EMI Reduction Evaluation with Flexible Absorbing Materials and Ferrite Cores Applied on Cables

Cables, represented by monopole antennas and coated with magneto-dielectric absorbing materials or containing ferrite cores, can be used to estimate how much electromagnetic interference (EMI) reduction the corresponding coatings cause. Two-dimensional finite element method (2D-FEM) has been developed to calculate the EMI reduction by taking advantage of the axial symmetry of the geometry. A standard technique based on the 7/3-mm coaxial air line and vector network analyzer measurements is used to extract the relative permeability and permittivity of the flexible absorbing materials or ferrites. With the extracted parameters, both the input impedance and the EMI reduction on cables coated with absorbing materials or containing a ferrite choke can be calculated by the 2D-FEM, and the input impedance is also compared with the experiment result. At last, EMI reduction values of absorbing sheet material and ferrite are evaluated by 2DFEM based on realist geometry of cables.