Calculation Of Reflection Coefficients Research Articles

Computational ultrasound testing for non-destructive evaluation of multilayered structures: 3D modeling of longitudinal wave propagation signal responses

Non-destructive evaluation (NDE) using ultrasonic imaging (UI) is essential for detecting defects in complex multilayered structures, which are commonly encountered in aerospace, automotive, and medical fields. A thorough understanding of material properties, wave propagation, and dispersion behavior is crucial for accurate defect detection. The Transfer Matrix Method (TMM) provides a comprehensive approach by modeling the entire UI process, including the control system, ultrasonic transmitter, wave propagation (both bulk and guided modes), and receiver response. This study focuses on predicting the backscattered ultrasonic signal during longitudinal wave propagation in a multilayer structure immersed in water, considering normal incidence and specific frequencies. TMM, employing a quadrupole formalism, integrates stress and velocities at layer boundaries and models the multilayer structure as a transfer matrix derived from individual layer matrices. This approach allows for the calculation of reflection coefficients across a wide frequency spectrum. TMM generates detailed distance-time and distance-frequency representations that illustrate the propagation of various longitudinal modes in configurations, such as plexiglass/water/glass under direct (PWG) and reverse (GWP) insonation. Comparisons between PWG and GWP distance-time planes may be affected by layer arrangement and properties, which influence the reflection coefficient, highlighting the system's sensitivity to layer order even with similar thicknesses and materials.

High precision ultrasonic measurement method for thin-walled parts

Thin-walled parts are extensively utilized in the aerospace industry, where over thinning defects in these parts would significantly compromise mechanical safety. Ultrasound measurement methods are commonly employed for thickness non-destructive testing. Manual calibration of reference signals is usually necessary, negatively impacting automation, robustness, and accuracy. This paper proposes a high-precision ultrasound amplitude method for thin-walled component inspection, getting rid of manual calibration. Firstly, the measured signal is preprocessed to extract the spectrum in the effective frequency range. Then, the spectrum is approximated using the asymmetrical Gaussian amplitude model to estimate the spectrum of reference signal and reflection coefficient. Moreover, initial propagation time is estimated from autocorrelation of the signal. Finally, the accurate thickness is obtained from the numerical calculation of reflection coefficient with the initial time. Simulations and experiments demonstrate that the proposed method can accurately measures metal plates as thin as 0.5 mm. Compared to the traditional correlation method, it greatly improves measurement accuracy and stability, reducing them to 1/2 and 1/4 of the latter, respectively. Additionally, the proposed method also demonstrates high accuracy for curved thin plates, with an average relative error of only 0.57 %. Furthermore, the method exhibits high levels of automation, robustness, and accuracy, and holds significant potential for thickness detection in thin-walled structural components.

Comment on Lu et al. Ultrathin Terahertz Dual-Band Perfect Metamaterial Absorber Using Asymmetric Double-Split Rings Resonator. Symmetry 2018, 10, 293

In this study, the design of a dual-band terahertz absorber, previously published by Lu et al. (Symmetry 2018, 10, 293), was re-simulated. Our findings showed significantly different absorption results from those published in the article. A detailed analysis was conducted to explain this discrepancy, which was attributed to the reflection of an unaccounted orthogonal component of the waves from the design, rather than absorption. The metasurface design has two resonances at 4.48 THz and 4.76 THz, respectively. It was reported that at these frequencies, the structure achieved absorption of 98.6% and 98.5%, respectively. However, in our results, it was found that at the second resonance (4.76 THz), the structure acted as a strong cross-polarization converter, reflecting a significant amount of incident energy in the cross-polarization component of the reflected wave. When this component is considered in the reflection coefficient calculations, the absorption reduces to 41% (from 98.5%), which is not an acceptable level for an absorber. In addition, the structure was simulated for both lossy and lossless (FR4) substrate cases to understand the effect of substrate losses. The results showed that the absorption response significantly deteriorates at the first resonance (4.48 THz) in the case of a lossy FR4 substrate.

Frequency-Domain Reverse-Time Migration with Analytic Green's Function for the Seismic Imaging of Shallow Water Column Structures in the Arctic Ocean.

Seismic oceanography can provide a two- or three-dimensional view of the water column thermocline structure at a vertical and horizontal resolution from the multi-channel seismic dataset. Several seismic imaging methods and techniques for seismic oceanography have been presented in previous research. In this study, we suggest a new formulation of the frequency-domain reverse-time migration method for seismic oceanography based on the analytic Green's function. For imaging thermocline structures in the water column from the seismic data, our proposed seismic reverse-time migration method uses the analytic Green's function for numerically calculating the forward- and backward-modeled wavefield rather than the wave propagation modeling in the conventional algorithm. The frequency-domain reverse-time migration with analytic Green's function does not require significant computational memory, resources, or a multifrontal direct solver to calculate the migration seismic images as like conventional reverse-time migration. The analytic Green's function in our reverse-time method makes it possible to provide a high-resolution seismic water column image with a meter-scale grid size, consisting of full-band frequency components for a modest cost and in a low-memory environment for computation. Our method was applied to multi-channel seismic data acquired in the Arctic Ocean and successfully constructed water column seismic images containing the oceanographic reflections caused by thermocline structures of the water mass. From the numerical test, we note that the oceanographic reflections of the migrated seismic images reflected the distribution of Arctic waters in a shallow depth and showed good correspondence with the anomalies of measured temperatures and calculated reflection coefficients from each XCDT profile. Our proposed method has been verified for field data application and accuracy of imaging performance.

Fast Twist Angle Mapping of Bilayer Graphene Using Spectroscopic Ellipsometric Contrast Microscopy.

Twisted bilayer graphene provides an ideal solid-state model to explore correlated material properties and opportunities for a variety of optoelectronic applications, but reliable, fast characterization of the twist angle remains a challenge. Here we introduce spectroscopic ellipsometric contrast microscopy (SECM) as a tool for mapping twist angle disorder in optically resonant twisted bilayer graphene. We optimize the ellipsometric angles to enhance the image contrast based on measured and calculated reflection coefficients of incident light. The optical resonances associated with van Hove singularities correlate well to Raman and angle-resolved photoelectron emission spectroscopy, confirming the accuracy of SECM. The results highlight the advantages of SECM, which proves to be a fast, nondestructive method for characterization of twisted bilayer graphene over large areas, unlocking process, material, and device screening and cross-correlative measurement potential for bilayer and multilayer materials.

Feature extraction method of HPLC communication signal based on genetic algorithm

AbstractCommunication quality is a key factor affecting the effectiveness of distribution network operation status management. Therefore, it is required that the communication performance of the distribution network management system be good, and the communication signal can directly reflect the communication quality. Therefore, a genetic algorithm (GA) based HPLC communication signal feature extraction method is proposed. The process of constructing reference samples, training recognition models, constructing noise samples, self‐coding denoising processing, and denoising sample recognition has completed the identification of power line channel transmission characteristics. The state feature quantity of the topological line is based on the positioning results of the diagnostic function, and the calculated value of the reflection coefficient calculation model at the head end of the topological line is compared with the measured value. By optimizing the feature quantities containing topological line states through GAs, abnormal feature quantities close to the true state of topological lines are obtained. Experimental analysis shows that this method can correctly identify the position of reactive power compensation in the transmission line, and can also correctly identify the extraction of topological anomaly features. Therefore, the research method is of great significance in improving the safe operation of power systems and extending the service life of topology lines.

Quantitative evaluation of gas hydrate reservoir by AVO attributes analysis based on the Brekhovskikh equation

AVO (Amplitude variation with offset) technology is widely used in gas hydrate research. BSR (Bottom simulating reflector), caused by the huge difference in wave impedance between the hydrate reservoir and the underlying free gas reservoir, is the bottom boundary mark of the hydrate reservoir. Analyzing the AVO attributes of BSR can evaluate hydrate reservoirs. However, the Zoeppritz equation which is the theoretical basis of conventional AVO technology has inherent problems: the Zoeppritz equation does not consider the influence of thin layer thickness on reflection coefficients; the approximation of the Zoeppritz equation assumes that the difference of wave impedance between the two sides of the interface is small. These assumptions are not consistent with the occurrence characteristics of natural gas hydrate. The Brekhovskikh equation, which is more suitable for thin-layer reflection coefficient calculation, is used as the theoretical basis for AVO analysis. The reflection coefficients calculated by the Brekhovskikh equation are complex numbers with phase angles. Therefore, attributes of the reflection coefficient and its phase angle changing with offset are used to analyze the hydrate reservoir's porosity, saturation, and thickness. Finally, the random forest algorithm is used to predict the reservoir porosity, hydrate saturation, and thickness of the hydrate reservoir. In the synthetic data, the inversion results based on the four attributes of the Brekhovskikh equation are better than the conventional inversion results based on the two attributes of Zoeppritz, and the thickness can be accurately predicted. The proposed method also achieves good results in the application of Blake Ridge data. According to the method proposed in this paper, the hydrate reservoir in the area has a high porosity (more than 50%), and a medium saturation (between 10% and 20%). The thickness is mainly between 200m and 300m. It is consistent with the previous results obtained by velocity analysis.

The Application of Stochastic Seismic Inversion Method of Geostatistical Inversion in Putaohua X Area

Stochastic seismic inversion is an important part of geostatistical inversion method, and is the combination of seismic inversion and sequence simulation. In the process of random seismic inversion, firstly, the histogram distribution of random variables is counted, the variation function of random variables is calculated, and the variation range of random variables in different directions is determined. Then, for each implementation, the seismic traces are synthesized at the seismic channel position according to the calculated reflection coefficient, and the error between the synthetic traces and the original seismic traces is compared, and the inversion results are output after the required accuracy is reached. Geostatistical inversion can improve the vertical and horizontal resolution of the reservoir and accurately describe the spatial distribution of the reservoir. Taking the Heidimiao oil layer in the west slope area of Daqing Placanticline as an example, this paper expounds the application of geostatistical inversion in the work area as a whole. Combined with the results of seismic attribute analysis and well logging curve preprocessing, the inversion results formed by accurate time-depth calibration and other processes of reservoir sensitivity parameter analysis provide a basis for optimizing the target well location in the work area.

Petrophysical modeling of rocks dominik formation as the basis of interpretation of seismic data

The paper is devoted to theoretical modeling of effective elastic properties of rock samples of domanik deposits. To determine the effective elastic properties of rocks, depending on their composition and morphological characteristics, the methods of effective medium theory were used. The aim of the work was to determine the parameters characterizing the microstructure of the investigated rock samples; creation of a seismic-geological model and calculation of reflection coefficients for it. The main attention in the work is paid to the influence of the content of kerogen and the degree of its maturity (porosity) on the measured physical quantities (velocities of elastic waves, reflection coefficients).

Inexpensive indoor acoustic material estimation for realistic sound propagation

AbstractFor the realistic and immersive experience in a virtual environment, it is important to estimate and reflect the acoustic characteristic of the real indoor scenes. This article proposes a method of directly measuring the reflection coefficient of a surface, which is an acoustic characteristics in the real environment. Because expensive optimization‐based studies that mainly aim to reproduce recorded sounds indirectly estimate acoustic materials, new estimates are required whenever the actual environment changes. Our approach utilizes the method of the acoustics field to enable anyone to easily and directly measure the reflection coefficient of a real environment and generate sound in a virtual environment. We obtain the impulse response (IR) for the target surface, separate the direct sound and the reflected sound, and calculate the reflection coefficient for each surface. The measurement of the IR and the reflection coefficient calculation takes about 2 s. Our result produces a sound with a similar reverberation time to the sound recorded in the real environment.

Reflection Coefficient Calculation of a Structure Including a Porous Silicon Layer with Transfer Matrix Method and FDTD

Porous silicon is an important material for a variety of application area such as anti-reflective coating for solar cells. Today, solar cell market is mostly dominated by silicon based solar cells. Porous silicon thin films are easy to fabricate and it is compatible with silicon technology. Designing porous silicon anti-reflective coating layers is a critical issue to enhance silicon based solar cell performance. There are several methods to calculate reflection coefficient of porous silicon thin layers. In this study, transfer matrix method and finite-difference time-domain method are used to calculate reflection coefficient of porous silicon thin layers. Because finite-difference time-domain method gives more accurate results, the results obtained with finite-difference time-domain method are used to control the results obtained with transfer matrix method. In transfer matrix method, refractive indices of the porous silicon layers are calculated with Bruggeman effective medium approximation.

Physical property studies to elucidate the source of seismic reflectivity within the ICDP DSeis seismogenic zone: Klerksdorp goldfield, South Africa

Petrophysical properties of cylindrical core specimens from three boreholes from the International Continental Scientific Drilling Program, the DSeis project, measured at ambient pressure and room temperature conditions in various laboratories are presented and compared with downhole petrophysical data (sonic and density). The measured properties are from sixty-six rock specimens constituting metasediments, metabasalts and intrusives. Seismic velocities were measured using 0.5 MHz P- and S-wave transducers. To investigate the source of seismic reflectivity observed on the 2D legacy seismic data, we computed synthetic seismograms for adjacent rock units using downhole petrophysical data and compared them with seismic reflections from the reflection seismic profile. The experimental measurements show that the metasediments exhibit lower bulk densities and seismic velocities than the metabasalts and intrusive specimens. The porosity was found to be less than 2% for all the samples. No clear trends emerge when the Poisson's ratio is plotted against the P-wave velocities and porosities of the samples. A positive relationship is observed between the bulk modulus and P-wave velocities of the rock samples. The highest calculated reflection coefficients (RC) are associated with the metasediment-intrusive interfaces in all three boreholes. The intrusive-metabasalt and the metasediment-metabasalt interfaces exhibit low RC. Synthetic seismograms reveal strong reflections that coincide with high RC calculated using the bulk density and velocity data. The synthetic seismograms also revealed additional strong reflections that were not identified using the reflection coefficients calculated from the rock specimens, due to core loss in some lithological units. Successful correlations are carried out between the synthetic seismic data and the real seismic data, enabling us to correlate the stratigraphic sequence drilled in the boreholes to the seismic reflections observed on the legacy 2D reflection seismic data.

Double-wavelength coherent perfect absorption laser in Thue-Morse PT-symmetric photonic crystals

Coherent perfect absorption laser points (CPA-LPs) are investigated in the Thue-Morse (Th-M) PT-symmetric photonic crystals. CPA-LPs are induced as incident light impinges perpendicularly upon the structure. The operating wavelengths of the CPA-LPs are dependent on the Th-M sequence number, the incident angle and the gain-loss factor of materials. Especially, two CPA-LPs may be achieved with the same value of incident angle for a specific gain-loss factor. Double-wavelength laser consequently is supported in this structure and the corresponding transmittance of the CPA-LPs is optional. An abrupt jump in the calculated reflection coefficient phase could be found at the CPA-LPs as well. This study may be helpful in potential applications for lasers and highly sensitive sensors.

Investigation of thermoacoustic oscillation attenuation by modified Helmholtz dampers with dual frequency bands

Two modified Helmholtz dampers with multi-adjustable frequency bands are proposed to overcome the drawback of Helmholtz dampers and Quarter-lambda tubes by which multi-irregular eigenfrequencies in gas turbine combustors cannot be simultaneously treated via one interface. Theoretical impedance models of these dampers are established and experimentally validated in an impedance tube. Enhanced thermoacoustic instability attenuation by modified dampers is validated in a Rijke tube. A Helmholtz-based method is combined with damper impedance models to predict the limit cycle behavior of a Rijke tube equipped with dampers. Results indicate that the impedance models can effectively calculate reflection coefficients of modified and traditional dampers with cooling purge air. The amount of the secondary tube influences the reflection coefficients of modified dampers. Experimental results indicate that amplitudes of the overall pressure fluctuation and each order fluctuation at the limit cycle are further attenuated by modified dampers compared with those by traditional ones. Larger purge flow rates for dampers lead to more pulsation attenuation caused by vortex shedding dissipation. The numerical method can predict the eigenfrequencies, velocity fluctuation ratios, and mode shapes at the limit cycle after using different types of dampers. When activating modified dampers, weaker fluctuations are successfully captured by this numerical approach.

Polarization twist reflector antenna — A systematic design approach

In this paper, we present an easy and systematic design approach to realize a polarization twist reflector antenna. Detail description has been provided on how to design a transreflector antenna and its constituents including the transreflector, the polarization twist-reflector, and the feed horn. Simple relations for calculation of reflection coefficients of the trans-reflector and the twist- reflector with plane wave incidence have been considered. Simple transmission line model based analyses have been presented. As it does not involve any integral equation or summation of series of some functions, the final results can be obtained within few seconds with the minimum computational resource requirement. Conductive gratings have been conceived for both trans-reflector and twist-reflector. Their performances have been optimized individually in terms of their grating parameters. A linearly polarized pyramidal horn located at the prime focus of the transreflector has been used for the excitation. A prototype of the complete antenna has been designed at Ka-band, fabricated and experimentally measured. 19% impedance bandwidth with average gain of ≈32.3 dBi has been demonstrated.

Changes in elastic wave velocity during brittle deformation of gabbro and peridotite: Implications for oceanic Moho reflectivity

Cracks that develop during brittle deformation easily modify rocks' physical properties; therefore, understanding of seismic properties of oceanic rocks during deformation is essential for interpretation of the seismic observations of the oceanic lithosphere. Here we measured elastic wave velocities of gabbro and peridotite during triaxial deformation experiments at room temperature, a confining pressure of 20 MPa, and a strain rate of ∼10−6 s−1. Gabbroic rocks showed significant decrease in elastic wave velocities approaching the maximum stress, which is comparable to that of typical crystalline rocks. On the other hand, peridotite showed relatively sudden and small decrease in elastic wave velocities close to the maximum stress. We inverted the observed velocities to crack density tensor based on an effective medium theory. The different changes in elastic wave velocities between gabbroic rocks and peridotites were interpreted by different characteristics of crack development, where limited number of cracks were opened in peridotite than in gabbroic rocks. The calculated reflection coefficient of the interface between the gabbro and peridotite increases from <0.1 to ∼0.25 as approaching the maximum stress. Synthetic seismograms computed from the crack-dependent velocity structures of the oceanic lithosphere indicate that the Moho reflectivity is highly sensitive to the contrast of crack-damage across the crust-mantle boundary. The existence of a heterogeneous crack-damaged zone in the oceanic lithosphere, which is likely related to intra-plate earthquakes, may result in the spatial variations of Moho reflection.

Wave propagation across a functionally graded interphase between soft and hard solids: Insight from a dynamic surface elasticity model

Joining soft to hard materials is a challenging problem in modern engineering applications. In order to alleviate stress concentrations at the interface between materials with such a mismatch in mechanical properties, the use of functionally graded interphases is becoming more widespread in the design of the new generation of engineered composite materials. However, current macroscale models that aim at mimicking the mechanical behavior of such complex systems generally fail in incorporating the impact of microstructural details across the interphase because of computational burden. In this paper we propose to replace the thin, but yet finite, functionally graded interphase by a zero-thickness interface. This is achieved by means of an original model developed in the framework of surface elasticity, which accounts for both the elastic and inertial behavior of the actual interphase. The performance of the proposed equivalent model is evaluated in the context of elastic wave propagation, by comparing the calculated reflection coefficient to that obtained using different baseline models. Numerical results show that our dynamic surface elasticity model provides an accurate approximation of the reference interphase model over a broad frequency range. We demonstrate application of this modeling approach for the characterization of the graded tissue system at the tendon-to-bone interphase, which fulfills the challenging task of integrating soft to hard tissues over a submillimeter-wide region.

The Influence of Wave Resonance Phenomena on the Sound Insulation of a Single-layer Building Partition in the Application of Calculation Models with the Concentrated Parameters

The article presents calculation formulas for calculating sound insulation before and after the frequency of wave coincidence, obtained through the joint solution of the equations of the momentum conservation law and kinetic energy conservation. The process of occurrence of wave interference phenomena in a construction partition, due to the movement of waves traveling along it and reflected from its anchoring nodes, is described. Formulas for corrections to sound insulation for resonances are given. A formula for finding the reflection coefficient of the oscillation velocity using the basic provisions of the method of concentrated parameters is obtained. A special case of determining the reflection coefficient of the oscillation velocity in a single-layer partition with a cruciform hinge joint in a panel building is considered. Formulas for computation of reflection coefficient of the oscillation velocity are written. As an example, frequency characteristics of two panel inter-apartment walls in buildings of standard series are found. Sound insulation graphs are constructed according to the applied method and the method of the Russian code of rules, and comparison with experimental measurements is provided.

Application of the extended Mattis-Bardeen theory for the calculation of reflection coefficient of superconducting NbTiN thin films

Problem formulating. NbTiN is becoming the subject of interest because of unique properties in RF. Therefore, the problem of investigation of this material’s electrical properties rises sharply. Goal. This work is aimed at theoretical description of the superconductive films’ reflection coefficient with considering imaginary part of the superconductive gap and to apply the results to calculate the reflection coefficient from NbTiN film at frequencies up to 2500 GHz. Result. The formulas for calculation of the reflection coefficient with high precision was obtained. Parameters of NbTiN were calculated. Practical meaning. Currently there are many factors which reduce the quality of NbTiN films and thus restricting their application. Therefore, the proposed method of calculations is useful in research activities in this area.

The radial Teukolsky equation for Kerr–Newman–de Sitter geometry: revisited

We use Heun-type solutions given in Suzuki et al. (Prog Theor Phys 100:491, 1998) for the radial Teukolsky equation written in the background metric of the Kerr–Newman–de Sitter geometry to calculate reflection coefficient for waves coming from the de Sitter horizon and reflected at the outer horizon of the black hole.