Abstract
The open-ended coaxial probe (OECP) method is frequently used for the microwave dielectric property (DP) characterization of high permittivity and conductivity materials due to inherent advantages including minimal sample preparation requirements and broadband measurement capabilities. However, the OECP method is known to suffer from high measurement error. One well-known contributor to the high error rates is tissue heterogeneity, which can potentially be managed through the selection of a probe with a proper sensing depth (SD). The SD of the OECP is dependent on many factors including sample DPs and probe aperture diameter. Although the effects of sample DPs on SD have been investigated to some extent in the literature, the probe aperture diameters, particularly small diameters, have not been fully explored. To this end, the SDs of probes with three different apertures (0.5, 0.9 and 2.2 mm-diameters) were analyzed in this study. Probes’ SDs were first investigated with simulations using a double-layered sample configuration (skin tissue and olive oil). Next, experiments were performed using a commercial OECP with a 2.2 mm aperture diameter. The SD was categorized based on 5%, 20% and 80% DP change. Among these threshold values, a 5% DP change was selected as the benchmark for SD categorization. The findings suggest that probes with a smaller aperture size and correspondingly smaller SD should be utilized when measuring the DPs of thin and multilayered samples, such as healthy and diseased skin tissues, to increase the measurement accuracy.
Highlights
Each biological tissue has a unique set of dielectric properties (DPs) based on their molecular structure
The open-ended coaxial probe (OECP) method is superior to other dielectric property measurement techniques for the dielectric property characterization of biological tissues due to its measurement simplicity
Minimizing the effect of skin tissue heterogeneity and the sensing depth of the probe is an important amendment for classifying skin tissue anomalies and the detection of skin cancer through dielectric property discrepancy
Summary
Each biological tissue has a unique set of dielectric properties (DPs) based on their molecular structure. At microwave frequencies, biological tissues can be characterized based on their water content. The interaction of the biological tissues with electromagnetic fields can be determined based on their DPs [1,2]. Tissue types or anomalies can theoretically be identified by analyzing the interaction between the field and tissue. Based on this principle, the DP characterization of both healthy and diseased tissues has been a research interest for scientists, primarily to enable the development of microwave diagnostic and therapeutic applications [3,4]. The DPs of many different tissue types, including but not limited to breast, liver and skin, were characterized with the open-ended coaxial probe (OECP) for cancer diagnosis and treatment [3,5,6,7,8]
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