Electromechanical Displacement Research Articles

Gradation and porosity’s effect on Love waves in a composite structure of piezoelectric layers and functionally graded porous piezoelectric material

Love waves propagation in a composite structure lying over an elastic half-space are studied. The composite structure contains n piezoelectric layers and a functionally graded porous piezoelectric material(FGPPM) layer. The linear and exponential gradation of mechanical and electrical properties of the FGPPM layer are considered. The WKB technique is applied for obtaining the solution of the equations in the FGPPM layer. The transfer matrix is obtained for multilayers of piezoelectric materials. The frequency equations for both electrically open and short boundaries have been obtained. Numerical computations have been done to solve the frequency equations and to obtain electromechanical coupling, stress and displacements. The effect of porosity, wavenumber and gradation on the phase velocity and group velocity of Love waves have been studied and observed that group velocity is more affected by porosity than the phase velocity. Better resolution without compromising the magnitude of surface wave velocity seems to be achievable for piezoceramic having 20% to 30% porosity. Apart from these, the variations of attenuation and electromechanical coupling factor with grading parameters and porosity have also been examined and noticed that the grading type has a considerable effect on the coupling factor and attenuation quality factor. A relative study is conducted to demonstrate the impact of the number of piezoelectric layers above the FGPPM layer on dispersion curves and it is found that more energy is trapped with layering in a stack and an initial increase in the number of layers in the stack of composites is more effective. The effects of porosity and wavenumber on mechanical displacement, electrical displacement and stress have been studied numerically. Also, lateral and vertical variations of the mechanical displacement, electrical displacement and stress have been studied. The findings of the study are expected of use in improving the efficiency of SAW devices.

Dielectric and piezoelectric properties of 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 modified with sodium niobate

In this paper, we present the dielectric and piezoelectric properties of tetragonal 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 modified with NaNbO3 ((1-x)[0.8Na0.5Bi0.5TiO3-0.2BaTiO3]-xNaNbO3). Our experimental study has revealed that the ferroelectric phase in these compositions is suppressed with the increase of sodium niobate concentration. A broad anomaly, resembling relaxor ferroelectrics, appears in the 325–450 K temperature interval. The investigation of the electric field dependence of polarization has indicated that the double hysteresis loop behaviour is characteristic of the modified compositions, which is associated with the 1st order phase transition under the applied electric field. The experiments below room temperature have revealed that the range of stability of the ferroelectric phase is shifted to lower temperatures upon the increase of sodium niobate concentration. The electromechanical displacement in the modified compositions shows a similar maximum displacement in the whole concentration range. The electromechanical response in 0.8Na0.5Bi0.5TiO3-0.2BaTiO3 solid solutions is due to the piezoelectric effect, while, in the mixed compositions, it is related to the jump-like change of the lattice constants in the vicinity of electric fieldinduced 1st order phase transition.

Voltage- and Frequency-Based Separation of Nanoscale Electromechanical and Electrostatic Forces in Contact Resonance Force Microscopy: Implications for the Analysis of Battery Materials

In piezoresponse force microscopy and electrochemical strain microscopy (PFM, ESM), not only nanoscale electromechanical surface displacements (e.g., Vegard strain in case of ESM) are amplified in ...

Generalized displacements and momenta formulations of an electromechanical plunger

This paper deals with four different derivations of the governing equations of a solenoid plunger with lumped-parameter. Energy-based modeling is employed with extended Hamilton's principle with independent generalized coordinates and generalized momenta in order to be applicable to composite Lagrange's equations. In the electromechanical models, displacements and charges are regarded to be generalized coordinates, mechanical momenta and flux linkages are the generalized momenta. The derived systems of differential equations are solved numerically with the Runge-Kutta method.

Enhancement of Biodegradable Poly(Ethylene Oxide) Ionic–Polymer Metallic Composite Actuators with Nanocrystalline Cellulose Fillers

Biodegradable ionic polymer metallic composite (IPMC) electroactive polymers (EAPs) were fabricated using poly(ethylene oxide) (PEO) with various concentrations of lithium perchlorate. Nanocrystalline cellulose (NCC) rods created from a sulfuric acid hydrolysis process were added at various concentrations to increase the EAPs’ elastic modulus and improve their electromechanical properties. The electromechanical actuation was studied. PEONCC composites were created from combining a 35-mg/mL aqueous NCC suspension with an aqueous, PEO solution at varying vol.%. Due to an imparted space charge from the hydrolysis process, composites with an added 1.5 vol.% of NCC suspension exhibited an electromechanical tip displacement, strain, and elastic modulus that was 40.7%, 33.4% and 20.1% higher, respectively, than those for PEO IPMCs without NCC. This performance represented an increase of 300% in the energy density of these samples. However, the electromechanical response decreased when the NCC content was high. NCC without the space charge were also tested to verify the analysis. Additionally, the development of new relationships for modeling and evaluating the time-dependent instantaneous tip angular velocity and acceleration was discussed and applied to these IPMCs.

Spring constant measurement using a MEMS force and displacement sensor utilizing paralleled piezoresistive cantilevers

This paper reports on a method to measure a spring constant on site using a micro electro mechanical systems (MEMS) force and displacement sensor. The proposed sensor consists of a force-sensing cantilever and a displacement-sensing cantilever. Each cantilever is composed of two beams with a piezoresistor on the sidewall for measuring the in-plane lateral directional force and displacement. The force resolution and displacement resolution of the fabricated sensor were less than 0.8 µN and 0.1 µm, respectively. We measured the spring constants of two types of hydrogel microparticles to demonstrate the effectiveness of the proposed sensor, with values of approximately 4.3 N m−1 and 15.1 N m−1 obtained. The results indicated that the proposed sensor is effective for on-site spring constant measurement.

Simulation of a Love wave device with ZnO nanorods for high mass sensitivity

The paper presents 3D finite element simulation and analysis of Love wave resonator with different guiding layer materials and investigation of the coupled resonance effect with ZnO nanorods on the device surface. Analytical estimation of phase velocity and mass sensitivity of Love wave device with SiO2, ZnO, gold, SU-8, and parylene-C as guiding layer materials is performed for comparative analysis. Simulations are carried out to study the variation in electromechanical coupling coefficient, displacement profile and frequency response of the Love wave resonator. SU-8 offers high mass sensitivity of 1044 m2/kg while gold layer provides maximum K2 of 8.6%. In comparison to SiO2 and ZnO, polymers exhibit sharp rise and fall in K2 within a narrow range of normalized layer thickness (0.03–0.1). ZnO nanorods of varying height and surface nanorod density are designed over the Love wave resonator with SiO2 as the waveguiding layer. In the presence of coupled resonance, the nanorods and substrate vibrate in unison causing an increase in average stress and mass sensitivity but leads to decrease in the electromechanical coupling coefficient of the device. Surface nanorod packing density of 25 μm−2 offers high mass sensitivity of 1304 m2/kg that is 20 times greater in comparison to the mass sensitivity of a plain Love wave device.

Quasi longitudinal Lamb acoustic modes along ZnO/Si/ZnO structures

A novel structure consisting of a Si plate sandwiched between two ZnO layers is suggested as propagation medium for Quasi Longitudinal (QL) acoustic Lamb waves. Considering a low-dispersive quasi-longitudinal mode as an example, the phase velocity v, electromechanical coupling constant k2 and mechanical displacements U1, U3 versus plate and ZnO layers thicknesses have been calculated starting from uncoated plate through the same plate with one layer to the plate with two layers onto opposite faces. A remarkable increase in the electromechanical coupling, together with an essential decrease in the vertical displacement U3, at the ZnO surface, have been theoretically demonstrated and experimentally verified for definite combinations of the films/plate thicknesses. This property of the structure is attractive for applications to microwave liquid sensors.

Near-field radiative heat transfer between parallel structures in the deep subwavelength regime.

Thermal radiation between parallel objects separated by deep subwavelength distances and subject to large thermal gradients (>100 K) can reach very high magnitudes, while being concentrated on a narrow frequency distribution. These unique characteristics could enable breakthrough technologies for thermal transport control and electricity generation (for example, by radiating heat exactly at the bandgap frequency of a photovoltaic cell). However, thermal transport in this regime has never been achieved experimentally due to the difficulty of maintaining large thermal gradients over nanometre-scale distances while avoiding other heat transfer mechanisms, namely conduction. Here, we show near-field radiative heat transfer between parallel SiC nanobeams in the deep subwavelength regime. The distance between the beams is controlled by a high-precision micro-electromechanical system (MEMS). We exploit the mechanical stability of nanobeams under high tensile stress to minimize thermal buckling effects, therefore keeping control of the nanometre-scale separation even at large thermal gradients. We achieve an enhancement of heat transfer of almost two orders of magnitude with respect to the far-field limit (corresponding to a 42 nm separation) and show that we can maintain a temperature gradient of 260 K between the cold and hot surfaces at ∼100 nm distance.

Bistable switching of polymer stabilized cholesteric liquid crystals between transparent and scattering modes

Abstract

Color-Tunable Mirrors Based on Electrically Regulated Bandwidth Broadening in Polymer-Stabilized Cholesteric Liquid Crystals

We report on the preparation of color-tunable mirrors based on electrically regulated bandwidth broadening of the circularly polarized reflection of polymer-stabilized cholesteric liquid crystals (PSCLCs). A number of improvements relating to the practical implementation of these materials are detailed including color and bandwidth stability, baseline optical properties, and response times. Experimentation reported herein focuses on the contribution of structural chirality, viscoelastic properties of the polymer network architecture, and electro-optic drive schemes. Through the examination of samples prepared in different conditions and compositions, we further elucidate the dominant role of structural chirality as well as the impact of cross-linking of the polymer stabilizing network on the threshold voltage and relative change in bandwidth per voltage (Δ(Δλ)/V). Furthermore, the appearance of nonideal optical properties (scatter and haze) in some samples is shown to be correlated with the polymer/LC compatibility and effectiveness of structural templating. Due to the employment of an electromechanical displacement mechanism, the switching times of the PSCLCs are slower than mechanisms based on liquid crystal reorientation. However, a potential approach is identified to reduce the on and off switching times to approximately 1 s.

Electromechanical modelling for piezoelectric flextensional actuators

The piezoelectric flextensional actuator investigated in this paper comprises three pre-stressed piezoceramic lead zirconate titanate (PZT) stacks and an external, flexure-hinged, mechanical amplifier configuration. An electromechanical model is used to relate the electrical and mechanical domains, comprising the PZT stacks and the flexure mechanism, with the dynamic characteristics of the latter represented by a multiple degree-of-freedom dynamic model. The Maxwell resistive capacitive model is used to describe the nonlinear relationship between charge and voltage within the PZT stacks. The actuator model parameters and the electromechanical couplings of the PZT stacks, which describe the energy transfer between the electrical and mechanical domains, are experimentally identified without disassembling the embedded piezoceramic stacks. To verify the electromechanical model, displacement and frequency experiments are performed. There was good agreement between modelled and experimental results, with less than 1.5% displacement error. This work outlines a general process by which other pre-stressed piezoelectric flextensional actuators can be characterized, modelled and identified in a non-destructive way.

Effect of La on piezoelectric properties of Pb(Ni1/3Sb2/3)O3–Pb(ZrTi)O3 ferroelectric ceramics

Piezoceramic compositions Pb1−zLaz(NiSb)0.05[(Zr0.52Ti0.48)1−Z/4]0.95O3 with Z = 0.01–0.05 were synthesized by mixed oxide route to study the effect of Lanthanum (La) on crystal structure, microstructure, piezoelectric and ferroelectric properties. Calcination was performed at 1,060 °C and sintering at 1,270 °C for 1 h. X-Ray diffraction pattern indicated the polycrystalline microstructure along with co-existence of tetragonal and rhombohedral perovskite phases. Dielectric constant ( $$ K_{3}^{T} $$ ) was increased whereas piezoelectric voltage constant (g 33) was decreased with increase in lanthanum. Dense microstructure was observed for the composition containing 3 mol% of lanthanum. This was resulted in optimum piezoelectric charge constant (d 33 = 468 × 10−12 C/N), electromechanical coupling factor (k p = 0.68), remanent polarization (P r = 24.65 μC/cm2) and displacement (D = 2,012 nm). Results indicated that the composition Pb0.97La0.03(NiSb)0.05[(Zr0.52Ti0.48)0.9925]0.95O3 could be suitable for actuator applications. The composition Pb0.98La0.02(NiSb)0.05[(Zr0.52Ti0.48)0.995]0.95O3 resulted into moderately high value of voltage constant (g 33 = 39.3 × 10−12 V m/N) and optimum value of Figure of Merit (d 33 × g 33 = 16.2 × 10−12 C V m/N2) indicated the usefulness for sensor and power harvesting applications.

A theoretical study of the propagation of Rayleigh waves in a functionally graded piezoelectric material (FGPM)

An exact approach is used to investigate Rayleigh waves in a functionally graded piezoelectric material (FGPM) layer bonded to a semi infinite homogenous solid. The piezoelectric material is polarized when the six fold symmetry axis is put along the propagation direction x 1. The FGPM character imposes that the material properties change gradually with the thickness of the layer. Contrary to the analytical approach, the adopted numerical methods, including the ordinary differential equation (ODE) and the stiffness matrix method (SMM), treat separately the electrical and mechanical gradients. The influences of graded variations applied to FGPM film coefficients on the dispersion curves of Rayleigh waves are discussed. The effects of gradient coefficients on electromechanical coupling factor, displacement fields, stress distributions and electrical potential, are reported. The obtained deviations in comparison with the ungraded homogenous film are plotted with respect to the dimensionless wavenumber. Opposite effects are observed on the coupling factor when graded variations are applied separately. A particular attention has been devoted to the maximum of the coupling factor and it dependence on the stratification rate and the gradient coefficient. This work provides with a theoretical foundation for the design and practical applications of SAW devices with high performance.

Electrospun Fullerenol-Cellulose Biocompatible Actuators

Though there are many stimuli-responsive polymer actuators based on synthetic polymers, electroactive natural biopolymer actuators are very rare. We developed an electrospun fullernol-cellulose biocompatible actuator with much lower power consumption and larger electromechanical displacement in comparison with a pure cellulose acetate actuator. Morphology of the electrospun membranes resembles the nanoporous structure of extracellular matrix in natural muscles. Presence of minute concentrations of fullerenol leads to sharp increase in the degree of crystallinity and substantial increase in tensile strength of membranes. Chemical interactions between cellulose acetate and fullerenols are confirmed by three shifts in carboxylate, carboxy, and carbonyl linkages from the Fourier-transform infrared spectrometry. Much larger tip displacement, nearly 3-fold even at 0.5 wt % fullerenol content, was observed with much lower power consumption under both alternating and direct current conditions.

A double-mode piezoelectric single-crystal ultrasonic micro-actuator

Ternary Pb(In(1/2)Nb(1/2))O(3)-Pb(Mg(1/3)Nb(2/3))O(3)-PbTiO(3) (PIN-PMN-PT) single crystals with higher coercive field (E(C) ~9 kV/cm) and higher ferroelectric-transition temperature (T(R-T) = 108°C) were grown, and correspondingly, a double-mode piezoelectric ultrasonic micro-actuator made of PIN-PMN-PT crystal brick (5 x 1.5 x 1.32 mm) and operated in the first longitudinal and the second bending modes was developed. The ferroelectric, dielectric, electromechanical, and resonance displacement properties of the micro-actuator were characterized for miniature linear piezo-motor applications. The longitudinal displacement of the actuator is ~0.11 μm (with an applied voltage of 5 V), which is comparable to that of a multilayer piezoelectric-ceramic actuator of the same size. This crystal micro-actuator was successfully used to drive a slider moving linearly.

Electromechanical displacement of piezoelectric-electrostrictive monolithic bilayer composites

We examine the electromechanical displacement of piezoelectric-electrostrictive monolithic bilayer composites with various piezoelectric volume percentage obtained by cosintering piezoelectric 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 and electrostrictive 0.9Pb(Mg1/3Nb2/.3)O3-0.1PbTiO3 under unipolar and bipolar electric field excitation up to 10 kV/cm experimentally. It is shown that the effective d33 of the composites is limited by the electrostrictive layer, which acts as a capacitor in series to the piezoelectric layer, causing incomplete poling. We show that by controlling the volume content of the piezoelectric layer and constraining it with an electrostrictor, substantial strain amplification (15 μm for bipolar excitation) can be achieved while inducing asymmetry to the displacement with respect to the polarity of the applied field, which we discuss in the context of symmetry superposition.

Large-scale actuating performance analysis of a composite curved piezoelectricactuator

In this paper, the electromechanical displacements of curved piezoelectric actuatorscomposed of PZT ceramic and laminated composite materials are calculated on thebasis of high performance computing technology and the optimal configurationof the composite curved actuator is examined. To accurately predict the localpre-stress in the device due to the mismatch in the coefficients of thermal expansion,carbon/epoxy and glass/epoxy as well as PZT ceramic are numerically modelledby using hexahedral solid elements. Because the modeling of these thin layersincreases the number of degrees of freedom, large-scale structural analyses areperformed using the PEGASUS supercomputer, which is installed in our laboratory. Inthe first stage, the curved shape of the actuator and the internal stress in eachlayer are obtained by cured curvature analysis. Subsequently, the displacementdue to the piezoelectric force (which results from the applied voltage) is alsocalculated. The performance of the composite curved actuator is investigatedby comparing the displacements obtained by variation of the thickness and theelastic modulus of laminated composite layers. In order to consider the finitedeformation in the first stage of the analysis and include the pre-stress due to the curingprocess in the second stage, nonlinear finite element analyses are carried out.

Polygonal finite element method for nonlinear constitutive modeling of polycrystalline ferroelectrics

In meso-mechanistic analyses, crystal grains are often idealized as polygons. Presuming that each grain possesses its own unique and uniform crystallographic structure, it is highly desirable to model a grain by only one basic computational sub-domain. To this end, polygonal finite element models are developed for constitutive modeling of polycrystalline ferroelectrics. The success of these models relies on a hybrid electromechanical variational principle with equilibrating assumed electromechanical stress ( stress + electric displacement ). To construct the element electromechanical stiffness matrix, only piecewise boundary interpolations of the electromechanical displacement ( displacement + nodal electric potential ) are required. Higher-order elements are made available by inserting side-nodes along the element edges and enriching the electromechanical stress. By incorporating an energy-based nonlinear constitutive model, characteristic features in electric saturation and domain switching are successfully reproduced in the finite element simulation. The effect of microcracking on the macroscropic response of ferroelectrics is also studied.

Investigation of actuating displacement performance of curved actuator by large-scalecomputation

In this paper, the electromechanical displacements of curved actuators such as THUNDERare calculated by the finite-element method to design the optimal configuration of curvedactuators. To predict the internal stress in the device due to the mismatch in coefficients ofthermal expansion, the adhesive as well as metal and PZT ceramic is also numericallymodeled by using hexahedral solid elements. Also, the nonlinear finite-element formulationis implemented to include the variation of material constants during the curing process andacquire more accurate actuating displacements. Because the modeling of these thinlayers causes the numbers of degree of freedom to increase, large-scale structuralanalyses are performed in a cluster system in this study. The curved shape andinternal stress in the actuator are obtained by the cured curvature analysis, andthe displacement subject to the piezoelectric force by an applied voltage is alsocalculated to investigate the performance of curved actuators. The thickness of metalsand adhesive, and the number of metal layers, are chosen as design variables.