Sensing volume of open-ended coaxial probes for dielectric characterization of breast tissue at microwave frequencies

To achieve accurate measurements, the tissue sample should be homogeneous within a volume large enough so that the measured reflection coefficient is identical to that of a sample filling the entire half-space. Thus, the question arises of the appropriate size of the tissue sample. Sensing volume guidelines have been previously investigated in terms of somewhat arbitrarily chosen constraints on the relative errors in the measured reflection coefficient of tissue-equivalent liquids. In this paper we report sensing volume guidelines that have been developed by first choosing acceptable levels of error in the permittivity and then deriving the appropriate constraints on the errors in the measured reflection coefficient.