Dielectric dispersion of biological matter: model combining Debye-type and "universal" responses.

The remarkably broad dielectric dispersions exhibited by solid dielectrics are well-known examples of the failure of Debye's relaxation theory; such dispersions are much better represented by a "fractional power law" described by Jonscher [A. K. Jonscher, Nature 267, 673 (1977)] as the "universal dielectric response." As it happens, however, recent experimental advances in this field suggest that neither of the two approaches is general enough to cope with the dielectric response of biological tissues, which combines striking features from both types of behavior. A phenomenological function is therefore proposed, which not only reproduces observations on biological tissues but also includes all of Jonscher's "universal response," the Debye, Cole-Cole, and Davidson-Cole functions, as its special cases.