Investigation of internal resonance on widening the bandwidth of energy harvester based on a cantilevered double pendulum structure

With the development of small-scale electronic elements and wireless sensor networks, energy harvesting technologies have attracted much attention because they can offer environment-friendly, long-lifetime, and no replacement requirements. However, energy harvesting techniques for collecting ultralow frequency vibrations remain a challenge because of the ultralow frequency, low excitation amplitude, and non-continuous vibrations. This study proposes an ultralow frequency broadband energy harvester based on a double-pendulum structure and cantilevered beam, which utilizes the internal resonance to widen the bandwidth of the energy harvester. The double pendulum oscillator with appropriate parameters can yield two resonance frequencies in an ultralow frequency band (from 1 to 5 Hz). The cantilevered beam can achieve 1:2 internal resonance with the double pendulum oscillator in the second resonance frequency of the double pendulum oscillator. The experiment result shows that the internal resonance vibration piezoelectric energy harvester based on a double-pendulum structure can obtain a bandwidth of 4.4 Hz under 0.4 g excitation.