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Effect of Aspect Ratio on the Permittivity of Graphite Fiber in Microwave Heating

Department of Applied Chemistry, Tohoku University, 6-6 Aoba, Aramaki, Aoba, Miyagi 980-8579, Japan
Department of Chemical Science and Engineering, School of Materials and Chemical Technology, Tokyo Institute of Technology, Ōokayama 2-12-1, Meguro, Tokyo 152-8552, Japan
Faculty of Engineering, Chubu University, 1200 Matsumoto-cho, Kasugai, Aichi 487-8501, Japan
Research Institute for Sustainable Humanosphere, Kyoto University, Gokasho, Uji, Kyoto 611-0011, Japan
Department of Mechanical Engineering, Chubu University, 1200 Matsumoto-cho, Kasugai, Aichi 487-8501, Japan
National Institute of Technology, Okinawa College, 905 Henoko, Nago-city, Okinawa 903-0213, Japan
Author to whom correspondence should be addressed.
Materials 2018, 11(1), 169;
Received: 21 November 2017 / Revised: 11 January 2018 / Accepted: 17 January 2018 / Published: 22 January 2018
(This article belongs to the Special Issue Electromagnetic Wave Absorbing Structures)
PDF [3083 KB, uploaded 22 January 2018]


Microwave (MW) heating has received attention as a new heating source for various industrial processes. Some materials are expected to be a more effective absorber of MW, and graphite is observed as a possible candidate for high-temperature application. We investigated the dependence of the aspect ratio of graphite fibers on both their heating behavior and permittivity under a 2.45 GHz MW electric field. In these experiments, both loss tangent and MW heating behavior indicated that the MW absorption of conductive fibers increases with their aspect ratio. The MW absorption was found to be well accounted for by the application of a spheroidal model for a single fiber. The absorption of graphite fibers decreases with increasing aspect ratio when the long axis of the ellipsoid is perpendicular to the electric field, whereas it increases with the aspect ratio when the long axis is parallel to the electric field. The analytical model indicated that MW heating of the conductive fibers is expected to depend on both the shape and arrangement of the fibers in the electric field. View Full-Text
Keywords: microwave heating; electrical permittivity; graphite; shape effect microwave heating; electrical permittivity; graphite; shape effect

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Fukushima, J.; Tsubaki, S.; Matsuzawa, T.; Kashimura, K.; Mitani, T.; Namioka, T.; Fujii, S.; Shinohara, N.; Takizawa, H.; Wada, Y. Effect of Aspect Ratio on the Permittivity of Graphite Fiber in Microwave Heating. Materials 2018, 11, 169.

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