MEMS Vibration Harvesting for Wireless Sensors

The recent development of “low-power” (10's-100's of µW) sensing and data transmission devices, as well as protocols with which to connect them efficiently into large, dispersed networks of individual wireless nodes, has created a need for a new kind of power source. Embeddable, non-life-limiting power sources are being developed to harvest ambient environmental energy available as mechanical vibrations, fluid motion, radiation, or temperature gradients. While potential applications range from building climate control to homeland security, the application pursued most recently has been that of aircraft structural health monitoring (SHM).

This SHM application and the power levels required favor the piezoelectric harvesting of ambient vibration energy, compared to other transduction principles. Current work focuses on harvesting this energy with MEMS resonant structures of various geometries. Coupled electromechanical models for uniform beam and plate structures have been developed to predict the electrical and mechanical performance obtainable from ambient vibration sources. The optimized models have been validated by comparison to prior published results and verified by comparison to tests on a macro-scale device. A non-optimized, uni-morph beam prototype has been designed and modeled. Dual optimal frequencies with equal peak power and unequal voltages and currents are characteristic of the response of such coupled devices when operated at optimal load resistances. Design tools to allow device optimization for any given vibration environment have been developed for both geometries. Future work will focus on fabrication and testing of optimized uni-morph and proof-of-concept bi-morph prototype beams. This work will include system integration and development, including modeling the power electronics.