Abstract. While measuring the effective permittivity of dispersive material it may be
of interest to distinguish between conductivity losses (caused by free
electrons) and dielectric losses (caused by bounded electrons) which both are
included in the imaginary part. This usually turns out to be a non-trivial
task unless suitable dispersion models for the dielectric and/or the
conductivity properties of the material are assumed. In this paper we present
a more general method based on the Kramers-Kronig transformations to separate
the conductivity from the effective complex permittivity of a dispersive
material. The Kramers-Kronig transforms (or KK-transforms) are unique
integral relations between the real and the imaginary part of a complex
quantity describing a causal system. The proposed method and the
corresponding algorithm are tested by first supposing some fictitious values
of the complex permittivity satisfying the KK-transforms. Then, different
values of a conductivity are added leading to a change of the imaginary part
of the effective permittivity while the real part remains the same. The
effective permittivity (including a conductivity part) does generally not
satisfy the KK-transforms. This fact will be employed to retrieve the
conductivity from that effective complex permittivity. Finally the method is
applied to measured values found in the literature to retrieve the
conductivity from the effective permittivity of composite material.