Experimental investigation of optimal damping ratio for magnetostrictive energy harvester under free vibration

The energy-harvesting efficiency of a magnetostrictive energy harvester feeding a load with a resistive input impedance is described with four non-dimensional parameters: electromagnetic-mechanical spring constant ratio, primary damping ratio, coil damping ratio, and damping ratio of input resistance. Among the parameters, the damping ratio of input resistance has an optimal value while the energy-harvesting efficiency becomes high as the electromagnetic-mechanical spring constant ratio increases or as the primary damping ratio or the coil damping ratio decreases. This paper presents experimental investigation methods to find and validate the optimal damping ratio of a magnetostrictive energy harvester under free vibration. It was found that the unimorph magnetostrictive energy harvester investigated in this study can harvest 10.1% of given mechanical energy with the optimally tuned damping ratio of input resistance.