Analysis of Alternative Ring Resonator Designs

Report No. ARL-TR-7040
Authors: Christopher S. Kenyon
Date/Pages: August 2014; 22 pages
Abstract: Variants of a ring resonator for measurement of dielectric constants of soil were modeled using FEKO computational electromagnetic software with the aim of improving performance. The variations explored included use of an alternative dielectric laminate, with lower dielectric constant and dissipation factor, various thicknesses of the laminates, and opening the ring on one side so as to change the ring strip to a "C" shaped strip. Comparisons of changes in the resonances appearing in the frequency dependent S21 parameter of the antenna were analyzed to assess potential performance improvements in the respective antenna designs. For these new designs computer modeling showed that the major sensitivity of the ring resonator was still within the first 2 mm of the surface of the soil in contact with the ring strip of the antenna as in the case of the original design. Both the alternative dielectric laminate and the increased thickness laminate reduced sensitivity to changes in the measured parameters, namely the frequency ratios and changes in the inverse Q. These alternatives did both generally increase the penetration of the sensing region, but they still left more than 80% of the sensing effect within the first 2 mm of the soil sample. The modeling further confirmed the limited sampling depth or volume for the soil helping to explain the difficulty in measuring all but very homogeneous samples. Also, it was inferred that finer sampling of the S21 curves could substantially improve the relative error in determining the soil dissipation factor.
Distribution: Approved for public release
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Last Update / Reviewed: August 1, 2014