Impedance analysis for piezoelectric energy harvesting devices under displacement and force excitations

To harvest energy from mechanical vibration with piezoelectric materials, different installations might be adopted according to the vibration conditions of the substrate structures. Surface mount (deformation preferred) and base excitation (movement preferred) are two of the commonly utilized installations. These configurations can be modeled as a general piezoelectric energy harvesting (PEH) device under displacement and force excitations, respectively. Comparison on the dynamics as well as power generation for PEH devices with a real harvesting interface circuit under these two excitations was not made in the previous literatures, since they oversimplified either the mechanical or electrical part. Yet, based on the equivalent impedance network of a general PEH device, the overall dynamics can be investigated. In this paper, the impedance technique is utilized to analyze a PEH device under either excitation condition. Three of the commonly studied interface circuits, including standard energy harvesting (SEH), parallel synchronized switching harvesting on inductor (P-SSHI), and series synchronized switching harvesting on inductor (S-SSHI), are connected in turn as the interface circuit, so as to provide more insights on the harvesting performances of different harvesting devices under different excitations.