A Japanese research group prototyped an "electret thermal power generation" device, which generates electricity by utilizing the time variation of temperature.

The group is led by Yuji Suzuki, professor at the Department of Mechanical Engineering, the University of Tokyo. The device has a potential to play a complementary role for thermoelectric transducers, which generate electricity by utilizing temperature difference. The group exhibited the new device at Techno-Frontier 2013, which runs from July 17 to 19, 2013.

The electret thermal power generation device consists of a dielectric capacitor and electret. When the temperature of the dielectric capacitor changes, the capacitance changes because the dielectric constant changes. As a result, a current flows to restore the charge balance between the electret and dielectric capacitor.

The research group prototyped the device by using barium titanate (BaTiO3) as a dielectric material because the variation in its dielectric constant is wide near the Curie temperature, at which a ferromagnetic material changes into a paramagnetic material.

This means that the power generation efficiency of the device is dependent on the Curie temperature of a dielectric material. However, the temperature can be controlled. For example, the Curie temperature of BaTiO3 is 120-130°C. But it can be lowered to about 60°C by adding impurities. If it can be lowered to a body temperature, electricity can be generated by using body temperature.

The largest amount of electricity generated by a device prototyped by the group has been as small as 30nJ. However, Suzuki considers that it is possible to increase the amount by 1,000 times to 30μJ. As a potential application, he expects to realize an adhesive plaster that is attached to a human body, generates electricity by using body temperature and transmits temperature data, etc once.