A MEMS-based energy harvester for generating energy from non-resonant environmental vibrations

This paper presents a non-resonant vibration based electromagnetic MEMS energy harvester, which generates energy from low frequency vibrations with low displacement amplitude. The harvester is composed of an energy harvester chip, housing two electroplated copper micro coils realized on parylene cantilevers and a miniature NdFeB magnet with two mechanical barrier arms. The structure uses the mechanical frequency up conversion (mFupC) principle for energy generation. The non-resonant operation is maintained by attaching the chip and the magnet to two different platforms, which move with respect to each other. The prototype generates 2.1 mV RMS voltage and 18.5 nW RMS power from both coils on the average, under 10 Hz, 5 mm peak to peak (1 g) external vibrations. The RMS value of the generated voltage during the mFupC duration is calculated as 9.5 mV, leading to 363 nW power and 1.1 mu J energy delivery from each coil to equivalent resistive loads at each occurrence of the mFupC. Serial connection of the coils is also studied and it is concluded that this configuration has a non-significant effect on the generated power since the waveforms of the coil voltages have both phase and resonance frequency differences, canceling out some portion of the signal when they are added together. During the tests, it is observed that excessive stress around the cantilever fixed edges eventually break the coil lines at this region. This is handled by applying an epoxy to this region, lowering the stress on the copper line. With this configuration, the generated power is slightly reduced due to the decreased resonance frequency and increased damping ratio of the cantilevers. The epoxy-applied prototype has been tested under various vibration conditions with no damage on the coil, and the non-resonant operation behavior of the energy harvester has been verified. (C) 2013 Elsevier B.V. All rights reserved.