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The results of measurements using an open-ended coaxial probe of the audio/radiofrequency dielectric properties of human skin in vivo, either dry or moistened with physiological saline, are reported. Permittivity and conductivity dispersion curves were parametrized by using a newly reported dispersion function (Raicu V 1999 Dielectric properties of biological matter: model combining Debye-type and 'universal' responses Phys. Rev. E 60 4677), and the results obtained are discussed in the light of the recent advances in this field. It is suggested that the coaxial probe reports on the properties of the superficial layer, the stratum corneum, when the skin surface is dry, whilst the signal from deeper skin layers becomes dominant after wetting the skin with conductive physiological saline.

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Numerical assessment is made regarding Pauly and Schwan's theory which describes the dielectric behavior of a suspension of "shell spheres" as a model of biological membrane-bounded particles. The results indicate that approximate expressions of the theory may give rise to serious errors when applied to particles smaller than about 1 mum in diameter. With a view to performing analysis according to a general expression of the theory, some of the characteristic responses of dielectric parameters upon changes in phase parameters are examined with particular reference to some numerical ranges of biological interest. On this basis a simplified and systematic procedure is proposed for estimating the phase parameters of particles whose shell phase can be regarded as non-conductive. As the application of the procedure proposed, a set of dielectric data of a synaptosome suspension is analyzed, so that the following three phase parameters are successfully determined: membrane capacitance (or shell phase dielectric constant), interval phase conductivity and internal phase dielectric constant. Some limitations of the procedure are discussed for the cases of conducting shells and small particles.