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.

Non-contact vital sign detection using radar is relevant for many applications. In search and rescue missions in disaster-stricken areas, this technology can be used to non-invasively detect live survivors on the ground. However, in a very large disaster area, a fast and effective detection approach is required. This need has suggested radar mounted on a flying platform such as a drone as the most feasible approach. This task is challenging, since human respiration is weak, and the signal recorded is easily affected by disturbances such as noise and movement of the platform. Therefore, in this study, we propose a signal processing technique to deal with this problem. Human respiration signals modulate a hyperbolic pattern recorded by moving radar because of distance projection, leading us to applying sequential image processing steps and hyperbolic pattern reconstruction to extract respiration signals. A Fourier transform is then applied to seek the respiration frequency component. The results of laboratory experiments show that the proposed method can detect human respiration. As an important note, the flying speed of the platform should be determined carefully to cope with slow human respiration.

Cherenkov radiation (CR) is a promising method to generate high-power terahertz (THz) electromagnetic (EM) waves, which are highly desired in numerous practical applications. For the purpose of economy energy, naturally occurred materials with flat surface (e.g. graphene), which can support highly-confined surface-plasmon-polariton (SPP) modes, have been proposed to construct high-efficiency terahertz CR source; however, these emerging materials cannot be easily fabricated nor flexibly designed. Here, we propose a designer-SPP metamaterial scheme to pursue terahertz CR. The metamaterial is a structure-decorated metal surface, which is compatible with planar fabrication, and can support SPP-like EM modes in terahertz frequencies, also named as designer SPP. Due to the structure dependence of designer SPP, its dispersions can be flexibly designed by changing the structure geometries as well as choosing proper dielectric medias. Numerical results clearly demonstrated this scheme. Our proposal may promise future high-efficiency and intense THz source with design flexibilities.

Fluorescence confocal laser scanning endomicroscopy is a novel tool combining confocal microscopy and endoscopy for in-vivo subcellular structure imaging with comparable resolution as the traditional microscope. In this paper, we propose a three-channel fluorescence confocal microscopy system based on fiber bundle and two excitation laser lines of 488nm and 650nm. Three fluorescent photomultiplier detecting channels of red, green and blue can record multi-color fluorescence signals from single sample site simultaneously. And its ability for in-vivo multi-channel fluorescence detection at subcellular level is verified. Moreover, the system has achieved an effective field of view of 154μm in diameter with high resolution. With its multi-laser scanning, multi-channel detection, flexible probing, and in-vivo imaging abilities it will become a powerful tool in bio-chemical research and diagnostics, such as the investigation of the transport mechanism of nano-drugs in small animals.

In this paper, the effectiveness for inferring the responses to electromagnetic threats of the finite difference time domain method combined with a multi-conductor, multi-shield and multi-branched cable harness transmission line solver is validated by comparing simulation results with measurements performed on an equipped cockpit partially made by carbon fiber composite. A complete lightning indirect effects and high-intensity radiated field testing campaign was carried out in this cockpit within the scope of the European research and technology project Clean Sky 2 whose main goal is to reduce the aviation environmental impact by, for instance, building low-weight aircrafts with the increasing use of carbon fiber. Simulations are performed with EMA3D and MHARNESS obtaining very good agreement with measurements for a variety of observables and in a wide frequency range, thus proving the predictive capacity of these numerical methods for estimating the electromagnetic behavior of complex structures.

In this article, a novel dual-band multi-port compact rectenna design for RF energy harvesting is proposed. An E-shaped coaxial fed microstrip antenna combined with an inverted L-shaped structure is used to achieve a dual-band operation at 0.9 GHz (GSM900) and 2.4 GHz (WiFi) frequency bands with gains of 0.8 dBi and 4.4 dBi, respectively. A shorting post is incorporated in the design, which restricts the antenna size to 50 mm x 47 mm, making the overall rectenna compatible with any sensor nodes. Further, a compact rectifier circuit covering both the frequency bands is designed to obtain a conversion efficiency up to 50% for an input power as low as -20 dBm. The matching circuit ensures that the nonlinear impedance of the rectifier matches with that of the antenna under varying operating conditions. Finally, the rectennas designed are combined and arranged together to form a cubical structure to produce an output voltage as large as 0.5 V for an input power of -20 dBm. With 360˚ coverage and orthogonal polarization reception, the cubical antenna arrangement ensures improved harvesting efficiency making the proposed design suitable for powering low power IoT devices.

In this paper, two microstrip antennas with a U-slot on the patch are presented for base station applications to provide simultaneous communications for uplink and downlink respectively. The intended antennas are expected to operate in triple bands, i.e., to cover GSM and LTE bands. The three designated bands for uplink antenna are from 823 MHz to 830 MHz for lower band, 1.738 GHz to 1.761 GHz for middle band and 2.321 GHz to 2.355 GHz for upper band. Similarly, the antenna which is designed for downlink operates in three bands from 872 MHz to 880 MHz for lower band, 1.81 GHz to 1.85GHz for middle band, and 2.338 GHz to 2.375 GHz for upper band. These frequency band(s) satisfy the requirements of GSM850, GSM1800, and LTE2300 bands. Comparisons among designed, simulated and measured results are presented. Isolation parameters and the Envelope Correlation Coefficient (ECC) values of Multiple Input Multiple Output (MIMO) antenna in all specified bands are also presented.