Herein, a piezoelectric vibration energy harvester (PVEH) using liquid as an energy-capturing medium is proposed to simultaneously achieve ultralow frequency, low intensity, and multidirectional vibration energy harvesting in a horizontal plane, which is difficult to realize using traditional PVEHs. The proposed harvester comprises a cylindrical container with a certain liquid, a piezoelectric cantilever beam, ropes, and floater-lever arrays. The experimental results indicate that the proposed harvester with a single floater-lever can generate 9.8 μW under an ultralow frequency (2.6  Hz) and a low intensity vibration excitation (0.03 g), and the normalized power density is 8.89 μW/(cm3 g2 Hz). Under a multidirectional vibration excitation (360° in the horizontal plane) with frequencies below 3  Hz and an acceleration of 0.03 g, the two proposed harvesters with three and four floater-levers indicate a maximum output power (Pmax) deviation of 24.92% and 28.31%, respectively, and an angle bandwidth of 360° (using 2/2Pmax as the standard). All the experimental results indicate that the proposed PVEH is highly promising as an energy supply of wireless sensor networks distributed in ultralow frequency, low intensity, and multidirectional applications.

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In the past two decades, piezoelectric vibration energy harvesters (PVEHs) have attracted considerable attention as an effective technology for replacing the batteries in self-power wireless sensor networks. However, because of the low Curie temperature limitations of piezoelectric materials, conventional PVEHs can only be used in low-temperature environments. In this paper, we report a PVEH for high temperature (HT) applications using Ca3TaGa3Si2O14 piezoelectric crystals. We investigated how the electromechanical performance of the device varied with temperature, from room temperature (RT) to 800 °C. Our research showed that the HT PVEH produced a steady output under a constant mechanical excitation. Furthermore, we found that the optimal output power at 350 °C was approximately four times higher than that at RT (25 °C). The results demonstrate that the proposed PVEH has great potential for applications as a self-power source in high temperature wireless sensors.

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