Batteries and Portable Power

Electret MEMS Energy Harvesting Systems

The Electret Energy Harvester Alliance was at Techno Frontier for the second year demonstrating its progress in the development of small harvesters and systems based on electret technology. The Electret Allince was founded by Professor Yuji Suzuki, in the Department of Mechanical Engineering at the University of Tokyo. Corporate members currently include: OMRON Corp., Asahi Glass Co., Ltd, THHINK Wireless Technologies Japan Co., Ltd., Techno Design Co., Ltd., and Konishiyasu Co., Ltd.

The efforts of the Electret Alliance have already begun to yield results. THHINK was demonstrating a series of three energy harvesters based on this technology. All are currently in sampling, with production anticipated in 2015. All three deliver an output of 5.2Vdc and operate from vibrational energy of 30Hz and 0.15G. They generate from 0.1mW up to 1.0mW. A next-generation design was being demonstrated that harvest rotational energy (for example from a micro wind turbine) and can produce several mW of output.

Each member of the Electret Alliance is making a specific contribution to the development; The University of Tokyo is supplying basic research and analyzing the mechanisms of electret generators; Omron Corporation is involved with the design and manufacture of electret generators; Asahi Glass Co., Ltd. is manufacturing the electret materials; THHINK Wireless Technologies Japan Co., Ltd. is performing marketing research and designing electrical circuit; Techno Design Co., Ltd. is producing the electret vibration generator; and Konishiyasu Co., Ltd. is doing the marketing and market development of electret materials, generators, and modules.

The University of Tokyo has developed new fluorinated amorphous polymer material based on CYTOP by adding animosilane and demonstrate extremly-high surface charge density above 2 mC/m^2 (at the film thickness of 15 um), which is up to 5 times larger than that of conventional electret materials. It is also found that nano clusters are formed in the animonsilane-doped CYTOP film by local phase separation between the polymer matrix and the additives. These clusters should work as the charge trapping site in the CYTOP films.

"We develop a novel MEMS process for Parylene high-aspect ratio structure (HARS) for soft but robust HARS spring. We also propose a passive gap-spacing control method using electret in order to avoid stiction between top and bottom substrates. Out-of-plane repulsive force is successfully demonstrated with our early prototype both in air and liquid. By using the present electret-based levitation method to keep the air gap, a MEMS electret generator has been developed for energy harvesting applications," stated Dr. Suzuki .

"Dual-phase electrode arrangement is adopted in order to reduce the horizontal electrostatic damping force. With the present prototype, the total power output of 6 µW has been obtained at an acceleration of 1.4 G with 40 Hz. In addition, with the aid of a non-linear polymer spring system, power generation at a broad frequency range of 16-40 Hz has also been demonstrated. We have also developed an early prototype of battery-less sensor network node with the MEMS energy harvester and accomplished intermittent wireless data transmission," Dr. Suzuki concluded.

For eletret transducers, charging techniques are important as well as the electret material. In the present study, novel photoionization charge technologies with soft X-ray and vacuum UV have also been developed for through-substrate charging and charging “vertical electrets” such as the side wall of comb drives. With the aid of the soft X-ray charging technique, new types of electret generator using comb fingers and trench-filled piezoelectric polymer electret are also being developed. In addition, electrostatic power generation system from unsteady thermal field is under development.

THHINK Wireless Technologies , Electret Energy Harvester Alliance
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