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This article explains the frequency limitation in designing microstrip circuits based on a complementary split-ring resonator (CSRR) and reports a novel technique for increasing its operating frequency, which makes the CSRR suitable for high-frequency applications. This study helps in synthesizing the dimensions of symmetric CSRR (SCSRR) and asymmetric CSRR (ACSRR) circuits, which shows the applicability of the proposed technique in designing mm-wave circuits. It is observed that the upper frequency limit of the microstrip-coupled SCSRR is mainly due to weak electric coupling. The weak coupling implicates radiation loss in the structure, and the frequency at which the SCSRR has maximum loss due to radiation is found to be much less than the cutoff frequency of the higher order mode of the microstrip line, thus effectively limiting the operating frequency range of the circuit. In this article, the type of coupling and associated electrical parameters, e.g., reflected power, transmitted power, radiated power, losses, quality factor, voltage standing wave ratio, and gain, are investigated in detail. The allowable bandwidth of the fundamental mode of the microstrip line can be utilized to design CSRR with improved coupling. It is found that the ACSRR enhances the coupling coefficient using the cross-coupling effect. At higher frequencies, where the electric coupling is becoming too weak for the SCSRR, it is possible to design a magnetically coupled ACSRR of the same dimensions as the SCSRR. Finally, the design profile for both the SCSRR and ACSRR is studied in detail, and the radiating condition is discussed as a function of the height and dielectric constant of the substrate. For practical-verification purposes, two circuit prototypes are fabricated on a 1.5-mm-thick Rogers RT5880 substrate, and the measured results are found to be in good agreement with the proposition. It is found that, for a given microwave substrate, the maximum allowable resonating frequency of the ACSRR structure is nearly twice that of the SCSRR structure. [ABSTRACT FROM AUTHOR]

In this article, an attractive resonant technique is devised for calculating the dielectric properties of arbitrary length material under test (ALMUT), which is partially filled inside a waveguide cavity sensor. The proposed technique exempts two major assumptions viz. the depolarization effect and the theory of images, which were neglected in earlier cavity perturbation methods. A numerical model of the depolarizing factor, which precisely considers the impact of the relative permittivity and the sinusoidal variation of the electric field, is also formulated. First, the technical modification and the numerical analysis are provided and after that, a new set of formulas for characterizing the complex permittivity of ALMUT is developed. The numerical results suggest the accuracy and validity of the scheme for a broad range of dielectric samples, including the typical case, i.e., the full-length dielectric sample. The novelty of the presented technique can be ascertained from the fact that it provides higher accuracy irrespective of the actual sample length when compared with standard cavity techniques. A few standard dielectric samples with the partially filled arrangement are measured using the WR90 cavity, and the results are compared with their corresponding values obtained using the earlier reported conventional and modified techniques. It is found that the results evaluated using the devised scheme are consistent and independent of the actual dimensions of ALMUT. On the other hand, error in estimated complex permittivity using the earlier reported approaches shows substantial dependence on the sample size. [ABSTRACT FROM AUTHOR]

In this paper, the improved planar resonant sensors based on the generalized split ring resonator (SRR) configuration are proposed for the permittivity and the permeability testing of magneto-dielectric samples. It is observed that the proposed inter-digital capacitor-based SRR and the meandered line-based SRR provide better sensitivity for dielectric and magnetic measurement, respectively, when compared with the standard SRR-based microwave sensors. Both the sensors are first modeled under unloaded condition, using the full wave electromagnetic solver, the CST Microwave Studio, in order to ensure their operating frequency range near 2.45 GHz of industrial, scientific and medical band. In the next step, the numerical simulation of these sensors is carried out by loading them with a number of reference materials in order to develop empirical model for the determination of permittivity and permeability of test samples. Additionally, the equivalent circuit models of these sensors are obtained using the Advanced Design System circuit simulator and results are compared with the numerical simulation. All the sensors are designed and fabricated on 1.27-mm-thick RT/Duroid 6006 substrate, and testing is carried out using the network analyzer. A number of standard dielectric and magneto-dielectric samples are tested using the proposed scheme in order to retrieve their permittivity and permeability values. The measured data of each sample are in good match with the corresponding reference values available in literature having a typical error of less than 6%. [ABSTRACT FROM PUBLISHER]

A novel microwave noninvasive planar sensor based on the complementary split ring resonator (CSRR) is proposed for an accurate measurement of the complex permittivity of materials. The CSRR is etched in the ground plane of the planar microstrip line. Two CSRRs of rectangular and circular cross-sections are chosen for the sensitivity analysis, where the later is found to possess higher sensitivity and hence appears to be more appropriate for the sensor design. At resonance, the electric field induced along the plane of CSRR is found to be quite sensitive for the characterization of specimen kept in contact with the sensor. A numerical model is developed here for the calculation of the complex permittivity as a function of resonant frequency and the quality factor data using the electromagnetic simulator, the Computer Simulation Technology. For practical applications, a detailed air gap analysis is carried out to consider the effect of any air gap present between the test sample and the CSRR. The designed sensor is fabricated and tested, and accordingly the numerically established relations are experimentally verified for various reference samples e.g., teflon, polyvinyl chloride, plexiglas, polyethylene, rubber, and wood. Experimentally, it is found that the permittivity measurement using the proposed sensor is possible with a typical error of 3%. [ABSTRACT FROM PUBLISHER]

The applications of magnetic composites in electromagnetic shielding, resonance imaging, and biomedical drug research are growing rapidly. Therefore, there is a huge demand to characterize these materials in order to obtain their dielectric and magnetic properties in the microwave frequency range. In this paper, a novel rectangular cavity method is proposed to obtain the complex permeability and permittivity of the test sample placed in the $E$ -plane of the rectangular cavity. The proposed method eliminates the need of physical relocation of a specimen in the $H$ -plane, which is usually required in the case of presently available methods to characterize the magnetic samples. The closed-form formula for this unified approach is developed from the first principle, and is later modified to consider some practical consideration. The proposed method is first numerically tested and verified for various standard samples, where the data are taken from the literature. Thereafter, the $X$ -band rectangular cavity is designed and fabricated to measure a number of available samples. The significance of the proposed approach can be appreciated from the fact that even for finite-size samples, the permeability and permittivity can be extracted with the typical errors of 5% and 2%, respectively. [ABSTRACT FROM AUTHOR]

A novel planar multilayered epsilon-near-zero (ENZ) tunnel sensor based on fully laminated surface integrated waveguide (SIW) technology is proposed for the microwave measurement of dispersive materials. The proposed sensor is designed and optimized using parametric analysis to obtain the multilayered ENZ tunnel dimensions. It is observed that the width of the upper tunnel of the designed two-tunnel sensor should be at least half of the SIW width of the actual SIW structure for the multiband operation. The complex permittivity measurement using the proposed sensor is possible at two frequencies with a single set of measurement data. The proposed method is based on perturbation of the squeezed electric field having constant magnitude and high intensity inside the multilayered ENZ tunnel, which eventually increases the sensitivity of the proposed sensor. The sensitivity and accuracy of the proposed sensor are tested using both the simulated and the experimented data. It is found that the proposed sensor is highly sensitive, and typically demonstrates 6% error under ideal conditions, thus making it a good candidate for the microwave measurement of dispersive materials. [ABSTRACT FROM AUTHOR]

A generalized cavity method relaxing the major assumptions of conventional cavity perturbation technique is presented for characterization of the powdered sample in the microwave frequency range. The unified method, which is based on the inverse optimization technique, eliminates the complexity of measurement caused due to the existence of sample holder and produces an accurate result. In this paper, an attractive numerical calibration approach is proposed in lieu of the practical calibration technique which usually requires either a set of standards or a number of reference samples. The sample holder especially made of borosilicate glass is designed to contain the powdered samples, and the X-band rectangular cavity is fabricated. For verification of the proposed technique, the pulverized alumina and polyethylene oxide with various packing fractions are measured using the fabricated cavity and the vector network analyzer. The dielectric constant of these samples is extracted using the proposed unified approach which is found to be in good agreement with the theoretical data obtained by Landau-Lifshitz and Looyenga model. The accuracy of the proposed generalized cavity method for powdered samples is found to be better than the conventional resonator methods available in the literature. [ABSTRACT FROM AUTHOR]

A novel split-ring resonator (SRR)-based microwave sensor for accurately determining the real parts of the complex permittivity and the complex permeability of magnetodielectric composites is proposed. The proposed sensor is realized using the microstrip technology, where two SRRs coupled magnetically with the microstrip line are printed on two sides of the line. The sensor is designed using the full-wave electromagnetic solver and its equivalent circuit model is obtained. A numerical model of the proposed sensor is developed for extracting the magnetic and the dielectric properties of the sample under test in terms of change in resonance frequency after loading the device with the test specimen. The proposed methodology is validated by fabricating the sensor on RT/duroid 6006 substrate and testing various standard dielectric and magnetodielectric samples viz. Teflon, Poly vinyl chloride, Plexiglas, Polyethylene, Carbonyl iron, Ni0.6Co0.4Fe2O4, and Cobalt (30%)/Polystyrene composite in S-band. The measured relative permeability and the relative permittivity of the test specimens are found to be in close agreement with their values available in literature with maximum error of less than 8%. [ABSTRACT FROM PUBLISHER]

A novel cavity-based unified approach to measure the complex permittivity of dielectric samples placed in the E-plane of a rectangular cavity is presented. The proposed generalized cavity method is not limited to test specimens of smaller electrical dimensions, and requires two basic steps. The first step modifies the conventional cavity perturbation technique, where the effects of possible air gap between the cavity slot and the test specimen are also considered. The second step of the proposed approach employs a numerical optimization scheme, where the actual 3-D geometry of the fabricated cavity is simulated using the numerical field simulator, the Computer Simulation Technology (CST) Microwave Studio. The dielectric properties of the test specimen in this case are determined with the help of a MATLAB-based optimization routine, which calls the CST modules over the component object model interface and minimizes the error between the measured and the simulated scattering coefficients. The permittivity of the test specimen determined using the first step is provided as the initial guess to improve the convergence of the numerical optimization scheme. The proposed unified approach is validated by designing two rectangular cavities having different slot sizes operating in the TE107 mode. A number of standard dielectric samples are measured with the help of a vector network analyzer, and a very good agreement is observed between the measured permittivity values and the published data available in the literature having a typical error of less than 2% for samples of even larger dimensions. [ABSTRACT FROM PUBLISHER]

A novel microwave sensor with the mu-near-zero (MNZ) property is proposed for testing magnetodielectric material at 4.5 GHz. The sensor has a double-layer design consisting of a microstrip line and a metal strip with vias on layers 1 and 2, respectively. The proposed sensor can detect a unit change in relative permittivity and relative permeability with a difference in the operating frequency of 45 MHz and 78 MHz, respectively. The MNZ sensor is fabricated and assembled on two layers of Taconic RF-35 substrate, with thicknesses of 0.51 mm and 1.52 mm, respectively, for the measurement of the sample under test using a vector network analyzer. The dielectric and magnetic properties of two standard dielectric materials (Taconic CER-10 and Rogers TMM13i) and of yttrium–gadolinium iron garnet are measured at microwave frequencies. The results are found to be in good agreement with the values available in the literature, which shows the applicability of the prototype for sensing of magnetodielectric materials. [ABSTRACT FROM AUTHOR]