Bandwidth Improvement of a Piezoelectric Micro Energy Harvester

Abstract

Energy harvesting is a technology where electricity is generated from ambient energy resources. A piezoelectric energy harvester, which converts vibrations to electricity, is a promising power supply for sensors connected to the Internet of Things (IoT). This kind of power supply is self sustainable and does not need any maintenance nor external fuels. The aim of this study is to propose a harvester design with large bandwidth for an IoT application on micro scale. The eigenfrequencies and frequency response of the harvester are predicted by finite element simulations and the simulation model is compared to experimental data. An electromechanical model (EMM) is compared to a simplified pure mechanical model (PMM) and a correlation is found between the two models. The frequencies are shifted by a factor 0.95, i.e. fEMM=fPMM = 0:95, and 1mV corresponds to 7MPa. Key factors for bandwidth improvement are a small eigenfrequency gap and a high enough voltage level. The eigenfrequency gap is reduced with a back folded cantilever beam design with similar beam lengths and constant uniform thickness. For a given amplitude of the vibration source the total voltage output can be increased with a smaller coverage of piezoelectric material. Improved bandwidth is shown for three different beam lengths. The tolerance from the centre frequency is about 1 %, which corresponds to a 114 Hz bandwidth in the 4100 Hz region.