation of the wavenumber for BEEM and the frequency for CPD is obtained by using a four-point Teager-Kaiser algorithm based on the use of finite difference. Numerical simulations and experimental results show that the combination of BEEM and CPD for space-wavenumber and time-frequency analysis provides an accurate tool for damage inspection of thin-walled structures.

Presented is an approach to damage localization for guided wave structural health monitoring (GWSHM) in plate-like structures. In this mode of SHM, transducers excite and sense guided waves in order to detect and characterize the presence of damage. The premise of the presented localization approach is simple: use as the estimated damage location the point on the structure with the maximum a posteriori probability (MAP) of being the location of damage (i.e., the most probable location given a set of sensor measurements). This is accomplished by constructing a minimally-informed statistical model of the GWSHM process. Parameters of the model which are unknown, such as scattered wave amplitude, are assigned non-informative Bayesian prior distributions and averaged out of the a posteriori probability calculation. Using an ensemble of measurements from an instrumented plate with stiffening stringers, the performance of the MAP estimate is compared to that of what were found to be the two most effective previously reported algorithms. The MAP estimate proved superior in nearly all test cases and was particularly effective in localizing damage using very sparse arrays of as few as three transducers.

Single edge notches provide a very well defined load and fatigue crack size and shape environment for estimation of the stress intensity factor K, which is not found in welded elements. ASTM SE(T) specimens do not appear to provide ideal boundary conditions for proper recording of acoustic wave propagation and crack growth behavior observed in steel bridges, but do provide standard fatigue crack growth rate data. A modified versions of the SE(T) specimen has been examined to provide small scale specimens with improved acoustic emission(AE) characteristics while still maintaining accuracy of fatigue crack growth rate (da/dN) versus stress intensity factor (ΔK). The specimens intend to represent a steel beam flange subjected to pure tension, with a surface crack growing transverse to a uniform stress field. Fatigue test is conducted at low R ratio. Analytical and numerical studies of stress intensity factor are developed for single edge notch test specimens consistent with the experimental program. ABAQUS finite element software is utilized for stress analysis of crack tips. Analytical, experimental and numerical analysis were compared to assess the abilities of AE to capture a growing crack.

A full-scale four-story steel building was tested on the shaking table of the E-defense project on September, 2007. During the shaking table tests, the building was damaged progressively through various levels of seismic excitations, and finally collapsed on the first floor. To evaluate the modal parameters, low-amplitude white noise excitations were applied to the building and the response of the building was measured at various levels of damage due to the seismic excitations. The subspace identification method is then applied to identify the modal parameters of the building based on the measured data. This paper focuses on detecting damage of this building based on changes in identified modal parameters. A finite element model updating strategy is applied to identify (detect, localize and quantify) the damage in the building at each damage state considered. The residuals used in the updating procedure are based on the identified natural frequencies and mode shapes for the first two X direction and Y direction vibration modes of the building. At last the correlation between the damage detection results and the actual damage observed in the building is carefully examined. They do not exactly coincide but the concentration regions of damage are highly consistent with each other.

A new approach suitable for cable-stayed bridge is presented in this paper. Moving force identification method for cablestayed bridge was seldom reported. In previous research bridges were modeled as Timoshenko beams or orthotropic plates, while cable-stayed bridge can't be modeled as beams or plates. In this paper, the deck of bridge was separated from other parts, by replacing the cables with equivalent forces based on measurements. And according to D'Alembert principle the equation of motion of deck can be established, from which the moving external forces can be obtained, given measured time-varying cable forces and accelerations. However this is typically an inverse and ill-posed problem, because the measured global variables is not so sensitive to local loads such as vehicle loads for a large-span bridge meanwhile the noise plays an essential role in measured signals. The Tikhonov regularization methods are adopted for solving the ill-posed problem. Simulation studies are used to verify the method. The main contributions of this paper are: a. to propose a method for identifying moving forces on cable-stayed bridge; b. both the location and the magnitude of the force can be identified; c. the vehicles in different lanes can be identified.

This work illustrates the possibility to extend the field of application of the Multi-Scale Finite Element Method (MsFEM) to structural mechanics problems that involve localized geometrical discontinuities like cracks or notches. The main idea is to construct finite elements with an arbitrary number of edge nodes that describe the actual geometry of the damage with shape functions that are defined as local solutions of the differential operator of the specific problem according to the MsFEM approach. The small scale information are then brought to the large scale model through the coupling of the global system matrices that are assembled using classical finite element procedures. The efficiency of the method is demonstrated through selected numerical examples that constitute classical problems of great interest to the structural health monitoring community.

Based on the lattice dynamics approach the dependence of the time-of-flight (TOF) on stress has been modeled for transversal polarized acoustic waves. The relevant dispersion relation is derived from the appropriate mass-spring model together with the dependencies on the restoring forces including the effect of externally applied stress. The lattice dynamics approach can also be interpreted as a discrete and strictly periodic lumped circuit. In that case the modeling represents a finite element approach. In both cases the properties relevant for wavelengths large with respect to the periodic structure can be derived from the respective limit relating also to low frequencies. The model representing a linear chain with stiffness to shear and additional stiffness introduced by extensional stress is presented and compared to existing models, which so far represent each only one of the effects treated here in combination. For a string this effect is well known from musical instruments. The counteracting effects are discussed and compared to experimental results.

In this paper, a new method is developed to quantify the defect due to porosity in a composite structure using the principle of wave propagation in structures. A model developed, based on a modified rule of mixture is used to include the influence of porosity on the stiffness and density of the composites. The values thus obtained from the modified rule of mixture model are used in a conventional spectral finite element model to develop a new model for solving wave propagation problems for porous laminated composites. The influence of the porosity content on the spectrum relations, dispersion relations and the velocity responses is studied first, in the forward problem. These numerically obtained responses are further used for the estimation of porosity in a measured response, by solving a nonlinear optimization problem.

Acoustic Emission has shown itself to be a valuable technology for reliably detecting damage initiation and growth in large structures. Monitoring of a structure, throughout its life, is possible with sparse sensor arrays. However aerospace structures can be geometrically complex and contain many structural features, the most common being stringers. Stringers are arranged in a way that they can span the length of the wings or fuselage, separated by less than 200mm in certain cases. Therefore it is almost inevitable that, for any reasonable sensor spacing, acoustic emission events propagating guided waves will interact with multiple stringers. A large aerospace aluminium panel is used to minimise the effects of edge reflections and to allow the two fundamental guided wave modes to separate before reception. It is shown that stringer foot height has a noticeable impact on guided wave propagation, for typical aerospace arrangements. A reduction in transmitted signal amplitude was noted as the stringer thickness was increased. However a local maximum was seen when the stringer foot thickness was equal to that of the plate thickness. This paper discusses quantitative analysis of stringer interaction with the fundamental guided wave modes. The effect of the stringer as a feature has been divided into three main interactions; stringer dimensions, coupling media and riveting. Stringer dimensions and coupling media interactions has been investigated here to quantify their effect on transmission and reflection of the fundamental guided wave modes.

In the field of Structural Health Monitoring, tests and sensing systems are intended as tools providing diagnoses, which allow the operator of the facility to develop an efficient maintenance plan or to require extraordinary measures on a structure. The effectiveness of these systems depends directly on their capability to guide towards the most optimal decision for the prevailing circumstances, avoiding mistakes and wastes of resources. Though this is well known, most studies only address the accuracy of the information gained from sensors without discussing economic criteria. Other studies evaluate these criteria separately, with only marginal or heuristic connection with the outcomes of the monitoring system. The concept of "Value of Information" (VoI) provides a rational basis to rank measuring systems according to a utility-based metric, which fully includes the decision-making process affected by the monitoring campaign. This framework allows, for example, an explicit assessment of the economical justifiability of adopting a sensor depending on its precision. In this paper we outline the framework for assessing the VoI, as applicable to the ranking of competitive measuring systems. We present the basic concepts involved, highlight issues related to monitoring of civil structures, address the problem of non-linearity of the cost-to-utility mapping, and introduce an approximate Monte Carlo approach suitable for the implementation of time-consuming predictive models.

Stiffener is one of the major components of aircraft structures to increase the load carrying capacity. Damage in the stiffener, mostly in the form of crack is an unavoidable problem in aerospace structures. Stiffener is bonded to the inner side of the aircraft panel which is not accessible for immediate inspection. A sensor-actuator network can be placed on the outer side of the panel that is accessible. Ultrasonic lamb waves are transmitted through stiffener using the sensoractuator network for detecting the presence of damages. The sensor-actuator network is placed on both halves of the stiffened section on the accessible surface of the plate. Detecting damage in stiffener by using this technique has significant potential for SHM technology. One of the major objectives of the present work is to determine the smallest detectable crack on the stiffener using the proposed technique. Wavelet based damage parameter correlation studies are carried out. In the proposed scheme, with increase in the damage size along the stiffener, it is found that the amplitude of the received signal decreases monotonically. The advantage of this technique is that the stiffened panels need not be disassembled in a realistic deployment of SHM system.

Lamb wave inspection is one of the most widely used damage detection techniques based on ultrasonic waves. Many signal processing techniques have been developed for extraction of signal features related to damage. The majority of these investigations focus on amplitude analysis. The paper analyses Lamb wave instantaneous phase and frequency. The Hilbert transform is used to obtain signal instantaneous characteristics. Application examples are related to smart structural repair. Cracked metallic plates are repaired using bonded aluminium patches instrumented with low-profile, surface bonded piezoceramic transducers. The study demonstrates that phase and frequency information from Lamb waves is very useful for monitoring structural repair.

Guided ultrasonic waves are widely used in Structural Health Monitoring applications for inspections of large plate-like structures. Wave propagation phenomena associated with guided ultrasonic waves are difficult to model for complex engineering structures. Various simulation algorithms used in practice are not accurate and very expensive computationally. The paper demonstrates new parallel computation technology offered by modern Graphics Processing Units (GPUs) and Compute Unified Device Architecture (CUDA) used in low-cost graphical cards available in standard PCs. Such systems enable calculations of very large models in minutes. The Local Interaction Simulation Approach (LISA) algorithm have been implemented and used for wave propagation modelling. Application examples are related to structural damage detection. The results demonstrate good accuracy and effective computational performance.

Varieties in results obtained from similar wave distribution experiments in light of environment's geometry have been subjects of many studies. One such difference has been observed while using small coupons or belts as experiment samples in comparison with bigger sheets in industrial scale. The difference in question is perhaps more noticeable here than in any other application. A principal contributor to the existence of such differences is known as Back Wall effect. This phenomenon, in addition to strengthening the signal energy and increasing the number of peaks with same thresholds of signal recording, changes the frequency content of the analyzed signal within the designated time frame. In this investigation, simulation of similar conditions are carried out by generating acoustic waves within an aluminum sheet to study the Back Wall effect received from the outermost wall through wavelet analysis. Obtained results from this investigation however, will not only be limited to small coupons or belts alone. They are extendable to long sheets at the time of sensor installation at sidewalls.

During an MR procedure, the patient absorbs a portion of the transmitted RF energy, which may result in tissue heating and other adverse effects, such as alterations in visual, auditory and neural functions. The Specific Absorption Rate (SAR), in W/kg, is the RF power absorbed per unit mass of tissue and is one of the most important parameters related with thermal effects and acts as a guideline for MRI safety. Strict limits to the SAR levels are imposed by patient safety international regulations (CEI - EN 60601 - 2 - 33) and SAR measurements are required in order to verify its respect. The recommended methods for mean SAR measurement are quite problematic and often require a maintenance man intervention and long stop machine. For example, in the CEI recommended pulse energy method, the presence of a maintenance man is required in order to correctly connect the required instrumentation; furthermore, the procedure is complex and requires remarkable processing and calculus. Simpler are the calorimetric methods, also if in this case long acquisition times are required in order to have significant temperature variations and accurate heat capacity knowledge (CEI - EN 60601 - 2 - 33). The phase transition method is a new no-calorimetric method to measure SAR in MRI which has the advantages to be very simple and to overcome all the typical calorimetric method problems. It does not require in gantry temperature measurements, any specific heat or heat capacity knowledge, but only mass and time measurement. On the other hand, it is necessary to establish if all deposited power SAR can be considered acquired and measured. In this paper, that will be shown.

MatCAKE (www.cake.unisa.it) is a toolbox for integrating 2D NMR spectra by the CAKE (Monte CArlo peaK volume Estimation)1 algorithm within the Matlab environment (www.mathworks.com). Quantitative information from multidimensional NMR experiments can be obtained by peak volume integration. The standard procedure (selection of a region around the chosen peak and addition of all values) is often biased by poor peak definition because of peak overlap. CAKE is a simple algorithm designed for volume integration of (partially) overlapping peaks. Assuming the axial symmetry of two-dimensional NMR peaks, as it occurs in NOESY and TOCSY when Lorentz-Gauss transformation of the signals is carried out, CAKE estimates the peak volume by multiplying a volume fraction by a factor R. It represents a proportionality ratio between the total and the fractional volume, which is identified as a slice in an exposed region of the overlapping peaks. The volume fraction is obtained via Monte Carlo Hit-or-Miss technique, which proved to be the most efficient because of the small region and the limited number of points within the selected area. Due to the large number of software packages available for processing nuclear magnetic resonance data, MatCAKE is designed just for implementing the new CAKE algorithm. In MatCAKe, in fact, only already processed bidimensional spectra are imported and, at the moment, the only volume integration (by CAKE and by the most simple standard procedure) are allowed. MatCAKE is a free software at disposal for the scientific community and can be obtained on line at the web address cake.unisa.it.

Structural health monitoring (SHM) has been adopted as a technique to monitor the structure performance to detect damage in aging infrastructure. The ultimate goals of implementing an SHM system are to improve infrastructure maintenance, increase public safety, and minimize the economic impact of an extreme loading event by streamlining repair and retrofit measures. With the recent advances in wireless communication technology, wireless SHM systems have emerged as a promising alternative solution for rapid, accurate and low-cost structural monitoring. This article presents an enabling, developing damage algorithm to advance the detection and diagnosis of damage to structures for SHM using networks of wireless smart sensors. Networks of wireless smart sensors are being used as a vibration based structural monitoring network that allows extraction of mode shapes from output-only vibration data from an underground structure. The mode shape information can further be used in modal methods of damage detection. These sensors are being used to experimentally verify analytical models of post-earthquake evaluation based on system identification analysis. Damage measurement system could play a significant role in monitoring/recording with a higher level of completeness the actual seismic response of structures and in non-destructive seismic damage assessment techniques based on dynamic signature analysis.

THz and millimeter wave technology have shown the potential to become a valuable medical imaging tool because of its sensitivity to water and safe, non-ionizing photon energy. Using the high dielectric constant of water in these frequency bands, reflectionmode THz sensing systems can be employed to measure water content in a target with high sensitivity. This phenomenology may lead to the development of clinical systems to measure the hydration state of biological targets. Such measurements may be useful in fast and convenient diagnosis of conditions whose symptoms can be characterized by changes in water concentration such as skin burns, dehydration, or chemical exposure. To explore millimeter wave sensitivity to hydration, a reflectometry system is constructed to make water concentration measurements at 100 GHz, and the minimum detectable water concentration difference is measured. This system employs a 100 GHz Gunn diode source and Golay cell detector to perform point reflectivity measurements of a wetted polypropylene towel as it dries on a mass balance. A noise limited, minimum detectable concentration difference of less than 0.5% by mass can be detected in water concentrations ranging from 70% to 80%. This sensitivity is sufficient to detect hydration changes caused by many diseases and pathologies and may be useful in the future as a diagnostic tool for the assessment of burns and other surface pathologies.

Microbial corrosion of reinforce concrete structure is a new branch of learning. This branch deals with civil engineering , environment engineering, biology, chemistry, materials science and so on and is a interdisciplinary area. Research progress of the causes, research methods and contents of microbial corrosion of reinforced concrete structure is described. The research in the field is just beginning and concerted effort is needed to go further into the mechanism of reinforce concrete structure and assess the security and natural life of reinforce concrete structure under the special condition and put forward the protective methods.

The microorganism index, physical and chemical property such as the pH value, water content and organic matter of silt around pier in the typical area of yellow river are determined. These get ready to research the microorganism corrosion of pier in the silt of the typical area of yellow river and have very important theoretical significance and realistic meaning for researching systematically the microorganism corrosion of pier in the silt of the typical area of yellow river.