Induced Surface Currents Research Articles

Detecting Scattering Centers of Complex Scatterers Through Induced Surface Currents [Em Programmer’s Notebook

Detecting Scattering Centers of Complex Scatterers Through Induced Surface Currents [Em Programmer’s Notebook

Analysis of electromagnetic scattering from array of time-modulated graphene ribbons.

An accurate and fast method is presented for the analysis of scattering of electromagnetic waves from an array of time-modulated graphene ribbons. We derive a time-domain integral equation for induced surface currents under subwavelength approximation. Using the method of harmonic balance, this equation is solved for a sinusoidal modulation. The solution of the integral equation is then used to obtain the transmission and reflection coefficients of time-modulated graphene ribbon array. The accuracy of the method was verified through comparison with results of full-wave simulations. In contrast with previously reported analysis techniques, our method is extremely fast and can analyze structures with a much higher modulation frequency. The proposed method also provides interesting physical insights useful for designing novel applications and opens up new vistas in the fast design of time-modulated graphene-based devices.

Direct Simulation of the Surface Manifestation of Internal Gravity Waves with a Wave–Current Interaction Model

Abstract Internal solitary waves in the ocean are characterized by the surface roughness signature of smooth and rough bands that are observable in synthetic aperture radar satellite imagery, which is caused by the interaction between surface gravity waves and internal wave–induced surface currents. In this work, we study the surface signature of an internal wave packet in deep water over a large range of spatial scales using an improved wave–current interaction model that supports a moving surface current corresponding to a propagating internal gravity wave. After validating the model by comparison to previously published numerical results by Hao and Shen, we investigate a realistic case based on a recent comprehensive field campaign conducted by Lenain and Pizzo. Distinct surface manifestation caused by internal waves can be directly observed from the surface waves and the associated surface wave steepness. Consistent with observations, the surface is relatively rough where the internal wave–induced surface current is convergent (∂U/∂x < 0), while it is relatively smooth where the surface current is divergent (∂U/∂x > 0). The spatial modulation of the surface wave spectrum is rapid as a function of along-propagation distance, showing a remarkable redistribution of energy under the influence of the propagating internal wave packet. The directional wavenumber spectra computed in the smooth and rough regions show that the directional properties of the surface wave spectra are also rapidly modulated through strong wave–current interactions. Good agreement is found between the model results and the field observations, demonstrating the robustness of the present model in studying the impact of internal waves on surface gravity waves. Significance Statement The purpose of this study is to better understand the physical processes leading to the bands of rough and smooth surface waves arising from internal gravity waves. The surface manifestation of internal gravity waves allows them to be measured remotely via surface imagery, which can provide insight into their nonlinear behavior and sources and fate and which can ultimately inform the local stratification for assimilation into larger-scale models. Our results highlight the application of wave–current interaction models to the study of the interaction of surface waves with internal gravity waves and indicate strong modulation of the surface wave spectra over relatively short time scales despite the long time scales associated with the internal wave propagation.

Q Factor Enhancement of Open 2D Resonators by Optimal Placement of a Thin Metallic Rod in Front of the Longitudinal Slot

A rigorous approach was employed for the accurate evaluation of the electromagnetic interaction between a thin metallic rod and a two-dimensional (2D) slotted cavity. The problem was posed as a classical boundary value problem for the Helmholtz equation in which a 2D slotted open cavity is bounded by an arbitrary but otherwise smooth contour with a longitudinal slit. Using the method of analytical regularization, the problem was transformed to well-conditioned coupled infinite systems of linear algebraic equations for the Fourier coefficients in the expansions of induced surface currents on the rod and slotted cavity. When truncated to finite size, their solutions exhibit fast convergence to the exact solution as the order is increased. This feature makes it possible to investigate the spectral and scattering characteristics of the coupled cavity and rod to within any desired accuracy. In this paper, the complex eigenvalues for a slotted cavity in the presence of a thin rod and the dependence upon their relative location were investigated, particularly to find where there is significant or optimal enhancement of the Q factor. Such optimisation may be exploited in the design of advanced slot antennas and slotted waveguides.

Determination of the Forward Electromagnetic Coupling Radius in Chaff Cloud

Chaff cloud is a passive jammer that is widely used in many tactical applications. It contains huge numbers of metallic fibers to produce a strong echo. However, electromagnetic (EM) scattering estimation for the chaff cloud is a challenging task since complex EM coupling between chaff elements needs to be taken into account. Actually, if the distance and the angle between two chaff elements are large enough, the EM coupling becomes ignorable. This letter presents an estimation method of the EM coupling radius to designate a region, out of which EM coupling effect can be ignored. A current attenuation formula is first proposed to indicate the relationship between the induced surface currents of any two chaff elements. Using Dijkstra's algorithm, we then find the coupling paths with the weakest attenuation. The EM coupling radius is finally determined by measuring the distance between two ends of the selected paths. Simulation results show that the averaged EM coupling radius is 3.7 times wavelength of the radar in our discussions.

On Differential Imaging Using Electromagnetic Simulation for Vehicular Antenna Signature Analysis.

The current trend in vehicles is to integrate a wide number of antennae and sensors operating at a variety of frequencies for sensing and communications. The integration of these antennae and sensors in the vehicle platform is complex because of the way in which the antenna radiation patterns interact with the vehicle structure and other antennae/sensors. Consequently, there is a need to study the radiation pattern of each antenna or, alternatively, the currents induced on the surface of the vehicle to optimize the integration of multiple antennae. The novel concept of differential imaging represents one method by which it is possible to obtain the surface current distribution without introducing any perturbing probe. The aim of this study was to develop and confirm the assumptions that underpin differential imaging by means of full-wave electromagnetic simulation, thereby providing additional verification of the concept. The simulation environment and parameters were selected to replicate the conditions in which real measurements were taken in previous studies. The simulations were performed using Ansys HFSS simulation software. The results confirm that the approximations are valid, and the differential currents are representative of the induced surface currents generated by a monopole positioned on the top of a vehicle.

On the Use of Hybrid CFIE–EFIE for Objects Containing Closed–Open Surface Junctions

To effectively solve the electromagnetic scattering or radiation properties from the perfect electric conductor objects containing closed-open surface junctions, how to establish the hybrid combined field integral equation-electric field integral equation (CFIE-EFIE) is studied, which is different from the existing scheme for the objects, where the closed and open parts are separate. Furthermore, it is found that when the integral equation is solved using the method of moments, if the widely used RWG basis functions are employed to expand the induced surface current, the CFIE-EFIE may give inaccurate numerical results for the objects containing fine structures. The numerical accuracy can be improved by introducing the linear-linear (LL) basis functions. Moreover, to pursue a high computational efficiency, the LL and RWG basis functions are simultaneously used to expand the current on the fine structures and other relatively smooth surfaces, respectively, whose validity is verified by the numerical results.

The Transient Motion of A Current Loop Along A Conducting Cylindrical Shell.(Dept.E)

A mathematical and an analytical procedure for calculating the induced surface eddy currents in a cylindrical shell due to an arbitrary moving concentric current loop is developed. The consideration involves both uniform and accelerated motions. The accelerated motion, has the form of a finite ramp function, by which the current loop moves with a constant acceleration during a given time interval to a certain velocity. The surface currents induced in the cylindrical shell are governed by a time-dependent linear differential equation, which is then solved by the method of Laplace transforms. A solution in the form of Fourier and convolution integrals is achieved. The analytical solution is demonstrated in a graphical form in which the induced surface currents for both uniform and accelerated motion are presented. The solution so obtained is then extended to an arbitrary motion. The force acting on the moving current loop is also calculated and the results are presented in analytical and graphical forms.

Single-layer metasurface for ultra-wideband polarization conversion: bandwidth extension via Fano resonance

In this paper, we propose a method of designing ultra-wideband single-layer metasurfaces for cross-polarization conversion, via the introduction of Fano resonances. By adding sub-branches onto the unit cell structure, the induced surface currents are disturbed, leading to coexistence of both bright and dark modes at higher frequencies. Due to the strong interaction between the two modes, Fano resonance can be produced. In this way, five resonances in all are produced by the single-layer metasurface. The first four are conventional and are generated by electric and magnetic resonances, whereas the fifth one is caused by Fano resonance, which further extends the bandwidth. A prototype was designed, fabricated and measured to verify this method. Both the simulated and measured results show that a 1:4.4 bandwidth can be achieved for both x- and y-polarized waves, with almost all polarization conversion ratio (PCR) above 90%. This method provides an effective alternative to metasurface bandwidth extension and can also be extended to higher bands such as THz and infrared frequencies.

Reverse trajectory study of oil spill risk in Cyclades Islands of the Aegean Sea

The impact of hypothetical oil spills in Cyclades Islands (Aegean Sea, Eastern Mediterranean) is investigated by a reverse trajectory method whereby tracers have been back-tracked using surface current and wind data from 2013 to 2018. Results show that the westernmost islands of the archipelago (Kithnos, Kea, Andros) are at high risk all year round due to the proximity to the western oil tanker route (Bosphorus to Western Mediterranean). The arrival time of oil to these islands is less than 1 day, with the involvement of the entire perimeter of each island. The eastern islands are exposed to oil coming from the eastern oil tanker route (Bosphorus to Suez). In the summer, oil can reach the northern coast of Amorgos and Donousa in less than 1 day and Naxos in less than 2 days due to persistent ‘meltemi’ and induced surface current. Oil surveillance (for example by SAR) should focus all year round on the western route and on the eastern route north of the archipelago during the summer.

A Low Cost and Portable Microwave Imaging System for Breast Tumor Detection Using UWB Directional Antenna array

Globally, breast cancer is a major reason for female mortality. Due to the limitations of current clinical imaging, the researchers are encouraged to explore alternative and complementary tools to available techniques to detect the breast tumor in an earlier stage. This article outlines a new, portable, and low-cost microwave imaging (MWI) system using an iterative enhancing technique for breast imaging. A compact side slotted tapered slot antenna is designed for microwave imaging. The radiating fins of tapered slot antenna are modified by etching nine rectangular side slots. The irregular slots on the radiating fins enhance the electrical length as well as produce strong directive radiation due to the suppression of induced surface currents that radiate vertically at the outer edges of the radiating arms with end-fire direction. It has remarkable effects on efficiency and gain. With the addition of slots, the side-lobe levels are reduced, the gain of the main-lobe is increased and corrects the squint effects simultaneously, thus improving the characteristics of the radiation. For experimental validation, a heterogeneous breast phantom was developed that contains dielectric properties identical to real breast tissues with the inclusion of tumors. An alternative PC controlled and microcontroller-based mechanical MWI system is designed and developed to collect the antenna scattering signal. The radiated backscattered signals from the targeted area of the human body are analyzed to reveal the changes in dielectric properties in tissues. The dielectric constants of tumorous cells are higher than that of normal tissues due to their higher water content. The remarkable deviation of the scattered field is processed by using newly proposed Iteratively Corrected Delay and Sum (IC-DAS) algorithm and the reconstruction of the image of the phantom interior is done. The developed UWB (Ultra-Wideband) antenna based MWI has been able to perform the detection of tumorous cells in breast phantom that can pave the way to saving lives.

Analytical and rigorous method for analysis of an array of magnetically-biased graphene ribbons

A sheet of graphene under magnetic bias attains anisotropic surface conductivity, opening the door for realizing compact devices such as Faraday rotators, isolators and circulators. In this paper, an accurate and analytical method is proposed for a periodic array of graphene ribbons under magnetic bias. The method is based on integral equations governing the induced surface currents on the coplanar array of graphene ribbons. For subwavelength size ribbons subjected to an incident plane wave, the current distribution is derived leading to analytical expressions for the reflection/transmission coefficients. The results obtained are in excellent agreement with full-wave simulations and predict resonant spectral effects that cannot be accounted for by existing semi-analytical methods. Finally, we extract an analytical, closed form solution for the Faraday rotation of magnetically-biased graphene ribbons. In contrast to previous studies, this paper presents a fast, precise and reliable technique for analyzing magnetically-biased array of graphene ribbons, which are one of the most popular graphene-based structures.

Intensive vertical orientation Smith-Purcell radiation from the 2D well-array metasurface.

We present an intensive vertical orientation Smith-Purcell radiation with the 2D well-array metasurface. It is shown that the moving electrons can induce three induced surface currents at the well-array metasurface, where a strong coupling among them takes place. The coupling significantly improves the radiated field intensity and shapes the radiation angle-distribution. The theoretical results show that the Smith-Purcell radiation's field intensity is 3 times larger than the one within a conventional grating structure with directional radiation at 90 degree. Therefore, much stronger intensity and more centralized directional radiation will provide a promising way to develop electron beam driven THz sources.

Estimating Quadrature Errors in the EFIE-Based MoM Matrix, Due to Inner Integrals

The method of moments based on the electric-field integral equation is widely used for numerically solving induced surface currents on conducting structures. To set up the impedance matrix, weakly singular and near-singular inner-surface integrals must be evaluated. A leading numerical integration scheme for this purpose is Radial-Angular- ${\rm R}^{1}$ -Sqrt (RA- ${\rm R}^{1}$ -Sqrt), near and true singularity cancellation transformation quadrature. For outer integrals, standard Gauss–Legendre quadrature is used. A new and improved, closed-form, RA- ${\rm R}^{1}$ -Sqrt quadrature error estimate is derived. It is then used for a priori matrix entry error estimation due to inner integral, near-singularity quadrature. Standard, Rao–Wilton–Glisson basis functions on flat triangle elements are considered.

A Novel Dielectric Strip Resonator Filter

In this letter, a novel half-wavelength dielectric strip resonator that consists of a thin dielectric strip with high permittivity and a low-permittivity substrate with the bottom ground plane is proposed and theoretically investigated. The dielectric strip is used to replace the metal strip of the traditional microstrip line. Since there is no induced surface current on the dielectric strip, the unloaded quality factor ( $Q_{u}$ ) of the proposed resonator can be improved significantly, especially at high frequency. Meanwhile, the proposed resonator can be easily excited by the tapped microstrip line for constructing the bandpass filter (BPF), because its E-field distribution is similar to the microstrip counterpart. For demonstration, a third-order dielectric strip resonator BPF centered at 10.5 GHz is designed, implemented, and measured. Good agreement between the simulated and measured results can be observed. The minimum in-band loss is only 0.6 dB.

Scattering of E Polarized Plane Wave by Rectangular Cavity With Finite Flanges

AbstractThe rigorous Method of Regularization is implemented for accurate analysis of wave scattering by rectangular cavity with finite flanges. The solution is free from limitations on problem parameters. The calculation of the induced surface current, bistatic radar cross section (RCS) and frequency dependence of monostatic RCS are performed with controlled accuracy in a wide frequency band.

Reflectivity of two-dimensional airfoils illuminated by H-polarized plane wave: Rigorous approach

ABSTRACTThis article presents the implementation of the rigorous method of analytical regularization for the scattering of an H-polarized plane wave by the classical airfoil described by the Zhukovski transform. The reflectivity of airfoils is studied over a wide frequency band. The results obtained complement the previous studies concerning E-polarized waves. A comparative analysis for cases of the E- and H-polarization is carried out. Accurate calculations of the induced surface current, far-field scattering patterns, and frequency dependence of the monostatic radar cross section are presented.

Surface waves at the interface between a dielectric and a topological insulator

Surface waves that propagate along the interface between an isotropic linear or nonlinear (of the Kerr type) dielectric and a topological insulator have been studied theoretically. A dispersion relation for surface waves, which are represented by superpositions of TE and TM waves, has been obtained. This hybridization occurs because, upon passage through the interface, the polarization of a surface wave changes, which is caused by an induced surface current (which is transverse to the electric field vector of the wave). The surface current of this kind is characteristic of topological insulators. Expressions for the energy flux transferred by a surface wave have been given.

Thermodynamics of polarized relativistic matter

We give the free energy of equilibrium relativistic matter subject to external gravitational and electromagnetic fields, to one-derivative order in the gradients of the external fields. The free energy allows for a straightforward derivation of bound currents and bound momenta in equilibrium. At leading order, the energy-momentum tensor admits a simple expression in terms of the polarization tensor. Beyond the leading order, electric and magnetic polarization vectors are intrinsically ambiguous. The physical effects of polarization, such as the correlation between the magneto-vortically induced surface charge and the electro-vortically induced surface current, are not ambiguous.

Evaluation of steel fiber distribution in cement-based mortars using active microwave thermography

The non-uniform distribution of steel fibers in fiber-reinforced cement-based mortars (FRCMs) can lead to heterogeneous properties of hardened material with direct impact on mechanical properties. Among various nondestructive testing techniques, the active microwave thermography (AMT) has shown good potential for inspection of cement-based materials. AMT utilizes combination of microwave energy to generate controlled and localized heating and uses commercially-available infrared cameras to capture surface thermal images in real-time. Utilizing AMT, four FRCM samples made with different steel fiber volumes ranging from 0 to 3 % were investigated to evaluate the feasibility of this method for detecting and quantifying fiber distribution. Full-wave coupled electromagnetic-thermal numerical modeling was also conducted to evaluate the effect of dielectric properties, fiber depth, and fiber clumping on surface thermal profile. The results of simulations indicate that increase in fiber depth results in lower surface temperature, due to lower heating associated with induced surface current. Based on AMT measurement results, samples with higher fiber contents were shown to undergo greater increase in surface temperature, as observed for samples with 1 and 2 % fibers. However, this tendency was reversed with further fiber addition from 2 to 3 %, due to the potential of fiber clumping. Furthermore, the fiber clumping and lower level of fiber homogeneity for FRCM with 3 % fiber resulted in 55 % lower flexural toughness compared to the FRCM containing 2 % fiber. The results of fiber homogeneity measured from freshly cast prism were found to correlate well with those obtained from AMT technique determined on hardened samples.