Electromagnetic wave absorption properties of ZnO-based materials modified with ZnAl₂O₄ nanograins

Considering the widespread presence of electromagnetic interferences (EMI), it is necessary to develop new electromagnetic wave (EM) absorbing materials with low reflection coefficient and large operating frequency band. The well-known EM absorbing materials have a microstructure combining a low permittivity phase with a high electrical conductivity phase. In the present work, a phase in nanoscale with medium permittivity is added into the well-known EM absorption materials to obtain an EM absorption material with low EM reflection coefficient and wide absorption band. Composite powders with special microstructure have been synthesized via sol-gel process, which are composed of submicrometer-sized ZnO acting as electrically lossy phase and ZnAl ₂O₄ nanograins acting as a medium permittivity phase. When the composite powders are mixed with paraffin, the as-received materials exhibit appropriate permittivity and electrical conductivity, which can be attributed to the high carrier concentration and mobility at the interfaces in nanoscale. The high absorption coefficient, small reflection coefficient, and wide absorption band can be obtained. Absorption coefficient per unit thickness increases from 0.01 to 0.13/mm, the minimum reflection coefficient reaches -25 dB, and the effective absorption bandwidth covers the whole X-band (8.2-12.4 GHz). The ZnO/ZnAl₂O₄ composite materials exhibit excellent EM absorption properties.