Modeling and Experimental Characterization of an Electromagnetic Energy Harvester for Wearable and Biomedical Applications

This work presents the modeling and the experimental validation of a linear electromagnetic energy harvester (EMEH) actuated by random low-g external acceleration or by a very slow imposed movement. By combining these two different ways of energy scavenging, the system is particularly suited for powering wearable and biomedical electronic devices where the human-motion and movement can be considered as random and non predictable. The design is composed of a mobile stack of head-to-head ring-shaped permanent magnets in which a fixed wounded ferromagnetic core, composed of two coils, is located. A custom co-simulation is presented: a finite element analysis (FEA) and a one dimension (1D) two degrees of freedom (2DOF) system model. The FEA is used to optimize the geometry of the EMEH and its form factor, allowing an significative down-scaling. The 1D 2DOF model describes the dynamics of the EMEH in its real environment by considering all the leading mechanical and electrical parameters. The geometry can drastically change the behavior of the system as well as its dynamics: the goal of this double structure is to reduce the magnetic force exerted between the fixed part and the moving part while keeping the magnetic flux gradient in each coil as large as possible. This force was characterized experimentally by using a custom designed test bench, to validate the FEA results. It was observed that the maximum produced energy is reached when the system sweeps across different equilibrium positions rather than oscillating around a given stable position. The second degree of freedom helps the system to settle in a large number of equilibrium positions when submitted to random external accelerations and therefore broadens the frequency response of the EH. Results show a theoretical electrical power output (RMS) of 2 mW for a 10 cm³ cylindrical harvester submitted to a short external acceleration pulse of 27.5 m/s².