This work presents a noninvasive measurement technique to detect the blood glucose level for diabetic individuals using a fractal microwave resonator printed on an FR-4 substrate. The proposed fractal is based on the 1st order of Minkowski open loops (MOL) coupled with an open-stub transmission line (OSTL) to increase the resonator selectivity at 2.45 GHz. Moreover, an air gap in the middle path of the OSTL is filed with multi wall carbon nanotubes patch (CNT) to increase the field fringing at a specific region. The proposed resonator is designed numerically with CST Microwave Studio. The size limitations for biomedical devices are considered to account for wearable applications. Later, an analytical study is presented on the proposed resonator sensitivity. The detection technique is based on the resonant frequency tuning, bandwidth variation, impedance matching change, and phase displacement for the S-parameters in the S₁₁ and S₁₂ spectra. The sample under test is mounted on an CNT patch of the OSTL which employs the characterization of the specimen. The proposed design idea could be generalized for a wide variety of biomedical detection liquids.

An accurate rigorous modal theory has been applied to investigate the propagation characteristics in a rectangular waveguide filled with multilayer left-handed and right-handed metamaterials. It is shown that such a waveguide supports different passbands below the waveguide's cutoff frequency, and the number of passbands is related to the corresponding layers of different left-handed metamaterials (LHMs) filled in the waveguide. The rigorous modal analysis of this structure reveals in detail how the waveguide geometry and left-handed metamaterial parameters may be selected to design rectangular waveguides supporting double or triple below-cutoff passbands. The efficient power transmissions in these below-cutoff passbands are validated by using the full-wave simulation software HFSS. These structures supporting multiple below-cutoff passbands could find applications in waveguide components requiring miniaturization and multiband properties, such as miniaturized multifunctional antennas and filters.

Wireless communication plays a vital role in transmitting information from one point to another. Wireless devices have to be smart, intelligent, compact in size and cost effective to meet the demand of wireless communication. A multi-layered, Split Ring Resonator (SRR), negative permeability material inspired antenna has been designed, analyzed, fabricated, and measured. The developed antenna resonates at 1.13 GHz, 2.47 GHz, and 2.74 GHz frequencies with gain of 3.73 dBi, 6.18 dBi, 1.35 dBi, and bandwidth of 2.10%, 2.81%, and 2.09%, respectively. The structure utilizes FR4 material as a substrate. The engineered model has applications in navigation, WiFi, and satellite communication applications.

This paper presents a fifth-generation (5G) wireless smart antenna for performing both power substation communication (in space domain beam-steering) and electrostatic discharge (in time domain Ultra-high Frequency ``UHF'' impulse) detection. The same smart antenna used to communicate with other wireless antennas in the switchyard, as well as with the control room is utilized to cyclically gather data from power apparatus, busbars and switches where electrostatic discharge (ESD) may occur. The ESD poses a major threat to electrical safety and lifetime of the apparatus as well as the stability of the power system. The same smart antenna on which beam rotation in space-domain is designed by implementing an artificial neural network (ANN) is also trained in time-domain to identify any of the received signals matching the ultra-high frequency band electrostatic discharge pulses that may be superimposed on the power frequency electric current. The proposed system of electrostatic discharge detection is tested for electrostatic pulses empirically simulated and represented in a trigonometric form for the training of the Perceptron Neural model. The working of the system is demonstrated for electrostatic discharge pulses with rising times of the order of one nanosecond. The artificial intelligence system driving the 5G smart antenna performs the dual role of beam steering for 5G wireless communication (operating in the space domain) and for picking up any ESD generated UHF pulses from any one of the apparatus or nearby lightning leaders (operating in the time domain).

In wide-angle synthetic aperture radar (SAR), the scattering behavior of many illuminated objects might vary with the observation angle, which results in the degradation of the resolution and interpretability of the reconstructed imagery. To solve this problem, a sparse-based methodology is proposed in this paper to implement the separation of the anisotropic scattering target data and imaging processing simultaneously. The distinct reflection characteristics of the illuminated targets are employed to formulate a composite projection operator. Then, the sparse constraint is utilized to suppress cross-projection energy. Finally, the imagery of the anisotropic scattering targets could be derived with improved focal quality and interpretability. Numerical simulations could verify the validity of the proposed methodology.

In this paper, a substrate integrated waveguide (SIW) quasi-uniform leaky-wave antenna (LWA) is proposed for a dynamically steerable beam design at a single frequency through the use of a thin layer of nematic liquid crystal (LC) underneath the substrate. The orientation of the LC molecules, and therefore the effective dielectric properties of the LC cell, is controlled via an externally low-frequency, low-strength bias voltage. The radiation occurs through a series of closely placed transverse slots etched on the top plane of the SIW. This antenna was designed to operate based on the fundamental space harmonic (n=0) in the frequency range between 24.25 GHz and 29 GHz, which covers one of the future 5G frequency bands to be deployed in some parts of the world. This novel antenna design concept was verified numerically using a commercial software based on the Finite Element Method (FEM), and the results are presented and discussed herein.

For the first time, a real sized complex target that is coated with an absorber material is discriminated from the uncoated one using an aspect independent discrimination method based on natural resonances. This resonance based technique provides a real-time, accurate and aspect independent solution for stealth target discrimination. First, the discrimination is studied for a complex shaped aircraft of electrical size 1.5λ. The Perfectly Electrically Conducting (PEC) target is coated uniformly with sintered nickel-zinc-ferrite, a magnetic Radar Absorbing Material (RAM) with complex dielectric and magnetic properties. The resonant range Radar Cross Section (RCS) of the aircraft for different coating thicknesses is computed using the Method of Moments (MoM). The resonances contained in the RCS are extracted using the vector fitting method, and the dominant resonances representing the target are determined by applying the power criteria. The variation in the pole placements with the increasing coating thickness is also studied. A one number quantifier of discrimination --- ``Risk'' in dB is defined to express the amount of mismatch between the compared targets. Further, the discrimination technique is also studied for an aircraft of electrical length, 7λ. A Risk value of 2 dB and more is obtained in this study at all aspects. This demonstrates the capability of the algorithm to discriminate between targets of identical structure but with different material compositions.

Designs of a polygon shape microstrip antenna for increasing number of side lengths are studied. A detailed analysis is presented for the variations observed in the first and second order mode resonance frequencies in a polygon shape patch, from triangle to square to pentagon, ending up in a circle. Among all the polygon shapes, close spacing between the first two frequencies is obtained in the pentagon shape patch. A design of a pentagon shape microstrip antenna with a pair of slots is proposed. It gives impedance bandwidth of more than 700 MHz (>55%), which is maximum amongst all the polygon shapes employing a pair of rectangular slots. The proposed design offers peak broadside gain of 9 dBi over the bandwidth. A resonant length formulation and subsequent design methodology for the pentagon shape patch and its slot loaded variation are presented. This helps in the redesigning of a similar configuration in a given frequency range, using proximity and coaxial feeds.

A compact wearable antenna operating at 2.45 GHz with a novel Electromagnetic Band Gap (EBG) structure as a reflector is proposed. The broadband monopole is used as the main radiator of the antenna, and the gradient feeder structure and etched slot on the ground are used to adjust the matching effect of the antenna port. The current path is extended, and the structure is made more compact by slotting the surface of the EBG cell. Then, a 3 x 3 EBG reflector is constructed and loaded to the bottom of the antenna to improve the antenna gain performance and reduces the specific absorptivity (SAR). A three-layer human model (skin-fat-muscle) has been built in High Frequency Structure Simulator (HFSS) to analyse the influence of human tissue on the wearable antenna system. Combined with the practical application background, the radiation performance of the system under bending is also explored. The simulation results show that the application of EBG reflector can increase the antenna gain by about 4.77 dBi and the front-to-back ratio by 17dB, reduce SAR by more than 95%, and the overall size of the system is only 60.3 x 60.3 x 3.5 mm³ (0.49λ). The antenna system has the characteristics of simple structure, small size, high gain, and low SAR value, which is of certain reference value for the research on the wearable antenna.

In this article, a meander line dipole antenna for radio frequency identification (RFID) tag is presented. The loaded meander antenna has a simple meander line structure with a spiral inductor at the end for size miniaturization, a T-match structure and an inductively coupled parasitic element for impedance matching with the tag IC. The antenna is designed to operate in North American UHF RFID frequency band of 915 MHz. The size of the proposed tag antenna is 50 mm × 12 mm and has good impedance matching with Alien Higgs IC chip of 13.5-j111 Ω at the desired frequency band. The proposed tag antenna provides omnidirectional radiation pattern with a maximum read range of 3.5 m at an effective isotropic radiated power of 4 W. Simulation results are in good agreement with measurement results.

A novel computational technique is proposed for heat conduction analysis. The heat transfer equation is expanded in the complex frequency domain and solved using the finitedifference method (FDM). The results in the complex frequency domain are transformed into the time domain via fast inverse Laplace transform. In the proposed approach, the instantaneous temperature at a specific time can be easily obtained. Moreover, the computational time for the conventional explicit FDM is reduced by employing the time-division parallel computing method.

We recently proposed a two-dimensional synthetic space including one spatial axis and one synthetic frequency dimension in a one-dimensional ring resonator array [Opt. Lett. 41, 741 (2016)]. Nevertheless, the group velocity dispersion (GVD) of the waveguides that compose rings was ignored for simplicity. In this paper, we extend the previous work and study the topological one-way edge states in such a synthetic space involving GVD. We show that the GVD brings a natural vague boundary in the frequency dimension, so the topological edge state still propagates at several frequency modes unidirectionally along the spatial axis. Positions of such vague boundary can be controlled by changing the magnitude of the GVD. In particular, a relatively strong GVD can degrade this two-dimensional synthetic space to one-dimensional spatial lattice, but yet the one-way state is still preserved in simulations. Our work therefore exhibits the impact of the GVD on topological photonics in the synthetic space, which will be important for future practical experimental implementations.

A compact U-shaped ultra-wideband (UWB) multiple-input-multiple-output (MIMO) antenna with novel complementary modified Minkowski fractal (CMMF) for isolation enhancement is proposed. This antenna consists of two identical U-shaped monopole elements, a novel CMMF and a slot in the bottom of the ground plane for the isolation enhancement. The novel CMMF is designed by a technique iterated function system (IFS). The overall dimension of this compact antenna is 22 x 28 mm². The impedance bandwidth of this antenna is 10.35 GHz, ranging from 3.06 GHz to 13.41 GHz. The minimum isolation is 17.07 dB for the operating frequency range and 18.4 dB for the UWB frequency range 3.1 to 10.6 GHz. The diversity parameters are also determined for the proposed MIMO antenna, and all are found satisfactory. The proposed MIMO antenna is fabricated, and its prototype measured results are found in good agreement with the simulated ones.

This paper presents a modified version of minimum description length (MDL) method, referred as multifrequency MDL (FMDL), for scatterers enumeration before using the multiple signal classification (MUSIC) algorithm in microwave imaging applications. The inclusion of data from multiple frequencies should make an attempt to reduce the error in number estimation due to noise and multiple scattering. Data fusion in multiple frequencies is performed based on two schemes called averaging and maximization rules. The solution for MDL criterion which is a minimum for one frequency is not likely to be the solution for other frequencies, so by averaging the MDL criterion over the total frequencies or by maximization of the solution for each frequency, we can achieve the correct source number. Furthermore, a whitening step before applying FMDL method is employed to compensate the aspect limitations of the measured data due to the limited number of antennas. The superiority of the proposed FMDL approach with respect to the other competing methods is confirmed by both the numerical examples and the Institut Fresnel experimental dataset. The results indicate that the FMDL yields more accurate estimate of the targets number specially for the cases of low SNR values and very colsely spaced scatterers.

A meshless method for fast solution of the electromagnetic scattering problem related to arbitrary shaped radially inhomogeneous cylinders is proposed. This is an important problem since radially inhomogeneous circular cylinders are common in various engineering applications, and deformations such as notches, grooves and noncircular holes on such cylinders are required for different purposes. This approach is basically an extension of the previously proposed method, which is based on Fourier series representation of the electric field on boundaries. In the original method, a multilayer cylinder with arbitrary shaped homogeneous layers is considered, and accordingly, the general solution of the cylindrical wave equation in homogeneous medium is used. Here we modify the method by considering the general solution in radially inhomogeneous medium, and derive compact expressions for the field.

A substrate integrated waveguide circular cavity (SIWCC) bandpass filter is developed using printed circuit board technology. A circular cavity structure using TM₁₁₀ mode was employed in the design of the filter to operate at the frequency of 4.75 GHz, which is in the C-band frequency range. The filter was designed based on double-layer elements comprising a substrate integrated circular cavity (SICC) and a transmission line (TL) that produce single-mode resonance. In the proposed structure, circular resonators consisting of vias and a rectangular patch at the top layer are combined into a circular substrate integrated waveguide (SIW) structure. To achieve the desired resonance frequency, a triangle probe is etched at both sides of the microstrip line feeding section. The proposed structure is put in a conducting box to prevent radiation to the outside and eliminate radiation loss. Furthermore, the desired centre frequency and bandwidths of the passbands can be obtained by adjusting the dimension of the filter. To prove the concept, the filter structure is fabricated using Rogers RO₄₃₅₀B^TM circuit materials with a dielectric constant of ε_r = 3.48 and height of the substrate of 1.52 mm. The design was simulated using Ansoft HFSS simulator and measured using a vector network analyser. Simulation and fabrication results are compared for verification. The proposed SIWCC bandpass filter has potential applications in satellites and wireless communication systems.

In a probabilistic approach, the performance of the control is characterized by statistical indi-cators such as the Probability of Detection (PoD) which describes the probability of detecting a defect of a given size knowing that it is present in the inspected structure. In this paper, an experimental analysis and simulation using FEM of the eddy current testing on three-dimensional riveted structure is performed on small fatigue cracks to identify and quantify probability of detec-tion curves. The PoD curves are plotted in terms of characteristic dimensions of the defect (depth, length, orientation, etc.) and are dependent on a number of factors including material, geometry, defect type, operator, and environmental effects.

The recent growth of terahertz (THz) applications has sparked interest in the design of novel electromagnetic structures for this frequency regime. One of the structures is the THz absorber, used in sensing and imaging applications. Metamaterial based designs are commonly used to achieve the desired absorption characteristics. Absorbers whose spectra can be tuned by changing the temperature are a subclass in the broad family of THz absorbers that are used for temperature sensing. In the beginning years, single band temperature tunable absorbers were designed, and at present the focus has shifted to the design of multi-band temperature tunable absorbers. Absorbers with six tunable bands have already been proposed. In this paper an octa-band temperature tunable terahertz metamaterial absorber is proposed, whose unit cell consists of four orthogonally placed tapered triangular structures connected by a ring resonator on top of an InSb dielectric substrate. At 210K it is observed that the structure's absorption spectra are: 98.7% at 1.026 THz, 79.5% at 1.245 THz, 90.4% at 1.301 THz, 95.2% at 1.442 THz, 97.44% at 1.585 THz, 96.4% at 1.644 THz, 97.1% at 1.756 THz, and 90.4% at 2.071 THz. The temperature sensitivities of the proposed structure in eight of its absorption bands are 10.3 GHz/K, 8.22 GHz/K, 7.96 GHz/K, 7.02 GHz/K, 6.44 GHz/K, 6.17 GHz/K, 5.5 GHz/K, and 3.2 GHz/K, respectively. Thus, the proposed design can have practical applications in terahertz temperature sensing applications.

This paper describes a theoretical characterization of a Transverse Electric (TE)-polarized vortex beam antenna in the microwave range. The main body of the antenna consists of a cylindrical waveguide that is excited by a traveling-wave current ring feeder. A new design of the feeder is proposed. Closed-form formulas are obtained for the fields and the antenna input impedance following a conventional derivation based on the electric vector potential. A detailed dispersion analysis is used for accurate evaluation of the relevant spectrum and propagation properties. The effectiveness of the theoretical derivations is validated via full-wave numerical simulations.

As ionosphere is one of the most prominent sources of error, ionospheric TEC and scintillation studies are necessary for improving the performance of a navigation system. In this paper, the behavior of the correlation coefficient (ρ) between Rate of TEC Index (ROTI) and amplitude scintillation index (S₄) over low latitude station Hyderabad (Latitude: 17.44° (deg.) N, Longitude: 78.74° (deg.) E) for different seasons is analyzed. Also, the analysis is extended for nearly same longitude stations like Trivandrum, Bangalore, Bhopal, Delhi and Shimla for the higher values of total K_p index for 60 days (most disturbed 5 days per month). For Trivandrum (lowest latitude station), it is observed that both S₄ and ROTI are high as compared to Bangalore, Bhopal, Delhi, and Shimla. It is found that there is a good correlation between the temporal variations of ROTI with S₄ after post sunset hours. The confidence intervals for computed correlation coefficients at 95% confidence level are also given.