A Paradoxical Approach to Enhance the Output Power of Vibrational Energy Harvester Beyond the Impedance Matching Conditions

The classical circuit theory tells us that the output from a power generator is maximized when a load resistance is set to match with the internal impedance of the power source. It is also believed that there exists one and only one impedance matching condition for a given power source system. In this paper, however, we discover another optimal condition that arises particularly when the mechano-electric conversion efficiency is enhanced in the electret based vibrational energy harvesting device. Such a condition is found to deliver more power than the conventional matching conditions do. In other words, the impedance matching condition is not a unique solution for the system but it changes with the excitation amplitude to the energy harvester.