A Comparison of Two Planar Electromagnetic Vibrational Energy Harvesters Designs

Electromagnetic vibrational energy harvesters (EM-VEHs) are generally used to convert ambient vibrations into electricity to energise low-power sensor nodes forming the Internet of Things (IoT). Usually such VEHs comprise of coils and magnets orientated in the vertical direction (z-direction) but these devices tend to be quite bulky and it is hard to integrate them into printed circuit board technology. Configuring coils and magnets in a planar arrangement can lead to a more compact device and to better integration. Two planar EM-VEHs with different coil-magnet arrangements are presented in this paper. Both EM-VEHs (referred as Design 1 and Design 2) employed the same stack of five magnets in Halbach arrangement, magnetic springs and same housing. In Design 1 the stack oscillated below four coils, while in Design 2 four coils were wrapped around the housing and the stack oscillated through them. Harmonic excitation was used to experimentally compare the two prototypes and it was found that Design 2 could generate significant higher output power than Desing 1 (percentage increase ranging from 8292% at a_rms = 0.2g to 559% at a_rms = 0.6g).