INTERFACE PHENOMENA AND DIELECTRIC PROPERTIES OF BIOLOGICAL TISSUE

The dielectric properties of biological cells and tissues are very remarkable. They typically display extremely high dielectric constants at low frequencies, falling off in more or less distinct steps as the excitation frequency is increased. Their frequency dependence permits identification and investigation of a number of completely different underlying mechanisms, and hence, dielectric studies of biomaterials have long been important in electrophysiology and biophysics. As an example, Hober (1, 2) deduced from dielectric studies that erythrocytes are composed of a poorly conducting envelope enclosing a conducting electrolyte, and in 1925, Fricke (3) derived a value of 3.3 nm for the thickness of this envelope. Hence their bioimpedance research provided early indication of the ultrathin cell membrane. As we shall see later, interfaces play a significant role in the frequency dependence of complex materials, particularly at audio and subaudio frequencies.