Case Of Oblique Incidence Research Articles

Modified Fresnel equations for the case of oblique incidence on an isotropic gyrotropic medium

Modified Fresnel equations for the case of oblique incidence on an isotropic gyrotropic medium

Diffraction of a scalar plane wave oblique incidence on a flat screen with a one thin slit

In the framework of this work, we discuss the problem of diffraction of a plane and time-harmonic field on a flat screen with a single narrow slit. As a rule, this problem is considered for the case of normal incidence. At the same time, for a number of applied problems, in particular, the absorption of solar radiation by photocells, it is interesting to consider the general case of oblique incidence. In this work, the problem is solved in the Fraunhofer approximation. An analytical dependence of the intensity of the diffracted field on the direction of observation, the slit length, and the wavelength of the incident radiation is obtained.

Effects of pulse-like ground motions on tunnels in saturated poroelastic soil for obliquely incident seismic waves

It has been widely recognised that near-fault ground motions can be distinctly different from far-fault ground motions, in terms of their amplitudes and spectral characteristics, and there are a number of studies investigating the effects of near-fault ground motions on the structural response. However, only a few studies focus on underground tunnels, and most of them consider vertically incident seismic waves, neglecting the wave passage effect which is critical for long tunnels. This paper investigates the consequences of near-fault pulse-like ground motions on the seismic tunnel response, with an example of a tunnel embedded in saturated poroelastic soil. The input motions are represented by obliquely incident P1 waves, and the wave passage effect along the longitudinal direction is considered by a 2.5D modelling technique. The seismic tunnel response for near-fault pulse-like and far-fault ground motions is compared. Additionally, artificial ground motions, which have consistent acceleration response spectra with the near-fault pulse-like ground motions, but without velocity pulses, are generated to gain further insight into the contribution of velocity pulses. It is shown that the near-fault pulse-like ground motions can noticeably increase the tunnel internal forces, due to large seismic energy associated with the velocity pulses. For pulse-like ground motions with similar acceleration response spectra, the fling-step velocity pulse can be more detrimental to the tunnel than the forward-directivity velocity pulse. Moreover, the amplification effect of the near-fault pulse-like ground motions on the tunnel internal forces tends to be more prominent for large vertical angles of incidence, highlighting the significance of considering the oblique incidence case for seismic design.

A Semianalytical Method for Electromagnetic Scattering by Infinitely Long Arbitrary Shaped Multilayer Cylinders at Oblique Incidence

A simple and fast method for determining the field scattered from an infinite, arbitrary-shaped multilayer cylinder that is obliquely illuminated by a TMz plane wave is presented. The proposed method is a generalization of the meshless method that was previously introduced for the normal incidence case. The main structure of the procedure is similar to the one given for the normal incidence case. However, in the oblique incidence case, the problem cannot be handled as a scalar problem by considering only one field component, namely, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$E_{\text {z}}$ </tex-math></inline-formula> for a TMz plane wave. Accordingly, all components of both the electric and magnetic field vectors are involved in the procedure and at each layer, and they are expressed as series of cylindrical functions with unknown coefficients. These coefficients are determined through the solution of a linear system of equations, which is constructed by first enforcing the continuity of the tangential components of the electric and magnetic field vectors on each boundary between the layers, then expressing the cylindrical functions in these continuity relations as Fourier series, and using the orthogonality of complex exponentials. After determining the coefficients, all field components at any point can be easily computed through the series representations.

Cheaper, Wide-Band, Ultra-Thin, and Multi-Purpose Single-Layer Metasurface Polarization Converter Design for C-, X-, and Ku-Band Applications

This article presents the design of wide-band, ultra-thin, and multi-purpose polarization converter utilizing metasurface for C-, X-, and Ku-band applications. Having a topology on a FR-4 substrate with metasurface metallic patterns on the front and an all-metallic surface finish on the back, the unit cell of converter design has symmetry in the x−y plane with unique features of having both linear polarization (LP) and circular polarization (CP) property. While the polarization conversion ratio (PCR) of converter in normal incidence case is more than 90% in three different frequency bands of 6.46–6.78 GHz, 10.52–11.85 GHz, and 16.49–17.37 GHz, it shows linear-to-linear polarization feature and a linear-to-circular polarization feature with left-handed circular polarization (LHCP) for the frequency range between 7.28 and 9.40 GHz and right-handed circular polarization (RHCP) for the frequency range between 13.38 and 15.19 GHz. It is also seen that the converter has a PCR value of around 90% for oblique incidence case with incidence angles up to 45°. Extensive simulations have been conducted to prove the performance of suggested converter with the aid of a commercially-available simulation platform, called CST Microwave Studio. The advantages of suggested polarization converter are low-cost, wide-band, ultra-thin, and having both LP and CP conversion in C-, X-, and Ku-bands.

Excitonic model and circular dichroism spectrum of bacteriorhodopsin

This paper presents a theoretical study of the excitonic spectra of a hexagonal two-dimensional lattice of trimers of bacteriorhodopsin (BR). The investigations follow the treating of the electronic excitations in molecular and organic solids. Formalism of dielectric permittivity and of gyration tensor allows to calculate their components near the frequency of electronic excitation of chromophore of retinal with λ ≈ 570 nm. The excitonic spectra of noninteracting trimers and their demonstration in the linear absorption and circular dichroism (CD) spectra represent the model of the spectra of hexagonal 2D lattice with excitonic inter-trimer transfers between the nearest neighbors. The two cases of oblique and perpendicular incidence of left- and right-circularly polarized electromagnetic waves have been considered and corresponding CD signals have been calculated. In accordance with the experimental data a negative CD couplet appears (at oblique incidence) connected with the chiral excitonic coupling whereas at perpendicular incidence a single CD band of Lorentz-type is caused by the intrinsic gyrotropy of the molecules.

Ultra-Narrowband Anisotropic Perfect Absorber Based on α-MoO3 Metamaterials in the Visible Light Region.

Optically anisotropic materials show important advantages in constructing polarization-dependent optical devices. Very recently, a new type of two-dimensional van der Waals (vdW) material, known as α-phase molybdenum trioxide (α-MoO3), has sparked considerable interest owing to its highly anisotropic characteristics. In this work, we theoretically present an anisotropic metamaterial absorber composed of α-MoO3 rings and dielectric layer stacking on a metallic mirror. The designed absorber can exhibit ultra-narrowband perfect absorption for polarizations along [100] and [001] crystalline directions in the visible light region. Plus, the influences of some geometric parameters on the optical absorption spectra are discussed. Meanwhile, the proposed ultra-narrowband anisotropic perfect absorber has an excellent angular tolerance for the case of oblique incidence. Interestingly, the single-band perfect absorption in our proposed metamaterials can be arbitrarily extended to multi-band perfect absorption by adjusting the thickness of dielectric layer. The physical mechanism can be explained by the interference theory in Fabry–Pérot cavity, which is consistent with the numerical simulation. Our research results have some potential applications in designs of anisotropic optical devices with tunable spectrum and selective polarization in the visible light region.

Dielectric Meta-lattices with Tunable Reflectivity

We report a study on the reflective performance of a dielectric meta-lattice formed by a one-dimensional periodic arrangement of silicon nanotubes. It was found that switching from transparent state to reflective state can be done by simply varying one optical parameter of the meta-lattice. The meta-lattice was shown to be capable of providing near-zero and near-unity reflectance at any desired wavelength, even in oblique incidence cases. The results are thus very promising for the development of future optical devices.

A study on health care monitoring of femoral shaft fracture healing by using implanted antenna for wireless in-to-out body channel communication

This work proposes a health care monitoring method of femoral fractured bone healing as a novel application, based on the oblique incidence case and transmission of electromagnetic waves. The difference between the transmitted average power densities of normal and fractured bone cases is used to monitor the bone healing status. The study demonstrates the in-to-out body channel characteristics regarding the electromagnetic wave propagation and angle of incidence on a multi-layered human tissue in the range of frequencies from 100 MHz to 10 GHz. The monitoring method is presented by the analysis of electromagnetic wave propagation through a multilayer model and simulated by the CST Microwave studio. Fully insulated planar and meander half-wave dipole antennas are designed and used to simulate both types of bone fracture healing. Results show good monitoring of common types of fractures. Verification is carried out by experimental measurements on non-living animal tissues.

Homogenization of woven composites for shielding applications: the case of oblique incidence

When reinforced with conductive fibers, woven composites can exhibit interesting shielding properties. This paper focuses on their response for obliquely incident plane waves in the high-frequency range (500 MHz to 40 GHz). A two-step homogenization technique is carried out. First, the composite response (shielding effectiveness and reflection coefficient) is computed using a 3D finite element simulation, then the effective properties are estimated by implementing an optimization process to solve the inverse problem. Results show that composites effective properties are independent of the angle of incidence and wave configuration. This suggests that oblique incidence scenarios can be studied by homogenizing the material based on the case of normal incidence.

Super-broadband geometric phase devices based on circular polarization converter with mirror symmetry

We propose a simple implementation to obtain super-broadband geometric phase devices (GPD) by means of circular polarization converter (CPC) with mirror symmetry. We demonstrate that the best choice of wideband GPDs and CPCs is a mirror symmetric structure. Based on a two-rotation model on the Poincaré sphere, optimization parameters and time are significantly reduced. The CPC can be extended to super-broadband GPD, such as polarization gratings (PGs), by using geometric phase holography. We simulate diffraction efficiencies of the super-broadband PGs. In the normal incident case, the diffraction efficiency is over 99% in 420–945 nm, and in the oblique incident case, the first-order diffraction efficiency is over 90% in the range of ±30°. The super-broadband GPDs show potential advantages in wide color display and spectral imaging.

Experimental realization of ultrasonic retroreflection tweezing via metagratings

Acoustic tweezing and contactless object manipulation are significant and has become a research hotspot. Here, we present a prototype of retroreflection tweezer based on the metagratings, which can be used for implementing particle levitation and contactless movement. Different from previous tweezers, where the standing wave was typically generated from normal incidence, the retroreflection tweezer proposed here operates for the oblique incidence case that provides more degrees of freedom for real-time observation. We also give the exact relation between the metagrating geometries and retroreflection angles in a wide range based on the grating theory and optimization algorithm. Experiments are conducted to show the retroreflection at a preset angle on the designed metagrating, where levitation and contactless movement of particles are demonstrated.

Broadband mirrors for surface plasmon polaritons using integrated high-contrast diffraction gratings

We propose and numerically investigate integrated high-contrast gratings (HCGs) for surface plasmon polaritons (SPPs) propagating along metal-dielectric interfaces, which consist of periodically arranged silicon pillars located on the gold surface. We demonstrate that such on-chip HCGs can be used as broadband plasmonic mirrors, which have subwavelength footprint in the SPP propagation direction and mean reflectance exceeding 85% in a 200-nm-wide spectral range for both the cases of normal and oblique SPP incidence. In order to increase the HCG efficiency and design practically feasible structures, we utilize a parasitic scattering suppression technique based on the use of two-layer grating pillars. The presented results may find application in two-dimensional optical circuits for steering the SPP propagation.

Tunneling modes induced by interface states in 1D photonic crystals with single negative materials

We investigate the electromagnetic wave propagating in one dimensional photonic crystals with alternating layers of negative permittivity materials and negative permeability metamaterials. The band structure and transmission spectra are obtained. In the negative effective permittivity and negative effective permeability regime, we find new interface modes propagating along the interfaces between the two different media with even and odd parities, respectively. For the oblique incident case, the new propagation modes result in the emergence of a transmission band within the zero-ϕeff gap of these photonic crystals. By adjusting the plasma density or the thickness of the plasma layer, the zero-ϕeff gap as well as the transmission band of the interface modes can be tuned, which can facilitate the design of tunable filters at the microwave frequency range.

Influence of Oblique Incidence on the Reflection Losses in a Multilayer Human Body Medium

Implantable antennas have many important healthcare applications. One key aspect for a successful communication process from the implantable device to the on or off-body receiver is the accurate evaluation of the in-body path losses. These losses include, mainly, the attenuation and the reflection losses. Usually, normal incidence is considered for the calculation of the reflection losses between the tissue layers. However, this is not very accurate as the incident wave may be oblique at the boundary between the tissue layers. Therefore, in this paper the influence of oblique incidence on the reflection losses in a multilayer human body model is investigated. The reflection losses at the bone/muscle, muscle/fat and fat/skin layers are calculated at 403 MHz considering the cases of parallel and perpendicular polarization oblique incidence. The results are analyzed and compared with those of normal incidence. They show that larger losses are obtained at some angles for the case of oblique incidence compared to those for the case of normal incidence (about 241.16% larger reflection loss is obtained at an incident angle of 85° for the case of oblique incidence/perpendicular polarization at the fat/skin interface in comparison with that for normal incidence). Hence, it is very important to take the oblique incidence into consideration to provide more accurate in-body path loss calculations.

Detection of spinning objects at oblique light incidence using the optical rotational Doppler effect

The optical rotational Doppler effect of light beams with angular momentum has recently found applications in the remote sensing of spinning objects. However, most of the reported experimental demonstrations rely on the particular condition of normal incidence, while the general case of oblique incidence has not been addressed yet. Herein, we investigate the optical rotational Doppler effect at oblique incidence based on a local scattering model and formulate the quantitative relation between the Doppler frequency shift and the tilt angle. The analytic results indicate that even if the rotational axis of the spinning object is oriented at a specific tilt angle relative to the light propagation direction, the rotational speed can still be extracted from an asymmetrically broadened Doppler signal. The geometric mean value of the extreme frequency shift is a constant despite the variation of the incident angle. An experiment with obliquely incident and superimposed optical vortices is executed to verify our theoretical predictions, achieving a successful detection of the rotational speed at relatively large tilt angles with a relative error less than 2%. The scheme proposed in this study may be useful for practical applications of rotational Doppler effect in remote sensing and metrology.

Mechanism of polaritons coupling from perspective of equivalent MLC circuits model in slit arrays.

Magnetic polariton is a significant mode in tailoring thermal radiative properties with micro/nanostructures metamaterials and can be explained by equivalent inductor-capacitor circuit model. However, the equivalent inductor-capacitor circuit model is out of operation when the magnetic polariton resonance frequency is close to the surface plasmon polariton excitation frequency and cases of oblique incidence. In this work, we present a mutual inductor-inductor-capacitor circuit model to describe magnetic polariton resonance conditions. The mechanism of coupling between the surface plasmon polariton and magnetic polariton is explained from the perspective of equivalent circuits. The interaction between the surface plasmon polariton and magnetic polariton is studied and considered as a mutual inductance in the MLC circuit model. This model is still applicable in the case of oblique incidence. Slit arrays with different geometric parameters and incident angles are calculated to verify the rationality of the mutual inductor-inductor-capacitor circuit model. This study may allow us to predict features and parameters and achieve tailoring of the thermal radiative properties of the micro/nano-structures metamaterials.

Plane wave diffraction from a finite soft cone at oblique incidence

The canonical problem of diffraction of the plane acoustic wave on a finite hollow soft cone in the general case of oblique incidence is solved. The corresponding diffraction problem is formulated as a first-kind boundary value problem for the Helmholtz equation with respect to the scattered velocity potential for each perturbed azimuthal harmonic. The diffracted field is presented as a series of eigenfunctions for the subregions formed by the cone. The pertinent diffraction problem is reduced to an infinite system of linear algebraic equations (ISLAE) for each azimuthal harmonic by using the continuity conditions and the orthogonality properties of the associated Legendre functions. The use of the analytical regularization approach transforms the ISLAE to the second kind and allows to justify the truncation method for obtaining the numerical solution in the required class of sequences. The limiting transition to the disc is considered and the simplified regularization operator for this particular case is derived. The low-frequency approximation of the problem is examined and the analytical solution in the explicit form is derived. By means of illustration, we establish the relationship between the wave size of the cone and the order of reduction of the polar and azimuthal harmonics. We examine the scattering features of a finite soft cone as a function of the incident angle. We validate the obtained results by comparing them to the ones known in literature.

Mitigation of structural responses of a very large floating structure in the presence of vertical porous barrier

The effectiveness of partial vertical permeable barriers of three different configurations located at a finite distance from a very large floating structure is analyzed for mitigating the wave-induced response of the structure. The eigenfunction expansion method is employed to obtain solution in case of normal incidence and the study is extended to the case of oblique incident waves. In case of normalized incident waves, a detailed analysis of the results on various physical quantities such as the reflection and transmission coefficients, wave force on the barrier, free surface elevation, plate deflection, shear force and surface strain on the floating structure are presented. For the case of oblique incidence, results on reflection coefficient for various structural parameters are presented. Using Green's identity, energy balance relations are derived in both the cases of normally and obliquely incident surface waves and certain results for normally incident waves are compared for accuracy. The study reveals that wave reflection follows an oscillatory pattern and the minima in the oscillatory pattern increase with an increase in structural porosity. Wave reflection and dissipation attain their optima for the same wave number irrespective of barrier configurations. Occurrences of wave diffraction are observed in case of long waves for barriers of varied configurations with a narrow gap which decreases with the introduction of barrier permeability. Moreover, when the distance between the barrier and the very large floating structure is close to an integer multiple of half of the wavelength, both the wave reflected by the barrier as well as wave forces acting on the barrier attains their optima.

Resonant interaction of electromagnetic wave with plasma layer and overcoming the radiocommunication blackout problem

We present an analysis of the possibility of penetrating electromagnetic waves through opaque media using an optical-mechanical analogy. As an example, we consider the plasma sheath surrounding the vehicle as a potential barrier and analyze the overcoming of radiocommunication blackout problem. The idea is to embed a «resonator» between the surface on the vehicle and plasma sheath which is supposed to provide an effective tunneling of the signal to the receiving antenna. We discuss the peculiarities of optical mechanical analogy applicability and analyze the radio frequency wave tunneling regime in detail. The cases of normal and oblique incidence of radiofrequency waves on the vehicle surface are studied.