A MULTIPLE-DEGREE-OF-FREEDOM VELOCITY-AMPLIFIED VIBRATIONAL ENERGY HARVESTER: PART A, EXPERIMENTAL ANALYSIS
Vibrational energy harvesters (VEHs) are devices which convert ambient vibrational energy into electrical power, offering an alternative to batteries for powering wireless sensors. Detailed experimental characterisation of a 2-degree-of-freedom (2-dof) VEH is presented in Part A of this paper, while a theoretical analysis is completed in Part B. This design employs velocity amplification to enhance the power harvested from ambient vibrations, while also seeking to increase the bandwidth over which power can be harvested. Velocity amplification is achieved through sequential collisions between free-moving masses. Electromagnetic induction was chosen as the transduction mechanism as it can be readily implemented in a velocity amplified system, although other transduction mechanisms can also be used. The VEH prototype was tested experimentally under both sinusoidal excitation and exponentially correlated Gaussian noise, with different VEH geometries. The maximum power generated under a sinusoidal excitation of arms = 0.6 g was 12.95 mW for a resistive load of 13.5 Ω at 12 Hz, while the maximum power under exponentially correlated Gaussian noise with σ = 0.8 grms, autocorrelation time τ = 0.01s and resistive load 13.5 Ω was 5.3 mW. Maximum bandwidths of 54% and 66%, relative to the central frequency, were achieved under sinusoidal and noise excitation, respectively. The device shows resonant peaks at approximately 15 and 30 Hz, while significant power is also generated in the 17-20 Hz range due to non-linear effects. The VEH component dynamics were analysed using a laser Doppler vibrometer (LDV), while LabVIEW was used to control the electromagnetic shaker, read the LDV signal and record the VEH output voltage. The aim of this investigation is to achieve a more complete understanding of the dynamics of velocity-amplified systems to aid the optimization of velocity amplified VEH designs.