Omnidirectional MEMS inertial switch

In this paper, a novel MEMS inertial switch is designed and characterised for the purpose of crash sensing for ammunition systems in which high-speed response is required for triggering the detonator. In order to keep the same sensitivity in different direction, the structure of an annular proof-mass suspended by four serpentine flexures is designed. The motion of the inertial switch is analysed by dynamic simulation, the simulation results show that the response time is 0.142 ms and the contact time of the switch is about 5 us under the 700 g threshold acceleration. It illustrates that the response time is short enough and the impact time satisfy the ask. The Von-Mises stress of the structure is calculated, the maximum stress occurs in the serpentine flexures, the value is 60.61 MPa, much less than the yield strength of the silicon, the switch can be used time after time. The static behaviour of the serpentine flexures is researched, and the width of the serpentine flexure is determined as the most important factor to the threshold acceleration. With the width of the serpentine flexure increasing, the threshold of the switch will increase, and the response time of the inertial switch will decrease.