Millimeter-wave absorption properties of BaTiO3/Co3O4 composite powders controlled by high-frequency resonances of permittivity and permeability

Abstract

Development of high-efficiency millimeter-wave-absorbing materials is important to attenuate electromagnetic pollution occurring due to rapid development of information technology and to defend against radar detection for military stealth technology. In this study, BaTiO₃ (BTO)/Co₃O₄ millimeter-wave absorption composite powders with hierarchical microstructures were successfully prepared by the sol–gel method. The results indicated that the Co₃O₄ phase was preferentially formed at low temperature of 800–900 °C and BTO was formed at high temperature of 1000–1100 °C. A composite with perfect crystallization of both constituent phases and uniform microstructure was obtained when its molar ratio of BTO/Co approached 1 and the sintering temperature was around 900 °C. Both permittivity and permeability resonances were generated typically in composites, due to which ε_r and μ_r values were relatively closer and ε′′ and μ′′ were high at high-frequency range of 30–40 GHz. In the composite with molar ratio of BTO/Co of 4/6 sintered at 900 °C, double absorption peaks with appropriate frequency difference were generated, and absorption intensity from −40 to −50 dB and bandwidth of 5 GHz were successfully obtained with sample matching thickness of 1.8 mm around 35 GHz. It completely covered the atmosphere window at 35 GHz, which has the strongest transparency of millimeter wave. This composite can be used as a highly efficient absorption material of millimeter-wave rays.