This PDF file contains the front matter associated with SPIE Proceedings Volume 8341, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Energy harvesting from human locomotion is a challenging problem because the low frequencies involved are incompatible with small, light-weight transducers. Furthermore, frequency variations during changing levels of activity greatly reduce the effectiveness of tuned resonant devices. This paper presents the performance analysis and parameter study of energy harvesters utilizing magnetic interactions for frequency up-conversion. Ferrous structures are used to periodically attract a magnetic tip mass during low-frequency oscillations, producing a series of impulses. This technique allows resonant structures to be designed for much higher natural frequencies and reduces the effects of excitation frequency variation. Measured vibrational data from several human activities are used to provide a time-varying, broadband input to the energy harvesting system and are recreated in a laboratory setting for experimental validation. Optimal load resistances are calculated under several assumptions including sinusoidal, white noise, and band-limited noise base excitations. These values are tested using simulations with real-world accelerations and compared to steady-state power optimization results. The optimal load is presented for each input signal, and an estimation of the maximum average power harvested under idealized conditions is given. The frequency up-conversion technique is compared to linear, resonant structures to determine the impact of the nonlinearities. Furthermore, an analysis is performed to study the discrepancies between the simulated results and the predicted performance derived from frequency response functions to determine the importance of transients.

For many reasons, it would be beneficial to have the capability of powering a wildlife tag over the course of multiple migratory seasons. Such an energy harvesting system would allow for more data collection and eliminate the need to replace depleted batteries. In this work, we investigate energy harvesting on birds and focus on vibrational energy harvesting. We review a method of predicting the amount of power that can be safely harvested from the birds such that the effect on their longterm survivability is not compromised. After showing that the safely harvestable power is significant in comparison to the circuits used in avian tags, we present testing results for the flight accelerations of two species of birds. Using these measured values, we then design harvesters that matched the flight acceleration frequency and are sufficiently low mass to be carried by the birds.

A novel magnetostrictive-material-based device concept to convert ambient mechanical vibration into electricity has been designed, fabricated, and tested. In order to harvest energy over a greater frequency range as compared to state-of- the-art devices, an L-shaped beam which is tuned so that the first two (bending) natural frequencies have a (near) two-to-one ratio is used as a mechanical transducer to generate nonlinear oscillations. Under harmonic excitation, an internal resonance or autoparametric, dynamic response can occur in which one vibration mode parametrically excites a second vibration mode resulting in significant displacement of both modes over an extended frequency range. A magnetostrictive material, Metglas 2605SA1, is used to convert vibration into electricity. Vibration-induced strain in the Metglas changes its magnetization which in turn generates current in a coil of wire. Metglas is highly flexible so it can undergo large displacement and does not fatigue under extended excitation. Demonstration devices are used to study how this nonlinear response can be exploited to generate electricity under single-frequency, harmonic and random base excitation.

In this study, an extension of linear-quadratic-Gaussian (LQG) control theory is used to determine the optimal state feedback controller for a nonlinear energy harvesting system that is driven by a stochastic disturbance. Specifically, the energy harvester is a base-excited single-degree-of-freedom (SDOF) resonant oscillator with an electromagnetic transducer embedded between the ground and moving mass. The electromagnetic transducer used to harvest energy from the SDOF oscillator introduces a nonlinear Coulomb friction force into the system, which must be accounted for in the design of the controller. As such, the development of the optimal controller for this system is based on statistical linearization, whereby the Coulomb friction force is replaced by an equivalent linear viscous damping term, which is calculated from the stationary covariance of the closed-loop system. It is shown that the covariance matrix and optimal feedback gain matrix can be computed by implementing an iterative algorithm involving linear matrix inequalities (LMIs). Simulation results are presented for the SDOF energy harvester in which the performance of the optimal state feedback control law is compared to the performance of the optimal static admittance over a range of disturbance bandwidths.

The control of vibrating structures using piezoelectric elements connected to simple control circuits, known as shunts, is a widely studied field. Many different shunts have been researched that haven been shown to obtain strong performance in both narrow and broadband frequency ranges. Yet, the choice for the exact parameters of these shunts can be found different ways. In this work, a new method of selecting the components of a negative capacitance shunt is presented. An impedance model of a piezoelectric patch is developed and used to predict the control of a vibrating structure. The model predicts the magnitude of the strain induced voltage caused by the vibrating substrate through the computation of two voltage readings within the shunt. It is then confirmed experimentally, that it is possible to obtain experimentally the shunt parameters that produce maximum control through measurement of the shunt response.

Structural vibrations can be reduced by shunted piezoelectric elements. The passive piezoelectric damper considered here, consists of a piezoelectric element connected to a host structure and shunted by an inductor-resistor network. The paper gives an in depth analysis on the tuning of the inductor and resistor parameters of the electric network with regard to different optimization goals. The calculations are based on a 2-degree-of-freedom model of the host structure and the shunted piezoelectric element. Three optimization goals are studied: The objective of eigenvalue optimization is to get both pairs of eigenvalues to be equal. Then the damping ratio of the host structure is maximized, leading to a minimized decay time of the free vibration. In the H₂ optimization the total vibration energy within the host system is minimized, leading to optimal results in case of a broad-band excitation. In the H_∞ optimization the objective is to minimize the maximum amplitude of the host structure over the whole frequency spectrum. Analytical solutions for these optimization goals are already known in the special case of a host structure without damping. In the more general case of a viscously damped host structure analytical solutions for the eigenvalue and H₂ optimization goal are derived. In case of the H_∞ optimization goal an analytical solution cannot be found and perturbation theory is used to calculate an analytical approximation. The approximation is compared to the numerical solution in order to check its accuracy.

This paper presents an advanced controller design methodology for vibration alleviation of helicopter rotor sys- tems. Particularly, vibration alleviation in a forward ight regime where the rotor blades experience periodically varying aerodynamic loading was investigated. Controller synthesis was carried out under the time-periodic H₂ and H_∞ framework and the synthesis problem was solved based on both periodic Riccati and Linear Matrix Inequality (LMI) formulations. The closed-loop stability was analyzed using Floquet-Lyapunov theory, and the controller's performance was validated by closed-loop high-delity aeroelastic simulations. To validate the con- troller's performance an actively controlled trailing edge ap strategy was implemented. Computational cost was compared for both formulations.

A star-shaped biphasic composite has been characterized and successively manufactured. This particular shape could potentially provide an enhancement in terms of strain energy dissipation when compared against classical composites with circular inclusion. The rationale of this work is to demonstrate by means of FE analysis and successively by dynamic testing that this topology effectively provides an increase in damping

This research investigates a bi-stable oscillator which, through snap-through actions, can significantly increase energy dissipation loss factor and provide passive damping adaptability with respect to input amplitude and frequency. The increase in motion generated during snap-through leads to a significant increase in the energy dissipated by the embedded damper and the corresponding loss factor. The system parameters can be designed such that the snap-though threshold occurs at different input amplitudes. Overall, the device can be programmed to adjust damping to changes in the loading environment in a passive manner.

A nonlinear piezoelectric wind energy harvester is proposed which has a low startup wind speed and is not restricted to a specific wind speed. By using the piezoelectric transduction mechanism, the gearbox is eliminated from the system and the start up speed is improved. Permanent magnets are placed in the blade part of the windmill. The interactions between the rotating magnets, positioned on the blades, and the tip magnets mounted on the piezoelectric beams directly and parametrically excite the beams. The nonlinear magnetic force makes the vibrations of the beams nonlinear and can make the beams bi-stable. This phenomenon is utilized to enhance the power output and to improve the robustness of the power production. Two designs are presented which incorporate parametric and ordinary excitations to generate electric power. The performance of each design is examined through experimental investigations. An analytic model is developed which is verified by the experimental results and explains the nonlinear phenomena captured by the experimental investigations.

The primary purpose of this research effort is to propose a novel efficiency boosting design feature in a drag type vertical axis wind turbine (VAWT), explore practicality through design and fabrication, and test the viability of the design through wind tunnel experiments. Using adaptive control surface design and an improved blade shape can be very useful in harnessing the wind's energy in low wind speed areas. The new design is based on a series of smaller blade elements to make any shape, which changes to reduce a negative resistance as it rotates and thus maximizing the useful torque. As such, these blades were designed into a modified Savonius wind turbine with the goal of improving upon the power coefficient produced by a more conventional design. The experiment yielded some positive observations with regard to starting characteristics. Torque and angular velocity data was recorded for both the conventional configuration and the newly built configuration and the torque and power coefficient results were compared.

Energy harvesting from flowing fluids using flapping wings and fluttering aeroelastic structures has recently gained significant research attention as a possible alternative to traditional rotary turbines, especially at and below the centimeter scale. One promising approach uses an aeroelastic flutter instability to drive limit cycle oscillations of a flexible piezoelectric energy harvesting structure. Such a system is well suited to miniaturization and could be used to create self-powered wireless sensors wherever ambient flows are available. In this paper, we examine modeling of the aerodynamic forces, power extraction, and efficiency of such a flapping wing energy harvester at a low Reynolds number on the order of 1000. Two modeling approaches are considered, a quasi-steady method generalized from existing models of insect flight and a modified model that includes terms to account to the effects of dynamic stall. The modified model is shown to provide better agreement with CFD simulations of a flapping energy harvester.

Exploiting human motion for the purpose of energy harvesting has been a popular idea for some time. Many of the approaches proposed can be uncomfortable or they impose a significant burden on the person's gait. In the current paper a hardware in-the-loop simulator of an energy harvesting backpack is employed in order to investigate the effect of a suspended-load backpack on the human gait. The idea is based on the energy produced by a suspended-load which moves vertically on a backpack while a person walks. The energy created from such a linear system can be maximised when it resonates with the walking frequency of the person. However, such a configuration can also cause great forces to be applied on the back of the user. The system which is presented here consists of a mass attached on a rucksack, which is controlled by a motor in order to simulate the suspended-load backpack. The advantage of this setup is the ability to test different settings, regarding the spring stiffness or the damping coefficient, of the backpack harvester, and study their effect on the energy harvesting potential, as well as on the human gait. The present contribution describes the preliminary results and analysis of the testing of the system with the help of nine male volunteers who carried it on a treadmill.

Energy harvesting technology is critical in the development of self-powered electronic devices. Over the past few decades, several transduction mechanisms have been investigated for harvesting various forms of ambient energy. This paper provides an investigation of a novel transducer material for vibration energy harvesting; piezoelectret foam. Piezoelectrets are cellular ferroelectret foams, which are thin, flexible polymeric materials that exhibit piezoelectric properties. The basic operational principle behind cellular ferroelectrets involves the deformation of internally charged voids in the polymer, which can be represented as macroscopic dipoles, resulting in a potential developed across the material. Both the mechanical and electromechanical properties of this material are investigated in this work. Mechanical testing is performed using traditional tensile testing techniques to obtain experimental measures of the stiffness and strength of the materials. Electromechanical testing is performed in order to establish a relationship between input mechanical energy and output electrical energy by dynamically measuring the piezoelectric constant, d₃₃. Additionally, the properties of ferroelectret foams are compared to those of polyvinylidene fluoride (PVDF), a conventional polymer-based piezoelectric material whose crystalline phase exhibits piezoelectricity through dipole orientation. Finally, the feasibility of vibration energy harvesting using piezoelectret materials is investigated.

This study presents the manufacturing process, experimental characterization, and analytical modeling of fluidic artificial muscles (FAMs) with millimeter-scale diameters. First, a fabrication method was developed to consistently deliver low-cost, high-performance, miniature FAMs using commercially available materials. The quasi-static behavior of these FAMs was determined through experimentation on a single actuator with an active length of 39.16 mm (1.54 in) and a diameter of 4.13 mm (0.1625 in) using compressed air as the working fluid. Tests were carried out at several discrete actuation pressures ranging from 207 kPa (30 psi) to 552 kPa (80 psi) in order to demonstrate the full evolution of force with displacement over a broad spectrum of operating pressures. The results of these tests also revealed the blocked force and free contraction capabilities of the FAM at each internal pressure. When pressurized to 552 kPa (80 psi), the actuator was capable of delivering a maximum blocked force of 132.9 N (29.87 lb) and a maximum free contraction of ΔL/L₀ = 0.0688. Furthermore, it is the goal of this work to compare the data from these experiments to previously developed models for full-scale PAMs. Using two formulations, one derived using a force balance approach and the other obtained using virtual work methods, the experimental data was validated against existing analytical models. With the inclusion of correction factors to account for physical phenomena encountered during testing, comparison between the models and the experimental results indicate that the improved models accurately predict the behavior of these miniature FAMs at low contractions.

We present a proof of concept (POC) for haptic interaction when audio or visual feedback is not practical. The POC includes addressable arrays of two-way Shape Memory Alloy (SMA) springs which can operate at a lower voltage and temperature compatible with mobile devices. They will form different shapes due to the thermal effect as current travels through the springs. The POC can simultaneously realize multiple methods for conveying haptic information such as dimension, force, texture and temperature due to the flexible array design. The haptic interface can go back to the original shape by itself after the current is off due to the advance of two way SMA. We are developing applications with different POC designs for tangible interactions.

In this paper, we cover our studies on accelerating the molding process of a polymer by applying acoustic stress-wave time reversal. Tests carried out on an epoxy polymer mixed with a curing agent have shown evidence that the introduction of unfocused acoustic energy during the molding process will accelerate that process. The effects of focusing acoustic energy at a mold discontinuity while curing are explored. We also detail our investigations on focusing acoustic energy at a crack location by iteratively applying time reversal. Multiple types of media were tested.

This paper compares six different filtering protocols used in Acoustic Emission (AE) monitoring of fatigue crack growth. The filtering protocols are combination of three different filtering techniques which are based on Swansong-like filters and load filters. The filters are compared deterministically and probabilistically. The deterministic comparison is based on the coefficient of determination of the resulting AE data, while the probabilistic comparison is based on the quantification of the uncertainty of the different filtering protocols. The uncertainty of the filtering protocols is quantified by calculating the entropy of the probability distribution of some AE and fracture mechanics parameters for the given filtering protocol. The methodology is useful in cases where several filtering protocols are available and there is no reason to choose one over the others. Acoustic Emission data from a compact tension specimen tested under cyclic load is used for the comparison.

Passive dampers can be used to connect two adjacent structures in order to mitigate earthquakes induced pounding damages. Theoretical and experimental studies have confirmed efficiency and applicability of various connecting devices, such as viscous damper, MR damper, etc. However, few papers employed optimization methods to find the optimal mechanical properties of the dampers, and in most papers, dampers are assumed to be uniform. In this study, we optimized the optimal damping coefficients of viscous dampers considering a general case of non-uniform damping coefficients. Since the derivatives of objective function to damping coefficients are not known, to optimize damping coefficients, a heuristic search method, i.e. the genetic algorithm, is employed. Each structure is modeled as a multi degree of freedom dynamic system consisting of lumped-masses, linear springs and dampers. In order to examine dynamic behavior of the structures, simulations in frequency domain are carried out. A pseudo-excitation based on Kanai-Tajimi spectrum is used as ground acceleration. The optimization results show that relaxing the uniform dampers coefficient assumption generates significant improvement in coupling effectiveness. To investigate efficiency of genetic algorithm, solution quality and solution time of genetic algorithm are compared with those of Nelder-Mead algorithm.

The development of a prototype two degree-of-freedom parallel mechanism for application to unmanned ground vehicle target tracking is presented. The mechanism is extremely simple, decoupling the two end-effector degrees-of- freedom (DOFs) with an easily fabricated and inexpensive connection of passive joints. A summary of the parallel mechanism's kinematic design and singularity analysis is provided. A 2-DOF tracking system using a digital camera with a large time delay is presented. A command feedforward controller is designed to extend the tracking bandwidth by approximately two octaves beyond that of the feedback controller without violating causality. Experimental data is presented that shows improvement in the tracking performance by a factor of 2.4 over the feedback system alone.

Shear mode or rotary drum-type magnetorheological energy absorbers (MREAS) are an attractive option for use in occupant or payload protection systems that operate at shear rates well over 25,000 s^-1. However, their design is still performed using material properties measured using low-shear rate (<1,000 s^-1) characterization techniques. This paper details a method for characterizing MR fluids at high shear rates, and presents characterization results for three commercially available MR fluids. It is proposed to utilize the perspective of apparent viscosity (the ratio of shear stress over shear rate) vs. shear rate to describe the behavior of the fluid at these shear rates. Good agreement between the measured data and predictions of MR fluid behavior are achieved using this framework. By expanding the knowledge of MR fluid behavior to these high shear strain rates, the design of MREAs is enabled for occupant protection systems for crash and mine blast events.

This paper describes the development of a safety-clutch by using magnetorheological fluids (MRF) to switch the transmission torque between a motor and a generator in a bus-like vehicle. The clutch is based on a new design combining an axial MRF-actuator and a ball coupling mechanism. This so called "MRF-ball-clutch" avoids the disadvantages of traditional bell- or disc-MRF-clutch designs where the torque is transmitted by the MRF which leads to a self-heating due to the shearing forces in the fluid and a more or less significant drag torque caused by limitations of the relation between minimal and maximal transmittable torque. The safety clutch based on the new MRF-clutch design requires a minimum of power consumption and allows switching high torsional moments in a very compact, lightweight and robust design. The work was done within the Fraunhofer System Research for Electromobility FSEM, founded by the German Federal Ministry of Research and Technology.

This paper is aimed to provide a feasibility study of self-powered magnetorheological (MR) damper systems, which could convert vibration and shock energy into electrical energy to power itself under control. The self-powered feature could bring merits such as higher reliability, energy saving, and less maintenance for the MR damper systems. A self-powered MR damper system is proposed and modeled. The criterion whether the MR damper system is self-powered or not is proposed. A prototype of MR damper with power generation is designed, fabricated, and tested. The modeling of this damper is experimentally validated. Then the damper is applied to a 2 DOF suspension system under on-off skyhook controller, to obtain the self-powered working range and vibration control performance. Effects of key factors on the self-powered MR damper systems are studied. Design considerations are given in order to increase the self-powered working range.

Smart structures with tunable damping and stiffness characteristics are of high interest to aerospace applications, but often require an external power source to be activated. This can be avoided by using highly concentrated silica suspensions, which exhibit a shear-thickening behavior, linked to a dramatic increase in viscous dissipation. These materials are however liquid at rest, and sensitive to humidity, so they are difficult to implement as such into structural applications. In the present work, highly concentrated solutions of monodisperse silica particles in PEG were selected for their strong thickening effect at rather low critical shear strain. Damping properties were characterized by measuring the energy dissipated per cycle at low frequency (<2Hz) during oscillatory tests using a rheometer. STF were impregnated in an open-cell foam scaffold and encapsulated into a RTV-silicone to produce patches that can be handled easily. Silicone also protects the STF against outgassing or humidity pickup. Experimental results show a simultaneous increase of stiffness and damping properties for theses patches at low frequencies and large strains. Damping is thus getting closer to the range of elastomeric commercial damping materials, possibly overtaking them in specific conditions.

This paper investigates the potential of designing a vibratory energy harvester which utilizes a ferrofluid sloshing in a seismically excited tank to generate electric power. Mechanical vibrations change the orientational order of the magnetic dipoles in the ferrofluid and create a varying magnetic flux which induces an electromotive force in a coil wound around the tank, thereby generating an electric current according to Faraday's law. Several experiments are performed on a cylindrical container of volume 5x10^-5 m³ carrying a ferrofluid and subjected to different base excitation levels. Initial results illustrate that the proposed device can be excited at one or multiple modal frequencies depending on the container's size, can exhibit tunable characteristics by adjusting the external magnetic field, and currently produces 28 mV of open-circuit voltage using a base excitation of 2.5 m/s² at a frequency of 5.5 Hz.

This work presents the optimization of radio frequency (RF) to direct current (DC) circuits using Schottky diodes for remote wireless energy harvesting applications. Since different applications require different wireless RF to DC circuits, RF harvesters are presented for different applications. Analytical parameters influencing the sensitivity and efficiency of the circuits are presented. Results showed in this report are analytical, simulated and measured. The presented circuits operate around the frequency 434 MHz. The result of an L-matched RF to DC circuit operates at a maximum efficiency of 27 % at -35 dBm input. The result of a voltage multiplier achieves an open circuit voltage of 6 V at 0 dBm input. The result of a broadband circuit with a frequency band of 300 MHz, achieves an average efficiency of 5 % at -30 dBm and open circuit voltage of 47 mV. A high quality factor (Q) circuit is also realized with a PI network matching for narrow band applications.

The electrical response of multiple piezoelectric oscillators connected in parallel and endowed with various energy harvesting circuits is investigated here. It is based on the idea of equivalent load impedance of piezoelectric capacitance coupled with harvesting circuits. The main result is the matrix formulation of generalized Ohm's law whose impedance matrix is explicitly expressed in terms of load impedance. It is validated numerically through standard circuit simulations.

Electromagnetic vibration energy harvesters have been widely used to convert the vibration energy into electricity. However, one of the main challenges of using electromagnetic vibration energy harvesters is that they are usually in very large size with low power density. In this paper, a new type of electromagnetic vibration energy harvester with remarkably high power density is developed. By putting the strong rare-earth magnets in alternating directions and using high-magnetic-conductive casing, magnetic flux density up to 0.9T are obtained. This configuration also has a small current loop with less electrical reluctance, which further increases the high power density when the coil is designed to follow the current loop. The prototype, the size of which is 142x140x86 mm³, can provided up to 727Ns/m damping coefficient, which means 428 kNs/m⁴ damping density when it is shunt with 70Ω external resistive load which is set to the same as the internal resistor of the harvester to achieve maximum power. The corresponding power density is 725 μW/cm³ at 15HZ harmonic force excitation of 2.54mm peak-to-peak amplitude. When shot-circuited, 1091Ns/m damping coefficient and 638 kNs/m⁴ damping density is achieved. The effectiveness of this novel vibration energy harvester is shown both by FEA and experiments. The eddy current damper is also discussed in this paper for comparison. The proposed configuration of the magnet array can also be extended for both micro-scale and large-scale energy harvesting applications, such as vibration energy harvesting from tall buildings, long bridges and railways.

This paper outlines a new class of piezoelectric flight control actuators which are specifically intended for use in guided hard-launched munitions from under 5.56mm to 40mm in caliber. In March of 2011, US Pat. 7,898,153 was issued, describing this new class of actuators, how they are mounted, laminated, energized and used to control the flight of a wide variety of munitions. This paper is the technical conference paper companion to the Patent. A Low Net Passive Stiffness (LNPS) Post Buckled Precompressed (PBP) piezoelectric actuator element for a 0.40 caliber body, 0.50 caliber round was built and tested. Aerodynamic modeling of the flight control actuator showed that canard deflections of just ±1° are more than sufficient to provide full flight control against 99% atmospherics to 2km of range while maintaining just 10cm of dispersion with lethal energy pressure levels upon terminal contact. Supersonic wind tunnel testing was conducted as well as a sweep of axial compression. The LNPS/PBP configuration exhibited an amplification factor of 3.8 while maintaining equivalent corner frequencies in excess of 100 Hz and deflection levels of ±1°. The paper concludes with a fabrication and assembly cost analysis on a mass production scale.

Natural laminar flow is one of the challenging aims of the current aerospace research. Main reasons for the aerodynamic transition from laminar into turbulent flow focusing on the airfoil-structure is the aerodynamic shape and the surface roughness. The Institute of Composite Structures and Adaptive Systems at the German Aerospace Center in Braunschweig works on the optimization of the aerodynamic-loaded structure of future aircrafts in order to increase their efficiency. Providing wing structures suited for natural laminar flow is a step towards this goal. Regarding natural laminar flow, the structural design of the leading edge of a wing is of special interest. An approach for a gap-less leading edge was developed to provide a gap- and step-less high quality surface suited for natural laminar flow and to reduce slat noise. In a national project the first generation of the 3D full scale demonstrator was successfully tested in 2010. The prototype consists of several new technologies, opening up the issue of matching the long and challenging list of airworthiness requirements simultaneously. Therefore the developed composite structure was intensively tested for further modifications according to meet requirements for abrasion, impact and deicing basically. The former presented structure consists completely of glass-fiber-prepreg (GFRP-prepreg). New functions required the addition of a new material-mix, which has to fit into the manufacturing-chain of the composite structure. In addition the hybrid composites have to withstand high loadings, high bending-induced strains (1%) and environmentally influenced aging. Moreover hot-wet cycling tests are carried out for the basic GFRP-structure in order to simulate the long term behavior of the material under extrem conditions. The presented paper shows results of four-points-bending-tests of the most critical section of the morphing leading edge device. Different composite-hybrids are built up and processed. An experimental based trend towards an optimized material design will be shown.

This paper details experimental characterization of an autonomous gust alleviation system building upon recent advances in harvester, sensor and actuator technology that have resulted in the possibility of thin, ultra-light weight multilayered wing spars. This multifunctional spar considers an autonomous gust alleviation system for small UAV powered by the harvested energy from ambient vibration during their normal flight conditions. Experimental characterization is performed on cantilever wing spars with micro-fiber composite transducers controlled by reduced energy controllers. Energy harvesting abilities of monolithic and micro fiber composite transducers are also compared for the multifunctional wing spar. Normal flight vibration and wind gust signals are simulated using Simulink and Control desk and then generated for experimental validation analysis for gust alleviation. Considering an aluminum baseline multifunctional wing spar, a reduction of 11dB and 7dB is obtained respectively for the first and the second mode. Power evaluations associated with various electronic components are also presented. This work demonstrates the use of reduced energy control laws for solving gust alleviation problems in small UAV, provides the experimental verification details, and focuses on applications to autonomous light-weight aerospace systems.

This paper outlines the design, fabrication and testing of a new, high performance piezoelectrically driven aircraft flutter test vane. This flutter test vane utilizes low-net passive stiffness (LNPS) actuator configurations to produce deflection amplification ratios on the order of 5:1 while maintaining full blocked moment generation capability. With an order of magnitude lower weight than conventional vanes, the LNPS flight flutter test vane is capable of producing larger amplitude structural deflections with smaller force levels because vane forcing waveforms, frequencies and phasing can be very exactingly controlled with respect to each other. The paper covers the fundamental driving theories behind the device, actuator geometry, test article layout, fabrication and testing. This device was wind tunnel tested at airspeeds up to 110 ft/s with excellent correlation between theory and experiment. Experimental tests show an improvement in angular deflection and delta lift forces from approximately ±1.8 deg. and 0.45 lb_f to ±8.5 deg. and 1.45 lb_f, respectively. The flutter test vane consumes only 1W of peak power at max. actuation frequency, drastically reducing the impact of electrical power supply lines on the modal mass of the wing. This paper describes the modeling, testing and evaluation of the adaptive flutter test vane and quantifies the implications on the current state of flight flutter testing.

Piezoelectric materials have been proposed as a means of decreasing turbomachinery blade vibration either through a passive damping scheme, or as part of an active vibration control system. For polymer matrix fiber composite (PMFC) blades, the piezoelectric elements could be embedded within the blade material, protecting the brittle piezoceramic material from the airflow and from debris. Before implementation of a piezoelectric element within a PMFC blade, the effect on PMFC mechanical properties needs to be understood. This study attempts to determine how the inclusion of a packaged piezoelectric patch affects the material properties of the PMFC. Composite specimens with embedded piezoelectric patches were tested in four-point bending, short beam shear, and flatwise tension configurations. Results show that the embedded piezoelectric material does decrease the strength of the composite material, especially in flatwise tension, attributable to failure at the interface or within the piezoelectric element itself. In addition, the sensing properties of the post-cured embedded piezoelectric materials were tested, and performed as expected. The piezoelectric materials include a non-flexible patch incorporating solid piezoceramic material, and two flexible patch types incorporating piezoelectric fibers. The piezoceramic material used in these patches was Navy Type-II PZT.

The natural frequency coupling of 2 components of a sounding rocket system is studied, the forward bulkhead (commonly referred to as the "bulkhead" or "BH") and the payload cavity within the fairing. The bulkhead was modeled as a thin, flat, circular plate with a clamped boundary condition. The payload cavity was modeled as a column of air with closed ends contained by the rocket fairing. Both components were studied individually, and added together to obtain a coupled effect. The components were studied in terms of theoretical calculations and understanding, while testing the theory against experiments conducted in the laboratory. When appreciable differences between theory and experimental results were within reason for the individual components, the coupled system was tested. This methodology enabled a "piecewise" approach to studying and acquiring natural frequency shifting of the sounding rocket model through coupling. Experimental work for frequency tuning of the bulkhead through internal pressure modulation is presented. Guidelines for improvement of the vibroacoustic response through structural redesign and frequency tuning of sounding rockets are detailed.

Buckling is an important design constraint in light-weight structures as it may result in the collapse of an entire structure. When a mechanical beam column is loaded above its critical buckling load, it may buckle. In addition, if the actual loading is not fully known, stability becomes highly uncertain. To control uncertainty in buckling, an approach is presented to actively stabilise a slender flat column sensitive to buckling. For this purpose, actively controlled forces applied by piezoelectric actuators located close to the column's clamped base stabilise the column against buckling at critical loading. In order to design a controller to stabilise the column, a mathematical model of the postcritically loaded system is needed. Simulating postbuckling behaviour is important to study the effect of axial loads above the critical axial buckling load within active buckling control. Within this postbuckling model, different kinds of uncertainty may occur: i) error in estimation of model parameters such as mass, damping and stiffness, ii) non-linearities e. g. in the assumption of curvature of the column's deflection shapes and many more. In this paper, numerical simulations based on the mathematical model for the postcritically axially loaded column are compared to a mathematical model based on experiments of the actively stabilised postcritically loaded real column system using closed loop identification. The motivation to develop an experimentally validated mathematical model is to develop of a model based stabilising control algorithm for a real postcritically axially loaded beam column.

In this paper, a wide-band vibration energy harvester using a nonlinear hardening oscillator with self-excitation circuit is presented. A vibration energy harvester is one of the energy-harvesting devices that collects unused energy from vibrating environment. For the conventional linear vibration energy harvester, the resonance frequency is matched to the source frequency, and the mechanical Q factor is designed as large as possible to maximize the oscillator's amplitude. The large Q factor, however, bounds the resonance in a narrow frequency band, and the performance of the vibration energy harvester can become extremely worth when the frequency of the vibration source fluctuates. As is well known, the resonance frequency band can be expanded by introducing a hardening (or softening) nonlinear oscillator. However, it is difficult for the nonlinear vibration energy harvester to maintain the regenerated power constant because such nonlinear oscillator can have multiple stable steady-state solutions in the resonance band. In this paper, a control law that switches the load resistance between positive and negative values according to the instantaneous displacement and the velocity is proposed to give the oscillator a self-excitation capability, which ensures the oscillator entrained by the excitation only in the largest amplitude solution. Moreover, an adaptive adjustment of the control law is proposed to quicken the entrainment process. Numerical analysis shows that the nonlinear vibration energy harvester with resistance switching can maintain the large amplitude response even when the excitation frequency abruptly changes.

This paper describes the development and construction of an energy harvesting device to provide a safe, reliable source of electrical energy onboard gravity-dropped weapons such as aerial bombs. The generators collect and store mechanical energy as the weapon falls away from the aircraft. Only after the weapon has fallen away from the aircraft is the stored mechanical energy released, generating electricity through a hybrid piezoelectric and electromagnetic generation method. The design, construction, and testing of the generator is discussed at length. Conceptual designs for integrating the described energy harvester alongside current and alternative sources of electrical power are also discussed.

With the continued advancement in electronics the power requirement for micro-sensors has been decreasing opening the possibility for incorporating on-board energy harvesting devices to create self-powered sensors. The requirement for the energy harvesters are small size, light weight and the possibility of a low-budget mass production. In this study, we focus on developing an energy harvester for powering a pulse rate sensor. We propose to integrate an inductive energy harvester within a commonly available pen to harvest vibration energy from normal human motions like jogging and jumping. An existing prototype was reviewed which consists of a magnet wedged between two mechanical springs housed within a cylindrical shell. A single copper coil surrounds the cylindrical shell which harvests energy through Faraday's effect during magnet oscillation. This study reports a design change to the previous prototype providing a significant reduction in the device foot print without causing major losses in power generation. By breaking the single coil in the previous prototype into three separate coils an increase in power density was achieved. Several pulse rate sensors were evaluated to determine a target power requirement of 0.3 mW. To evaluate the prototype as a potential solution, the harvester was excited at various frequencies and accelerations typically produced through jogging and jumping motion. The improved prototype generated 0.043 mW at 0.56 g_rms and 3 Hz; and 0.13 mW at 1.14 g_rms at 5 Hz. The design change allowed reduction in total volume from 8.59 cm³ to 1.31 cm³ without significant losses in power generation.

Vibration energy harvesters have been usually designed as single-degree-of-freedom (1DOF) systems. The fact that such harvesters are only efficient near sole resonance limits their applicability in frequency-variant and random vibration scenarios. In this paper, a novel multiple-DOF piezoelectric energy harvester model (PEHM) is developed, which comprises a primary mass and n parasitic masses. The parasitic masses are independent of each other but attached to the primary mass. The piezoelectric element is placed between the primary mass and the base for energy generation. First, a 2DOF model is analyzed and characterized. Through parametric analysis, it is found that with a slight increase of the overall weight to the original 1DOF harvester (without parasitic masses), two close and effective peaks or one effective peak with significantly enhanced magnitude can be achieved in the power response. Subsequently, the 2DOF model is generalized to an n-DOF model and its analytical solution is derived. This solution provides a convenient tool for parametric study and design of a multiple-DOF piezoelectric energy harvester (PEH). Useful multimodal energy harvesting can be achieved with a slight increase of the overall weight. Finally, a prototype of the proposed multiple- DOF model is devised for proof of concept.

Post-earthquake rapid recovery of bridge is one of the prime objectives for performance based design. Shape Memory Alloy (SMA) has the unique ability to undergo large deformation, but can regain its undeformed shape through stress removal (i.e. superelasticity), which brings about an added advantage in seismic regions. In an attempt to reduce permanent damage of concrete bridges, a hybrid RC bridge pier configuration is presented here. In the proposed configurations of bridge piers, the plastic hinge region is reinforced with SMA and the remaining portion with regular steel. Residual displacement is a critical parameter for performance based earthquake engineering as it dictates the functionality of a member after an earthquake. This paper evaluates fragility-based seismic vulnerability of SMA reinforced concrete bridge pier considering residual displacement. Fragility curves have also been used to assess the relative performance of SMA with conventional steel RC bridge pier. Probabilistic Seismic Demand Model (PSDM) has been used in generating the fragility functions. The development of these fragility curves for bridge piers aid in expressing the potential impact of SMA on the bridge pier vulnerability.

Piezoresistive sensors, which have been widely studied and applied to several applications, are usually made of a piezoresistive membrane attached to a flexible substrate, a plate. A topology optimization formulation for the design of piezoresistive plate-based sensors, for which the piezoresistive membrane disposition is optimized together with the substrate, is proposed in this work. The objective is to maximize the sensor sensitivity to external loading, as well as the stiffness of the sensor to particular loads. A material model for the piezoresistive membrane based on the Solid IsotropicMaterial with Penalizationmodel, and perfect coupling conditions between the plate and the membrane based on the "layerwise" theory for laminated plates are employed. Results for an AFM probe suggest that the performance of the sensors can be improved by using the proposed approach.

Large mechanical structures are often affected by high level vibrations due to their flexibility. These vibrations can reduce the system performances and lifetime and the use of active vibration control strategies becomes very attractive. In this paper a combination of resonant control and a disturbance estimator is proposed. This solution is able to improve the system performances during the transient motion and also to reject the disturbance forces acting on the system. Both control logics are based on a modal approach, since it allows to describe the structure dynamics considering only few degrees of freedom.

This study is focused on control of a scaled building structure using a new semi-active Variable Stiffness and Damping Isolator (VSDI). The proposed VSDI system consists of a traditional steel-rubber vibration absorber, and a magnetorhelogical elastomer (MRE) with a controllable stiffness and damping behavior. To demonstrate the feasibility of using VSDIs a 1:16 scaled, three-story building is constructed and installed on a shake table and its base is supported by four prototype VSDIs. The VSDIs can be regulated in real time by varying the applied magnetic field through a controller. A phenomenological model is proposed and implemented on VSDI devices. The scaled El Centro earthquake excitation is applied to the system, and the vibration mode is controlled by a Lyapunov-based control strategy. Results show that the a significant reduction in structural response can be achieved for both displacement and acceleration.

A method for measuring the stress and strain distribution in composite materials and the residual stress near the interface in smart composite has been developed. The strains are measured using electron Moiré method. In this method a very fine model grid is fabricated using the optical and electron lithography techniques on the surface of the specimen and an electron beam scan of which the spaces are almost same as that of the model grid used for the master-grid. The difference in the amount of secondary electrons per a primary electron produces the Moiré fringes that consist of bright and dark parts. The residual strain and stress around the fibers of the smart composite materials and thermal expansion ratio of a fiber and Al matrix were measured by this method.

Vibrational energy harvesting devices are oftentimes constructed in a manner identical to classical tuned-massdampers used in vibration control applications. However, many applications and models in past work assume that the harvesters will have negligible influence on the host structure (e.g. harvesters on a bridge). In contrast, this work adopts the perspective that the energy harvester is analogous to an electromechanical vibration absorber, attenuating the structural vibrations via a dominant mechanical influence while converting the absorbed energy into electric power. One embodiment of a device serving these two purposes-passive vibration attenuation and energy harvesting-is introduced. The device utilizes a distributed piezoelectric spring layer such that as the spring is strained between the top mass layer and the vibrating host structure the piezoelectric spring generates a voltage potential across its electrodes. Two experimental studies are detailed which investigate the capability for energy harvesting vibration absorbers to meet both goals. It is found that achievement of both objectives may require compromise but with proper device design still yields a viable electrical output.

With increasing demand for wireless sensor nodes in automobile, aircraft and rail applications, the need for energy harvesters has been growing. In these applications, energy harvesters provide a more robust and inexpensive power solution than batteries. In order to enhance the power density of existing energy harvesters, a variety of multimodal energy harvesting techniques have been proposed. Multi-modal energy harvesters can be categorized as: (i) Multi-Source Energy Harvester (MSEH), (ii) Multi-Mechanism Energy Harvester (MMEH), and (iii) Single Source Multi-Mode Energy Harvester (S²M²EH). In this study, we focus on developing MMEH which combines the inductive and piezoelectric mechanisms. The multi-mechanism harvester was modeled using FEM techniques and theoretically analyzed to optimize the performance and reduce the overall shape and size similar to that of AA battery. The theoretical model combining analytical and FEM modeling techniques provides the system dynamics and output power for specific generator and cymbal geometry at various source conditions. In the proposed design, a cylindrical tube contains a magnetic levitation cavity where a center magnet oscillates through a copper coil. Piezoelectric cymbal transducers were mounted on the top and bottom sections of the cylindrical shell. In response to the external vibrations, electrical energy was harvested from the relative motion between magnet and coil through Faraday's effect and from the piezoelectric material through the direct piezoelectric effect. Experimental results validate the predictions from theoretical model and show the promise of multimodal harvester for powering wireless sensor nodes in automobile, aircraft, and rail applications.

A novel technique is presented for transmitting forces to piezoelectric elements in electrical energy harvesting applications. The approach results in amplifying any force transmitted to the piezoelectric element. Additionally, the frequency of any cyclical input force is doubled. The increased performance and scalability of the technique make possible its employment in a wide variety of energy harvesting applications. The methods and designs may be mated to a number of intermediate energy harvesting techniques, which are discussed in detail with analysis of complete energy harvesting devices including specific applications in munitions.

A Multifunctional smart material system consists of two or more different smart material phases in the form of a hybrid system, in which every phase performs a different but necessary function. In this work, we show how thermally responsive Shape memory alloys (SMA) and Shape Memory Polymers (SMP) can be combined to form a Multifunctional Smart Material system (MSMS). The transformation temperatures M_f, M_s, A_s and A_f of SMA and the glass transition T_g for the SMP play a critical role in designing such a MSMS. We illustrate how varying the T_g of SMP between the transformation temperatures M_f and A_f of SMA results in a multi-state smart bias system with varying stiffnesses. In addition, we establish guidelines for the volume fractions of the individual constituents of such MSMSs to form "smart-bias" tools/devices. We further propose various ideas for smart devices that can operate through three temperature ranges, with one material constituent being passive and the other active at a given temperature.

Carbon fiber structures are claimed to offer several advantages such as contained mass, high stiffness and low thermal expansion. However, these structures are characterized by a very low mechanical damping and, therefore, they are easily subjected to potentially dangerous vibratory phenomenon. Active control techniques have been widely developed to suppress vibration and great progresses have been achieved. On the other hand the research on sensors and actuators to be used is still a field of interest. The paper discusses the opportunity to use piezoelectric actuators (PZT) and Fiber Bragg Grating sensors (FBG) to realize a smart structure including in itself both the sensing and the actuating devices. Fiber optic strain sensors, such as Fiber Bragg Gratings, have a great potential in the use in smart structures thanks to their small transversal size and the possibility to make an array of many sensors. Even if this is not the case of the reported study, they can be embedded between carbon fiber layers and their effect on the structure is usually negligible. Such a structure is able to measure its state of excitation and to reduce the amplitude of vibration using the PZT actuators. Different control strategies have been implemented on a test rig consisting on a carbon fiber cantilever beam with 14 FBG sensors and 3 PZT actuators. Control forces are designed to increase the damping of the structures, allowing to increase of damping of the first modes of vibration of about 10 times.

This paper presents design and analysis of a 10GHz inductance-capacitance (LC)-Voltage-Controlled Oscillators (VCO) implemented with a very high quality (Q) factor on-chip Micro-Electro-Mechanical Systems (MEMS) inductor using 0.25μm silicon-on-sapphire (SOS) technology. A new symmetric topology of suspended MEMS inductor is proposed to reduce the length of the conductor strip and achieve the lowest series resistance in the metal tracks. This MEMS inductor has been suspended above the high resistivity SOS substrate to minimise the substrate loss and therefore, achieve a very high Q-factor inductor. A maximum Q-factor of 191.99 at 11.7GHz and Q-factor of 189 at 10GHz has been achieved for a 1.13nH symmetric MEMS inductor. The proposed inductor has been integrated with a VCO on the same substrate using the Metal layers in SOS technology removing the need for additional bond wire. The 10GHz LC-VCO has achieved a phase noise of -116.27dBc/Hz and -126.19dBc/Hz at 1MHz and 3MHz of offset frequency, respectively. It consumes 4.725mW of power from 2.5V supply voltage while achieving a Figure of Merit (FOM) of -189.5dBc/Hz.

This paper presents design of a Film Bulk Acoustic Wave Resonators (FBARs) consisting of piezoelectric film, aluminium nitride (AlN) with top and bottom electrodes of ruthenium (Ru). The lumped Butterworth-Van Dyke (BVD) Circuit model is used to investigate the theoretical harmonic response and extraction equivalent circuit of the FBAR. A three-dimensional (3D) Finite Element Method (FEM) is used to evaluate the electro-mechanical performance of the FBAR. The one-dimension (1D) numerical and the 3D FEM simulation results are analysed and compared. The results show that coupling coefficient (k² _eff) up to 7.0% can be obtained with optimised thickness ratio of electrode/piezoelectric layers. A Figure of Merit (FOM) that considers k² _eff and quality (Q) factor is used for comparison. The area of FBAR is 900μm² and the active filter area size of the FBAR filter is 5400μm². The FBAR filter is designed for operation in Kuband with centre frequency of 15.5 GHz and fractional bandwidth of 2.6%. The proposed FBAR filter has insertion loss of -2.3dB which will improve the performance of Ku-band transceiver and improve communication range and data rates in Ku-band communication links.

Sensitive deformation of polymer gel actuator induced by various stimuli has been intensively investigated. The utilization of light however will significantly broaden their applications. Here we show that photo-responsive gels prepared from rigid poly(amide acid) chains having azobenzene moieties in main chains can undergo a macroscopic deformation induced by photo-isomerization. A rod-shape gel can sharply and swiftly bend by blue laser irradiation and reversibly straighten when exposed to visible light. By using a scanning microscopic light scattering, the optimal preparing condition of the gels was determined and the reversible change in mesh-size between 2.1 nm and 0.83 nm was observed.

It is well known that power density of piezoelectric transformers is limited by mechanical stress. The power density of piezoelectric transformers calculated by the stress boundary can reach 330 W/cm³. However, no piezoelectric transformer has ever reached such a high power density in practice. The power density of the piezoelectric transformer is limited to 33 W/cm³ typically. This fact implies that there is another physical limitation in piezoelectric transformer. In fact, it is also known that piezoelectric material is constrained by vibration velocity. Once the vibration velocity is too large, the piezoelectric transformer generates heat until it cracks. To explain the instability of piezoelectric transformer, we will first model the relationship between vibration velocity and resulting heat by a physical feedback loop. It will be shown that the vibration velocity as well as the heat generation determines the loop gain. A large vibration velocity and heat may cause the feedback loop to enter into an unstable state. Therefore, to enhance the power capacity of piezoelectric transformer, the heat needs to be dissipated. In this paper, we used commercial thermal pads on the surface of the piezoelectric transformer to dissipate the heat. The mechanical current of piezoelectric transformers can move from 0.382A/2W to 0.972A/9W at a temperature of 55°C experimentally. It implies that the power capacity possibly increases 3 times in the piezoelectric material. Moreover, piezoelectric transformers that are well suited in applications of high voltage/low current becomes also well suited for low voltage/high current power supplies that are widely spread. This technique not only increases the power capacity of the piezoelectric transformer but also allows it to be used in enlarged practical applications. In this paper, the theoretical modeling will be detailed and verified by experiments.

During the last years, more and more mechanical applications saw the introduction of active control strategies. In particular, the need of improving the performances and/or the system health is very often associated to vibration suppression. This goal can be achieved considering both passive and active solutions. In this sense, many active control strategies have been developed, such as the Independent Modal Space Control (IMSC) or the resonant controllers (PPF, IRC, . . .). In all these cases, in order to tune and optimize the control strategy, the knowledge of the system dynamic behaviour is very important and it can be achieved both considering a numerical model of the system or through an experimental identification process. Anyway, dealing with non-linear or time-varying systems, a tool able to online identify the system parameters becomes a key-point for the control logic synthesis. The aim of the present work is the definition of a real-time technique, based on ARMAX models, that estimates the system parameters starting from the measurements of piezoelectric sensors. These parameters are returned to the control logic, that automatically adapts itself to the system dynamics. The problem is numerically investigated considering a carbon-fiber plate model forced through a piezoelectric patch.

Recently, piezocomposite generating elements (PCGEs) have been proposed for improving the electricity generation performance of piezoceramic wafers. The residual stress in the PZT layer after curing is one of the main reasons for PCGE's enhanced performance, and the outer epoxy-based composites protect the brittle PZT layer. In this work, we propose a d₃₃-mode PCGE that can be used for energy harvesting. The piezoelectric coefficient d₃₃ of the generating element was used as a measure of the electricity generating performance. We fabricated several PCGEs and conducted energy harvesting experiments to verify the concept of the d₃₃-mode coefficient of generating element.

Work in piezoelectric vibration energy harvesting has typically focused on single member cantilevered structures with transverse tip displacement at a known frequency, taking advantage of the optimal coupling characteristics of piezoceramics in the 3-1 bending mode. Multi-member designs could be advantageous in delivering power to a load in environments with random or wide-band vibrations. The design presented in this work consists of two hinged piezoceramic (PZT-5A) beams x-poled for series operation. Each beam measures 31.8mm x 12.7mm x 0.38mm and consists of two layers of nickel-plated piezoceramic adhered to a brass center shim. The hinge device consists of two custom-machined aluminum attachments epoxied to the end of a beam and connected using a 1.59mm diameter alloy steel dowel. A stainless steel torsion spring is placed over the pin and attached to the aluminum body to provide a restoring torque when under rotation. The design is modeled using the piezoelectric constitutive equations to solve for voltage and power for a set of electromechanical boundary conditions. Experimental measurements on the design are achieved by bolting one end of the structure to a vibration shaker and fixing the other to a rigid framework of industrial aluminum framing material. For a given frequency of vibration, power output of the structure can be obtained by measuring voltage drop across a resistive load.

Experimental studies are conducted t