Turning motion into electric power
Batteries remain the preferred power choice for small devices like wireless sensors, data transmitters and implantable medical devices. Nonetheless, they have not kept pace with the devices' increasing demands for electric power. In addition, due to their limited life span, regular replacements are needed and this can be a costly process. Among the alternative solutions, researchers working on the EU-funded project HIPER (High performance energy harvesters) explored compact vibration energy harvesting devices. Such micro-power generators can provide a continuous power supply permitting autonomous operation. The standard approach adopted to date for vibration energy harvesting is based on resonant linear oscillators that are stimulated by ground shaking, machine vibration or body motion. HIPER scientists proposed a different approach to overcome most of their limitations. Specifically, the scientists investigated the possibility of combining the properties of resonant linear oscillators with those of non-linear oscillators. A suspension, for example, can be made to exhibit near-zero stiffness along one axis, while remaining stiff along the other axes. This allows very low resonant frequencies to be achieved even in a small device. A series of prototype silicon suspensions were fabricated using the traditional microfabrication technique of deep reactive ion etching as well as laser micromachining. The superior performance of these structures was established by finite element analysis. Additional experimental work proved that it is possible to harvest ambient vibration at low frequencies and over a wide frequency range. HIPER results revealed the potential of micro-energy harvesters to allow low power portable devices to run independently throughout their lifetime.
Keywords
Electric power, energy harvesting, nonlinear oscillator, power generator, batteries, silicon suspensions
