A Tunable Micromachined Multithreshold Inertial Switch

In this article, we present a multithreshold microelectromechanical tunable inertial switch. The device aims to provide quantitative information on acceleration while retaining the attractive energy-saving features of binary threshold switches. The designed proof-of-concept device with three thresholds is composed of four serpentine springs, a suspended proof mass, and three stationary electrodes placed at various positions in the sensing direction. In addition, the tunability of the acceleration threshold is demonstrated based on the softening effect of the electrostatic force. The dynamic behavior of the switch is investigated analytically. Results are shown for the relationship between the bias voltage and tunable threshold. The fabricated switch prototypes are tested using a drop-table shock system. The test results demonstrate that the multithreshold switch can detect an acceleration range of 131-400 g. The simulated and analytical results are in good agreement with the experimental data. The demonstrated device concept is promising to categorize the shock impact for several applications, such as for head impact and brain injuries.