Polarization Of Incident Wave Research Articles

Parametric Analysis of an Optical Log-Spiral Nano-Antenna for Infrared Energy Harvesting

In this paper, we present the design of a spiral nano-antenna dedicated to infrared energy harvesting at 28.3 THz. A comprehensive, detailed parametric study of key parameters such as the initial angle at the origin arm, width of the spiral arms, gap between the two arms, thickness of substrate, length of substrate, thickness of patch and number of turns of the nano-antenna is also presented and discussed in order to harvest maximum electric field in the gap of the spiral antenna in the frequency range of 28 – 29 THz. The maximum electric field is simulated at 28.1, 28.3, 28.5 and 28.7 THz. A variation of the electric field of the antenna for different value of incident wave angle at the resonance frequency 28.3 THz has been simulated. The main advantages of the studied structure are its ability to reach high confined electric field within its gap, its wideband behavior around the operating frequency 28.3 THz, and its insensitivity to polarization of incident electromagnetic waves.

Abnormal Fano Profile in Graphene-Wrapped Dielectric Particle Dimer

We give a theoretical study on the near field enhancement and far field spectrum of an adjacent graphene-wrapped sphere dimer with different radii. The Fano profile is found in the near field enhancement spectrum of such a symmetry-broken dimer system, which is, however, hidden in the far field spectrum. We demonstrate that this kind of Fano profile is rising from the coupling of dimer’s plasmon hybridization modes by analyzing the dipole moments of each sphere. Moreover, different orientation of incident wave polarization will lead to the different plasmon hybridization coupling, thus giving rise to a different Fano profile. By changing the Fermi energy level, we could achieve tunable Fano profile in near field enhancement.

Frequency Selection to Avoid Medium Effects on RCS of Conducting Objects With Plane E Wave Polarization

AbstractWe aim to select the range of frequencies where the medium parameters have less effects on the scattered waves, and as a result we achieve high precision of computed radar cross section (RCS). Ideal object detection can be obtained through calculation of RCS assuming a plane wave incidence in the far field. Numerical results are conducted to investigate effects of medium characteristics and target configuration on its RCS. We postulate convex illumination region of partially convex contour. Targets are taking fairly large sizes in the range of five wavelengths to suit the practical dimensions of objects such as aircraft. In this work, waves propagation from targets in free space and random medium are considered while assuming E polarization of incident wave.

Mathematical interpretation of wave propagation, standing wave resonance, and absorption in a metasurface absorber

We propose a mathematical model of multiple interference phenomena occurring inside the dielectric cavity of the metasurface absorber. Subsequently, it derived the expressions for electric and magnetic fields within the structure. The model enables one to mathematically interpret wave propagation, standing wave formation, and absorption in terms of electric and magnetic fields. We also discussed the effect of change in the polarization angle of the incident electromagnetic wave on the standing wave pattern and surface-current orientation. The study reveals that the theory is equally applicable for transverse electric and transverse magnetic polarized incident waves. All the mathematical aspects of the theory have been analytically established through the validation of simulation data. It has been found that the theory is in good agreement with the analytically obtained results.

Anisotropic metasurface with high-efficiency reflection and transmission for dual-polarization

Recently, accelerating advances in coding metasurfaces linking metamaterial and digital codes have enabled unexampled route for electromagnetic (EM) waves manipulation, including perfect reflection and transmission. In this paper, an anisotropic coding metasurface with a semi-discontinuous metallic ground sheet are proposed, which realizes dual independent functionalities by changing the polarization of incident waves. The ultrathin metasurface is composed of eight coding elements based on a simple rectangle metal patch and the reflective phases of these elements fully cover 360°. Both numerical and measured results show that our design is able to near-perfectly reflect the normally incident y-polarized wave to desired reflection angle and transmit the y-polarized plane wave with high efficiency. In addition, considering the simple structure, easy fabrication process and decent control ability on EM waves, the proposed coding metasurface may be exploited for more complex functionalities.

On the Use of Compound and Extracted Models in Thermal Dosimetry Assessment

This paper deals with thermal analysis of realistic models of the human eye and brain using the finite element method. The research presented in this paper is the sequel to the electromagnetic dosimetry model presented in the previous work by the authors. The paper presents the numerical results for the specific absorption rate (SAR) and the related temperature increase in various models of the human eye and the brain/head exposed to high-frequency (HF) electromagnetic (EM) radiation. Based on the numerical results for the induced electric field, the distribution of SAR in the human brain and human eye is determined, subsequently used as input to the thermal model. The thermal dosimetry model of both the brain and eye are based on the form of Pennes’ bioheat transfer equation, numerically solved using the finite element method (FEM). The comparison between the extracted models and the compound models of both the eye and brain, placed inside the realistic head model is presented. In case of the human eye, generally, comparable results were obtained for both SAR and temperature increase, while the compound eye model is found to be more suitable when the polarization of incident wave is considered. Moreover, the extracted eye model underestimated the temperature rise, attributed to better heat exchange than the compound model. The results for the compound eye indicate that in some situations, the eye lens could be omitted from simulation, facilitating the model preparation. The numerical results for all three brain models showed similar distributions of SAR and temperature rise. Also, the obtained results show that the peak SAR does not exceed the basic restriction limit for localized SAR, for occupational exposure. The thermal dosimetry assessment of the human brain exposed in four considered scenarios indicates the temperature should not exceed 0.1°C. Finally, the use of a geometrically simplified model may also be found useful in the initial dosimetry assessment prior to dealing with models with more anatomical features.

Metasurfaces for Wideband and Efficient Polarization Rotation

An efficient wideband polarization-rotation thin metasurface based on oval pattern is presented. The aim of this structure is to manipulate the polarization of incident electromagnetic waves in reflect band. The oval pattern is split by strip lines to outperform the results. It is shown that the proposed polarization converter converts the incident linearly or circularly polarized waves into orthogonal counterpart over a frequency band of 10.2–20.5 GHz. A prototype of the proposed structure is fabricated to validate the numerical simulation. The experimental and simulation results confirm that polarization conversion ratio (PCR) is greater than 90% at the same frequency band with high stability to oblique incidence angle. Numerical simulation reveals that the strong electric and magnetic resonances between top and bottom layers lead to wideband polarization conversion. Equivalent impedance surface method is discussed to further analysis the polarization conversion mechanism.

Propagation of the first order annular Bessel Gaussian beams in a uniaxial crystal along the optical axis governed by the Pockels effect.

We investigate the first order annular Bessel Gaussian beams propagating in a strontium barium niobate (SBN) crystal governed by the Pockels effect. The left-hand circularly polarized incident waves propagating along the optical axis in the crystal give rise to the right-hand circularly polarized vortex fields with a topological charge of 2. If an external dc field is applied along the optical axis of the SBN crystal, the anisotropy strength can be controlled rapidly, and the rotational invariance around the optical axis is still maintained. In this case, the normalized intensity in the focal region, the power exchange between left-hand and right-hand components, and the exchange between the spin and orbit contributions of the angular momentum flux can be manipulated. We also consider the case where the incident waves are linearly polarized along the x axis. The cylindrical symmetry of two Cartesian components is broken during propagation due to the anisotropy, and the intensity distribution as well as the polarization state of the beams can be regulated electrically.

Programmable terahertz metamaterial with multiple logic characteristics

We present a design of programmable terahertz (THz) metamaterial (PTM) with multiple logic characteristics. The proposed PTM device is composed of a cut-wire resonator (CWR) sandwiched two face-to-face split-ring resonators (SRRs). By moving CWR along z-axis direction to change vertical distance between CWR and substrate, the programmable coding digits could be switched from four digits to five digits by alternating the polarization of incident THz wave. The electromagnetic responses of PTM device are stable in TE mode and can be tuned by moving vertical distance of CWR in TM mode. These results indicate the potential possibilities of PTM to be used as a stable polarization switch and an effective programmable metamaterial in the THz frequency range.

Polarization Detection of Electromagnetic Waves Using Cascaded Wilkinson Power Dividers

This letter presents a new technique for determining the polarization of the electromagnetic waves by using a passive circuit. The necessary mathematical operations required to retrieve the polarization are achieved using a passive circuit built with the cascaded Wilkinson power dividers. This technique is robust and simple, and enables the detection of all necessary characteristics for determining the incident-wave polarization. It requires two orthogonal linearly polarized antennas for amplitude measurements only. Measurement results with two circularly polarized patch antennas are shown in order to validate the proposed technique. A comparison with a classic method is also provided, which confirms the accuracy and simplicity of the technique.

Transmissivity and Reflectivity of a Transverse‐Electric Polarized Wave Incident on a Microcavity Containing Strongly Coupled Excitons with In‐plane Uniaxially Oriented Transition Dipole Moments

This work examines the reflectivity and transmissivity of a transverse‐electric (TE) polarized wave incident on a microcavity containing strongly coupled excitons with in‐plane uniaxially oriented transition dipole moments, and a different interpretation to a previous report is presented. The propagation of the electric field inside the cavity is discussed, and a distinction is made between two different physical cases: the first, previously observed, and the second, which enables the interpretation of measurements carried out on a microcavity containing an oriented layer of liquid‐crystalline poly(9,9‐dioctylfluorene). In all cases, the reflected and transmitted electric fields derive from photons leaking parallel and perpendicular to the transition dipole moment orientation.

Low RCS Antenna Array With Reconfigurable Scattering Patterns Based on Digital Antenna Units

In this communication, a low radar cross section (RCS) antenna array with reconfigurable scattering patterns based on digital antenna units is proposed. The digital antenna unit has two scattering states that are controlled by p-i-n diodes. For $y$ -polarized normally incident waves, the phases of the two reflected states exhibit a 180° phase difference at approximately 5 GHz. For $x$ -polarized incident waves, the antenna units act as meta-absorbers, and the incident power is absorbed by the antenna units. Moreover, the radiation properties of these two states are approximately the same at 5 GHz. Thus, the scattering patterns of the antenna array can be tuned by controlling the scattering states of the digital antenna units without affecting the radiation performance. By tuning the directions of the scattering pattern nulls to dynamically align to the direction of the incident wave, both the monostatic and bistatic RCS can be significantly reduced. An $8\,\, {\times }\,\,8$ antenna array was fabricated and measured to validate the proposed concept. The measured results are in good agreement with the simulated ones. This indicates that the proposed antenna array is a promising solution to address the challenges of bistatic radar systems.

Electromagnetic Duality Protected Scattering Properties of Nonmagnetic Particles

Optical properties of nonmagnetic structures that support artificial optically-induced magnetic responses have recently attracted surging interest. Here we conduct symmetry-dictated investigations into scattering properties of nonmagnetic particles from perspectives of electromagnetic duality with discrete geometric rotations. For arbitrary scattering configurations, we reveal that far-field scattering patterns are invariant under duality transformations, which in particular means that scattering patterns of self-dual clusters with random particle distributions are polarization independent. Based on this revelation, it is further discovered that scattering bodies of combined duality-(n-fold) rotation symmetry, for any polarizations of incident waves, exhibit also n-fold rotationally symmetric scattering patterns with zero backward components, satisfying the first Kerker condition automatically. We employ both coupled dipole theory and full numerical simulations to demonstrate those scattering properties, solely based upon nonmagnetic core-shell particles that support optically-induced dipolar resonances. Those substantiated scattering properties are fully induced by fundamental symmetry principles, and thus can survive any non-symmetry-breaking perturbations, which may find applications in a wide range of optical devices that require intrinsically robust functionalities.

Reflection spectra of a thin-film GeSbTe diffraction grating on a silicon nitride waveguide

Recent advances in nanophotonics are due to the implication of new approaches to the photonic devices and components design, not only related to structural features, such as subwavelength periodic arrangements, but also new materials, e.g., phase-change materials like GeSbTe (GST) alloys. We consider recently proposed optical non-volatile GST memory cell with a GST diffraction grating instead of a continuous film placed on a silicon nitride waveguide. The grating allows diminishing the energy budget of an incident electromagnetic beam in case of an optically induced phase transition of GST due to excitation of the resonant guided mode in the grating. The excitation of this mode results in anomalous reflectance spectra of the waveguide-grating structure. Here, we present the reflection spectra of GST diffraction gratings on a silicon nitride waveguide calculated with the use of the matrix Riccati equation technique in the theory of multiple electromagnetic wave scattering in inhomogeneous media. We show how the reflection changes with variation of different parameters – grating period and height, incident wave polarization, and phase of the GST film.

Two-Dimensional Scattering From Homogenous Anisotropic Cylinders Using a Multifilament Current Method

Implementation of the multifilament current method (MFCM) to analyze the scattering from homogeneous anisotropic cylinders is introduced. The ${z}$ -directed electric and magnetic line sources are used to associate with TM and TE polarizations, respectively. The radiation fields of a line source in unbounded space occupied with an anisotropic material are derived in detail. With the help of the derived fields, the application of the MFCM is expanded to anisotropic materials. The scattering field is then obtained in terms of these line sources. Monostatic and bistatic scattering widths of cylinders with and without sharp edge are investigated under different incident wave polarizations and material characteristics. Apart from homogeneous anisotropic cylinders, the scattering from an anisotropic shell-coated PEC cylinder is also straightforwardly analyzed without additional considerations in the formulation. The oscillation phenomenon of filament currents in representing the scattered fields and the ill-conditioned issue of the constructed matrix are also discussed in detail. Numerical results obtained with this proposed scheme are also in good agreement with published ones, whereas the proposed technique has its merits on simplicity and conciseness in comparison to the existing numerical methods.

Elastic stubbed metamaterial plate with torsional resonances

We report on a new mechanism involving the torsional resonance of stubs to achieve the negative effective shear modulus of an elastic metamaterial plate. Combined with a mechanism to create a negative mass density, we develop a general method to set up and enlarge a shear-horizontal-polarized double-negative branch in the elastic metamaterial plate with stubs on both sides. We explore the capabilities of this structure for polarization filtering, mode conversion and abnormal refraction. It is shown that, this metamaterial plate behaves divergently against the polarization of incident waves propagating along ΓX direction in a square lattice crystal: it behaves as a double-negative system for zero-order shear horizontal (SH0) wave but as a single-negative one for zero-order antisymmetric (A0) or symmetric (S0) Lamb waves. Mode conversion is achieved when the propagation deviates from ΓX direction. Moreover, we observe abnormal refracted patterns with both positive and negative refraction occurring at the interface between a prism-shaped supercell and the surrounding plate. Furthermore, we propose a chiral pillar to efficiently couple the torsional resonance with an incident A0 Lamb wave.

Extraction of the terahertz constitutive tensors of multilayer graphene-dielectric stacks

In this paper, we present a reliable method to extract the electromagnetic constitutive tensors of complex synthesized multilayer graphene-dielectric stacks in the terahertz band. This macroscopic electromagnetic characterization method uses the transmission and reflection coefficients of a normal-incident circularly polarized electromagnetic wave on the material structure. The employment of circularly polarized waves has the advantage of overcoming the ambiguity at high frequencies attributed to the multi-branching discontinuities in the extracted permeability and permittivity tensors of natural or synthesized materials. The retrieved permeability and permittivity tensors are validated by the data obtained from analytical and numerical solutions of the original electromagnetic problem for the case of circularly polarized wave incidence.

Tunable metasurface with controllable polarizations and reflection/transmission properties

Metasurfaces attract significant attention and are widely applied in modern communication systems due to their powerful capabilities to control the polarization, amplitude, and phase of electromagnetic waves. However, it is considerably challenging to control polarization and amplitude of incident waves for a passive metasurface. Specifically, we integrate the transmission and reflection functions by loading a middle layer with PIN diodes while the upper and lower structures are used to manipulate the polarizations of incident waves. As a proof of concept, we fabricate a sample having 18 × 18 meta-atoms. Beam deflectors for the circularly polarized waves dependent on Helicity are realized when the PIN diodes are turned off. A transmissive polarization converter for x-polarization and a reflective polarization keeper for y -polarization are achieved as the PIN diodes are turned on. More importantly, the functionalities exhibit extremely high efficiencies in the range 86.4%–90.3% for reflective functionalities and 75.4% for transmissive functionalities. Our findings provide a new method to design multifunctionalities metasurface via tunable devices and yield many applications in multifunctional systems.

Polarization-Insensitive Rectenna Arrays With Different Power Combining Strategies

This letter presents two 2 × 2 polarization-insensitive dual-polarized rectenna arrays with different power combining strategies for wireless power transmission applications. With a dual-polarized antenna array, the incident wave can be received and decomposed into the horizontally and vertically polarized components, which are equally redistributed by a hybrid coupler. By this means, the efficiency of the rectenna, in which the power is equally input to the two rectifiers in parallel, is independent of the incident wave's polarization. Based on the equal power routing mechanism, two rectenna arrays using the RF and dc combining strategies are designed and analyzed. Measurement results show that both rectenna arrays are insensitive to the incident wave's polarization, and have their own advantages and disadvantages.

Circularly Polarized Spin‐Selectivity Absorbing Coding Phase Gradient Metasurface for RCS Reduction

AbstractA novel spin‐selectivity absorbing coding phase gradient metasurface (SACPGM) is proposed and demonstrated. The coding element consists of spin‐selectivity absorbing unit cells, which exhibit different absorption characteristics for left‐handed circularly polarized and right‐handed circularly polarized incidence wave due to their spin‐selectivity absorbing properties. The scattering patterns of the SACPGM can be synthetically manipulated by the reflection of the spin‐selectivity absorbing unit cells, the phase gradient of the coding elements, and the coding sequences. As an example, a two‐bit SACPGM with random coding sequence is designed to reduce radar cross section (RCS) by a combination of absorption, beam deflection, surface wave coupling, and diffusion scattering. Both simulated and measured results agree well and demonstrate that the SACPGMs possess excellent performance for RCS reduction. This strategy can help realize stealth applications under bi‐static detections.