Modified Reflection Coefficient Research Articles

Application of electrical sounding to determine the spatial distribution of groundwater quality in the coastal area of Jiangsu Province, China

In most coastal alluvial plains, the groundwater area of the aquifer is a rich environment that has experienced an extended period of marine deposition and is highly vulnerable to increasing urbanization. Excessive exploitation of groundwater has resulted in recent seawater intrusion and connate water leakage, leading to freshwater salinization. In this study, a novel workflow is designed for groundwater appraisal. First, revised one-dimensional direct transformation schemes were developed and applied to extensive vertical electrical sounding (VES) points sampled by a Schlumberger array to obtain the VES-based calibrated transformed resistivity (V-CTR), as calibrated by the modified reflection coefficient and novel depth correction factor. Next, the interfaces of all leaky confined aquifers (LCAs) and the saline water zone were quantitatively determined via hybrid interpretation methods. Finally, to better understand the salt level (i.e., fresh, brackish, or saline) and perform assessments of the groundwater quality, total dissolved solids (TDS) planar distributions were interpolated using two different power functions linking the V-CTR and measured TDS from the sampled boreholes for the corresponding aquifer unit. The workflow was examined based on hydrological and geophysical data acquired at the Yangtze River Delta (Nantong Region, Jiangsu Province, China). The interpreted results are of great significance for understanding the groundwater distribution associated with the Quaternary geology and hydrogeology and can be potentially used to analyze and guide the development and utilization of water resources in the study area.

No-Slip Boundary Conditions for Electron Hydrodynamics and the Thermal Casimir Pressure

We derive modified reflection coefficients for electromagnetic waves in the THz and far infrared range. The idea is based on hydrodynamic boundary conditions for metallic conduction electrons. The temperature-dependent part of the Casimir pressure between metal plates is evaluated. The results should shed light on the “thermal anomaly,” where measurements deviate from the standard fluctuation electrodynamics for conducting metals.

A Time-domain Double Diffraction for Non-perfectly Conducting Wedges

A time-domain (TD) double diffraction solution is proposed with the source illumination for one or both sides of non-perfectly conducting wedges. The frequency domain redefined reflection angles as well as modified reflection coefficients are used in the different angular region of wedges for developing TD double diffraction. The accuracy of the proposed model is confirmed with IFFT- FD solution. Finally, the table of computational efficiency has been given for both the methods (TD and IFFT-FD) for hard polarization.

High-Frequency Method for Scattering from Coated Targets with Extremely Electrically Large Size in Terahertz Band

This article presents a high-frequency method for the prediction of radar cross-section of coated targets with extremely electrically large size in the terahertz band in free space. To consider the scattering characteristics of the coated targets with a rough surface in the terahertz band, taking into account the effect of surface roughness, the reflection coefficients on the smooth coating surface can be modified; the equivalent electric and magnetic currents on the surface can then be corrected by the modified reflection coefficients to obtain the electric and magnetic induced current densities on the rough coating surface. Therefore the physical optics method, which was combined with the graphical electromagnetic computing method and improved using the partition display algorithm, can be used to solve the scattered fields, and the radar cross-section of the coated targets with a rough surface in the terahertz band can then be obtained. Numerical results for several coated targets, such as the mother warhead of the Minuteman III intercontinental ballistic missile and VFY-218 aircraft, are given and discussed. The results provide an important basis and method for applications of terahertz radar in many fields, such as military, astronomy, and remote sensing, in the future.

WHY SCREENING EFFECTS DO NOT INFLUENCE THE CASIMIR FORCE

The Lifshitz theory of dispersion forces leads to thermodynamic and experimental inconsistencies when the role of drifting charge carriers is included in the model of the dielectric response. Recently modified reflection coefficients were suggested that take into account screening effects and diffusion currents. We demonstrate that this theoretical approach leads to a violation of the third law of thermodynamics (Nernst's heat theorem) for a wide class of materials and is excluded by the data from two recent experiments. The physical reason for its failure is explained by the violation of thermal equilibrium, which is the fundamental applicability condition of the Lifshitz theory, in the presence of drift and diffusion currents.

Modification of the UTD Model for Cellular Mobile Communication in an Urban Environment

In this paper we modified the reflection coefficient of electromagnetic wave incident on the wall of buildings or obstacles that occurs in the mobile communication path by solving the nonlinear Riccati equations. For this purpose, the building walls are assumed to be inhomogeneous layers of brick and concrete where permittivity changes as a function of the wall thickness. Based on reflection coefficient modification, we proposed a new propagation model using uniform geometrical theory of diffraction (UTD) and geometrical theory of diffraction (GTD) for multiple diffraction paths in cellular mobile radio communication, and calculate the diffraction loss as well as the path loss for a row of buildings with two inhomogeneous faces. The measured reflection coefficient and diffraction loss are then compared to the theoretical results obtained from the proposed model. Our observations reveal good agreement between measurement data and theoretical results. Therefore it can be concluded that the modified reflection coefficient can adequately predict the reflective properties of the wall surfaces with different dielectric properties. So the modified reflection coefficient as well as the new UTD model can directly be applied for field estimation or diffraction loss calculation, as well as multipath signal strength or delay prediction in ray tracing algorithms used in mobile communication, radar, and radio links.

On the modeling of reflected energy from building faces in microcellular mobile radio planning tools

A semideterministic model of electromagnetic scattering from exterior urban building walls that is capable of modeling scattering from large-scale discontinuities such as ledges, windows, etc., is presented. The model is in quantitative agreement with spatiotemporally resolved measurements of scattering from a building wall at 2.4 GHz and can be used to construct relatively simple modified reflection coefficients that can be used in ray-optical microcellular planning tools.

A comparison of theoretical and empirical reflection coefficients for typical exterior wall surfaces in a mobile radio environment

This paper presents microwave reflection coefficient measurements at 1.9 GHz and 4.0 GHz for a variety of typical smooth and rough exterior building surfaces. The measured test surfaces include walls composed of limestone blocks, glass, and brick. Reflection coefficients were measured by resolving individual reflected signal components temporally and spatially, using a spread-spectrum sliding correlation system with directional antennas. Measured reflection coefficients are compared to theoretical Fresnel reflection coefficients, applying Gaussian rough surface scattering corrections where applicable. Comparisons of theoretical calculations and measured test cases reveal that Fresnel reflection coefficients adequately predict the reflective properties of the glass and brick wall surfaces. The rough limestone block wall reflection measurements are shown to be bounded by the predictions using the Fresnel reflection coefficients for a smooth surface and the modified reflection coefficients using the Gaussian rough surface correction factors. A simple, but effective, reflection model for rough surfaces is proposed, which is in good agreement with propagation measurements at 1.9 GHz and 4 GHz for both vertical and horizontal antenna polarizations. These reflection coefficient models can be directly applied to the estimation of multipath signal strength in ray tracing algorithms for propagation prediction.

Modified reflectance and geometrical deformations of Gaussian beams reflected at a dielectric interface

The geometrical interpretation of Gaussian-beam deformations under reflection at a linear dielectric interface is revised. It is proved that, besides the four known geometrical effects, namely, the lateral, focal, and angular shifts and the beam-waist modification, an independent nonspecular effect termed the complex amplitude modification exists and that all these effects are necessary for a complete description of the deformed beam. The new effect is described as a product of reflectance and propagation nonspecular modifications. The amplitude-based and intensity-based definitions of the modified reflection coefficient are given, and substantial differences between them and the Fresnel reflectance are shown. The significance of the propagation modification in the evaluation of the modified reflectance is also explained. Analytical expressions for all the nonspecular effects and for the interrelations among them are derived, and an accurate numerical procedure for their evaluation is discussed.

Quasi-specular sea scatter with modified reflection coefficient

The paper deals with the relationship between the sea surface wind speed (U) and the backscattering coefficient (σ0) for microwave frequencies and quasi specular range of angles. Valenzuela’s effective reflection coefficient based on the theory of scattering of electromagnetic waves from rought dielectric surfaces has been introduced in the expression of backscattering coefficient and the final result compared with the σ0-U relationship derived fromSEASAT scatterometer and concurrent sea truth data.

Measurement of small optically pulse-modulated reflection coefficients

The letter presents a new method for measuring small pulse modulated complex reflection coefficients of which both phase and magnitude are a rapidly varying function of time. The method is based on a single-point dynamic balance of two differently pulse-modulated signals produced in a modified reflection coefficient bridge. The measuring procedure is described in detail, and the first experimental results are discussed.

Design features of multi-port reflectometers

Guidelines are developed, based on least-error criteria, for the design of reflectometers working on the 6-port power measurement principles. A general matrix analysis is established which yields solutions for all designs of coupler. In particular, it is shown that it is not necessary to single out a special port for determining the reference power, provided that the coupler is designed with an appropriate form. One such ideal design without a reference port is discussed. The performance of the ideal couplers are related to realisable couplers through modified reflection coefficients and modified scattering matrices. These transformations from the realisable to the ideal help in the understanding of practical systems and their design. Finally, a 10-port reflectometer is described, where the extra information is used to either extend the dynamic range or to increase the level of accuracy. The system, with an extended dynamic range, could measure |ρ| > 1 as well as |ρ| ≤ 1, and so find particular use in the measurement of active systems as well as passive devices.

A Modified Reflection Coefficient for Layered Media

The energy leaving an antenna is considered as a series of rays reflected to a distant antenna. Each ray forms many reflected rays at each layer and invariant imbedding is used to study those rays of interest (i.e., rays forming a triangular zone connecting the antennas) and all others are considered lost.The modified reflection coefficient differs by several dB in some cases from the conventional plane‐wave reflection coefficient.

Wave Scattering and Transmission at Irregular Surfaces

Marsh's theory of surface scattering is applied to the case of imperfect reflectors. The result for backscattering is quite simple for it is only the product of Marsh's result and the absolute value of a modified reflection coefficient squared. Using backscattering data, a method of obtaining the absolute value of the modified reflection coefficient, roughness spectrum, and the physical properties of the surface material is shown for the cases of laboratory sand surfaces, sea bottom, and Arctic-ice cover. Lambert's law is also discussed.

An Impedance Transformation Method for Finding the Load Impedance of a Two-Port Network

An unknown load impedance terminating a lossy two-port junction can be calculated if the input impedance and junction parameters are known. It is to be shown that there exists a linear relationship, dependent upon two calibration constants, between the input reflection coefficient and a modified reflection coefficient of the load. Applying the linear transformation to the junction input impedance permits evaluation of the unknown load impedance. Calibration is accomplished by terminating the transmission line in at least three different reactance and measuring the corresponding input reflection coefficients. These data plot into the usual circular configuration on a Smith chart from which the necessary calibration data is obtained. When several load reactances are used, the calibration accuracy can be considerably increased, since the averaging advantage of plotting a mean straight line is utilized. Furthermore, once the junction has been calibrated, its equivalent T-network impedances and scattering coefficients may be found.