Showing papers on "Bimorph published in 2005"

Modeling of electric energy harvesting using piezoelectric windmill

Abstract: This letter reports a theoretical model for determination of generated electric power from piezoelectric bimorph transducers in low frequency range far from the piezoelectric resonance. The model is divided into two parts. In the first part the open circuit voltage response of the transducer under the ac stress is computed based on the bending beam theory for bimorph. In the second part, this open circuit voltage acts as the input to the equivalent circuit of the capacitor connected across a pure resistive load. The results of the theoretical model were verified by comparing it with the measured response of a prototype windmill. The prototype piezoelectric windmill consisting of ten piezoelectric bimorph transducers was operated in the wind speed of 1–12 mph. A power of 7.5 mW at the wind speed of 10 mph was measured across a matching load of 6.7kΩ. The theoretical model was found to give very accurate prediction of the generated power and matching load and an excellent matching was found with the experim...

Piezoelectric Ceramics with Functional Gradients: A New Application in Material Design

Abstract: Internal strain amplification can be utilized in piezoelectric ceramics to obtain relatively large displacements. The monomorph described in the present work is a bending bar made from a single piece of material into which a smooth gradient of piezoelectric activity is introduced. The application of a voltage then causes the bar to bend due to the differential stresses that are induced. These are relatively uniformly distributed and do not peak in the center as in a conventional bimorph. Significantly increased life and reliability can then be achieved.

Optimal energy density piezoelectric bending actuators

Abstract: The design and analysis of piezoelectric actuators is rarely optimized for low mass applications. However, emerging technologies such as micro air vehicles, and microrobotics in general, demand high force, high displacement, low mass actuators. Utilization of generic piezoceramics and high performance composite materials coupled with intelligent use of geometry and novel driving techniques yields low cost, rapidly prototyped, ultra-high energy density bending actuators for use in such applications. The design is based upon a laminate plate theory model for a stacked multimorph cantilever actuator, encompassing all possible layups, layer anisotropies, internal and external excitations, and intrinsic and extrinsic geometries. Using these principles, we have fabricated 12 mg PZT bimorph actuators with greater than 2 J kg −1 energy density. This gives a performance increase of an order of magnitude or greater compared to existing commercially available piezoelectric bending actuators.

Piezoelectric Windmill: A Novel Solution to Remote Sensing

Abstract: This study demonstrates a technology, "Piezoelectric Windmill", for generating the electrical power from wind energy. The electric power-generation from wind energy is based on piezoelectric effect and utilizes the bimorph actuators. Piezoelectric Windmill consists of piezoelectric actuators arranged along the circumference of the mill in the cantilever form. Using the camshaft gear mechanism an oscillating torque is generated through the flowing wind and applied on the actuators. A working prototype was fabricated utilizing 12 bimorphs (60 ×20 ×0.5 mm3) having a preload of 23.5 gm. Under a nominal torque level corresponding to normal wind flow and oscillating frequency of 6 Hz, a power of 10.2 mW was successfully measured across a load of 4.6 kΩ after rectification. Combined with the wireless transmission, this technology provides a practical solution to the remote powering of sensors and communication devices.

Performance of a piezoelectric bimorph for scavenging vibration energy

Abstract: We analyze the performance of a piezoelectric bimorph in the flexural mode for scavenging ambient vibration energy and evaluate the dependence of the performance upon the physical and geometrical parameters of the model bimorph. The analytical solution for the flexural motion of the piezoelectric bimorph shows that the output power density increases initially, reaches a maximum, and then decreases monotonically with increasing load impedance, which is normalized by a parameter that is a simple combination of the physical and geometrical parameters of the scavenging structure, the bimorph, and the frequency of the ambient vibration, underscoring the importance for the load circuit to have the impedance desirable by the scavenging structure. The numerical results illustrate the considerably enhanced performances achieved by adjusting the physical and geometrical parameters of the scavenging structure.

Comparative analysis of deformable mirrors for ocular adaptive optics.

Abstract: We have evaluated the ability of three commercially available deformable mirrors to compensate the aberrations of the eye using a model for aberrations developed by Thibos, Bradley and Hong. The mirrors evaluated were a 37 actuator membrane mirror and 19 actuator piezo mirror (OKO Technologies) and a 35 actuator bimorph mirror (AOptix Inc). For each mirror, Zernike polynomials and typical ocular aberrated wavefronts were fitted with the mirror modes measured using a Twyman-Green interferometer. The bimorph mirror showed the lowest root mean square error, although the 19 actuator piezo device showed promise if extended to more actuators. The methodology can be used to evaluate new deformable mirrors as they become available.

A thermal bimorph micromirror with large bi-directional and vertical actuation

Abstract: This paper reports a novel large vertical displacement (LVD) microactuator that can generate large piston motion and bi-directional scanning at low driving voltage. A LVD micromirror device has been fabricated by using a unique deep reactive ion etch (DRIE) post-CMOS micromachining process that simultaneously provides thin-film and single-crystal silicon microstructures. The bimorph actuation structure is composed of aluminum and silicon dioxide with an embedded polysilicon thermal resistor. With a size of only 0.7 mm × 0.32 mm, the LVD micromirror demonstrated a vertical displacement of 0.2 mm at 6 V dc. This device can also be used to perform bi-directional rotational scanning through the use of two bimorph actuators. The micromirror rotates over ±15 ◦ at less than 6 V dc, and over ±43 ◦ (i.e., >170 ◦ optical scan angle) at its resonant frequency of 2.6 kHz.

Resonant micro-mirror excited by a thin-film piezoelectric actuator for fast optical beam scanning

Abstract: A silicon resonant torsional micro-mirror excited by piezoelectric bimorph actuators is presented. The bimorph actuators consist of a single-crystal silicon flexible beam or membrane and a PZT thin film. The mechanical elements are etched in the 20 μm thick superficial layer of a SOI substrate, thereby ensuring the flatness of the 500 μm-diameter gold-coated mirror. This device achieves optical beam scanning with large angular deflection at high frequency. In air, we have measured scanning up to 19.8° at 1.8 kHz, 99.1° at 10.6 kHz and 40.8° at 25.4 kHz. The applied driving voltage is sinusoidal with an amplitude under 42 V PP and with a 6 V DC bias voltage. At large oscillation amplitude, a non-linear hard-spring effect has been observed. In vacuum, a 78° optical scanning has been obtained with less than 1 V PP .

Equivalent modeling for ionic polymer–metal composite actuators based on beam theories

Abstract: Equivalent beam and equivalent bimorph beam models for IPMC (ionic polymer–metal composite) actuators are described in the ensuing paper. Important physical properties of IPMCs including Young's modulus and electro-mechanical coupling coefficient were determined using the rule of mixture, bimorph beam equations, and measured force–displacement data of a cantilevered IPMC actuator. By using a beam equation with estimated physical properties, the actuation displacements of a cantilevered IPMC actuator were calculated to show an excellent agreement between the computed tip displacements and the measured data. Finite element analysis (FEA), along with the predetermined physical properties, was used to predict the force–displacement relationship of an IPMC actuator, which is key data to effectively design many engineering devices of interest. Indicated by the results from the FEA agreeing with the measured data, the proposed models can be adopted for modeling of IPMC actuators with advanced shapes and other boundary conditions.

Comparison of microtweezers based on three lateral thermal actuator configurations

Abstract: Thermal actuator-based microtweezers with three different driving configurations have been designed, fabricated and characterized. Finite element analysis has been used to model the device performance. It was found that one configuration of microtweezer, based on two lateral bimorph thermal actuators, has a small displacement (tip opening of the tweezers) and a very limited operating power range. An alternative configuration consisting of two horizontal hot bars with separated beams as the arms can deliver a larger displacement with a much-extended operating power range. This structure can withstand a higher temperature due to the wider beams used, and has flexible arms for increased displacement. Microtweezers driven by a number of chevron structures in parallel have similar maximum displacements but at a cost of higher power consumption. The measured temperature of the devices confirms that the device with the chevron structure can deliver the largest displacement for a given working temperature, while the bimorph thermal actuator design has the highest operating temperature at the same power due to its thin hot arm, and is prone to structural failure.

Layerwise Laminate Analysis of Functionally Graded Piezoelectric Bimorph Beams

Abstract: A layerwise finite element formulation developed for piezoelectric materials is used to investigate the displacement and stress response of a functionally graded piezoelectric bimorph actuator. The formulation is based on the principles of linear thermopiezoelectricity and accounts for the coupled mechanical, electrical, and thermal responses of piezoelectric materials. The layerwise laminate theory is implemented into a linear beam element in order to provide a more accurate representation of the transverse and shear effects that are induced by the increased inhomogeneities introduced through-the-thickness by the functionally graded materials. The accuracy of the formulation is verified with previously published experimental results for a piezoelectric bimorph actuator. Additional studies are conducted to analyze the impact of electric and thermal loads on the deflections and stresses in a bimorph actuator. Results of the study help to demonstrate the capability of the layerwise theory to provide a more ...

Design, fabrication and initial results of a 2g autonomous glider

Abstract: Utilizing the core technologies of emerging microrobotic structures, the rapid design and prototyping of a passive micro air vehicle with the final goal of locating an audio source while avoiding hazardous obstacles is presented. The airfoil and control surfaces are optimized empirically to maximize lift and maneuverability while minimizing drag. Bimorph piezoelectric bending cantilevers actuate the control surfaces. Since such actuators require high voltages, an efficient boost circuit is presented along with appropriate high voltage electronics. To locate audio sources, a pair of acoustic sensors is designed and prototyped using a phase detection algorithm while a custom optic flow sensor is developed to avoid obstacles and give estimates of object distances and velocities. Finally, each subsystem is demonstrated and the complete glider is integrated to demonstrate initial open loop control performance.

3D free space thermally actuated micromirror device

Abstract: A thermally actuated free space single crystal silicon micromirror device has been developed using one wafer low cost fabrication process. The device consists of a central mirror plate symmetrically joined with four thermal bimorph actuators through flexural springs. All the structural components of the device are fabricated in single crystal silicon using bulk silicon micromachining technology. Composite cantilevers of single crystal silicon, silicon dioxide, and aluminum are used as bimorph thermal actuators. This is an analogue micromirror device, which operates very accurately within an angular range for steering light beam in free space. The micromirror was demonstrated to achieve up to 10° repeatable angular deflection, 8–13 ms thermal response time, and 29 cm radius of curvature. The device was operated continuously for 100 million switching cycles at 40 Hz; no change in performance was observed which shows a good structural reliability. The target application area is optical communication networks; however, the device is equally useful for other scanning type of applications.

An electro-thermal bimorph-based microactuator for precise track-positioning of optical disk drives

Abstract: Electro-thermal actuations are very attractive since they can generate large deflections and forces with low actuating voltages and their fabrication process is compatible with the general integrated circuit (IC) fabrication process. In this paper, we present a novel electro-thermal bimorph-based microactuator as a precise-tracking positioner for high-density optical disk drives (ODD). In the proposed microactuator, four thermal bimorph cantilevers suspend a mirror plate by linkage hinges at the free ends of the cantilever, whose opposing ends are rigidly attached to the substrate. Each bimorph cantilever comprises two material layers with different thermal expansions. Due to the bimorph effect, the mirror can be displaced upwards in the out-of-plane parallel to the substrate by passing electric current through the cantilevers. Thermal-mechanical analysis, transient responses and mechanical vibrations are investigated by analytical modeling and finite element simulation. The overall device, with an area of 700 µm × 700 µm, is fabricated successfully by MEMS technology compatible with the standard IC process. The experimental and simulation results show that the mirror can be vertically moved up 1 µm, which is equivalent to 1.4 µm displacement in the track direction of the spinning optical disk, by a lower driving voltage at 3 V with 3 mW power consumption. Its mechanical frequency of 7 kHz is high enough to support high bandwidth servo control in high-density ODD.

Design and fabrication of a novel bimorph microoptomechanical sensor

Abstract: We have designed a so-called flip-over bimaterial (FOB) beam to increase the sensitivity of micromechanical structures for sensing temperature and surface stress changes. The FOB beam has a configuration such that a material layer coats the top and bottom of the second material at different regions along the beam length. By multiple interconnections of FOB beams, the deflection or sensitivity can be amplified, and the out-of-plane motion of a sensing structure can be achieved. The FOB beam has 53% higher thermomechanical sensitivity than a conventional one. Using the FOB beam design, we have developed a microoptomechanical sensor having a symmetric structure such that beam deflection is converted into a linear displacement of a reflecting surface, which is used for optical interferometry. The designed sensor has been fabricated by surface micromachining techniques using a transparent quartz substrate for optical measurement. Within a sensor area of 100 /spl mu/m/spl times/100 /spl mu/m, the thermomechanical sensitivity S/sub T/=180 nm/K was experimentally obtained.

Fabrication and characterization of diamond-like carbon/Ni bimorph normally closed microcages

Abstract: Normally closed microcages based on highly compressively stressed diamond-like carbon (DLC) and electroplated Ni bimorph structures have been simulated, fabricated and characterized. Finite-element and analytical models were used to simulate the device performance. It was found that the radius of curvature of the bimorph layer can be adjusted by varying the DLC film stress, the total layer thickness and the thickness ratio of the DLC to Ni layers. The angular deflection of the bimorph structures can also be adjusted by varying the finger length. The radius of curvature of the microcage was in the range of 18–50 µm, suitable for capturing and confining micro-objects with sizes of 20–100 µm. The operation of this type of device is very efficient due to the large difference in thermal expansion coefficients of the DLC and the Ni layers. Electrical tests have shown that these microcages can be opened by ~90° utilizing a power smaller than 20 mW. The operating temperatures of the devices under various pulsed currents were extracted through the change in electrical resistance of the devices. The results showed that an average temperature in the range of 400–450 °C is needed to open this type of microcage by ~90°, consistent with the results from analytical simulation and finite-element modelling.

Development and characterization of single wall carbon nanotube-Nafion composite actuators

Abstract: The development and characterization of thin film polymeric actuators has been performed for single wall carbon nanotube (SWNT)–Nafion composite systems. Previous work in our laboratory illustrated that incorporation of highly conductive SWNTs into an ionomeric matrix promoted an actuation response by enhancing the electro-osmotic effect at relatively low doping levels, ∼0.1% (w/w). Further investigation has shown the effects of frequency and applied voltage on the composite bimorph actuator systems. The results indicate a displacement response that is linearly dependent on voltage and inverse to frequency.

A novel microfabrication of a self-aligned vertical comb drive on a single SOI wafer for optical MEMS applications

Abstract: A novel method for fabricating a self-aligned electrostatic vertical comb drive using a single layer of a SOI wafer is introduced. The fixed combs are anchored to bimorph cantilevers made of two materials with dissimilar thermal coefficients of expansion, i.e., silicon dioxide and single crystal silicon. The cantilever, which provides the vertical offset between the fixed comb and the movable comb, is deflected by residual stress during cooling down from oxidation temperature to room temperature. In piston motion, the vertical amplitude at the resonant frequency of 3.5 kHz is 30 µm. In torsional motion, the angle of optical deflection at the resonance of 830 Hz is changed by 6.5°. The measured resonant frequencies correspond to the results from a finite element analysis within 10%. This vertical comb drive is useful for optical and biophotonic MEMS requiring out-of-plane torsional or piston motion.

Piezoelectric/electrostrictive multimaterial PMN-PT monomorph actuators

Abstract: Fused deposition of multimaterials (FDMM), a CAD-based layered manufacturing technique, was utilized to fabricate monolithic piezoelectric/electrostrictive multimaterial monomorphs. The samples, comprised of piezoelectric 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 and electrostrictive 0.90Pb(Mg1/3Nb2/3)O3-0.1PbTiO3, have been successfully prototyped and co-sintered. Bimorphs, that are isometric with the co-fired samples, have also been prepared by attaching individual piezoelectric and electrostrictive layers with conductive epoxy, and were used as a comparison for displacement properties. The dielectric permittivity, displacement, and polarization hysteresis were investigated. The permittivity of the multimaterial co-sintered samples followed the two-capacitors in-series model, showing a dielectric constant of 5800 at room temperature. The P–E loop of the multimaterial samples exhibited a saturation polarization, remnant polarization, and hysteresis between that of the single material electrostrictive 0.9PMN-0.1PT and the single material piezoelectric 0.65PMN-0.35PT. Displacement hysteresis was shown to be lower for the monolithic monomorph as compared to the bimorph and reached ∼11 μm at ∼3 kV/cm.

Theoretical modeling, experiments and optimization of piezoelectric multimorph

Abstract: This paper deals with the static and dynamic electromechanical responses of piezoelectric layered structures (multimorphs). Based on the Bernoulli?Euler plate model including the dynamics of piezoelectric, electrode and substrate layers, we obtain the natural frequencies, maximum displacement and resultant force of a symmetric cantilevered multimorph. The proposed theoretical model is verified by experiments using a 20-layered PZT (plumbum?zirconate?titanate) multimorph, and it is compared to the conventional bimorph model. Experimental results agree with the analytical predictions on the natural frequencies and vertical displacement. With the analytical solution for multimorph, we investigate the effects of the layer number and the layer thickness on natural frequency, maximum deflection and output force. It is found that there exists an optimum number of piezoelectric layers to maximize the transverse deflection. There also exists a specific value of the thickness ratio between piezoelectric and structure layers to maximize both the tip deflection and force.

Tunable radio frequency MEMS inductors with thermal bimorph actuators

Abstract: We have developed a CMOS-compatible micromachining process that allows us to build high quality, tunable radio frequency inductors. Inductors play a key role in wireless front ends; the additional flexibility offered by tunability can offer adaptability to devices such as filters, matching circuits and voltage-controlled oscillators. Our inductors have a tuning range of up to 30% with a quality factor of 25 and self-resonance over 35 GHz.

A piezoelectric bimorph micro-gripper with micro-force sensing

Abstract: A new piezoelectric bimorph micro-gripper with micro-force sensing is presented in the paper The micro-gripper is based on the dual cantilevers structure and is driven by two piezoelectric bimorphs Sticking two strain gauges on both sides of the base of the piezoelectric bimorph to sense free end transmutation of the bimorph, we can get displacement-voltage relationship and force-strain relationship respectively As a result the gripper has the ability to detect micro-force when it is gripping micro-parts The experiment results show that the gripper works reliably and safely It is satisfied with the tasks of micro assembly

Small piezoelectric or electrostrictive linear motor

Abstract: The present invention provides a small piezoelectric/electrostrictive ultrasonic linear motors which are installed in cell phones or PDAs, etc. to drive their camera lenses. In the present invention, a movable shaft (30) is coupled to a unimorph or bimorph, which is made by attaching a piezoelectric or electrostrictive substrate to an elastic body (20) (metal), so that a movable body (40) fitted over the movable shaft (30) is linearly moved along the movable shaft (30) by vibration of the piezoelectric or electrostrictive substrate, thus simplifying a manufacturing process, being easily practicable according to a basic principle, and having superior characteristics.

Wireless bimorph micro-actuators by pulsed laser heating

Abstract: We report an experimental and theoretical investigation on wireless bimorph micro-cantilever (BMC) actuated by pulsed laser heating. The micromachined BMC consists of a thin gold layer deposited on a polysilicon layer. A pulsed Nd:YAG laser of wavelength = 355 nm and pulse width = 12 ns was used to heat the BMC. The movement of the BMC was measured by a displacement sensor. Experimental results revealed the frequency of BMC vibration upon laser heating. A two-dimensional (2D) discrete model was developed to simulate the laser pulse response of the cantilever. The simulation results agreed well with experimental observation, except the minor differences in vibration amplitudes in the model.

Design of a Comfortable Rotor Airfoil Using Distributed Piezoelectric Actuators

Abstract: In the present study, several design methodologies are developed for determining the optimal distribution of a limited amount of piezoelectric material aft of the spar in a conformable rotor airfoil section. The design objectives are to maximize the trailing-edge deflection under actuation loads and simultaneously minimize the airfoil deflection under aerodynamic loads. Energy-like functions, mutual potential energy (MPE) and strain energy (SE), are used as measures of the deflections created by the actuation and aerodynamic loads, respectively. The design objectives are achieved by maximizing a multicriteria objective function that represents a ratio of the MPE to SE. Several design optimization techniques are evaluated including topology, geometry, sequential topology-geometry, and concurrent topology-geometry optimizations. The results of the study indicate that the optimized conformable airfoil section obtained using the concurrent topology-geometry optimization can produce a downward trailing-edge deflection equivalent to 4.24 deg of effective flap angle from the actuation loads, with the peak-to-peak deflection being nearly twice the downward deflection. The airfoil deformation caused by the aerodynamic loads alone is extremely small (less than 0.24 deg). Key features of the optimized airfoil are arrangement of actuators near the spar that act to stretch and shrink the skin and a bimorph like mechanism from midchord to the trailing edge. Additional results include a strain analysis, aerodynamic lift-and-drag increment study, and an examination of the effects of skin thickness and volume constraint of the active material.

Focused ion beam fabrication of thermally actuated bimorph cantilevers

Abstract: Focused ion beam (FIB) technology was used to fabricate thermally actuated cantilever arrays using silicon nitride membrane chips for microelectromechanical systems (MEMS) applications. Sequential modification and test is made possible by the dualbeam FIB/SEM. A fabrication route based largely on the use of FIB etch and deposition steps applied to a silicon nitride membrane chip resulted in the formation of readily released bimorph structures with lengths

Method and apparatus for obtaining quantitative measurements using a probe based instrument

Abstract: A cantilever probe-based instrument (10, 110) is controlled to counteract the lateral loads imposed on the probe as a result of probe sample interaction. The probe preferably includes an active cantilever, such as a so-called bimorph cantilever. Force counteraction is preferably achieved by monitoring a lateral force-dependent property of probe operation such as cantilever free end deflection angle and applying a voltage to at least one of the cantilever and one or more separate actuators under feedback to maintain that property constant as the probe-sample spacing decreases. The probe could further uses at least one of contact flexural and torsional resonances characteristics to determine contact and release points. With the knowledge of the tip profile, quantitative mechanical data for probe sample interaction can be obtained.

Acoustic vibration generating piezoelectric bimorph element

Abstract: PROBLEM TO BE SOLVED: To provide an acoustic vibration generating piezoelectric bimorph element in which unnecessary high-frequency components are eliminated without an increase in the number of parts and a cubic volume in a configuration of an acoustic system for applying a piezoelectric bimorph element. SOLUTION: A resonant mode in a high-frequency range is suppressed to reduce outputs of high-frequency components by providing a blank part where an electrode is eliminated at a free-end side of the piezoelectric type bimorph 4. As a result, the acoustic system where a howling phenomenon is hardly caused can be provided without the increase in the cubic volume and the number of parts of the piezoelectric bimorph 4. COPYRIGHT: (C)2006,JPO&NCIPI