M. Jaleel Akhtar

Embedding instruments & modules into an IEEE1451-FPGA-Based Weblab infrastructure

A LabVIEW based general purposed module to understand and visualize the electromagnetic field patterns inside commonly used microwave devices is developed. The module provides both the electric and magnetic field patterns for any arbitrary mode configuration inside the rectangular waveguide and the cavity, which are the microwave devices mostly being taught at undergraduate levels in the electrical engineering. The developed module helps the user in gaining a better and deeper understanding of the electric and magnetic field patterns and modes inside the guiding and closed structures.

Investigation and performance evaluation of carbon black- and carbon fibers-based wideband dielectric absorbers for X-band stealth applications

This paper presents the design, preparation, and electromagnetic testing of wideband dielectric absorbers based on carbon fibers and carbon black powders for stealth applications. The specially prepared absorbers are characterized using the partially filled waveguide technique for the complex permittivity, and the return loss of the sample is measured using the free-space system in the X-band frequency region. A maximum return loss of 29 dB i.e. absorption of 99% at 10.3 GHz is achieved with minimum 97% absorption throughout the X-band frequency region. The fabricated absorber having density of 0.28 gm/cc and thickness of 2 mm makes it a potential candidate for stealth applications especially for the defense targets. A multilevel fast multipole method-based electromagnetic simulation is carried out on the artillery shell model, and on the leading edge model of the aircraft using the measured electromagnetic properties of designed absorber for the radar cross-section (RCS) reduction. The maximum RCS reduction of 27 and 20 dB has been observed for the artillery shell model, and for the leading edge of stealthy aircraft model, respectively, as compared to that of the PEC structure at 10.3 GHz frequency.

Microwave Imaging of Stratified Media From Band-Limited Reflection Coefficient Data

A novel analytical approach for the 1-D microwave imaging of the stratified dispersive media is presented. The proposed approach provides the depth-dependent permittivity profile of the target area in terms of the spectral-domain reflection coefficients, which are measured at the surface of the interrogating medium over a band of frequencies depending upon the available antennas and other measuring equipment. The inverse solution of the depth-dependent permittivity profile is obtained with the help of a newly derived integral transform, which is the amended form of the conventional Fourier transform valid under situations where the spectral-domain reflection data are present only over a band of frequencies. The derived inverse solution is also made applicable for the dispersive media, such as the rectangular waveguides, by facilitating the separation of spectral and spatial variables in an innovative way. The applicability of the proposed approach is validated by reconstructing the depth-dependent permittivity profiles of a number of multilayered and stratified media using both the simulated and the measured reflection coefficient data with the help of the developed algorithm.

Directivity enhancement of double slot Vivaldi antenna using anisotropic zero-index metamaterials

In this paper, a compact design of the ultra-wideband (UWB) highly directive double slot Vivaldi antenna (DSVA) is presented for microwave application in the frequency range of 2-10 GHz. In order to improve the directivity of the proposed DSVA, the zero index metamaterial (ZIM) unit cells are loaded on the E-plane of the antenna. It is found that the directivity of the ZIM loaded DSVA is increased by 5.5 dB as compared with the reference tapered slot Vivaldi antenna. The proposed antenna is fabricated on the FR-4 substrate and the return loss is measured using the vector network analyzer in the non-anechoic environment. Preliminary results show that the directivity of the proposed antenna is significantly increased in the frequency range of 5 to 9 GHz.

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.

Design of anisotropic zero-index metamaterial loaded tapered slot vivaldi antenna for microwave imaging

In this paper, a compact design of conventional tapered slot antenna (TSA) loaded with the anisotropic zero-index metamaterial (ZIM) for the frequency range of 1 to 10 GHz is presented. The proposed TSA loaded with the ZIM exhibits an increase in the directivity up to 2.6 dB. The designed antenna is fabricated on the FR-4 substrate and tested. A good agreement between the simulated and the measured results is obtained.

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.

A novel half space time-domain measurement technique for one-dimensional microwave imaging

In this paper, the moisture content for cement based materials having different water to cement (w/c) ratios is measured using the microwave free space technique. The overall process is non-destructive and employs the time-domain measurement data. The measurement system consists of a vector network analyzer, a wide-band lens horn antenna, cement based material of having different water to cement (w/c) ratio and associated microwave components. The main focus here is to determine the permittivity, the effective conductivity and the thickness of test specimens under the situation, where only reflection measurements can be carried out due to the restricted access of the object from the other side. It is observed that the effective conductivity is directly proportional with the moisture content or the w/c ratios of these test samples.

Design of Flexible Hybrid Nanocomposite Structure Based on Frequency Selective Surface for Wideband Radar Cross Section Reduction

This paper presents the design, synthesis, and testing of a novel flexible hybrid nanocomposite (FHN) structure for the wideband radar cross section (RCS) reduction of targets. The proposed FHN structure consists of a frequency selective surface (FSS) pattern printed on a thin flexible polyimide film backed by aluminum foil, which is then integrated with a customized flexible nanocomposite sheet. The nanocomposite sheet consists of graphite fillers combined with zinc oxide powders, which are embedded into the thermoplastic polyurethane matrix. The fabricated nanocomposite sheet is first characterized for the effective permittivity and the dielectric loss tangent using the free-space measurement technique, and the measured electromagnetic properties are then used for the design of an FHN structure. The proposed FHN structure having overall thickness of 1.335 mm shows minimum reflection coefficient (RC) of −28 dB at 10.2 GHz, along with −10 dB RC bandwidth in the entire

Automated RF measurement system for detecting adulteration in edible fluids

X