Investigation of the Sensing Volume of Open-Ended Coaxial Probe for Heterogeneous Tissue Dielectric Properties Measurement at Microwave Frequencies

Open-ended coaxial probe method is currently one of the most commonly used techniques for measuring the dielectric properties (DPs) of tissues. However, when measuring the surface of heterogeneous biological tissues, the effective sensing volume of the probe remains unclear, potentially leading to deviations in results if the target tissue volume is too small, causing non-target tissues to also be measured. In this study a measurement device was developed for the investigation of sensing volume (including sensing depth and sensing radius) of the coaxial probe method based on a layered DPs model. The influence of probe radius, DPs of the materials being measured, and frequency on the sensing volume was then discussed. Furthermore, the experimental results are compared and validated with electromagnetic simulation results. The results show that the effective sensing volume of the probe gradually increases with the radius of the coaxial probe. Within the frequency range of 300 MHz to 1.5 GHz, the effective sensing volume of the probe does not change significantly. Electromagnetic simulation results further validated these findings.