Design of a Low Frequency Piezoelectric Energy Harvester for Rodent Telemetry

Abstract

This work presents the design and simulation of a piezoelectric-based device to generate electrical power by harvesting the kinetic energy available from the natural movement of small animals, such as rodents. Telemetry acquisition from rodents is important in biomedical research, where rodent behavior data is used to study disease models, or in biology research, involving animal tracking. In both applications, a long-term powering scheme for telemetry electronics and radios is needed. A major challenge is the relatively small size and low frequency motion of rodents. The proposed energy harvester design is simulated and the results reported. The design consists of a cantilever beam with a piezoelectric layer, a proof mass, and motion limit pads. Its mass and size are intended for use with a rodent, to provide continuous power for monitoring without limiting rodent mobility. Maximum power is obtained when the excitation source (animal movement) frequency corresponds to the resonant frequency of the energy harvester. As well, we demonstrate that the harvester electrical impedance is important, and must match the impedance of the application circuit load, to maximize the electrical power harvested. An experiment is conducted to record typical rodent (mouse) running motion in three axes of acceleration. A power spectral density (PSD) was computed for all axes, and the highest power is observed in the x-axis (forward/backward) motion at a frequency of 11.7 Hz, which is the typical gait frequency. Hence, the proposed energy harvester has been specifically designed to resonate at 11.7 Hz. The response of the proposed design is simulated using finite element analysis (FEA) software, to predict the electrical power and proof mass displacement. The model is excited with both a pure sine wave, and also with an arbitrary waveform consisting of the actual displacement of the rodent movement. A multi-scale FEA meshing approach is used to accommodate the thin thickness and long length of the cantilever design using mapped meshes. Additionally, a transient simulation is used to simulate the proposed design with different applied excitation frequencies, to determine the ideal matched load impedance for maximum electrical power.