Electromagnetic interference shielding efficiency and noise suppression in a transmission line for carbon-coated magnetic composite films

We report on the electromagnetic interference (EMI) shielding in the far-field and the near-field regions and on the noise suppression characteristics for carbon-coated Fe-Si-Al/polymer composite films in the frequency range from 20 MHz to 5 GHz. The carbon-coated Fe-Si-Al/polymer composite films were placed in a single microstrip line (MSL) and the reflection and transmission coefficients were measured to determine the noise suppression characteristics (i.e., power loss). The near-field EMI shielding efficiencies (SEs) were measured using the double MSLs method. The frequency dependence of the near-field EMI SE was similar to that of the dielectric constant and the permeability of the composite films. The far-field EMI SEs were measured for the composite films with various surface resistances. The EMI SE in the far-field region and the noise suppression of the composite films increased with decreasing surface resistance of the composite films. The measured EMI SEs and their frequency dependences in the far-field and the near-field regions qualitatively agree with the theoretical results obtained from the computer simulations.