Reflection Andtransmission Research Articles

Resource allocation for practical phase shift STAR-RIS enabled MISO-NOMA wireless network with non ideal hardware

This study investigates the sum secrecy rate SRsum of a simultaneous transmission and reflection reconfigurable intelligent surface (STAR-RIS)-enabled multiple input single-output (MISO) non-orthogonal multiple access (NOMA) downlink network with non-ideal hardware defects (HWDs) at the transceivers. Earlier STAR-RIS studies assumed an ideal phase shift model, with each element reflect and transmit the signal without regard to its phase shift. The proposed practical phase shift model accounts for the phase-dependent amplitude variation in the reflection and transmission (RAT) coefficients. The goal is to maximize the SRsum through an alternating optimization (AO) iterative algorithm, leverages a classical semidefinite relaxation (SDR) for beamformer vector design (BVD), and employs an interior point method (IPM) to calculate NOMA power allocation factors αt,αr. The analysis focuses on the evaluation of the SRsum in scenarios with eavesdroppers, under the consideration of both ideal and practical phase shift cases. The study examines the impact of different non-ideal HWDs on the SRsum of the system and provides insights into vulnerabilities and limitations arising from these effects.

The use of a parametric array source and nearfield scanning in the characterisation of panel materials for underwater acoustics

The properties of the materials used in underwater acoustics are important for applications such as acoustic windows, reflectors and baffles, acoustic barriers or screens, decoupling materials, and anechoic coatings. To characterise the performance of such materials at frequencies above 1 kHz, measurements are typically undertaken on samples of the material in the form of finite sized panels. Such measurements suffer from uncertainty due to the finite size of the panel (leading to contaminating signals from edge diffraction), and the difficulty in simulating the ideal plane-wave insonification. This paper describes work at the UK National Physical Laboratory to minimise these effects by use of: (i) a parametric array as a sound source that provides a directional beam and short broadband pulses; and (ii) nearfield scanning using a hydrophone to sample the complex sound pressure field interacting with the test sample, decomposing the sound field into its plane-wave components. Results are presented of these techniques applied to measurements in laboratory test tanks at frequencies between a few kilohertz and a few hundred kilohertz to determine the reflection and transmission performance of a range of test samples, including panels consisting of homogeneous polymers and materials with regular periodic structure.

Analysis for Scattering of Non-homogeneous Medium by Time Domain Volume Shooting and Bouncing Rays

In order to evaluate scattering from hypersonic vehicles covered with the plasma efficiently, time domain volume shooting and bouncing rays (TDVSBR) is first introduced in this paper. The new method is applied to solve the transient electromagnetic scattering from complex targets, which combines with non-homogeneous dielectric and perfect electric conducting (PEC) bodies. To simplify the problem, objects are discretized into tetrahedrons with different electromagnetic parameters. Then the reflection and transmission coefficients can be obtained by using theory of electromagnetic waves propagation in lossy medium. After that, we simulate the reflection and transmission of rays in different media. At last, the scattered fields or radiation are solved by the last exiting ray from the target. Compared with frequency-domain methods, time-domain methods can obtain the wideband RCS efficiently. Several numerical results are given to demonstrate the high efficiency and accuracy of this proposed scheme.

Anomalous divergence of the multiple-beam method revisited

The multiple-beam method to evaluate optical multilayer reflection and transmission coefficients suffers divergence under certain conditions. An algorithm based on the concept of reduced layer systems and a mapping of the partial beams to corridor paths was developed to re-gain convergence. Further examples, including the case of frustrated total reflection, demonstrate the variability of the convergence rate. The algorithm provides the means to extend methods specialised to layers with particular properties with the effect of multiple reflections when embedded within a multilayer.

Tunable Fano-like resonances in bent single-mode waveguide-based Fabry-Perot resonator: erratum.

In this erratum, we correct an error in the numerical simulation results published in Opt. Lett.44, 231 (2019)OPLEDP0146-959210.1364/OL.44.000231. The error arose from disregarding cladding modes in the straight input and output waveguide sections [Fig. 2(a) in the original paper]. Although these modes do not contribute directly to the calculated power in the reflected and transmitted fundamental modes in those sections, they do, nevertheless, play a significant role in shaping the reflection and transmission spectra of the bent resonator, as was found after the paper had been published. While the main findings of the original paper remain largely intact, quantitatively the spectra in Figs. 3-6 are inaccurate and must be replaced with the correct ones given in this erratum. Some minor modifications to the conclusions of the original paper that are required in view of the corrected results are also discussed.

Solar radiative transfer in Antarctic blue ice: spectral considerations, subsurface enhancement, inclusions, and meteorites

Abstract. We describe and validate a Monte Carlo model to track photons over the full range of solar wavelengths as they travel into optically thick Antarctic blue ice. The model considers both reflection and transmission of radiation at the surface of blue ice, scattering by air bubbles within it, and spectral absorption due to the ice. The ice surface is treated as planar whilst bubbles are considered to be spherical scattering centres using the Henyey–Greenstein approximation. Using bubble radii and number concentrations that are representative of Antarctic blue ice, we calculate spectral albedos and spectrally integrated downwelling and upwelling radiative fluxes as functions of depth and find that, relative to the incident irradiance, there is a marked subsurface enhancement in the downwelling flux and accordingly also in the mean irradiance. This is due to the interaction between the refractive air–ice interface and the scattering interior and is particularly notable at blue and UV wavelengths which correspond to the minimum of the absorption spectrum of ice. In contrast the absorption path length at IR wavelengths is short and consequently the attenuation is more complex than can be described by a simple Lambert–Beer style exponential decay law – instead we present a triple-exponential fit to the net irradiance against depth. We find that there is a moderate dependence on the solar zenith angle and surface conditions such as altitude and cloud optical depth. Representative broadband albedos for blue ice are calculated in the range from 0.585 to 0.621. For macroscopic absorbing inclusions we observe both geometry- and size-dependent self-shadowing that reduces the fractional irradiance incident on an inclusion's surface. Despite this, the inclusions act as local photon sinks and are subject to fluxes that are several times the magnitude of the single-scattering contribution. Such enhancement may have consequences for the energy budget in regions of the cryosphere where particulates are present near the surface. These results also have particular relevance to measurements of the internal radiation field: account must be taken of both self-shadowing and the optical effect of introducing the detector. Turning to the particular example of englacial meteorites, our modelling predicts iron meteorites to reside at much reduced depths than previously suggested in the literature (< 10 cm vs. ∼ 40 cm) and further shows a size dependency that may explain the observed bias in their Antarctic size distribution.

A method of recognition and elimination to the pseudo defect signals by ultrasonic guided wave NDT for pipes

The detected signals using ultrasonic guided wave non-destructive testing (NDT) for pipes with the method of excited and received to one end of pipe, which run with come-and-go many times of reflection and transmission between the two ends of pipe and the defect location in pipe until its energy dissipation over. The multiple reflection and transmission process lead to the appearance of the pseudo defect signals which seriously affect the judgement of the defect numbers and its locations in pipes. Aiming at the difficulty problem of the pseudo defect signal identification, the sketch map of the propagation path of ultrasonic guided wave in pipeline is drawn. The position characteristic of the pseudo defect signal is summarized. Namely: the pseudo defect signal does not appear in the first reflection cycle of the detected signals or its amplitude of the signal is negligible; meanwhile, the larger amplitude of the pseudo defect signal appear from the the second reflection cycle of the detected signals, and which is symmetric with the real defect signal about the time domain midpoint of the signal period in the second reflection cycle. The correctness of this characteristic law is verified by using numerical simulation and experimental results. According to the characteristic law of the pseudo defect signal, the defect wave packet signals in the ultrasonic guided wave detected signals were identified and extracted, and the matching pursuit method and the numerical comparison assignment method were used to eliminate the pseudo defect signal. The conclusion are shown that the proposed method of the pseudo defect signal recognition and elimination in the ultrasonic guided wave NDT for pipes is practical and effective, which achieves the goal of discarding the false and retain the true detected signals, and solve the the detected signals recognition difficulty problem in ultrasonic guided wave NDT for pipes, and also greatly promotes the application of the ultrasonic guided wave NDT technology.

Polarization transformations by a magneto-photonic layered structure in the vicinity of aferromagnetic resonance

Polarization properties of a magneto-photonic layered structure are studied at frequenciesclose to the frequency of ferromagnetic resonance. The investigations are carried outtaking into account a large value of dissipative losses in biased ferrite layers inthis frequency band. The method is based on analysis of solution stability of anordinary differential equation system regarding the field inside a periodic stack ofdielectric and ferrite layers. The electromagnetic properties of the structure areascertained by analysis of the eigenvalues of the transfer matrix of the structure period.The frequency boundaries of the stopbands and passbands of the eigenwavesare determined. The frequency and angular dependences of the reflection andtransmission coefficients of the stack are presented. Frequency dependences of apolarization rotation angle and ellipticity of the reflected and transmitted fields areanalyzed. An enhancement of polarization rotation due to the periodic stack ismentioned, in comparison with the rotation due to some effective ferrite slab.

Optical reflection and transmission properties of exfoliated graphite from a graphenemonolayer to several hundred graphene layers

The optical reflection contrast and optical transmission contrast of graphitic films onglass ranging in thickness from a monolayer to the limit of bulk graphite havebeen experimentally measured. For samples with more than 10 graphene layerswhere optical contrast quantization becomes difficult to observe, atomic forcemicroscopy was used to measure the sample thickness. The visible optical reflectionand transmission of thin graphitic films is found to depend strongly on the realcomponent of the optical conductance per graphene layer, and comparatively weaklyon the imaginary component of optical conductance. This observation in partexplains the significant variation in the refractive index of graphene and graphitereported in the literature to date. Spectroscopic measurements reveal a strongdispersion in the optical conductance of even a 10 layer film, consistent with animaginary conductance arising from virtual transitions at the band edges of theπ andσ bands atthe M and Γ points, respectively.

Rayleigh scattering in multilayered structures of porous silicon

The possibility of growing high-quality porous silicon (por-Si) multilayered structures[1,2], which can consist of hundreds of layers with different, controllable porosity [3], revealed variousnew ways of using this material in optoelectronics and photonics. Apart from obvious applications of por-Si multilayered structures as mirrors, optical filters, etc., the most attractive goal is to combine the photonicmanipulation with the por-Si luminescence, which, in principle, would allow the fabrication of Si-basedlasers with adjustable properties [4].The photon transport through the por-Si multilayered structure is usually described using the transfermatrix method [5]. In this approximation it is assumed that the individual por-Si layers can be characterizedby a well defined refractive index, which depends on porosity. The general features of the reflection andtransmission coefficients are reproduced by this method (see, e.g., the recent observation of the photonicBloch oscillations [6]). However, even in the case when the absorption is negligible, not all interferencepeaks predicted by the transfer matrix calculations are seen experimentally, and the observed peaks arenoticeable suppressed [6,7]. To get more insight in this phenomenon it is convenient to study some simplemultilayered structures, in particular those containing a single microcavity, where the resonant transmit-tance peak is well separated and could be analyzed in details. Below we present the experimental data onthe transmittance spectra of several structures of this sort. The observed suppression of the resonant peaksis then interpreted by taking into account the Rayleigh scattering of light on the microscopic structuredisorder of por-Si—the effect, which is not allowed for in the transfer matrix calculations.

Anomalous scaling of conductance cumulants in one-dimensional Anderson localization

The mean and the variance of the logarithm of the conductance(lng) in the localized regime in the one-dimensional Anderson model are calculated analyticallyfor weak disorder, starting from the recursion relations for the complex reflection andtransmission amplitudes. The exact recursion relation for the reflection amplitudes isapproximated by improved Born approximation forms which ensure that averagedreflection coefficients tend asymptotically to unity in the localized regime, for chain lengths. In contrast, the familiar Born approximation of perturbation theory would not beadapted for the localized regime since it constrains the reflection coefficient to be lessthan one. The proper behaviour of the reflection coefficient (and of other relatedreflection parameters) is responsible for various anomalies in the cumulants oflng, in particular for the well-known band centre anomaly of the localization length. While asimple improved Born approximation is sufficient for studying cumulants at a generic bandenergy, we find that a generalized improved Born approximation is necessary to accountsatisfactorily for numerical results for the band centre anomaly in the mean oflng. For thevariance of lng at the band centre, we reveal the existence of a weak anomalous quadratic term proportional toL2, besides the previously found anomaly in the linear term. At a generic band energy the variance oflng is found tobe linear in L and is given by twice the mean, up to higher order corrections whichare calculated. We also exhibit the offset terms independent ofL in the variance, which strongly depend on reflection anomalies.

On the reflection and transmission of sound in a thick shear layer

The propagation of sound across a shear layer of finite thickness is studied using exact solutions of the acoustic wave equation for a shear flow with hyperbolic-tangent velocity profile. The wave equation has up to four regular singularities: two corresponding to the upper and lower free streams; one corresponding to a critical layer, where the Doppler-shifted frequency vanishes if the free streams are supersonic; and a fourth singularity which is always outside the physical region of interest. In the absence of a critical layer the matching of the two solutions, around the upper and lower free streams, specifies exactly the acoustic field across the shear layer. For example, for a sound wave incident from below (i.e. upward propagation in the lower free stream), the reflected wave (i.e. downward propagating in the lower free stream) and the transmitted wave (i.e. upward propagating in upper free stream) are specified by the continuity of acoustic pressure and vertical displacement. Thus the reflection and transmission coefficients, which are generally complex, i.e. involve amplitude and phase changes, are plotted versus angle of incidence for several values of free stream Mach number, and ratio of thickness of the shear layer to the wavelength; the vortex sheet is the particular case when the latter parameter is zero. The modulus and phase of the total acoustic field are also plotted versus the coordinate transverse to the shear flow, for several values of angle of incidence, Mach number and shear layer thickness. The analysis and plots in the present paper demonstrate significant differences between sound scattering by a shear layer of finite thickness, and the limiting case of the vortex sheet.

A robust photo-interferometric technique to obtain the refractiveindex and thickness of non-absorbing stand-alone films

We present a non-contact robust method for the determination ofthe refractive index and the thickness (d≳1 µm) ofnon-absorbing stand-alone films or pellicles. It only uses reflection andtransmission optical signals instead of the respective photometricmagnitudes. A new observable magnitude permits us to determine thereflectance at one surface of the film and then the dispersive refractiveindex n(λ). From the refractive index n and an interference spectrum, wealso obtain the thickness of the film d. The main advantages are that (1) wedo not need to measure a reference, (2) the technique is not sensitive tothe instrumental functions (e.g. thickness inhomogeneity, wavelength orangular bandwidth etc) and (3) it is simple in formulation. The methodhas been applied to the characterization of an anisotropic polyester filmin the visible range of 450-600 nm with a precision of ~0.8%, both innand d.

Thin-film optical filters with diffractive elements and waveguides

The chief principles and properties of optical reflection and transmission guided-mode resonance (GMR) filters are presented. These devices are based on GMR effects in dielectric structures comprising gratings and homogeneous thin films. Detailed characteristics are calculated using rigorous coupled-wave analysis for bandpass filters operating in reflection and transmission for TE- and TM-polarized incident waves. High resonance efficiency with narrow or wide linewidths is achievable with near-zero reflectance or transmittance sidebands over extended wavelength ranges. To illustrate the potential of this technology, example GMR reflection and transmission characteristics are presented for filters operating in the visible spectral region. Excellent reflection-filter features are found when antireflection conditions prevail away from the resonance wavelength. Furthermore, long-range, low sidebands are found to be obtainable for a single-layer GMR reflection filter with a TM-polarized plane wave incident at the Brewster angle. The transmission filter is optimized when the structure is highly reflective off resonance. GMR filter fabrication tolerances are discussed with examples illustrating the sensitivity of the filter center wavelength to variations in layer thickness, grating shape, and incident angle. GMR filters are found to exhibit loss-dependent wavelength shifts such that the reflection peak occurs at a different wavelength than the corresponding transmission notch. However, under antireflection conditions, the resonance location becomes insensitive to loss. Finally, reflective GMR thinfilm structures that support multiple waveguide modes are studied. These devices exhibit unique characteristic angular and spectral signatures.