Differential Analysis in Microwave Dielectric Probing for Transcutaneous Biomedical Sensing

Transcutaneous in-vivo microwave biomedical dielectric spectroscopy is challenging due to the complex structure of the skin. Tissue-penetrating microwaves interact with many substances degrading measurements of targeted subcutaneous biomarkers, such as blood glucose. In this paper, a model for differential analysis using two open-ended coaxial probes with different diameters is presented. Considering a layered structure and by applying the proposed differential admittance model, the permittivity of the bottom layer can be estimated independent of the top layer. The model is validated in a lab controlled environment using two-layered phantom samples estimating the dielectric permittivity of the bottom layer with an error below the 6% with respect to the control permittivity over the frequency band 10–18 GHz. The proposed methodology is intended for transcutaneous blood glucose measurements of shallow veins.