High-frequency energy harvesting with mechanical frequency conversion

点击翻译按钮获取中文摘要

Energy harvesting for small wireless autonomous devices such as intelligent sensors has attracted much interest in the last decade. One of the oldest energy harvesting devices is the automatic mechanical wrist watch, where the harvested energy is stored in a spring (long before the term energy harvesting was coined). In most modern devices ambient energy is converted to electrical energy and often piezoceramics are used as transducers. Since the energy converted per cycle in a piezo-element from mechanical to electrical is small, it would be convenient to operate the transducer at high frequency. In most piezoelectric motors this is done: the power electronics generates an electrical input signal e.g. in the 100 kHz range, while the mechanical output energy at the shaft is obtained at a low frequency (e.g. 1-20 Hz), as required for many applications. In piezoelectric generators or harvesters, this has not been done in the past. The main reason for this is probably the fact that high frequency mechanical vibrations have to be produced from low frequency inputs.In the Darmstadt dynamics group an ample competence has been generated since the 1980’s both in the research in materials behavior with regard to piezoelectric motors, as well as in the mechanical frequency conversion in this type of drives. In addition, during the same period the generation of mechanical vibrations of high frequency from a mechanical low frequency signal, via contact forces, such as in the generation of brake squeal, has been studied both experimentally and by producing adequate simulation models.This project aims at exploring the feasibility of designing small piezo-generators, or harvesters, using mechanical frequency conversion from low to high frequency at the input side. This could lead to applications in autonomous intelligent sensors, for example for damage detection in the axles of high speed trains. The goal of the planned research is a deeper understanding of the mechanisms of frequency conversion in both directions, their mathematical modeling and the development of prototype generators of this type.