Theoretical modeling of longitudinal piezoelectric characteristic for cellular polymers

Efficient energy harvesting is a difficult challenge that consists in the development of systems allowing charging autonomous and low-power devices. In addition to traditional piezoelectric polymers, mono-crystals, and ceramics, cellular electrets offer consistent solutions by converting wasted vibration energy from the environment to usable electrical energy. This paper presents an electromechanical model to study the energy harvesting capability of cellular polymers. The theoretical study models the response of these materials to investigate the effect of different parameters on the piezoelectric coefficient d33, particularly. The model considers the percentage of porosity, surface charge density in each polymer–gas surface, the properties of the polymer matrix and the gas encapsulated in the pores, and the Young’s modulus of the porous film. For poly(ethylene-co-vinyl acetate), the results showed that the piezoelectric performance of the film declines with the increase of the film thickness. However, the variation of the d33 as a function of the percentage of porosity is exponential and can achieve 4.24 pC/N for a porosity of 80%. Compared to a previously published experiment, the theoretical results have proven a good agreement with only 3.3% error.

Dynamic Anti-Plane Behaviors on Two Dissimilar Piezoelectric Media with an Interfacial Non-Circular Cavity

Dynamic anti-plane behaviors are studied on two dissimilar piezoelectric media with an interfacial non-circular cavity subjected to time harmonic incident anti-plane shearing. Based on Greens function and conformal mapping method, the dynamic stress concentration factors at the edge of the non-circular cavity are obtained by applying the orthogonal function expansion technique. Numerical cases about two dissimilar piezoelectric media with an elliptic cavity are provided with different elliptic axial length ratio, different wave number and different piezoelectric characteristic parameter. The calculating results show that dynamic analyses are of importance at lower frequencies and larger piezoelectric characteristic parameters.

A New Thin-Film Piezoelectric Sensor for Easuring Methane Gas

To measure the concentration of CH4, we developed a thin film piezoelectric acoustic sensor (TFPAS), it accomplishes the detection of CH4 by the absorption of CH4 which can change the oscillation frequency of the piezoelectric crystal. The sensor is mainly composed by the piezoelectric film, sensitive film, silicon substrate and electrodes. The sensitive film is made up of nanometer-sized MgO scattered on pitch-based activated carbon fibers which has a strong adsorption of CH4. The piezoelectric film is a ZnO film which has very high piezoelectric characteristic parameters. The experimental results show that the sensitivity of the sensor to CH4 is very high. The response of the sensor to the presence of CH4 tested was found to be linear within a certain detection range and the detection error is less than 5%.

Dynamic Antiplane Interaction of Subsurface Circular Cavities in a Semi-Infinite Piezoelectric Medium

In the present work, dynamic interaction is investigated theoretically between several circular cavities near the surface in a semi-infinite piezoelectric medium subjected to time-harmonic incident anti-plane shearing. The analyses are based upon the use of complex variable and multi coordinates. Dynamic stress concentration factors at the edges of the subsurface circular cavities are obtained by solving boundary value problems with the method of orthogonal function expansion. Some numerical solutions about two interacting subsurface circular cavities in a semi-infinite piezoelectric medium are plotted so as to show how the frequencies of incident wave, the piezoelectric characteristic parameters of the material and the structural geometries influence on the dynamic stress concentration factors.

Dynamic Anti-Plane Behaviors of Interacting Circular Cavities in an Infinite Piezoelectric Medium

In this article, dynamic interaction is investigated theoretically between several circular cavities in an infinite piezoelectric medium under time-harmonic incident anti-plane shear wave load. The theoretical formulations are based upon the use of complex variable and multi-coordinates. Dynamic stress concentration factors at the edges of the circular cavities are obtained by solving boundary value problems with the method of orthogonal function expansion. As examples, some calculating results of two interacting circular cavities in an infinite piezoelectric medium are plotted to show how the frequencies of incident wave, the piezoelectric characteristic parameters of the material and the structural geometries influence on the dynamic stress concentration factors.

Dynamic Stress Concentration on a Semi-Infinite Piezoelectric Medium With a Circular Cavity Near the Surface

Dynamic interaction is investigated theoretically between a circular cavity and the surface in a semi-infinite piezoelectric medium subjected to time-harmonic incident anti-plane shearing in the present paper. The formulations are based on the method of complex variable and wave function expandedness. Dynamic stress concentration factors at the edge of the circular cavity are obtained by solving boundary value problems with the method of orthogonal function expansion. The calculating results are plotted so as to show how the frequencies of incident wave, the piezoelectric characteristic parameters of the material and the structural geometries influence upon the dynamic stress concentration factors.

Dynamic Anti-Plane Characteristic of an Infinite Piezoelectric Medium With a Non-Circular Cavity

In this paper, dynamic stress concentrations are studied in an infinite piezoelectric medium with a non-circular cavity under time harmonic incident anti-plane shear wave and inplane electric field. Based on complex variable and conformal mapping method, the dynamic stress concentration factors and the electric field concentration factors at the boundary of the non-circular cavity are obtained by applying the orthogonal function expansion technique. Numerical examples about an infinite piezoelectric medium with an elliptic cavity are provided with different elliptic axial length ratios, different wave numbers and different piezoelectric characteristic parameters. The calculating results show that dynamic analyses are very important to an infinite piezoelectric medium with a non-circular cavity at lower frequencies and larger piezoelectric characteristic parameters.