Investigation of an ultra-low frequency piezoelectric energy harvester with high frequency up-conversion factor caused by internal resonance mechanism

The collection of ultra-low frequency mechanical energy that distributed in ambient environments remains challenging so far. This paper presents a frequency up-converting energy harvester based on a component pendulum, a pair of magnetic coupled cantilever beams, and two mechanical stoppers. The pendulum-like oscillator with ultra-low natural frequency can efficiently capture ambient mechanical energy and the designed 1:2:6 internal resonance mechanism can upconvert the frequency with a high conversion factor, presenting great potential for application in real-world systems with low vibration frequencies in the range of 1 to 5 Hz. Modeling and design are conducted, theoretical dynamic predictions are given and confirmed by experimental results. The proposed frequency up-converting harvester could generate a relatively high output power (about 2 mW) at a low excitation frequency and amplitude (around 2 Hz and 0.37 g). Moreover, the electromechanical coupling coefficient of the harvester can be further optimized, increasing the above-mentioned output power directly.