Chapter 69 - Dielectric Properties of Biological Tissues; Variation With Age

Abstract

Knowledge of the dielectric properties of body tissues is central to all areas of studies where electromagnetic fields interact with biological materials including people. The interaction occurs at all levels of organization of cellular, molecular, and ionic; it informs on possible biological effects. In this chapter the dielectric properties are defined, related to the structure and composition of tissues, and their frequency dependence described in mathematical models. Prominence is given to the dielectric properties of water, as it is one of the main constituents of tissues and one that varies with age. Age-related variations were observed in the dielectric properties of some tissues and the question arose as to whether this would affect the absorption of electromagnetic energy in children compared to adults. Research groups around the world investigated the absorption of electromagnetic fields in the heads of children and adults when using mobile phones taking into account the impact of age-related dielectric properties. A review of the subject revealed that, by and large, the age-related variation in dielectric properties had little effect on the exposure to the head when using metrics for safe exposure. However, there remain situations where the outcome of the exposure of a single tissue, such as bone marrow, can be significantly different. It is possible that one day such differences may be exploited in the medical field, in the concept of devices for diagnostic or therapeutic purposes.