Design and Locomotion Study of Stick-Slip Piezoelectric Actuator Using Two-Stage Flexible Hinge Structure

A novel piezoelectric actuator using a two-stage flexure hinge structure is proposed in this paper, which is used in a compact and high-precision electromechanical field. The two-stage flexure hinge structure is used to provide horizontal thrust and vertical clamping force to the driving feet, which solves the problems of unstable clamping force and insufficient load capacity in traditional stick-slip piezoelectric actuators. Firstly, the main structure of the driver and the working process under the triangular wave excitation voltage are briefly introduced. Secondly, after many simulation tests, the structure of the actuator is optimized and the stability of the structure in providing clamping force is verified. Finally, through the research of the operating performance, when the amplitude is 150 V and the frequency is 3.25 kHz as the excitation source, the maximum speed can reach 338 mm/s and can bear about 3 kg load. It can be seen from the analysis that the two-stage flexure hinge structure can improve the displacement trajectory.

The Effect of Defects in Piezoelectric Composite Half-Planes with Surface Electrodes

An analysis for the prediction of the electromechanical field in composite piezoelectric half-planes with attached surface electrode is presented. The composite half-planes are composed of distinct constituents and may include internal defects in various locations. The solution is carried out in a sufficiently large rectangular region, the boundary conditions of which are obtained from the corresponding solution of a homogeneous piezoelectric half-plane. This is followed by the application of the discrete Fourier transform at the domain of which a boundary-value problem is formulated. The solution of this boundary-value problem, followed by the inversion of the Fourier transform, provides, in conjunction with an iterative procedure, the electromechanical field at any point of the rectangular region. Applications are given for a piezoelectric half-plane with defects in the form of a cavity and of short and semi-infinite cracks as well as of a periodically bilayered composite with a crack in one of its layers.

Enhanced Internal Quantum Efficiency of Bandgap-Engineered Green W-Shaped Quantum Well Light-Emitting Diode

To improve the internal quantum efficiency of green light-emitting diodes, we present the numerical design and analysis of bandgap-engineered W-shaped quantum well. The numerical results suggest significant improvement in the internal quantum efficiency of the proposed W-LED. The improvement is associated with significantly improved hole confinement due to the localization of indium in the active region, leading to improved radiative recombination rate. In addition, the proposed device shows reduced defect-assisted Shockley-Read-Hall (SRH) recombination rate as well as Auger recombination rate. Moreover, the efficiency rolloff in the proposed device is associated with increased built-in electromechanical field.

Field distributions in piezoelectric composites with semi-infinite cracks

A method is offered for the prediction of the electromechanical field in periodic piezoelectric composites with embedded semi-infinite cracks. It is based on the knowledge of the K-field in piezoelectric materials in which the material constants are replaced by the effective moduli of the piezoelectric composite. In addition to the existing semi-infinite crack, the proposed method can analyze localized inhomogeneities near the crack tip. The established effective K-field is applied at the boundaries of a rectangular domain that should be sufficiently far away from the crack tip and the other inhomogeneities. The proposed approach is based on the combined utilization of a micromechanical analysis, the representative cell method and the higher-order theory. The micromechanical analysis establishes the effective electromechanical constants of the piezoelectric composite, and the representative cell method reduces the periodic composite that is discretized into numerous identical cells to a single cell problem in the Fourier transform domain. The governing equations and constitutive relations that are formulated in this single cell are solved by employing the higher-order theory where discretization into subcells is employed. The inverse of the Fourier transform provides the electromechanical field at any point in the composite. The proposed approach is verified for crack fronts that are parallel and perpendicular to the poling direction (axis of symmetry). Applications are given for a cracked porous piezoelectric material, cracks that have been arrested by cavities and for a periodically bilayered composite with a semi-infinite crack.

Dynamic Electromechanical Field Concentrations Near Electrodes in Piezoelectric Thick Films for the Design of MEMS Mirrors

This paper studies the dynamic electromechanical response of piezoelectric mirrors driven by piezoelectric lead zirconate titanate (PZT) thick films both numerically and experimentally. The resonant frequency and the mirror tilt angle of piezoelectric mirrors under ac electric fields were analyzed by three-dimensional finite element method. The dynamic electromechanical field concentrations due to electrodes were also simulated and the results were discussed in detail. The mirrors consisted of four partially poled PZT unimorphs. The resonant frequency was then measured, and a comparison was made between the analysis and the experiment. The finite element method is shown to be capable of estimating the electromechanical field concentrations in the PZT films, making it a useful tool for designing future microelectromechanical systems (MEMS) mirrors.

Fracture of piezoelectric materials with the X-FEM

We present an application of X-FEM to the fracture analysis of piezoelectric materials. These materials are increasingly used in actuators and sensors. Under in service loading, phenomena of crack initiation and propagation may occur due to high electromechanical field concentrations. In the past few years, the extended finite element method (X-FEM) has been applied mostly to model cracks in structural materials. The present paper focuses on the definition of new enrichment functions suitable for cracks in piezolectric structures. The approach is based on specific asymptotic crack tip solutions, derived for piezoelectric materials.