Hybrid PZT Lateral Bimorphs and 3-D-Printed Spring-Mass Resonators for Batteryless RF Transmission and Vibration Identification

Abstract

3-D-printed structures integrated with laser-cut spiral PZT bimorphs are used to obtain low mechanical resonance frequencies for energy harvesting and a vibration-activated mechanical switch. This structure is used to realize a batteryless vibration event detector and RF transmitter, using the energy in the vibration and a mechanical switch as a comparator. The low-resonance frequency of the 3-D-printed mechanical resonators is used to supply significant mechanical resonance gain and trigger the impulse response of the PZT bimorphs, resulting in an upconversion of resonance frequencies. RF pulses are generated by an LC resonator and transmitted by a loop antenna for reporting event detection. The 3-D-printed structure has resonances as low as 17.5 to 40 Hz corresponding to the vibration energy spectrum readily available in the environment. Theory and experiments to verify RF output are presented. At 40 Hz and 0.75 g excitation, the resulting RF pulse is at a carrier frequency of 10.9 MHz with energy extracted from the bimorph of 0.95 nJ per pulse. As a demonstration of the device, the wireless sensor node is used to identify operational modes of a portable gasoline electric generator.