Phase Of Reflection Coefficient Research Articles

Design of Reflective Surface With Linear and Controllable Reflection Coefficient Phase

In this letter, a new method is presented for synthesis of an artificial reflective surface with linear reflection coefficient phase and controllable slope over a wide frequency band. To this end, a circuit model is introduced based on the theory of continued fractions expansion. The resonant elements are then designed according to the circuit model, to provide linear reflection coefficient phase with controllable slope. These resonant elements are realized through dogbone-type configuration to operate in the X-band. The reflection coefficients of fabricated elements are measured using the waveguide method; the good agreement with simulation results confirms the accuracy of the proposed method.

Design and Analysis of Different Shapes for Unit-Cell Reflectarray Antenna

This paper presents an analysis and design of unit cell reflectarray antenna using different shapes of radiating elements: square patch, rectangular slot, triangular slot, square loop and Minkowski element are employed in separate unit-cell design operating in X -Band (8-12GHz) at the center frequency of 10GHz. In order to investigate the scattering characteristics of the unit cell studied, commercially available computer models of CST Microwave Studio is used, based on the method of finite integration technique, and using the approach of Floquet (Infinite periodic approach). The analyses of reflection coefficient and reflection phase curves for each resonant element are presented, and Figure of Merit has been defined for the comparison of reflection phase curves obtained by simulation. It has been demonstrated that among the resonant elements square loop acquires higher static phase range of 203°, and the maximum reflection loss of 7.11dB.

Use of gadolinium as a reference layer for neutron reflectometry

The possibility of using gadolinium as a reference layer to obtain information on the phase of the complex reflection coefficient in neutron reflectometry is considered in this paper. The results of model numerical experiments for a simple one-layer Si/Ti (90 A) system are presented.

Simulation and detection of photonic Chern insulators in a one-dimensional circuit-QED lattice

We introduce a simple method to realize and detect photonic topological Chern insulators with one-dimensional circiut quantum electrodynamics arrays. By periodically modulating the couplings of the array, we show that this one-dimensional model can be mapped into a two-dimensional Chern insulator model. In addition to allowing the study of photonic Chern insulators, this approach also provides a natural platform to realise experimentally Laughlin's pumping argument. Based on scattering theory of topological insulators and input-output formalism, we show that the photonic edge state can be probed directly and the topological invariant can be detected from the winding number of the reflection coefficient phase.

Phase spectroscopy of topological invariants in photonic crystals

We propose a method of measuring topological invariants of a photonic crystal through phase spectroscopy. We show how the Chern numbers can be deduced from the winding numbers of the reflection coefficient phase. An explicit proof of existence of edge states in system with nonzero reflection phase winding number is given. The method is illustrated for one- and two-dimensional photonic crystals of nontrivial topology.

Optical Huygens’ Metasurfaces with Independent Control of the Magnitude and Phase of the Local Reflection Coefficients

Implementation of abrupt phase discontinuities along a surface has been the theme of recent research on electromagnetic metasurfaces. Simple functionalities such as reflecting, refracting, or focusing plane waves have been demonstrated with devices featuring phase discontinuities, but optical surfaces allowing independent magnitude and phase control on the scattered waves have yet to emerge. In this paper, we propose the first true optical Huygens’ surface, which explicitly utilizes orthogonal electric and magnetic responses to realize total control on an optical surface’s local reflection coefficients. This extends the functionality of metasurfaces to an unprecedented level. We first demonstrate that a nanorod gap-surface plasmon resonator can act as a Huygens’ source. Thereafter, by properly tuning and rotating these resonators, we realize arbitrary reflection optical metasurfaces—surfaces for which the local reflection coefficients can be independently tailored in both magnitude and phase. We demonstrate the versatility of this approach through designs of a metasurface that asymmetrically reflects two copolarized beams and a Dolph-Tschebyscheff optical reflectarray.

On the Effect of Atmospheric Temperature Gradients and Ground Impedance on Sound

The acoustic wave equation is solved exactly in a polytropic atmosphere over a flat impedance ground. The effects of atmospheric stratification on sound are presented as a correction to the amplitude and phase of a plane wave compared to a homogeneous medium corresponding to sea level conditions. It is shown that: (i) the direct effect of atmospheric stratification on sound amplitude is very small over the entire audible range 20Hz-20kHz, even for altitude ranges in excess of 1 Km: (ii) the atmospheric stratification causes significant phase changes relative to an homogeneous medium for frequencies above 500Hz even over altitude ranges of less than 100m; (iv) the phase changes due to atmospheric stratification can affect significantly interference between acoustic waves, for example in the case of multiple sound sources or multiple reflections by nearby obstacles. The exact solution of the wave equation for the acoustic potential specifies also the velocity and pressure perturbation that appear in the impedance boundary condition over flat ground. This specifies the amplitude and phase of the ground reflection coefficient and also the amplitude and phase of the total obsorption factor of the atmosphere plus ground. The amplitude and phase of the reflection coefficient are plotted as a function of the angle of incidence for a fixed altitude of propagation of the wave for a source above ground, such as an aircraft near an airport and several values of the ground impedance. The theory applies to wavelengths smaller, comparable or larger than the lenghthscales of variation of atmospheric properties, since it is based on an exact solution of the wave equation, without ray, parabolic equation, or any other approximations.

Noncontact method applied to determine thickness of thin layer based on laser ultrasonic technique

This paper describes a novel method to non-destructively determine the thickness of thin layer in a non-contact way. A model of wave interference was established based on the multireflection of shear wave in layered system. Furthermore, its expression of reflection coefficient phase was deduced to provide the principle of thickness measurement. A formed laser source by focusing a line on the layer surface was used to generate shear wave, while an electromagnetic acoustic testing (EMAT) sensor was proposed to receive the wave. An example of the method and experimental measurement for comparison is given for a thin steel sheet with the thickness of approximate 0·4 mm. The relative error between the present method and metallography method is less than 4%, which shows laser-EMAT technique is very suitable to non-destructive assess the thickness of the layer.

A WIDEBAND AND HIGH GAIN DUAL-POLARZIED ANTENNA DESIGN BY A FREQUENCY-SELECTIVE SURFACE FOR WLAN APPLICATION

A new dual-polarized antenna loading frequency-selective surface (FSS) is proposed for 5G wireless local networks (WLANs) application. The antenna consists of two orthogonal bow-tie dipoles and a ground plane. A new wideband FSS is designed comprising ring-slot connecting rectangular slots. The reflection coefficient of wideband FSS is less than 0.9 from 4-6.5 GHz. The phase of reflection coefficient is −163 ◦ at 5.5 GHz. The novel cell analyzed by the equivalent circuit is given and simulated. The wideband FSS is employed as a superstrate layer for bandwidth enhancement and radiation gain improvement of the antenna. After loading wideband FSS, the measured bandwidth is 5.3-6.3 GHz (17.2%) with S11 and S22 both less than −10 dB, which cover various 5G WLAN bandwidths. The gain of the antenna is 12.1 dBi at 5.5 GHz. The bandwidth of antenna with FSS increases 40%, and gain improves 5.6 dBi. The simulated and measured results agree well.

Study of Dual Open Ended Coaxial Sensor System for Calculation of Phase Using Two Magnitudes

A dual open ended coaxial sensor system to determine complex permittivity was studied in detail. This paper focuses on determination of a reflection coefficient phase from two magnitudes using modified capacitance model from 300 kHz to 8 GHz. The phase information can then be used for calculation of the sample's complex permittivity. Factors such as range and limitation of the model, sample's permittivity, operating frequency, and size of sensor were investigated. Sensitivity of calculated phase with respect to small changes in measured magnitude was carried out.

Non-destructive microwave evaluation of plasma sprayed TBCs porosity

Porosity of top coating (TC) in thermal barrier coatings (TBCs) is one of the main factors affecting the thermal conductivity and causing failure of TBCs. To ensure the quality of the TBCs, the evaluation of TC porosity was carried out using a microwave non destructive technique. The reflection coefficient at the interface of TC and waveguide probe was studied with regard to the TC porosity using computer simulation technology-microwave studio (CST-MWS). The results showed that the greater the porosity of the TC the larger the phase difference when the microwave was operated at the sensitive frequency. And the sensitive frequency is different when TC thickness changes. Besides, a network analyzer was used to measure the reflection coefficient phase which can be used in the evaluation of the TC porosity. The results showed that the phase difference increases linearly with increasing porosity of TC when the network analyzer operating over the frequency range of 30GHz to 40GHz. Therefore, the porosity of TC can be calculated by measuring the phase of the reflection coefficient. The experimental results are consistent with the theory simulation ones.

Rapid Surface-Wave Dispersion and Plane-Wave Reflection Analyses of Planar Corrugated Surfaces by Asymptotic Corrugations Boundary Conditions Even for Oblique Azimuth Planes

The asymptotic corrugations boundary condition (ACBC) is used together with classical theory of vector potentials to analyze planar corrugations. A transcendental characteristic equation is derived, from which the dispersion diagram can be obtained, thereby conveying surface wave passband and stopband properties, even for propagation within oblique azimuth planes as well as both principal TE and TM polarizations. From the formulation, field distributions for the regions within the grooves and above the corrugations can also be generated. When compared with the dispersion graphs obtained from characteristic equations derived by the classical transverse resonance technique (TRT), the newly presented ACBC method provides superior accuracy. Explicit formulas for the complex reflection coefficient (amplitude and phase) for both TE and TM polarized plane-wave incidences are also derived as closed-form analytic functions of all parameters (especially the azimuth phi angle of incidence) using a novel concept of unusual transversely phased plane-waves. These proposed approaches are massively more efficient than full-wave solvers, providing unparalleled speedup of computation by thousands of times. The surface-wave and reflection properties of planar corrugations are thus herein analyzed in a unified, complete, and elegant manner that is also highly efficient but yet accurate. This thorough work is thus a great boost to the continued use of corrugated surfaces as artificial magnetic conductors (AMC), electromagnetic bandgap (EBG) structures, and soft/hard surfaces in all walks of antenna design, especially in terms of speed and accuracy.

Unidirectional wideband circularly polarised aperture antennas backed with artificial magnetic conductor reflectors

The reflection coefficient phase is studied for four different artificial magnetic conductors (AMCs) having canonical frequency selective surface (FSS)-type two-dimensional periodic structures to be used as back reflectors for an aperture antenna. The bidirectional circularly polarised (CP) radiation of the octagonal-shaped aperture (OSA) antenna is made unidirectional using these AMC surfaces as ground planes. The antenna height measured from the upper surface of AMC reflector to the OSA radiator is chosen to be small to realise low-profile antenna: 0.0825λ o at the lowest analysis frequency of 4.5 GHz. Different antenna parameters like voltage standing wave ratio (VSWR) of 2, 3-dB axial ratio (AR) bandwidth, gain, and front-to-back ratio are studied and compared for these four AMCs and the conventionally used perfect electric conductor (PEC) ground plane as back reflectors. Four different aperture shapes with fixed aperture perimeter are designed to integrate with the square-loop AMC as back reflector to realise a low-profile unidirectional wideband CP aperture antenna. Hexagonal-shaped aperture antenna over the square-loop AMC shows the largest measured 3-dB AR bandwidth of 23.33% (5.65-7.05 GHz), VSWR of 2 bandwidth of 36.67% (5.16-7.36 GHz), and the gain of around 7 dBic over the band for overall antenna volume of 0.72λ o × 0.60λ o × 0.19λ o at 6.0 GHz.

Performance analysis of journal bearings using ultrasonic reflection

One method that shows potential for non-invasive oil film measurement is the use of ultrasonic reflection. In the current work, ultrasonic transducer is coupled to the outside of a bearing and a wave transmitted through the bearing shell. The wave is partially reflected when it strikes an oil film. Experiments were conducted to study ultrasonic reflection coefficient technique in plain journal bearing. Measurements of multiple reflection coefficients were recorded and used to map the viscosity profiles, oil-film thickness and bearing cavitation. In addition, an alternative method using the reflection coefficient phase from film thickness measurement was used for verification. The results revealed that the evaluation of phase method is slightly lower compared to that of the amplitude method. The film thickness profile obtained in the converging region agreed well with classical hydrodynamic predictions.

Feasibility Study on Defects Detection of Thermal Barrier Coatings Using Millimeter Wave

The objective of this study is to investigate feasibility of millimeter wave nondestructive testing to detect the defects of TBCs and to determine sensitivity of detection when frequency changed. The simulation to monitor the delamination of TBCs and TGO are carried out using computer simulation technology-microwave studio. WR18 rectangular waveguide(40-50 GHz) and WR14 rectangular waveguide(50-60 GHz) are used to detect the delamination of TBCs. The depth of cracks(parallel to the interface of TC and BC),the size of the shape of delimation,the thickness of delimation are studied. Four rectangular waveguides,including WR42(18-26.5 GHz),WR28(26.5-40 GHz),WR18(40-50 GHz) and WR14(50-60 GHz),are used to detect TGO. The changes in the phase of reflection coefficient are primarily studied. The results show that the phase difference of reflection coefficients can represent not only the existence of the defect,but also the depth of the defect. When the delamination surface is less than the aperture of the waveguide probe,the phase of reflection coefficient can represent the size of delamination. When the delamination surface is more than the aperture of the waveguide probe,the phase of reflection coefficient can represent the thickness of delamination. The phase difference of reflection coefficient can represent the TGO thickness. Besides,the sensitivity is greater in high frequency than low frequency.

Novel Miniaturized Artificial Magnetic Conductor

The design of a novel miniaturized artificial magnetic conductor (AMC) using interdigital capacitors is presented. The operation of the AMC is evaluated using finite element method (FEM) simulations. A prototype is manufactured and characterized based on reflection coefficient phase in an anechoic chamber. The performance of the AMC unit cell for both normal and oblique incidence is also studied.

One directional polarized neutron reflectometry with optimized reference layer method

In the past decade, several neutron reflectometry methods for determining the modulus and phase of the complex reflection coefficient of an unknown multilayer thin film have been worked out among which the method of variation of surroundings and reference layers are of highest interest. These methods were later modified for measurement of the polarization of the reflected beam instead of the measurement of the intensities. In their new architecture, these methods not only suffered from the necessity of change of experimental setup but also another difficulty was added to their experimental implementations. This deficiency was related to the limitations of the technology of the neutron reflectometers that could only measure the polarization of the reflected neutrons in the same direction as the polarization of the incident beam. As the instruments are limited, the theory has to be optimized so that the experiment could be performed. In a recent work, we developed the method of variation of surroundings for one directional polarization analysis. In this new work, the method of reference layer with polarization analysis has been optimized to determine the phase and modulus of the unknown film with measurement of the polarization of the reflected neutrons in the same direction as the polarization of the incident beam.

Linearly Polarized Fed Circularly Polarized DRA Reflectarray

Two dielectric resonator antennas are discussed to generate circularly polarized waves in a reflectarray anten- na . In this case, two models are discussed here, one is DRA supported on cross slot, while the second is aperture coupled DRA supported on cross strip line coupled to DRA by cross slot. The verification of reflection coefficient phase of cell is satisfied by CST microwave studio and HFSS package. A complete array of 15 x 15 fed by a circular horn tilted by 45 de- gree was designed and simulated at X-band by full wave package. The simulated results show that the obtained 1.5-dB gain bandwidth and 3-dB axial ratio bandwidth of the reflectarray with aperture coupled DRA can reach as large as 25% and 12.5%.

ANN Characterization of Multi-Layer Reflectarray Elements for Contoured-Beam Space Antennas in the Ku-Band

The analysis of a 1.2-meter, contour-shaped reflectarray antenna through the use of Artificial Neuronal Networks (ANNs) is carried out in this paper. The analysis is a two-step procedure: reflectarray element modeling and pattern synthesis. In the first step, artificial neural networks are found to reproduce both the amplitude and the phase of the complex reflection coefficient of the three-layered reflectarray element. For this task, up to 9 free input parameters are considered: six geometrical parameters, the incident angle in terms of azimuth, θ, and elevation, φ, and the frequency. Because of this large number of free parameters, a new artificial neural network training methodology has been developed regarding both the training set and the training process itself. In the second step, extensive full wave electromagnetic computation is replaced by trained artificial neural networks to calculate the electric field on the planar structure and the radiation pattern. A good agreement is obtained compared to an analogous analysis carried out by Method of Moments. Thanks to this methodology, the speed up factor in terms of time is in the order of 7×102, which represents a significant improvement in Computer Aided Design (CAD) of reflectarray antennas.

Investigating the effects of smoothness of interfaces on stability of probing nano-scale thin films by neutron reflectometry

Most of the reflectometry methods which are used for determining the phase of complex reflection coefficient such as reference method and Variation of Surroundings medium are based on solving the Schr\"odinger equation using a discontinuous and step-like scattering optical potential. However, during the deposition process for making a real sample the two adjacent layers are mixed together and the interface would not be discontinuous and sharp. The smearing of adjacent layers at the interface (smoothness of interface), would affect the reflectivity, phase of reflection coefficient and reconstruction of the scattering length density (SLD) of the sample. In this paper, we have investigated the stability of reference method in the presence of smooth interfaces. The smoothness of interfaces is considered by using a continuous function scattering potential. We have also proposed a method to achieve the most reliable output result while retrieving the SLD of the sample.