Piezoelectric Stack Research Articles

MIMO Multi-Frequency Active Vibration Control for Aircraft Panel Structure Using Piezoelectric Actuators

Undesirable vibration of aircraft panel structures has a significant impact on the safety of their occupants and the operational reliability of various systems. The traditional time-domain controller based on the parallel multi-frequency filtered-x least mean square (FxLMS) control algorithm is simple and effective. However, the mutual influence of convergence steps and the induced harmonic components will limit its performance. An improved parallel multi-input multi-output multi-frequency FxLMS (MIMOMF-FxLMS) algorithm is proposed, considering the multi-input multi-output (MIMO) control requirement of the aircraft panel structure active vibration control (AVC) system and its inevitable channel coupling phenomenon. The feedback error signal and the control channel model are processed by frequency division in the MIMOMF-FxLMS algorithm, so that the FxLMS algorithm of each control channel runs independently, effectively avoiding mutual interference between convergence steps and the generation of induced harmonic components. Simulation and experimental research on multi-frequency AVC of the panel structure model is performed using a new type of piezoelectric stack actuator. The test results show that the proposed controller reduces the vibration level of each observation point by more than 98%, and the vibration responses of the first two-order frequency component are significantly suppressed, which also has strong adaptability and anti-noise ability.

Design and feedforward control of a two-degree-of-freedom positioning stage with bidirectional piezoelectric drive

The positioning stage composed of piezoelectric stacks and flexible mechanisms is highly competitive in the field of micro/nanomanipulation. Driving stroke and positioning accuracy are the two most important factors to evaluate the positioning stage. However, the attenuation of the driving stroke caused by the stiffness load of the flexible mechanism is an important but neglected problem. On the other hand, the hysteresis of piezoelectric ceramics directly affects the positioning accuracy of the platform. In this study, a two-degrees-of-freedom positioning stage with low displacement attenuation and hysteresis is proposed. Static and dynamic models of the positioning stage were established to derive analytical models of the displacement amplification ratio, structural stiffness, and natural frequency. The displacement transfer coefficient was introduced to establish an equivalent physical model for structural stiffness and displacement attenuation. Genetic algorithms were used to optimize the structural parameters. Finite element analysis is performed to verify the accuracy of the analytical model. The hysteresis is suppressed by the combination of bidirectional piezoelectric driving and inverse Bouc-Wen model feedforward compensation. The measurement results indicated that the proposed positioning stage had a displacement transfer coefficient of 0.82, which was 95.89% lower than the hysteresis of the piezoelectric stack.

Fatigue behaviour of piezoelectric ceramic stack under large cyclic dynamic loading

The fatigue behaviour of a piezoelectric ceramic stack co-fired at low temperatures under the influence of a large cyclic dynamic load was studied. The piezoelectric ceramic stack is equivalent to a parallel plate capacitor with a charge source in parallel. The equations for the total current, output current and capacitor charging current of an equivalent device for an applied load were derived using Kirchhoff’s theoretical formula. A new type of fatigue test equipment was developed for continuous long-term M-shaped wave output. The piezoelectric ceramic stack is positioned between two concrete slabs, forming a pavement-subgrade piezoelectric structure. The fatigue behaviour of the piezoelectric ceramic stack was observed for 800,000 cycles of dynamic load. The results show that the dynamic load studied produced fatigue damage in the piezoelectric ceramic stack. As the number of dynamic loads increased, the electric output capacity of the piezoelectric ceramic stack decreased. Evident stage divisions were observed in the fatigue behaviour of the piezoelectric ceramic stack under cyclic dynamic loading. The electric output capacity of the stack decreased as the number of dynamic loads increased in the early and late stages, whereas it exhibited negligible change during the stable period.

Development of high uniformity Al1-xScxN piezoelectric film stack dry etching process on 8-inch silicon wafers

This paper have investigated the basic properties of inductively coupled plasma reactive ion etching (ICP-RIE) of scandium doped aluminum nitride (Al1-xScxN) thin films on 8-inch silicon wafers, and presented a pretreatment scheme which can effectively improve the etching uniformity and wafer yield in the mass fabrication of Al1-xScxN-MEMS (micro-electromechanical systems) devices. Based on BCl3/Ar pretreatment and Cl2/Ar main etching scheme, an etching rate of 128 nm/min is obtained, with the low nonuniformity, and selectivity of 1.8 with respect to the loss of molybdenum (Mo) electrode is achieved, respectively. The relationship between etching parameters and etching uniformity is revealed in detail by the 5-step Al1-xScxN etching model. Meanwhile, to optimize the etching compatibility in the fabrication of Al1-xScxN-piezoelectric MEMS devices, a variety of etching masks (e.g. photoresist and silicon dioxide) are respectively used to obtain the consistent sidewall profile at different locations, with photoresist of 24° and silicon dioxide of 57°.

A closed loop system to control transverse deformations in LHC collimators

This work presents a novel closed-loop control system for the detection and control of thermal deformations integrated in the secondary collimators of the Large Hadron Collider (LHC). Interactions between spurious particles lost transversally from the circulating beam core and the collimator jaws that make up the active area of the collimator will result in thermally induced deformations in those jaws. This interaction can push the jaw’s straightness out of the tolerance and force the jaw either into the beam core or away from it. This action can result in reductions in beam cleaning efficiency and increases in impedance on the beam. Whilst deformations in either direction are to be avoided, deformations into the beam are considered more of an issue as too much deformation can provoke beam dumps if beam losses are too high. To minimize this unavoidable thermal effect a novel adaptive closed-loop monitoring and actuation system, comprising of multiple intrinsic Fabry–Pérot interferometric (IFPI) optical sensors, and several integrated piezoelectric stack actuators, has been developed. When operating, this system can transiently monitor the jaws straightness and when required correct for deformations up to 500μm. In addition, subsequent steps to use this system as an active damper to reduce vibratory response, as experienced when the jaw undergoes a direct beam impact, are also discussed.

Experimental research of a dual-beam compressive-mode piezoelectric energy harvester

In this article, we present a dual-beam compressive-mode piezoelectric energy harvester (DC-PEH). The DC-PEH is made up of a force amplifier, a piezoelectric stack, and a pair of symmetrically arranged cantilever-mass systems, supported by a base that is fixed on a rod. A two-stage force amplification mechanism of the DC-PEH is realized by coupling the elastic beams with the force amplifier. We first established a force analysis to describe the two-stage force amplification effect of the DC-PEH. Furthermore, a prototype has been fabricated and we carried out a series of experiments. We examined the open-circuit voltage and working bandwidth of the DC-PEH to verify the two-stage force amplification effect under different accelerations. Moreover, a parametric study was performed to investigate the influence of structure parameters on the output performance of the DC-PEH. We conducted the frequency sweep response and power output comparisons with different lengths of beams and different masses.

Multi-directional active vibration control of 1D smart structure inspired by automotive engine mounting system

Recently, active mounting system is being gradually applied to automotive engine mounts for mitigating structure-borne vibration effectively throughout the whole vehicle chassis. This paper presents modeling, analysis, and control of a source structure with an active mounting system in multi-directions, considering position and direction of actual automotive engine mounts. The active mount consists of a piezoelectric stack actuator in series with an elastomeric (rubber) mount. When harmonic excitation forces are employed, secondary force required for each active mount is calculated mathematically and the control signal can reduce the vibration through the destructive interference with input signal. In addition, the horizontal vibration can also be mitigated by setting a variable parameter through the dynamic relation of source structure. A series of simulation results demonstrate that the excitation vibration could be reduced along with this multi-directional (vertical and horizontal) active mounts. Based on this result, it can be expected that noise vibration harshness(NVH) performance can be improved by controlling the vibration of the actual automotive engine structure with rubber mount and secondary force of actuators in both vertical and horizontal directions.

Design and Analysis of a Hybrid Displacement Amplifier Supporting a High-Performance Piezo Jet Dispenser

In this study, a compliant amplifier powered by a piezoelectric stack is designed to meet high-performance dispensing operation requirements. By studying the issue of low frequency bandwidth on the traditional bridge-type amplifier mechanism, we propose a displacement amplifier mechanism, hybrid bridge-lever-bridge (HBLB), that enhances its dynamic performance by combining the traditional bridge-type and lever mechanism. A guiding beam is added to further improve its output stiffness with a guaranteed large amplification ratio. An analytical model has been developed to describe the full elastic deformation behavior of the HBLB mechanism that considers the lateral displacement loss of the input end, followed by a verification through a finite element analysis (FEA). Results revealed that the working principle of the HBLB optimizes the structural parameters using the finite element method. Finally, a prototype of the displacement amplifier was fabricated for performance tests. Static and dynamic test results revealed that the proposed mechanism can reach a travel range of 223.2 μm, and the frequency bandwidth is 1.184 kHz, which meets the requirements of a high-performance piezo jet dispenser.

Modeling and electromechanical performance of improved smart aggregates using piezoelectric stacks

Smart aggregates (SAs) are often formed by embedding lead zirconate titanate (PZT) patches into concrete or marble blocks. They not only have the advantages of low cost, quick response, high reliability, and long service life, but also possess comprehensive actuating and sensing abilities, and have been widely used in structural health monitoring in the field of civil engineering. However, due to the plate-like geometry of the PZT patch and the limited number of layers, SAs have a relatively short sensing range. To solve this issue, a new type of SA using piezoelectric stacks was developed. Theoretical modeling of this new transducer was established, and prototypes were fabricated. Comparisons between the theoretical predictions and the experimental results are presented, and good agreement can be found. The effects of the key parameters, including the total height of the specimen, the elastic modulus of the cement, the radius of the piezoelectric stack, the thickness of the piezoelectric layer, and the number of piezoelectric layers in the piezoelectric stack, on the electromechanical properties were analyzed, and the guidelines for optimal design were presented. In addition, the improved and the traditional SAs were used to monitor the water content in soil specimens based on the electromechanical impedance technique. The results showed that the improved SAs using piezoelectric stacks are more sensitive than the traditional ones, and have good potential in structural health monitoring in the field of civil engineering.

A new algorithm to calculate complex material parameters in piezoelectric stacks

In this paper, the hybrid differential evolution and symbiotic organism search (HDS), is the first-time developed for general solutions of a piezoelectric stack in ultrasonic transducers. The convergence and reliability of the new algorithm are verified through comparison with corresponding data from similar previous publications and differential evolution (DE) algorithm. This study also presents and discusses the calculation results using HDS for commercial piezoelectric stacks. The Matlab HDS programs for a segmented piezoelectric (PZT) model have advanced features including its applicability to any configurations, thickness and arbitrary layer numbers of PZT. Using the novel proposed technique, there is no requirement for initial data guess, no limitations for piezoelectric stacks and the convergence rate is much faster than DE. Therefore, the HDS is promising for direct evaluation of specific aging or degradation mechanisms of ultrasonic transducers.

Experimental performance evaluation on piezo-hydraulic pump using flexurally amplified piezoelectric actuators

This paper presents an experimental study on a piezo-hydraulic pump using two different flexurally amplified piezoelectric (FAP) actuators. FAP actuators produce amplified displacement using piezoelectric stack actuators as prime mover. FAP376 and FAP640, having different characteristics are used as pumping actuator to pump the fluid from the piezo-hydraulic pump. The pumping chamber is made of stainless-steel metallic bellows and unidirectional valves are connected to the inlet and outlet port of the piezo-hydraulic pump. Mathematical model is developed for theoretical calculations on the flowrate of piezo-hydraulic pump. Also, pump flowrate is determined experimentally using flowmeter for two different FAP actuators and compared with the respective theoretical values. Further, performance evaluation is done by comparing the flowrate developed by the piezo-hydraulic pump at different actuation frequencies using two different FAP actuators.

An Inchworm and Stick-Slip Dual Mode Piezoelectric Linear Actuator for Cell Injection

Cell injection system for biomedical engineering demands that actuators have large stroke, high resolution and speed for cell positioning and injection. Single mode piezoelectric actuators could meet some of these requirements but hardly all. Stick-slip actuator is easy to achieve high-speed operation, but it is prone to setback; The speed characteristics of the inchworm actuator are lower than those of the stick-slip actuator, but the step is more stable and the setback is lower. This study proposes an inchworm and stick-slip dual mode piezoelectric actuator (ISSPA) for cell injection. It integrates two working modes into one actuator and both modes drive the same slider. The stick-slip mode works at high frequency for fast positioning to the cell and the inchworm mode drives the needle to puncture the cell membrane and accurately locates to the specified location. The structure and working principle of the ISSPA are provided. A prototype of the proposed ISSPA is fabricated and experiments are conducted. When the driving voltage of the piezoelectric stack is 100 V and the frequency is 500 Hz,the maximum speed of the ISSPA is 2.287 mm/s in the stick-slip mode. When the driving voltage of the piezoelectric stack is 60 V, the frequency is 3 Hz and the load is 0.5 kg,the minimum step displacement is 57 nm in inchworm mode. Demonstration of cell injection is carried out by using the ISSPA to positioning and puncturing a zebrafish embryo. Fast positioning with the stick-slip mode and accurate puncture with the inchworm mode are achieved with the ISSPA alone, taking 12 seconds for the whole injection process. It could be expected to apply the ISSPA to cells with wide range of diameter, as the frequency of the stick-slick mode and the voltage of the inchworm mode could be well regulated.

Response analysis of undamped primary system subjected to base excitation with a dynamic vibration absorber integrated with a piezoelectric stack energy harvester

Dynamic vibration absorber (DVA) integrated with a piezoelectric stack energy harvesting subjected to base excitation is introduced in this paper. The system of dynamic vibration absorber and piezoelectric stack energy harvesting system (DVA-PSEH) has two functions, the first is to reduce vibrations for the primary system, and the second is to convert a part of the vibrational energy into electricity through the piezoelectric effect. The mechanical and electrical responses of the electromechanical system are determined by the complex amplitude method, then the numerical simulations are carried out to investigate the characteristics of DVA-PSEH.

Dynamic modeling and disturbance rejection compensation for hysteresis nonlinearity of high voltage piezoelectric stack actuators

High voltage piezoelectric stack actuators (HVPSA) are widely used in the field of active vibration control of engineering structures due to their strong load capacity, fast response rate, and high mechanical output efficiency. However, their inherent hysteresis will have a direct impact on the stability and control efficiency of the piezoelectric active control system. To compensate the hysteresis nonlinearity of HVPSA, a high-precision dynamic hybrid method based on linear active disturbance rejection control (LADRC) is proposed. Starting from the hysteresis analysis of piezoelectric actuators, an exponential function butterfly-shape hysteresis operator is constructed and combined with the asymmetric Bouc–Wen model to present a novel hybrid static hysteresis model. In order to implement rate-dependent hysteresis modeling, the Hammerstein rate-dependent hysteresis model of HVPSA is further established, and its inverse model is built for feedforward compensation. Subsequently, the LADRC is used to adjust the driving voltage in real time to form the hysteresis closed-loop compensator of HVPSA. The experimental results show that the Hammerstein rate-dependent hysteresis model established has satisfactory modeling accuracy in the working voltage range and frequency band under consideration. Furthermore, compared with the traditional inverse model feedforward compensation strategy, the proposed hybrid compensation method based on LADRC improves the compensation efficiency by more than 11% and reduces the hysteresis nonlinearity of HVPSA to less than 3%, with strong anti-disturbance ability.

Hysteretic behaviour and structural control performance of a piezoelectric friction damper

This study proposes a novel piezoelectric friction damper (PFD). Experiments and numerical simulations are carried out to investigate the mechanical model of the PFD, and the effects of loading speed, displacement amplitude, voltage, friction plate material, piezoelectric stack actuator dimensions, and spring parameters on the hysteretic characteristics of the PFD. Results show that the PFD attains a stable mechanical performance within the design loading speed and displacement amplitude. The piezoelectric stack actuator functioning as a friction control device, can increase friction by 54% at 120 V. In damper design, an appropriate increase of the constraint stiffness of the damper and a piezoelectric stack actuator with the same stiffness as the damper constraint can achieve greater output force, and the preload of the spring should be greater than the friction to prevent residual displacement. The PFD has better seismic performance for large-span cable dome structures than the traditional friction damper. The vertical peak displacement and acceleration reduction ratio reached 45.1% and 67.7% with PFDs, respectively. The PFD with semi-active control is suitable for large-span spatial structures.

A small piezoelectric stack motor designed for vacuum and micro-dust environment

With the development of moon exploration, higher requirements have been proposed for the adaptability of small motors under vacuum and micro-dust conditions. In this paper, a rotational motor based on piezoelectric stacks is proposed, which can be driven by a single-phase direct current with a simple drive circuit. The motor dimensions are 24 mm × 24 mm × 24 mm (length × width × height), and the mass is 11.4 g. In air environment, the maximum output rotational speed of the motor is 1372 rpm, and the maximum stall torque is 3.2 mN m at 40 V DC and 5.93 kHz. An open-loop control system is established to drive the stepping motion of the motor, and the minimum stepping angle is measured as 0.122 mrad. An environmental experiment of the motor is conducted in a lunar simulator module, which can simulate a high vacuum (6.7 × 10−5 Pa) and micro-dust (average 75 μm) environment of the lunar surface. The result shows that the motor can work steadily in the vacuum and micro-dust environment with an average speed of 1723 rpm, which demonstrates its potential applications in the space environment.

Modeling and Design Optimization of a New Piezoelectric Inchworm Actuator with Screw Clamping Mechanisms.

A new piezoelectric inchworm actuator with screw clamping mechanisms has been developed recently for the wing folding mechanism of a small unmanned aircraft where the actuator power density is a great concern. Considering that the prototype actuator was designed just with engineering intuition and the performance optimization through experimental developments would take a vast amount of cost and time, a mathematical model was developed to investigate the actuator's critical design parameters and optimize its presently undesirable performance. Based on the lumped parameter method reported previously, and taking full account of the detailed modeling of the complex actuator housing and the actual nonlinear behaviors from the high-force contact and friction occurring at the screw-nut interface, as well as the output performance of the main drive elements including the piezoelectric stack and hollow ultrasonic motors (HUSMs), this model was built and then was experimentally verified for its accuracy and availability. Finally, nine design parameters were studied for their individual effect on the actuator's output using the proposed model. The simulation results indicate that the performance can be considerably improved by performing a slight modification to the prototype, and the dynamic modeling and parameter optimization methods used in this study can also serve as a useful reference for the design of similar piezoelectric inchworm actuators with intermittent clamping behaviors.

Development of a novel high bandwidth piezo-hydraulic actuator for a miniature variable swept wing

Piezoelectric hydraulic actuators, instead of electromagnetic actuators, have a wide application prospect in the field of aerospace due to the merits of light weight, compact structure, non-magnetic interference, etc. Many researches have been devoted to boosting output powers of actuators with the help of large-scale piezoelectric stacks. However, the existing actuator operates at a relatively low frequency, limiting the output power improvement and the application. In this work, a high bandwidth piezo-hydraulic actuator (PHA) is proposed based on a resonant active valve piezoelectric pump with sandwich bending transducers (SBTs). The configuration and principle of the PHA are presented and analyzed. A tested setup of the PHA is established, and the maximum output velocity and thrust are measured to be 30.5 mm/s and 53.2 N under 1.6 kHz, and the output power reaches up to 294 mW under the load of 30 N. In addition, a variable swept wing (VSW) driven by the PHA is studied. The composition and deformation process of the PHA-Based VSW are discussed; the dynamic model of the PHA-Based VSW is derived; the tested results indicate that the maximum angular velocity and torque of the PHA-Based VSW are 1.135 rad/s and 1.701 N·m, and the swept angle range is 15.9° ∼ 64.1°

Energy harvesting from gravity-induced deformation of rotating shaft for long-term monitoring of rotating machinery

Energy harvesting from rotating machines for self-powered sensor networks has attracted increasing attentions in the last decade. In this work, an energy harvester employing piezoelectric stacks for rotating machinery is proposed, which cannot only harvest kinetic energy from bending deformation of rotating shaft but also has the capability of rotor fault detection. The structure and working concept of the energy harvester are initially presented. Afterward, a theoretical model for the energy harvester is established to clarify its output characteristics. Then, vibration tests under different rotating speeds are carried out with a prototype mounted on a rotor test rig. The effects of electrical connections of piezoelectric stacks, rotor geometry, energy harvester location, and fastener preload on the output performance of energy harvester are evaluated. Finally, the applications of powering a scientific calculator and detecting typical faults of rotor systems including rotor crack and rub impact faults are demonstrated. Apart from fault detection capability, the proposed energy harvester has the advantages of long lifespan and causing little interference with the rotational motion, which overcomes the inherent deficiencies of commonly studied beam-type energy harvesters and manifest the potential of proposed energy harvester for the long-term condition monitoring of rotating machines.

Experiments on the localized interaction at the interface fuel rod/spacer grid in pressurized water reactors

The release of fissile material into the coolant caused by fretting of the fuel rods at the interface with spacer grids is a significant safety issue and cause of financial losses in the operation of Pressurized Water Reactors (PWRs). Each fuel rod is kept in position inside spacer grids through friction from the preload exerted by retaining elements (springs and dimples). Fretting of the fuel rods occurs at the contact with the springs and dimples. In severe fretting cases the integrity of the fuel rod cladding is compromised and fission byproducts enter the primary coolant circuit. The reciprocating motion at the contact interface of the fuel rods and spacer grids resulting in material fretting is due to the Flow-Induced Vibrations (FIV) of fuel rods, caused by the unstable surrounding coolant flow, which in PWRs is predominantly parallel to the length of fuel rods (axial flow). Under specific flow conditions, fretting develops rapidly. The vibrations of fuel rods, as well as the relationship of fretting wear mechanisms with several factors associated with the fission process and coolant flow dynamics and stability (vibration amplitude, preload, oscillating loads, irradiation, axial slip, spring relaxation, temperature, oxidation, material of spacer grids and fuel rods), have been considered in the literature. However, direct experimental measurements of the contact force and axial slip during FIV have not been treated in the literature, likely because of the absence of suitable measurement methods. This gap in experimental measurement techniques is addressed in this work, specifically for the analysis of PWR fuel assemblies, by installing a piezoelectric stack and aiming laser Doppler vibrometers on a one-meter-long fuel rod, supported by two full-scale spacer grids, in-air or immersed in quiescent water. In the presence of small- and large- amplitude forced vibrations, the signal of the piezoelectric force transducer increases with the amplitude of vibration, but it is also affected by vibrations perpendicular to the excitation, which appear for large-amplitude excitations. The axial motion of the fuel rod at the spacer grid has a complex evolution and is significant for large-amplitude vibrations only. At any rate, the time histories of contact force and axial motion display the effects of impacts and slips, particularly during the tests in water. The measurement system shows that the severity of the interaction at the spacer grid interfaces is influenced strongly by the amplitude of the forced fuel rod vibrations. Since fuel rods and fuel assemblies are prone to several nonlinear phenomena, as demonstrated by recent studies, it follows that the usage of nonlinear models will be essential to numerically estimating the severity of fretting.