Measured Reflection Data Research Articles

Analysis of CeO2/SiO2 double-layer thin film stack with antireflection effect for silicon solar cells

This study introduces CeO2/SiO2 double-layer film stacks and its antireflection coating effect. Optical properties were analyzed by spectrophotometer measurements; surface morphology and cross-sections were observed by Scanning Electron Microscopy (SEM); elemental distributions and crystallographic properties were determined by Energy Dispersive Spectroscopy (EDS) and X-ray Diffraction (XRD) measurements. Average reflectance of single-layer 0.3MSiO2, 0.6MSiO2, and 0.3MCeO2 thin films were 30.54%, 20.12%, and 14.23%, respectively. Average reflectance was decreased significantly down to 5.9% by 0.3MCeO2/0.6MSiO2 double-layer thin films comparing to those of the results of single-layer films and bare silicon surface reflection (~40%). Antireflective effect of the films on solar cells was estimated by simulation using the measured reflection data. Simulated solar cells indicate that 0.3MCeO2/0.6MSiO2 double-layer antireflective coatings are capable to increase the efficiency significantly and conversion efficiency of 21.7% could be achieved.

Design, implementation and application of the Marchenko plane-wave algorithm

The Marchenko algorithm can suppress the disturbing effects of internal multiples that are present in seismic reflection data. To achieve this, a set of coupled equations with four unknowns is solved. These coupled equations are separated into a set of two equations with two unknowns using a time window. The two unknown focusing functions can be resolved by an iterative or direct method. These focusing functions, when applied to reflection data, create virtual point-sources inside the medium. Combining individual virtual point-sources into a plane-wave leads to an efficient computation of images without internal multiples. In this study the internal multiples are eliminated in a redatuming step which is part of the imaging algorithm. To use the Marchenko algorithm with plane-wave focusing functions, the time window that separates the unknowns must be adapted. The design of the plane-wave Marchenko algorithm is explained and illustrated with numerically modeled and measured reflection data.

Simultaneous joint migration inversion for high‐resolution imaging/inversion of time‐lapse seismic datasets

ABSTRACTThe current time‐lapse practice is to exactly repeat well‐sampled acquisition geometries to mitigate acquisition effects on the time‐lapse differences. In order to relax the rigid requirements on acquisition effects, we propose simultaneous joint migration inversion as an effective time‐lapse tool for reservoir monitoring, which combines a joint time‐lapse data processing strategy with the joint migration inversion method. Joint migration inversion is a full‐wavefield inversion method that explains the measured reflection data using a parameterization in terms of reflectivity and propagation velocity. Both the inversion process inside the imaging/inversion scheme and the extra illumination provided by including multiples in joint migration inversion makes the obtained velocity and reflectivity operator largely independent of the utilized acquisition geometry and, thereby, relaxes the strong requirement of non‐repeatability during the monitoring. Because simultaneous joint migration inversion inverts for all datasets simultaneously and utilizes various constraints on the estimated reflectivities and velocity, the obtained time‐lapse differences have much higher accuracy compared to inverting each dataset separately. It allows the baseline and monitor parameters to communicate with each other dynamically during inversion via a user‐defined spatial weighting operator. In order to get more localized time‐lapse velocity differences, we further extend the regular simultaneous joint migration inversion to a robust high‐resolution simultaneous joint migration inversion process using the time‐lapse reflectivity difference as an extra constraint for the velocity estimation during inversion. This constraint makes a link between the reflectivity‐ and the velocity difference by exploiting the relationship between them. We demonstrate the feasibility of the proposed method with a highly realistic synthetic model based on the Grane field offshore Norway and a time‐lapse field dataset from the Troll Field.

Classification and Prediction of Wave Chaotic Systems with Machine Learning Techniques

The wave properties of complex scattering systems that are large compared to the wavelength, and show chaos in the classical limit, are extremely sensitive to system details. A solution to the wave equation for a specific configuration can change substantially under small perturbations. Due to this extreme sensitivity, it is difficult to discern basic information about a complex system simply from scattering data as a function of energy or frequency, at least by eye. In this work, we employ supervised machine learning algorithms to reveal and classify hidden information about the complex scattering system presented in the data. As an example we are able to distinguish the total number of connected cavities in a linear chain of weakly coupled lossy enclosures from measured reflection data. A predictive machine learning algorithm for the future states of a perturbed complex scattering system is also trained with a recurrent neural network. Given a finite training data series, the reflection/transmission properties can be forecast by the proposed algorithm.

Seafloor sound-speed profile characterization with non-parallel layering by the image source method: Application to CLUTTER'09 campaign data.

The image source method was originally developed to estimate sediment sound speed as a function of depth assuming plane-layered sediments. Recently, the technique was extended to treat dipping, i.e., non-parallel layers and was tested using synthetic data. Here, the technique is applied to measured reflection data with dipping layers and mud volcanoes. The data were collected with an autonomous underwater vehicle towing a source (1600-3500 Hz) and a horizontal array of hydrophones. Data were collected every 3 m criss-crossing an area about 1 km(2). The results provide a combination of two-dimensional sections of the sediment sound-speeds plotted in a three-dimensional picture.

The dual polarization method for characterization of dielectric materials

The nondestructive characterization of in situ conductor-backed media is an important task for many commercial and military applications. These and similar applications may require completely nondestructive and noncontact free space material characterization methods. Free space methods which fit these characteristics are at premium. One such of these methods is the dual polarization method. The dual polarization method utilizes the measurement of the reflection coefficient at both parallel and perpendicular polarization to determine the permittivity and permeability of an unknown material sample. This paper presents an overview of the dual polarization method to characterize conductor-backed media and two additional implementations of the method specific only to dielectric materials. These additional implementations include the characterization of conductor-backed dielectrics with either known or unknown sample thickness. All three implementations of the dual polarization method presented are demonstrated with measured reflection data from a conductor-backed Plexiglas sample and are shown with accompanying sensitivity analysis.

Reflection-coefficient inversion for compressional- and shear-wave dispersion in porous and elastic layered media

This paper considers Bayesian inversion of seabed reflection-coefficient data for the compressional- and shear-wave velocity dispersion and attenuation-frequency dependence in arbitrarily layered porous and elastic media. The seabed is modeled using Buckingham's viscous grain shearing model which obeys causality. Seabed layers are parametrized in terms of six fundamental parameters, including thickness, porosity, compressional and shear grain-to-grain moduli, material exponent, and the compressional visco-elastic time constant. These fundamental parameters are used to compute density, compressional- and shear-wave dispersion curves, and compressional and shear attenuation-frequency curves for each layer. The curves are used in the inversion to predict spherical-wave reflection coefficients as a function of frequency (300–3000 Hz) and grazing angle (12–75 degrees), which include the effects of shear waves in arbitrarily layered media. In addition, the seabed layering is estimated from the data by applying a trans-dimensional Bayesian model. The ability to resolve shear-wave velocity and attenuation structure is studied using simulated data. Finally, compressional- and shear-wave dispersion are presented and discussed from measured reflection data at a sandy site in the Tyrrhenian Sea. [Work supported by ONR Ocean Acoustics.]

Optical properties of polyvinyl alcohol doped (Se80Te20)100–xAgx (0 ≤ x ≤ 4) composites

Polyvinyl alcohol (PVA) doped (Se80Te20)100–xAgx (0 ≤ x ≤ 4) thin films were prepared by the spin-coating technique on a quartz substrate. The optical parameters of PVA-doped (Se80Te20)100–xAgx (0 ≤ x ≤ 4) composites at the same chalcogen concentration (S0 = 0.1 mg ml−1) and PVA/(Se80Te20)96Ag4 composites at three different chalcogen concentrations viz. S1 = 0.3 mg ml−1, S2 = 0.6 mg ml−1 and S3 = 1 mg ml−1 have been studied. The semi-crystalline nature of the as-deposited thin filmsisdetermined by X-ray diffraction. The transmission and reflection spectra of PVA-doped Se–Te–Ag thin films were obtained in a 350–650 nm spectral region. The optical-band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical-band gap increases, but the refractive index, extinction coefficient, and the real and imaginary parts of the dielectric constant decrease, with increase in Agcontent in PVA-doped (Se80Te20)100–xAgx (0 ≤ x ≤ 4) thin films. Such type of behavior is explained on the basis of decrease in density of the defect states. However, the optical-band gap has been found to be decreased and all other optical parameters show increase in their values with increase in concentration of (Se80Te20)96Ag4 glass in PVA-doped composites. The results have been explained on the basis of cluster-size formation at the time of dissolution. This study shows that the optical properties of new composites are affected by the change in silver and chalcogen concentration.

Optical and electrical properties of as-prepared and annealed (Se80Te20)100 − xAgx (0 ≤ x ≤ 4) ultra-thin films

Optical and electrical properties of the (Se80Te20)100−xAgx (0≤x≤4) ultra-thin films have been studied. The ultra-thin films were prepared by thermal evaporation of the bulk samples. Thin films were annealed below glass transition temperature (328K) and in between glass transition temperature and crystallization temperature (343K). Thin films annealed at 343K showed crystallization peaks for Se–Te–Ag phases in the XRD spectra. The transmission and reflection of as-prepared and annealed ultra-thin films were obtained in the 300–1100nm spectral region. The optical band gap has been calculated from the transmission and reflection data. The refractive index has been calculated by the measured reflection data. It has been found that the optical band gap increases, but the refractive index, extinction coefficient, real and imaginary dielectric constant decrease with increase in Ag content. The optical band gap and refractive index show the variation in their values with increase in the annealing temperature. The extinction coefficient increases with increasing annealing temperature. The surface morphology of ultra-thin films has been determined using a scanning electron microscope (SEM). The measured dc conductivity, under a vacuum of 10−5mbar, showed thermally activated conduction with single activation energy in the measured temperature range (288–358K) and it followed Meyer–Neldel rule. The dc activation energy decreases with increase in Ag content in pristine and annealed films. The results have been analyzed on the bases of thermal annealing effects in the chalcogenide thin films.

G‐BRDFs: An Intuitive and Editable BTF Representation

Abstract Measured reflection data such as the bidirectional texture function (BTF) represent spatial variation under the full hemisphere of view and light directions and offer a very realistic visual appearance. Despite its high‐dimensional nature, recent compression techniques allow rendering of BTFs in real time. Nevertheless, a still unsolved problem is that there is no representation suited for real‐time rendering that can be used by designers to modify the BTF's appearance. For intuitive editing, a set of low‐dimensional comprehensible parameters, stored as scalars, colour values or texture maps, is required. In this paper we present a novel way to represent BTF data by introducing the geometric BRDF (g‐BRDF), which describes both the underlying meso‐ and micro‐scale structure in a very compact way. Both are stored in texture maps with only a few additional scalar parameters that can all be modified at runtime and thus give the designer full control over the material's appearance in the final real‐time application. The g‐BRDF does not only allow intuitive editing, but also reduces the measured data into a small set of textures, yielding a very effective compression method. In contrast to common material representation combining heightfields and BRDFs, our g‐BRDF is physically based and derived from direct measurement, thus representing real‐world surface appearance. In addition, we propose an algorithm for fully automatic decomposition of a given measured BTF into the g‐BRDF representation.

Millimeter wave reflectivity used for measurement of skin hydration with different moisturizers

A new non-invasive method for determining the free water content in human skin has been developed. The method analyzes the reflection of millimeter (mm) wavelength electromagnetic waves. The amount of reflection of mm waves depends on an electrical property (namely, the permittivity) of the skin, and this depends upon the free water content of the various skin layers. The aim of the present study was to use the mm wave reflectometry method for determination of free water content in healthy skin treated with different hydrating substances. Skin lotion, pure water, glycerol, and petroleum jelly (an occlusive substance) were used for hydration of skin. The amount of free water was calculated using the permittivity values of skin layers found from fitting a three layer skin model to measured reflection data. The skin model consisted of (1) the stratum corneum (SC), (2) the viable epidermis plus the dermis, and (3) fat layers. Mm wave reflection was significantly affected by the water content of the thick SC of the palm but not by the very thin SC of the forearm. Treatment of the forearm and palm skin with different hydrating substances produced notable changes of the free water content in the SC, but not in the viable epidermis or dermis. The greatest hydration was produced by pure water and skin lotion, and the lowest by petroleum jelly. However, petroleum jelly produced prolonged retention of water in the SC following its hydration by other moisturizers. The content of free water was found to return to its baseline value after removal of moisturizers in as short a time as 8.3 min. The study shows that mm wave reflectometry can be used as a sensitive technique for the non-invasive determination of water content in living skin.

Full Newton method for inverse transmission line problems, utilising explicit second order derivatives

The full Newton's method is considered as an optimisation approach to the inverse transmission line problem in the frequency-domain. For the sake of accuracy and computational efficiency, the gradient and the Hessian of the cost-functional, with respect to parameter functions in the L2-space, are derived explicitly by means of the adjoint transmission line problem and the first and second order Frechét differentials of the cost-functional. The numerical implementation, when reducing to a finite dimensional parameter space, and a regularisation technique for the resulting ill-conditioned Hessian matrix are presented. For the reconstruction of one or two parameters, the algorithm is tested on synthetic reflection data contaminated with gaussian noise. The algorithm is also tested on measured reflection data to reconstruct a piecewise constant shunt-capacitance. The generalisation to the three-dimensional inverse scattering problem for bianisotropic media is presented.

Using the inverse scattering series to predict the wavefield at depth and the transmitted wavefield without an assumption about the phase of the measured reflection data or back propagation in the overburden

The starting point for the derivation of a new set of approaches for predicting both the wavefield at depth in an unknown medium and transmission data from measured reflection data is the inverse scattering series. We present a selection of these maps that differ in order (i.e., linear or nonlinear), capability, and data requirements. They have their roots in the consideration of a data format known as the T-matrix and have direct applicability to the data construction techniques motivating this special issue. Of particular note, one of these, a construction of the wavefield at any depth (including the transmitted wavefield), order-by-order in the measured reflected wavefield, has an unusual set of capabilities (e.g., it does not involve an assumption regarding the minimum-phase nature of the data and is accomplished with processing in the simple reference medium only) and requirements (e.g., a suite of frequencies from surface data are required to compute a single frequency of the wavefield at depth when the subsurface is unknown). An alternative reflection-to-transmission data mapping (which does not require a knowledge of the wavelet, and in which the component of the unknown medium that is linear in the reflection data is used as a proxy for the component of the unknown medium that is linear in the transmission data) is also derivable from the inverse scattering series framework.

Chebyshev collocation and Newton-type optimization methods for the inverse problem on nonuniform transmission lines

A frequency-domain inverse problem for the nonuniform LCRG transmission line is considered. The parameters of the nonuniform line are interpolated by Chebyshev polynomials, and the Telegraphers equations are solved by a collocation method using the same polynomials. The interpolation coefficients for the unknown parameters are reconstructed by means of Newton-type optimization methods for which the Jacobian matrix has been calculated explicitly. For the reconstruction of one or two parameters, the algorithm is tested on synthetic data, and the necessity to use regularization is discussed. Finally, the algorithm is tested with measured reflection data to reconstruct shunt capacitances with piecewise constant profiles.

Experimental testing of a random medium optical model of porous silicon for photovoltaic applications

AbstractWe have developed a model for light propagation in porous silicon (PS) based on the theory of wave propagation in random media. The low porosity case is considered, with silicon being the host material assuming randomly distributed spherical voids as scattering particles. The specular and the diffuse part of the light could be determined and treated separately. The model is applied to the case in which porous silicon would be used as a diffuse back reflector in a thin‐film crystalline silicon solar cell realized in an ultrathin (1–3 μm) epitaxially grown Si layer on PS. Three layer structures (epi/PS/Si) have been fabricated by atmospheric pressure chemical vapor deposition (APCVD) of 150–1000 nm epitaxial silicon layers on silicon wafers of which 150–450 nm of the surface has been electrochemically etched. An excellent agreement is found between the experimentally measured reflection data in the 400–1000 nm wavelength range and those calculated using the proposed model. The values of the layer thickness agree, within a reasonable experimental error, with those obtained independently by cross sectional transmission electron microscopy (XTEM) analysis. This provides an experimental verification of the random medium approach to porous silicon in the low porosity case. The analysis shows that the epitaxial growth process has led to appreciable porosity decrease of an initially high porosity layer from about 60% to 20–30%. Copyright © 2001 John Wiley & Sons, Ltd.

New Anomalous Grazing X-ray Reflection Method for Determining the Atomic Number Density in Multi-layered Thin Film

A new method has been proposed for determining the atomic number density of a specific element in multi-layered thin films using grazing X-ray reflection and anomalous dispersion effect with the help of the Fourier filtering technique. The essential equations for analyzing the measured reflection data using the anomalous grazing X-ray reflectometry (AGXR) were given and the capability of this new method was demonstrated by obtaining the atomic number densities of constituents in a multi-layered thin film consisting of GaAs/AlAs/GaAs heterostructure.

Structural Characterization of Surfaces and Interfaces of Materials by Applying X-ray Total External Reflection Phenomena

An in-house grazing incidence x-ray scattering (GIXS) apparatus has been newly developed for characterizing the surface structure at a microscopic level. Using this apparatus, surface diffraction profiles from the oxidized SUS304 stainless steel were measured in the vicinity of the critical angle with the GIXS geometry. The depth profile was discussed from the integrated intensities of both oxidized phase and stainless steel bulk. An in-house grazing x-ray reflection apparatus (GXR) has also been newly built for studying the liquid surface, and the liquid/solid and liquid/liquid interfaces. This system was tested by measuring x-ray reflectivity profiles from free surface of mercury and the water/mercury interface. In addition, a new method has been proposed for determining the atomic number density of a near-surface element in materials using grazing x-ray reflection and anomalous dispersion effect. The essential equations for analyzing the measured reflection data were given and the capability of this anomalous grazing x-ray reflection (AGXR) method was well-confirmed by obtaining the atomic number densities of near surface elements with some selected examples of ZrO 2 -Y 2 O 3 crystal and the passivated stainless steel.

Acoustic impedance measurement on normal ears of children.

In order to provide the fundamental knowledge on outer and middle ear of children, acoustic impedance measurements were performed on 205 subjects. They ranged from 3 years old to 11 years old and had normal hearing. We utilized the acoustic inverse method for reconstruction of the ear canal area functions. The results show (a) the children have smaller ear canal radius than the adults and (b) the ear canal volume and the ear canal radius increase as a function of the age. The acoustic impedance at the eardrum were calculated from the reconstructed area function of the ear canals and the measured reflection data. It is shown that (c) mean resistance of the eardrum impedance remains between 300 and 350 cgs acoustic ohms above 2 kHz, and the value is not so much different from the reported data on the adults. On the other hand, (d) middle ear of the children has small compliance and its values approach to the adults data as the age increases. This is evident in lower frequencies below 1 kHz.

Influence of welded boundaries in anelastic media on energy flow, and characteristics of P, S‐I, and S‐II waves: Observational evidence for inhomogeneous body waves in low‐loss solids

A general computer code, developed to calculate anelastic reflection‐refraction coefficients, energy flow, and the physical characteristics for general P, S‐I, and S‐II waves, quantitatively describes physical characteristics for wave fields in anelastic media that do not exist in elastic media. Consideration of wave fields incident on boundaries between anelastic media shows that scattered wave fields experience reductions in phase and energy speeds, increases in maximum attenuation and Q−1, and directions of maximum energy flow distinct from phase propagation. Each of these changes in physical characteristics are shown to vary with angle of incidence. Finite relaxation times for anelastic media result in energy flow due to interaction of superimposed radiation fields and contribute to energy flow across anelastic boundaries for all angles of incidence. Agreement of theoretical and numerical results with laboratory measurements argues for the validity of the theoretical and numerical formulations incorporating inhomogeneous wave fields. The agreement attests to the applicability of the model and helps confirm the existence of inhomogeneous body waves and their associated set of distinct physical characteristics in the earth. The existence of such body waves in layered, low‐loss anelastic solids implies the need to reformulate some seismological models of the earth. The exact anelastic formulation for a liquid‐solid interface with no low‐loss approximations predicts the existence of a range of angles of incidence or an anelastic Rayleigh window, through which significant amounts of energy are transmitted across the boundary. The window accounts for the discrepancy apparent between measured reflection data presented in early textbooks and predictions based on classical elasticity theory. Characteristics of the anelastic Rayleigh window are expected to be evident in certain sets of wide‐angle, ocean‐bottom reflection data and to be useful in estimating Q−1 for some ocean bottom reflectors.