Effects of Impedance and Dielectric Loss on the Electromagnetic Shielding Performance of an Ultrathin Carbon Nanotube Buckypaper-Reinforced Silicon Carbide Nanocomposite

An ultrathin carbon nanotube buckypaper-reinforced silicon carbide (CNT/SiC) nanocomposite with a thickness of 500 μm and density of 1.78 g cm⁻³ is prepared by combining a CNT buckypaper preform and an in situ-synthesized SiC matrix. A uniform CNT distribution and a high CNT content (≈35 vol%) are achieved in the nanocomposite. The SiC matrix is composed mostly of nearly spherical nanograins and submicrometer grains. No residual Si is found. The imaginary permittivity and loss tangent of the nanocomposite throughout the X-band are 96–257 and 0.44–7.03, respectively. The normalized input impedance is 0.0012–0.0174 over the X-band. The nanocomposite has an average total shielding effectiveness (SE) of 30 dB throughout the X-band. The nanocomposite has a reflection coefficient of 0.9651–0.9915, an absorption coefficient of 0.0077–0.0338, and a transmission coefficient of no more than 0.0012 throughout the X-band, indicating excellent electromagnetic SE. The nanocomposite is well suited for shielding applications, and the SE due to internal absorption (SE_A) depends mostly on the impedance matching condition rather than the dielectric loss capacity. The variation with frequency of SE_A is not consistent with that of the imaginary permittivity or loss tangent but approximately consistent with that of the normalized input impedance.