Fabrication and characterization of double-layered wide-band electromagnetic wave absorber consisting of composite ceramics

A wide-band electromagnetic wave absorber was developed using a double-layered monolith consisting of highand low-permeability (μ,) composite ceramics. The low-μ, layer was formed from a powder mixture of Ni 0.7Zn0.1Cu0.2Fe2O4 and SiO2-based glass. Ferrite mixtures of low-firing Ni 0.2Zn0.6Cu0.2Fe2O4 and Ni0.3Zn0.7Fe2O4 with less sinterability were used to adjust the densification characteristics of the high-μ, layer. Co-firing of green compacts of the ferrite: glass powder (90:10% in mass-base) for the low-μ, layer and low-firing ferrite: less-sinterable ferrite (60:40% in mass-base) for the high-μ layer resulted in the production of a monolithic doublelayered ceramic at 1100°C. Scanning electron microscopy and electron microprobe analysis of the monolithic double-layered ceramic showed that Ni-Zn interdiffusion and glass diffusion occurred across the layer boundary, leading to the diffusion bonding. An absorption band of the double-layered absorber was more than 10 dB in a wide frequency range from 6 MHz to 1.8 GHz.