Dependence Of Reflection Coefficient Research Articles

Измерения спектральной зависимости коэффициента отражения комплектного алюминиевого зеркала спектрофотометра Shimadzu UV-2700

In this paper, we present the results of experimental investigation of the spectral dependence of the aluminum mirror reflection coefficient in the operating range of 185…900 nm. The aluminum mirror is a part of the Specular Reflectance Measurement Attachment to the Shimadzu UV-2700 spectrophotometer. We used experimental data obtained on the same spectro-photometer for a standard incidence angle of 5° for the reflection coefficient of a fused silicon dioxide plate as a reference sample. This is because the spectral characteristics of the optical parameters of fused silicon dioxide determined by the Sellmeier formular are well known. We used a standard quartz glass plate with a thickness of 2,2 mm and a spectrophotometer slit of 5 nm in our experiment. In this case it is possible to neglect interference effects due to multiple reflection. We found from our experimental data the spectrum of the absorption coefficient required for determining the calculated spectral dependence of its reflection coefficient in the spectrophotometer operating range. On the basis of this absorption spectrum the absolute values of the reflection coefficient of the quartz plate were calculated. This calculation was made for the normal incidence approximation and taking into account multiple reflections and dispersion of the refractive coefficient of fused quartz in accordance with the Sellmeier formula. The comparison of the spectra of calculated absolute and relative values of the reflection coefficient of the quartz plate measured on a spectrophotometer with experimental data for the reflectance of aluminum mirror made it possible to obtain the spectral dependence for the aluminum mirror for the entire operating range from 185 to 900 nm. It was found that spectral dependence of the reflection coefficient of a complete aluminum mirror was nonmonotonic. In case under consideration the deviations of its reflection coefficient from an ideal unit value do not exceed 10 % only in the spectral range from 350 to 670 nm. Thus, it is necessary to take into account the obtained spectral dependence of the reflection coefficient of the complete aluminum mirror for quantitative measurements in the entire operative range of the Shimadzu UV-2700 spectrophotometer from 185 to 900 nm.

Метод обобщенного импеданса для расчета отражения и прохождения волны через многослойную структуру. Часть 4. Критерий применимости ступенчатого приближения для неоднородной среды

The correctness of applicability of stepped approximation for calculation the reflection, propagation and dissipation coefficients by falling the wave to multi-layer structure is investigated. The starting distribution is the linear increasing of wave number from initial to final points of structure. As an approach it is employed the presentation of structure as a combination from layers in each if it’s the wave number is constant but from one layer to other increases by stepped manner. It is formed 12 distributions with increasing fractional of distribution of structure to steps. It is shown that the dependence of reflection coefficient from the fractional distribution of structure with constant of its length has powerfully indented resonance character. It is shown that for expulsion the possibility of resonances excitation the half of minimum wave length must be more then whole length of structure. From this demand it is found the critical as so maximum value of wave number which is equal to ratio of number “pi” to the whole length of structure. It is found that the correct approximation of linear increasing by stepped is the so as which maximum of wave number is less than critical. It is found that in practice near the critical value for the achieve the correction (near 5%) it is enough the distribution of structure on seven steps which have equal high and length. When the maximum of wave number is more than critical number the anyone increasing of distribution (so as increasing of steps quantity) for increasing of approximation precision of linear structure by stepped does not achieved.

Метод обобщенного импеданса для расчета отражения и прохождения волны через многослойную структуру. Часть 3. Падение волны на ступенчато нарастающий барьер

The application of generalized impedance method in the variant of successive calculation of amplitude for calculation of coefficients of reflection, passage and absorption in the case of wave incidence on multi-layer structure is investigated. The slide configuration of structure is established as barrier which wave number is distributed in slides by stepped increasing manner. The forming of vibrations amplitude by different length of structure is investigated. It is shown that in the case when length of structure is less then half of maximum wave length the distribution of wave amplitude along the structure is monotony increased or decreased. In the case when length of structure is more then half of maximum wave length the distribution of wave amplitude along the structure is oscillated. The period of these oscillations is equal to the half of maximum wave length. For the medium without of dissipation the coefficient of reflection by changing of structure length is investigated. It is found the dependencies of reflection coefficient from the structure length by different meanings of maximum wave length. The coefficient of passage of wave by the changing of structure length is investigated. The reflection, passing and absorption of waves in stepped increased structure which slides have positive dissipation is investigated. It is shown that in this case the medium becomes absorbed and when the structure length is increased the absorption coefficient is also increased. The reflection, passing and absorption in medium with negative dissipation is investigated. It is mentioned that in the frame of energy balance maintained the increasing of reflection, passage and absorption by the increasing of structure length demands the additional energy from external source which in lasers is the pumping source.

ON SOME FEATURES OF ULTRASOUND REFLECTION WATER-SAMPLE IN AN INCLINED FALL (PHYSICAL MODELING)

In recent years, the analysis of the dependence of reflection coefficients on the magnitude of the angle of incidence of reflected waves has been successfully used in the practice of seismic research. AVO analysis is one of the methods of dynamic analysis that is used to estimate changes in the amplitude of reflected waves depending on the distance between the explosion points and the receivers. The AVO method is based on the analysis of the dependence of the reflection coefficients on the angle of incidence. In real conditions, this dependence can be determined, for example, by the roughness of the boundaries. This determines the relevance of studying the features of reflection coefficients on uneven boundaries on objects with well-controlled properties. The aim of the work is to determine the nature of the influence of different-scale roughness of seismic boundaries on the reflection coefficients of elastic waves. The work also used the technique of isolating standing waves to determine the wave velocity. As a result, graphs were obtained demonstrating the dependence of the reflection coefficients on the magnitude of the angle of incidence of reflected waves from a rough surface. Reflection coefficients were also obtained for the boundary of an isotropic medium in the direction of the isotropy plane and possible ways of applying the results were analyzed. Based on the data obtained, we can say that when the azimuth changes relative to the direction of the surface, the reflection coefficients change significantly only at the supercritical angles of incidence.

ON SOME FEATURES OF ULTRASOUND REFLECTION WATER-SAMPLE IN AN INCLINED FALL (PHYSICAL MODELING)

In recent years, the analysis of the dependence of reflection coefficients on the magnitude of the angle of incidence of reflected waves has been successfully used in the practice of seismic research. AVO analysis is one of the methods of dynamic analysis that is used to estimate changes in the amplitude of reflected waves depending on the distance between the explosion points and the receivers. The AVO method is based on the analysis of the dependence of the reflection coefficients on the angle of incidence. In real conditions, this dependence can be determined, for example, by the roughness of the boundaries. This determines the relevance of studying the features of reflection coefficients on uneven boundaries on objects with well-controlled properties. The aim of the work is to determine the nature of the influence of different-scale roughness of seismic boundaries on the reflection coefficients of elastic waves. The work also used the technique of isolating standing waves to determine the wave velocity. As a result, graphs were obtained demonstrating the dependence of the reflection coefficients on the magnitude of the angle of incidence of reflected waves from a rough surface. Reflection coefficients were also obtained for the boundary of an isotropic medium in the direction of the isotropy plane and possible ways of applying the results were analyzed. Based on the data obtained, we can say that when the azimuth changes relative to the direction of the surface, the reflection coefficients change significantly only at the supercritical angles of incidence.

The calculation of reflections of linear polarization plane electromagnetic wave from the boundary of the «air – wet soil» based on heterogeneous Maxwell Garnett and Brughehman models

In this work we calculated the reflection coefficients modules of a linear polarization plane electromagnetic wave depending on soil moisture with a relative complex dielectric constant described by the heterogeneous Maxwell Garnett and Bruggeman models. A comparison is made of the calculated dependences of reflection coefficients for incident E- and H-polarization waves on soil moisture according to the two proposed heterogeneous two-component models. The correctness of the applied models is shown within the soil moisture content up to 10 %. Within the limits of soil moisture change from 10 to 50 %, there are slight discrepancies in the calculation results for two heterogeneous models. The reflection level of an electromagnetic wave from the soil surface in the case of its H-polarization is less than in the case of E-polarization. With an increase in soil moisture, a monotonous increase in the reflection level is observed. The proposed heterogeneous models of wet soil and the calculation method can be used for remote radar sensing of the Earths surface in order to determine the moisture content in the rooted layer of the soil.

Quasi-analytical and rigorous modeling of interference microscopy

We present an extended vectorial Kirchhoff model of coherence scanning interferometry including several vector rotations occurring in the imagining and scattering process as well as polarization dependent reflection coefficients. For validation simulated results are compared to those of the conventional scalar Kirchhoff model and a rigorous finite element modeling.

Reflection of plane wave at free boundary of micro-polar nonlocal semiconductor medium

This work presents the reflection phenomena of thermo-elastic waves in nonlocal micro-polar semi-conducting solid. The thermo-elasticity theory of factional-order time derivative three phase lag thermo-elastic model is applied to study the thermal effect on the waves. Governing equations of the problem are decomposed by using the Helmholtz decomposition. Two frequency dispersion relations corresponding to couple longitudinal and transverse waves are obtained. It is observed that three coupled longitudinal and two coupled transverse waves are propagating through the elastic solid. Relations for amplitude ratios, Energy flux balance are obtained analytically. All the results obtained mathematically are represented graphically for the selected material. The silicon crystal has been selected for computational purpose to check the variation of amplitude ratios against incident angle. The dependence of reflection coefficients upon nonlocal and fractional order parameters is been represented graphically.

Investigation of corner diffraction for different materials in vehicular channels at urban street intersection

This paper investigates diffraction around building corners in non line-of-sight vehicle-to-vehicle scenario at a typical urban street intersection. Diffraction from building corner depends on several geometrical parameters. Mobile vehicles moving towards a street intersection cause rapid changes in these geometrical parameters. The effect of varying geometrical parameters along with dependence of reflection coefficient on material constitutive parameters, angle of incidence and surface roughness causes the Diffraction coefficient to change differently for different building materials. The combined effect of varying Diffraction coefficients for all the corners in a typical urban street intersection is investigated. The results show that total diffracted power from materials with rough surfaces may become comparable to power from perfect electrical conductor near the street intersection.

Reflection of plane waves from the boundary of a thermo-magneto-electroelastic solid half space

The theory of generalized thermo-magneto-electroelasticity is employed to obtain the plane wave solutions in an unbounded, homogeneous and transversely isotropic medium. Reflection phenomena of plane waves is considered at a stress free and thermally insulated surface. For incidence of a plane wave, the expressions of reflection coefficients and energy ratios for reflected waves are derived. To explore the characteristics of reflection coefficients and energy ratios, a quantitative example is set up. The half-space of the thermo-magneto-electroelastic medium is assumed to be made out of lithium niobate. The dependence of reflection coefficients and energy ratios on the angle of incidence is illustrated graphically for different values of electric, magnetic and thermal parameters.

Specific Features of the Reflection of Whistler Electromagnetic Waves, Incident on the Ionosphere from Above, in Day- and Nighttime Conditions

A numerical solution of the wave equations for whistler electromagnetic waves incident on the ionosphere from above is obtained. For the calculations, we used a matrix algorithm for the approximate solution of wave equations in a stratified smoothly inhomogeneous medium and the collocation method for solving the boundary problem. Dependences of reflection coefficients R are obtained and analyzed on the frequency and angle of incidence of the wave for different seasons and time of day. At night, for waves with frequencies from 1 to 10 kHz, the values of R vary from 0.1 to 0.7. In daytime conditions, the value of R, on average, is two orders of magnitude lower and does not exceed 0.04. The smallest values of the reflection coefficient are associated with waves, the reflection of which occurs in the region of strong attenuation at heights of 80–110 km. The results obtained explain the specific features of the conditions for the excitation of the plasma magnetospheric maser.

Reflection and refraction of a plane sound wave in an elastic plate with an inhomogeneous anisotropic coating

In paper the problem of the reflection and refraction of a plane harmonic sound wave by a homogeneous isotropic elastic plate with an continuously inhomogeneous anisotropic elastic coating is considered. It is assumed that the plate is adjoin to ideal fluids. The propagation of small perturbations in a ideal fluid in the case of steady state oscillations is described by Helmholtz’s equation. The propagation of elastic waves in a uniform isotropic elastic plate is described by scalar and vector Helmholtz’s equations for longitudinal and transverse waves. Oscillations of an inhomogeneous anisotropic elastic coating are described by general motion equations of the continuous medium. The boundary-value problem for the system of ordinary second order differential equations is constructed for determination of the displacement field in inhomogeneous anisotropic coating. An analytical description of the reflected and transmitted through the plate acoustic fields is obtained. Particular cases when the material of an inhomogeneous coating is transversely isotropic and isotropic are considered. The results of numerical calculations of dependence of reflection coefficient of a homogeneous isotropic plate with a transversely isotropic coating from the incidence angle of plane wave are presented.

Nanofiltration of saline oil-water emulsions: Combined and individual effects of salt concentration polarization and fouling by oil

This study employed NF270 nanofiltration membranes and SDS-stabilized hexadecane to identify mechanisms of membrane fouling by highly saline oil-water emulsions. Concentration dependencies of NaCl reflection coefficient σ and NaCl permeability coefficient B were measured and used to determine the separate contributions of osmotic pressure and fouling to the overall flux decline. The NaCl permeability coefficient asymptotically converged to the same steady state value across a range of feed salinities and concentration polarization conditions. The measured near-hyperbolic dependence of the reflection coefficient on the transmembrane concentration differential (σΔπm≈ const) negated the effect of concentration polarization on permeate flux. Oil caused an abrupt decrease in permeate flux but only for more saline feeds (seawater level and higher), which was interpreted as a result of membrane surface sealing by coalesced oil. Headloss analysis showed that over the longer term, the additional hydraulic resistance due to a layer of oil droplets on the membrane surface became the dominant fouling mechanism.

A Note on Brewster Effect for Lossy Inhomogeneous Rough Surfaces

This article attempts to examine the Brewster effect of incoherent scattering from a lossy inhomogeneous rough surface with a vertical dielectric profile. Five typical dielectric profiles are selected for the purpose of illustration. In calculating the reflection coefficients, a transition model is used to convert the angle of incidence to local incidence, which accounts for the surface roughness. Numerical results show that the Brewster angle gradually moves to the large incident angle with an increase in the background dielectric constant and in the surface root-mean-squared (rms) height. The angular dependence of reflection coefficients, both the level and the trend, is slightly affected by the correlation length. The scattering strength is much more sensitive to the rms height than to the correlation length. The results could be useful in the retrieval of vertical soil moisture content when proper radar observation is available.

Means for monitoring the dielectric parameters of liquid media based on quasiperiodic Bragg microwave structures in a coaxial waveguide

The main characteristic of the converter element in resonant microwave sensors that determines the sensitivity of the conversion is the quality factor of the resonance line. In structures with periodic inhomogeneity of the classical topology, the quality factor of the circuit at high values of the signal-to-noise ratio may turn out to be low, which entails the emergence of restrictions on the maximum achievable conversion parameters. One of the ways to increase both the Q factor and the modification of other properties of the microwave structure that affect the overall efficiency of the converter element is the use of quasiperiodic elements. The coaxial cable, where the holes in the dielectric act as inhomogeneity, is presented, forming structure with phase shift. Using the method of flow graphs, we obtained the analytical dependence of the reflection coefficient for this structure. The analysis of the frequency response of the microwave reflection coefficient was carried out for different values of the phase shift and the location of the phase shift section along the length of the cable. A numerical and physical experiments were carried out to determine the frequency dependence of the microwave reflection coefficient with a π-phase shift for various values of the automobile fuel permittivity introduced into the cells.

УПРАВЛЯЕМЫЙ ДУПЛЕКСНЫЙ ВЕНТИЛЬ ТЕРАГЕРЦЕВОГО ДИАПАЗОНА

The paper studies the devices of THz frequency range for modern telecommunication. There has been presented a two-frequency duplex isolator constructed on the basis of anisotropic layered structure with arbitrary direction of anisotropic axis. Such device is widely used in antenna-feeder paths for decoupling of transmitted and received signals. The isolator consists of two transceiving antennas, two solenoids and an anisotropic plate. Its basic element is an anisotropic plate having nonreciprocal properties. The optimum isolator structure includes twelve two-layer periods and provides the best nonreciprocal properties. The operation principle of the isolator is determined not by Faraday's effect, but by dependence of structural parameters on the direction and size of external magnetic field. Such approach allows to pass a wave of the defined working frequency in one (straight) direction and not to pass this wave in the return direction. At the same time, the wave at another working frequency can extend only in the return direction and can’t extend directly. The offered device has selective properties as well. In fact, the integrated device combines the duplex two-frequency isolator and the strip filter. To calculate general characteristics there were used the matrix method of transformation and matrix method of reflection. Dependences of duplex isolator characteristics on direction of falling a harmonious wave and anisotropic axis orientation have been presented. There have been given calculation results of wave numbers in a uniform ferrite layer and dependences of reflection coefficients

Time domain generalized telegrapher’s equations for the electromagnetic field coupling to finite-length wires buried in a lossy half-space

The paper deals with a derivation of a time domain variant of the generalized telegrapher’s equations for transient electromagnetic field coupling to buried wires. The formulation is based on the thin wire antenna theory in the time domain. The influence of a lossy half-space is taken into account by means of the time dependent reflection coefficient approximation arising from the modified image theory (MIT), while the per-unit-length surface impedance accounts for the conductor losses. The obtained space-time integral expressions are handled analytically. The concept of the scattered voltage is naturally included in the full model formulation. Computational examples are given for the induced currents along the buried wire and compared to the results obtained by using the transmission line (TL) approximation.

Metadiffusers: Deep-subwavelength sound diffusers

We present deep-subwavelength diffusing surfaces based on acoustic metamaterials, namely metadiffusers. These sound diffusers are rigidly backed slotted panels, with each slit being loaded by an array of Helmholtz resonators. Strong dispersion is produced in the slits and slow sound conditions are induced. Thus, the effective thickness of the panel is lengthened introducing its quarter wavelength resonance in the deep-subwavelength regime. By tuning the geometry of the metamaterial, the reflection coefficient of the panel can be tailored to obtain either a custom reflection phase, moderate or even perfect absorption. Using these concepts, we present ultra-thin diffusers where the geometry of the metadiffuser has been tuned to obtain surfaces with spatially dependent reflection coefficients having uniform magnitude Fourier transforms. Various designs are presented where, quadratic residue, primitive root and ternary sequence diffusers are mimicked by metadiffusers whose thickness are 1/46 to 1/20 times the design wavelength, i.e., between about a twentieth and a tenth of the thickness of traditional designs. Finally, a broadband metadiffuser panel of 3 cm thick was designed using optimization methods for frequencies ranging from 250 Hz to 2 kHz.

Dynamic thermal response of aluminum films induced by femtosecond-pulsed lasers with temperature dependent optical properties

This paper reports two optical models of temperature dependent reflectivity, R, and absorption coefficient, α, during femtosecond laser interaction with aluminum. After a comparison with existing experimental data, the critical point model (CPM) was incorporated into a two-temperature model (TTM) to simulate laser energy deposition and thermal response in an aluminum film irradiated by femtosecond laser pulses. The dynamic change of optical properties R and α, distribution of laser heat density, electron and lattice temperature of an aluminum film were investigated. Compared with constant reflectivities and absorption coefficients, dynamic reflectivities and absorption coefficients are recommended to be employed in modeling ultrafast laser heating.

Carbon Fibre Filled Radiation Absorbing Nonwovens

The dependence of electromagnetic radiation reflection coefficient of nonwovens on the content in them of carbon fibres cut to various lengths is studied. A technique for inserting electroconductive carbon fibres, which ensures formation of an intermediate layer of these fibres between fabrics from dielectric fibres, is described. The frequency dependence of the reflection coefficient on the intermediate layer composition and carbon fibre cut length for fabrics and multilayered materials obtained by joining fabrics is determined. It is shown that the multilayered materials are of interferential-absorptive type, but are also capable of absorbing low-frequency electromagnetic radiation.