Electromagnetic absorbing materials using nonwoven fabrics coated with multi-walled carbon nanotubes

We calculated the complex permittivity of materials required to achieve a single-layer electromagnetic absorber with a high absorption coefficient in the 60-GHz band. The calculation results indicated that an absorption coefficient of 0.95 can be achieved for a 5-mm sheet when the real part of the relative permittivity εr′ is close to that of the free space and the conductivity σ is around 3 S/m. On the basis of the findings, we developed three types of nonwoven fabrics with high porosity in which the fibers were coated with multi-walled carbon nanotubes (MWCNTs). The εr′ of 1.12-1.32 and σ of 0.107-12.4 S/m were obtained depending on the porosity of the fabrics. The measured absorption coefficients reached 0.97 at 60 GHz in agreement with the calculations. The present MWCNTs-coated nonwoven fabrics will be useful materials for high performance electromagnetic absorbers.