Low-Frequency Broadband Piezoelectric Vibration Energy Harvester Based on Double L-shaped Beam Structures

Background Wireless sensor networks (WSNs) have found increasing applications and call for more reliable and environmentally friendly power supply. Piezoelectric vibration energy harvesters, with high conversion efficiency and relatively simple structure, have been a promising choice for sensor-powering applications. Tremendous efforts are made to enhance the output performances of piezoelectric vibration energy harvesters. Nevertheless, gaps are still present and to be bridged before piezoelectric vibration energy harvesters can be practically implemented. A major concern is the working bandwidth of these devices. Purpose The current study focuses on the structural approach to improve the performances of piezoelectric vibration energy harvesters. With the aim to achieve a higher peak output voltage, efforts are made to improve the low-frequency response of the device. Methods A new design of piezoelectric energy harvester is proposed based on double L-shaped beam structures (DL-PVEH) added to a primary cantilever beam. In the low range of operation frequency, finite element analysis is conducted to find out the involved vibration modes of the proposed piezoelectric energy harvester. Influences of structural parameters upon output performances are further systematically investigated. Prototypes are then built and tested with the constructed test rig. Results The proposed design is suitable for low-frequency range applications with its third-order resonant frequency under 10 Hz. Given an amplitude of base excitation acceleration of 0.015g, the RMS output voltage of the proposed device reaches as much as 5.5 V, with an optimal average power output of 0.2 mW. Its RMS output voltage and output average power per unit acceleration are 366.7 V/g and 13.3 mW/g, respectively. Conclusion The length of the horizontal sub-beam is a more effective parameter to adjust the natural frequency of DL-PVEH, compared with the effect of length of the main bimorph beam. In addition, the proposed vibration energy harvester shows good output performance under the excitation of ultra-low acceleration.