On AC resistance of two-layered wires

In this paper, AC resistance of a two-layered wire is numerically analyzed. The resistance is caused by the skin effect and proximity effect which are theoretically formulated, respectively. It is demonstrated by the numerical results that a high-resistive wire covered by copper layer such as a copper-clad-steel (CCS) wire can suppress an increase of resistance with increasing frequency. A CCS wire is evaluated theoretically and experimentally. It is shown that the CCS wire has a lower resistance even than a pure copper wire in a specific frequency range. The range is demonstrated to depend on thickness of Cu layer and is able to compute by our simple formula. This surprising phenomenon is satisfactorily explained by the theory.