Characterizing the Complex Permittivity of an Isotropic Scatterer in a Homogeneous Environment Using an Open-Ended Coaxial Probe

Electromagnetic-based biomedical technologies often depend on accurately estimating tissues' dielectric properties. The open-ended coaxial probe (OECP) technique is one of the simplest and most commonly used methods to obtain the complex permittivity of tissues over the radio or microwave frequency ranges. However, when considering diseased tissues, we encounter tissue heterogeneities, which alter the measured parameters. To quantify this effect, we focus on characterizing an isotropic scatterer within an otherwise homogeneous medium using OECPs. We present an analytical model relating the reflection coefficient to the scatterer properties and derive a closed-form expression for the effective measured admittance. Based on full-wave simulations, we demonstrate that our theoretical model provides accurate estimates of the scatterer permittivity. We use the analytical model to characterize the sensing depth of different OECP systems, providing a performance guideline.