Development of a hybrid type smart pen piezoelectric energy harvester for an IoT platform

Abstract

We propose a smart pen piezoelectric energy harvester (SP-PEH) that simultaneously produces energy in both d31 and d33 modes during writing. Two piezoelectric devices were installed in SP-PEH, a cantilever type device and an impact type device. With preliminary Fast Fourier Transform analysis on the writing conditions, power generation tests were conducted. For cantilever type, the harvester generated instantaneous maximum power of 1.5 μW (3 MΩ) at a writing frequency of 3 Hz (most frequent value during actual writing) and a writing length of 12.5 mm. For impact type, it generated 2.6 μW at a load resistance of 5 MΩ. With those power generations, the stored energy in the two capacitors were 1 μJ (47 μF, cantilever type) and 0.05 μJ (220 μF, impact type) separately for 10 s, and a total energy of 3.1 μJ (about 3 times higher than sum of two types) was stored in an actual writing test because of movement in all directions rather than just a single direction. The proposed device successfully turned on a ZigBee wireless sensor after 10 s, which confirmed the possibility of the battery-less smart pen that harvests energy and collects and transmits environmental and biological data from writing.