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In this article, an attractive multimodal substrate integrated waveguide (SIW) based methodology is presented for the characterization of magnetic materials in the broadband microwave frequency. The proposed approach employs a modified feed under-coupled SIW cavity instead of conventional feed over-coupled multiple SIW cavities; it uses the modified closed-form expression, developed from the first principle to consider the effect of finite sample dimensions, and mode-specific sinusoidal field variations, which were not considered before for magnetic testing using the over-coupled SIW cavity and conventional formulations. The metallic cavity borne approximations i.e., very small frequency shift for the imaginary part calculation, and very high Q-factor for the real permeability estimation are also relaxed in the modified formulations. The proposed technique is numerically verified using the full-wave electromagnetic (EM) simulator for several dispersive and nondispersive standard samples; thereafter, it is validated for the estimation of complex permeability of synthesized dispersive magnetic composites. It can characterize the dispersive magnetic composites, where the permeability value varies from paramagnetic to diamagnetic range, with improved accuracy than that of the conventional cavity perturbation approach. The modified formulation provides 34% and 12% better estimation of loss tangent and real permeability, respectively, as compared with the conventional technique. The uncertainty analysis for change in sample volume, sample misalignment, and the possible air gap is also carried out in detail. The proposed scheme typically provides more than 92% and 84% accuracy in the measured values of real permeability and loss tangent data, respectively, for various synthesized magnetic samples in broadband of microwave frequency (10–22 GHz). [ABSTRACT FROM AUTHOR]

In this paper, an attractive measurement technique is proposed to retrieve the broadband permittivity and permeability of the magneto-dielectric materials. The proposed technique is quite novel which mitigates the major problems associated with the conventional broadband RF material characterization techniques such as numerical instability and phase uncertainty when the length of the sample exceeds the integer multiple of half-wavelength. The approach adopted in this paper is quite unique as it alleviates the error normally caused by the sensitive phase measurement, since it only employs the relative amplitude of the scattering parameters, thus minimizing the measurement uncertainty. The proposed methodology here is based on the development of a unified scheme for the retrieval of dielectric and magnetic properties of magneto-dielectric samples, which is first tested for a number of reference samples using the numerically generated scattering coefficient data. Finally, the proposed technique is experimentally validated by measuring a number of standard samples over a broad microwave frequency range with the help of the coaxial line and the network analyzer. The dielectric and magnetic properties of samples retrieved using the proposed approach is always found to be in good agreement with their actual values available in the literature. [ABSTRACT FROM AUTHOR]

A robust cavity technique is proposed to quite accurately measure the complex permeability of the magnetic materials, which gives promising results for arbitrary length samples. This technique takes into account many factors such as magnetic field correction inside the sample under test, the effect of demagnetization, and the image theory, which was not considered in past. In this paper, a numerical model of the magnetometric demagnetization factor is developed, which precisely considers the effects of the relative permeability of sample and the nonuniform magnetic field over sample volume. The sensitivity of proposed technique is better than conventional and recently modified technique assuming arbitrary length sample. The proposed scheme typically provides 98% accurate result for the sample length greater than $0.15\times $ the width of the rectangular cavity. The proposed method is quite novel and can be appreciated due to the fact that it gives higher accuracy for all the cases when compared with other standard cavity techniques. [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]

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]

An improved rectangular cavity (RC) approach is proposed for the accurate complex permeability determination of materials in the microwave frequency band. The proposed approach assumes the bar-shaped magnetic specimen to be placed along the width of the cavity to increase the sensitivity of the measurement. A generalized closed-form formula is derived accordingly to determine the complex permeability of these bar-shaped samples in terms of the cavity parameters measured under both loaded and unloaded conditions. The proposed formula is found to improve the accuracy of the original RC approach where samples are placed in the $H$ -plane traversing the maximum width of the cavity for permeability measurement. The improvement in accuracy is facilitated by considering the sinusoidal magnetic field variation over the test sample, which is otherwise neglected in most of the earlier approaches. The modified formula is numerically tested for a number of samples having wide range of permeability variations, and the obtained results are typically 40% more accurate than the values obtained using the original formula. Finally, the synthesized magnetic samples, viz., the carbonyl iron-epoxy composite and the manganese ferrite, are measured by placing them inside the fabricated X-band cavity with the help of a vector network analyzer. The proposed approach is quite advantageous for magnetic materials as finite-size samples having sample to cavity volume ratio of less than 3e-3 can be characterized quite accurately with typical errors of 2% and 3% in the real and imaginary parts of the complex permeability, respectively. [ABSTRACT FROM PUBLISHER]

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 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]