The present invention relates to an apparatus for generating electric energy by means of using at least one cavity resonator composed of a vibration plate, at least one side-wall unit, a supporting board and at least one piezoelectric substrate.
An energy conversion technique from mechanical vibration to electric power is hopeful as one of the techniques for recovering energy to charge. For example, batteries in a sensor system used in a wide range of applications are requested to have a compact and efficient power supply. The energy conversion technique is mainly based upon a piezoelectric effect, a magnetic induction effect or an electrostatic capacitance effect. Thus, a device having almost the same construction as a microphone is conveniently utilized. One of the most popular devices is a floor type, which has piezoelectric substrates mounted on a vibrating board and generates electric power from mechanical vibration by receiving a pressure on the floor. Recently, an energy conversion device with ZnO wires on the nanometer scale, of which each has a piezoelectricity and can be multi-directionally bended in accordance with mechanical vibration of electrode, has been presented (X. Wang et al., Science, vol. 316, pp. 102-105, 2007). However, there exist still many problems in efficiency of the energy conversion, because these conventional techniques make use of nothing but dimensional change of piezoelectric material accompanied by mechanical vibration. In other words, conventional techniques pass over a resonance vibration phenomenon in piezoelectric materials.