Analysis of Dielectric Data: Experience Gained with Biological Materials

Techniques advanced by Robert Cole and his colleagues to analyze dielectric data have been applied to biological materials. Three major and distinct relaxation effects characterize the total dielectric response from dc to GHz, and several minor ones are superimposed. Three examples are chosen to illustrate how straightforward orward the analysis is in some cases, and difficult in others. The dielectric properties of erythrocytes at radio frequencies (rf) illustrate a one-time constant Maxwell-Wagner relaxation effect, with small deviations disappearing earing when cell concentration is reduced anlls become spherical. Muscle tissue data at rf indicate a constant phase element for membranes and the "universal dielectric response." However, the analysis indicated this to be fortuitous: Different relaxations of the whole cell, contained proteins and organelles combine to produce the effect. Finally, ultra-high frequencies and microwave data for the cellular cytoplasma and microemulsions are discussed. They demonstrate reduced translational and "average" rotational motion, and suggest a broad distribution function. Once again, different mechanisms account for the apparent translational and rotational effects and the abundant tissue water appears to be identical with normal water. Hence, apparently continuous distribution function behavior can result from a summation of entirely different mechanisms.