Effective Reflection Coefficient Research Articles

A Non-Compact Effective Impedance Model for Can-to-Can Acoustic Communication: Analysis and Optimization of Damping Mechanisms

Abstract Can-annular combustors can feature azimuthal instabilities even if the acoustic coupling between the individual cans is weak. Recently, various studies have focused on modeling the acoustic communication between adjacent cans in can-annular systems. In this study, a coupling model is presented that, in contrast to previous models, includes the effect of density fluctuations, mean flow, and dissipative effects at the connection gaps. By assuming plane acoustic waves inside each can and exploiting the discrete rotational symmetry of the can-annular system, the acoustic can-to-can interaction can be represented by an effective Bloch-type impedance. A single can modeled with the effective impedance at the downstream end emulates the acoustic response of the entire can-annular arrangement. We then propose the idea of installing a liner just upstream of the first turbine stage to damp azimuthal instabilities. By using the proposed can-to-can coupling model, we discuss in detail the effect that the impedance of the liner has on the effective reflection coefficient for different Bloch wavenumbers. In the low-frequency limit, we derive an analytical condition for achieving maximum damping at a specific Bloch-number. We show that the damping of azimuthal modes depends on the porosity of the liner, mean flow parameters and the Bloch-structure of the mode. These results suggest the possibility of targeting the damping of modes of certain azimuthal order by geometric variations of the liner or of the connection gap. As an exemplary application of the theory, we setup a network model of a generic industrial 12-can combustor and investigate a cluster of acoustic and thermoacoustic eigenvalues for a varying liner porosity. The findings of this study provide a deeper understanding of the mechanisms that drive the can-to-can acoustic communication, and open the path for devising passive damping strategies aimed at stabilizing specific modes in can-annular combustors.

Application of heuristic UTD formulation for describing scattering by a thin and multilayer anisotropic slab

The previously developed heuristic uniform theory of diffraction (UTD) corner and wedge diffraction coefficients for a thin lossless anisotropic slab are generalized and applied for predicting electromagnetic scattering by a thin and multilayer anisotropic slab with complex permittivity and permeability tensors. The effective reflection and transmission coefficients of a thin and multilayer slab are used in the heuristic formulation to determine the scattered fields. Numerical results are provided for various scattering problems that demonstrate the application of the heuristic formulations for a thin and multilayer structure.

A High-Frequency Solution for Scattering by a Multilayer Anisotropic Slab

The previously developed heuristic uniform theory of diffraction corner and wedge diffraction coefficients for a thin lossless anisotropic slab are generalized and applied for predicting electromagnetic scattering by a lossy/lossless multilayer anisotropic slab. The effective reflection and transmission coefficients of a multilayer slab are used in the heuristic formulation to determine the scattered fields. The heuristic coefficients derived for a thin slab are applied to a multilayer slab with a finite thickness. Numerical results are provided for various scattering problems that demonstrate the validity of the heuristic formulations for a multilayer structure.

Amplification of optical activity in a fiber loop resonator.

In this paper, we have theoretically studied an effective amplification of optical activity by a fiber loop resonator. We propose a scheme in which an optically active element is placed in the loop segment of the resonator. Assuming that the coupling in the resonator is polarization-independent, we have shown that initially small polarization plane rotation, which arises due to the optically active element, can be significantly amplified by tuning the resonator's closed-path phase. We have also studied the influence of losses on the amplification of optical activity. We have shown that the maximal amplification takes place under the condition of critical coupling, at which the attenuation parameter is equal to the resonator's effective reflection coefficient. We have also studied effective dichroism in such a system and shown the relevance of a critical coupling regime to that effect.

Application of Historical Geophysical Materials in Searching for Cu-Ag Ore Deposits—A New Direction of Research

This paper presents a new instrument in geological exploration, which uses historical geophysical data for the indication of potential zones of the occurrence of Cu-Ag ore, based on the example of the newly discovered Nowa Sól deposit in south-western Poland. Basic historical seismic and gravimetric data were applied along with transformed maps. The new method of effective reflection coefficients (ERC) allowed the utilization of archival seismic records for a more precise determination of the most vaguely traced interfaces within the Permian Zechstein unit. Compared to an amplitude-based seismic section, an ERC section is characterized by its highly increased resolution of imaging. The tracing of changes in the facies and the tectonics of Zechstein sediments, particularly in a zone of their contact with Rotliegend rocks, along with the new ERC method, enabled the establishing of precise locations of prospecting boreholes. The combined use of ERC and historical well logs also allowed more precise identification of the shape of oxidized areas and the adjacent orebodies.

Multiple input multiple output dielectric resonator antenna with circular polarized adaptability for 5G applications

ABSTRACT In this paper, the concept of the circularly polarized agile, multiple-input multiple-output (MIMO) dielectric resonator antenna (DRA) structure for fifth generation (5G) new radio application in mobile terminal is presented. Two prototypes have been fabricated, namely one with cylindrical DRA (CDRA) referred as A1 and a second one with ring DRA (RDRA) named as A2. These practical realizations of dual-port MIMO antennas have been mounted on a Rogers 5870 substrate of octagonal shape with proper ground architecture. The proposed dual-port MIMO antennas have been excited with conformal probes and L-type feed network aiming to achieve circular polarization (CP). Measured impedance bandwidth of A1 and A2 are 21.2% (3.15–3.9 GHz) and 22.2% (3.12–3.9 GHz), respectively. Moreover, for both antennas low mutual coupling between ports with minimum isolation of dB over entire impedance bandwidth has been obtained by using triangular head slots in the ground plane. Measured axial ratio bandwidths in broadside direction are 5.66% (3.26–3.45 GHz) and 4.25% (3.45–3.6 GHz), respectively. Maximum gains are 7.3 and 7.2 dBi, in that order. MIMO antenna parameters such as envelope correction coefficient, diversity gain (DG), mean effective gain and total active reflection coefficient are also calculated to verify MIMO performance parameters. The proposed antennas also demonstrate CP agility with insertion of concentric cylindrical shells of different radii.

Compact eight‐port MIMO/diversity antenna with band rejection characteristics

A new compact three-dimensional multiple-input-multiple-output (MIMO) antenna comprised of eight antenna elements is presented. The unit cell of the proposed MIMO/diversity antenna consists of three elliptical rings connected together in the region close to the feed line and a rectangular-shaped modified ground plane. To achieve polarization diversity with the proposed eight-port MIMO configuration, four antenna elements are horizontally arranged and the remaining four are vertically oriented. The proposed antenna has an impedance bandwidth (S11 < −10 dB) of 25.68 GHz (3.1-28.78 GHz) with a wireless local area network notch-band at 5.8 GHz (5.2-6.5 GHz). In addition to polarization diversity, the proposed antenna provides a reliable link with wireless devices. The prototype antenna design is fabricated and measured for diversity performance. Also, the proposed MIMO antenna provides good performance metrics such as apparent diversity gain, channel capacity loss, envelope correlation coefficient, isolation, mean effective gain, multiplexing efficiency, and total active reflection coefficient.

Spin-dependent electron scattering in cobalt interconnects

We use state-of-the-art ab initio simulation methods to study fundamental electron scattering mechanisms in cobalt conductors for applications in advanced interconnect technology. In particular, we consider electron scattering at intrinsic defect sites, twin grain boundaries, and at the Co/metal/Co interfaces present in vertical interconnects. Effective resistivity values and reflection coefficients are calculated in each case. The explicit treatment of electron spin results in distinct majority and minority spin behavior, with majority spin states exhibiting less scattering than minority states. Our results indicate that grain boundary scattering dominates over scattering at intrinsic point defect sites. Vertical resistance calculations indicate that Co vias can have substantially lower resistance than corresponding Cu vias at comparable dimensions. These results help build a fundamental understanding of electron scattering mechanisms in non-Cu conductors for advanced interconnect applications.

Proximity-coupled two-port multi-input-multi-output graphene antenna with pattern diversity for THz applications

A proximity coupled graphene patch based two-port multi-input-multi-output (MIMO) antenna with pattern diversity is implemented for THz applications. The MIMO and diversity performance parameters of the antenna like envelop correlation coefficient (ECC), diversity gain (DG) and mean effective gain (MEG) and total active reflection coefficient are calculated and found within the acceptable limits. The antenna offers the ECC <0.01, DG ≈10dB, and MEG ≤−3 dB. The antenna provides the 10 dB impedance bandwidth of 6.06% (1.76 −, 1.87 THz). The isolation between the ports of the proposed MIMO antenna remains more than 25 dB in the operating passband. The aspect ratio of graphene patch and physical parameters of the antenna are selected for obtaining the single mode operation with the resonance of TM12, mode. The utilization of the graphene material provides the flexibility in tuning the antenna response.

Prediction of signatures of airgun arrays using dual near‐field hydrophones

ABSTRACTSuccessful estimation of airgun‐array signatures from near‐field measurements depends on the accuracy of poorly controlled model parameters such as the effective sea surface reflection coefficient and source depth. We propose a method for prediction of robust source signatures, which are insensitive to fluctuations of the latter parameters. The method uses vertical pairs of near‐field hydrophones to measure near‐field pressure and its vertical gradient, combination of which eliminates sea surface reflections from the near‐field data. This excludes the uncertainty related to the fluctuating sea state and source depth from the process of inversion of the near‐field data for source signature. The method explicitly separates the recorded near‐field pressure into its up and down going components, which allows one to measure the effective frequency‐ and angle‐dependent sea surface reflection coefficient right at the source, as well as to estimate the actual source depth. Tests on synthetic and field data demonstrate robust performance of the method.

ЭКСПЕРИМЕНТАЛЬНОЕ ИССЛЕДОВАНИЕ ОТРАЖЕНИЯ УПРУГИХ ВОЛН ОТ ШЕРОХОВАТЫХ ГРАНИЦ

The results of physical modeling show that the influence of boundary roughness on its reflectivity depends on the ratio of roughness characteristic dimension and wavelength. The boundary roughness leads to a decrease in the effective reflection coefficients at subcritical and to their increase at supercritical angles of incidence. A change in the azimuth of the plane of incidence with respect to the roughness direction appreciably affects the reflection coefficients only at supercritical angles.

Radiometric microwave field measurements of the complex dielectric constant of the water surface

The paper describes the new remote method of radiometric in situ measurements of the real and imaginary parts of the dielectric constant (permittivity) of the underlying sea surface, which is an important parameter for remote sensing of the Earth. The method does not require absolute calibration of a radiometer, but uses the black body with the underlying surface temperature, which simplifies the measurement and allows one to measure the effective reflection coefficient at specified polarizations. It is shown that, for a fixed value of the reflection coefficient in sensing to the nadir, R(θ = 0°) = const, the reflection coefficient at the horizontal polarization is almost independent of the of dielectric loss angle. The reflection coefficient at the vertical polarization is most sensitive to the loss angle in the vicinity of the Brewster angle Rv(θ = θBr). The paper presents the results of measurements of the sea surface reflection coefficient using the radiometer operating at frequency of 37.5 GHz. The reflection coefficients at vertical and horizontal polarizations are calculated taking into account the antenna pattern and the distribution of slopes of a weakly roughened sea surface. The paper presents the example of determining the real and imaginary parts of the permittivity based on experimentally measured values of reflection coefficients at incidence angles close to the nadir and the reflection coefficient Rv(θ = θBr) at the Brewster angle. The obtained experimental values correspond to the theory within the limits of diversity of existing models.

Analysis of coupled micro rings resonators and coupled Fabry–Pérot resonators with a single physical view

Coupled micro ring resonators gained a lot of interest in recent years in the field of silicon photonics. Although it is well recognized that coupled ring resonators and coupled Fabry–Pérot resonators operate with similar physical principles, their analysis in the literature is artificially separated, often each resonator type is analysed with different physical arguments, techniques and nomenclature. As a result, coupled rings resonators and coupled Fabry–Pérot resonators appear as two different problems, and the similarity in the physical principles that govern their operation is blurred. What is more unfortunate is that the established physical intuition, familiar from Fabry–Pérot analysis, is lost in notation when dealing with coupled micro rings. Here, we argue how a lossless boundary between two dielectrics and a lossless waveguide-coupler can be viewed as a single entity: an abstract ‘boundary’ that transmits and reflects optical fields according to Stokes relations. Using this view, Fabry–Pérot and micro rings become a single type of resonator. Accordingly, we calculate effective reflection and transmission coefficients of several configurations of coupled Fabry–Pérot and rings resonators. We calculate these coefficient by the intuitive method of summing reflected fields and by the method of transfer matrix. We illustrate that the effective reflection and transmission coefficients of a coupled ring resonator is similar to 3 layers Fabry–Pérot resonator and discuss the subtle difference. It is hoped that the common nomenclature and analysis used for both types of coupled resonators will give the reader a clear and basic understanding of both types of resonators.

Geophysical study of deep basement structure of NW Poland using effective reflection coefficients

The paper presents the possibility of applying the method of effective reflection coefficients (ERC) to recognise the deep basement structure for a case study of seismic profile GB1-III-86/89 from NW Poland. Two sectors of the seismic profile were selected in areas of occurrence of deep fractures bounding the Trans-European Suture Zone (TESZ) from the southwest and the northeast, respectively. At certain time intervals, due to transformation of the amplitude into an impulse form, seismic wave traces have been presented as effective reflection coefficients. An interpretation of the two sectors of profile GB1 provides a more detailed image of the complex geological structure of the Earth's crust in the southwestern and northeastern edges of the TESZ. The work has allowed for the identification of boundaries of reflection coefficients by distinguishing a number of layers and complexes (among others transition zones to the consolidated basement), and the determination of lines and seismic discontinuity zones, including the nature and location of the two deep tectonic fracture zones bounding the TESZ, as well as the Moho position. In particular, the southwestern sector of the profile shows cross-sections of two areas with different seismic structures, with a boundary that can be correlated with a deep fracture zone – the Trans-European Fault (TEF). The location and course of the boundary correlated with the Moho discontinuity is also defined. The northeastern sector of the profile, analysed at three time intervals, characterises the zone of deep fracture occurring in the northeastern part of the TESZ. Interpretation of the seismic section in its upper part illustrates seismic horizons that may define the Caledonian Deformation Front (CDF) and the northeastern limit of the Teisseyre–Tornquist Zone (TTZ), bounding the TESZ to the northeast. In the lower part, it represents the crustal structure and an attempt to identify areas of different structures: the lower laminated part and the upper homogenous part, as well as seismic discontinuity lines of tectonic and/or lithological origin. The applied method has delivered satisfactory results for the Lower Palaeozoic and older basement formations down to the Moho. The new form of seismic record, compared with the previously acquired wave image of profile GB1-III-86/89, significantly increases the possibility of interpretation and reliability of the results. The results confirm and justify the earlier concepts concerning the main tectonic features presented by researchers of this area. The experience and results justify the need for continuing the work using this method to verify and provide details about the extent of the structural-tectonic elements to the northwest and southeast, with reference to the research results from Poland and adjacent areas of Germany and the southern Baltic Sea.

A geometrical optics model based on the non-Gaussian probability density distribution of sea surface slopes for wind speed retrieval at low incidence angles

ABSTRACTIn this study, a large amount of data from precipitation radar (PR) and National Data Buoy Center (NDBC) buoys are collocated for the development and validation of a Geometrical Optics Model, in order to retrieve wind speed at small incidence angles. The omni-directional model is developed based on the combination of the quasi-specular scattering theory and non-Gaussian probability density distribution of ocean surface slope, and can be applied at incidence angles as high as 15°. There are four parameters included in the proposed model: the effective Fresnel reflection coefficient, the mean square slope, and the two coefficients associated with the kurtosis of the sea surface slope distribution. Using one half of the collocated data, the dependence of the four parameters on the in situ wind speed is acquired. The results show that the effective Fresnel reflection coefficient has a decrease relative to that obtained in previous studies. We combine the proposed model with the maximum-likelihood estimation (MLE) technique to retrieve the ocean surface wind speed at the 10 m height. The retrieved wind speeds are then validated against those measured by the NDBC buoys. The comparison shows that the root mean square error (RMSE) and bias between the model retrievals and buoy observations are 1.54 m s–1 and 0.1 m s–1, respectively, revealing high agreements in the wind speed estimations. The results of this study indicate that the proposed model and the PR measurements at low incidence angles can provide reasonably accurate estimates of the surface wind speeds within the range of 0–20 m s–1.

단축 이방성 박막들이 코팅된 시료의 타원식

단축이방성 박막들과 등방성 박막들이 코팅되어 있는 시료에 비스듬히 입사한 빛의 유효반사계수 표현들을 유도하였다. 단축 이방성 박막 내에서의 다중반사 효과를 반영하여 여러 층의 등방성 박막들과 이방성 박막들이 섞여 있는 시료의 유효반사계수 표현들과 타원상수 표현들을 제시함으로써 시료면에 수직한 방향으로 균일하지 않은 단축이방성 분포를 가진 시료의 광학이방성을 여러 개의 단축이방성 박막으로 나누어 분석할 수 있도록 하였다. The effective reflection coefficients for light obliquely incident upon a substrate coated with uniaxially anisotropic films and with isotropic films are derived. Multiple reflections inside anisotropic films, as well as those inside isotropic films, are properly treated. These expressions, together with the related ellipsometric expressions, can be used to find the nonuniform distribution of an uniaxially anisotropic film perpendicular to the film's surface, by approximating it as consisting of uniaxially anisotropic uniform layers and applying the conventional modeling technique for spectroscopic ellipsometry.

두개의 단축이방성 박막이 있는 다층박막 시료의 타원식

광축의 각도가 서로 다른 두 단축이방성 박막이 다층박막 기층시료 위에 코팅되어 있을 때 비스듬히 입사한 빛의 유효반사계수 표현들을 유도하였다. 유효반사계수로부터 타원상수 표현들을 구하고 이 타원상수의 단축이방성 박막 광축각도 의존성으로부터 단축이방성 박막의 표면 이방성에 의한 효과와 주층 이방성에 의한 효과를 구분하여 해석할 수 있도록 하였다. Explicit expressions are derived for the effective reflection coefficients of obliquely incident light on a multilayered substrate coated with two uniaxially anisotropic films. Based on these reflection coefficients, ellipsometric constants are obtained as function of the tilt and azimuthal angles of the optical axes of the uniaxial films. Explicit expressions are provided, which can be used to separate the effects of surface anisotropy for anisotropic film from that of its bulk anisotropy, so that these expressions may be utilized in characterizing the surface anisotropy of alignment layers.

Effective modeling of ground penetrating radar in fractured media using analytic solutions for propagation, thin-bed interaction and dipolar scattering

We propose a new approach to model ground penetrating radar signals that propagate through a homogeneous and isotropic medium, and are scattered at thin planar fractures of arbitrary dip, azimuth, thickness and material filling. We use analytical expressions for the Maxwell equations in a homogeneous space to describe the propagation of the signal in the rock matrix, and account for frequency-dependent dispersion and attenuation through the empirical Jonscher formulation. We discretize fractures into elements that are linearly polarized by the incoming electric field that arrives from the source to each element, locally, as a plane wave. To model the effective source wavelet we use a generalized Gamma distribution to define the antenna dipole moment. We combine microscopic and macroscopic Maxwell's equations to derive an analytic expression for the response of each element, which describes the full electric dipole radiation patterns along with effective reflection coefficients of thin layers. Our results compare favorably with finite-difference time-domain modeling in the case of constant electrical parameters of the rock-matrix and fracture filling. Compared with traditional finite-difference time-domain modeling, the proposed approach is faster and more flexible in terms of fracture orientations. A comparison with published laboratory results suggests that the modeling approach can reproduce the main characteristics of the reflected wavelet.

Effective source mismatch uncertainty evaluation using resistive power splitter up to 18 GHz

CSIR-National Physical Laboratory (NPL) India is a National Metrology Institute (NMI), which disseminate traceability of the physical parameters in the country. In the field of microwave, it is one of the apex laboratories to provide traceability. In this paper, the method for precession measurement of effective source reflection coefficient using resistive power splitter and mismatch uncertainty evaluation are reported and discussed. Juroshek method is implemented in conjunction with Vector Network Analyzer (VNA) for mismatch uncertainty evaluation by measuring source reflection coefficient from measured S parameters. The measurement results and their associated uncertainty are presented and discussed from 1 MHz to 18 GHz of the resistive power splitter. The complex reflection coefficient of the effective source is determined using indigenously developed automation software. The method adopted is the most convenient way of measuring effective source reflection coefficient whose values are smaller than the manufacturer specs. The mismatch uncertainty has been improved, which is beneficial during the calibration of power sensors along with power meters.

Modern Coaxial Microwave Power Calibrators in the Frequency Band Up To 50 GHz

Coaxial power calibrators and ways of improving them for checking terminal-type wattmeters are considered. Measurement of the complex effective reflection coefficient $$ {\dot{\Gamma}}_{\mathrm{eff}} $$ of the output of the calibrators enables the Γ-correction method to be used when transmitting the unit of power by the direct comparison microwave method, which considerably reduces the mismatch error. The errors in measuring $$ {\dot{\Gamma}}_{\mathrm{eff}} $$ are analyzed and the results of measurements by different methods are compared. An automated system for checking wattmeters using Γ-correction is described.