Achieve frequency-self-tracking energy harvesting using a passively adaptive cantilever beam

Abstract The frequency of the vibration in the ambient environment varies frequently, which imposes a great challenge for robust energy harvesting. To maintain the high performance of harvesting the variant-frequency vibration, one efficient means is to make the energy harvester track the excitation frequency by itself. To obtain a frequency-self-tracking (FST) energy harvester, an interesting system, e.g., the passively self-adaptive structure, has attracted a lot of attention recently. Though passively self-adaptive systems designed based on symmetric structures have been considerably reported, the passive self-adaptation of asymmetric structures is still an open question to be explored. To this end, this paper investigates the dynamics of a cantilever beam with a sliding mass. Experimental results indicate that the passively self-adaptive behavior occurs in the second eigenmode rather than the fundamental eigenmode, which is essentially different from the symmetric structures reported in the existing literature. The proposed FST system can self-adjust its natural frequency to match the excitation frequency and achieve large response without any external manual intervention, showing a promising potential to attain high-efficient energy harvesting from variant-frequency vibration. Therefore, this novel passive self-adaptation behavior is employed for piezoelectric energy harvesting. By introducing a piezoelectric transducer, an FST vibration energy harvester (VEH) is achieved. Owing to the passive self-adaptation capability, the proposed FST-VEH exhibits a significantly enhanced energy harvesting performance over a wide range of frequency and an increase of the output voltage amplitude for more than 800%. In general, the proposed FST-VEH demonstrates a great potential to make a significant breakthrough in harvesting variant-frequency vibration energy.