Effect of Electrical Damping Ratio on Maximum Average Power of an Electromagnetic Vibration Harvester at Resonance and off-Resonance Conditions

Abstract

Energy harvesting has opened up new ways to power low energy electronics without any need for batteries. The most advanced types of harvesters are piezoelectric, electrostatic and electromagnetic which use kinetic energy in form of vibrations. Electromagnetic harvesters (EHs) are efficient, less costly and offer huge design flexibility. As such, in this paper some analytical and experimental studies on maximum average harvestable power (Pave) from typical design of EH using the popular coupling architecture (a cylindrical magnet oscillating in a copper coil) have been carried out. The effect of frequency of excitation and electrical (ζe ) and mechanical damping ratios (ζm) on Pave obtained from an EH has been investigated. For this purpose, an EH using NdFeB (neodymium magnet) magnet oscillating in a copper coil has been designed and developed. An experimental test set up has developed which comprises of (i) a cam-follower type drive mechanism to simulate a vibration source with variable amplitude and frequency of base excitation, (ii) a spring-mass system with an EH system in parallel with the spring to provide the relative motion between the magnet and the copper coil, (iii) the attendant instrumentation comprising of ultrasonic sensor to sense the displacements of base and mass, motor drive speed measurement and an open source platform (ARDUINO) with programmable circuit board and software and data acquisition system. Using the developed experimental set up, (i)frequency response curve for vibrating system with EH has been obtained from which equivalent electrical damping ζe has been determined using half power point method, and (ii)the values of relative displacements of magnet and coil, at various excitation frequencies have been recorded. Using the analytical expression for the Pave of SDOF EH has been determined both at resonance and off resonance conditions, for three different values of ζe namely ζe = ζm, ζe = 5ζm, and ζe = 10ζm. It is observed that the maximum Pave is obtained for condition ζe = ζm. As the value of ζe increases, the Pave increases, at resonant frequency and considerable power is made available at off-resonance frequencies. It is concluded that ζe should be increased to enhance the maximum average harvestable power from EH and vibrating system should be so designed to have ζm, as small as possible.