Abhishek Kumar Jha

Design and Application of the CSRR-Based Planar Sensor for Noninvasive Measurement of Complex Permittivity

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%.

A Generalized Rectangular Cavity Approach for Determination of Complex Permittivity of Materials

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.

An Improved Rectangular Cavity Approach for Measurement of Complex Permeability of Materials

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.

Improved Resonator Method for Microwave Testing of Magnetic Composite Sheets

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.

Design of Multilayered Epsilon-Near-Zero Microwave Planar Sensor for Testing of Dispersive Materials

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.

SIW cavity based RF sensor for dielectric characterization of liquids

A novel microwave SIW cavity based microfluidic sensor is designed and fabricated for detection and determination of dielectric constant of common liquids at 2.45 GHz. The technique is based on material perturbation theory. The developed sensor is the miniaturized version of the conventional rectangular cavity where the lateral walls are shorted with copper film coating. The proposed sensor is planar, highly sensitive, cost effective and about 100 times smaller than corresponding waveguide cavity. The electric coupling is provided by means of 3.5 mm SMA connector. In this paper, the calibration of fabricated SIW cavity is performed with water which provides easier way to calculate coefficients of perturbation. Various types of liquids are tested to verify the sensitivity and obtained results are in close agreement with the published data.

Automated RF measurement system for detecting adulteration in edible fluids

In this paper, an automated RF system is presented to find the adulteration in common edible products and liquids. The proposed system is based on measurement of the complex permittivity using a modified rectangular waveguide cavity setup. The developed measurement system is automated to evaluate the percentage of adulteration in the test fluid by measuring the complex permittivity of the adulterated sample and comparing it with the reference data. The designed RF system is able to typically detect a contamination of up to 5% in most of the edible products.

Design of SRR-Based Microwave Sensor for Characterization of Magnetodielectric Substrates

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%.

Permittivity measurement of common solvents using the CSRR based sensor

In this paper, the microwave characterization of common polar and non-polar solvents has been carried out using the planar resonant sensor. The proposed sensor resonates at 2.65 GHz due to the etched complementary split ring resonator (CSRR) in the ground plane of the microstrip-line. The test solvent is filled into a container which covers the CSRR and is mechanically pressed against the ground plane with water proof adhesive filling the gap between them. The solvent inside the container changes the capacitance of the CSRR which causes a shift in the resonant frequency. This frequency shift is used for the measurement of the dielectric properties of solvent samples. The proposed sensor is numerically verified and experimentally tested to estimate the dielectric properties of various standard solvents with a typical error of 2-4%.

Generalized RF Time-Domain Imaging Technique for Moving Objects on Conveyor Belts in Real Time

In this paper, an attractive time-domain RF imaging technique is proposed for online monitoring of moving objects over conveyor belts. The proposed technique combines the strength of the time-domain approach and the Riccati equation-based ultrawideband reconstruction method in order to image the stratified lossy dielectric medium. The applicability of the proposed method is first tested under stationary condition by reconstructing the permittivity and conductivity image of the target area comprising of various standard samples placed in free space. For moving objects under real-world scenario, two antenna arrays comprised of ultra-wideband Vivaldi elements are designed and tested. These arrays are then employed to produce the 2-D microwave image of various wooden-based samples and human mannequins carrying metal object concealed behind the cloth. The obtained real-time microwave image of the test medium shows that the proposed RF imaging technique is best suited for online monitoring of stationary as well as moving targets, where the structural as well as the electrical properties of the test medium can be obtained through a nondestructive process without using any iterative scheme.