Interaction between electromagnetic waves and biological materials

Applications of radio frequency and microwave in medicine and biology are diverse, as exemplified by what will be covered in the future chapters of this book or found in many other articles and books. In many of those applications, the interaction between electromagnetic waves and biological materials should be characterized. This often necessitates having proper knowledge of the complex permittivity of these materials. Complex permittivity of biological substances is dispersive and is often modeled by Debye or Cole-Cole relaxation models. In this chapter, the relaxation theory of dielectrics, which explains the frequency variation of complex permittivity at DC through millimeter wave frequencies, is discussed. Moreover, various relaxation mechanisms and complex permittivity dispersion modeling for biological materials are explained. In addition, some methods of measurement of complex permittivity, using resonant, reflection, and transmission (two-port) techniques are presented.