Faculty Bibliography

A novel shock switch based on a micro-electro-mechanical system (MEMS) for vibration monitoring was designed and fabricated by non-silicon surface micromaching technology. It consisted of three main parts: the proof mass as the movable electrode, the cross beam as the stationary electrode and the movable contact point to prolong the contact time. The ANSYS model was built, by which the modal analysis was carried out showing that the new design reduced the sensitivity to off-axis accelerations compared with the previous design, and the physical parameters were extracted from the structure so they could be used in the Simulink model. Through the dynamic simulation, the contact-enhancing mechanism was verified and compared with the traditional design. The fabricated micro shock switch was tested with a dropping hammer experiment. Test results indicated that the threshold acceleration was about 145 g and a stable contact time of over 50 μs was observed under a half-sine wave shock load acceleration with 1ms duration, in agreement with the simulation results. The contact effect was improved significantly as expected and the proposed model was able to describe the device's behavior correctly.

Based on non-silicon surface micromachining technology, a simple but reliable micro electro-mechanical system (MEMS) electrical inertia micro-switch with single sensitive direction and reverse impact protection is designed and fabricated on glass substrate. In this design, conjoined serpentine springs are used to fix and suspend the mobile electrode (mass) and blocks are used to protect the device against reverse impulse. The switch is laterally driven (i.e. its sensitive direction is parallel to the substrate). Fabrication is carried out by low-cost and convenient multi-layer electroplating technology. The relationship between threshold acceleration and mass thickness has been investigated by theoretical analysis and finite element analysis (FEA) simulation. After fabrication and packaging, micro-switches are tested by using drop weight. The results show that the threshold accelerations distribute between 58 g and 72 g, which basically fulfils the expected 60 g; and the response time to 100 g half-sine waved shock is in the order of 10^-4 s, which is in agreement with simulation result.

Vertically and laterally driven MEMS inertia switches are designed. The solid modeling and finite element dynamics analysis of the Nickel micro-spring in the switch are conducted. The stress distribution and the displacement-time response curve of the micro-spring under dynamic load are obtained. The influence of configuration parameters on the spring constants (including klevel and kvertic) are compared under static and dynamic loads. The finite element dynamics analysis is considered to be a useful method in evaluating the spring constant in MEMS devices, especially for the spring in inertia micro devices working under the dynamic load.