Increased Power Output from Piezoelectric Energy Harvesters by Pre-biasing

This paper presents, for the first time, experimental results demonstrating a new approach to increasing the power output of piezoelectric energy harvesters by applying a bias charge at the beginning of each half cycle of motion. Ultimate power limits of inertial energy harvesters depend only on the device size and nature of the excitation, rather than on the transduction mechanism. However, practical devices generally perform well below the theoretical limit, often because a sufficiently high transducer damping force cannot be achieved. For such cases, we show that the generator effectiveness is improved by a pre-biasing technique, and present simulation results with experimental verification. These results show that the effectiveness of the piezoelectric generator is improved by more than 10 times compared to an optimised purely resistive load. In practice our gains were limited by the voltage breakdown of the components used.