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27 March 2012 Electromagnetic vibration energy harvesting with high power density using a magnet array
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Electromagnetic vibration energy harvesters have been widely used to convert the vibration energy into electricity. However, one of the main challenges of using electromagnetic vibration energy harvesters is that they are usually in very large size with low power density. In this paper, a new type of electromagnetic vibration energy harvester with remarkably high power density is developed. By putting the strong rare-earth magnets in alternating directions and using high-magnetic-conductive casing, magnetic flux density up to 0.9T are obtained. This configuration also has a small current loop with less electrical reluctance, which further increases the high power density when the coil is designed to follow the current loop. The prototype, the size of which is 142x140x86 mm3, can provided up to 727Ns/m damping coefficient, which means 428 kNs/m4 damping density when it is shunt with 70Ω external resistive load which is set to the same as the internal resistor of the harvester to achieve maximum power. The corresponding power density is 725 μW/cm3 at 15HZ harmonic force excitation of 2.54mm peak-to-peak amplitude. When shot-circuited, 1091Ns/m damping coefficient and 638 kNs/m4 damping density is achieved. The effectiveness of this novel vibration energy harvester is shown both by FEA and experiments. The eddy current damper is also discussed in this paper for comparison. The proposed configuration of the magnet array can also be extended for both micro-scale and large-scale energy harvesting applications, such as vibration energy harvesting from tall buildings, long bridges and railways.
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Xiudong Tang, Teng Lin, and Lei Zuo "Electromagnetic vibration energy harvesting with high power density using a magnet array", Proc. SPIE 8341, Active and Passive Smart Structures and Integrated Systems 2012, 83410Y (27 March 2012);

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