Dielectric Cylinder Research Articles

Research on Transmission Characteristics of Two-Dimensional Superconducting Photonic Crystal in THz-Waves

In this paper, the transmission characteristics of two-dimensional photonic crystal with Hg-1223 cylindrical array in transverse magnetic mode are studied in terahertz-waves by shift operator finite-difference time-domain method. The effects of external temperature and pressure and the period and radius of the dielectric cylinders on the transmission properties of superconducting photonic crystal in terahertz-waves are studied. The simulation results show that external temperature and pressure can be used to change the plasma frequency of superconductor, thus adjusting band gap width of superconducting photonic crystal. The decreasing of the external temperature or the increasing of the pressure have resulted in the increasing of the band gap width of superconducting photonic crystal, while increasing external temperature or decreasing the pressure can decrease the band gap width, which gradually becomes apparent as temperature increases or pressure decreases. In addition, the increasing of the periods and radius of superconducting cylinders can also broaden the band gap of superconducting photonic crystal in terahertz-waves. The research in this paper is in terahertz-waves, and all the cutoff frequencies of band gap are between 0.1 and 6 THz, which provides references for practical application of superconducting photonic crystal.

An enhanced finite difference time domain method for two dimensional Maxwell's equations

AbstractAn enhanced finite‐difference time‐domain (FDTD) algorithm is built to solve the transverse electric two‐dimensional Maxwell's equations with inhomogeneous dielectric media where the electric fields are discontinuous across the dielectric interface. The new algorithm is derived based upon the integral version of the Maxwell's equations as well as the relationship between the electric fields across the interface. To resolve the instability issue of Yee's scheme (staircasing) caused by discontinuous permittivity across the interface, our algorithm revises the permittivities and makes some corrections to the scheme for the cells around the interface. It is also an improvement over the contour‐path effective permittivity algorithm by including some extra terms in the formulas. The scheme is validated in solving the scattering of a dielectric cylinder with exact solution from Mie theory and is then compared with the above contour‐path method, the usual staircasing and the volume‐average method. The numerical results demonstrate that the new algorithm has achieved significant improvement in accuracy over other methods. Furthermore, the algorithm has a simple structure and can be merged into current FDTD software packages easily. The C++ source code for this paper is provided as supporting information for public access.

Unidirectional helical edge states for all-dielectric topological photonic crystals

The study of one-way edge states of electromagnetic wave based on quantum Hall effect in photonic crystals (PCs) has recently made a great progress. In particular, the pseudo-spin states in topological PCs made of dielectric materials can be realized by breaking pseudo-time-reversal symmetry. We perform a research on the influence of parameters, such as lattice constant, dielectric permittivity of cylinders, radius of the dielectric cylinder and scaling factor of PCs, on the photonic bandgaps of topological PCs. Based on the analysis results, we present a 2D topological PC configuration that supports robust unidirectional helical edge states along zigzag interface between the topologically trivial and nontrivial PCs. With the structure, an operating bandwidth as larger as of $$0.0173\;(2\pi c/a)$$, robust helical edge states with energy-condensed and great nonreciprocity can be achieved by exciting a circularly polarized source. Utilizing this kind of architecture, we construct Z-shaped channel to demonstrate the robustness of helical edge states transport in different cases. The research offers a valid way for realizing unidirectional edge states with robust transport in practicable quantum communication applications.

Electrically tunable mantle cloaking utilizing graphene metasurface for oblique incidence

An analytic formulation to achieve mantle cloaking of a dielectric cylinder using scattering cancellation method for TMz polarized oblique incidence is presented. To obtain this goal, a closed form expression for the required surface impedance of the covering metasurface is derived. By properly tuning the chemical potential of graphene, its surface impedance is adjusted for the invisibility of the considered cylinder for arbitrary angles of the impinging plane wave. The scattering width reduction of 15.7 dB and 21.27 dB is obtained with 3-dB bandwidth of 18.7% and 10.6% at 1 THz and 1.5 THz, respectively for the incident angle of 60 degrees. Furthermore, by optimizing the surface impedance of graphene, finite cylinders can also be cloaked. The results indicate 11.4 dB and 13.5 dB radar cross section (RCS) reduction with 30% and 22% 3-dB bandwidth for the incident angles of 45 and 80 degrees, respectively. Full-wave simulations verify the analytical results. The effect of the cloaking is examined by comparing the input impedance of a pyramidal horn antenna when it is loaded with an array of bear and cloaked cylinders positioned in the aperture.

On anomalous absorption of electromagnetic radiationby a subwave metal wire

Background: The effect of anomalously strong absorption, scattering and attenuation of microwave electromagnetic radiation by thin conductive wires is considered. The investigated effect can be used in the development of radio-absorbing and radio-masking materials for various purposes. The aim of the work is to clarify the physical nature of the effect. Materials and methods:. On the basis of the generalized Lorentz-Mi theory the mathematical model of diffraction interaction of microwave radiation with a cylindrical object which material is characterized by a complex refractive index is constructed. The case of normal incidence of a plane electromagnetic wave of E- and H-polarizations on a cylinder is considered. Numerical calculations of the field distribution were performed in the MathCard environment. Results: It is shown that for thick cylinders with a diameter greater than the wavelength, characteristic resonant peaks of absorption and scattering of wave energy are observed. For very thin cylinders, the diameter of which is much smaller than the wavelength, there are maxima of absorption and scattering of energy of incident radiation, which cannot be explained by resonant phenomena. Simplified analytical expressions for the efficiency coefficients of attenuation, absorption and scattering of electromagnetic radiation by thin cylinders are obtained. The field distributions inside and outside the dielectric and metal cylinders at different ratios of their diameter and wavelength of incident radiation are calculated. The efficiency of radiation absorption by a thin wire at different ratios of its diameter and skin-layer thickness for wire material has been studied. Conclusion: It was found that the effect of abnormally strong absorption of microwave radiation by very thin metal wires is due to the existence of a skin effect for conductive materials that interact with microwave radiation. It is obtained that the maximum efficiency of radiation absorption is achieved when the diameter of the wire is twice less than the thickness of the skin layer. The observed effect of anomalous absorption is nonresonant.

Magnetic mirror metasurfaces based on spoof surface plasmonic structures

Mirrors can be seen everywhere in daily life and play an important role in modern optical systems. A traditional mirror, which is made of noble metals, usually has a zero electric field strength and maximal magnetic field strength at its surface induced by the out-of-phase of electric field and in-of-phase of magnetic field between the reflected field and incident field due to the boundary condition of perfect electric conductor. As the magnitude of local electric field determines the strength of the light-matter interaction, it is clear that this interaction is suppressed near the mirror surface. Magnetic mirror, which can enhance electric field on the surface, has been widely applied to strong light-matter interaction for biological sensing, material analysis, and imaging. However, the conventional smooth magnetic mirror with a plane surface is difficult to induce sufficient light-matter interaction when the matter has a complex geometrical shape. Here in this work, we propose a concept of magnetic mirror with a rough interface designed by an array of artificial surface plasmonic structures. The artificial surface plasmonic structure on a subwavelength scale is designed by periodically inserting spiral metallic strips into a dielectric cylinder to support the strong magnetic dipolar resonant mode. The magnetic dipolar resonance of the excited structure is induced by the displacement current circle. Therefore, the resonant frequency is related to the geometrical parameters of the helical structure closely. When we reduce the outer radius of the structure, the magnitude of the displacement current circle will change, resulting in blue-shift of the resonant frequency. At the same time, we also find that increasing the spiral degree of the structure will cause the magnetic dipolar resonance frequency to become red-shifted. Particularly, the same magnetic dipolar mode can be supported in a spiral structure of different size by tuning the spiral degree accordingly. In this context, we design a rough magnetic mirror constructed by the artificial surface plasmonic structures with various sizes, and demonstrate that the efficiency of rough magnetic mirror is in agreement with that of smooth magnetic mirror. The proposed rough magnetic mirror can provide the unique ability to enhance the interaction between light and complicated matter for the application of biological sensing and imaging in microwave and terahertz band.

The Method of Point Electric Moments in the Problem of Calculating Disturbed Electric Fields

The article is devoted to solving the urgent problem of increasing the efficiency of methods for calculating the electric field. A meshless method for calculating disturbed stationary electric fields is proposed, based on the use of point electric moments. In this case, the accuracy of the calculation of the potential increases and the numerical instability caused by the error in the difference between close values when calculating the potential of the dipole is excluded. Replacing sources with distributed parameters is performed by a set of point sources. This makes it possible to exclude the operations of integration over the volume and surface, replacing them by summing the contributions of the moments. The absence of a grid significantly reduces the total number of un-knowns. The application of the method is shown by examples. The electric fields disturbed by the introduction of a dielectric cylinder, a conducting cylinder and a conducting rod of rectangular cross-section into a uniform field are calculated. The results obtained show the high efficiency of the developed method.

Analysis of Thin Truncated Cylinder Scatterers Using Incomplete Hankel Functions and Surface Impedance Boundary Conditions

The incomplete Hankel functions (IHFs) are employed to evaluate the scattered field from thin truncated cylinders excited by uniform plane waves or by arbitrarily oriented elemental current sources. Metallic and dielectric lossy structures are modeled by means of impedance boundary conditions (IBCs) including surface curvature effects. The scattering currents, expanded in triangular basis functions, are determined upon solving electrical field integral equations (EFIEs) by means of the point-matching method of moments (MoM). The scattered field is then expressed in closed analytical form in terms of IHFs, thus yielding highly accurate numerical results. Furthermore, accurate IHFs approximants are also derived to reduce the computational burden in the analysis of large electrical structures. The proposed approach is demonstrated in practical applications involving cylindrical dielectric structures used in planar lenses, lossy dielectric cylinders suitable to model cane-like vegetation, as well as polarization rotators featuring multiple stages composed of thin metallic wire arrays.

Design of Low-Profile Dual-Band Printed Quadrifilar Helix Antenna With Wide Beamwidth for UAV GPS Applications

In the paper, a low-profile dual-band printed quadrifilar helix antenna (PQHA) with wide beamwidth is presented for UAV GPS applications. The antenna is composed of a hollow dielectric cylinder with four arms of dual-helix metal strips and a hollow dielectric ring with four pairs of circular metal strips. To provide dual-band operation, different lengths of the dual-helix metal strips are applied. By loading the circular metal strips on the dual-helix metal strips, size reduction of the antenna height is realized. Moreover, wide beamwidth is obtained. A miniaturized quad-feed network is also designed to provide equal amplitude signals with sequentially quadrature phases. To validate the proposed structure, a prototype is fabricated. The height of the antenna is 18.5 mm. The experimental results show that good impedance matching (|S11| <; -18$ dB) and axial ratio (<; 2 dB) are obtained at GPS L1/ L2 bands. At 1.227 GHz, the measured 3-dB axial ratio beamwidths (ARBWs) are 186° and 187° at xoz and yoz planes, respectively. While the values are 167° and 163° at 1.575 GHz. The measured half-power beamwidths (HPBWs) are both more than 120° at the two bands. The results indicate that the proposed PQHA is a good candidate for UAV GPS applications.

ИСПОЛЬЗОВАНИЕ МЕТОДА ДИАГРАММНЫХ УРАВНЕНИЙ ДЛЯ АНАЛИЗА ДИФРАКЦИИ НА МАЛЫХ РАССЕИВАТЕЛЯХ

Scattering of electromagnetic waves by small particles is an important key task of diffraction theory. This is due to a wide range of practical applications of the effects associated with the scattering of electromagnetic waves by particles, small in com-parison with the wavelength. From the moment of the appearance of the first papers devoted to this subject and up to the present, the most used mathematical model used in solving the problem of scattering by small bodies is the dipole approximation (Rayleigh approximation). This approach is described in sufficient detail for particular cases of scattering by balls and ellipsoids, when the solution of the auxiliary electrostatic problem can be obtained in explicit form. Note that the solution of the problem in the electrostatic approximation in the general case, in itself, is quite complicated and time-consuming compared with the solution of the original wave problem. Existing methods for solving it have a number of fundamental limitations. In this paper, we developed a technique based on the use of the method of Pattern Equations Method (PEM), first proposed in 1992. In a significant number of publications, it has been clearly demonstrated that PEM have important advantages over many alternative methods and are very effective in solving a wide class of problems. In constructing a new approach to the analysis of scattering by small bodies, we used the high convergence rate of the PEM established in our previous papers. Indeed, as shown in previous works of the authors of this article, to solve the problem of scattering by impedance bodies, whose characteristic size is comparable with the wavelength of the incident field, it suffices to take into account, depending on the polarization of the incident field, one to three terms in the Fourier decomposition of the scattering pattern. This circumstance made it possible to obtain explicit formulas for the integral scattering characteristics applicable to complex-shaped impedance scatterers. In this work, explicit formulas are obtained for the integrated scattering characteristics that are applicable to small, compared with the incident radiation wavelength, scatterers. A review is given of the application of an approximate methodology for calculating the integral scattering characteristics of small diffusers of arbitrary shape, in particular, thin dielectric cylinders, based on the use of PEM. As the above results show, the approximate relations obtained have sufficient accuracy in a wide range of problem parameters.

New separation technique of metal/polymer granular materials using an electrostatic sorting device

Electric curtain consisting of a series of parallel electrodes and powered by a polyphase voltage has been extensively used for transporting and/or separating micronized insulating particles. The aim of this work is to investigate a new electrostatic sorting device (ESD) similar to an inter-digitated electrode configuration for the separation of millimeter-size metal/plastic particles, based on the electro-adhesive force applied on the metal granules. The granular mixture is deposited on a dielectric cylinder covered by two-phase inter-digitated electrodes and rotating at a controlled speed. An experimental analysis was carried out to analyze the influence of various factors on the performance of this new separator. The obtained results showed that the new separator makes it possible to obtain high-purity products; its performance depends on several factors such as the level of the applied voltage, the signal frequency and the rotation speed of the drum.

Interaction between dielectric particles enhances the Q-factor

We study behavior of resonant modes with a distance between two identical dielectric cylinders and disks. We reveal two basic scenarios of evolution of resonances with the distance between the cylinders. For larger distances and respectively weaker interaction of particles the resonances are bound around the Mie resonances and evolve by spiral way. For shorter distances and respectively stronger interaction the resonances bypass the Mie resonances. Both scenarios demonstrate considerable enhancement of the Q factor compared to the case of isolated particle.

Global polarizability matrix method for efficient modeling of light scattering by dense ensembles of non-spherical particles in stratified media.

We introduce a numerical method that enables efficient modeling of light scattering by large, disordered ensembles of non-spherical particles incorporated in stratified media, including when the particles are in close vicinity to each other, to planar interfaces, and/or to localized light sources. The method consists of finding a small set of fictitious polarizable elements-or numerical dipoles-that quantitatively reproduces the field scattered by an individual particle for any excitation and at an arbitrary distance from the particle surface. The set of numerical dipoles is described by a global polarizability matrix that is determined numerically by solving an inverse problem relying on fullwave simulations. The latter are classical and may be performed with any Maxwell's equations solver. Spatial non-locality is an important feature of the numerical dipoles set, providing additional degrees of freedom compared to classical coupled dipoles to reconstruct complex scattered fields. Once the polarizability matrix describing scattering by an individual particle is determined, the multiple scattering problem by ensembles of such particles in stratified media can be solved using a Green tensor formalism and only a few numerical dipoles, thereby with a low physical memory usage, even for dense systems in close vicinity to interfaces. The performance of the method is studied with the example of large high-aspect-ratio high-index dielectric cylinders. The method is easy to implement and may offer new possibilities for the study of complex nanostructured surfaces, which are becoming widespread in emerging photonic technologies.

Resonant-state expansion applied to three-dimensional open optical systems: Complete set of static modes

We present two alternative complete sets of static modes of a homogeneous dielectric sphere, for their use in the resonant-state expansion (RSE), a rigorous perturbative method in electrodynamics. Physically, these modes are needed to correctly describe the static electric field of a charge redistribution within the optical system due to a perturbation of the permittivity. We demonstrate the convergence of the RSE towards the exact result for a perturbation describing a size reduction of the basis sphere. We then revisit the quarter-sphere perturbation treated in [Doost {\it et al.}, Phys. Rev. A {\bf 90}, 013834 (2014)], where only a single static mode per each angular momentum was introduced, and show that using a complete set of static modes leads to a small, though non-negligible correction of the RSE result, improving the agreement with finite-element simulations. As another example of applying the RSE with a complete set of static modes, we calculate the resonant states of a dielectric cylinder, also comparing the result with a finite-element simulation.

Scaling relationships between acoustic and electromagnetic scattering by an infinite cylinder

The conversion relationships, including the scaling of frequencies and sizes, between the scattering of a uniform plane electromagnetic wave by a dielectric cylinder and the scattering of a uniform plane acoustic wave by a non-shear-stress cylinder are studied. Owing to the dependence of electromagnetic scattering on polarization, especially for dielectric materials, a simulation method using two acoustic materials is proposed for cases with complex polarization, such as circular polarization. The scaling relationships are verified by simulation. This approach proves to be an effective supplement to the indirect method of measuring electromagnetic scattering by acoustic scattering. A preliminary study of scattering by three-dimensional objects is also performed for the simplest case of spheres. Although the results are not as good as those for two-dimensional objects, the errors after processing are sufficiently small for these results to be accepted as estimates.

Propagation of Waves in Randomly Distributed Cylinders Using Three-Dimensional Vector Cylindrical Wave Expansions in Foldy–Lax Equations

In this article, we develop a hybrid method to calculate the propagation of microwaves in randomly distributed dielectric cylinders. The hybrid method combines off-the-shelf techniques for single object and our developed techniques of Foldy–Lax (FL) method that include extracting the T-matrix for single object, vector translation addition theorem, and solving FL multiple scattering equations. For cylindrical scatterers such as tree trunks, the T-matrix in vector three-dimensional cylindrical waves are extracted from infinite cylinder approximation (ICA). In solving FL to calculate statistical moments, we iterate one order of multiple scattering at a time, with averaging over realizations performed after each order. This physically based iterative method of calculating statistical moments converges faster than the traditional iterative method of calculating the exact solution for each realization. The main purpose is to simulate tall tree trunks at the L-band and ICA is of sufficient accuracies. Numerical results are illustrated for a large number of cylinders of up to 196 and cylinder lengths of up to 94 wavelengths, which are typical of forests at the L-band. Results of the simulations of the hybrid method show that the transmission coefficients of waves are several times larger than that of the commonly used models of the radiative transfer equation and distorted Born approximation.

Large‐Area, Ultrathin Metasurface Exhibiting Strong Unpolarized Ultrabroadband Absorption

AbstractLarge‐area, ultrathin devices with strong ultrabroadband absorption and high angular tolerance are in demand for applications such as ultraviolet protection, energy harvesting, photodetectors, and thermal imaging technology. Although there have been considerable efforts to design and fabricate these devices, the simultaneous realization of all desired properties has not been achieved. A 330 nm thick metasurface with an area of 3 cm2 is experimentally developed, which incorporates dielectric cylinder arrays, a titanium nitride (TiN) layer, and silicon nitride (SiNx) layers. The developed metasurface absorbs ≈87% of ultrabroadband light in the range of 250–2250 nm, which covers almost the entire solar spectrum, and has a low hemispherical thermal emittance of ≈29% in the long‐infrared range (5–13 µm). Moreover, the structure exhibits strong ultrabroadband absorption over a wide range of incident angles (82% at 60°). In addition, due to the high temperature resistance of TiN and its excellent spectral and angular performance, the device made from this material is ideal for solar‐thermal applications.

Tunable mantle cloaking utilizing graphene metasurface for terahertz sensing applications.

Design of sensors which are able to probe electromagnetic radiation with larger cross section and at the same time with having negligible perturbation in measurement has attracted significant attention. For this purpose, scattering-cancellation sensors or cloaking sensors are introduced. However, tunable cloaking sensors are very challenging. In this regards, here, a metasurface based on graphene strips is proposed to cloak a dielectric cylinder under illumination of TEz and TMz polarized incident waves in terahertz range. According to the in plane effective surface impedance tensor for the considered metasurface and the required surface impedance for achieving invisibility under TE and TM polarized impinging waves, the geometrical parameters of the covering structure and characteristics of graphene are obtained. Numerical simulations show radar cross section reduction for both TE and TM polarizations. Furthermore, the introduced metasurface is able to cloak the cylinder for incoming waves with circular polarization. In addition, it is shown that by properly adjusting the chemical potential of graphene, the required surface impedance to have cloaking for the two polarizations in other frequencies can also be achieved, which results in a tunable dual polarized cloaking. The proposed structure provides 2-11 dB reduction in scattering strength relative to the uncloaked configuration for 0.3eV variation of graphene chemical potential.

Dynamics of destructive Fano resonances

Based on the substantial difference in the response time for the resonant and background partitions at stepwise variations of the exiting signal, a simple exactly integrable model describing the dynamic Fano resonance (DFRs) is proposed. The model does not have any fitting parameters, may include any number of resonant partitions and exhibits high accuracy. It is shown that at the point of the destructive interference any sharp variation of the amplitude of the excitation (no matter an increase or a decrease) gives rise to pronounced "flashes" in the intensity of the output signal. In particular, the flash should appear behind the trailing edge of the exciting pulse, when the excitation is already over. The model is applied to explain the DFRs at the light scattering by a dielectric cylinder with two resonant modes excited simultaneously and exhibits the excellent agreement with the results of the direct numerical integration of the Maxwell equations.

Modelling, Calibration and Fabrication of Electrical Capacitance Tomography Sensor for Bone Imaging

Electrical capacitance tomography is a technique to measure internal permittivity distribution based on external capacitance measurements which in turn generate a cross-sectional image representing the permittivity distribution thereby the material distribution. It possesses the advantages of non-radioactive, non-intrusive, non-invasive, high imaging speed and low cost over the conventional medical imaging techniques. Inter-electrode measurements are done by placing electrodes around the non-conductive dielectric medium cylinder inside which, the medium to be imaged is placed. This paper emphasizes on modelling and fabricating an electrical capacitance tomography sensor using ANSYS APDL for bone for which the sensor is calibrated using air and water. ECT sensor is modelled and fabricated by mounting 12 identical rectangular copper electrodes were placed symmetrically outside the Poly-vinyl chloride (PVC) cylindrical tube. The output from sensors can be converted to digital voltage values used for image reconstruction in MATLAB.