Predicting the Sensing Radius of a Coaxial Probe Based on the Probe Dimensions

The coaxial probe technique is used to acquire the dielectric properties of biological tissues in the microwave frequency range. To dielectrically characterize heterogeneous samples, the sensing radius of the probe must be known. Thus, in this article, for the first time, both experimental and numerical investigations were conducted to analyze and model the sensing radius dependence on the probe dimensions. The results suggest that 1) the sensing radius increases linearly with the inner radius of the outer conductor and is not affected by the width of the outer conductor; 2) the inner conductor has higher impact than the insulator on the sensing radius; and 3) although the sensing radius depends on the dielectric properties of the investigated samples, the trend of the sensing radius relative to the probe dimensions is the same across different samples. Furthermore, a method for predicting the sensing radius, through use of neural networks, is proposed.