Dispersion and Dielectric Spectroscopy

Schwan emphasized the concept of dispersion in the field of dielectric spectroscopic analysis of biomaterials. Dispersion has already been introduced in Section 3.4.1 dispersion means frequency dependence according to relaxation theory. Biological materials rarely show a single time constant Debye response as described in Section 3.4.2. Knowing how complex and heterogeneous living tissue is, the concept of a distribution of 

Dispersion is therefore a hroad concept, and many types of DRTs are possible. The Cole brothers proposed a certain DRT corresponding to the apparently simple Cole—Cole equation (Section 9.2). The Cole—Cole equation presupposes a CPE. However, other distributions than the Cole—Cole type are also found to be in agreement with measured tissue values. The Cole—Cole model is attractive however because the mathematical expressions are so simple. Dispersion models as described below therefore pertain to many types of dispersion mechanisms, among those are also Cole—Cole systems. 

Sometimes dispersions are related to defined frequency ranges, and to a lesser extent to possible relaxation mechanisms. 

We do not know so much about the a-dispersion. Newer findings have shown that the a-dispersion must be extended down to the Hz (or mHz) frequency range (Table 3.3). a-dispersion is the first to disappear when tissue dies. Blood has no a-dispersion. 

3 1 kHz-100 MHz Maxwell—Wagner effects, passive cell membrane capacitance, intracellular organelle membranes, protein molecule response. 

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