Two-degree-of-freedom velocity-amplified vibrational energy harvester for human motion applications

Conventional vibrational energy harvesters (VEHs) are generally based on a linear mass-spring oscillator model that features narrow bandwidth and high resonant frequencies at small scales. To overcome these limitations, a two-degree-of-freedom (2-Dof) velocity-amplified VEH was developed. The harvester comprises two masses, relatively oscillating one inside the other, between four sets of magnetic springs. Impacts between the two masses are allowed, and momentum is transferred from the larger outer mass to the smaller inner mass, thereby providing velocity amplification. Electromagnetic transduction was chosen because it can be easily implemented in a velocity-amplified VEH. The harvester was tested with harmonic excitation of different amplitudes and two peaks of similar heights were observed at a_rms = 0.6 g, resulting in a −3 dB bandwidth of 10 Hz. The VEH was also tested under human motion and at a running speed of 10 km/h the harvester generated P = 0.44 mW, a power level that could be accumulated in a storage medium over time and used for powering wireless sensor nodes.