High-frequency energy harvesting with mechanical frequency conversion

在过去的十年里，智能传感器等小型无线自主设备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，收集的能量储存在弹簧中(早在能量收集一词被创造出来之前)。在大多数现代设备中，环境能量被转化为电能，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的每个周期转换的能量很小，因此换能器在高频下操作将是方便的。在大多数压电马达中，这是这样做的：电力电子装置产生电输入信号，例如在100 kHz范围内，而轴上的机械输出能量是在低频(例如1-20赫兹)获得的，这是许多应用所需的。在压电式发电机或收割机中，这在过去是没有做过的。其主要原因可能是高频机械振动必须由低频输入产生。自20世纪80年代S以来，达姆施塔特动力学小组在压电马达的材料行为研究以及这类驱动器的机械频率转换方面都产生了很强的能力。此外，在同一时期，通过实验和建立适当的仿真模型，对机械低频信号通过接触力产生高频机械振动进行了研究，例如在产生刹车尖叫时。本项目旨在探索在输入侧使用机械频率从低频到高频转换来设计小型压电式发电机或收割机的可行性。这可能会导致自主智能传感器的应用，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变频机理、数学模型和开发这种类型的原型发电机。

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.