In coaxial cables, the skin effect is the movement of alternating current (AC), where the current density is larger near the surface of the conductor and decreases within the conductor. The skin effect is a decrease in current density, and the skin depth is a measure of the depth at which the current density drops to a value of 1 / e near its surface. More than 98% of the current flows in a layer that is four times the depth of the skin of the surface. At high frequencies, the skin depth becomes smaller. When a signal arrives and moves along the surface of the inner conductor, the skin effect loss typically occurs at high frequencies, which results in additional RF losses at higher frequencies.
The resistance per unit length is the ratio of specific resistance or resistivity to the cross-sectional area of a given conductor in ohms per meter. As the skin effect is lost, the resistance R1 per unit length and the inductance L1 per unit length increase with the square root of the frequency.
The skin effect loss is resistive and is caused by the narrowing of the conductive path. When calculating losses, the loss per unit length includes skin effect loss and dielectric loss.