Study On Technique Of The Mems Inertial Switch Used In Fuse

The inertial MEMS switch is required to convert the acceleration signal which comes from the impact to the duration of the ON-state. The inertial MEMS switch is also called acceleration switch, threshold switch and G-switch. In particular, there is a need in the munitions fuze area for an ultra-miniature, fast-acting, inexpensive inertial switch that can be integrated with external circuit. The switch used in munitions fuze area need to follow some special conditions, against high overload, general-purpose, multi-directional sensing acceleration and so on, the general switch can not satisfy the conditions. At the time of the switch close, the MEMS switch worked in the multi-physics field, the work principle is complex, and the related design theoretics can not satisfy the devising demands yet, so the step of using MEMS switch in munitions fuze is slowed down badly. In this paper the theories of electrostatic field, elastic force field, inertial force field, damping field and the question of the multi-physics field are studied. Two kinds of switches are designed to satisfy the general-purpose and multi-directions sensing acceleration respectively in fuze.The pull-in effect is analyzed, which results from the coupling between the elastic force of micro-cantilever structure and the electrostatic force. The pull-in voltage is calculated. The negative spring effect is analyzed, that the effective spring constant will be decreased with the electrostatic force increasing. Three methods are presented for calculating the distortion of the micro cantilever under the electrostatic force, equivalent method, mode addition method and the finite element method with feed back. The advantages and disadvantages of the three methods are discussed, and the applicability of each method is analyzed. The distortion of the micro cantilever under the electrostatic force is simulated with equivalent method and the finite element method with feed back respectively.Combing the Renault equation which is used to describe the performance of the liquid with the micro-cantilever, the squeeze-film damping model is presented for the micro cantilever switch under the effect of electrostatic force, elastic force and inertial force coupling together. The squeeze-film damping coefficient formula for the cantilever switch is derived, and the analytical formula is presented to calculate the squeeze-film damping coefficient.To resolve the general-purpose question of the switch in fuze, a novel inertial switch with threshold adjusting is designed, the acceleration threshold can be adjusted by adjusting the bias voltage of the switch. Based on the electrostatic force driving, the liner relationship formula between the acceleration threshold and the bias voltage of the switch is derived. The systemic model of the cantilever MEMS switch is established in the coupled multi-physics fields and the static and the dynamic characteristic are researched based on the systemic model. The acceleration threshold is controlled from500g to2500g, adjusting500g every time, the response time is less than10%of the load duration, the contact time of the switch is greater than300μsTo resolve the multi-directional sensing acceleration question of the switch in fuze, the multi-elastic supported, annular MEMS inertial switch is designed. The dynamic differential equation of the movable electrode in switch is established. The static characteristic is researched, based on Castigliano’s2nd Theorem which is one of the energy methods and Hooke’s law, the spring constants of the folded serpentine micro-cantilever are derived and computed. The spring constant of the folded serpentine micro-cantilever is calculated by Finite element analysis using ANSYS software to validate the theoretic calculation. Compared with the Finite element simulation, the relative errors of the folded serpentine micro-cantilever are all less than3%. The results show that the formula deduction of the folded serpentine micro-cantilever is logical. The dynamic characteristics of the switch are researched by using finite element method. The response time of the switch is0.12ms and the contact time is about35μs.The technics process of the multi-elastic supported, annular MEMS inertial switch is introduced and the measurement techniques of the switch are researched. Based on the phase-stepping microscopic interferometry, the width of the cantilever and the gap between the two electrodes are measured and the error distribution is obtained, and the reason that the error will be effect the acceleration threshold is analyzed. The drop test is designed to test the acceleration threshold of the switch and the duration time of the acceleration can be adjusted by using buffer cushion. To test the capability of the switch that against high overload, Maehete test is used to offer3000g high acceleration, the test results show that the plastic deformation does not occur in the switch under the30000g acceleration and it can keep work commendably.