Surface impedance of normal metals

For a normal metal at microwave frequencies the imaginary part of the conductivity can be neglected and the real part is equal to the dc conductivity a do In this case a simple expression for the surface impedance follows from Maxwell s equations and Ohm s law  

Equation (5.4) is valid as long as the skin depth is large in comparison to the mean free path of the electrons in the metal. This holds true in the microwave range at room temperature, for cryogenic temperature the surface resistance lies above the values predicted by Equation (5.4) and exhibits a f2 3 rather than a f1 2 frequency dependence (anomalous skin effect [7]). 

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