High-frequency energy harvesting with mechanical frequency conversion

在过去十年中，小型无线自主设备（如智能传感器）的能量收集引起了人们的极大兴趣。最古老的能量收集装置之一是自动机械腕表，将收集到的能量储存在弹簧中（早在能量收集这个词被创造出来之前）。在大多数现代装置中，环境能量被转换成电能，通常使用压电陶瓷作为换能器。由于压电元件从机械到电气每周期转换的能量很小，因此可以方便地在高频下操作换能器。在大多数压电电机中都是这样做的：电力电子设备产生一个电气输入信号，例如在100 kHz范围内，而轴上的机械输出能量以低频（例如1-20 Hz）获得，这是许多应用所需要的。在压电发电机或收割机中，这在过去是没有做到的。其主要原因可能是高频机械振动必须由低频输入产生。在达姆施塔特动力学组，自20世纪80年代以来，在压电电机材料行为的研究以及这种类型驱动器的机械变频方面，已经产生了足够的能力。此外，在同一时期，通过接触力从机械低频信号产生高频机械振动，例如在制动尖叫的产生中，已经通过实验和产生足够的仿真模型进行了研究。本项目旨在探索设计小型压电发电机或收割机的可行性，在输入端使用从低频到高频的机械频率转换。这可能会导致自动智能传感器的应用，例如高速列车车轴的损伤检测。计划研究的目标是更深入地了解两个方向的频率转换机制，它们的数学建模和这种类型的原型发电机的开发。

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.