Tiny vibration power generator by Omron
Omron Corporation has unveiled a prototype of a compact size vibration powered generator. The device is a size of a 100 yen coin (20 x 20 x 8mm) and is able to generate 10 microwatt of power with vibration inputs at 20Hz frequency and 1G acceleration. The generated power will be accumulated in a capacitor in duration of several tens of second up to several minutes which would be enough to operate a device such as wireless communication devices. This accumulation of energy is necessary since 10?W of power will not be enough to run wireless devices. Omron is planning to introduce this power generator in devices that are installed in the pillars supporting highway structures which are responsible for detecting road problems through wireless transmit sensor signals. The company would also like to introduce such device in future in tire pressure monitoring systems (TPMS) which are installed inside tires. This is a good target due to strong vibration by tire while running making it a suitable candidate for power generation. The idea is to replace the existing batteries for TPMS with power generating devices to extend their operating life significantly. Extending TPMS operating life is an important issue since replacement of TPMSs is difficult due to the reason of being installed inside the tires. The power generation device employs the electret power generation system where the capacitance changes depending on the position of two opposing electrodes. As a result of capacitance changes electric current is generated. In this prototype the electret is made of “CYTOP” which is an amorphous fluorocarbon polymer manufacture by Asahi Glass Co Ltd. The charge density of the prototype electret is at 2C/m2.
The key point in designing the generator is the gap size between the two electrodes, the company said. When the gap is small, the two electrodes are likely to contact each other. If this happens, the generator will not function because the charge stored in the electret flows to the opposing electrode. However, if the gap is too large, the potential between the electrodes drops, reducing the production of electricity.
In this prototype the gap was set at about 70?m. In order to maintain the gap, the stationary electrode is equipped with a spacer shaped like a solder ball. The material and processing method of this spacer were not disclosed, but “a low-friction material was selected because the spacer contacts the moving part,” Omron said.
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