Design and prototyping of an electromagnetic mems energy harvester for low frequency vibrations

Türkyılmaz, Serol
This thesis study presents the design, simulation, and fabrication of a low frequency electromagnetic micro power generator. This power generator can effectively harvest energy from low frequency external vibrations (1-100 Hz). The main objective of the study is to increase the efficiency of the previously proposed structure in METU-MEMS Center, which uses the frequency up-conversion technique to harvest energy from low frequency vibration. The proposed structure has been demonstrated by constructing several macro scale prototypes. In one of the constucted prototypes, the diaphragms are connected to a fixed frame via metal springs. The upper diaphragm having lower resonance frequency carries a magnet, and the lower diaphragm carries a hand wound coil and a magnetic piece for converting 6 Hz external vibrations up to 85 Hz, resulting a maximum voltage and power levels of 11.1 mV and 5.1 µW, respectively. In an improved prototype, the metal springs are replaced with rubber ones, providing higher energy conversion efficiency and flexibility to tune the resonance frequency of both diaphragms to desired values. This prototype provides 104 µW maximum power and 37.7 mV maximum voltage in response to vibration levels of 30 Hz. The proposed structure is also suitable to be realized by using microfabrication techniques. Hence, the structure to be microfabricated is studied and optimized for this purpose. When scaled to microelectromechanical dimensions, the expected maximum power and voltage from the 10 x 8.5 x 2.5 mm3 generator is 119 nW and 15.2 mV, respectively. A microfabrication process has also been designed for the proposed generator structure. According to this process, the structure consists of a stack of two pieces, each carrying different diaphragms. The diaphragms are made of parylene, and the coil and the magnetic piece are electroplated copper and nickel, respectively. As a result of this study, a new topology is proposed for harvesting energy at low frequency vibrations by the frequency up-conversion technique, and an efficiency improvement is expected with more than three orders of magnitude (119 nanoWatts output for the same size) compared to the study realized in our laboratory in converting low frequency (70-150 Hz) environmental vibrations to electrical energy.


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Citation Formats
S. Türkyılmaz, “Design and prototyping of an electromagnetic mems energy harvester for low frequency vibrations,” M.S. - Master of Science, Middle East Technical University, 2011.