Innovative electromagnetic vibration energy harvester with free-rotating mass for passive resonant frequency tuning

Vibration energy harvesters (VEHs) can be used to power wireless electronic devices by converting mechanical energy into electrical energy. However, these harvesters are generally resonant structures with narrow bandwidth, posing challenges with respect to the operating frequency range. This paper presents a novel electromagnetic VEH with a structure that passively tunes its resonant frequency. The proposed design is primarily composed of a flat spring and a freely rotating mass. The design was simulated and tested experimentally. Tests showed that the mass can rotate towards the resonant position, dynamically changing the resonant frequency of the structure, to match the vibration frequency. The VEH demonstrated a resonant frequency range of 10 Hz, from 60 to 70 Hz, and when compared to the same structure with a fixed mass, it showed a 90 % improvement in bandwidth, from 12 to 22 Hz. These results show that passive resonant frequency tuning can significantly improve the operating frequency range of VEHs for practical use. The normalized power density of the VEH was 1.64 kgs/m 3 in vibrations of 60 Hz and 1 g, demonstrating that it is capable of powering wireless electronics. • First passive tuning of resonant frequency in an electromagnetic vibration harvester with a free-rotating mass. • A passive resonant frequency range of 10 Hz is demonstrated. • The bandwidth is improved by 300 %, from 5 Hz to 20 Hz, when compared to a fixed mass. • A normalized power density of 1.64 kgs/m 3 is demonstrated in 60 Hz and 1 g vibrations.