Performance comparison of electromagnetic energy harvesters based on magnet arrays of alternating polarity and configuration

Abstract

Electromagnetic energy harvesters have been studied intensively in the past decade as non-stop power solutions for low-power wireless electronic devices. We here exploit a new way, i.e., forming an abrupt change of magnetic flux density, to improve harvester performance. A new transducer is proposed, which is primarily composed of a set of magnet array, a pair of springs and a coil array. Four cases are investigated: cubic magnets in Halbach and alternative configurations; triangle magnets in Halbach and alternative configurations. We examined the magnetic flux density distribution via the finite element method (FEM) and ensured the nonexistence of phase difference in two contiguous coils. We fabricated a prototype and conducted comprehensive tests, of frequency sweep with and without external resistances, of matching impedance and of obtaining maximum RMS power output. The FEM analysis indicates that the harvester in the cubic alternative case has the largest changing rate of the magnetic flux density (MFD) in terms of the magnitude and the distance range of the change. Experiments verify the FEM simulation and the prototype with the cubic alternative magnet array shows the highest voltage response of 20 V and a maximum RMS power output of 35.5 mW under a harmonic excitation of 9.8 m/s2, which is much higher than those in the other cases. In term of the volume and mass power density, the alternative arrangement of cubic magnets displays the most desirable outputs at 0.4955 mW/cm3 and 0.28 mW/g, respectively, which are three and two times as high as those of the second best case - the triangle Halbach case. This detailed study reveals the considerable benefits brought by the magnet arrays of alternating polarity and configuration, and paves a new way to improve the performance of electromagnetic energy harvesters.