Modeling of linear micro electromagnetic energy harvesters with nonuniform magnetic field for sinusoidal vibrations

Abstract

Different architectures for vibration-based linear electromagnetic energy harvesters (EMEHs) have been developed and reported in the literature for applications in autonomous wireless sensor nodes. In the majority of the linear EMEHs the magnetic field over the coil is nonuniform. This paper presents the modeling and simulation for the electromechanical transduction of linear EMEHs with a nonuniform magnetic field configuration excited by harmonic vibrations. Models are developed based on Faraday's law of electromagnetic induction and the Lorentz force law. For a more accurate prediction of the performance of the EMEHs where the entire coil does not experience the same gradient of the normal component of the magnetic flux density, the analytical solution of the off-center magnetic flux density for a square magnet is used. The simulation results of the developed models show good agreement with the experimental results. Simulations of our previously developed EMEH show an improvement of load voltage and the power when the gap between the magnet and the coil is optimized. Moreover, maximizing the number of turns of the coil for the optimized gap, simulations of the optimized device predict a load voltage amplitude (90.2 mV) almost twice and a load power (40.7 μW) almost four times the experimental results obtained for the current prototype.