Open-Ended Coaxial Dielectric Probe Effective Penetration Depth Determination

• Published in: IEEE transactions on microwave theory and techniques Vol. 64; no. 3; pp. 915 - 923
• Main Authors: Meaney, Paul M., Gregory, Andrew P., Seppala, Jan, Lahtinen, Tapani
• Format: Journal Article
• Language: English
• Published: United States IEEE 01.03.2016; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Coaxial cables; Dielectric; Dielectric constant; Dielectric measurement; Dielectric properties; Dielectrics; Liquids; Microwave measurement; Microwaves; open-ended coaxial probe; Penetration depth; Permittivity; probe diameter; Probes; Saline; Simulation; tissue properties; probe diameter; penetration depth; open-ended coaxial probe; Dielectric; tissue properties
• ISSN: 0018-9480; 1557-9670
• DOI: 10.1109/TMTT.2016.2519027

We have performed a series of experiments, which demonstrate the effect of open-ended coaxial diameter on the depth of penetration. We used a two-layer configuration of a liquid and movable cylindrical piece of either Teflon or acrylic. The technique accurately demonstrates the depth in a sample for which a given probe diameter provides a reasonable measure of the bulk dielectric properties for a heterogeneous volume. In addition, we have developed a technique for determining the effective depth for a given probe diameter size. Using a set of simulations mimicking four 50- Ω coaxial cable diameters, we demonstrate that the penetration depth in both water and saline has a clear dependence on the probe diameter, but is remarkably uniform over frequency and with respect to the intervening liquid permittivity. Two different 50- Ω commercial probes were similarly tested and confirm these observations. This result has significant implications to a range of dielectric measurements, most notably in the area of tissue property studies.