Asymmetric Quad Leg Orthoplanar Spring for Wideband Piezoelectric Micro Energy Harvesting

Piezoelectric energy harvesters (EH) generate their highest energy levels at the resonant frequencies of the transducer devices. To provide a wide-band EH solution, nonlinear mechanical resonators with multiple resonant modes can be used. We present a new asymmetric quad-leg orthoplanar spring (QOPS) EH microstructure to increase the harvesting bandwidth. The proposed design is implemented in CMOS compatible microfabrication processes. Finite element analysis show that the asymmetric designs increases the bandwidth by maximum 27% compared with symmetric designs. In order to measure the electrical output, one symmetric and three asymmetric piezoelectric devices implemented on the same microchip are exposed to mechanical vibrations over a wide frequency bandwidth. Experimental results approve the increase in the frequency bandwidth of resonators introduced by asymmetries added to the spring, as compared to the symmetrical configuration.