A micro electromagnetic low level vibration energy harvester based on MEMS technology

Abstract

This paper presents a micro electromagnetic energy harvester which can convert low level vibration energy to electrical power. It mainly consists of an electroplated copper planar spring, a permanent magnet and a copper planar coil with high aspect ratio. Mechanical simulation shows that the natural frequency of the magnetspring system is 94.5 Hz. The resonant vibration amplitude of the magnet is 259.1 lm when the input vibration amplitude is 14 lm and the magnet-spring system is at resonance. Electromagnetic simulation shows that the linewidth and the turns of the coil influence the induced voltage greatly. The optimized electromagnetic vibration energy harvester can generate 0.7 lW of maximal output power with peak-peak voltage of 42.6 mV in an input vibration frequency of 94.5 Hz and input acceleration of 4.94 m/s 2 (this vibration is a kind of low level ambient vibration). A prototype (not optimized) has been fabricated using MEMS micromachining technology. The testing results show that the prototype can generate induced voltage (peak-peak) of 18 mV and output power of 0.61 lW for 14.9 m/s 2 external acceleration at its resonant frequency of 55 Hz (this vibration is not in a low ambient vibration level).

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“…Operation principle of an electrostatic energy harvester is quite similar to storing electrons in a capacitor except that the capacitance is changed in vibration-dependent varactors, commonly known as variable capacitor, due to coupled external mechanical motions (8) . Electromagnetic energy harvesters (9)- (10) simply adopt Faraday's law while piezoelectric energy harvesters use piezoelectric effect (11)- (16) to transform mechanical motions into electricity. To obtain optimal electric energy output, both electromagnetic and piezoelectric energy harvesters need to operate at or close to their mechanical resonant modes.…”

Design and Fabrication of Low Frequency Driven Energy Harvester Using Electromagnetic Conversion

“…Therefore, the power can be determined as (8) By replacing z(t) with its equivalent equation, the equation of power yields the following (9) The energy transferred during one complete cycle of vibration is (10) where, (11) and (12) Combining equations 10, 11, and 12, the total energy during one cycle can be achieved as (13) The average power can be estimated by (14) Taking total energy into consideration, average power can also be expressed as (15) Incorporating the vibration amplitude of the mass into equation 15 gives the average power delivered to the electrical do- …”

“…CNC machines can be used continuously 24 hours a day and are programmed with a design which can then be manufactured hundreds or even thousands of times. Each manufactured product will be exactly the same, thus itsaves time and cost compared with semiconductor and laser processing [9,10]. The permanent magnets are attached to the center of the spring which is 1 mm width, 200 μm thickness, and has a 1 mm gap.…”

Magnetic Nanocomposite Cilia Energy Harvester

“…However, due to difficulty in fabricating the coils and incorporating a micro-scale permanent magnet, the miniaturization of electromagnetic harvesters has proven to be quite challenging. In most micro-scale electromagnetic energy harvesters, a discrete permanent magnet, affixed after the microfabrication process serves as the flux source [5], [6]. This solution is hardly elegant and does not lend itself to easy batch manufacturing.…”