Electromagnetic properties of Si-C-N based ceramics and composites

Besides the excellent high-temperature mechanical properties, Si ₃N₄ and SiC based ceramics containing insulating or electrically conductive phase are attractive for their tunable dielectric properties, which may vary from electromagnetic (EM) wave transparent to absorption and shielding. Consequently, SiC, Si₃N₄, SiON, SiBN, SiBC, SiCN and SiBCN ceramics have attracted extensive interest in recent years. SiO₂, Si₃N₄, Si₃N _4-SiO₂, Si₃N_4-BN, and Si ₃N_4-SiO_2-BN are promising EM wave transparent materials for applications in microelectronic packaging, microwave transparent reaction chamber, radome and antenna window. C, SiC, SiC-C, Si₃N _4- C and Si₃N_4-SiC are potential EM wave shielding materials, which can be used as electronic packaging of highly integrated circuits, and be used in wireless communication system, telecommunication base stations and the other electronic devices. Si ₃N_4-SiBC, Si₃N_4-SiCN and Si ₃N_4-SiBCN are attractive EM wave absorbing materials for potential applications in amplifier, accelerator, microwave heating, anechoic chambers, stealth aircraft and ship. Other potential harsh environment or high-temperature applications will also benefit from the Si-C-N ceramic system. The concept of hybrid structure and EM metamaterials (MMS) opens up new avenues in developing EM wave absorption materials. The key developments and future challenges in this field are summarised. The main issues regarding permittivity of high-temperature structural ceramics are discussed, with an emphasis on the EM wave transparent, shielding and absorbing mechanisms that are responsible for the EM wave properties.