A study of the dielectric properties of biological tissues: Ex-vivo vs preserved samples

Dielectric properties are the most important parameters determining energy deposition when biological tissues are exposed to microwave fields. Energy absorption is determined by the specific absorption rate (SAR), which distributions can be computed accurately only if the complex relative permittivity of the target tissue is known to a sufficiently high accuracy. Presently there is a lack of data on the dielectric properties of biological tissues at high frequencies. This work describes in detail the measurements of ex-vivo dielectric properties of fat tissue and their correlation to preserved samples. In addition, the temperature variability of fat tissue dielectric properties is shown. Measurements were conducted using an open-ended reflection technique and the frequency band considered for this study ranged from 1 GHz up to 20 GHz. The measurement system was controlled via a PC and the complex reflection coefficient was recorded for a given number of frequencies. The complex reflection coefficient (S
₁₁
parameter) was converted to complex permittivity (ε) utilizing the Agilent software 85070E. A one-pole Cole-Cole model was used to fit the measured data as a function of frequency and the dispersion parameters.