Novel design for wideband piezoelectric vibrational energy harvester (P-VEH)

Vibrational energy harvesters (VEH) are increasingly becoming the favourite approach towards making self sustained low power systems. However, obtaining frequencies close to those of ambient vibrations has been a challenge. In the current work we have proposed a novel design of the piezoelectric-VEH (P-VEH) consisting of a micro-machined thick silicon proof mass suspended with quad-beams carved out of monolithic single crystal silicon, which provides a physically stable structure with low resonance frequencies. The stiffness of the Si beams and the mass of the suspended proof mass plays a significant role in the design of the resonant structure capable of generating a high voltage output using ZnO as piezoelectric layer. In our design, after fixing the thickness of the quad Si beams through initial iterations, we have fixed the structure size to 5000, 7000 and 10,000 μm and worked out the optimum ratio of the length of the beams (L_c) to the edge length (L_p) of the proof mass to obtain minimum natural frequency. A 3×3 array of such devices has been designed to obtain a wideband VEH for ambient vibrations of 100-500 Hz. It gives out a typical output of 0.4 V at ambient vibrations of the order of 1g.