Experimental Study of a Passive Impedance Matching Interface Based on a Centimeter-Size High Inductance Coil for Practically Enhanced Piezoelectric Energy Harvester Performance at Low Frequency

This paper presents an experimental study of a passive impedance matching interface based on a centimeter-size high inductance coil for practically enhanced piezoelectric energy harvester performance at low frequency. Because of the dielectric behavior of piezoelectric energy harvesters, vibrations of the low frequency range lead to large capacitive reactance values, which are impractical to be matched by use of common inductors for the achievement of the maximum power transfer conditions. For this study, PC-perm alloy material was used to implement a passive interface, which consists of a single toroidal coil, so as to match the impedance of a M8528-P2 Macro-Fiber Composite (MFC) piezoelectric patch at the frequency of 10 Hz. Experimental results of the performance of the implemented interface, connected between the piezoelectric energy harvester and a resistive load, are presented for applied strain levels and frequencies in the range between 480-1170 μstrain peak-to-peak and 2.5-10 Hz, respectively. The influence of the interface on the voltage, current and power transferred to the electrical load were examined and compared with the results from standard MFC characterization in similar working conditions. An increment of power equal to 94.6% was measured under an excitation of 480 μstrain at 10 Hz, in correspondence to a resistive load reduced by over 70%, being higher the improvement achieved at lower strain levels. Despite the active controls required by the state-of-art impedance matching techniques for linear and non-linear treatments of the signal generated by piezoelectric energy harvesters, the developed interface is easier to be implemented and doesn´t need additional power sources, partitions of the harvested energy-flow or switching conditions to be satisfied.