Cheng Lichun

Microwave Absorbing Properties of Ni/Ferrite Mixture

Abstract The Sr-W type planar hexagonal ferrite was synthesized by a sol-gel method, and its morphology and phase structure were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The microwave absorbing properties of the mixtures with different ratios of Ni/ferrite were studied by vector network analyzer (VAZ). The results demonstrate that with the increase of hexagonal ferrite content, the microwave absorbing peaks of the mixtures shift to higher frequencies, and when the mixture consists of 20% Ni and 80% Sr-W-type ferrite, its microwave absorbing performance is the most advantageous. When absorbing coating thickness is 2 mm, the minimum reflectivity and absorbing peak frequency is −20.69 dB at 12.08 GHz and the bandwidth less than −10 dB reaches 4 GHz. The absorbing peak shifts to low-frequency with the increase of absorbing coating thickness, and when the coating thickness reaches a certain value, the two absorbing peaks appear in the mixture in the frequency range of 2∼18 GHz, which is of significance to explore the absorbing material with bandwidth effect.

Microwave Absorbing Properties of MnAl Alloy Powder

Abstract Mn55Al45 alloy powder was prepared by the combined use of arc melting, high energy ball milling and tempering heat treatment process. The phase structure and the microstructure of the alloy powder were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), and then their microwave absorbing properties were tested by a vector network analyzer. The results show that an increase of phases for Al2Mn3 and Al11Mn14 are accompanied by the increased milling time; the resonant frequency and the absorption peaks of ɛ″ and μ″ shift towards lower frequency region simultaneously. A better result of electromagnetic properties is brought to the alloy powder when the ball milling time is set to 18 h in first attempt. While the ball milling time is increased to 24 h during later experiment, the minimum reflectivity value reaches to −28 dB at a frequency of 16 GHz. The Al2Mn3 phase increases with an artificial increase of tempering temperature. The Mn55Al45 alloy powder ball milled for 18 h and tempered at 400 °C exhibits preferably comprehensive microwave absorbing properties in the range of 6∼8 GHz. The minimum reflectivity value and absorption peak frequency at the coating thickness of 2.0 mm are −26.4 dB, 17 GHz, respectively.