Showing papers on "Bimorph published in 2014"

Rotational piezoelectric wind energy harvesting using impact-induced resonance

Abstract: To improve the output power of a rotational piezoelectric wind energy harvester, impact-induced resonance is proposed to enable effective excitation of the piezoelectric cantilevers' vibration modes and obtain optimum deformation, which enhances the mechanical/electrical energy transformation. The impact force is introduced by forming a piezoelectric bimorph cantilever polygon that is fixed at the circumference of the rotating fan's internal surface. Elastic balls are placed inside the polygon. When wind rotates the device, the balls strike the piezoelectric cantilevers, and thus electricity is generated by the piezoelectric effect. The impact point is carefully chosen to use the first bending mode as much as possible, and thus maximize the harvesting efficiency. The design enables each bimorph to be struck in a similar area and every bimorph is struck in that area at different moments. As a result, a relatively stable output frequency can be obtained. The output frequency can also be changed by choosing different bimorph dimensions, which will also make the device simpler and the costs lower. A prototype piezoelectric energy harvester consisting of twelve piezoelectric cantilevers was constructed. The piezoelectric cantilevers were made from phosphor bronze, the lead zirconium titanate (PZT)-based bimorph cantilever had dimensions of 47 mm × 20 mm × 0.5 mm, and the elastic balls were made from steel with a diameter of 10 mm. The optimal DC output power was 613 μW across the 20 kΩ resistor at a rotation speed of 200 r/min with an inscribed circle diameter of 31 mm.

A spongy graphene based bimorph actuator with ultra-large displacement towards biomimetic application

Abstract: Bimorph actuators, consisting of two layers with asymmetric expansion and generating bending displacement, have been widely researched. Their actuation performances greatly rely on the difference of coefficients of thermal expansion (CTE) between the two material layers. Here, by introducing a spongy graphene (sG) paper with a large negative CTE as well as high electrical-to-thermal properties, an electromechanical sG/PDMS bimorph actuator is designed and fabricated, showing an ultra-large bending displacement output under low voltage stimulation (curvature of about 1.2 cm−1 at 10 V for 3 s), a high displacement-to-length ratio (∼0.79), and vibration motion at AC voltage (up to 10 Hz), which is much larger and faster than that of the other electromechanical bimorph actuators. Based on the sG/PDMS bimorph serving as the “finger”, a mechanical gripper is constructed to realize the fast manipulation of the objects under 0.1 Hz square wave voltage stimulation (0–8 V). The designed bimorph actuator coupled with ultra-large bending displacement, low driven voltage, and the ease of fabrication may open up substantial possibilities for the utilization of electromechanical actuators in practical biomimetic device applications.

Modeling and Analysis of a Piezoelectric Energy Harvester with Varying Cross-Sectional Area

Abstract: This paper reports on the modeling and on the experimental verification of electromechanically coupled beams with varying cross-sectional area for piezoelectric energy harvesting. The governing equations are formulated using the Rayleigh-Ritz method and Euler-Bernoulli assumptions. A load resistance is considered in the electrical domain for the estimate of the electric power output of each geometric configuration. The model is first verified against the analytical results for a rectangular bimorph with tip mass reported in the literature. The experimental verification of the model is also reported for a tapered bimorph cantilever with tip mass. The effects of varying cross-sectional area and tip mass on the electromechanical behavior of piezoelectric energy harvesters are also discussed. An issue related to the estimation of the optimal load resistance (that gives the maximum power output) on beam shape optimization problems is also discussed.

A concept for energy harvesting from quasi-static structural deformations through axially loaded bilaterally constrained columns with multiple bifurcation points

Abstract: A major obstacle limiting the development of deployable sensing and actuation solutions is the scarcity of power. Converted energy from ambient loading using piezoelectric scavengers is a possible solution. Most of the previously developed research focused on vibration-based piezoelectric harvesters which are typically characterized by a response with a narrow natural frequency range. Several techniques were used to improve their effectiveness. These methods focus only on the transducer?s properties and configurations, but do little to improve the stimuli from the source. In contrast, this work proposes to focus on the input deformations generated within the structure, and the induction of an amplified amplitude and up-converted frequency toward the harvesters? natural spectrum. This paper introduces the concept of using mechanically-equivalent energy converters and frequency modulators that can transform low-amplitude and low-rate service deformations into an amplified vibration input to the piezoelectric transducer. The introduced concept allows energy conversion within the unexplored quasi-static frequency range (?1?Hz). The post-buckling behavior of bilaterally constrained columns is used as the mechanism for frequency up-conversion. A bimorph cantilever polyvinylidene fluoride (PVDF) piezoelectric beam is used for energy conversion. Experimental prototypes were built and tested to validate the introduced concept and the levels of extractable power were evaluated for different cases under varying input frequencies. Finally, finite element simulations are reported to provide insight into the scalability and performance of the developed concept.

Fast optimization of a bimorph mirror using x-ray grating interferometry.

Abstract: An x-ray grating interferometer was employed for in situ optimization of an x-ray bimorph mirror. Unlike many other at-wavelength techniques, only a single interferogram image, captured out of the focal plane, is required, enabling the optical surface to be quickly optimized. Moire fringe analysis was used to calculate the wavefront slope error, which is proportional to the mirror’s slope error. Using feedback from grating interferometry, the slope error of a bimorph mirror was reduced to <200 nrad (rms) in only two iterations. This technique has the potential to create photon beams with spatially homogeneous intensities for use in synchrotron and free electron laser beam lines.

Magnetic energy harvesting properties of piezofiber bimorph/NdFeB composites

Abstract: The magnetic energy harvesting properties of piezoelectric bimorph/magnet composite are studied in this Letter. The devices are fabricated with NdFeB magnets and piezofiber (d33 mode), whose magnetoelectric (ME) coefficient reaches 526 V/cm·Oe (RMS) at the resonant frequency (27.3 Hz), and the maximum power density of which is 38.8 mW/cm3 at 9.78 Oe. Factors influencing the magnetoelectric property of the piezoelectric/magnet composite are discussed, which might guide further enhancement of its energy harvesting ability. This particular ME composite possesses far better energy harvesting abilities than magnetostrictive/piezoelectric composites, able to scavenge energy from power-frequency magnetic fields to support wireless sensor network.

Structure-performance relationships for cantilever-type piezoelectric energy harvesters

Abstract: This study provides comprehensive analysis of the structure–performance relationships in cantilever-type piezoelectric energy harvesters. It provides full understanding of the effect of all the practical global control variables on the harvester performance. The control variables considered for the analysis were material parameters, areal and volumetric dimensions, and configuration of the inactive and active layers. Experimentally, the output power density of the harvester was maximum when the shape of the beam was close to a square for a constant bending stiffness and a fixed beam area. Through analytical modeling of the effective stiffness for the piezoelectric bimorph, the conditions for enhancing the bending stiffness within the same beam volume as that of a conventional bimorph were identified. The harvester configuration with beam aspect ratio of 0.86 utilizing distributed inactive layers exhibited an giant output power of 52.5 mW and power density of 28.5 mW cm−3 at 30 Hz under 6.9 m s−2 excitation. The analysis further indicates that the trend in the output power with varying damping ratio is dissimilar to that of the efficiency. In order to realize best performance, the harvester should be designed with respect to maximizing the magnitude of output power.This study provides comprehensive analysis of the structure–performance relationships in cantilever-type piezoelectric energy harvesters. It provides full understanding of the effect of all the practical global control variables on the harvester performance. The control variables considered for the analysis were material parameters, areal and volumetric dimensions, and configuration of the inactive and active layers. Experimentally, the output power density of the harvester was maximum when the shape of the beam was close to a square for a constant bending stiffness and a fixed beam area. Through analytical modeling of the effective stiffness for the piezoelectric bimorph, the conditions for enhancing the bending stiffness within the same beam volume as that of a conventional bimorph were identified. The harvester configuration with beam aspect ratio of 0.86 utilizing distributed inactive layers exhibited an giant output power of 52.5 mW and power density of 28.5 mW cm−3 at 30 Hz under 6.9 m s−2 excitatio...

Ultra-Low Wind Speed Piezoelectric Windmill

Abstract: We report an ultra-low start-up speed windmill that consists of a 72 mm diameter horizontal axis wind turbine rotor with 12 alternating polarity magnets around its periphery and a 60 mm × 20 mm × 0.7 mm piezoelectric bimorph element having a magnet at its tip. This wind turbine operates at very low Reynolds number of around 2×104, but still it has reasonably high power coefficient of about 11% at the optimal tip speed ratio of 0.7. It was found to produce peak electric power of 450 μW at the rated wind speed of 4.2 mph. An extremely low start-up wind speed of 2.4 mph was achieved by operating the bimorph in actuator mode.

Segmented bimorph mirrors for adaptive optics: segment design and experiment

Abstract: We discuss the concept of lightweight segmented bimorph mirrors for adaptive optics. The segment consists of a monocrystal silicon substrate actuated by an array of in-plane piezoceramic (PZT) actuators with honeycomb electrodes. We focus on technological aspects of the segment design that are critical for space applications and describe a single segment demonstrator. The morphing capability of the segment is evaluated experimentally. We also discuss the local deformations (dimples) associated with the shape of the electrodes acting on the PZT array.

Design and Validation of Silicon-on-Insulator Based U Shaped Thermal Microactuator

Abstract: method compatible with standard microelectronics. The basic two-arm electrothermal actuators design uses the principle of Joule heating for thermal expansion and movement. The thermal actuator can be categorized as in-plane and out of plane actuator (10), (11), where driving mechanism behind the two type of actuator is hot (narrow arm) and cold (wider arms) beam actuation and bimorph actuation. The potential application of electrothermal actuators includes optical switching (12), (13) and microgrippers (14) and micro robotic application (15). Among the different type of thermal actuators, the horizontal U shaped microactuator is more common compared to the V shaped and bimorph actuation mechanism. The horizontal U shape microactuator has a narrow hot cold arm. It operates based on the differential thermal expansion of these arms, when a voltage is applied between its contact pads (16). Two-arm actuators design consists of a thin arm, wide arm and flexure arm connected together at one end and constrained elastically at the anchors, which in turn are rigidly attached to the substrate. Application of a potential difference at the anchors generates a non uniform electrical field. The large current density in the thin arm causes a greater thermal expansion than that in the wide arm. This basic microactuator has been improved in various ways to produce higher deflections. In the present work, a FEM modeling and characterization of fabricated actuator are presented to explain the behavior of thermal actuator. These actuators are typically fabricated by a MUMPS (Multi User MEMS Process) bulk micromachining process that utilizes silicon as a structural layer. Commercial MEMS software's COMSOL 4.2 multiphysics tool is used for FEM simulation. In order to improve the performance of thermal actuator specifically mechanical motion, a better way is to vary the geometrical parameter of the structure rather than change the applied voltage. This works includes the study of geometrical parameters of thermal microactuator for enhanced mechanical motion. The effects of the variation in geometrical parameters on thermal actuator performance are also established. The fabricated actuator was tested and validated experimentally with simulated results.

Piezoelectric vibration device for mobile terminal

Abstract: A piezoelectric vibration device for a mobile terminal is disclosed. A bimorph piezoelectric vibrator includes a pair of piezoelectric element layers connected to one of positive and negative poles and a middle electrode plate interposed between the piezoelectric element layers and connected to the other pole. The piezoelectric vibrator generates vibration due to up/down bending displacement by fixing both end portions thereof to an inner surface of a casing of a mobile terminal. A voltage-boosting transformer raises a power source voltage of a mobile terminal to a driving voltage. A driving chip receives the raised driving voltage from the voltage-boosting transformer and drives the piezoelectric vibrator. Weights are attached to at least one of both sides of the piezoelectric vibrator to amplify vibration. Insulation members are provided at both end portions of the piezoelectric vibrator to prevent electricity applied to the piezoelectric vibrator from leaking to the casing.

An Efficient Spectral Element Model with Electric DOFs for the Static and Dynamic Analysis of a Piezoelectric Bimorph

Abstract: An efficient spectral element (SE) model for static and dynamic analysis of a piezoelectric bimorph is proposed. It combines an equivalent single layer (ESL) model for the mechanical displacement field with a sublayer approximation for the electric potential. The 2D Gauss-Lobatto-Legendre (GLL) shape functions are used to discretize the displacements and then the governing equation of motion is derived following the standard SE method procedure. It is shown numerically that the present SE model can well predict both the global and local responses such as mechanical displacements, natural frequencies, and the electric potentials across the bimorph thickness. In the case of bimorph sensor applicat ion, it is revealed that the distribution of the induced electric potential across the thickness does not affect the global natural frequencies much. Furthermore, the effects of the order of Legendre polynomial and the mesh size on the convergence rate are investigated. Comparison of the present results for a bimorph sensor with those from 3D finite element (FE) simulations establishes that the present SE model is accurate, robust, and computationally efficient.

Prediction of thermally-controlled actuation for shape memory alloy film-based bimorph cantilevers

Abstract: A model is proposed for predicting the deflection of bimorph cantilevers made of a shape memory alloy film deposited onto solid substrates, by taking into account the changes in the thermal and elastic properties of the film during the martensitic phase transformation. The zero actuation reference temperature is the deposition or annealing temperature, with the film in the austenite phase. On cooling from this point, the thermoelastic stress building up in the bimorph causes bimetal-type behavior until the onset of the austenite–martensite transformation, which now controls the actuation up to its completion, when the bimetal actuation reappears. By adapting the classical bimetal thermostat model to the case when one component undergoes martensitic transformation, the deflection during heating and cooling is calculated by averaging the isostrain and isostress phase distribution bounding approximations; the case of a Ti50.1Ni49.9 film/Si was examined. Predictions in good agreement with the recorded deflection of a Ti49.2Ni50.8/Si cantilever (up to a temperature shift explained by composition change and stress developed in the film during the transformation) resulted, indicating a strong effect (attributed to the differences between the elastic and thermal constants of the two phases) of the martensitic phase transformation on the deflection slope and sign.

A piezoelectric gyroscope based on thickness-shear modes of an AlN bimorph with inclined c-axes

Abstract: We propose a new structure for piezoelectric gyroscope application. It consists of a two-layered plate of AlN with inclined c-axes. Through a theoretical analysis, it is shown that when the plate is electrically driven into thickness-shear (TSh) vibration in one direction and is rotating about the plate normal, the rotation causes a TSh vibration in a perpendicular direction with an electrical output which can be used to measure the angular rate of the rotation. Since AlN can be made into thin film devices much smaller than conventional crystal acoustic wave devices, the proposed gyroscope can be made much smaller than existing piezoelectric gyroscopes. The structure can also work with other crystals of class 6mm such as ZnO and polarized ceramics.

Fabrication and Characterization of a Polymer/Metal Bimorph Microcantilever for Ultrasensitive Thermal Sensing

Abstract: In this paper, we demonstrate a novel polymer/metal bimorph microcantilever, which is promising to have an ultrahigh thermal sensitivity. Based on the analysis of the thermoelastic behavior of the bimorph cantilever, polyvinyl chloride (PVC) and aluminum (Al), which have a large mismatch in coefficient of thermal expansion and an appropriate ratio of Young's modulus, were chosen and the thermal sensitivity was maximized by optimizing the thickness ratio of the two layers. The PVC layer was formed via spin coating and patterned by plasma etching. The fabrication process for the cantilever is compatible with standard micro-fabrication techniques. The thermal responses of the cantilevers were characterized by measuring the thermal deflections during thermal cycles and isothermal holding tests. Experimental results showed that the PVC/Al microcantilevers with a length of 200 μm had an ultrahigh thermal sensitivity above 2044 nm/K. Also, the cantilevers annealed at a temperature above the glass transition point (Tg) of the polymer possessed good linearity and reproducibility of thermal deflection in the temperature range of 28°C-49°C. When heated above room temperature, the cantilevers started to creep, which affected the thermal sensitivity and then introduced inaccuracy.

Design, fabrication and characterization of a piezoelectrically actuated bidirectional polymer micropump

Abstract: We present the design, fabrication and characterization of a new, piezoelectrically actuated fully polymeric three chamber peristaltic micropump. An optimized bimorph bending actuator has been designed to deform the polymer membranes in an optimal and most-efficient way. The piezoelectric actuators of the micropump are driven with actuation voltages of ±260 V. The pump has a total size of 46 × 18 × 4 mm, is produced by hot embossing and is assembled in a very simple way. The presented design is able to pump water with a flow rate of 4.8 ml/min and achieves a maximum back pressure of app. 200 mBar.

Piezoelectric Resonance Sensors of DC Magnetic Field

Abstract: The operational principle, methods of calculation, and designs of the dc magnetic field sensors using the combination of the Ampere force, the piezoelectricity, and the acoustic resonance have been described. The prototypes of the sensors based on a lead zirconate titanate ring and bimorph structures with radial or bending oscillations excited by the alternative current have been fabricated and investigated. The sensitivity of the sensors reached 245 V/(A·T) and the measured field range was from ~10-5 T up to several Teslas.

Integration of Energy Harvester for Self-Powered Wireless Sensor Network Nodes

Abstract: This paper reports an energy harvester suitable for self-powered wireless sensor network (WSN) nodes consisting of a piezoelectric cantilever, an energy harvesting circuit, and a storage capacitor. Having the same size as a credit card, the proposed WSN nodes can be easily integrated into various applications, such as motor and air conditioning equipment. The WSN node is powered by an integrated bimorph piezoelectric generator that harvests energy from ambient vibration. The paper has developed a method to optimize the harvester parameters to attune it to the dominant vibration frequency. Tests carried out on the proposed harvester show that the proposed design can meet the energy requirements of a WSN node and achieve an efficiency of 79%.

Degradation of Piezoelectric Materials for Energy Harvesting Applications

Abstract: The purpose of energy harvesting is to provide long term alternatives to replaceable batteries across a number of applications. Piezoelectric vibration harvesting provides advantages over other transduction methods due to the ability to generate large voltages even on a small scale. However, the operation in energy harvesting is different from typical sensors or actuators. The applied stress is often at the material limit in order to generate the maximum power output. Under these conditions, the degradation of the materials becomes an important factor for long term deployment. In this work bimorph piezoelectric beams were sub jected to lifetime testing through electromagnetic tip actuation for a large number of cycles. The results of two measurement series at different amplitudes are discussed. The dominant effect observed was a shift in mechanical resonance frequencies of the beams which could be very detrimental to resonant harvesters.

A sensitive piezoelectric composite lattice: Experiment

Abstract: Lattice structures based on bimorph rib elements are fabricated and studied experimentally. The effective piezoelectric sensitivity d is observed to be much larger, by a factor of at least 10 000, in magnitude than that of material comprising the lattice ribs. Bending of the ribs in response to input voltage is responsible for the large sensitivity.

Analysis of Thermomechanical Behavior of Shape-Memory-Alloy Bimorph Microactuator

Abstract: Shape-memory-alloy (SMA) has attracted considerable attention in recent years as a smart and efficient material due to their unique properties SMA microactuators are recognized as one of the potential solutions for unresolved issues in the rapid development of micro electromechanical systems This paper presents the study and analysis of thermomechanical behaviour of bimorph-SMA structure when parameters such as the thickness of SMA layer, the type of the stress layer and their thickness, and the processing temperature are changed The analysis was performed using a finite element method Materials such as SiO2, Si3N4, and Poly-Si are used as stress layer in these analyses to mimic the materials that can be deposited using Plasma Enhanced Chemical Vapor Deposition (PECVD) process Results show that bimorph SMA structure achieves maximum displacement when SiO2 is used as stress layer For a SMA structure with dimension of 10 mm (length) x 2 mm (width) x 50 µm (thickness), a maximum displacement of 1859 µm is achieved when 6 µm of Si3N4 layer deposited at temperature of 400 °C

In-situ characterization of ferromagnetic shape memory alloy / silicon bimorph nanoactuators

Abstract: Nano scale actuators consisting of a free-standing bilayer of ferromagnetic shape memory alloy (FSMA) and silicon with critical lateral dimensions of 250 nm are designed, nanofabricated and characterized in-situ in a scanning electron microscope (SEM). Upon Joule heating and cooling, fully reversible nano actuation in out-of-plane direction of up to 4 % of actuator length is observed. In-situ measurements allow the correlation of resistivity and deflection revealing the presence of the shape memory effect superimposing the bimorph thermal expansion.

Energy Harvesting From Controlled Buckling of a Horizontal Piezoelectric Beam

Abstract: A piezoelectric vibration energy harvester is designed to generate electricity under the weight of passing crowds The piezoelectric beam buckles to a controlled extent when the device is stepped on The device is a seven bar mechanism The upper and lower bars as well as the lateral links are rigid The middle horizontal beam is a bimorph piezoelectric beam Damages to the piezoelectric beam are avoided by constraining its axial deformation This constrain is implemented by limiting squeezing of the mechanism When a person moves over the mechanism or steps off the devices it causes the bimorph to buckle or return to the unbuckled condition The transitions result in vibrations of the piezoelectric beam and thus generate energyIn this paper, the energy harvester is analytically modeled The electro-mechanical coupling and the geometric nonlinearities have been included in the model for the piezoelectric beam The design criteria for the device are discussed It is demonstrated that the device can be realized with commonly used piezoelectric patches and can generate hundreds of milliwatts of power A three part beam is also investigated The effect of design parameters on the generated power and required tolerances are illustratedThe proposed device could be implemented in the sidewalks producing energy from the weight of people passing over it Other possible applications are portable smart phones chargers and shoe hill energy harvesting Dance floor of a club is another applicable example for using this harvester The main advantage of using horizontal configuration instead of a vertical arrangement is the ease of placement in the pavements© 2014 ASME

Modeling of the through-the-thickness electric potentials of a piezoelectric bimorph using the spectral element method.

Abstract: An efficient spectral element (SE) with electric potential degrees of freedom (DOF) is proposed to investigate the static electromechanical responses of a piezoelectric bimorph for its actuator and sensor functions. A sublayer model based on the piecewise linear approximation for the electric potential is used to describe the nonlinear distribution of electric potential through the thickness of the piezoelectric layers. An equivalent single layer (ESL) model based on first-order shear deformation theory (FSDT) is used to describe the displacement field. The Legendre orthogonal polynomials of order 5 are used in the element interpolation functions. The validity and the capability of the present SE model for investigation of global and local responses of the piezoelectric bimorph are confirmed by comparing the present solutions with those obtained from coupled 3-D finite element (FE) analysis. It is shown that, without introducing any higher-order electric potential assumptions, the current method can accurately describe the distribution of the electric potential across the thickness even for a rather thick bimorph. It is revealed that the effect of electric potential is significant when the bimorph is used as sensor while the effect is insignificant when the bimorph is used as actuator, and therefore, the present study may provide a better understanding of the nonlinear induced electric potential for bimorph sensor and actuator.

A novel electrical configuration for three wire piezoelectric bimorph micro-positioners

Abstract: This paper describes a new method for driving bimorph and multimorph piezoelectric benders. The 'Biased Bipolar Configuration' uses a bias voltage applied to the top electrode, a control voltage applied to the centre electrode, and a grounded bottom electrode. Using this technique the predicted deflection and force for a given piezoelectric bender is approximately 2.2 and 1.3 times greater than traditional methods. Experimental results demonstrate that the biased bipolar configuration provides an approximate 2.4 and 1.4 times improvement in the maximum deflection and force which correlates well with the predicted improvement.

Low Frequency Vibration Energy Harvesting using Arrays of PVDF Piezoelectric Bimorphs

Abstract: Power harvesters based on the piezoelectric effect are more promising in harnessing energy from ambient vibrations. In this paper, piezoelectric bimorph resonators in the form of Polyvinylidinefluoride (PVDF) cantilevers are studied and used in an array with optimal terminal combination for maximizing the power generated from low frequency vibrations. The thickness of the passive sandwich layer and the poling direction in each film are observed to be crucial in determining the total power generated from the PVDF bimorph. Experimentally, bimorph cantilevers made of 55 μm thick PVDF film and sized to resonate between 30 to 40 Hz are used in similarly poled as well as oppositely poled configurations and their output measured as voltage across a 1 MΩ load resistance. The similarly poled bimorph outperforms the oppositely poled configuration by more than doubling the output voltage. Further enhancement in the output is observed by introducing a sandwich layer of 50 μm thick copper foil between the two similarly poled PVDF layers. Experiments with three such devices connected in parallel in an array and resonating at 33 Hz with an input acceleration of 0.8 g results in 2.8 μW power generation. This result shows the promise of PVDF as a candidate material for energy harvesting resonators despite its low electromechanical coupling coefficient (k e ). Low cost and ease of production may be especially attractive for PVDF.

Wide aperture (more than 500 mm) deformable mirrors for high power laser beam correction

Abstract: Wide aperture bimorph mirrors for laser beam correction and formation were developed and investigated. Different types of substrates and active piezoceramics materials were considered to fabricate temperature independent shape of the mirror surface and to maximize the sensitivity of the mirror. High reflectivity coatings for different wavelengths were studied.

Electrohydroelastic dynamics of macro-fiber composites for underwater energy harvesting from base excitation

Abstract: Low-power electronic systems are used in various underwater applications ranging from naval sensor networks to ecological monitoring for sustainability. In this work, underwater base excitation of cantilevers made of Macro-Fiber Composite (MFC) piezoelectric structures is explored experimentally and theoretically to harvest energy for such wireless electronic components toward enabling self-powered underwater systems. Bimorph cantilevers made of MFCs with different length-to-width ratios and same thickness are tested in air and under water to characterize the change in natural frequency and damping with a focus on the fundamental bending mode. The real and imaginary parts of hydrodynamic frequency response functions are identified and corrected based on this set of experiments. An electrohydroelastic model is developed and experimentally validated for predicting the power delivered to an electrical load as well as the shunted underwater vibration response under base excitation. Variations of the electrical power output with excitation frequency and load resistance are obtained for different length-to-width ratios. Underwater power density results are reported and compared with their in-air counterparts. Specifically a nonlinear dependence of the power density to the cantilever width is reported for energy harvesting from underwater base excitation.

Segmented bimorph mirrors for adaptive optics: morphing strategy.

Abstract: This paper discusses the concept of a light weight segmented bimorph mirror for adaptive optics. It focuses on the morphing strategy and addresses the ill-conditioning of the Jacobian of the segments, which are partly outside the optical pupil. Two options are discussed, one based on truncating the singular values and one called damped least squares, which minimizes a combined measure of the sensor error and the voltage vector. A comparison of various configurations of segmented mirrors was conducted; it is shown that segmentation sharply increases the natural frequency of the system with limited deterioration of the image quality.