Experimental Investigation of Coil Thickness in Electromagnetic Energy Harvesters for Power Density Improvement

In this paper, the effects of the coil thickness on output voltage and power of the electromagnetic energy harvesters are investigated. A configuration which is mainly comprised of two coil arrays, a pair of restoration springs and a magnet array is designed. The coil arrays are symmetrically distributed on both sides of the magnet array. Ten kinds of coil thicknesses are selected to examine how they influence the electric responses. Based on a series of fabricated prototypes, four experimental studies from the following aspects for comparison purposes: frequency sweep, constant frequency, impedance matching and charging capacitors are conducted. The results show that the resonant frequency of the prototypes is 20 Hz, well agreeing with the theoretical one of 19.7 Hz. The case of h = 5.7 mm (h is coil thickness) reaches the maximum voltage (26.61 V) at the excitation of 1.0 g, 20 Hz. The maximum peak-to-peak power (312.05 mW) and the power density (2.56 mW/cm³) come from the case of h = 4.7 mm at the excitation of 1.0 g, 20 Hz. The case of h = 4.7 mm displays the best charging performance for the capacitor of 220 μF. It is also one of the best cases regarding the charging rates for 680 µF, 1000 µF, 2200 µF and 6800 µF capacitors.