Skin effect

This is a calculator for the depth at which the current decays to 1/e=0.37 times the surface of the conductor. A signal propagating through a conductor tends to flow more easily on the surface of the conductor and less easily on the inside. The higher the frequency of the signal, the stronger the tendency. Impulse noise and electrostatic noise have higher frequencies and tend to flow more easily to the surface of the conductor or board due to the skin effect.