Multi-mode vibration based electromagnetic type micro power generator for structural health monitoring of bridges

This article presents the development of multi-mode vibration based electromagnetic type micro power generator (MPG). Along the stainless steel planar spring (SPS) and magnet assembly, a movable coil (MC) is a novel addition to the resonant frequencies of the device. The design with MCs on either side of the magnet provide higher power generation for the same footprint of the device at multiple modes. Computer numerical control (CNC) milling machine, wire-cut electric discharge machine (EDM) and 3D printer are used to fabricate the MCs, SPS and spacers respectively to yield a MPG with an overall volume of 29.03 cm3. The developed MPG is characterized to generate power at four different resonant frequencies below 100 Hz. At 3rd mode (82 Hz) the developed MPG is able to produce a maximum 33 mV open circuit voltage, 14.5 mV load voltage and a power of 68.4 μW. Furthermore, the present development and experimentation of the MPG with a yielded power density of 2.35 μW/cm3 at 2 g acceleration can be regarded as guidelines for multi-mode devices.