Showing papers on "Bimorph published in 2010"

Nonlinear piezoelectricity in electroelastic energy harvesters: Modeling and experimental identification

Abstract: We propose and experimentally validate a first-principles based model for the nonlinear piezoelectric response of an electroelastic energy harvester The analysis herein highlights the importance of modeling inherent piezoelectric nonlinearities that are not limited to higher order elastic effects but also include nonlinear coupling to a power harvesting circuit Furthermore, a nonlinear damping mechanism is shown to accurately restrict the amplitude and bandwidth of the frequency response The linear piezoelectric modeling framework widely accepted for theoretical investigations is demonstrated to be a weak presumption for near-resonant excitation amplitudes as low as 05 g in a prefabricated bimorph whose oscillation amplitudes remain geometrically linear for the full range of experimental tests performed (never exceeding 025% of the cantilever overhang length) Nonlinear coefficients are identified via a nonlinear least-squares optimization algorithm that utilizes an approximate analytic solution obta

A T-shaped piezoelectric cantilever for fluid energy harvesting

Abstract: This paper proposes a T-shaped piezoelectric cantilever for generating electric power from fluid flow. The working principle of the device is based on aeroelastic flutter and utilizes a bimorph cantilever with T-shape which hastens occurrence of flutter at a low fluid speed. A prototype device (100×60×30 mm3) was tested in a wind tunnel. The device was found to provide power from a wind speed of 4 m/s and a continuous peak electrical power output of 4.0 mW. The simplicity of the present device consisting of only a bimorph cantilever is considered to be cost effective.

Modeling and experimental verification of proof mass effects on vibration energy harvester performance

Abstract: An electromechanically coupled model for a cantilevered piezoelectric energy harvester with a proof mass is presented. Proof masses are essential in microscale devices to move device resonances towards optimal frequency points for harvesting. Such devices with proof masses have not been rigorously modeled previously; instead, lumped mass or concentrated point masses at arbitrary points on the beam have been used. Thus, this work focuses on the exact vibration analysis of cantilevered energy harvester devices including a tip proof mass. The model is based not only on a detailed modal analysis, but also on a thorough investigation of damping ratios that can significantly affect device performance. A model with multiple degrees of freedom is developed and then reduced to a single-mode model, yielding convenient closed-form normalized predictions of device performance. In order to verify the analytical model, experimental tests are undertaken on a macroscale, symmetric, bimorph, piezoelectric energy harvester with proof masses of different geometries. The model accurately captures all aspects of the measured response, including the location of peak-power operating points at resonance and anti-resonance, and trends such as the dependence of the maximal power harvested on the frequency. It is observed that even a small change in proof mass geometry results in a substantial change of device performance due not only to the frequency shift, but also to the effect on the strain distribution along the device length. Future work will include the optimal design of devices for various applications, and quantification of the importance of nonlinearities (structural and piezoelectric coupling) for device performance.

Vibration energy scavenging via piezoelectric bimorphs of optimized shapes

Abstract: Compact autonomous power sources are one of the prerequisites for the development of wireless sensor networks. In this work vibration energy harvesting via piezoelectric resonant bimorph beams is studied. The available analytical approaches for the modeling of the coupled electromechanical behavior are critically evaluated and compared with a finite element (FEM) numerical model. The latter is applied to analyze thoroughly the stress and strain states, as well as to evaluate the resulting voltage and charge distributions in the piezoelectric layers. The aim of increasing the specific power generated per unit of scavenger volume is pursued by optimizing the shape of the scavengers. Two optimized trapezoidal configurations are hence identified and analyzed. An experimental set-up for the validation of the proposed numerical model and of the obtained optimized structures is developed. Results of a preliminary experimental assessment, confirming the improved performances of optimized scavengers, are finally given.

Novel, Bidirectional, Variable-Camber Airfoil via Macro-Fiber Composite Actuators

Abstract: This study aims to enable solid-state aerodynamic force generation in high-dynamic-pressure airflow. A novel, high-load-output, bidirectional variable-camber airfoil employing a type of piezoceramic composite actuator known as a Macro-Fiber Composite is presented. The novel airfoil employs two active surfaces and a single four-bar (box) mechanism as the internal structure. The unique choice of boundary conditions allows variable and smooth deformation in both directions from a flat camber line. The paper focuses on actuation modeling and response characterization under aerodynamic loads. A parametric study of aerodynamic response is employed to optimize the kinematic parameters of the airfoil. The concept is fabricated by implementing eight Macro-Fiber Composite 8557-P1-type actuators in a bimorph configuration to construct the active surfaces. The box mechanism generates deflection and camber change as predicted. Wind-tunnel experiments are conducted on a 12.6% maximum thickness, 127 mm chord airfoil. Aerodynamic and structural performance results are presented for a flow rate of 15 m /s and a Reynolds number of 127,000. Nonlinear effects due to aerodynamic and piezoceramic hysteresis are identified and discussed. A lift coefficient change of 1.54 is observed purely due to voltage actuation. Results are compared with conventional, zero-camber NACA and other airfoils. A 72% increase in the lift-curve slope is achieved when compared with a NACA 0009 airfoil.

Harvested power and sensitivity analysis of vibrating shoe-mounted piezoelectric cantilevers

Abstract: This paper presents a preliminary investigation on energy harvesting from human walking via piezoelectric vibrating cantilevers. Heel accelerations during human gait are established by correlating data gathered from the literature with direct experimental measurements. All the observed relevant features are synthesized in a typical (standard) acceleration signal, used in subsequent numerical simulations. The transient electromechanical response and the harvested power of a shoe-mounted bimorph cantilever excited by the standard acceleration signal is computed by numerical simulations and compared with measurements on a real prototype. A sensitivity analysis is finally developed to estimate the mean harvested power for a wide range of scavenger configurations. Acceptability criteria based on imposed geometrical constraints and resistance strength limits (e.g. fatigue limit) are also established. This analysis allows a quick preliminary screening of harvesting performance of different scavenger configurations.

Multifunctional self-charging structures using piezoceramics and thin-film batteries

Abstract: Multifunctional material systems combine multiple functionalities in a single device in order to increase performance while limiting mass and volume. Conventional energy harvesting systems are designed to be added to a host structure in order to harvest ambient energy surrounding the system, but often cause undesirable mass loading effects and consume valuable space. Energy harvesting systems can benefit from the introduction of multifunctionality as a means of improving overall system efficiency. This paper presents the investigation of a novel multifunctional piezoelectric energy harvesting system consisting of energy generation, energy storage, and load bearing ability in a single device. The proposed self-charging structures contain piezoelectric layers for power generation, thin-film battery layers for energy storage, and a central metallic substrate layer, arranged in a bimorph configuration. Several aspects of the development and evaluation of the self-charging structure concept are reviewed. Details are provided on the fabrication of a piezoelectric self-charging structure. An electromechanical model is employed to predict the response of the harvester under harmonic base excitation. Experimentation is performed to confirm the ability of the device to simultaneously harvest and store electrical energy. Finally, both static and dynamic strength analyses are performed to determine the load bearing ability of the structure.

Improving the performance of a piezoelectric energy harvester using a variable thickness beam

Abstract: In recent years, researchers have shown a growing interest in the possibility of harvesting mechanical energy from vibrating structures. A common way to proceed consists of using the direct piezoelectric effect of a bimorph cantilever beam with integrated piezoelectric elements. Several studies focused on the development of analytical models describing the electromechanical coupling. Historically, most of these models have been limited to simple structures such as a constant cross-section cantilever beam harvester. This paper studies the effect of a variable thickness beam harvester on its electromechanical performance. A semi-analytical mechanical model was developed using Rayleigh–Ritz approximations with a trigonometric functions set. The model was next validated by a finite element (FE) modeling. Numerical simulations were then performed for different beam slope angles in order to find the optimum for a given maximal strain across the piezoelectric elements. For the case under study, it is shown that tapered beams lead to a more uniform strain distribution across the piezoelectric material and increase the harvesting performance by a factor of 3.6.

Thermally Actuated Omnidirectional Walking Microrobot

Abstract: We describe a walking microrobot that is propelled by cilialike thermal bimorph actuator arrays. The robot consists of two actuator array chips, each having an 8 × 8 array of “motion pixels,” which are composed of four orthogonally oriented cilia. Each group of unidirectional cilia is controlled independently for each chip, which provides planar motion with three degrees of freedom (x, y, θ). The robot is approximately 3 cm in length, 1 cm in width, and 0.9 mm in height and has a mass of 0.5 g. By varying the actuation frequency and motion gait strategy, the direction and velocity of the motion can be controlled. In this paper, we present the system architecture, control mechanism, and modeling of the robot, as well as experimental results, during linear and rotary motion. The robot can carry loads up to seven times its own mass, and it can operate at speeds up to 250 μm/s with step sizes from 1 to 4 μm.

Macro-Fiber Composite actuated simply supported thin airfoils

Abstract: A piezoceramic composite actuator known as Macro-Fiber Composite (MFC) is used for actuation in the design of a variable camber airfoil intended for a ducted fan aircraft. The study focuses on response characterization under aerodynamic loads for circular arc airfoils with variable pinned boundary conditions. A parametric study of fluid–structure interaction is employed to find pin locations along the chordwise direction that result in high lift generation. Wind tunnel experiments are conducted on a 1.0% thick, 127 mm chord MFC actuated bimorph airfoil that is simply supported at 5% and 50% of the chord. Aerodynamic and structural performance results are presented for a flow rate of 15 m s − 1 and a Reynolds number of 127 000. Non-linear effects due to aerodynamic and piezoceramic hysteresis are identified and discussed. A lift coefficient change of 1.46 is observed, purely due to voltage actuation. A maximum 2D L/D ratio of 17.8 is recorded through voltage excitation.

Utilisation of smart polymers and ceramic based piezoelectric materials for scavenging wasted energy

Abstract: Piezoelectric smart polymer and ceramic materials can be deployed as a mechanism to transform mechanical energy into electrical energy that can be stored and used to power portable devices. This paper focuses on the development and comparison of a micropower based harvesting generator using piezoelectric PZT (lead zirconate titanate) ceramic, PVDF (polyvinylidene fluoride) membrane and PP (polypropylene) foam polymer with the intention of establishing power output from temperature fluctuations. Unimorph and bimorph strips of various sizes were prepared and subjected to vibration and impact experiments in order to directly compare the voltage output. The effect of the ceramic fibre diameter, laminate thickness, impact area, weight of the free falling mass, vibration frequency and temperature on the voltage output were studied. Experiments are outlined detailing the performance characteristics of such piezoelectric fibre laminates. Results show voltage outputs of nearly 40 V which is considered sufficient for potential applications in powering microsystems.

Resonant manifestation of intrinsic nonlinearity within electroelastic micropower generators

Abstract: This letter investigates the nonlinear response of a bimorph energy harvester comprised of lead zirconate titanate (PZT-5A) laminates. For near resonant excitations, we demonstrate significant intrinsic nonlinear behavior despite geometrically linear motion. Fourth order elastic and electroelastic tensor values for PZT-5A are identified following methods recently published concerning a PZT-5H bimorph. A response trend indicative of a nonlinear dissipative mechanism is discussed as well as the inadequacy of linear modeling. The PZT-5A bimorph exhibits an increased softening frequency response in comparison to PZT-5H. The results contained herein are also applicable to electroelastic sensor and actuator technologies.

Actuator patterns for unimorph and bimorph deformable mirrors

Abstract: The actuator pattern of an adaptive mirror determines the amplitudes and the fidelities of the mirror deformations that can be achieved In this study, we analyze and compare different electrode patterns of piezoelectric unimorph deformable mirrors using a numerical finite element model The analysis allows us to determine the optimum actuator pattern, and it is also applicable to bimorph mirrors The model is verified by comparing its predictions with experimental results of our prototype of a novel unimorph deformable mirror

Experimental validation of a distributed parameter piezoelectric bimorph cantilever energy harvester

Abstract: Recent rapid advances in low-power portable electronic applications have motivated researchers and industry to explore schemes to embed an endless power supply mechanism within these systems. These self-charging embedded power supply systems convert ambient energy (vibration, solar, wind, etc) into electrical energy and subsequently provide power to these portable applications. Ambient vibration is one of the most promising sources of energy as it is abundantly present in indoor/outdoor systems. This paper discusses briefly the mathematical model of a bimorph piezoelectric cantilever beam with distributed inertia, and its experimental validation. Research on such a component typically included a tip mass, which reduced the influence of the distributed inertia of the beam and restricted effective operation to low frequencies. The present work excludes the tip mass and only the distributed mass of the harvester is considered. Due to the coupled electromechanical nature of piezoelectric materials, the effects of electrical coupling on the mechanical properties of the harvester are investigated, particularly the dependence of the induced additional stiffness and damping on the electrical load. Both the model and the experimental results show that the resonance frequency and the response amplitude of the harvester exhibit considerable shifts due to the electrical coupling. The experimental work uses both magnitude and Nyquist plots of the electromechanical frequency response functions to thoroughly validate the accuracy and applicability of the distributed parameter model at higher frequencies than previously considered.

A novel passive wireless ultrasensitive RF temperature transducer for remote sensing

Abstract: A wireless passive ultrasensitive temperature transducer is presented in this paper. The transducer consists of micro bimorph cantilevers (Aluminum-Silicon) and split ring resonators, operating at millimeter wave frequencies around 30 GHz. As the temperature changes, the bilayer cantilevers deflect and thus alter the resonant frequencies of the resonators. The design achieves a sensitivity of 1.05 GHz/um with respect to cantilever deflection, corresponding to a sensitivity of 150 MHz/°C, three orders of magnitude higher than existing passive wireless temperature sensors. The sensor design has high Q factor, is ultra-compact, easily fabricated and integrated with other passive sensors in sensing networks. Depending on material choices, the proposed design can also be utilized in harsh environments. To demonstrate the proof-of-concept, scaled designs around 4 GHz are presented, utilizing Aluminum-PET (Polyethylene terephthalate) bilayer cantilevers, achieves a sensitivity of 2.14 MHz/°C.

Design and fabrication of bimorph transducer for optimal vibration energy harvesting

Abstract: High energy density piezoelectric composition corresponding to 0.9Pb(Zr0.56Ti0.44)O3-0.1Pb[(Zn0.8/3Ni0.2/3) Nb2/3]O3 + 2 mol% MnO2 (PZTZNN) and 0.8[Pb(Zr0.52Ti0.48) O3]-0.2[Pb(Zn1/3Nb2/3)O3] (PZTPZN) were synthesized by conventional ceramic processing technique using three different sintering profiles. Plates of the sintered samples were used to fabricate the piezoelectric bimorphs with optimized dimensions to exhibit resonance in the loaded condition in the range of ~200 Hz. An analytical model for energy harvesting from bimorph transducer was developed which was confirmed by experimental measurements. The results of this study clearly show that power density of bimorph transducer can be enhanced by increasing the magnitude of product (d · g), where d is the piezoelectric strain constant and g is the piezoelectric voltage constant.

Comparative material study between PZT ceramic and newer crystalline PMN-PT and PZN-PT mateirals for composite bimorph actuators.

Abstract: The advent of commercially available giant piezoelectric coefficient monocrystalline materials such as PMN-PT (lead magnesium niobate - lead titanate) or PZN-PT (lead zinc niobate - lead titanate) broadens the gate for silicon-integrated applications (PiezoMEMS). Becoming more compatible with microtechnology batch processes, further advances are expected in terms of miniaturization, optimization, functionality or integration with electronics, all while reducing manufacturing costs. Subsequently, operating voltage will be lower and devices response time will improve dramatically. The paper compiles a base knowledge for composite bimorph actua- tors in line with a bottom-up approach for further more complex piezoelectric device designs dfTYRdvAZTcCcCSCedC_�TYZawBReVcZR)acCaVceZVdR_UTC_deZefeZgVVbfReZC_dCWaZVkCV)VTecZT bimorph cantilevers are initially overviewed. Analytical and finite elements modeling (FEM) are afterwards performed on two designs: classical PZT on copper cantilevers and innovative PMN- PT and PZN-PT on silicon. Comparative results clearly report quantitative improvement of PMN- PT on Si design in terms of tip displacement and blocking force.

Deformable mirrors for laser beam shaping

Abstract: 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.

A Bimorph Multi-layer Piezoelectric Vibration Energy Harvester

Abstract: This paper reports a bimorph piezoelectric vibration energy harvester incorporating multiple PZT layers. The advantage of a multi-layer generator is that it produces a higher power than a single-layer generator having the same total thickness. In addition, a lower voltage is required to polarize a multi-layer generator reducing the risk of breakdown during polarization. Moreover, the optimum resistive load of a multi-layer generator is much lower than that of a single-layer generator, which makes it easier to couple to the electrical domain. In this work, it was found, experimentally, that a double-layer generator produces 41.5% and 19.4% more power than a singlelayer generator with the same total thickness of PZT and resonant frequency. This was verified theoretically. The generators have been fabricated by screen printing which is attractive for low cost mass production.

Post-Buckled Precompressed Techniques in Adaptive Aerostructures: An Overview

Abstract: An overview of the development and application of post-buckled precompressed (PBP) piezoelectric actuators is presented. It has been demonstrated that PBP actuators out-perform conventional piezoelectric actuators by relying on axial compression to counter the inherent stiffness in the actuator element. In doing so, the mechanical work output has been shown to increase threefold compared with conventional bimorph actuators. Actuator stroke has been demonstrated to increase up to 300% without compromising the blocked force capability. This has resulted in an expansion of the design space of piezoelectric bender elements and has made them excellent candidates for potentially replacing certain classes of conventional electromechanical flight control actuators. The successful application of PBP elements can be found in unmanned aerospace systems ranging from subscale vertical-take-off and-landing vehicles to supersonic missile fins. With respect to conventional electromechanical servoactuators, it is demonstrated that PBP actuator elements induce a lower systems weight fraction, a substantially higher bandwidth, and an order of magnitude lower power consumptions and part count.

Modeling of a walking piezo actuator

Abstract: Piezoelectric actuators are often used in positioning devices that require (sub)nanometer resolution. In this paper, we develop an electro-mechanical dynamic model of a walking piezo actuator. The derived model structure can be used for the dynamic modeling of bimorph piezo motors in general. Furthermore, the physical nature enables the model to be used in design optimizations to derive new motors with different properties and for a dynamic analysis to investigate the maximum allowable driving frequency in relation to the dynamic effects of the motor. The walking piezo actuator contains four legs, each with two electrically separated piezo stacks. The legs are modeled as a connection of coupled mass-spring-damper systems. Using a Lagrange approach, the nonlinear system dynamics are derived. The variation in the system dynamics is assessed using linearization around different equilibrium positions. Also a static linearized approximation is derived, which describes the static relation between the supply voltages and the tip trajectories of the legs. The dynamic analysis shows that the motor can be modeled sufficiently accurate using a connection of six lumped mass-spring-damper systems. The variation in system dynamics appears to be most significant in the movement perpendicular to the leg orientation. Experiments show that the static linearized model accurately describes the tip trajectories of the legs for both sinusoidal and asymmetric waveforms.

A Tip-Tilt-Piston Micromirror Array for Optical Phased Array Applications

Abstract: A tip-tilt-piston micromirror array based on electrothermal bimorph actuation is presented. The micromirror uses a compactly folded actuator design that can realize high fill-factor with a simple fabrication process. A 4 × 4 micromirror array with sub-apertures of 0.9 mm and a fill-factor of 54% is demonstrated. A piston actuation of about 200 μm and tip-tilt scanning of ±18° optical angles are obtained at a driving voltage as small as 4.5 Vdc. The mirror's tip-tilt steering capability and piston control make it promising for optical phased array applications. The phased array concept is demonstrated by phasing two adjacent mirrors on the mirror array. Other device characterizations including frequency, transient response, and mirror surface quality are also reported.

Modeling and Comparison of Bimorph Power Harvesters with Piezoelectric Elements Connected in Parallel and Series

Abstract: Power harvesting devices are designed to convert the ambient energy surrounding a system to usable electric energy. The strong desire to create self-powered systems, which do not rely on traditiona...

A Novel Adaptive Bimorph Focusing Mirror and Wavefront Corrector with Sub-Nanometre Dynamical Figure Control

Abstract: We present the design, fabrication and characterization of a novel adaptive X-ray optic by bringing together bimorph adaptive technology and the novel Elastic Emission Machining "super-polishing" technique. This super-polished adaptive mirror provides variable focal distance and local figure control in the sub-nm range. The optic has the potential to generate distortion-free beams, and enable wavefront control.

Design and development of a millimetre-wave novel passive ultrasensitive temperature transducer for remote sensing and identification

Abstract: The millimetre-wave passive temperature transducer consists of micro bimorph cantilevers (Au-Silicon) and split ring resonators, operating around 30 GHz. The temperature change causes a deflection on the bimorph cantilevers, thus results in a shift of resonant frequencies of the split ring structure. The design achieves sensitivity of 2.62 GHz/um in terms of frequency shift response to cantilever deflection, corresponding to a sensitivity of 498 MHz/°C, three order of magnitude higher than existing sensors. In terms of deflection versus temperature, the material choices for the bimorph cantilevers can be varied and adapted to different applications including those operating in harsh environments. To demonstrate proof-of-concept, a scaled prototype operating around 3 GHz is presented with Radar Cross Section measurements for remote identification.

Development and Dynamic Modeling of a New Hybrid Thermopiezoelectric Microactuator

Abstract: This paper presents a new hybrid microactuator based on the combination of piezoelectric and thermal effects. The proposed actuator can perform both a high-stroke coarse positioning through the thermal actuation and a high-resolution fine positioning through the piezoelectric actuation. The microactuator structure is a unimorph piezoelectric cantilever, which also constitutes a thermal bimorph that is very sensitive to temperature variation. While electrical voltage is used to control the piezoelectric actuation, we use a Peltier module to provide the temperature variation and to control the thermal functioning. In order to understand the behavior of the hybrid actuator, a model is developed. For better precision, but at the same time for model simplicity, the thermal part is modeled with the thermal network, whereas the Prandtl-Ishlinskii (PI) hysteresis approach is used to model the nonlinearity of the piezoelectric part. Finally, a series of experimental results validate the developed model.

Design and fabrication of twisting-type thermal actuation mechanism for micromirrors

Abstract: This paper reports the design and fabrication of a novel micromirror actuation system. The actuating mechanism for driving the micromirror combines two paralleled bimorph actuators bending in opposite directions for rotational control of the micromirror. Each actuator is structured by nickel and silicon nitride thin-films. Based on thermal and structural analyses, the geometry of the actuation system is optimized to achieve larger tilting angles of micromirrors whose sizes are of the order of 100 × 100 μm2. Operation of the actuation system shows total vertical displacements about 90 μm and tilting angles about 28° for micromirrors of 150 × 150 μm2 in size at input powers about 170 mW and about 60 μm and about 20° for micromirrors of 80 × 80 μm2 in size at input powers about 60 mW, which agree well with predictions from theoretical models and simulations using a commercial code.

Subcutaneous piezoelectric bone conduction hearing aid actuator and system

Abstract: An implantable bone-conduction hearing actuator based on a piezoelectric element, such as a unimorph or bimorph cantilever bender, is described Unlike other implantable bone conduction hearing actuators, the device is subcutaneous and once implanted is entirely invisible The device excites bending in bone through a local bending moment rather than the application of a point force as with conventional bone-anchored hearing aids

Theoretical and experimental studies of beam bimorph piezoelectric power harvesters

Abstract: This paper presents a theoretical model for simulating a piezoelectric beam bimorph power harvester consisting of a laminated piezoelectric beam, a proof mass, and an electrical load. The vertical offset of the proof mass center from the beam centroid couples the bending and longitudinal motions, which makes it necessary to consider both longitudinal and lateral vibrations simultaneously. Experiments were carried out on a beam bimorph prototype mounted on a shaker to measure the electrical output. Numerical results obtained using the proposed procedure for piezoelectric bimorph power harvesters are in good agreement with the experimental data.