Electromechanical Coupling Effect Research Articles

Flexoelectric effect in PVDF-based copolymers and terpolymers

Compared with their inorganic counterparts, the flexoelectric effect of polymers is much less studied, and the mechanisms underlying this gradient electromechanical coupling effect have rarely been explored. In this work, the temperature dependence of the flexoelectric coefficients of PVDF-based copolymers and terpolymers was measured, and the mechanisms that affect the flexoelectric response of the polymers were investigated. For these polymers, the flexoelectric response decreases abruptly in the temperature range where the peaks of dielectric loss or mechanical loss are observed. These loss peaks originate from the phase transition or polymer chain relaxation processes. Based on this observation, we propose that the temperature dependence of the flexoelectric response of the polymers is closely related to polymer chain mobility and relaxation processes. Our study provides an in-depth understanding of the flexoelectric effect in polymers.

Modeling of capacitor charging dynamics in an energy harvesting system considering accurate electromechanical coupling effects

This paper presents an iterative numerical method that accurately models an energy harvesting system charging a capacitor with piezoelectric patches. The constitutive relations of piezoelectric materials connected with an external charging circuit with a diode bridge and capacitors lead to the electromechanical coupling effect and the difficulty of deriving accurate transient mechanical response, as well as the charging progress. The proposed model is built upon the Euler-Bernoulli beam theory and takes into account the electromechanical coupling effects as well as the dynamic process of charging an external storage capacitor. The model is validated through experimental tests on a cantilever beam coated with piezoelectric patches. Several parametric studies are performed and the functionality of the model is verified. The efficiency of power harvesting system can be predicted and tuned considering variations in different design parameters. Such a model can be utilized to design robust and optimal energy harvesting system.

Dynamic characteristic of electromechanical coupling effects in motor-gear system

Dynamic characteristics of an electromechanical model which combines a nonlinear permeance network model (PNM) of a squirrel-cage induction motor and a coupled lateral-torsional dynamic model of a planetary geared rotor system is analyzed in this study. The simulations reveal the effects of internal excitations or parameters like machine slotting, magnetic saturation, time-varying mesh stiffness and shaft stiffness on the system dynamics. The responses of the electromechanical system with PNM motor model are compared with those responses of the system with dynamic motor model. The electromechanical coupling due to the interactions between the motor and gear system are studied. Furthermore, the frequency analysis of the electromechanical system dynamic characteristics predicts an efficient way to detect work condition of unsymmetrical voltage sag.

Electroelastic modeling of thin-laminated composite plates with surface-bonded piezo-patches using Rayleigh–Ritz method

Laminated composite panels are extensively used in various engineering applications. Piezoelectric transducers can be integrated into such composite structures for a variety of vibration control and energy harvesting applications. Analyzing the structural dynamics of such electromechanical systems requires precise modeling tools which properly consider the coupling between the piezoelectric elements and the laminates. Although previous analytical models in the literature cover vibration analysis of laminated composite plates with fully covered piezoelectric layers, they do not provide a formulation for modeling the piezoelectric patches that partially cover the plate surface. In this study, a methodology for vibration analysis of laminated composite plates with surface-bonded piezo-patches is developed. Rayleigh–Ritz method is used for solving the modal analysis and obtaining the frequency response functions. The developed model includes mass and stiffness contribution of the piezo-patches as well as the two-way electromechanical coupling effect. Moreover, an accelerated method is developed for reducing the computation time of the modal analysis solution. For validations, system-level finite element simulations are performed in ANSYS software. The results show that the developed analytical model can be utilized for accurate and efficient analysis and design of laminated composite plates with surface-bonded piezo-patches.

On the thermal buckling of magneto-electro-elastic piezoelectric nanobeams

In this paper, the buckling response of nanobeams on the basis of the Euler-Bernoulli beam model with the von Karman geometrical nonlinearity using the modified couple stress theory is investigated under various types of thermal loading and electrical and magnetic fields. The modified couple stress theory, used in this paper, is capable to consider the higher-order electro-mechanical coupling effects besides size effects. The governing equations and boundary conditions are derived using minimum potential energy principle. The nanobeam is assumed to be under two types of thermal loading, uniform and linear, along thickness direction. The buckling response of nanobeams is studied using the Galerkin method and the effects of different parameters, such as size effect, length and thickness, on the critical buckling temperature are shown. The buckling behavior of nanobeam is illustrated significantly size-dependent particularly with an increase in thickness and decrease in length.

Proposition for sensorless self-excitation by a piezoelectric device

In this paper, we propose a method to realize self-excitation in an oscillator actuated by a piezoelectric device without a sensor. In general, the positive feedback associated with the oscillator velocity causes the self-excitation. Instead of measuring the velocity with a sensor, we utilize the electro-mechanical coupling effect in the oscillator and piezoelectric device. We drive the piezoelectric device with a current proportional to the linear combination of the voltage across the terminals of the piezoelectric device and its differential voltage signal. Then, the oscillator with the piezoelectric device behaves like a third-order system, which has three eigenvalues. The self-excitation can be realized because appropriate feedback gains can set two of the eigenvalues to be conjugate complex roots with a positive real part and the other eigenvalue to be a negative real root. To confirm the validity of the proposed method, we experimentally demonstrated the sensorless self-excitation and, as an application example, carried out mass sensing in a sensorless self-excited macrocantilever.

Joint excitation synchronization characteristics of fatigue test for offshore wind turbine blade

In the case of the stiffness of offshore wind turbine blade is relatively large, the joint excitation device solves the problem of low accuracy of bending moment distribution, insufficient driving ability and long fatigue test period in single-point loading. In order to study the synchronous characteristics of joint excitation system, avoid blade vibration disturbance. First, on the base of a Lagrange equation, a mathematical model of combined excitation is formulated, and a numerical analysis of vibration synchronization is performed. Then, the model is constructed via MATLAB/Simulink, and the effect of the phase difference on the vibration synchronization characteristics is obtained visually. Finally, a set of joint excitation platform for the fatigue test of offshore wind turbine blades are built. The parameter measurement scheme is given and the correctness of the joint excitation synchronization in the simulation model is verified. The results show that when the rotational speed difference is 2 r/min, 30 r/min, the phase difference is 0, π/20, π/8 and π/4, as the rotational speed difference and the phase difference increase, the time required for the blade to reach a steady state is longer. When the phase difference is too large, the electromechanical coupling can no longer make the joint excitation device appear self-synchronizing phenomenon, so that the value of the phase difference develops toward a fixed value (not equal to 0), and the blade vibration disorder is serious, at this time, the effect of electromechanical coupling must be eliminated. The research results provide theoretical basis for the subsequent decoupling control algorithm and synchronization control strategy, and have good application value.

A Non-Hysteretic Sub-60-mV/decade Subthreshold Slope and ON-Current Boosts in Electrostrictive-Piezoelectric Transistors

Sub-60-mV/decade subthreshold slope (SS) without the cost of hysteresis using smart electrostrictive-piezoelectric gate insulator of a field-effect transistor is presented. This exploits a combined effect of linear and non-linear electromechanical coupling of piezoelectricity and electrostriction in a gate insulator of the transistor. The electrostrictive-piezoelectric insulator in a gate stack of a transistor results in negative capacitance with an internal charge amplification, leading to a large on-current boost and sub-60-mV/decade SS in the transistor characteristics. Using load-line analysis and capacitance tuning of electrostrictive-piezoelectric gate insulator and semiconductor channel capacitors, the possibility of eliminating hysteresis in the device characteristics of sub-60-mV/decade steep transistors is discussed. The steep SS and the on-current boost can potentially enable the reduction of operating voltage of the transistor.

Evaluating transient performance of servo mechanisms by analysing stator current of PMSM

Abstract Smooth running and rapid response are the desired performance goals for the transient motions of servo mechanisms. Because of the uncertain and unobservable transient behaviour of servo mechanisms, it is difficult to evaluate their transient performance. Under the effects of electromechanical coupling, the stator current signals of a permanent-magnet synchronous motor (PMSM) potentially contain the performance information regarding servo mechanisms in use. In this paper, a novel method based on analysing the stator current of the PMSM is proposed for quantifying the transient performance. First, a vector control model is constructed to simulate the stator current behaviour in the transient processes of consecutive speed changes, consecutive load changes, and intermittent start-stops. It is discovered that the amplitude and frequency of the stator current are modulated by the transient load torque and motor speed, respectively. The stator currents under different performance conditions are also simulated and compared. Then, the stator current is processed using a local means decomposition (LMD) algorithm to extract the instantaneous amplitude and instantaneous frequency. The sample entropy of the instantaneous amplitude, which reflects the complexity of the load torque variation, is calculated as a performance indicator of smooth running. The peak-to-peak value of the instantaneous frequency, which defines the range of the motor speed variation, is set as a performance indicator of rapid response. The proposed method is applied to both simulated data in an intermittent start-stops process and experimental data measured for a batch of servo turrets for turning lathes. The results show that the performance evaluations agree with the actual performance.

Highly durable piezo-electric energy harvester by a super toughened and flexible nanocomposite: effect of laponite nano-clay in poly(vinylidene fluoride)

A highly durable piezoelectric energy harvester is introduced by integrating the toughness and flexibility of a non-electrically poled, laponite nano-clay mineral-induced γ-phase (up to 98%) in a poly(vinylidene-fluoride) (PVDF) matrix by a simple solvent evaporation technique. Owing to a superior electromechanical coupling effect, PVDF/laponite nanocomposites retain excellent biomechanical energy harvesting capabilities under external vibration (as high as 6 V output voltage and 70 nA output current under a compressive force of 300 N) and charge storage properties under an external high electric field (maximum of discharged energy density at a breakdown strength of 302 MV m−1). As a proof of concept, the fabricated nanogenerator (NG) possesses a high output power density (~6.3 mW m−2) that directly drives several consumer electronics without using any storage system or batteries. It paves the way for potential applicability in next generation electronics, particularly as a self-powered device and to configure sustainable internet of things (IoT) sensor networks.

A curved resonant flexoelectric actuator

Flexoelectricity is an electro-mechanical coupling effect that exists in all dielectrics and has the potential to replace piezoelectric actuating on the microscale. In this letter, a curved flexoelectric actuator with non-polarized polyvinylidene fluoride is presented and shown to exhibit good electro-mechanical properties. This provides experimental support for a body of theoretical research into converse flexoelectricity in polymeric materials. In addition, this work demonstrates the feasibility of lead-free microscale actuating without piezoelectricity.

Free edge stress field in smart piezoelectric composite structures and its control: An accurate multiphysics solution

A three-dimensional piezoelasticity based iterative analytical solution is presented for the multiphysics problem of free edge stresses in hybrid composite panels integrated with piezoelectric transducer layers. The formulation, applicable for general laminate configurations with arbitrary layup and materials properties, considers extension, bending, twisting and electric field actuation loadings with full electromechanical coupling. A mixed formulation approach based on the Reissner-type mixed variational principle is adopted to ensure exact point-wise satisfaction of all boundary and interlaminar continuity conditions, which is key to obtaining accurate results for the localized stresses near free edges. The solution is obtained using the recently developed mixed-field multiterm extended Kantorovich method, whose robustness, convergence and accuracy are illustrated for various laminates and loadings. The solution successfully captures singular nature of free edge interlaminar stresses under different loadings. The results show a significant effect of electromechanical coupling on the free edge stresses in hybrid laminates under mechanical loading. The effect of actuator thickness on the interfacial stress distributions under electric load is studied. Finally, it is shown how the free edge stresses due to extension, bending and twisting loads can be controlled by applying appropriate actuation potential.

Dynamic characteristics of motor-gear system under load saltations and voltage transients

Abstract In this paper, a dynamic model of a motor-gear system is proposed. The model combines a nonlinear permeance network model (PNM) of a squirrel-cage induction motor and a coupled lateral-torsional dynamic model of a planetary geared rotor system. The external excitations including voltage transients and load saltations, as well as the internal excitations such as spatial effects, magnetic circuits topology and material nonlinearity in the motor, and time-varying mesh stiffness and damping in the planetary gear system are considered in the proposed model. Then, the simulation results are compared with those predicted by the electromechanical model containing a dynamic motor model with constant inductances. The comparison showed that the electromechanical system model with the PNM motor model yields more reasonable results than the electromechanical system model with the lumped-parameter electric machine. It is observed that electromechanical coupling effect can induce additional and severe gear vibrations. In addition, the external conditions, especially the voltage transients, will dramatically affect the dynamic characteristics of the electromechanical system. Finally, some suggestions are offered based on this analysis for improving the performance and reliability of the electromechanical system.

Extrinsic contributions to piezoelectric Rayleigh behavior in morphotropic PbTiO3 - BiScO3

In situ, high-energy, time-resolved X-ray diffraction experiments are utilized to quantify contributions from non-180° domain wall motion to the macroscopic electromechanical coupling effect in the morphotropic phase boundary composition 0.64PbTiO3-0.36BiScO3 during the application of weak electric field amplitudes. Macroscopic piezoelectric coefficient measurements are compared with diffraction data. The results demonstrate a linear contribution of electric-field-amplitude-dependent non-180° domain wall motion at small field amplitudes, and therefore domain wall motion contributes directly to the Rayleigh behavior of piezoelectric coefficients.

Analysis of torsional stability and the dynamical characteristics of electromechanical systems

Electromechanical couplings have been reported to play a crucial role in determining important behavior of nonlinear systems. In this study, we analyzed the nonlinear dynamic characteristics of the electromechanical coupling system. First, considering the electromechanical coupling effect of the system, differential equation of the system was obtained by combining the Park equation of a permanent-magnet synchronous motor with the rotor dynamics equation. Then, the coordinate plane projection method was used to analyze the chaotic phenomenon of the electromechanical coupling system. Through calculating the weight value of the 10 projection planes of the electromechanical coupling system, four projection planes with smaller weight values were chosen. Finally, the analysis of the four projection planes of the system indicated that the whole system could reach to the stable state by only controlling the rotational speed in the steady state. In this perspective, the 5-degree-of-freedom system reduced to 2-degr...

Dynamic behavior of an electrostatic MEMS resonator with repulsive actuation

Static and dynamic analyses of an electrostatic microbeam under repulsive force actuation are presented. The repulsive force, created through a specific electrode configuration, generates a net electrostatic force on the beam pushing it away from the substrate. This allows large out-of-plane actuation and eliminates the pull-in instability. For example, a dynamic amplitude of 15 $$\upmu $$ m was recorded for a 500- $$\upmu $$ m-long cantilever at a DC voltage of 195 V and an AC voltage of 1 V, while the initial gap was only 2 $$\upmu $$ m. This study includes mathematical modeling and simulations for a cantilever and a clamped–clamped beam, as well as experimental validation. The beam is modeled using Euler–Bernoulli beam theory and electromechanical coupling effects. Cantilever tip displacement, clamped–clamped midpoint deflection, and natural frequency shifts are reported. Governing equations are solved numerically using the shooting method, which provides a complete picture of the beam dynamics. The numerical results are verified with experimental data from fabricated beams using PolyMUMPs standard fabrication. Frequency response results reveal a mixed softening and hardening behavior and secondary resonances originating from quadratic and cubic nonlinearities in the governing equations. The analysis provides insight for applications in optical and gas sensors where a large signal-to-noise ratio and, sometimes, a wide frequency bandwidth are desired.

Flexoelectric effect in PVDF-based polymers

Flexoelectricity is a gradient electromechanical coupling effect that exists in all dielectrics and is important for the understanding of a variety of gradient-induced physical phenomena and the design of new electromechanical devices. At present, the flexoelectric effect in polymer materials has not been well studied. In this work, thick rectangular poly(vinylidene fluoride) (PVDF)-based polymer samples were fabricated and the flexoelectric coefficient was measured. Our results show that the flexoelectric coefficient of the PVDF, which is on the order of several nC/m, is more than twice higher than that of P(VDF-CTFE) and P(VDF-HFP) polymers. All these materials exhibited a non-polar α phase, but the copolymers showed much smaller crystallinity values than the PVDF homopolymer. The difference in the flexoelectric response in these polymers is believed to be related to the crystallinity of the polymers.

Effects of cellular electromechanical coupling on functional heterogeneity in a one-dimensional tissue model of the myocardium

Based on the experimental evidence, we developed a one-dimensional (1D) model of heterogeneous myocardial tissue consisting of in-series connected cardiomyocytes from distant transmural regions using mathematical models of subendocardial and subepicardial cells. The regional deformation patterns produced by our 1D model are consistent with the transmural regional strain patterns obtained experimentally in the normal heart in vivo. The modelling results suggest that the mechanical load may essentially affect the transmural gradients in the electrical and mechanical properties of interacting myocytes within a tissue, thereby regulating global myocardial output.

Nanoscale mechanical energy harvesting using piezoelectricity and flexoelectricity

Due to the electromechanical coupling effect, mechanical energy can be converted into electrical energy in certain materials. A theoretical framework is established to investigate the circuit voltage, electric power of nanoscale mechanical energy harvesting, in which the mechanical vibration energy was converted into electrical energy by piezoelectric and flexoelectric effects. Analytical solutions for the maximum electric potential, circuit voltage and electric power generated in bent BaTiO3 (BT), ZnO nanowires (NWs) and Pb(Mg1/3Nb2/3)O3 (PMN) nanofilms (NFs) were derived. Static and dynamic analyses are conducted to obtain the fundamental information of these mechanical energy harvestings. Different from the previous studies, the flexoelectric-mechanism are included in the fundamental mechanical frameworks. The maximum electric potential generated in the BT, ZnO NWs and PMN NF is found to be enhanced by flexoelectricity in the static case, meanwhile the circuit voltage and electric power are dramatic enhanced by flexoelectricity when the geometric dimensions shrinks to dozens of nanometers. The mechanical limitation condition is employed to calculate the practical maximum electric potential, circuit voltage and electric power. This work tries to provide a comprehensive understanding of the mechanical energy harvesting capability of these nanoscale structures and provide valuable information for designing flexoelectricity-based nanogenerator devices.

Discrete singular convolution and spectral finite element method for predicting electromechanical impedance applied on rectangular plates

The impedance-based structural health monitoring using piezoelectric wafer-active sensor has been increasingly developed for aerospace, civil, and mechanical structures. Using electromechanical coupling effects of piezoelectric wafer-active sensor, impedance of piezoelectric wafer-active sensor can detect any change in a structure. Piezoelectric wafer-active sensor is embedded and bounded to the structure in order to monitor the structure in a preferred frequency range. This article presented a general model to predict the impedance of piezoelectric wafer-active sensor bounded to a plate structure and also developed a general model for the influence of interaction of piezoelectric wafer-active sensor and plate on the structural response in impedance-based structural health monitoring. To obtain equations of vibrations, in the first step, potential and kinetic energies of fully free Kirchhoff and Mindlin plates with piezoelectric wafer-active sensor are derived. Numerical solutions for structural vibration of the plate developed using discrete singular convolution methods and applied based on Rayleigh–Ritz method in very high frequencies. After calculating mass and stiffness matrices of structure and piezoelectric wafer-active sensor, impedance of piezoelectric wafer-active sensor was determined using piezoelectric constitutive equations. Also, a three-dimensional spectral finite element method was used to model impedance of plate. An experimental setup was used for modal analysis to obtain low natural frequencies and calculate the impedance of piezoelectric wafer-active sensor in high frequencies. Finally, the comparison of numerical results of three-dimensional spectral element method and experimental results verified this model.