Frequency dispersion observed in the immittance response of
conductive and dielectric systems has been attributed to a number
of phenomena, depending on the nature of the system being
investigated, without a definitive choice usually being possible
[1,2]. However, it is widely accepted that it results from the nonhomogeneous
distribution of some physical properties of the
system or from system disorder.
Relationship between frequency dispersion and heterogeneity
has been addressed for decades from different perspectives. One of
the approaches to the problem has considered that system
heterogeneity can be modeled by a distribution of time constants
associated with activation or relaxation processes. Two methodologically
opposite strategies, but complementary, have been
followed, say, the forward and the backward approach. The
backward approach consists in extracting the DFRT from immittance
spectra [3–14]. Immittance is assumed to have the form of a
kernel function of frequency and of the relaxation time (mostly the
Debye relaxation kernel) which is distributed according to the
unknown DFRT, giving a Fredholm integral equation of the
first