The paper presents a unified computer assisted automatic damage identification technique based on a damage index, associated with changes in the vibrational and wave propagation characteristics in damaged structures. An improved ultrasonic and vibration test setup consisting of distributed, high fidelity, intelligent, surface mounted sensor arrays is used to examine the change in the dynamical properties of realistic composite structural components with the appearance of damage. The sensors are assumed to provide both the low frequency global response (i.e., modal frequencies, mode shapes) of the structure to external loads and the (local) high frequency signals due to wave propagation effects in either passive or active mode of the ultrasonic array. Using the initial measurements performed on an undamaged structure as baseline, the damage indices are evaluated from the comparison of the frequency response of the monitored structure with an unknown damage. The technique is applied to identify impact damage in a woven stiffened composite plate that presents practical difficulties in transmitting waves across it due to scattering and other energy dissipation effects present in the material and the geometry of the structure. Moreover, a sensitivity analysis has been carried out in order to estimate a threshold value of the index below which no reliable information about the state of health of the structure can be achieved. The feasibility of developing a practical Intelligent Structural Health Monitoring (ISHM) System, based on the concept of "a structure requesting service when needed," is discussed.

Ultrasonic monitoring schemes for the detection of the solid-liquid interface during directional solidification have been developed including electronic equipment for the Material Science Laboratory (MSL) of the International Space Station (ISS). Special signal and data processing suitable for automatic monitoring, on board signal averaging, and operation under a limited data transfer condition is discussed. The achievable resolution in the micrometer regime as well as post experimental processing and evaluation for high resolution monitoring are presented and exemplified for typical applications.

Continuous real time structural health monitoring will be a requirement for future space launch missions. Reusable metallic cryotanks manufactured using Friction Stir Welding (FSW) technology for multiple missions, demands weld and microstructural integrity. The FS weld contains multiple interfaces and a variety of microstructures. To develop NDE-based health monitoring capability which detects damage and monitors the progression of damage, in the presence of these microstructural inhomogeneities, is a challenging task. Most structural health monitoring techniques are based on acoustic wave propagation. To design and develop efficient and optimized health monitoring capability based on acoustics, it is necessary to incorporate local elastic property variations that arise due to differences in the weld microstructure. These local elastic property changes across FSW regions have been measured using a focused acoustic beam. Measurements across the weld line show variations with a maximum change of 1% in the sound velocities. Macroscopic measurements of velocity of surface acoustic waves propagating across and also parallel the weld line in a large plate show significant variation. Experimental results of local and macroscopic sound velocity measurements from the changing microstructure along with their impact on the design of structural health monitoring system are discussed.

Vibration-based structural health monitoring has largely considered applied excitations as the primary means of inducing structural vibration. Here we consider how ambient vibrations might be used to assess the level of damage in a composite UAV wing. The wing consists of a foam core and a carbon fiber skin. We subject the wing to various amounts of impact damage in order to cause internal delaminations. The wing is then excited using a gust loading waveform in an effort to simulate the forcing the wing is expected to see in flight. We then use a probabilistic description of the structure's dynamics to assess the level of damage-induced nonlinearity in the wing. The approach is capable of making the diagnosis in the absence of a representative baseline data set from the "healthy" wing.

A model thermal protection system (TPS) was designed by bonding ceramic porous tiles to 2.2 and 3.5 mm thick 2124-T351 aluminum alloy plates. One of the goals of the present work was to investigate the potential of detecting simulated defects using guided waves. Simulated defects consisted of cracks, voids and delaminations at the tile-substrate interface. Cracks and voids were introduced into the porous tiles during the fabrication of the TPS. Delamination was created by cutting the gluing tape between the tile and the aluminum substrate. Guided wave propagation studies were conducted using the pitch-catch approach, while changing the angle of strike and the frequency of the transducer excitation to generate the appropriate guided wave mode. The receiver was placed at a distance so that only the guided waves were received during the immersion experiment. The delamination defect could be conclusively detected, however the presence of the imperfect bond between the tiles and the substrate interfered with the detection of the simulated cracks and voids in the porous tiles.

There is ongoing research at Carnegie Mellon University to develop a "baseline-free" nondestructive evaluation technique. The uniqueness of this baseline-free diagnosis lies in that certain types of damage can be identified without direct comparison of test signals with previously stored baseline signals. By relaxing dependency on the past baseline data, false positive indications of damage, which might take place due to varying operational and environmental conditions of in-service structures, can be minimized. This baseline-free diagnosis technique is developed based on the concept of a time reversal process (TRP). According to the TRP, an input signal at an original excitation location can be reconstructed if a response signal obtained from another point is emitted back to the original point after being reversed in a time domain. Damage diagnosis lies in the premise that the time reversibility breaks down when a certain type of defect such as nonlinear damage exists along the wave propagation path. Then, the defect can be sensed by examining a reconstructed signal after the TRP. In this paper, the feasibility of the proposed NDT technique is investigated using actual test data obtained from the Buffalo Creek Bridge in Pennsylvania.

Lamb waves have been widely used as an efficient means of detecting damage in plate-like structures. Numerous signal-processing techniques are available for evaluating and processing measured Lamb waves for damage identification. In this study, we investigated the use of a novel excitation that is created by frequency up-conversion of a standard Lorenz chaotic signal into the acoustic regime. Recent research has shown that high frequency chaotic excitation and state space reconstruction may be used to identify incipient damage (loss of preload) in a bolted joint. In this study, an experiment is undertaken using an aluminum plate with an array of piezoceramic patches bonded to one side. Damage is initiated through the process of electrolytic corrosion. A novel spatio-temporal prediction error algorithm is used to determine the existence, location, and extent of damage. This paper summarizes considerations needed to design such a damage identification system, experimental procedures and results, and additional issues that can be used as a guideline for future investigation.

Harsh environmental and operating conditions often leave pipeline systems prone to cracks, corrosion, and other aging defects. If left undetected, these forms of damage can lead to the failure of the pipeline system, which may have catastrophic consequences. Most current forms of health monitoring for pipeline systems involve nondestructive evaluation (NDE) techniques. These techniques often require a pipeline system to be taken out of operation at regularly scheduled intervals so that a technician can perform a prescribed NDE measurement. Such a measurement also requires direct access to the pipe's exterior or interior surface. This access may require excavation if the pipe is underground and the removal of insulating layers when present. This research proposes the use of Macro-fiber composite (MFC) actuators for damage detection in pipeline structures. Because MFC actuators are durable and relatively inexpensive, they can be permanently bonded to the surface of a pipe during installation. Therefore, measurements for damage detection can be performed at any time, even while the system is still in operation. The time reversal methods use the propagation of Lamb waves to evaluate the structural health of a pipeline system. A burst waveform is used to excite Lamb waves in a pipe at an initial location using an array of MFC patches. The measured response at the actuation location is reversed in time and used as the excitation signal at the second location. The initial excitation signal is then compared to the final response signal. The performance of the time reversal methods was compared to the traditional methods of Lamb wave propagations using standard tone burst waveforms.

Non-Destructive Evaluation (NDE) of plate structures is frequently carried out in industrial and laboratory environments. In this paper the wave scattering from horizontally oriented internal cavities or cracks in a plate are studied using DPSM (Distributed Point Source Method). DPSM has gained popularity in last few years in the field of ultrasonic field modelling. DPSM is a semi-analytical technique that can be used to calculate the ultrasonic field (pressure, velocity and displacement fields in a fluid, or stress and displacement fields in a solid) generated by ultrasonic transducers. So far the technique has been used to model ultrasonic field near a fluid-solid interface when a solid half-space is immersed in a fluid. This method has also been used to model the ultrasonic field generated in a homogeneous isotropic solid plate immersed in a fluid. The objective of this study is to present the theoretical modelling of the diffraction and scattering pattern of guided waves in the solid plate when the transducers of finite dimension are placed on both side of the defective plate

In this paper the Semi-Analytical Finite Element (SAFE) method for modeling guided wave propagation is extended to account for linear viscoelastic material damping. Linear viscoelasticity is introduced by allowing for complex stiffness constitutive matrices for the material. Dispersive characteristics of viscoelastic waveguides, such as phase velocity, attenuation, energy velocity and cross-sectional wavestructures are extracted. Knowledge of the above-mentioned dispersive properties is important in any structural health monitoring attempt that uses ultrasonic guided waves for long range inspection. The proposed damped formulation is applied to several waveguides with different mechanical and geometric properties. In particular, a viscoelastic isotropic plate, a railroad track and a pipe are studied.

This research demonstrates two methodologies for detecting cracks in a metal spindle housed deep within a vehicle wheel end assembly. First, modal impacts are imposed on the hub of the wheel in the longitudinal direction to produce broadband elastic wave excitation spectra out to 7000 Hz. The response data on the flange is collected using 3000 Hz bandwidth accelerometers. It is shown using frequency response analysis that the crack produces a filter, which amplifies the elastic response of the surrounding components of the wheel assembly. Experiments on wheel assemblies mounted on the vehicle with the vehicle lifted off the ground are performed to demonstrate that the modal impact method can be used to nondestructively evaluate cracks of varying depths despite sources of variability such as the half shaft angular position relative to the non-rotating spindle. Second, an automatic piezo-stack actuator is utilized to excite the wheel hub with a swept sine signal extending from 20 kHz. Accelerometers are then utilized to measure the response on the flange. It is demonstrated using frequency response analysis that the crack filters waves traveling from the hub to the flange. A simple finite element model is used to interpret the experimental results. Challenges discussed include variability from assembly to assembly, the variability in each assembly, and the high amount of damping present in each assembly due to the transmission gearing, lubricant, and other components in the wheel end. A two-channel measurement system with a graphical user interface for detecting cracks was also developed and a procedure was created to ensure that operators properly perform the test.

In recent years, substantial research has been conducted to advance structural control as a direct means of mitigating the dynamic response of civil structures. In parallel to these efforts, the structural engineering field is currently exploring low-cost wireless sensors for use in structural monitoring systems. To reduce the labor and costs associated with installing extensive lengths of coaxial wires in today's structural control systems, wireless sensors are being considered as building blocks of future systems. In the proposed system, wireless sensors are designed to perform three major tasks in the control system; wireless sensors are responsible for the collection of structural response data, calculation of control forces, and issuing commands to actuators. In this study, a wireless sensor is designed to fulfill these tasks explicitly. However, the demands of the control system, namely the need to respond in real-time, push the limits of current wireless sensor technology. The wireless channel can introduce delay in the communication of data between wireless sensors; in some rare instances, outright data loss can be experienced. Such issues are considered an intricate part of this feasibility study. A prototype Wireless Structural Sensing and Control (WiSSCon) system is presented herein. To validate the performance of this prototype system, shaking table experiments are carried out on a half-scale three story steel structure in which a magnetorheological (MR) damper is installed for real-time control. In comparison to a cable-based control system installed in the same structure, the performance of the WiSSCon system is shown to be effective and reliable.

To continue with the development of a wireless sensing unit built upon an off-the-shelf FPGA development board presented by the authors at SPIE 2005, this paper outlines a further effort consisting of embedding onboard computations, simulation and validation of the FPGA-based wireless sensing unit that is able to collect, process and transmit data. This research supports the concepts of decentralized wireless sensor networks and local-based damage detection, where individual wireless sensor nodes are capable of performing intricate tasks and can eventually transmit the processed results. An FPGA-based hardware platform is thus looked upon as a major contender for performing this function in a proficient manner. Throughout this research, the principal design complexities, in terms of both hardware and software development, are kept to a minimum. Development cycle and monetary cost of the hardware are other major considerations for this research. Data processing functions including windowing, Fast Fourier Transform (FFT), peak detection, are implemented into the selected FPGA, when limitations of different design options are explored to yield a solution that optimizes the resources of the selected FPGA. Numerical simulations and laboratory validations are carried out to scrutinize the operations and flexibility of the design.

Ultrasonic methods are widely applied for nondestructive evaluation of structural components during both the manufacturing process and subsequent field inspections. The field inspections often require expensive teardown in order to access the back surfaces of critical components. Active ultrasonic methods are also a subject of ongoing research for structural health monitoring whereby transducers are permanently attached to a structure and signals are monitored to detect changes caused by structural damage. This paper presents a methodology for effectively combining ultrasonic monitoring and inspection. During the monitoring phase, detection and localization of possible damage is demonstrated on several specimens using attached transducers. This detection phase is followed by demonstration of a new inspection method referred to as Acoustic Wavefield Imaging (AWI) which utilizes the attached transducers as sources and a single externally scanned air-coupled transducer as a receiver. The acoustic wavefield images are useful for both checking the viability of the attached transducers and quantifying the extent of damage. The AWI method approaches the sensitivity of conventional through transmission ultrasonic methods but does not require access to both sides of structural components. Thus, it is very well suited for rapid field inspection of structural assemblies.

Thermal protection system is a critical component of a space vehicle and is essential for safe re-entry into the atmosphere. The loss of stiffness in tile-based thermal protection system is an essential mode of damage and has lead to loss of a space vehicle due to excessive aero-dynamic heating during re-entry. The inherent nonlinear nature of the coupling of these tiles with the space vehicle body is well-known. This paper explores this nonlinear coupling and proposes a method based on continuation analysis of the nonlinear model to detect and track this damage. The model used was first proposed by Luo and Hanagud.¹ White, Adams and Jata (2005)² used modal analysis to conduct system identification and damage identification on a similar system using method of virtual forces. The present research presents another approach by utilizing periodic excitations to estimate the presence and degree of damage. Parametric studies are also conducted to study the effect of variations in mass on the detection of change in stiffness using the proposed method.

A small size prototype of a Structural Neural System (SNS) was tested in real time for damage detection in a laboratory setting and the results are presented in this paper. The SNS is a passive online structural health monitoring (SHM) system that can detect small propagating damages in real time before the overall failure of the structure is realized. The passive SHM method is based on the concept of detecting acoustic emissions (AE) due to damage propagating. Propagating cracks were identified near the vicinity of a sensor in a composite specimen during fatigue testing. In the composite specimen, in additions to a propagating crack, fretting occurred because of slipping contact between the load points and the composite specimen. The SNS was able to predict the location of damage due to crack propagation and also detect signals from fretting simultaneously in real time.

This paper presents the development of a high precision three-dimensional measurement system using laser doppler vibrometers. Two measurement systems were developed. Then, the following fundamental issues were studied and the results presented: measurement principle, accuracy with respect to long distance measurements and laser beam angles. As examples of possible applications of the system, measurements of ground motion, measurement of wave propagation in a plate and vibration measurement of a steel railway bridge were treated.

SASW has been well known as one of nondestructive testing methods for pavements. This method makes use of the dispersion characteristics to estimate the thickness and modulus of pavement layers. It is difficult to obtain accurate dispersion curves even if the analytical surface wave fields are used, where only the stiffness proportional damping is considered. However, the good agreement of dispersion curves has been found for the analytical surface wave fields if Rayleigh damping is adopted in the numerical simulation. In this paper, a dynamic general FEM software was developed to inverse the layer moduli and Rayleigh damping coefficient of the tested pavement structure using the portable FWD data. It shows that the predicted dispersion curves are well approximately to ones obtained from experimental SASW.

Safety criteria of aircraft industry require careful inspection of aircraft components for structural integrity since airworthiness of aging aircraft can be significantly affected by combination of corrosion and fatigue damage. Surface defects can be efficiently detected by visual or other surface inspection techniques. Detection of hidden defects, on the other hand, is still a challenging task. Therefore, it is essential to develop non-destructive methods that can inspect different layers of the aircraft structures for internal defects before they become a safety concern. Ultrasonic probes with the dry-coupled substrates are highly efficient for all modalities of ultrasonic techniques including pulse-echo, pitch-catch, or through-transmission modes. The probes can be deployed in conjunction with portable ultrasonic instruments for B- and C-scanning. The dry-coupled probes have already been tested on a number of aircraft for rapid inspections of the aircraft structures from the outside without any disassembly. However, adequate inspection for small pitting corrosion and incipient fatigue cracks in metallic structures or delaminations in composite panels may require superior sensitivity and resolution of the applied ultrasonic technique. Several novel configurations of the dry-coupled probes with increased sensitivity and resolution will be presented. Ultrasonic imaging with single- or double-element dry-coupled probes will be demonstrated on the specimens with heavy pitting corrosion, machined planar and volumetric defects, and embedded internal flaws.

We describe work carried out to monitor the structural health of a complex structure comprising both carbon fibre and metal components using ultrasound techniques. The work is designed to be used in a high performance car, but could find applications in other areas such as the aerospace industry. There are two different types of potential problem that need to be examined; the first is damage (e.g. holes, delaminations) to carbon fibre structure, and the second is damage to joints either between two carbon fibre components or between a carbon fibre component and a metallic one. The techniques used are based around the use of PZT transducers for both the generation and detection of ultrasonic Lamb waves. To date we have been carrying out experiments on mock-up samples, but are due to conduct tests on an actual vehicle. Lamb waves propagate in modes whose order is determined by the frequency thickness product. Their properties, such as phase and amplitude can be modified by the presence of damage, such as holes and delaminations. If we record the response of a healthy structure, we can then compare it with signals obtained on subsequent occasions to determine if any significant change has taken place. It is essential, however, to be able to differentiate between the effects of damage and those of environmental changes such as temperature. For this reason we have monitored the response of a sample at different temperatures both before and after drilling a hole in it to simulate damage. Depending on the positions of the transducers with respect to the damaged area, it is possible to detect either attenuation of the entire signal or changes in a specific portion of the signal produced by reflections. Results from these experiments will be presented at the conference. Signal processing techniques for separating damage from the effects of temperature will also be discussed. We also look at the deterioration of joints, which can either be epoxy bonded (carbon fibre to carbon fibre) or bolted together (carbon fibre to aluminium). In the case of the bonded structures we are looking at the effects of failure of the bond layer, whilst in the case of the bolted samples we are looking at loosening of the bolts. The debonding was simulated by joining together a flat plate of carbon fibre composite with an L-shaped carbon fibre piece using a couplant such as grease. Similar experiments were carried out using an aluminium anglebar bolted to the plate, with the bolts both tightened and loose. Signals of both the transmitted wave in the plate and the power coupled to the L piece were measured before and after debonding. This gives a more reliable measure of the change in power transfer between the two components as the joint/bond degrades. It was found that in order to get maximum coupling to the second component the frequency of the acoustic wave had to be altered. This is because in the bonding region the combined thickness of the components alters the modal propagation characteristics of the structure compared with those of the single component region.

This paper presents methods for characterizing nonlinearities and sudden disturbances in stationary/transient responses by decomposing signals using the Hilbert-Huang transform (HHT) and a sliding-window fitting (SWF) technique. Similar to the wavelet transform SWF uses windowed regular harmonics and their orthogonality to extract local harmonic components. However, SWF decomposes a signal into less components because it allows distorted harmonics, and it provides time-varying amplitudes and frequencies of extracted components that can reveal system's nonlinearities. To extract components from a signal HHT uses the apparent time scales shown by the local maxima and minima of the signal (instead of using orthogonality of chosen fitting functions) and cubic spline fitting of extrema to sequentially sift components of different time scales, starting from highfrequency ones to low-frequency ones. Because it does not use orthogonality of functions, HHT provides more accurate time-varying amplitudes and frequencies of extracted components for accurate estimation of system characteristics and nonlinearities. Because the first extracted component contains all original discontinuities, its time-varying amplitude and frequency are excellent indicators of sudden transient disturbances. However, the discontinuity-induced Gibbs' phenomenon makes HHT analysis inaccurate around the two data ends. On the other hand, the SWF analysis has no Gibbs' phenomenon at the two data ends, but it cannot extract accurate modulation frequencies due to the use of non-orthogonal basic functions in the sliding-window least-squares curve-fitting process. Numerical and experimental results show that HHT can provide accurate extraction of intrawave amplitude- and phase-modulation, distorted harmonic response under a single-frequency harmonic excitation, softening and hardening effects, different orders of nonlinearity, interwave amplitude- and phasemodulation, multiple-mode vibrations caused by internal/external resonances, and instants of impact loading on a structure from stationary/transient responses. These phenomena are keys for performing dynamics-based structural damage detection and health monitoring.

Dynamic interrogation of structures for the purposes of damage identification is an active area of research within the field of structural health monitoring with recent work focusing on the use of chaotic excitations and state-space analyses for improved damage detection. Inherent in this overall approach is the specific interaction between the chaotic input and the structure's eigenstate. The sensitivity to damage is theoretically enhanced by special tailoring of the input in terms of stability interaction with the structure. This work outlines the use of an evolutionary program to search the parameter space of a chaotic excitation for those parameters that are best suited to appropriately couple the excitation with the structure for enhanced damage detection. State-space damage identification metrics are used to detect damage in a computational model driven by excitations produced via the evolutionary program with non-optimized excitations used as comparison cases.

This paper presents Wireless Intelligent Sensor and Actuator Network (WISAN) as a scalable wireless platform for structural health monitoring. Design of WISAN targeted key issues arising in applications of structural health monitoring. First, scalability of system from a few sensors to hundreds of sensors is provided through hierarchical cluster-tree network architecture. Special consideration is given to reliable delivery of wireless data in real-world conditions. Second, a possibility of autonomous operation of sensor nodes from energy harvesters is ensured through extremely low power consumption in operational and standby modes of operation. Third, all the sensors and actuators operate in globally synchronized time on the order of a few microseconds through utilization of the beaconing mechanism of IEEE802.15.4 standard. Fourth, depending on application requirements, the system is capable of delivering real-time streams of sensor data or performing on-sensor storage and/or processing with result transmission. Finally, a capability to work with heterogeneous arrays of sensors and actuators is ensured by a variety of analog and digital interfaces. Results of experimental tests validate the performance of the WISAN.

This paper presents the development and applications of a miniaturized impedance sensor node for structural health monitoring. The principle behind the impedance-based structural health monitoring technique is to apply high frequency structural excitations (typically higher than 30 kHz) through the surface-bonded piezoelectric transducers, and measure the impedance of structures by monitoring the current and voltage applied to the piezoelectric transducers. Changes in impedance indicate changes in the structure, which in turn can indicate that damage has occurred. Although many proof-of-concept experiments have been performed using the impedance methods, the impedance-measuring device is bulky and impractical for field-use. Therefore, a recently developed, miniaturized, low-cost impedance measurement chip was used to measure and record the electric impedance of a piezoelectric transducer. The performance of this miniaturized and portable device has been compared to our previous results and its effectiveness has been demonstrated in detecting bolt preload changes in a bolted frame structure. Furthermore, the possibility of wireless communication and local signal processing at the sensor node has been investigated by integrating the device with a microprocessor and telemetry.

Recently, damage sensitive features extracted from the phase space reconstruction of a structural response have proven to be successful for use in the field of structural health monitoring. One such feature utilizes the evolutions of randomly selected points on a baseline attractor to predict evolutions of corresponding points on an attractor in some unknown state of health. The error based on this prediction can be used to determine the presence and/or extent of damage. One drawback of this approach is that some regions of the attractor geometry may be more or less sensitive to damage-induced changes in the dynamics. Thus, prediction error could incur large variances in its distribution, and results could change significantly depending on the size and location of the randomly selected subset of points used for prediction. This paper examines the effect of spatial location on prediction error in an effort to better utilize the geometry of phase space. Investigations will involve a chaos-driven oscillator subject to parametric changes simulating damage.

A composite optical bend loss sensor for the measurement of pressure and shear has been developed. The sensor is composed of two layers of fiberoptic mesh sensors that are molded into a thin polydimethylsiloxane (PDMS) substrate. A 3-D displacement map is generated based on bent-induced intensity attenuations in the fibers when the sensor is pressed. The new design overcame some of the coupling and instability problems in our previously reported microfabricated optical bend loss sensor. Here we will report our preliminary study on the sensor including results from the normal and shear load measurement. The paper will also discuss a RF based wireless data acquisition system that we have developed and demonstrate its operation with the composite sensor.

A high energy Nd:YAG laser source is used to determine the intrinsic adhesion strength of thin films deposited on substrates. The specimen is designed to convert the thermal energy of the short duration laser pulse to a strong compressive stress on the back face of the substrate. The compressive stress propagates through the layered structure, and upon reflection from the free surface of the film, generates a tensile wave which produces tensile failure of the interface. The stress associated with the interface failure is calculated from a theoretical model of wave propagation through the layered medium. The compressive stress produced by the laser source is determined from a second experiment involving the homogeneous substrate by removing the film. Examples of the applications of the technique in cell biology are presented.

The main objectives of PCB (Printed Circuit Board) testing are to find short and open circuits before attaching components to the PCB. An electrostatic imaging technique was described earlier by Zentai at al. in the SPIE-NDE 2003 conference and has been accepted as a US patent. The main goal of that application was to test the PCBs quickly and efficiently without attaching test probes to each of the traces. It was achieved with the proposed technique. However, we still had to use test probe matrix for generating test signals in the traces and the detected signal was greatly reduced in reference to the test signal because of capacitive sharing of charges caused by the insulator layer placed between the PCB and the TFT sensor array. A new idea has been developed for applying voltages to the traces with an addressing matrix, different from the pin addressing one. This matrix is similar to the readout matrix that the previous method referenced to, but instead of readout circuits, driver circuits are connected to the pixels to apply voltages to them. The printed circuit board is laid on top of the array, but rather than using an insulator foil, a directional conducting foam (rubber) layer can be applied between the excitation matrix (array) and the PCB. We get direct coupling of the matrix pixels to the PCB traces and no connection between neighboring pixels (traces) using the directional conductive layer, which conducts only in z direction and not in x (and y) direction. Therefore, by addressing each pixel separately, which is easy to do by software, we get an addressable voltage (pulse) injector matrix. The same directional conducting foam coupling can also be used for reading out the image of traces. Because the capacitive coupling is eliminated, the detected signal increases and so the sensitivity.

We have developed a soft lithography method to replicate polymer waveguides. In this method, the waveguides are produced by a two-step molding process where master mold is first formed on a negatively tone phototresist and subsequently transferred to a PDMS mold, and silicone rubber mold is then used as a stamp to transfer the final waveguide pattern onto a UV cure epoxy. Initial results show good pattern transferring in physical shape. The optical performance is measured based on the propagation loss. In our design, the measurement was measured at 0.26 dB/mm for 1.3μm and 0.24 dB/mm for 1.55μm.

This paper presents the analysis of the modes of a viscometer optical fiber vibration based on a simplified mathematical model. The initial quasilinear equation with discontinuous coefficients, which describes the vibration of an optical fiber partially immersed in liquid, is reduced to the telegraph equation with constant effective coefficients. The form of these coefficients is chosen such a way to capture the most important physics of the immersed fiber's vibration. The subsequent analytical solution of the model in an attempt to give results that accurately follow the trends of experimental results.

Synchronous operation of a confocal laser scanning microscope (CLSM) and a confocal vector contrast scanning acoustic microscope (phase sensitive scanning acoustic microscopy: PSAM) has been developed. Imaging is performed on objects mounted on a cover slide with the CLSM operated in reflection through the slide with an immersion fluid and PSAM operating in water respectively aqueous solutions from the other side (half space). Examples involving living cells and soft matter samples illustrating various combinatory schemes and advantages of multi-contrast optical and acoustic contrast are demonstrated. This includes combinations with fluorescence microscopy and ultrasonic topographical imaging as well as combinatory three-dimensional imaging.

The integration of autonomous wireless elements in health monitoring network increases the reliability by suppressing power supplies and data transmission wiring. Micro-power piezoelectric generators are an attractive alternative to primary batteries which are limited by a finite amount of energy, a limited capacity retention and a short shelf life (few years). Our goal is to implement such an energy harvesting system for powering a single AWT (Autonomous Wireless Transmitter) using our SSH (Synchronized Switch Harvesting) method. Based on a non linear process of the piezoelement voltage, this SSH method optimizes the energy extraction from the mechanical vibrations. This AWT has two main functions : The generation of an identifier code by RF transmission to the central receiver and the Lamb wave generation for the health monitoring of the host structure. A damage index is derived from the variation between the transmitted wave spectrum and a reference spectrum. The same piezoelements are used for the energy harvesting function and the Lamb wave generation, thus reducing mass and cost. A micro-controller drives the energy balance and synchronizes the functions. Such an autonomous transmitter has been evaluated on a 300x50x2 mm³ composite cantilever beam. Four 33x11x0.3 mm³ piezoelements are used for the energy harvesting and for the wave lamb generation. A piezoelectric sensor is placed at the free end of the beam to track the transmitted Lamb wave. In this configuration, the needed energy for the RF emission is 0.1 mJ for a 1 byte-information and the Lamb wave emission requires less than 0.1mJ. The AWT can harvested an energy quantity of approximately 20 mJ (for a 1.5 Mpa lateral stress) with a 470 μF storage capacitor. This corresponds to a power density near to 6mW/cm³. The experimental AWT energy abilities are presented and the damage detection process is discussed. Finally, some envisaged solutions are introduced for the implementation of the required data processing into an autonomous wireless receiver, in terms of reduction of the energy and memory costs.

This research experimentally implements a new method to identify the location and magnitude of a single impulsive excitation to ceramic body armor, which is supported on a compliant torso. The method could easily be extended to other flexibly supported components that undergo rigid body dynamics. Impact loads are identified in two steps. First, the location of the impact force is determined from time domain acceleration responses by comparing them to an array of reference acceleration time histories. Then based on the estimated location, reference frequency response functions are used to reconstruct the input force in the frequency domain through a least squares inverse problem. Experimental results demonstrate the validity of this method at both low energy excitations, which are produced by a medium modally-tuned impact hammer, and at high energy excitations, which are produced by dropping rods with masses up to 0.6 kilograms from a height of 2 meters. The maximum error in the estimated location or magnitude for the low energy excitations on the 10 cm square ceramic body armor was 7.07 mm with an average error of 1.09 mm. In comparing the estimated force for the low energy excitations to the force recorded by the transducer in the modal impact hammer, the maximum error in the predicted force amplitude was 6.78 percent and the maximum error in the predicted impulse was 6.44 percent. For the high energy excitations, which produced accelerations at the measurement locations up to 50 times greater than that of the low energy excitations, the maximum error in the predicted location of the input force was 15 mm with an average error of 6.64 mm. There was no force transducer to capture the input force on the body armor from the rod, but from non-energy-dissipative projectile motion equations the validity of the solutions was confirmed by comparing the impulses.

Two types of piezoelectric wafer active sensor (PWAS) oscillators, Colpitts-type PWAS oscillator and series-type PWAS oscillator, designed for in-vivo monitoring of capsule formation around soft tissue implants have been presented. Both of the oscillators were explored analytically and experimentally. Colpitts-type PWAS oscillator uses the inductive property of the PWAS in its resonant frequency range and operates at the first resonant frequency of the PWAS. However, it is too sensitive to the surrounding damping. Therefore, it may not be an appropriate candidate for in-vivo application. For the series-type PWAS oscillator, some preliminary experiments showed that this type of oscillator can tell the difference in viscosity/damping conditions of different media. More work, such as calibration of output of the oscillator, needs to be done before using it in in-vivo monitoring of capsule formation.

Acoustic and optical multiple contrast microscopy has been employed in order to explore characterizable parameters of red blood cells, including cells infected by the parasite Plasmodium falciparum, in order to investigate cellular modifications caused by the infection and to identify possible detection schemes for disease monitoring. Imaging schemes were based on fluorescence, optical transmission, optical reflection, and amplitude and phase of ultrasound reflected from the cells. Contrast variations observed in acoustic microscopy, but not in optical microscopy, were tentatively ascribed to changes caused by the infection.

Ultrasonic NDI methods have an impressive record of applications on metallic and composite structures. However, limitations arise from the need for a wet couplant between the specimen and the transducer and the rather long inspection times necessitated by point-by-point scanning of large structures. To overcome these constraints, a dry-contact large-area ultrasonic imaging system is being developed for real-time high-resolution NDI applications. This system includes the following: a large ultrasonic source, either piezoelectric or laser-based, a polymer dry-couplant, and a commercially available real-time ultrasonic CCD camera displaying easy-to-interpret images rather than A-scans. Applications of this real-time high-resolution ultrasonic imaging system on metallic and composite structures, using either PZT or laser-based ultrasound generation as the source, are presented. Aluminum and unidirectional and woven composites have been investigated. Images acquired in both through-transmission and pulse-echo modes are presented. Images of artificial defects of different types and shapes in the investigated materials will be demonstrated. The latest developments of the imaging system, with laser-based ultrasound generation as the source, are also reported. The laser-based source provides an efficient solution for some applications of the imaging system. In this configuration, the ultrasound is generated in a 1in. diameter area by an expanded laser beam which heats a constrained absorbing polymer layer. The soft polymer layer is also used as dry couplant to transmit the ultrasound between the test sample and the imaging system.

Surface focused acoustic transmission microscopy is employed for projection (tomographic) imaging of bonded materials including wafers. Short pulse excitation with apodized focusing transducers operated in transmission and two channel quadrature transient detection are employed for multiple contrast imaging. The achievable contrast schemes are based on mode selection for longitudinal, transverse, mode converted, and scattered modes. The identification of the involved modes including conversion schemes is experimentally accessible by time-gating of the recorded signal and by observation of spatially selected holograms. Perfect bonding, disbonding, and weak bonding can be studied and characterized by the developed mode selective imaging scheme. The characteristic features of weak bonding phenomena are demonstrated and characterized.

Many small scale image display systems, such as head mounted displays (HMDs), beam light from an optical fiber onto deflectable mirrors or rotating polygonal mirrors to produce an image on an image plane. This approach has many size limitations. For instance, light beams of less than 3 millimeters are impractical for displays using mirrors, because mirror scanners and grating deflectors must be significantly larger than the light beam diameter to avoid beam clipping or adding diffraction. Reducing the diameter of a conventional display device reduces the possible number of pixels, and thus reduces the resolution and/or field of view (FOV) of the device. Our proposed HMD system focus on reducing the hardware while maintaining a high resolution by utilizing a microfabricated 2D optical scanner combined with a field-programmable gate array (FPGA) controller for display.

Electric surface excitation of ultrasound in the Coulomb field of scanned electrically conductive spherical local probes and similar detection has been employed for imaging of the transport properties of acoustic waves in piezoelectric materials including singlecrystalline wafers. The employed Coulomb scheme leads to a fully predictable and almost ideal point excitation and detection. In combination with two-channel quadrature transient detection it allows high precision spatially and temporally resolved holographic imaging. Via modeling of the excitation and propagation properties, the effective elastic tensor and the piezoelectric properties of the observed materials can be determined with high resolution from a single measurement. The generation and detection scheme as well as the theoretical background are demonstrated and applications are exemplified.

In this paper a numerical technique for microwave imaging based on a two-dimensional inverse scattering method is proposed. This method is a non-destructive imaging technique that combines finite difference time domain (FDTD) analysis with genetic algorithm (GA) optimization to find the dielectric properties of the object under test. The applications of the proposed method can vary from medical imaging to nondestructive testing of materials and structures.

Anemia is a serious worldwide disorder affecting 2 billion people globally. While the only clinically accepted method of diagnosis remains an invasive blood draw and laboratory analysis, numerous attempts have been made to measure total blood hemoglobin noninvasively. Although the palpebral conjunctiva can be used as a poor qualitative indicator of anemia, a quantitative analysis of the conjunctiva using visible diffuse reflectance spectroscopy can provide an accurate and easy method of noninvasive measurement. Preliminary studies using a traditional grating based spectrometer have shown this method of analysis to be effective and accurate at diagnosing anemia and are presented here. An alternative device to collect diffuse reflectance spectroscopy based on tunable liquid crystal technology that is comparatively inexpensive and compact is also presented. Deformed helix ferroelectric liquid crystals (DHFLC) can be tuned fully across the visible spectrum and have a narrow bandwidth of reflection. A handheld microspectrometer facilitates this technique becoming a clinically viable method of analysis and enables total hemoglobin to be measured quickly, and without the need of a blood draw. The rapidity of this test can make total hemoglobin measurement a new vital sign, increasingly important because of the concurrent appearance of anemia with numerous other disorders.