A Multiple-Degree-of-Freedom Velocity-Amplified Vibrational Energy Harvester: Part A — Experimental Analysis

Abstract

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 Lab VIEW 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.

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“…In this area, researchers are looking at both thermoelectric as well as mechanical energy harvesting techniques. An example of the latter is the research in [87] and [88], based on vibration energy harvesting techniques for powering wireless sensors and small cell infrastructure. Moreover, an issue with all ambient environment energy sources, to varying degrees, is their intermittent nature.…”

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“…Sharma et al [19] study the influence of the cross-section of the dynamic magnifier on energy harvesting. O'Donoghue et al [20] and Nico et al [21], [22] propose and investigate an innovative multi-degree of freedom velocity amplified harvester.…”

A high figure of merit vibrational energy harvester for low frequency applications

“…The collisions between the two masses exploit velocity amplification, which is highly advantageous for electromagnetic energy harvesting. 4,6,8,9 The choice of cap height (H) can modify the spectral behavior of the device, as this varies the distance between the opposing magnets that FIG. 1.…”

“…The collisions between the two masses exploit velocity amplification, which is highly advantageous for electromagnetic energy harvesting. 4,6,8,9 The choice of cap height (H) can modify the spectral behavior of the device, as this varies the distance between the opposing magnets that form the outer magnetic springs. The presence of magnetic springs leads to strong nonlinear behavior, which is highly valuable for energy harvesting, as it allows the bandwidth to be increased and enables low resonant frequencies to be achieved with reduced volume penalty compared to what is achievable with mechanical springs.…”

“…These configurations have been shown to naturally enhance the frequency response and power generated in VEHs due to the nonlinear effects introduced by impacts within the device, which enable momentum transfer between masses. [3][4][5][6][7][8] To enable effective operation at the low frequencies typical of human motion applications (typically under 5 Hz), a nonlinear contribution to the system dynamics of the device described in this paper was added through the use of magnetic springs. Such an approach results in an efficient but small-scale VEH device that couples the high power and wide frequency response of the velocity amplified VEHs but enables operation at low frequencies and leads to high volumetric This paper outlines a design methodology to electrically optimize the harvester.…”