Relative Complex Permittivity

The permittivity of dielectrics is assumed to be complex, as follows:

which can also be expressed as

where e¢ is the real portion of e and from which the relative permittivity is defined as

where e₀ is the permittivity of free space and e''/e' is the dielectric loss tangent.

If a material’s losses due to bulk conductivity will be significant, such as in semiconductor dielectric materials, an additional bulk conductivity value, s, must be added. From the time harmonic form of Maxwell’s equations, the complex permittivity, e_c is defined as

where