Microfabricated Electromagnetic Energy Harvesters With Magnet and Coil Arrays Suspended by Silicon Springs

This paper presents two microfabricated electromagnetic energy harvesters (one with coil proof mass and the other with magnet proof mass) suspended by silicon springs on a silicon wafer. The fabrication steps are based on a planar batch process (similar to the process used for integrated circuits), and are ideally suited for mass production of energy harvesters. Rapid spatial variations of magnetic field are produced by a magnet array, and are coupled and aligned to an array of multiple-turn spiral coils (made of electroplated copper on a silicon) for maximum magnetic flux change. The narrow gap between the magnet and coil arrays is precisely controlled by silicon etching technique. Experimental results show that the energy harvester with a coil proof mass generates an induced electromotive force (EMF) of V
_p-p
= 18.2 mV with 0.75 μW power output (into 13.8 Ω load) when it is vibrated at 410 Hz with vibration amplitude of 6.7 μm (corresponding to 4.5 g acceleration). Another energy harvester with a magnet proof mass generates an EMF of V
_p-p
= 16.8 mV with 0.82 μW power output (into 10.8 Ω load) when it is vibrated at 350 Hz with vibration amplitude of 9.1 μm (corresponding to 4.5 g acceleration).