Energy harvesting is a relatively new research area that extracts energy from the surroundings to power autonomous systems. This project presents a generator that harnesses the motion of high speed rotational motors for machine health monitoring. Wireless accelerometer-based sensors for detecting crack initiation on rotating shafts are typically limited by the battery finite lifetime. Miniature generators attached to rotating shafts can scavenge small amounts of energy for powering such monitoring systems. Electromagnetic induction approaches (using coils and magnets) have been widely described in literature for larger machines but few at the micro-scale. This paper investigates a multiple-pole permanent magnet design with multiple-stacks of planar coils for energy generation without using Silicon-based processing at the micro-scale. Planar coils are manufactured from 18μm thick Copper-clad on 25μm thick polyimide. The 25mm diameter coils were stacked and bonded with cyanoacrylate for a stacked thickness of 360μm. The rotor was made of a 25mm in diameter (2mm thick) CNC machined PMMA disk with 20 slots (1mm×2mm×6mm) for placing commercial NdFeB permanent magnets. The entire generator had a volume smaller than 1.5cm3. Experimental results show that the generator is capable of producing an average voltage output of 15.5V and 727mW of power (with a matching load) at a constant rotational speed of 29,500rpm.

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