This paper reports a hula-hooping-like nonlinear buckled elastic string electromagnetic energy harvester for wideband vibration energy harvesting. The harvester is comprised of a magnetic rotor attached at the middle of a clamped-clamped buckled elastic string and a stator with an embedding coil array. Attributed to the geometric nonlinear characteristic of the elastic string, the harvester can convert the reciprocate vibration in arbitrary in-plane direction to a hula-hooping-like curvilinear translation plane motion. A hardening nonlinear wideband voltage response was demonstrated by sweep excitation from 5 ∼ 23 Hz. The output peak power for a single coil can reach 1.12 mW at a 5 ms −2 excitation. To overcome the phase delay effects between the voltages of three spatially distributed coils, they were rectified separately and connected serially or parallelly to provide the final output. An open circuit peak voltage of 0.53 V was obtained from the serial connection at a 4 ms −2 up-sweep excitation, under which a 100 µF capacitor was successfully charged to 0.35 V within 120 s. The omnidirectional energy scavenging performance of the harvester was further validated experimentally, suggesting its great promise for practical vibration energy harvesting.

This letter originally presents a magnetically coupled nonlinear T-shaped piezoelectric energy harvester with multiple resonance bands based on internal resonance principle. The proposed harvester consists of a clamped-clamped buckled beam and a vertical cantilever with tip magnetically coupled. The corresponding theoretical model is established. Two resonance bands with hardening nonlinear phenomenon are obtained. 1:2:3:4 internal resonance characteristics with the peak amplitude ratio of 1:1.81:0.56:0.31 are found for the generated voltage of the first resonance. The energy conversion efficiency can be enhanced by utilizing high frequency response under low-frequency excitations. The bandwidth of full width at half maximum output power reaches 13.8 Hz within the excitation between 5∼30 Hz. The response of random excitations is also investigated and an average power of 9.64 μW is achieved at the random excitation intensity of 0.001 g 2 Hz −1 . Overall, the proposed harvester can achieve ultra-wide working frequency range under low-level excitations and is suitable for low-frequency random vibrations.