Strain control for optimization of piezoelectric energy harvesting

A novel piezoelectric energy harvesting module with controllable strain was designed to allow investigations into the correlations among strain, frequency, and output power. Specifically, although conventional vibration modules allow control over strain only through variation in tip mass, the proposed module allows more accurate strain control through adjustment of the displacement of the free end of the cantilever (5-45 mm). Experiments showed that both types of modules exhibit an increase in open circuit output voltage with strain, but the piezoelectric material fails at severe strain. In addition, it was confirmed that the proposed module design can keep the output voltage constant by controlling the strain, which allows investigation into the relationship between frequency and output power. Thus, at constant strain, the matching impedance was found to be low at high frequency. Therefore, optimum conditions for harvesting maximum power are high frequency and the largest strain that does not damage the piezoelectric material.