A study on the electrically induced damping in piezoelectric energy harvesting for broadband, high-performance power generation

The article explores the utilization of electrically induced damping (electrical damping) as a dual indicator for both power and bandwidth in the context of vibration-based piezoelectric energy harvesting, in the effort to enhance both power output and broadband capacity. This damping phenomenon arises during the extraction of energy from a vibrating structure through external interface circuits, forming a crucial aspect of the energy harvesting process. Conventionally, its assessment involves comparing power dissipation across the electric load with that attributed to structural damping. Nonetheless, the quantification of electrical damping with respect to device parameters, along with its significance on bandwidth and power enhancement, remains relatively unexplored. To this end, this article presents an alternative perspective by leveraging the impedance-based unified model that uses an equivalent load impedance to represent the effect of external interface circuit. The electrical damping is quantified as an equivalent viscous damping ratio by involving halving the product of the electromechanical coupling factor and the real part of the normalized equivalent load impedance. This approach offers a well-defined formulation of electric damping, linked precisely to the coupling factor, normalized electrical load and frequency, tailored for commonly employed interface circuits. These include the purely resistive load (REH), standard energy harvesting circuit (SEH), synchronized switching harvesting on an inductor (SSHI), and synchronized electric charge extraction (SECE) circuits. Moreover, the fine-tuning of electrical damping using the proposed formulation opens avenues for expanding the resonant bandwidth and potentially achieving the power limit. This adaptability is exemplified through the design of a piezoelectric frequency up-conversion harvester operated under rotary magnetic plucking. By effectively tuning electrical damping in SSHI and SECE, the experiment confirms a significant reduction in power ripples, albeit with a minor trade-off of slightly reduced peak output power.