A wirelessly readable and resettable shock recorder through the integration of LC circuits and MEMS devices

Abstract

This paper presents a passive shock recorder to record shock events for tens of Gs with wireless reading and wireless resetting capabilities through the integration of LC circuits and two MEMS devices. With a micro mechanical-latch shock switch electrically connected to the sensing LC circuit, the shock event that leads to different latching states can be recorded and wirelessly read through the LC resonant frequency. With a micro electro-thermal actuator electrically connected to a wirelessly powered actuating LC circuit, the energy can be wirelessly sent to the micro actuator to provide the necessary unlatched force. By integrating the mechanical-latch shock switch and actuator with LC circuits, the latching state can be reset through the wireless actuation. Therefore, the shock recorder can be used repeatedly. Here, the mechanical-latch shock switch is designed to have a two-level shock recording capability. The fabrication of the shock switch and actuator are achieved by a Ni-based surface micromachining process. When the acceleration reaches 28.06 G, the latching state changes from the original state to the first latching state. The resonant frequency of sensing for the LC circuit is found to switch from 10.14 MHz to 9.16 MHz, correspondingly. By further applying acceleration up to 37.10 G, the latching state changes from the first latching state to the second state, and the resonant frequency shifts to 7.83 MHz. Then, with a current of 2.07 A(AC) wirelessly induced in the actuating LC circuit, the micro electro-thermal actuator is shown to provide sufficient displacement to reset the shock switch from a latched state back to the original unlatched state, and the resonant frequency is switched back to 10.14 MHz. The fabricated shock recorder is repeatedly tested five times. The wireless reading, resetting and shock recording capabilities are successfully verified.