In the field of bioimpedance measurements the Cole
impedance model, introduced by Kenneth Cole in 1940 [9], is
widely used for characterizing biological tissues and biochemical materials. In literature, this model has also been commonly
referred to as the Cole-Cole model or Cole-Cole impedance
model. However, the Cole-Cole model is actually a similar
model introduced by the Cole brothers in 1941 regarding
dielectric permittivity [10]. Therefore, care needs to be taken
when describing the model to prevent confusion between work
with dielectric permittivity and impedance.
The Cole model, shown in Fig. 2(a), is composed of three
hypothetical circuit elements. A high-frequency resistor , a
resistor and a CPE. The impedance of this model is then
given by
(3)
Noting that .
This model has become very popular because of its simplicity
and good fit with measured data, illustrating the behavior of
impedance as a function of frequency.