Piezoelectric Stack Research Articles

Construction of smart actuators brakes for smart city using geoinformation technologies

Actuator manufacturers are presently developing cutting-edge technologies, such as GIS technologies, that fulfill the necessary standards for performance, weight, and power consumption. Historically, manufacturers have selected actuators based on their ability to manipulate and regulate loads. This conceals the dynamic components of certain action solutions. Metrics of significant importance include the duration required to generate this mechanical energy and the amount of work the mechanism performs per unit mass. We utilized these values to establish a selection methodology. Considering the limitations in time and energy, it prioritizes actuators that are the most efficient in terms of weight. The concept of morphing for rotor blades was enhanced by integrating Gurney flap technology. Three control strategies were assessed, and simulations were conducted to test the amount of physical effort needed. Piezoelectric stack actuators are the most efficient method for actively controlling the rotor blade. The inherent universality of the process enables its utilization across a broad spectrum of applications.

Investigation of nonlinear magnetic stiffness based thin-layer stacked piezoelectric generators with a force-amplification structure

This paper investigates a nonlinear piezoelectric stack energy harvester incorporating a magnetic spring (NPEH) that utilizes impact-induced frequency modulation to augment the harvested power. The proposed configuration comprises a force amplifier, a piezoelectric stack, a spring-mass system, and a limiter. We formulate a two-degree-of-freedom (2DoF) theoretical model that accounts for the nonlinear characteristics of the system and corroborate it with experimental data. We examine the effects of system parameters on the output performance of the NPEH and demonstrate that the nonlinear magnetic spring facilitates a wideband energy harvesting. For instance, when the surface magnetic field intensities of the upper and lower magnets are 156 mT and 256 mT, respectively, the operational bandwidth reaches 5.23 Hz, which is 154 % greater than that of a linear spring system. Additionally, the nonlinear magnetic spring mitigates the voltage decay during the collision period due to its hysteresis response, thereby increasing the average power. At an excitation frequency of 9 Hz and with surface field strengths of the upper and lower magnets set at 156 mT and 256 mT respectively, the NPEH generates an RMS power of 2.2 mW (with an instantaneous power peak of 1.20 W). We provide design guidelines for optimizing the energy harvesting performance based on the parametric analysis.

A Simplified Inchworm Rotary Piezoelectric Actuator Inspired by Finger Twist: Design, Modeling, and Experimental Evaluation

Inchworm rotary piezoelectric actuators (PAs) have been widely utilized in the ultraprecision rotary positioning mechanisms because of their high precision and theoretical no backward motions. Existing inchworm rotary PAs are still bothered with the complicated structures driven by at least three piezoelectric stacks (PSAs) and relatively low speed. In this study, inspired by the finger structure, we present a simplified inchworm rotary PA driven by only two PSAs. The human finger twist motion is firstly imitated and utilized to increase the rotation from one to four times in one cycle, which improves the output speed and no backward motion can be observed in the rotation curves. Under a voltage of 150 V and a frequency of 20 Hz, the actuator achieved a maximum rotation speed of 0.16 rad/s, a carrying load of 0.5 kg and an output torque of 0.05 N·m. Furthermore, this actuator achieved a high step repeatability in the large scale of 360°, whose maximum deviation is less than 0.8 mrad.

Sensitivity of Piezoelectric Stack Actuators

This paper investigates the properties of a mass−attached piezoelectric stack actuator and analyzes its sensitivity, which is defined as the spectrum of the driving force (the output) caused by a single−frequency voltage (the input). The force spectrum is utilized because of the nonlinear hysteresis effect of the piezoelectric stack. The sensitivity analysis shows that the nonlinear dynamics of the actuator can be interpreted as a cascade of two subsystems: a nonlinear hysteresis subsystem and a linear mechanical subsystem. Analytical solutions of the nonlinear differential equations are proposed, which show that the nonlinear transformation can be described by a steady−state mapping of a single−frequency voltage input to a multiple−frequency driving force at the driving frequency and its odd harmonics. The steady−state sensitivity is then determined by the response of the mechanical subsystem to the line spectrum of the driving force. The maximum sensitivity can be achieved by setting the frequency of the input voltage close to the natural frequency of the mechanical subsystem. The analytical model is also validated by a numerical model and experimental results and it may be used for the analysis and design of piezoelectric actuators with different structural configurations.

Electromechanical coupling dynamics for a novel non-resonant harmonic piezoelectric motor

Most of the traditional piezoelectric motors are driven by the resonance of piezoelectric ceramics and can achieve a large output torque. However, these motors also have the defects of high speed and difficulty to adjusting the speed when working. To overcome these issues, a novel non-resonant harmonic rotary piezoelectric motor operating at low speed is presented. Electromechanically coupled vibration has a great influence on the dynamic performance of the piezoelectric motor, which may lead to instability of the output performance of the motor. Therefore, the electromechanical coupling dynamic characteristics of the proposed non-resonant piezoelectric motor are studied in this paper. The working principle of the motor is illustrated, and the electromechanical dynamic model and nonlinear dynamic equations are established. Utilizing the dynamic equations, the coupled natural frequencies, amplitude-frequency characteristics, and dynamic responses of the motor are developed. Meanwhile, the influence of parameters on natural frequency and nonlinear response is analyzed. What's more, the natural frequencies of the system are tested by building an experimental platform. Results show the minimum coupled natural frequency of the motor is 11231 rad/s. The length of the piezoelectric stack, the length, and mass block of the harmonic rod have an important influence on the natural frequency of the proposed non-resonant harmonic piezoelectric motor. The nonlinear piezoelectric effect has a larger effect on the forced response amplitude when the excitation frequency is far away from resonance, but a smaller effect on the forced response amplitude when the excitation frequency is near resonance. What's more, the maximum error between the theoretical natural frequencies and the test frequencies is 3%, which verifies the correctness of the theoretical model.

A cascaded Nitinol Langevin transducer for resonance stability at elevated temperatures

Across power ultrasonics and sensing, piezoelectric ultrasonic transducers commonly experience degradation in mechanical, electrical, and dynamic performance due to the relatively high sensitivity of piezoelectric materials to changes in temperature. These changes, arising for example through high excitation voltages or environmental conditions, can lead to nonlinear dynamic behaviours which compromise device performance. To overcome this, the excitation signal to the piezoelectric material is often pulsed, mitigating the influence of temperature rises. However, there remain constraints on suitable candidate piezoelectric materials for power ultrasonic devices. As a novel approach to mitigating the influence of temperature on the properties of piezoelectric materials, the phase-transforming shape memory alloy Nitinol is incorporated into the piezoelectric stack of a Langevin power ultrasonic transducer, in a cascade formation. The underlying principle is that the nonlinear hardening response of Nitinol to rising temperature can be used to dynamically compensate for the nonlinear softening of the piezoelectric materials. Thus, the dynamic response of the transducer can be linearised at elevated excitation levels. In this study, two configurations of Langevin transducer are designed and characterised. One transducer incorporates a Nitinol middle mass, and in the second, titanium. A combination of electrical and thermomechanical characterisation is undertaken, where it is demonstrated that the nonlinear softening of the piezoelectric stack can be mitigated through control of the Nitinol microstructure. The vibration amplitudes of the Nitinol-middle cascaded transducer are higher and more stable when the Nitinol is austenite rather than a combination of martensite and austenite at room temperature. It has also been shown that the vibration amplitude and resonance frequency of Nitinol-middle cascaded transducer remain stable as temperature changes from 20 °C to 45 °C, dependent of the excitation voltage. Moreover, the self-heating experiment demonstrates the resonance stability of the Nitinol-middle cascaded transducer for continuous operation.

Research on Stacked Piezoelectric Cymbal Vibrator.

As demand for haptic feedback increases, piezoelectric materials have become one of the best candidate materials due to their small size, high electromechanical coupling coefficient, and fast response. A stacked piezoelectric cymbal vibrator is proposed based on the common cymbal-type transducer, which is composed of a piezoelectric stack to drive and a cymbal disk to amplify displacement. A coupling theoretical model between the piezoelectric stack and the cymbal-type structure is established. The longitudinal and radial displacements of the stacked piezoelectric cymbal vibrator are calculated in the low frequency range (<1000 Hz) by the theoretical model and the finite element method. The theoretical and numerical results are in good agreement. The results show that the radial displacement can be converted into longitudinal displacement and then effectively amplified by the cymbal disk with an amplification ratio of 30. The feature is conducive to its widespread application in the field of consumer electronics.

Active Microvibration Control of Tool Platforms Installed on the Floors Subjected to Moving Vehicles in Industrial Factories

The vibration responses of tall flexible tool (or equipment) platforms subjected to floor excitations at the platform base are considered more crucial than those of the short ones. This study examined the microvibration control performance of the proposed active piezoelectric mass damper (APMD) or driver for tall platforms subjected to internal automated guided vehicle- (AGV-) induced floor vibrations with larger intensity and broader bandwidth in liquid-crystal-display (LCD) fabrication factories (fabs). The APMD did not require auxiliary spring and damping elements to tune the natural frequency and reduce the stroke of the mass block as required by typical active tuned mass dampers (ATMDs). The motion equation of the proposed analytical model including a continuous three-span beam (or floor) system and an active-controlled tool platform under the action of the AGV moving forces was derived. The APMD, consisting of piezoelectric stacks and a mass block, was installed on the platform subjected to the base rotation excitation, which could be attributed to the uneven vertical floor vibrations induced by AGVs. Moreover, the direct output feedback control algorithm was adopted to determine the optimal feedback gain matrix for calculating the active control force. Time history analyses of the continuous beam-platform model under different AGV weights moving at the same speed were performed, and the corresponding velocity vibration spectra of the floor and platform were further obtained through one-third octave band spectrum analysis. Numerical simulation results revealed that the microvibrations of the platform without APMD generally exceed the VC-A level regardless of the AGV weight. Significant reductions of over 90% on the platform microvibrations could be achieved after the platform was implemented with the APMD, and vibrations met the desired vibration limit (VC-B). Moreover, the APMD exhibits comparable microvibration control performance to the ATMD and requires less mass of the mass block, stroke, and applied voltage under the same active control force. In real-life high-tech production fabs, AGV-induced platform microvibrations occur all the time; therefore, the proposed APMD with less power consumption could be an economical and feasible approach for persistent microvibration control of tall platforms in LCD fabs.

Electro-mechanical transfer matrix modeling of piezoelectric actuators and application for elliptical flexure amplifiers

Mechanically amplified piezoelectric actuators (APAs) can be found in many scenarios of precision engineering and instrumental devices. However, the electro-mechanical design of curvilinear APAs is difficult due to the existence of curved flexure beams and multi-domain electro-elasto dynamics. In this paper, the electro-mechanical behavior of elliptical APAs is studied by exploiting a novel electro-mechanical transfer matrix method. The motivation is to facilitate both the static and dynamic analyses of such a complex APA with curvilinear flexure beams by considering the multi-domain dynamics of piezoelectric stacks and compliant mechanisms from an electro-mechanical viewpoint. To this end, an analytical electro-elasto transfer matrix of piezoelectric stacks operating at the d33 mode is derived in the form of Taylor's series based on Timoshenko beam theory. The dynamic response spectrum of displacement and impedance for elliptical APAs are insightfully captured by such an electro-mechanical model. Different topologies of elliptical APAs are also compared and the optimal configuration is suggested. At last, a proof-of-concept prototype is fabricated and tested with a special focus on experimental evaluation of the electro-mechanical coupling model.

Super-High-Frequency Bulk Acoustic Resonators Based on Aluminum Scandium Nitride for Wideband Applications.

Despite the dominance of bulk acoustic wave (BAW) filters in the high-frequency market due to their superior performance and compatible integration process, the advent of the 5G era brings up new challenges to meet the ever-growing demands on high-frequency and large bandwidth. Al1-xScxN piezoelectric films with high Sc concentration are particularly desirable to achieve an increased electromechanical coupling (Kt2) for BAW resonators and also a larger bandwidth for filters. In this paper, we designed and fabricated the Al1-xScxN-based BAW resonators with Sc concentrations as high as 30%. The symmetry of the resonance region, border frame structure and thickness ratio of the piezoelectric stack are thoroughly examined for lateral modes suppression and resonant performance optimization. Benefiting from the 30% Sc doping, the fabricated BAW resonators demonstrate a large effective electromechanical coupling (Keff2) of 17.8% at 4.75 GHz parallel resonant frequency. Moreover, the temperature coefficient of frequency (TCF) of the device is obtained as -22.9 ppm/°C, indicating reasonable temperature stability. Our results show that BAW resonators based on highly doped Al1-xScxN piezoelectric film have great potential for high-frequency and large bandwidth applications.

Design, modeling, and analysis of a novel XY micro-displacement scanning stage with an elliptical compliant restraint mechanism

This paper presents a novel piezoelectric XY micro-displacement scanning stage (MDSS), which features a parallel structure based on compliant mechanisms and has a compact configuration. Since the coupling problem between two motion axes, an innovative elliptical compliant restraint mechanism (ECRM) with a compact layout is proposed and utilized in XY MDSS to obtain high motion accuracy. And the XY MDSS can realize compact structure and lower input stiffness for a large workspace owing to the ECRM simultaneously. Due to the limited displacement of the piezoelectric stack actuator, compliant amplification mechanism is applied to achieve a large stroke. In order to estimate the static and dynamic characteristics theoretically, Castigliano’s second theorem and Lagrange’s method are utilized to establish the analytical models of the newfangled ECRM, compliant amplification mechanism, and XY MDSS. The finite element analysis and experimental tests are carried out to evaluate the performances of XY XDSS, and the results are all in correspondence with analytic solutions, which further validate the correctness of the analytical modeling methodologies. Experimental results show that the XY MDSS can realize a workspace of 58.8 μm × 51.5 μm with a resonance frequency of 576.5 Hz and nanometer-level resolution. The effectiveness of the designed ECRM is also proved simultaneously, which could well limit the coupling motion. The theoretical studies, finite element analysis, and experimental testing all demonstrate that the designed XY MDSS with ECRM has good performance while having a compact structure.

An electromechanical dynamic stiffness matrix of piezoelectric stacks for systematic design of micro/nano motion actuators

Piezoelectric stacks have proved to be effective for micro/nano motion actuators with large blocking forces. A critical problem is to build their electro-mechanical model for systematic design of statics and dynamics including piezoelectric hysteresis and elasto-kinematics of compliant mechanisms. To ease this issue, this paper proposes a new electro-mechanical dynamic stiffness matrix of piezoelectric stacks to enable a systematic analysis. Positive and inverse piezoelectric effects are included into the dynamic stiffness matrix of Timoshenko beams in the form of Taylor’s series with a clear definition of physical parameters. Consequently, the Jacobian matrix, input/output stiffness, natural frequencies, frequency-domain spectrums of mechanical displacement and electrical impedance as well as the time-domain response of piezoelectric hysteresis can be fully obtained with a single modeling process. Particularly, the time-domain response in the presence of piezoelectric rate-dependent hysteresis and dynamic resonance behaviors of compliant mechanisms is captured in a parameter-insightful way but not the manner in Hammerstein hysteresis model with a black-box transfer function. Experiments on a proof-of-concept prototype of precision positioning stage verify the easy operation and satisfying prediction accuracy of the presented approach.

Simulation of active vibration control of a moving stage

Active vibration control (AVC) has gained considerable interest due to its inherent adaptability and cost-effectiveness, with its ability to suppress vibrations in the controlled system across various applications. Existing studies focus on the AVC of non-moving systems and usually assume that the vibration signal to be controlled is known and can serve as the ideal reference signal in feedforward control systems. However, in many practical applications, the ideal reference signal is not accessible, and a sensor must be used to detect the reference signal. This can degrade the AVC performance, especially for a moving system. This study, therefore, aims to explore the potential application of piezoelectric stack actuators (PSA) to control the vibration of a moving stage driven by a stepper motor. The secondary path was estimated offline, and vibration data were collected at different moving speeds. The effects of the location of the reference sensor were initially investigated. Then, extensive simulations were conducted to evaluate the performance of different adaptive control algorithms regarding vibration reduction, convergence speed, computational complexities, etc. This research underlines the potential of integrating PSA within a moving system to effectively control its vibration.

Vibration characteristics of an active mounting system for motion control of a plate-like structure in future mobilities

The vibration and noise caused by electric motors in hybrid and electric vehicles (EVs) generate complex signals with a mid-frequency band, which causes uncomfortable vibration and noise. In order to isolate the vibration and noise, active engine mounting systems based on smart structures have attracted attention. Thus, in this study, the vibration attenuation performance was validated through simulation and feasibility experiments by applying an active mounting system using a piezoelectric stack actuator. A plate structure with three paths, consisting of two passive paths and one active path, was modeled using the lumped parameter method. The source part was excited by a sinusoidal and modulated signal with a mid-frequency band to validate the vibration attenuation performance. Furthermore, (1) mathematical modeling with a source-path-receiver structure was proposed based on lumped parameter modeling, (2) normalized least mean square (NLMS) and multi-NLMS algorithms were applied to implement motion control, and (3) a principal experimental setup was designed to validate the simulation results. Through this process, the vibration attenuation performance of the proposed active mount structure was validated.

Design and development of a piezoelectric-hydraulic hybrid actuator with quarter-wavelength tubes

The piezoelectric hydraulic actuator is a hybrid device consisting of a hydraulic pump driven by a piezoelectric stack connected to a hydraulic cylinder. For this type of piezoelectric actuator, the inertial force caused by the flow pulsation of the liquid will inhibit the movement of the piezoelectric vibrator and reduce its output performance. To solve these issues, two tubes were embedded into the piezoelectric-hydraulic hybrid actuation system for the first time to act as mechanical bandstop filters by interfering with the propagation of acoustic waves. The acoustic power transmission loss of the tube is derived from the one-dimensional wave equation. According to the experimental results, when the excitation frequency is close to the optimal operating frequency corresponding to the tubes, the liquid pulsation rate is reduced, the influence of inertial force on the actuator is weakened, and the output performance is relatively significantly improved. This strategy finally leads to a maximum no-load velocity of 153.5 mm s−1 and a maximum blocking force of 261.5 N for the hybrid actuator with 300 mm tubes; the maximum no-load velocity and blocking force of the hybrid actuator with 500 mm tubes are 94.45 mm s−1 and 230 N, respectively. Furthermore, this strategy can be used in other electrohydraulic actuators to enhance their capabilities.

Design of Two-Stage Force Amplification Frame for Piezoelectric Energy Harvester

This paper describes the design of a two-stage force amplification frame for the piezoelectric energy harvester to capture mechanical energy from walking human footsteps. The frame design optimises the stress distribution to improve the force amplification ratio on the existing footstep energy harvesters. The magnification of the input force exerted on a piezoelectric stack increases the system's power output. A combination of single and compound two-stage frame design with additional linkage support was proposed, which maximise the conversion of tension to compression forces. The proposed frame also significantly reduces the maximum displacement of the frame to ensure walking comfort. The frame is tested with the input force of 85 N to 120 N based on the adult footstep during walking and running. The simulated results show that the proposed frame has a force amplification ratio of 25.3, an 11.85% improvement from the existing frames. The frame also limits the maximum displacement to 1.02 mm, 22.14% compared to the existing frames.

Resonant-Type Piezoelectric Pump Driven by Piezoelectric Stacks and a Rhombic Micro Displacement Amplifier.

To obtain a high flow rate, a resonant-type piezoelectric pump is designed, fabricated, and studied in this paper. The pump consists of four parts: a piezoelectric vibrator, a pump chamber, a check valve and a compressible space. The designed piezoelectric vibrator is composed of a rhombic micro displacement amplifier, counterweight blocks and two piezoelectric stacks with low-voltage drive and a large output displacement. ANSYS software (Workbench 19.0) simulation results show that at the natural frequency of 946 Hz, the designed piezoelectric vibrator will produce the maximum output displacement. The bilateral deformation is symmetrical, and the phase difference is zero. Frequency, voltage, and backpressure characteristics of the piezoelectric pump are investigated. The experimental results show that at a certain operating frequency, the flow rate and the backpressure of the piezoelectric pump both increase with the increase in voltage. When the applied voltage is 150 Vpp, the flow rate reaches a peak of 367.48 mL/min at 720 Hz for one diaphragm pump, and reaches a peak of 700.15 mL/min at 716 Hz for two diaphragm pumps.

Dual-Amplifier Driving in Sequence Method with Switches for Piezoelectric Stack Actuators to Reduce Hysteresis

Dual-Amplifier Driving in Sequence Method with Switches for Piezoelectric Stack Actuators to Reduce Hysteresis

An active piezoelectric damping vibration control system for the sting used in wind tunnel

In wind tunnel tests, the cantilever sting supporting system often suffers from low-frequency and large-amplitude resonance due to its inherent low structural damping characteristic, resulting in the degradation of data quality and structural safety. To improve wind tunnel testing safety and data accuracy, this paper is dedicated to establish an active vibration control system using piezoelectric stack actuators. A novel methodology of vibration monitoring based on modal transformation, which uses measured strain and a Strain-to-Displacement Transformation (SDT) matrix to reconstruct dynamic displacement field, is proposed herein. Meanwhile, strain sensor positions are optimized by an improved Particle Swarm Optimization (PSO) algorithm to reduce systematic estimation errors of this method. Furthermore, a Back-Propagated Neutral Network (BPNN) is established to implement a self-adaptive control strategy. A series of verification tests are performed to demonstrate the validity of the proposed system. Experimental results indicate that the relative Root Mean Square Error (RMSE) between estimated vibration displacement and measured vibration displacement is less than 3%, and a vibration attenuation of over 14 dB/Hz is achieved in ground tests, proving the superiority of this intelligent active vibration suppression system.

A comprehensive dynamic continuous model of piezoelectric stack energy harvesters under arbitrary excitation considering electrodes and protective layers

Piezoelectric stack energy harvesters, by virtue of the higher mechanical-to-electrical energy conversion capability in the d 33 mode, have been used widely in various fields, such as railway system, roadway system, and human motion. Dynamic continuous models (DCMs) of piezoelectric stack energy harvesters can more accurately reflect the electromechanical behavior but are difficult to be established due to complex coupling between layers, particularly in the presence of arbitrary loads. The existing models often only considered harmonic excitations and often ignored electrodes and protective layers for simplicity. This paper proposed a comprehensive DCM of piezoelectric stack energy harvesters considering the electrodes and protective layers, which can be used to study the electromechanical performance of the energy harvester under both harmonic excitation and arbitrary excitation. Comparisons of the developed generic DCM with the analytical model based on piezoelasticity theory (a DCM which only considers the harmonic excitation) and the simplified model (a quasi-static continuous model which ignores inertia force of piezoelectric stack) are presented, with good agreements. Furthermore, the experiment results of two shapes of piezoelectric stacks, including tube and circular, are used to further confirm the reliability of the proposed model. In addition, effects of the electrode and protective layers on the dynamic properties are analyzed and discussed. The results show that the proposed DCM is effective and versatile to guide the design of piezoelectric stack energy harvesters subject to various types of loads.