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This paper presents a new vibration-based electromagnetic energy harvester using a mechanical frequency up-conversion method for harvesting energy from external low-frequency vibrations within a range of 1-10 Hz. The structure consists of a magnet placed on a diaphragm, a polystyrene cantilever carrying a pick-up coil, and a mechanical barrier which converts low-frequency vibrations to a higher frequency, hence increasing the efficiency of the system. The tested structure proved to generate 88.6 mV and 544.7 μW rms power output by up-converting 10-Hz external vibration to 394 Hz. The obtained power density is 184 μW/cm3, with a device volume of 2.96 cm3. An analytical model is developed to analyze the behavior of the energy harvester prototypes with various dimensions. The model predicts the performance parameters of the structures within 5% error range. The effect of scaling down the device dimensions is investigated through the developed model and fabricated prototypes. It is shown that the power density of the energy harvester is increased as its dimensions are scaled down, proving that the proposed structure is a good candidate to be used in low-power wireless microsystems operating at low-frequency vibrations.
Date of Publication: Feb. 2011