Numerical simulation on the noise suppression effect of nanogranular magnetic film CoFeHfO on PCB transmission lines

The noise suppression effects of nanogranular magnetic film CoFeHfO on the transmission lines on a printed circuit board were investigated by finite element modeling. Two kinds of transmission lines with CoFeHfO thin film, microstrip line (MSL) and coplanar waveguide (CPW), were simulated in the frequency range of 0.1-10 GHz by HFSS™ and their power absorption and S parameters were analyzed. The numerical simulation showed that soft magnetic film CoFeHfO with a high magnetic permeability and electrical resistivity could greatly reduce the noise of the transmission lines. With the magnetic film, the S₂₁ quickly dropped ~10 dB and the power absorption reached ~0.6 at 10 GHz. In order to further enhance the noise suppression, the electrical resistivity of the magnetic thin film was varied from 16 to ∞ μΩ·cm in the simulation, and the strongest noise suppression was obtained at an electrical resistivity of ~1.6×10⁵ μΩ·cm, which indicated that an optimal electrical resistivity was needed for magnetic material. In addition, the noise suppression mechanism was studied by the analysis of the electric field distribution near the transmission line.