Skin Depth

The skin depth equation is given below:
In Equation [1], the symbols are: f is the frequency of the current
Note that (=*)
This means that electric current flows only on the surface of a conductive material at RF frequencies (>10 MHz). For instance, the skin depth of copper at the WIFI or Bluetooth frequency (2.4 GHz = 2.4*10^9) is about 1 micron (1 micrometer = 1/1000 mm). Note that we used the resistivity for copper of 1.68*10^-8 Ohm-meters. To illustrate skin depth in a simple figure, below is a copper conductor with an electric current flowing through it. On the left, we have the current distribution for low frequencies (i.e. DC or 0 Hz) - the current flows uniformly through the wire's cross section. On the right, we have the current distribution for the RF (radio frequency) case (that is, for wires as small as 0.1mm in diamter and frequencies as low as 10 MHz. The right side shows that the electric current only flows along the surface, and the in the center of the wire no RF electric current flows: Figure 1. Illustration of Skin Depth The depth of the electric current into the wire can be found from Equation [1]: it is the skin depth.
In reality, the current density actually drops off exponentially from the surface, so that if
we have a wire that begins at
In Equation [1],
Figure 2. Current Decreasing With Distance From Surface
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