A Passive Impedance Matching Interface Using a PC Permalloy Coil for Practically Enhanced Piezoelectric Energy Harvester Performance at Low Frequency

This paper presents an analytical and experimental study of a passive impedance matching interface based on a large inductive reactance but with a centimeter-scaled size for practically enhanced piezoelectric energy harvester performance at low frequency. Low frequency vibration normally leads to a large capacitive reactance value for small-sized piezoelectric energy harvesters and it is impractical to achieve the maximum power transfer condition by use of a conventional inductor as its volume would be of a few cubic meters. In this paper, PC permalloy material was used to implement a passive impedance matching interface in order to reduce the size of the inductor to a few cubic centimeters as it has a very high initial magnetic permeability of 6×10
⁴
H/m. The implemented interface is capable to practically perform the complex conjugate load matching of a macrofiber composite energy harvester at a frequency ≤10 Hz. The effects of the interface on the voltage, current, and power transferred to resistive loads were examined through comparisons of the results between configurations with and without the interface for applied strain levels and frequencies in the range between 480-1170-με peak-to-peak and 2.5-10 Hz, respectively. An increment of the power around 94.6% was obtained under an excitation of 480 με at 10 Hz in correspondence to an optimal resistive load reduced by over 70%. Compared with the state-of-the-art active impedance matching techniques, which use additional power sources to control the signal generated by piezoelectric energy harvesters, the developed interface is totally passive, easier to be implemented, and can be potentially used for the enhancement of vibration energy harvesting performance.