Microwave resonators are widely used for numerous applications including communication, biomedical and chemical applications, material testing, and food grading. Split-ring resonators in both planar and nonplanar forms are a simple structure which has been in use for several decades. This type of resonator is characterized with low cost, ease of fabrication, moderate quality factor, low external noise interference, high stability, and so forth. Due to these attractive features and ease in handling, nonplanar form of structure has been utilized for material characterization in 1-5 GHz range. Resonant frequency and quality factor are two important parameters for determination of material properties utilizing perturbation theory. Shield made of conducting material is utilized to enclose split-ring resonator which enhances quality factor. This work presents a novel technique to develop shield around a predesigned nonplanar split-ring resonator to yield optimized quality factor. Based on this technique and statistical analysis regression equations have also been formulated for resonant frequency and quality factor which is a major outcome of this work. These equations quantify dependence of output parameters on various factors of shield made of different materials. Such analysis is instrumental in development of devices/designs where improved/optimum result is required.

Split‐ring resonator (SRR) finds its utility in various applications where moderate quality factor is required. Application areas for this type of microwave resonator include communication, biomedical, chemical, material testing, and food grading. Design is usually based for a particular band of frequency, dictated by its intended utility/application. A metallic cylindrical shield or cavity is used to enclose resonator for controlling environmental effects. Quality factor determines resonator's figure of merit. Resonant frequency, quality factor, and other output parameters are dependent mainly on critical dimensions and materials used to fabricate resonator and shield. Numerous models have been formulated to predict output parameters. In this study, variations in quality factor and resonant frequency have been analyzed for nonplanar form of SRR structure model based on parametric changes. Simulated and calculated results were analyzed for model validity. Sensitivity analysis was performed to determine sensitivity of output parameters over SRR dimensions. Output parameters of SRR structure fabricated to operate at 3 GHz, was measured for experimental verification of simulated and calculated results. © 2015 Wiley Periodicals, Inc. Microwave Opt Technol Lett 57:2358–2363, 2015

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This article presents a new technique for determining accurate values of resonant frequency and quality factor pertaining to the split-ring resonator. Different conducting shield materials have been used around a copper split-ring. The split-ring has been designed to operate at about 2.1 GHz. Various equations were worked out earlier to determine the values of resonant frequency and quality factor. However, these equations yielded different solutions. Therefore, simulations were used to obtain the values of the resonant frequency and quality factor of the split-ring resonator with different five-shield materials, using High-Frequency Structure Simulator (HFSS) software. In this work, a novel method has been introduced for obtaining values of resonant frequency which provides results with negligible error. An optimal technique, namely time-varying particle swarm optimization (TVPSO), was then performed to obtain two sets of equations for resonant frequency and quality factor. The two sets of equations, optimized using TVPSO, were compared for their effectiveness in matching the actual frequency and quality factor for each of the five materials. It was found that the TVPSO was significant in achieving the frequency and quality factor regression equation to accurately resemble the actual values portrayed by the low mean absolute error.