Skin Effect vs. Skin Depth: Understanding RF Current Behavior

This page describes the difference between skin effect and skin depth. As we are aware, at microwave frequencies, the wavelength is very small, and hence lumped electronic components do not work well at such low wavelengths. This is due to the following reasons:

• Component size and lead length become considerable relative to the wavelength.
• Inductance (L) and Capacitance (C) values become significant at microwave frequencies.

Skin Effect

Skin effect usually refers to the situation where alternating current (AC) flow concentrates on the surface of the conductor. Direct current (DC) flows through the entire cross-section of the conductor.

Skin depth is the measure of how far into the conductor the AC current penetrates. It’s defined as the depth at which the current density has decreased to 1/e (approximately 37%) of its value at the surface.

The skin depth ($\delta$) can be calculated using the following formula:

Where:

• $\delta$ = Skin depth
• $\omega$ = Angular frequency ($\omega = 2 \pi f$, where f is the frequency)
• $\mu$ = Permeability of the conductor
• $\sigma$ = Conductivity of the conductor

As mentioned in the equation, skin depth is a function of frequency, permeability ($\mu$), and conductivity ($\sigma$). A higher frequency leads to a smaller skin depth, meaning the current is more concentrated at the surface. Similarly, higher permeability and conductivity also decrease the skin depth.