Characterization of single-crystal macro-fiber composite-based piezoelectric energy harvesters in various temperature and humidity environments

Single-crystal macro-fiber composite (SFC)-based piezoelectric energy harvesters (PEHs) have garnered significant interest for use in self-powered low-power-consumption devices. The outdoor deployment of PEHs subjects SFCs to a wide range of temperatures and humidities, which affects their electrical and mechanical properties and thus their output power efficiency. In this study, the energy-harvesting performance of undoped and 1 mol.% Mn-doped PMN-PZT SFC-based PEHs was investigated by varying the temperatures from −20 to 70 °C and the relative humidity (RH) from 10 to 90% under different base acceleration conditions. Both PEHs showed a gradual decrease in resonance frequency and optimum load resistance with increasing temperature, whereas the root mean square (RMS) power (P_rms) was strongly composition-dependent. In particular, the P_rms of the undoped SFC-based PEH displayed an inverse relationship with the climatic temperature, whereas the Mn-doped SFC-based PEH showed a peak P_rms at 40 °C. In addition, the overall P_rms loss concerning the optimal temperature for undoped and Mn-doped samples in the measured temperature range was 50% and 18%, respectively. These different characteristics according to the temperature environment could be owing to the different structural transition behaviors (i.e., Curie temperatures) of the piezoelectric single-crystal fibers. Short-term humidity exposure had a negligible effect on the energy-harvesting efficacy of the PEHs at room temperature (25 °C); however, the efficacy was slightly influenced under harsh conditions (50 °C and >60% RH). This study provides an environmental reliability evaluation of SFC-based PEHs for future practical use.