Omron Corp prototyped a compact vibration-powered generator whose price is expected to be low because of its simple structure and packaging method.
"We will be able to offer it for less than ¥1,000 (approx US$10.36) in the future," Omron said.
The device will generate 10μW of power with vibrational inputs at 20Hz frequency and 1G acceleration. The power, which will be accumulated in a capacitor in several tens of seconds to several minutes, will intermittently operate the devices because 10μW is not enough to continuously operate, for example, wireless communication devices.
As a first step, the generator will be used in the devices that are installed in the pillars supporting highways and wirelessly transmit sensor signals for detecting road problems. The company has already started validation tests in collaboration with Nexco Higashinihon Engineering KK and others.
The dimensions of the prototype are 20 x 20 x 8mm. The next generation product is 4mm in height and is currently under development, according to the company.
The company plans to incorporate the generator in tire pressure monitoring systems (TPMS), which are installed inside automobile tires, in the future. Tires strongly vibrate while running and are suitable for power generation.
If the batteries used to drive air pressure sensors are replaced with the small generators, their operating life may be significantly extended. Maintenance work such as the replacement of TPMSs, is difficult because they are installed inside the tire. Therefore, the extension of TPMS operating life is an important issue.
Electret power generation system
For power generation, the new generator employs the "electret power generation system," in which the capacitance changes depending on the relative position of the two opposing electrodes. When the capacitance changes, electric current is generated.
An electret, which carries a unipolar-charge, is used for one of the two electrodes. By using an electret, charges can be accumulated in high density and the potential difference between the two electrodes can be enhanced. When the potential difference increases, a larger amount of electric current is generated. For the other electrode, Au or Cu conductor is generally used. The prototype adopted an Au conductor.
The electret is made of "CYTOP," amorphous fluorocarbon polymer manufactured by Asahi Glass Co Ltd. There are a number of candidate materials for manufacturing electrets. But the company employed CYTOP because "it is a liquid polymer material, which is easier to process and enhances the density of charges with less difficulty compared with inorganic materials," according to Omron.
The charge density of the prototype electret is 2C/m2. The potential difference of this prototype was enhanced to 700V by adopting the CYTOP as well as reducing the gap between the electrodes, according to Omron.
Easy to produce
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