Piezoelectric Unimorph Actuators Research Articles

A study on the piezoelectric actuation performance of prestressed piezoelectric unimorph actuators

The actuation performances of the prestressed piezoelectric unimorph actuators piezoelectric unimorph with mechanically prestressed substrate and thin layer unimorph driver are evaluated in terms of actuation displacement and force. During the performance tests, these prestressed piezoelectric unimorph actuators showed highly nonlinear behavior, in which their actuation performances were not proportional to the magnitude of the applied voltage, although normally they exhibit higher actuation performances at higher driving voltages. This means that the nominal piezoelectric material properties from the standard method were no longer valid for evaluating and predicting the actuation performances of the piezoelectric unimorph with mechanically prestressed substrate and thin layer unimorph driver actuators under high-voltage application. In this article, the nonlinear piezoelectric material properties, especially the elastic modulus and the piezoelectric strain coefficient, were obtained by considering the prestress, the applied voltage, and the re-poling treatment of the piezoelectric material inside the prestressed piezoelectric unimorph. Finally, actuation performance simulations were conducted using the nonlinear material properties, and the analytical results were compared and validated with the experimental results.

Hysteresis Property of Tip-Tilt-Piston Micromirror Based on Tilt-and-Lateral Shift-Free Piezoelectric Unimorph Actuator

This paper presents hysteresis property of tip-tilt-piston micromirror based on tilt-and-lateral shift-free piezoelectric unimorph actuator. The accuracy and the level of performance of piezoelectric actuator will be reduced for the reason of hysteresis behavior of piezoelectric device. To compensate the hysteresis behavior of the actuator, the properties should be researched and tested at first. The paper report the hysteresis behavior of micromirror with TLSF piezoelectric actuator under fixed frequency driving is stable with respect to the changes of the time and amplitude of driving voltage without considering the failure effect.

A large-scan-angle piezoelectric MEMS optical scanner actuated by a Nb-doped PZT thin film

Resonant 1D microelectromechanical systems (MEMS) optical scanners actuated by piezoelectric unimorph actuators with a Nb-doped lead zirconate titanate (PNZT) thin film were developed for endoscopic optical coherence tomography (OCT) application. The MEMS scanners were designed as the resonance frequency was less than 125 Hz to obtain enough pixels per frame in OCT images. The device size was within 3.4 mm × 2.5 mm, which is compact enough to be installed in a side-imaging probe with 4 mm inner diameter. The fabrication process started with a silicon-on-insulator wafer, followed by PNZT deposition by the Rf sputtering and Si bulk micromachining process. The fabricated MEMS scanners showed maximum optical scan angles of 146° at 90 Hz, 148° at 124 Hz, 162° at 180 Hz, and 152° at 394 Hz at resonance in atmospheric pressure. Such wide scan angles were obtained by a drive voltage below 1.3 Vpp, ensuring intrinsic safety in in vivo uses. The scanner with the unpoled PNZT film showed three times as large a scan angle as that with a poled PZT films. A swept-source OCT system was constructed using the fabricated MEMS scanner, and cross-sectional images of a fingertip with image widths of 4.6 and 2.3 mm were acquired. In addition, a PNZT-based angle sensor was studied for feedback operation.

A tip–tilt–piston micromirror with a double S-shaped unimorph piezoelectric actuator

This paper presents the design, fabrication and characterization of a tip–tilt–piston (TTP) piezoelectric micromirror. A unique double S-shaped unimorph piezoelectric (dSUP) actuator design is employed. The dSUP actuator design can generate large vertical displacement. With four such actuators symmetrically located on the four sides of the mirror plate, both tip and tilt as well as piston motion can be realized. Lead zirconate titanate (PZT) is used due to its high piezoelectric coefficient and it is fabricated with a sol–gel method. The Zr/Ti ratio of the PZT material is 53/47. The dSUP actuators consist of Pt/Ti/PZT/Pt/Ti/SiO2 multilayers. The thickness of the PZT layer is 0.7μm. The 1.1mm×1.1mm mirror plate is backed by a 50μm-thick single-crystal silicon layer to ensure the flatness. Backside deep silicon etching and front-side isotropic silicon undercut are used to release the device. Experiments show that the resonant frequency of the tip–tilt scan modes is 3.5kHz. 27μm vertical displacement was observed under 5V DC driving of one pair of opposite actuator and the scan angle can achieve 9.65° under sine wave resonant driving at 2V amplitude on one pair of opposite actuator.

Development of Ink Jet Printhead Equipped With a Large Monolithic Unimorph Piezoelectric Actuator Unit

Kyocera realized a trapezoidal actuator unit with one inch width approximately, in which 664 portions of individual unimorph piezoelectric actuators are formed in matrix of 16 rows. This actuator unit has been used for its own piezoelectric ink jet printheads known as KJ4 series, in which four units are used to cover 4.25 inch (108.25 mm) print width.Then, Kyocera has developed a larger actuator unit that covers 4.4 inch (112.35 mm) print width with monolithic rectangular body, in which numbers of individual active portions are arranged. And, it has been adopted for development of new ink jet printhead series.As the first model of the new printhead series, 4.4 inch (112.35 mm), 300 npi ink jet printhead for aqueous ink is introduced. It is equipped with nozzles forming a matrix of 16 rows × 166 columns in 4.4 inch × 1 inch (112.35 mm × 25.4 mm) rectangular region. Each group of adjacent eight nozzle rows belongs to individual channel group, in which nozzles are arranged in 300 npi. And, independent driving conditions in voltage and waveform can be applied to each nozzle group. Practically, this printhead is intended to pack two pieces of 300 npi printheads in 200mm × 36mm × 61mm single body for downsizing and simplification in printer design especially for multi-pass printing applications.

Temperature-compensated f iber optic Fabry-Perot accelerometer based on the feedback control of the Fabry-Perot cavity length

A temperature-compensated fiber optic Fabry-Perot accelerometer (FOFPA) formed by symmetrically bonding an all-silica in-line fiber Fabry-Perot etalon (ILFFPE) and a piezoelectric ceramic unimorph actuator (PCUA) to two surfaces of a silica cantilever is reported. The all-silica ILFFPE with feedback-controlled cavity length by the PCUA simultaneously senses acceleration and temperature. The results indicate that the fabricated FOFPA system simultaneously senses acceleration and temperature with active temperature compensation. The nonlinearity of the output voltage to acceleration is less than 0.65%. The nonlinearity of the control voltage to temperature is 1.75%. Furthermore, the maximum deviation of the sensitivity with temperature compensation at a temperature range from 25 to 50 oC is 0.025 V/g.

Finite element models of piezoelectric actuation for active flow control

A numerical procedure, based on the finite element method, capable to simulate the interaction of active structures with an incompressible fluid flow is discussed. In particular the active functionality of such structures is demanded to piezoelectric type actuators. The development of this interaction is connected to the study of problems that involve an active flow control for different potential applications such as drag reduction, noise reduction, separation control, mixing enhancement, etc. Two kinds of finite element models, one for the electromechanical field and the other for the fluid-dynamic field, are set up. The analyses are performed with a coupled iterative solver, based on the arbitrarian Lagrangian–Eulerian (ALE) description. A Reynolds-averaged Navier–Stokes Equations (RANS) formulation for the model of turbulent fluid is adopted. The results of some numerical analyses are correlated to an experimental benchmark case founded in literature with the aim to validate the procedure. A sample application to modify the features of separated flow from a backward facing step is described, in which a piezoelectric unimorph actuator is patched on a Euler–Bernoulli beam installed at the upper corner of the step. The numerical model describes the displacement of the incoming shear layer and the velocity perturbation produced by the periodic oscillations of the actuator and how these parameters are related to each other. In order to produce sensible amplitude for the oscillations, the actuator is driven near its natural frequency. A preliminary response analysis to examine the effects of the fluid on the resonant behaviour of the structure is illustrated.

A piezoelectric unimorph actuator based tip-tilt-piston micromirror with high fill factor and small tilt and lateral shift

This paper presents the design, fabrication and characterization of a piezoelectrically actuated high-fill-factor tip-tilt-piston (TTP) micromirror with small tilt and lateral shift during scanning. The piezoelectric material is a sol–gel lead zirconate titanate (PZT) thin film with a Zr/Ti ratio of 53/47. The small initial tilt and lateral-shift-free (LSF) of the mirror plate is achieved by a folded, three-segment piezoelectric unimorph actuator design. The piezoelectric unimorph actuation beams consist of Pt/Ti/PZT/Pt/Ti/SiO 2 multilayers, which are released via undercutting the substrate silicon. The fabricated piezoelectric micromirror can be actuated about two rotational axes in the mirror plane and for translational vertical scan (piston actuation). The resonant frequencies of the piston and rotation modes are 316 Hz and 582 Hz, respectively. At their respective resonant frequencies, the maximum piston magnitude at resonant driving is 32 μm, and the two-dimensional rotating scan ranges are about 5°, both measured at a 2V pp sinusoidal driving voltage.

Modeling and Testing of the Static Deflections of Circular Piezoelectric Unimorph Actuators

In this article, based on the classical laminated plate theory, a new static deflection model for CPUAs subjected to voltage is established and the bonding layer is taken into account as an individual layer. According to the established analytical model, the influences of the structural parameters and material properties of the CPUA on the transverse deflection are numerically simulated and the static and dynamic characteristics of the CPUA are experimentally tested. The research results show that the predicted static deflections of the CPUA by the established deflection model in this article agree well with the measured results, the established static deflection model considering the bonding layer is more accurate than the existing model neglecting the bonding layer, and the maximum relative error is reduced by 8.45%. The static deflections of the CPUA are apparently affected by the structural parameters and the material properties, which indicate that the performance of the CPUA can be optimized by the structural parameters and material properties. Because the hysteresis of the piezoelectric material is not considered when establishing the static deflection model, the apparent error exists when utilizing the static deflection model to predict the dynamic characteristics of the CPUA.

B-4 圧電マイクロミラーアレーによる光通信デバイスの作製(口頭発表:マイクロナノメカトロニクス)

We studied a new fabrication process for a micro mirror array device with piezoelectric unimorph actuators and simulated its actuation. In this fabrication process, piezoelectric thin film (PZT ; Pb(Zr,Ti)O_3) is deposited on SOI substrate by sputtering after actuator parts are released by BHF wet etching. Therefore, patterning or etching piezoelectric layer is not necessary, which means that proposed fabrication process can apply to various piezoelectric devices. Furthermore, we confirmed the actuation of proposed micro mirrors by FEM simulation.

Investigation of Unswept Normal Shock Wave/Turbulent-Boundary-Layer Interaction Control

An analytical model for the unswept normal shock wave/turbulent-boundary-layer interaction control using an upstream and downstream unimorph piezoelectric flap actuator has been proposed. The amount of flap deflection controls the bleed/suction rate through a plenum chamber. The cavity allows rapid thickening of the boundary layer approaching a normal shock wave, which splits into a series of weaker shocks forming a lambda shock foot, leading to a reduction in the wave drag. The analysis provides an understanding of the control influences produced in an experimental investigation of an unswept normal shock wave/turbulent-boundary-layer interaction at a Mach number of 1.5. It has also been validated by application to the normal shock wave/boundary-layer interaction control system using mesoflaps for aeroelastic transpiration described in previous transonic/supersonic shock wave/ boundary-layer interaction studies.

Development of piezoelectric actuators for active X-ray optics

Piezoelectric actuators are widely utilised in adaptive optics to enable mirrors having an actively controlled reflective surface for the purpose of the wavefront correction by reducing the effects of rapidly changing optical distortion. Two new prototype adaptive X-ray optical systems are under development with the aim of approaching the fundamental diffraction limit. One proposed technology is microstructured optical arrays (MOAs) involving two or four piezoelectric strips bonded to a silicon wafer to produce a micro-focused X-ray source for biological applications, and which uses grazing incidence reflection through consecutive aligned arrays of channels obtained using deep silicon etching. Another technology is large scale optics which uses a thin shell mirror bonded with 20–40 piezoelectric actuators for the next generation of X-ray telescopes with an aim to achieve a resolution greater than that currently available by Chandra (0.5"). PZT-based piezoelectric actuators are being developed in this programme according to the design and implementation of the proposed mirror and array structures. Viscous plastic processing is chosen for the preparation of the materials system, which is subsequently formed and shaped into the suitable configurations. Precise controls on the thickness, surface finish and the curvature are the key factors to delivering satisfactory actuators. Unimorph type piezoelectric actuators have been proposed for the applications and results are presented regarding the fabrication and characterisation of such piezo-actuators, as well as the related design concepts and comparison to modelling work.

Lifetime Improvement for Full-Width-Array Piezo Ink Jet Print Head Using Matrix Nozzle Arrangement

Upon driving the unimorph type piezoelectric actuator of an ink jet in a high temperature high humidity environment (38°C/80%), many failures occurred after approximately 1 billion pulses. We hypothesized that the failures occurred due to hydrogen that was generated from the electrolysis of water, causing the piezoelectric element to deteriorate. Based on this hypothesis, we examined electrode materials to reduce the frequency of failures. We found that failure rate can be improved if material with high standard electrode potential is used as the electrode material on the high potential side and material with low standard electrode potential is used on the low potential side, and more specifically, if metal oxide is used for the electrode on the low potential side. Based on these findings, a combination of silver palladium for the electrode on the high potential side and stannous oxide (Sn x O y ) for the low potential side was used as the combination of electrode materials that can be formed at low cost. Upon implementing a running test with this combination of electrode materials under a high temperature high humidity environment, we confirmed that failures do not occur even at a continuous drive of 30 billion pulses and that the long-term reliability of the unimorph type piezoelectric actuator improved significantly.

파형 및 주파수해석에 근거한 굽힘 압전 복합재료 작동기 손상모드의 비파괴적 평가

In this study, various damage modes in bending unimorph piezoelectric composite actuators with a thin sandwiched PZT plate during bending fracture tests have been evaluated by monitoring acoustic emission (AE) signals in terms of waveform and peak frequency as well as AE parameters. Three kinds of actuator specimens consisting of woven fabric fiber skin layers and a PZT ceramic core layer are loaded with a roller and an AE activity from the specimen is monitored during the entire loading using an AE transducer mounted on the specimen. AE characteristics from a monolithic PZT ceramic with a thickness of 250 ㎛ are examined first in order to distinguish different AE signals from various possible damage modes in piezoelectric composite actuators. Post-failure observations and stress analyses in the respective layers of the specimens are conducted to identify particular features in the acoustic emission signal that correspond to specific types of damage modes. As a result, the signal classification based on waveform and peak frequency analyses successfully describes the failure process of the bending piezoelectric composite actuator exhibiting diverse failure mechanisms. Furthermore, it is elucidated that when the PZT ceramic embedded actuators are loaded mechanical bending loads, the failure process of actuator specimens with different lay-up configurations is almost same irrespective of their lay-up configurations.

Actuation Displacement of Unimorph Piezoelectric Actuators with External Loading

In real applications, unimorph piezoelectric actuators always work under a certain carrying load. The center loading configuration can be found in the recent application of LIPCA (Lightweight Piezoceramic Composite Actuator) as the artificial muscle for flapping device. LIPCA is also used with tip loading configuration in our new model of MAV elevator. The loading performance of the device should be fully understood. This paper presents a study on the actuation displacement of unimorph piezoelectric actuators with two loading conditions: center loading and tip loading. The actuation displacement of loaded unimorph piezoelectric actuators is predicted by the finite element method and observed by experiments. Surprisingly, the predictions do not show the correct tendency of behavior of the device. Two typical kinds of piezoelectric unimorph actuator, LIPCA-C3 and THUNDER, are investigated numerically and experimentally. Some remarks on the observations are presented.

Surface-Tension-Driven Biologically Inspired Water Strider Robots: Theory and Experiments

Recent biological studies on water strider insects revealed how they maintain stability and maneuver on the surface of water. While macroscale bodies use buoyancy, these very small insects use surface tension force to balance their weight on water. This paper proposes a biologically inspired miniature robot that utilizes the unique scaling advantage of these insects. The paper focuses on understanding the physics of the interaction between the insect and the surface of water and on designing a robot that mimics their key features. Hydrophobic Teflon coated wire legs optimized to take the most advantage of the surface tension force are used to support the weight of the 1-g robot. It is shown that twelve of these legs can support up to 9.3 g of payload. A T-shape actuation mechanism with three piezoelectric unimorph actuators is designed and studied to enable controlled locomotion. Static and dynamic properties of the robot are analyzed and compared with the experimental results. The tethered robot can successfully make both linear and rotational motions. Maximum forward speed is measured to be 3 cm/s, and the rotational speed is 0.5 rad/s. This robot proposes a new way of locomotion on water surface for future robots and devices.

Analytical solutions for the transverse deflection of a piezoelectric circular axisymmetric unimorph actuator

This paper presents analytical solutions to the transverse deformation shape of a circular axisymmetric piezoelectric-metal composite unimorph actuator. The solutions account for both the influence of an applied electric field and a concentrated or uniformly distributed mechanical load. Using piezoelectric constitutive equations, combined with thin plate and small bending elastic theory, the generalized equation of motion for bending of thin piezoelectric-metal composite plates has been derived. Our approach predicts that there is an optimum thickness ratio between the piezoelectric and metal plates, which leads to a maximum combination of deflection and load carrying capabilities. Derived formulas are very simple that offer a quick method for engineering design and optimization of a circular unimorph piezoelectric actuator.

A Study on the Actuating Performance of Unimorph Piezoelectric Actuators with a Center Load

Research on piezoelectric unimorph actuators has been intensively increased during the past decade due to the wide applications of this actuator type in aerospace, vibration control, biomimetic robots, artificial muscles… Most analyses focused on the design performance with load-free actuating condition. Loading performance has not been considered adequately yet though in real application the actuators always work under certain carrying load. This paper introduces the measuring system, the experimental setup and presents the observed loading performance of the actuators with center load. Two typical kinds of piezoelectric unimorph actuator, LIPCA-C3 and THUNDER, are investigated. The numerical analyses are also conducted to illustrate the loading behavior of these devices. Some remarks and suggestions for future research activities are drawn.

An Ultrasonic Standing-wave-actuated Nano-positioning Walking Robot: Piezoelectric-metal Composite Beam Modeling

This paper proposes a design for a precision positioning miniature walking robot using piezoelectric unimorph actuators. The theoretical working equations of a uniform piezoelectric unimorph beam are derived based on the linear piezoelectric relations, Hamilton’s principle, and Euler-Bernoulli beam equation. Themodal superposition method is used to determine the response of the forced transverse vibration of the beam under the effect of electrical signal inputs to the patterned piezoelectric element. Two standing waves corresponding to the third and fourth bending vibration modes are utilized to achieve the bi-directional walking mechanism for a miniature positioning robot. Design strategies and the fabrication method for the proposed walking robot are introduced. Preliminary performance tests of the robot prototype are carried out successfully, and the robot achieves speeds of 5.86 cm/sec and 3.37 cm/sec in forward and backward motion, respectively.

Optimized Design of Piezoelectric Flap Actuators for Active Flow Control

Piezoelectric flap actuators are often used in active flow-control applications. However, effective design tools are lacking in the flow-control community. This paper discusses theoretical modeling, experimental validation, and optimal design of piezoelectric unimorph and bimorph flap actuators. First, two different finite element models are described. One is a simple beam model that assumes a perfect bond exists between the piezoelectric patch and the shim,whereasthesecondincorporatesalinearelasticshearelementforthebondlayer.Thesemodelsarethenusedto predict the magnitude of the dc response (tip displacement per unit applied voltage) and the natural frequency (a measureofthebandwidth)oftheseactuators.Next,anapproximateanalyticalmodelisdevelopedtofacilitatedesign optimization. The models are compared with experimental data obtained from a parametric study in which 10 otherwise identical unimorph piezoelectric actuators with varying piezoelectric patches are fabricated and characterizedusingalaserdisplacementsensor.Allmodelsproduceestimatesthatareaccuratetowithin15%and 10% for the dc response and natural frequency, respectively. The analytical model is also extended to bimorph actuators. Finally, a general design optimization procedure is presented, and representative results are provided.