Design of MEMS piezoelectric harvesters with electrostatically adjustable resonance frequency

In this paper the analytical analysis of an adaptively tuned piezoelectric vibration based energy harvester is presented. A bimorph piezoelectric energy harvester is suspended between two electrodes, subjected to a same DC voltage. The resonance frequency of the system is controllable by the applied DC voltage, and the harvested power is maximized by controlling the natural frequency of the system to cope with vibration sources which have varying excitation frequencies. The nonlinear governing differential equation of motion is derived based on Euler Bernoulli theory, and due to the softening nonlinearity of the electrostatic force, the harvester is capable of working over a broad frequency range. The steady state harmonic solution is obtained using the harmonic balance method and results are verified numerically. The results show that the harvester can be tuned to give a resonance response over a wide range of frequencies, and shows the great potential of this hybrid system.