Autonomous Resonance-Tuning Energy Harvesters Based on Adaptive Clamping Systems

Vibration energy harvesters typically exhibit narrowband natural frequencies, which causes a frequency mismatch problem between the harvester and the ambient vibration sources for mechanical resonance. Previous attempts to design energy harvesters with broadband response have encountered practical problems in terms of low output power, small improvements in bandwidth, resonance instability, and excessive energy consumption for tuning. Here, we report an innovative self-resonance tuning (SRT) energy harvester utilizing an adaptive clamping system driven by intrinsic mechanical mechanisms without additional energy outsourcing. The adaptive clamping system serves to modulate the natural frequency of the harvester main beam (MB) by adjusting the clamping position of MB. The pulling force induced by the large resonance vibration of the tuning beam (TB) provides the driving force to move the adaptive clamp and clamp MB for tuning. The SRT mechanism is possible via matching the natural frequencies of TB and clamping position modulated MB. The SRT bandwidth significantly increased by employing a number of adaptive clamps. Detailed investigations were conducted on optimization of the adaptive clamp tolerance, TB design to increase pulling force, and the connected load impedance matching. The energy harvester exhibited an ultra-wide resonance bandwidth of over 30 Hz owing to SRT function. The adaptive clamping system had a fast tuning time of 1 sec at 1.5 g acceleration. The practical feasibility was demonstrated by evaluating the SRT performance on an automobile engine with frequency variant conditions. The SRT energy harvester will open the avenue for the commercialization of vibration energy harvesters by eliminating the burden of frequency tuning.