Study Of Contact Enhancement And Axial Sensitivity In A Single-axis MEMS Inertial Switches

The MEMS inertial switch,sometimes also called collision switch or acceleration threshold switch,is designed to capture the change of external dynamic acceleration,and it is essentially both a threshold sensor and an actuator.It is widely used in automobile industry,aerospace,remote monitoring and Io T system due to the distinctive characteristics of small size,lightweight,low manufacturing cost and low energy consumption.Contact time is the key parameter of inertial switch.If contact time is short,it is necessary to improve the precision of external circuit,which will enhance difficulty of external circuit design,and the performance of external circuit resisting disturbance signals will also reduce.Thus,prolonging contact time can effectively improve the performance of inertial switch.The inertial micro-switch will be inevitably subjected to some overload shocks from different directions because of the complicated working environment.Low single-axis sensitivity could lead to the poor stability and short service life.With regards to this,the design structure and the optimized structure of inertial switch for contact enhance and single-axis sensitivity are proposed in the present work.The design structure mainly consists of three parts: the double-stair shape cantilever beam as movable electrode;one block located at the front of proof mass as fixed electrode and compact constraint structures consisting of constraint sleeve with holes and reverse constraint blocks.In the optimized structure,the symmetrical distribution of double layers serpentine springs is used to improve the single-axis sensitivity.The modal analysis,threshold level,contact time and the collision response in the inertial switch have been also simulated and discussed to confirm fabrication parameters.Finally,the proposed inertial switch has been fabricated successfully.The dropping hammer test results show that the threshold level of the design structure and optimized structure are 165 g and 272 g,respectively.And the maximum contact time is 220?s under overload acceleration.The combined efforts of double layers suspended springs and constraint structures effectively lower off-axis sensitivity and improve single-axis sensitivity.When overload acceleration is applied to the novel inertial micro-switch in the reverse,y-axis and z-axis direction,there is no spurious triggering.After testing,the inertial switch can maintain original threshold level and contact time.