Impedance Network for Power Optimisation in Piezoelectric Energy Harvesting Systems

Abstract

Distributed wireless sensor network would be autonomous by scavenging energy from the ambience. The piezoelectric materials provide one of the promising transduction mechanisms for harvesting the ambient vibration energy. In the piezoelectric energy harvesting (PEH) systems, even it was claimed that the harvested power can be optimised with the impedance matching theory, several fundamental issues were still not thoroughly investigated or even misunderstood. Retrospecting to the origin of the impedance matching theory, the equivalent impedance network for PEH systems is proposed in this paper with emphases on its scope, as well as the definition, available range, and composition of the electrical part equivalent impedance. Due to the distinctions between the equivalent impedance network of the PEH systems and the unconstrained impedance network, the conventional complex conjugate and resistive impedance matching theories can no longer be directly used for the harvested power optimisation. Instead, constrained impedance matching should be adopted. Experimental results obtained from a base excited PEH device show that the harvested power can be well predicted with the equivalent impedance network. The limitation on the electrical part equivalent impedance in the specific PEH system is also discussed with the matching index defined in this paper.

Keywords:

• Piezoelectric
• Energy Harvesting
• Impedance Matching
• Power Optimisation