Abstract
Wireless sensors are vital for real-time condition monitoring of rotating machinery. Traditionally, these sensors depend on batteries, a solution that is neither eco-friendly nor cost-effective due to high maintenance. Vibration energy harvesting has emerged as a promising alternative for powering these sensors. Nevertheless, current energy harvesters commonly disregard high-frequency energy, which is weak but contains abundant condition-monitoring information. Moreover, the destructive interference between multiple vibration sources further attenuates the high-frequency energy. To address these limitations, this paper proposed a novel energy harvesting method based on a symmetrical gradient metamaterial beam (SGMB). The SGMB structure is designed to have multiple bands to enhance the high-frequency energy and diminish the destructive interference of flexural waves from two vibration sources. Multiple piezoelectric patches are integrated into SGMB to convert the dynamic stress into harvestable electrical power, enabling multi-band dual-source energy harvesting. Based on the rainbow trapping mechanism, the SGMB was first designed and optimized for desired frequency bands. Subsequently, the band characteristics and piezoelectric output performance were adjusted and validated through finite element simulation. Finally, experimental evaluations were conducted to validate the performance of the designed metamaterial. The results demonstrate that the SGMB provides multiple enhanced bands within the range from 1000 Hz to 3500 Hz and improves the energy harvesting efficiency by a factor over 100, which represents a breakthrough in developing self-powered and self-sensing wireless sensors.