Submitted to: Transactions of the ASAE
Publication Type: Review article
Publication Acceptance Date: 12/2/1997
Publication Date: N/A
Citation: Interpretive Summary: The electrical characteristics of biological materials known as dielectric properties have been of interest in connection with high-frequency and microwave dielectric heating, absorption of electromagnetic energy by living systems, and for nondestructive measurements of nonelectrical properties such as moisture content of agricultural products. These applications, including health hazards of energy absorption, medical diagnostics, and electromagnetic heating of tissues for medical purposes have spurred research on determining dielectric properties of such materials. There has been much less concentration on studies of low-frequency properties of biological materials. However, the behavior of materials exposed to low-frequency electromagnetic fields, and a better understanding of these phenomena, may enable potentially useful measurements of important characteristics. With increasing interest in biological engineering opportunities, this review of low-frequency electrical properties was written to provide some background for those interested in pursuing such studies. It includes a review of dielectric relaxation theory applicable to biological materials and related phenomena, including colloidal particle mechanisms and membrane permeablility to ions, which are fundamental in the behavior of biological tissues. Examples of plant and animal tissue properties, which have been measured at low frequencies, are presented, and problems encountered.
Technical Abstract: Low frequency dielectric properties of biological tissues, characterized by alpha- and beta-dispersions, are reviewed with emphasis on physical mechanisms. Ion activities, tissue microstructure and composition are discussed. A new mechanism associated with membrane permeability is included. The counterion layer (electrical double layer) phenomenon is discussed. Electrode polarization, which always causes problems with low-frequency dielectric measurements, is also discussed.