Piezoelectric Unimorph Actuators Research Articles

Optimizing the Electrode Geometry of an In-Plane Unimorph Piezoelectric Microactuator for Maximum Deflection

Piezoelectric microactuators have been widely used for actuation, sensing, and energy harvesting. While out-of-plane piezoelectric configurations are well established, both in-plane deflection and asymmetric electrode placement have been underexplored in terms of actuation efficiency. This study explores the impact of asymmetric electrode geometry on the performance of slender unimorph actuators that deflect in-plane, where actuator length is much larger than width or thickness. After validating the finite element modeling method against experimental data, the geometric parameters of the proposed unimorph model are manipulated to explore the effect of different electrode geometries and layer thicknesses on actuation efficiency. Four key findings were that (1) the fringing field within the piezoelectric material plays a measurable role in performance, (2) symmetry in electrode placement is generally nonoptimal, (3) optimal electrode geometry is independent of scale, and (4) the smaller the ratio of width to thickness, the larger the deflection. The findings contribute to the development of efficient design strategies that optimize the performance of planar actuators for potential implications for microelectromechanical systems (MEMS). To aid designers of piezoelectric unimorph actuators in determining the optimal electrode geometry, three types of parameterized figures and two types of simulation apps are provided.

A miniature piezoelectric pump with high performance

The high performance and miniaturization of the piezoelectric pump are essential for its application. A single-chamber piezoelectric pump with a circular unimorph piezoelectric actuator and cantilever check valves is proposed in this work, which has good output performance and smaller overall size. The working principle of the piezoelectric pump was described, and the theoretical working characteristics of the cantilever check valve were analyzed in detail. The corresponding experimental prototype was made for the output performance assessment. The experimental results show that the pump has good self-suck ability under well-assembled process conditions, which provides a guarantee for the high flow rate and the output pressure of the piezoelectric pump. The maximum flow rate of 4.5 ml/min is obtained when the pump is driven by an offset sinusoidal voltage of 180Vpp at 50 Hz; the maximum output pressure of the pump reaches 52 kPa under 180Vpp at 150 Hz. In addition, at 70 Hz, 180Vpp, the comprehensive performance of the piezoelectric pump is better, with a flow rate above 3 ml/min and an output pressure over 35 kPa. The proposed piezoelectric pump has the characteristics of simple structure, high performance, small size, and low cost, which can be applied in microelectronic cooling, biomedical, and other fields.

A novel multi-channel silicon-based piezoelectric micropump with active piezoelectric valve array

In order to only use one piezoelectric micropump to simultaneously drive and control multi-channel flow fluids of complex microfluidic systems in biological, chemical and medical applications, and then improve the integration and reduce the size of systems, principle and structure of a multi-channel silicon-based piezoelectric micropump with active piezoelectric valve array are proposed and realized. The micropump is composed of one pumping unit and four active piezoelectric valves with annular boundaries, which form active piezoelectric valve array by uniformly distributing around pumping unit. All valves are connected to pumping unit by corresponding fluid channels and they can realize bidirectional fluid flowing. Therefore, pump can suck fluid from any one or more valves through pumping unit and can discharge fluid to the other one or more valves, which form its six working modes. Silicon-based pump body is processed by photoetching and the micropump is fabricated by fixing circular piezoelectric unimorph actuators on the silicon-based pump body. Flow rate model is established, the flow characteristics under each working mode are experimentally tested. Results show that the micropump can realize simultaneously multi-channel fluid input and output, when it works under three-in and single-out, it has the maximum flow rate and output pressure; the flow rate model can predict its flow rate, the maximum relative error between experimental test result and numerical simulation result is 9.99%; the micropump has high flow control accuracy, when amplitude of driving voltage varies from 35 V to 36 V with step of 0.1 V, it has the minimum change of flow rate of 1 μL min−1, the maximum flow rate deviation of 5 μL min−1 and the maximum relative standard deviation of flow rate control of 0.175%. Therefore, the micropump provide feasible scheme for piezoelectric micropumps to be applied in complex microfluidic systems with multi-channel flow fluids, such as lab-on-chip.

Electric field-induced nonlinear behavior of lead zirconate titanate piezoceramic actuators in bending mode

In this article, analytical solutions of piezoelectric bimorph and unimorph actuator in cantilever configurations are developed using the second-order constitutive equation. Tip deflection ratio (TDR), a dimensionless parameter, is defined to analyze the effect of second-order coefficients of piezoelectric materials on the response of bimorph and unimorph actuators. Four piezoelectric unimorphs of varying geometries are fabricated and tested to verify the nonlinear response under applied electric field. Furthermore, second-order coefficients of lead zirconate titanate (PZT; APC 850) are derived by fitting the experimental data with nonlinear analytical solution. The nonlinear response of all the piezoelectric unimorphs compares well with the experimental results.

Principle and structure of a multi-chamber piezoelectric pump with large flow rate integrated into printed circuit board

Parametric simulation of multi-chamber piezoelectric pump proposed by authors shows that its flow rate is positively correlated with chamber compression ratio when height of chamber wall is not less than central deflection of circular piezoelectric unimorph actuator (CPUA). Therefore, in this paper, principle and structure of multi-chamber piezoelectric pump with novel CPUAs with three-layer structure are proposed and realized, so as to improve its chamber compression ratio, and then improve its flow rate. Its processing technology compatible with PCB processing technology is studied and its flow rate model is established. Central deflection of CPUA with three-layer structure and the flow rate characteristics are tested. Experimental results show that when the central deflection of CPUA with three-layer structure reaches the maximum value of 106.8 μm, the chamber compression ratio and flow rate of multi-chamber piezoelectric pump reach the maximum value of 50% and 3.11 mL/min, respectively. The maximum flow rate is increased by 622% compared to unimproved pump. By comparing experimental results with numerical and finite element simulation results, the realized multi-chamber piezoelectric pump has large flow rate and the established flow rate model can predict its flow rate.

Fabrication and Characterization of Deformable Mirror Driven by Piezoelectric Unimorph Actuator Array

Fabrication and Characterization of Deformable Mirror Driven by Piezoelectric Unimorph Actuator Array

Wide Two-Degree-of-Freedom Static Laser Scanner with Miniaturized Transmission Mechanism and Piezoelectric Actuation.

In recent years, laser scanners have attracted significant attention for applications such as laser radars. However, the establishment of a two-degree-of-freedom scanner that can quasi-statically drive a large mirror with a large deflection angle has proven to be challenging. In this paper, we propose a laser scanner design and fabrication method by combining two unimorph piezoelectric actuators composed of piezoelectric single-crystal Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 and a miniature translation-rotation conversion mechanism with flexible polyimide hinges. The size of the entire scanner was 32 mm × 12 mm × 10 mm. We successfully demonstrated that the scanner could achieve a large quasi-static mechanical deflection angle amplitude of 20.5° in two axes with a 6-mm-square mirror.

A multi-chamber piezoelectric pump based on pumping unit with double circular piezoelectric unimorph actuators

For improving flow rate of multi-chamber piezoelectric pump with active valves, principle and structure of multi-chamber piezoelectric pump based on pumping unit with double circular piezoelectric unimorph actuators (CPUAs) are proposed. Double CPUAs are coaxially and symmetrically arranged on top and bottom of pump chamber and work in same frequency and phase at same time to provide driving force for pump. Two active piezoelectric valves with annular boundary are designed on left and right of pumping unit to ensure the multi-chamber piezoelectric pump bidirectionally pump fluid with high control accuracy and stop characteristics. Process compatible with printed circuit board (PCB) process is used to manufacture pump to ensure low cost. Flow rate model is established to numerically simulate flow characteristics of the pump. Pump is also experimentally tested and analyzed. Results show that proposed principle and structure can effectively improve flow rate and out pressure of multi-chamber piezoelectric pump with high control accuracy and stop characteristics of flow. Moreover, flow rate model can accurately describe its flow characteristics, which will be beneficial to design and optimize multi-chamber piezoelectric pumps with active valves. Proposed principle and structure of multi-chamber piezoelectric pumps with active valves have potential applications in complex microfluidic systems such as biochemical analysis, drug delivery and chip cooling.

Design, modeling and testing of a 3-DOF flexible piezoelectric thin sheet nanopositioner

This paper proposes a novel 3-DOF (degree-of-freedom) flexible nanopositioner constructed from unimorph piezoelectric actuators and compliant flexures, featured with a compact size, low-cost and large stroke design, which is significantly different from the typical piezo-stack driven micro/nano-stages and the existing thin sheet nanopositioners. The model of the flexible nanopositioner is established by the compliance matrix method, which can be used to analyze the relationship between the structural parameters and system output characteristics and dynamical properties. Meanwhile, the modeling and analysis approach provides a guidance of geometry optimization of the proposed piezoelectric nanopositioners and paves the road for control of such systems. Furthermore, a real-time experimental apparatus with two PSDs (position sensitive detectors) is also proposed and fabricated to validate the static and dynamic characteristics of the flexible piezoelectric thin sheet (PZT-5A) nanopositioner, where comprehensive experiments are deployed demonstrating good agreement between theoretical results and experiments.

Adaptive driving beam system with MEMS optical scanner for reconfigurable vehicle headlight

An adaptive driving beam (ADB) for vehicle headlights has been developed using a microelectromechanical systems optical scanner. A piezoelectric scanner is constructed using thin-film lead-zirconate-titanate oxide (PbZrTiO3, PZT) on a bonded silicon-on-insulator (SOI) wafer, respectively, processed by ion-milling and deep reactive ion etching. The PZT layer is laminated in metal films on the SOI layer to form a piezoelectric unimorph actuator, which are then arranged as a pair of twisting suspensions to drive the scanner at resonance. The same piezoelectric actuators are also arranged into another form of meandering suspensions to generate a large deflection angle. By the combination of these two mechanisms, two-dimensional optical scanner is constructed in a single chip. The scanner is used to draw a Lissajous pattern of a blue laser light on a phosphor material to create a structured light source that is projected forward for illumination. The lighting patterns and positions are electronically controlled and reconfigured depending upon the location of leading/oncoming vehicles, pedestrians, road signs, and the cruising speed of the vehicle. The paper discusses on the design of the piezoelectrically driven optical scanner along with the optomechanical performances. We also report on the road-test result of the developed on-vehicle ADB module.

Analytical analysis of a circular unimorph piezoelectric actuator in the range of low voltages and pressures

In this study, the static displacement behaviour of a three-layer axisymmetric circular piezoelectric unimorph actuator subjected to voltage and uniform pressure loads for different mechanical and geometric properties of layers was investigated. The closed-analytical model of piezoelectric actuator based on the classical laminated thin plate theory was performed. Kirchhoff’s thin plate theory for the mathematical model in closed form of the actuator was utilized. The superposition of transverse and lateral deflections expressions was used to obtain the displacement equation of the piezoelectric actuator. Then, the analytical model solutions were compared by finite element model solutions. It was observed that the results obtained from analytical model and finite element analysis were sufficiently compatible with each other. The effects of nondimensional physical and mechanical properties on the static deflection performance of the piezoelectric actuator were discussed using the analytical model. According to the results obtained, the physical and mechanical properties of the actuator had significant effects on the actuator displacement. Therefore, the results obtained in this study can be used to optimize the performance of the circular piezoelectric actuator.

Bioinspired Flapping-Wing Robot With Direct-Driven Piezoelectric Actuation and Its Takeoff Demonstration

In this letter, we present the design and the performance of a prototype bioinspired flapping-wing micro aerial vehicle with piezoelectric direct-driven actuation. This type of actuation is superior in terms of structural simplicity because it does not include any transmission mechanism. Instead, a unimorph piezoelectric actuator directly drives the wing. We designed and fabricated a two-wing prototype with a wingspan of 114 mm and successfully demonstrated takeoff using an external power source under a one-degree-of-freedom constraint. The total mass of the prototype was 598 mg, and the maximum measured lift force was 6.52 mN (665 mgf) at a driving voltage of 100 V. We achieved tethered flight using the proposed direct-driven piezoelectric actuator considering the constraint.

Design, Analysis, and Characterization of a Two-Legged Miniature Robot With Piezoelectric-Driven Four-Bar Linkage

This paper presents the design and development of a new type of piezoelectric-driven robot, which consists of a piezoelectric unimorph actuator integrated as part of the structure of a four-bar linkage to generate locomotion. The unimorph actuator replaces the input link of the four-bar linkage, and motion is generated at the coupler link due to the actuator deflection. A dimensional synthesis approach is proposed for the design of four-bar linkage that amplifies the small displacement of the piezoelectric actuator at the coupler link. The robot consists of two such piezo-driven four-bar linkages, and its gait cycle is described. The robot's speed is derived through kinematic modeling and experimentally verified using a fabricated prototype. The robot prototype's performance in terms of its payload capability and nominal operating power is also characterized experimentally. These results will be important for developing a motion planning control strategy for a autonomous robot locomotion, which will be part of future work.

Performance of direct-driven flapping-wing actuator with piezoelectric single-crystal PIN-PMN-PT

We present a prototype flapping-wing actuator with a direct-driven mechanism to generate lift in micro- and nano-aerial vehicles. This mechanism has an advantage of simplicity because it has no transmission system between the actuator and wing. We fabricated the piezoelectric unimorph actuator from single-crystal PIN-PMN-PT, which achieved a lift force up to 1.45 mN, a value about 1.9 times larger than the mass of the actuator itself. This is the first reported demonstration of an insect-scale actuator with a direct-driven mechanism that can generate a lift force greater than its own weight.

Modeling and experimental verification of the flow characteristics of an active controlled microfluidic valve with annular boundary

The principle and structural configuration of an active controlled microfluidic valve with annular boundary driven by a circular piezoelectric unimorph actuator is presented in this article. Its active controlled flowrate is modeled using the classical laminated plate theory and the extended Bernoulli equation in fluid mechanics. According to the established mathematical model, we simulate and analyze the influence of the voltage applied to the circular piezoelectric unimorph actuator and the structural parameters on the flow characteristics. The prototypes of the active controlled microfluidic valves with annular boundaries of three different combinations of the inner and outer radii are fabricated and tested. The experimental results show that the active controlled microfluidic valves with annular boundaries possess the on/off switching capability and the continuous control capability of the fluid with simple structure and easy fabrication processing; the maximum flowrate of the active controlled microfluidic valve with the annular boundary with the inner and outer radii of 1.5 and 3.5 mm, respectively, is 0.14 mL/s when the differential pressure of the inlet and outlet of the active controlled microfluidic valve is 1000 Pa and the voltage applied to circular piezoelectric unimorph actuator is 100 V; and the established flowrate model can accurately predict the controlled flowrate of the active controlled microfluidic valves with the maximum relative error of 6.7%.

Theoretical analysis on shear-bending deflection of a ring-shape piezoelectric plate

In this paper, the electromechanical coupling field in shear-bending mode for a ring-shape piezoelectric plate was theoretically established. According to the classical small bending elastic plate theory and piezoelectric constitutive equations, the analytical solution to the bending deformation of the piezo-actuator under electric field and a concentrated or uniformly distributed mechanical load was achieved. The mechanism for generating bending deformation is attributed to axisymmetric shear strain, which further induces the bending deformation of the single ring-shape piezoelectric plate. This mechanism is significant different from that of piezoelectric bimorph or unimorph actuators reported before. Our analysis offers guidance for the optimum design of a ring-shape shear-bending piezo-actuator.

A comparative study of piezoelectric unimorph and multilayer actuators as stiffness sensors via contact resonance

Piezoelectric bar-shaped resonators were proposed to act as hardness sensors in the 1960s and stiffness sensors in the 1990s based on the contact impedance method. In this work, we point out that both multilayer and unimorph (or bimorph) piezoelectric actuators could act as stiffness/modulus sensors based on the principle of mechanical contact resonance. First, the practical design and the performance of a piezoelectric unimorph actuator–based stiffness sensor were presented. Then the working principle of piezoelectric multilayer actuator–based stiffness sensors was given and verified by numerical investigation. It was found that for these two types of resonance-based sensors, the shift of the resonance frequency due to contact is always positive, which is different from that of the contact impedance method. Further comparative sensitivity study indicated that the unimorph actuator–based stiffness sensor is very suitable for measurement on soft materials, whereas the multilayer actuator–based sensor is more suitable for hard materials. Both multilayer (or bar-shaped) and unimorph (bimorph) piezoelectric actuators can be used as stiffness/modulus sensors based on the mechanical contact resonance.

Piezoelectric micro-lens actuator

This paper reports the design, simulation, fabrication and characterization of a piezoelectric actuation structure for out-of-plane micro-lens movement. The structure consists of eight unimorph piezoelectric actuators symmetrically attached to a lens holding frame at one end through eight connecting beams and to the silicon substrate at the other end. The unimorph piezoelectric actuator consists of a 1.5μm thick PZT (Lead Zirconate Titanate) film deposited on a 0.6μm thick ZrO2 seed layer that is coated on a 1μm thick SiO2 and 5μm thick monocrystalline silicon. The actuator is driven by a set of inter-digitated Pt/Ti top electrodes, of 10μm width and 5μm spacing, deposited on the 800μm long PZT film. The connecting beams and lens holding frame are single layers of 5μm thick silicon. Theoretical analysis of the actuator is confirmed by ANSYS simulation. The results show that the displacement range and response of the actuator can be controlled by the effective residual stress in the structure. The device has been successfully fabricated and characterized for its mechanical behavior. Both the simulation and theoretical results show good agreement with measurement. The actuator has been measured for its static out-of-plane displacement of 24μm at 60KV/cm with maximum displacement sensitivity to voltage of 0.52μm/V at 53KV/cm. The unloaded fundamental resonant frequency of the actuator is 2.42kHz. The resonant frequency is reduced to 752Hz after a 600μm diameter glass micro-lens weighing 320μg is loaded onto the lens holding frame. The static out-of-plane deflection characteristic is reduced slightly to 22μm deflection at 60KV/cm. The actuator demonstrates translation time of 10ms for 22μm displacement range with less than 5% ringing. In comparison to previously demonstrated lens actuation mechanism, the reported mechanism shows higher resonant frequency and hence suited for faster actuation.

Dynamic performance of unimorph piezoelectric bending actuators

Piezoelectric bending actuators utilise the inverse piezoelectric effect to convert input electric energy to useful mechanical work. A comprehensive analytical model of the dynamic electromechanical behaviour of a unimorph piezoelectric actuator has been developed and successfully validated against experimental data. The model provides a mapping between force, displacement, voltage and charge. Damping is modelled using experimental data. Experimental validation is based on measurement of mode shape and frequency response of a series of unimorph beams of varying length but of the same thickness and material. The experimental frequency response is weakly nonlinear with excitation voltage, with a reduction in natural frequency and increase in damping with increasing excitation amplitude. An expression for the electromechanical coupling factor has been extracted from the analytical model and is used as the objective for parametric design studies. The design parameters are thickness and Young’s modulus ratios of the elastic and piezoceramic layers, and the piezoelectric constant k31. The operational design point is defined by the damping ratio. It is found that the relative variation in the electromechanical coupling factor with the design parameters for dynamic operation is similar to static operation; however, for light damping, the magnitude of the peak electromechanical coupling factor will typically be an order of magnitude greater than that of static operation. For the actuator configuration considered in this study, it is shown that the absolute variation in electromechanical coupling factor with thickness ratio for dynamic operation is same as that for static operation when the damping ratio is 0.44.

Modeling Analysis and Experimental Study of Circular Piezoelectric Unimorph Actuator

The finite element model of a circular piezoelectric (PZT) unimorph actuator is set up, the static and dynamic characteristic of the circular PZT actuator are analyzed. For the investigated PZT actuator, comprehensive performance testing is carried out. Compared the simulation results of finite element method with experimental data, the central deflections of PZT actuator under the DC condition are same basically, the testing results show that the actual edge condition lies between clamped and pinned support. The impedance testing results of PZT actuators agree well with FEM analyses. Under AC condition, the central displacement which involves part of resonant component increases greatly by several times more than that under DC condition. While the displacement of actuator with resistance decreases greatly, and is slightly lower than that under DC condition. The relevant research methods lay foundation for the further study of PZT actuator under multi-field coupling condition. Key words: PZT actuator; Circular PZT unimorph; FEM; Static; Dynamic