Micromachined Energy-Harvester Stack With Enhanced Electromagnetic Induction Through Vertical Integration of Magnets

This paper presents a stacked microfabricated power generator that vertically integrates multiple magnets on silicon wafers in a batch process to enhance electromagnetic induction multiple times. The power output is increased by increasing the magnetic flux change for each power-generator unit in the stack, in addition to the increase due to increased number of units. A stack consisting of two arrays of four power-generator units is fabricated and characterized. Wax-bonded Nd-Fe-B powders are embedded in the silicon wafer and magnetized as an integrated micromagnet, which serves as a proof mass suspended by a parylene diaphragm. Dual-layer coils are isolated by a parylene layer, connected via a hole and fabricated with electroplating copper on the same wafer. Experimental results show an improvement by about a factor of four on the power output from the same coils when two power-generator arrays are stacked vertically. In particular, an array of four microfabricated power generators occupying a volume of 51 x 11 x 0.4 mm(3) in the stack produces an induced electromotive force of 1.02 mV with 0.55 nW power output when it is vibrated at 400 Hz with vibration amplitude of 10 mu m.