Electricity Generation Characteristics of Energy-Harvesting System with Piezoelectric Element Using Mechanical-Acoustic Coupling

Abstract

This paper describes the electricity generation characteristics of a new energy-harvesting system with piezoelectric elements. The proposed system is composed of a rigid cylinder and thin plates at both ends. The piezoelectric elements are installed at the centers of both plates, and one side of each plate is subjected to a harmonic point force. In this system, vibration energy is converted into electrical energy via electromechanical coupling between the plate vibration and piezoelectric effect. In addition, the plate vibration excited by the point force induces a self-sustained vibration at the other plate via mechanical-acoustic coupling between the plate vibrations and an internal sound field into the cylindrical enclosure. Therefore, the electricity generation characteristics should be considered as an electromechanical-acoustic coupling problem. The characteristics are estimated theoretically and experimentally from the electric power in the electricity generation, the mechanical power supplied to the plate, and the electricity generation efficiency that is derived from the ratio of both power. In particular, the electricity generation efficiency is one of the most appropriate factors to evaluate a performance of electricity generation systems. Thus, the effect of mechanical-acoustic coupling is principally evaluated by examining the electricity generation efficiency.

Electricity Generation System with Piezoelectric Element Using Acoustic Radiation Energy

“…Here, electro-mechanical coupling is based on the above several relationships, and then mechanical-acoustic coupling is also induced from the relationships between the vibrations of both plates and the sound field into the cylindrical cavity. Resultantly, this electricity generation phenomenon takes place under the situation of electro-mechanical-acoustic coupling, so that the plate vibrations, the sound field, and the electricity generation are governed by the following Equations (12) and (13), respectively [9]: 13, respectively, and these coefficients can be derived by solving the above simultaneous equations. However, Plate 1 is excited by the point force of its natural frequency and the behavior is assumed to be harmonic, so that j e t ω could be eliminated in Equations (12) and (13).…”

“…However, this system cannot avoid the influence derived from enlarging contact areas with the surrounding medium on both plate surfaces, so that harvesting acoustic energy radiated from the circular plate is one of important matters to improve electricity generation characteristics. In our previous work, some problems remained unsolved with respect to such an influence and the convergence of some theoretical solutions [9]. Therefore, the influence is considered theoretically using the equation of plate motion taking into account its radiation impedance and is estimated by the electricity generation efficiency, which is derived from the ratio of the electric power in the electricity generation and the mechanical power supplied to the plate, and then these results are verified by the electricity generation experiment.…”