Shock reliability analysis and improvement of MEMS electret-based vibration energy harvesters

Abstract

Vibration energy harvesters can serve as a replacement solution to batteries for powering tire pressure monitoring systems (TPMS). Autonomous wireless TPMS powered by microelectromechanical system (MEMS) electret-based vibration energy harvester have been demonstrated. The mechanical reliability of the MEMS harvester still has to be assessed in order to bring the harvester to the requirements of the consumer market. It should survive the mechanical shocks occurring in the tire environment. A testing procedure to quantify the shock resilience of harvesters is described in this article. Our first generation of harvesters has a shock resilience of 400 g, which is far from being sufficient for the targeted application. In order to improve this aspect, the first important aspect is to understand the failure mechanism. Failure is found to occur in the form of fracture of the device's springs. It results from impacts between the anchors of the springs when the harvester undergoes a shock. The shock resilience of the harvesters can be improved by redirecting these impacts to nonvital parts of the device. With this philosophy in mind, we design three types of shock absorbing structures and test their effect on the shock resilience of our MEMS harvesters. The solution leading to the best results consists of rigid silicon stoppers covered by a layer of Parylene. The shock resilience of the harvesters is brought above 2500 g. Results in the same range are also obtained with flexible silicon bumpers, which are simpler to manufacture.

Reliability of MEMS in Shock Environments: 2000–2020

“…They further optimized the reliability through the design of the buffer device. The shock resistance of the structure was approximately 400 g. Renaud, M., et al [64] further improved the shock resistance of the energy harvester to around 2500 g in 2018.…”

Shock reliability enhancement for MEMS vibration energy harvesters with nonlinear air damping as a soft stopper

“…Renaud et al [8] later devised a stopper for MEMS PVEH by the utilisation of spring anchors to redirect the impact force from the anchor of the device where it is most fragile to other less fragile parts of the PVEH. They designed three types of shock absorbing structures, namely rigid stoppers, Parylene-covered stoppers and silicon-only flexible stoppers.…”