Comparative Analysis of Active Impedance Matching Interfaces for Piezoelectric Energy Harvesters

This paper conducts a comparative study of the output energy generated by two compensation approaches for piezoelectric energy harvesters. These transducers are typically coupled to a cantilevered beam, and the compensation circuitry enhances the harvester's performance under an input mechanical vibration stimulus. The output power of the piezoelectric transducer relies on both the reflected and intrinsic mechanical impedance, along with the total output load. The electrical equivalent circuit of the structure, incorporating the transducer, is primarily capacitive, leading to an out-of-phase relationship between current and voltage in the electrical domain, resulting in the generation of reactive power and a subsequent reduction in the overall system efficiency. The system's first vibration mode, corresponding to a very low frequency, requires a significant passive inductor for impedance matching to ensure maximum power transfer to the load. In the first approach, a non-Foster circuit is implemented as a reactance for impedance matching, employing a Negative Impedance Converter (NIC) circuit. In another approach, the output of the cantilever beam is assessed using a synchronized switched inductor (SSHI). Both approaches are examined, and their feasibility limits are evaluated, taking into account the energy balance generated by the piezoelectric transducer. Experimental results illustrate that the active matching approach with a non-Foster reactance shows a greater enhancement in energy compared to the SSHI compensation method under conditions of harmonic mechanical oscillations.