The dynamics of microstructures under shock and acceleration

The modeling of micromechanical systems (MEMS) under shock conditions can be an extremely difficult task for MEMS engineers. Overall, this field of research is multiphasic nature, since different physical phenomena are strongly intertwined at microscale. This work concentrates on two physical domains: mechanical and electrical, since most of the microstructures use electrostatic forces to bias the system. This thesis will focus on MEMS switches and resonators under the effects of shock and acceleration forces.;This dissertation presents investigations into the static and dynamic behavior of MEMS devices and structures under shock. First, we study the effects of the vibration of a Printed Circuit Board (PCB) on the dynamics of MEMS microstructures when subjected to shock for survivability considerations. A two-degree-of-freedom model is used to simulate numerically over time the dynamic responses of the MEMS structures. We found that neglecting the effects of the higher order modes of the PCB and the location of the MEMS device can cause incorrect predictions of the response of the microstructure and may lead to failure of the device. Also, we validate the results by comparing the numerical results using a finite element model.;The second part of the thesis is concerned with investigating a new idea of a switch triggered by low-level of acceleration. We propose a capacitive sensor excited at resonance to be close to instability bands of frequency-response curves, where it is forced to pull-in if operated within these bands due to earthquake detection and low-g seismic applications. By careful tuning, the resonator can be made to enter the instability zone upon the detection of the earthquake signal, thereby pulling-in as a switch. Such a switching action can be functionalized for alarming purposes or can be used to activate a network of sensors for seismic activity recording. The electrostatically actuated resonant switch is modeled and its dynamic response is simulated using a nonlinear single degree of freedom model and a nonlinear two-degree-of-freedom model.;Moreover, we validate the switch concept through experimental investigation, in which we have demonstrated the capability of the switch to be triggered at small level of acceleration as low as 0.02 g. Experimental data and simulation results are compared showing good agreement. A two-degree-of-freedom concept is simulated numerically by assuming the resonator placed on a printed circuit board (second-degree-of-freedom) of a natural frequency close to that of the earthquake’s frequency. We found significant improvement on the detection limit of this switch.