A parametric analysis based design framework for MEMS g-switch accelerometers

Abstract

We present an experimentally verified novel design framework for MEMS g-switch acceleration switches. These switches need to engage a physical latch upon sensing a specified threshold acceleration. It is this physical contact between two surfaces under dynamic conditions that introduces nonlinearity in the system response and makes the task of design optimization difficult. We first find analytical solutions for displacement and velocity of the proof mass by linearizing the friction term using a single degree of freedom model and representing the acceleration profile by a Fourier series. We then use these solutions, along with latching constraints on them, to study how the lumped design parameters – mass, suspension spring stiffness, and latching spring stiffness – vary with increasing threshold acceleration. The latching constraints ensure that latching does not occur for any magnitude of acceleration less than the specified threshold value. Subsequently, we build a g-switch model in SIMULINK that uses the variation in design parameters for a given acceleration profile to find an optimal set of values of design parameters for a specified threshold acceleration. We verify our model by fabricating a latch accelerometer using the parameters obtained from this model for a 60g threshold acceleration. A shock input of 60g magnitude and 1.2 ms pulse width is given to the fabricated acceleration switch and the experimental response is recorded using high-speed video images. The analytical response and the experimental response show good agreement. Hence, we believe that this novel design framework can be used to fabricate a latch accelerometer for any arbitrary input shock profile.