Mathematical descriptions of opacity

When an electromagnetic wave travels through a medium in which it gets attenuated, it undergoes exponential decay as described by the Beer–Lambert law. However, there are many possible ways to characterize the wave and how quickly it is attenuated. This article describes the mathematical relationships among:attenuation coefficient; penetration depth and skin depth; complex angular wavenumber and propagation constant; complex refractive index; complex electric permittivity; AC conductivity (susceptance).

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