An investigation into the effects of electrostatic and squeeze-film non-linearities on the shock spectrum of microstructures

We present an investigation into the effects of some of the common microelectromechanical systems (MEMS) non-linearities on their shock response and shock spectrum. As a case study, a capacitive accelerometer is selected to investigate theoretically and experimentally the effect of non-linearities due to squeeze film damping (SQFD) and electrostatic actuation. For the theoretical investigation, a non-linear single-degree-of-freedom model is used to simulate the response of the device. It is shown that, in the case of light damping, the electrostatic forces soften the microstructure and raise its deflection significantly. Dynamic pull-in instability is predicted near the dynamic range zone of the shock spectrum. On the other hand, SQFD is found to highly suppress the deflection of the microstructure in the dynamic range, while it is of less effect in the quasi-static range. Experimentally, the capacitive accelerometer is powered with a DC load and then subjected to acceleration pulses generated by a shaker. Tests are conducted while the accelerometer is operated in air, where the squeeze film effect is significant, and while placed inside a vacuum chamber. Simulation results are compared to experimental data showing excellent agreement.