A bistable rotary-translational energy harvester from ultra-low-frequency motions for self-powered wireless sensing

This paper presents the design, theoretical modelling and experimental study of a bi-stable energy harvester (EH) using rotary-translation motion for ultra-low frequency and low excitation amplitude energy sources. A spherical magnet is adopted to produce the rotary-translational motion to convert ultralow-frequency kinetic energy into electricity over a wide frequency range. The bi-stable mechanism is realized by introducing two tethering magnets underneath the sphere magnet’s oscillating path, significantly enhancing the operating range of the harvester. A theoretical model including the impact dynamics, magnetic interaction and electromagnetic conversion has been established to explore the electromechanical behaviours of the harvester under different operating conditions. The results illustrate that the EH operates in intra-well or inter-well motion depending on whether the input excitation is adequate to conquer the potential barrier depth. A prototype is developed to illustrate the design and to validate the theoretical model. The prototype generates sufficient power (mW) at frequencies lower than 2 Hz with excitation amplitudes as low as 0.1 g. A peak output power of 9 mW (1.53 mW RMS) is obtained at 2 Hz and 0.7 g with 750 Ω external load. The developed EH is integrated with an off-the-shelf power management solution to power a wireless sensing system to successfully record real-time temperature variation in the environment.