STUDY ON THE MICROWAVE ABSORBING PROPERTY OF COMPOSITE MATERIAL CONTAINING CARBON NANOTUBES WITH NI COATING

Carbon nanotubes were prepared by catalytic decomposition of benzene using a floating transition method. The carbon nanotubes are straight with diameter 40?nm～70?nm, internal diameter 7?nm～10?nm and length 50?μm ～1?000?μm. The Ni coating on the carbon nanotubes was deposited by electroless deposition technique. The maximum absorbing peak of the microwave absorbing composite material containing the carbon nanotubes is 22.89?dB at 11.40?GHz. The maximum absorbing peak of the microwave absorbing composite material containing carbon nanotubes with Ni coating is 11.85?dB at 14.0?GHz. The absorbing peak of the composite material is moved from 11.40?GHz to 14.0?GHz, and absorbing peak becomes broader. The band width (R-10?dB) of the composites containing carbon nanotubes with thickness of 0.97?mm is 3.0?GHz, band width (R-5?dB) is 4.7?dB at the frequency range of 8?GHz～18?GHz. The band width (R-10?dB) of the composites containing carbon nanotubes with Ni coating with thickness of 0.97?mm is 2.3?GHz, band width (R-5?dB) is 4.6?dB at the frequency range of 8?GHz～18?GHz. The carbon nanotubes or carbon nanotubes with Ni coating are used as resonators to absorb the microwave. In the microwave absorbing material containing an electromagnetic loss substance and resonator, the resonator as an electron couple can generate an inductive current in the electromagnetic field. The induced current then causes a loss current and energy dissipation. In the electromagnetic loss substance, the electromagnetic wave energy is changed into heat energy. This is the main mechanism in microwave attenuation. So by controlling the composition, loss factor and impedance, performance of the microwave absorbing material can be optimized for a single narrow band frequency, multiple frequencies, or over a broad frequency spectrum.