A high Figure of Merit vibrational energy harvester for low frequency applications

Small-scale vibration energy harvesters that respond efficiently at low frequencies are challenging to realise. This paper describes the design and implementation of one such harvester, which achieves a high volumetric Figure of Merit (FoM_v = 2.6%} at 11.50 Hz) at the scale of a C-type battery and outperforms other state-of-the-art devices in the sub 20 Hz frequency range. The device employs a 2 Degree-of-Freedom (2DoF) velocity-amplified approach and electromagnetic transduction. The harvester comprises two masses oscillating one inside the other, between four sets of magnetic springs. Collisions between the two masses transfer momentum from the heavier to the lighter mass, exploiting velocity amplification. The paper first presents guidelines for designing and optimizing the transduction mechanism, before a nonlinear numerical model for the system dynamics is developed. Experimental characterisation of the harvester design is then presented to validate both the transducer optimization and the dynamics model. The resulting high volumetric figure of merit demonstrates the effectiveness of the device for low frequencies applications, such as human motion.