Showing papers on "Reflection coefficient published in 1974"
TL;DR: In this article, the authors measured run-up spectra and nearshore wave spectra associated with standing waves on a natural beach and found that the cross-spectra phase angles between data records had values near 0 or π at frequencies of high coherence.
Abstract: Simultaneous measurements of run-up spectra and nearshore wave spectra associated with standing waves have been made on a natural beach. Digital wave staffs and bottom-mounted pressure sensors were placed in a line at various distances offshore from a digital run-up meter. The run-up meter, which measured the position of the edge of the water, consisted of a series of electrical contacts suspended above the beach face and spaced 30 cm apart. Because of the possible influence of nonlinear interactions on the spectra, bicoherence was estimated, and the frequency range appropriate to a linearized model was defined. In this low-frequency region of the spectrum the cross-spectra phase angles between data records had values near 0 or π at frequencies of high coherence. The energy spectrum levels and the observed phase differences between records were in good agreement with the linear shallow water wave theory (Lamb, 1932) for standing waves on a plane beach. The general reflection coefficient for the data, estimated from the disagreement between data and standing wave theory, was found to be approximately 0.7. This result indicates that the theory of Miche (1944) for reflection from a plane beach predicts a reflection coefficient that is too high by a factor of approximately 1.5.
128 citations
TL;DR: In this paper, a simple frequency-domain method for measurement of the dielectric properties of materials is described, and theoretical analysis of the frequency dependence of the reflection coefficient of a shunt lumped capacitor located at the end of a transmission line and filled with a very small amount of the Dielectric (typically a few microliters) is given.
Abstract: A simple frequency-domain method for measurement of the dielectric properties of materials is described. Theoretical analysis of the frequency dependence of the reflection coefficient of a shunt lumped capacitor located at the end of a transmission line and filled with a very small amount of the dielectric (typically a few microliters) is given. Analysis and calculations of the overall uncertainty in permittivity measurements, as well as experimental results for some normal alcohols, are presented and limitation of the method discussed.
91 citations
TL;DR: In this article, the reflection coefficient of a flanged open-ended rectangular waveguide placed, next to a flat large sample is computed by a variational method as a function of the dielectric constant.
Abstract: A simple nondestructive method is presented for the measurement of the complex permittivity ?r of materials. The reflection coefficient ? of a flanged open-ended rectangular waveguide placed, next to a flat large sample is computed by a variational method as a function of the dielectric constant. Computer-generated charts and an optimization computer program are elaborated. ?r can then be easily determined from the measured amplitude and phase angle of the reflected wave in the waveguide. The method is best suited for materials having high dielectric constants and large losses.
70 citations
TL;DR: A theoretical analysis of the scalar wave field due to a point source above a plane impedance boundary is presented in this paper, where it is shown that, as a result of ducting of energy by the surface wave, the amplitude of the total wave near the boundary can be greater than it would be if the boundary were perfectly reflecting.
Abstract: A theoretical analysis of the scalar wave field due to a point source above a plane impedance boundary is presented. A surface wave is found to be an essential component of the total wave field. It is shown that, as a result of ducting of energy by the surface wave, the amplitude of the total wave near the boundary can be greater than it would be if the boundary were perfectly reflecting. Asymptotic results, valid near the boundary, are obtained both for the case of finite impedance (the soft-boundary case) and for the limiting case in which the impedance becomes infinite (the hard-boundary case). In the latter, the wave amplitude in the farfield decreases essentially inversely as the horizontal propagation distance; in the former (if the surface-wave term is neglected), it decreases inversely as the square of the horizontal propagation distance.
69 citations
TL;DR: A general evaluation procedure is described for calibration of a linear complex reflectometer (network analyzer) and for two-port measurements and new closed-form formulas and procedures are given for two practical cases.
Abstract: A general evaluation procedure is described for calibration of a linear complex reflectometer (network analyzer) and for two-port measurements. New closed-form formulas and procedures are given for two practical cases: 1) calibration or measurement with two known standards and a sliding termination; 2) calibration or measurement by one standard and two different sliding terminations. The reflection coefficient magnitudes and phases of these sliding terminations need not be known. The closed-form formulas make it possible to determine calibration constants by direct calculation without approximations or complicated multivariable iterations.
35 citations
TL;DR: In this paper, the authors compared axisymmetrical and offset near-field Cassegrainians and Gregorians; expressions for the reflection coefficient and increase in sidelobe level were given.
Abstract: Most Cassegrainian and Gregorian antennas have axial symmetry, in which case the subreflector and associated supporting members partially block the aperture. Consequently, relatively high sidelobes appear in the radiation pattern, and a reflection is produced in the transmission line of the feed. These undesirable effects can be largely eliminated using asymmetrical configurations. Here we compare axisymmetrical and offset near-field Cassegrainians and Gregorians; expressions for the reflection coefficient and increase in sidelobe level are given. The offset designs are found to have superior performance in both respects.
33 citations
01 Oct 1974
TL;DR: In this article, a method has been developed for precise non-destructive measurement of the dielectric constant and losses of slab-like samples, such as microstrip substrates for instance.
Abstract: A method has been developed for a precise non-destructive measurement of the dielectric constant and losses of slab-like samples, such as microstrip substrates for instance. The test setup basically consists of an open-ended rectangular waveguide whose flange is placed in contact with one side of the dielectric material, the other one being backed by a metal plate. The measured amplitude and phase of the reflection coefficient with respect to a short-circuit in the aperture plane are related to the real and imaginary parts of the permittivity by means of computer generated charts.
29 citations
TL;DR: In this article, the mutual impedance method for determining the reflection from a loaded dipole array is extended to the case of two parallel planar dipole arrays, and the criteria for the validity of a simple transmission line solution are given.
Abstract: The mutual impedance method for determining the reflection from a loaded dipole array is extended to the case of two parallel planar dipole arrays. The dipole arrays are illuminated by a plane wave with arbitrary incidence angle in either the E - or H -plane. The specular reflection coefficient obtained is shown, with proper design, to have a more narrow stop band with steeper skirts and a flatter top than that for a single array. The near-field coupling is included in the analysis, and the criteria for the validity of a simple transmission line solution are given. For close spacings the near fields may cause the reflection coefficient curve to: 1) not reach unity reflection; 2) attain unity reflection at one frequency; or 3) attain unity reflection at two frequencies, with a shallow dip between. The type of resonance curve obtained depends on the spatial arrangement of the two arrays. The evaluation of the mutual impedance sums is greatly simplified by certain impedance relationships that are presented. Calculated and measured reflection curves for various array separations are included.
29 citations
TL;DR: The results of line-of-sight over-sea propagation measurements over 37.2-and 35.5-km paths near Tokyo, Japan, are presented in this paper.
Abstract: The results of line-of-sight over-sea propagation measurements over 37.2- and 35.5-km paths near Tokyo, Japan, are presented. Measurements of the fading (0.25, 3.99, 4.15, 6.72, and 18.0 GHz) of the cross polarization distortion (linear polarized wave at 4.15 GHz and circular polarized wave at 6.72 GHz) of the space diversity effect at 4.15 GHz, of the height-gain patterns at 6.72 GHz, and of the frequency-sweep patterns from 18 GHz to 22 GHz are included. The following statistical results are presented: the frequency, seasonal, and path dependence of fading; the effect of different fading occurrence mechanisms, such as K-type, duct-type, and distorted raindrops, for the cross polarization distortion; the diversity improvement factor; the effective reflection coefficient of sea surface; and the path-length difference between direct and sea reflected waves.
27 citations
TL;DR: In this article, the effects of anisotropy on the reflection of SH-waves (horizontally polarized shear waves) from a transition layer are studied. But the results are only for the obliquely incident wave.
Abstract: The effects of anisotropy on the reflection of SH -waves (horizontally polarized shear waves) from a transition layer are studied. The transition layer is sand-wiched between two isotropic homogeneous half-spaces and is constituted by a medium which is both anisotropic and inhomogeneous. The SH -wave potentials are obtained for an anisotropic inhomogeneous medium in which both the anisotropy factor (ratio of the horizontal rigidity to the vertical rigidity) and vertical velocity vary with depth. An expression for the reflection coefficient of SH waves is obtained when the material mentioned above forms a finite transition zone between two isotropic homogeneous half-spaces. For further generalization, a second-order discontinuity along with the first-order on eis being assumed in the material properties, at the boundaries of the transition layer. The mathematical and numerical analyses show that the anisotropy factor, found at the top of the transition layer ( N / M ) produces considerable effect on the reflection coefficient for an obliquely incident SH wave. It has been noted that the greater the thickness of the transition layer, the greater is the dependence of the reflection coefficient upon the value of the anisotropy ( N / M ). The minima and maxima of the reflection of seismic energy are found dependent on the value of anisotropy. For greater values of the anisotropy, these maxima and minima shift toward the lower values of the wavelength of the propagating wave (or toward the higher values of the thickness of the transition layer). In fact, the values of the reflection coefficient at which these maxima and minima of seismic energy occur are found greater for the higher values of anisotropy. The effects of anisotropy are found more pronounced for the larger angles of incidence. This remains so until the angle of refraction becomes imaginary. However, no effects of the anistropy factor are found on the reflection coefficients for a normally incident wave. The results, mentioned above, are therefore discussed only for the obliquely incident wave. A geophysically interesting situation has been chosen for studying, quantitatively, the effects of the anisotropy factor on the reflection of SH waves.
26 citations
TL;DR: In this paper, the vibrational structure associated with the one-phonon inelastic scattering of light particles from the (001) surface of LiF is studied and expressed in terms of surface projected phonon densities.
Abstract: The vibrational structure associated with the one-phonon inelastic scattering of light particles from the (001) surface of LiF are studied and expressed in terms of surface projected phonon densities. The surface vibrations and the related densities for the semi-infinite ionic lattice are calculated in detail by means of the Green function method, in the framework of the breathing shell model. The inelastic reflection coefficient due to the creation of a phonon of given frequency and surface wave-vector is calculated within a semiclassical description of the particle motion, for Lennard-Jones interaction potentials. The nature and the amount of information on the surface dynamics obtainable from the velocity analysis of the scattered beam are discussed.
TL;DR: Time-domain reflectometer techniques have been used to test transmission line systems for over fifteen years and the technique described in this paper is an extension to present-day techniques and is designed particularly to detect small changes in the reflection coefficient of distributed systems versus time.
Abstract: Time-domain reflectometer (TDR) techniques have been used to test transmission line systems for over fifteen years. The technique described in this paper is an extension to present-day techniques and is designed particularly to detect small changes in the reflection coefficient of distributed systems versus time. The instrument uses some of the techniques of narrow-band TDR to provide a waveform, related to the distributed reflection coefficient of the system under test, to a small computer. The computer can then perform any of a number of manipulations to the waveform, depending on the wishes of the operator. One particular program produces a waveform profile on a storage oscilloscope which displays small changes in the distributed reflection coefficient with time. This capability of being able to display very small changes in reflection coefficients has resulted in the development of an obstacle detection scheme using so called "leaky" coaxial cable to detect objects at some distance from the cable.
TL;DR: It is shown that the commonly used predictions for edge‐mode radiation obtained by neglecting the influence of the fluid on the membrane displacement are valid except when the fluid loading is very high.
Abstract: Free wave motion on a fluid‐loaded semi‐infinite membrane whose plane is extended by a rigid baffle is discussed. We consider in particular the membrane displacement field and the associated acoustic radiation when a wave on the membrane is normally incident on the membrane boundary. Typical values for the reflection coefficient for the waves, and for the radiated acoustic power are given for a wide range of membrane in vacuo wavespeeds and fluid loading parameters. It is shown that the commonly used predictions for edge‐mode radiation obtained by neglecting the influence of the fluid on the membrane displacement are valid except when the fluid loading is very high.
TL;DR: In this paper, the fundamental element pattern-active reflection coefficient interrelationships in uniform phased arrays are summarized, extended, and integrated, and for central elements of sufficiently large arrays the results provide the basis for attractive measurement schemes of array parameters.
Abstract: Several fundamental element pattern-active reflection coefficient interrelationships in uniform phased arrays are summarized, extended, and integrated. For central elements of sufficiently large arrays the results provide the basis for attractive measurement schemes of array parameters.
TL;DR: In this paper, the mutual coupling in a finite planar array antenna, composed of open-ended circular waveguides in a ground plane, is analyzed using the element-by-element approach and the problem is formulated as an integral equation.
Abstract: This paper deals with mutual coupling in a finite planar array antenna, composed of open-ended circular waveguides in a ground plane. The element-by-element approach is used and the problem is formulated as an integral equation, by requiring the transverse electric and magnetic fields to be continuous across the apertures. The equation is then solved by the method of moments and the mutual coupling in a 127-element array is computed. Excellent agreement with measurements and with the active reflection coefficient for the corresponding infinite array is found. The presented method of coupling analysis can be considered as a supplement to the established periodic-structure approaches for infinite arrays and may be useful for the analysis of small or nonperiodic arrays.
TL;DR: In this paper, it was shown that if the boundary roughness is statistically homogeneous, the coherent (or average) wave satisfies a generalized impedance boundary condition on the average boundary, referred to as a ''smoothed'' boundary condition.
Abstract: The problem of scalar wave propagation in the half‐space bounded by a rigid, randomly rough surface which is a small perturbation of an infinite plane is considered. It is shown that, if the boundary roughness is statistically homogeneous, the coherent (or average) wave satisfies a generalized impedance boundary condition on the average boundary. This is referred to as a ``smoothed'' boundary condition. Applying it to plane waves yields an expression for the effective plane‐wave reflection coefficient Ce of the boundary. For the case of isotropic roughness, approximate expressions for Ce are obtained for both long (relative to the correlation length of the boundary roughness) and short waves. These expressions show that generally |Ce| < 1, and therefore that the amplitude of the coherent wave is diminished upon reflection from the boundary. This is the result of scattering of energy out of the coherent wave by the boundary roughness. It is also shown that this type of boundary can support a surface wave. ...
TL;DR: In this article, the reflection coefficients for various heavy ion potentials are calculated in an approximation which includes a wave mechanical surface reflection term in addition to the semiclassical WKB-term.
Abstract: The reflection coefficients for various heavy ion potentials are calculated in an approximation which includes a wave mechanical surface reflection term in addition to the semiclassical WKB-term. For potentials which are deep and strongly absorbing in the interior of the potential well reflection from the surface gives the dominant contribution to the reflection coefficients with small angular momenta. For shallow potentials these two terms are still not sufficient for the calculation of the reflection coefficients, indicating that higher order reflections are important.
TL;DR: In this paper, the reflection and transmission of Rayleigh waves by the edge of an isotropic thin film was solved within the first-order approximation relying on the Wiener-Hopf technique under the assumption that the film is thin enough compared to the wavelength.
Abstract: The reflection and transmission of Rayleigh waves by the edge of an isotropic thin film deposited on an isotropic substrate is solved within the first‐order approximation relying on the Wiener‐Hopf technique under the assumption that the film is thin enough compared to the wavelength. Straight‐crested Rayleigh waves are assumed to impinge on the edge of the film perpendicularly from the unplated side of the substrate. In formulating the problem mathematically, Tiersten's boundary condition is employed to take into account the effects which the deposited film imposes on the elastic waves in the substrate. Expressions for the radiation coefficients of both of the bulk waves, longitudinal and transverse, and for the reflection coefficient of the Rayleigh wave are derived and evaluated numerically for gold, aluminum, nickel, and copper films deposited on the fused‐silica substrate. It is found that the radiation coefficients, especially the one for the transverse bulk wave, exceed the reflection coefficient by a factor of 10 or more in magnitude. The reflection and transmission of the Rayleigh wave is influenced mainly by the shear velocity and shear modulus μ′ of the film material, whereas the Lame constant λ′ of the film does not have as much effect on both the reflection and transmission.
TL;DR: In this article, the rate at which electrons are transported from the body to the non-thermal tail of the distribution function in the nonlinear stage of reflective and absorptive parametric instabilities is computed.
Abstract: The rate at which electrons are transported from the body to the nonthermal tail of the distribution function in the nonlinear stage of reflective and absorptive parametric instabilities is computed. The calculation is performed by conserving energy and momentum between waves and particles in the nonlinear regime. For the case of reflection, the reflection coefficient and energy flux of nonthermal particles are computed. It is found that the principal effect of the trapped electrons is to increase the density gradient length scale by as much as a factor of twenty five, at given reflection coefficient. For absorption, the rate of production of energetic particles is found. Also, the transport of energetic particles into the core of a laser fusion plasma is examined.
TL;DR: In this article, the Bragg condition mλm = 2S n (m is an integer, S is the period of the distorted structure, and n is the average refractive index of the material).
Abstract: Light propagation along the helical axis of cholesteric liquid crystals, whose structure has been distorted by a magnetic or electric field perpendicular to the helix axis, is theoretically investigated. The solutions show several reflection bands whose centers are given by the Bragg condition mλm = 2S n (m is an integer, S is the period of the distorted structure, and n is the average refractive index of the material). The bands with m ≥ 2 consist of three subbands, each characterized by the dependence of the reflection on the polarization of the incident beam. Thus, for example, an incident beam linearly polarized in the direction of the distorting field will be reflected at only two of these subbands. Except for very strong applied fields, the band m = 1 is composed of two subbands only. Outside the reflection bands, the modes of propagation are orthogonal linear polarizations.
01 May 1974
TL;DR: In this paper, a plane-wave theory for the integrated optics grating guide is presented, and the characteristics of the guide are described using the wall reflection coefficient, including attenuation, minimum-bend radius, and field distribution.
Abstract: A plane-wave theory for the integrated optics grating guide is presented. The characteristics of the guide are described using the wall reflection coefficient. Calculations are made of the attenuation, minimum-bend radius, and field distribution. Some methods of realizing the grating guide are proposed.
TL;DR: In this paper, a relativistic electron-diffraction theory is presented, which solves the Dirac equation by the Green's-function method and incorporates spin polarization, and the exact reflection coefficient is suitable for the calculation of diffraction intensities of low-energy incident electrons from heavy-atomic-crystal surfaces.
Abstract: A relativistic electron-diffraction theory is presented, which solves the Dirac equation by the Green's-function method and incorporates spin polarization. For muffin-tin potentials, the reflection coefficient of a beam scattered elastically from either unpolarized or polarized incident electrons is very similar to that of its nonrelativistic counterpart. The atomic properties are included in the relativistic phase shifts. The geometric structure constants are related to the nonrelativistic structure constants. The polarization of the scattered electrons is analyzed by the density matrix. The relation between this theory and the nonrelativistic one is discussed. The exact reflection coefficient is suitable for the calculation of diffraction intensities of low-energy incident electrons from heavy-atomic-crystal surfaces. A pseudokinematic theory, which may be useful for incident energies up to several keV, is obtained by taking the first-order approximation.
TL;DR: Spectral amplitudes and theoretical seismograms in the vicinity of caustic and critical points are evaluated numerically for acoustic waves propagating in Epstein media in this article, where the amplitude decay into the region beyond the caustics is compared with the asymptotic results and good agreement is found at high frequency.
Abstract: Spectral amplitudes and theoretical seismograms in the vicinity of caustic and critical points are evaluated numerically for acoustic waves propagating in Epstein media. The amplitude decay into the region beyond the caustic is compared with the asymptotic results and good agreement is found at high frequency. At low frequencies the partial reflection enhances the amplitudes at sub-critical angles and the amplitude increases with decreasing thickness of the transition zone. For a thin transition and low frequencies a head wave exists whose amplitude is inversely proportional to frequency. The study of amplitudes near caustics and critical point is of significant theoretical and experimental interest to seismologists. Improved coverage by stations of the USCGS worldwide network has provided better data and their interpretation has lead to more accurate estimates of elastic wave velocities within the Earth (Johnson 1967). In regions of high velocity gradient in the upper mantle caustics are formed and triplications occur on the travel-time curves. In this paper the amplitude properties near caustics and critical point are studied for the Epstein velocity transitions (Epstein 1930). Epstein profiles represent a group of models with transition zones for which solutions of the wave equation exist in terms of familiar tabulated functions. Wave propagation has also been studied analytically for linear transition layers (Nakamura 1964; Gupta 1966; Hirasawa & Berry 1971; Ward 1973) and exponential and parabolic layers (Merzer 1971 ; Rydbeck 1943). Linear layers have discontinuities in velocity gradient which may not be realistic. Merzer’s study is concerned only with head waves and their amplitude dependence on frequency, layer thickness and shape of the transition. Using Epstein models the caustics, head waves and shadow can be studied. Epstein (1930), Rawer (1939) and Phinney (1970) studied the modulus of the reflection coefficient in order to estimate the partial reflection. The modulus of the reflection coefficient itself, however, cannot give a full description of the energy propagation when the waves interact with the strong velocity gradient. That can only be studied when the spectral amplitudes and theoretical seismograms are evaluated. In this paper the exact spectral amplitudes are computed by contour integration using the method of Phinney & Cathles (1969). For evaluation of the theoretical seismograms the technique of Chapman & Phinney (1972) is employed. The amplitude curves are evaluated in the neighbourhood of both ends of the triplication. At high frequencies the results agree with the asymptotic results. At low
TL;DR: In this article, the Smith chart contours from which the reflection properties of the medium can be determined from the measured waveguide reflection coefficient were used to measure the near field scattering from the external medium.
Abstract: A technique is developed for direct determination of the plane wave reflection properties of plane layered media. The approach is applicable for media containing a high-index absorber layer. A circular waveguide aperture is used to measure the near field scattering from the external medium. The analytical development results in a set of Smith chart contours from which the reflection properties of the medium can be determined from the measured waveguide reflection coefficient. The approach is demonstrated with measurements of a ferrite absorber panel.
TL;DR: In this paper, a three-layer system consisting of coupling prism, gap, and sample has been studied in an external magnetic field to calculate the attenuated-total-reflection spectrum due to surface plasmons.
Abstract: The three-layer system consisting of coupling prism, gap, and sample has been studied in an external magnetic field to calculate the attenuated-total-reflection spectrum due to surface plasmons. The sample is taken to be a nonpolar or polar semiconductor with free carriers, which becomes an anisotropic dielectric medium when the magnetic field is applied. Dispersion curves for the surface-polariton modes are discussed. Computed reflection spectra are shown for two of the three magnetic-field geometries considered. Computed results are compared with experimental results.
Patent•
22 Mar 1974
TL;DR: In this paper, an acoustic surface wave transducer having three conductive fingers per acoustic wavelength is described. But the transducers do not have the ability to control the number of fingers.
Abstract: Disclosed is an acoustic surface wave transducer having three conductive fingers per acoustic wavelength. Surface waves are excited by applying electrical signals across a pair of terminals. One terminal is connected to every third conductive finger in the transducer and the other terminal to the remaining conductive fingers.
Patent•
30 Sep 1974
TL;DR: In this paper, a high frequency coaxial cable exhibiting a low insertion loss and a low reflection coefficient, and incorporating an improved construction providing for convenient adjustment of impedance, is presented for high frequency communications.
Abstract: A high frequency coaxial cable exhibiting a low insertion loss and a low reflection coefficient, and incorporating an improved construction providing for convenient adjustment of impedance.
TL;DR: In this paper, the seasonal and diurnal characteristics of the reflection coefficient in Nigeria and the results of field observation have been applied to obtain a land use and reflection coefficient map for parts of Nigeria where detailed land-use studies have been undertaken.
TL;DR: In this paper, exact solutions for internal gravity waves incident upon a layered density anomaly embedded in a stably stratified fluid with constant Brunt-Vaisala frequency were obtained, where z increases downward; and N2−∞, N2+∞ and NH2 are parameters.
Abstract: Exact solutions are obtained for internal gravity waves incident upon a layered density anomaly embedded in a stably stratified fluid with otherwise constant Brunt-Vaisala frequency:where z increases downward; and N2−∞, N2+∞ and NH2 are parameters. The reflection coefficient is a complicated function of the horizontal and vertical wavenumbers and the parameters related to the Brunt-Vaisala profile. It is found that all wave energy is transmitted through the anomalous layer for waves propagating almost horizontally and a significant amount is reflected for vertically propagating ones, while the validity of a low reflection, WKB description is demonstrated for waves which possess a vertical wave-length much smaller than the scale height σ−1. Further, there can exist for some stratification conditions certain other directions of propagation for which the conditions for energy transfer are more favorable than they are for nearly contiguous angles θ+∞. The transmission “windows” are seen to accumulate...
TL;DR: In this paper, a dynamic photoelastic analysis of stress waves produced by a uniformly loaded line charge of lead azide (pb N6) is described. The line charge is inclined at an angle of 38° to the bench face so that the front of the incident P wave is parallel to the face.