Reflection coefficient

About: Reflection coefficient is a research topic. Over the lifetime, 11905 publications have been published within this topic receiving 159891 citations.

The effects of temperature and frequency on the dielectric properties, electromagnetic interference shielding and microwave-absorption of short carbon fiber/silica composites

Abstract: The dielectric spectroscopy of short carbon fiber/silica composite in the frequency range from 8.2 to 12.4 GHz at temperatures between 30 and 600 °C has been performed. The composite was prepared by conventional ceramic processing. The real part of the permittivity increases with increasing temperature, which is attributed to the shortened relaxation time of electron polarization, and the imaginary part also increases which is ascribed to the increasing electrical conductivity of the carbon fibers. The effect of frequency is found in reflection coefficient and absorption coefficient, and the corresponding mechanisms for the effect are proposed. Results indicate that the composite has good electromagnetic interference shielding property. By calculating the microwave-absorption as a single-layer absorber, we find that the reflection loss varies with the changes of thickness and temperature, due to the deviation of impedance matching condition.

Spatial variation of currents and fields due to localized scatterers in metallic conduction

Abstract: Localized scatterers can be expected to give rise to spatial variations in the electric field and in the current distribution. The transport equation allowing for spatial variations is solved by first considering the homogeneous transport equation which omits electric fields. The homogeneous solution gives the purely diffusive motion of current carriers and involves large space charges. The electric field is then found, and approximate space charge neutrality is restored, by adding a particular solution of the transport equation in which the electric field is associated only with space charge but not with a current. The presence of point scatterers leads to a dipole field about each scatterer. The spatial average of a number of these dipole fields is the same as that obtained by the usual approach which does not explicitly consider the spatial variation. Infinite plane obstacles with a reflection coefficient r are also considered. These produce a resistance proportional to r/(1-r).

A simplification of the Zoeppritz equations

Abstract: The compressional wave reflection coefficient R(θ) given by the Zoeppritz equations is simplified to the following: R(θ)=R0+[A0R0+Δσ(1-σ)2]sin2θ+1/2ΔVpVp(tan2θ-sin2θ). The first term gives the amplitude at normal incidence (θ = 0), the second term characterizes R(θ) at intermediate angles, and the third term describes the approach to critical angle. The coefficient of the second term is that combination of elastic properties which can be determined by analyzing the offset dependence of event amplitude in conventional multichannel reflection data. If the event amplitude is normalized to its value for normal incidence, then the quantity determined is A=A0+1(1-σ)2ΔσR0. A0 specifies the normal, gradual decrease of amplitude with offset; its value is constrained well enough that the main information conveyed is Δσ/R0, where Δσ is the contrast in Poisson’s ratio at the reflecting interface and R0 is the amplitude at normal incidence. This simplified formula for R(θ) accounts for all of the relations between R(θ...

Elastic wave behavior across linear slip interfaces

Abstract: A model for an imperfectly bonded interface between two elastic media is proposed. Displacement across this surface is not required to be continuous. The displacement discontinuity, or slip, is taken to be linearly related to the stress traction which is continuous across the interface. For isotropic interface behavior, there are two complex frequency dependent interface compliances, ηN and ηT, where the component of the slip normal to the interface is given by ηN times the normal stress and the component tangential to the interface is given by ηT times the shear stress and is in the same direction. Reflection and transmission coefficients for harmonic plane waves incident at arbitrary angles upon a plane linear slip interface are computed in terms of the interface compliances. These coefficients are frequency dependent even when the compliances are real and frequency independent. Examples of the effects of buried slip interfaces on reflection coefficient spectra and on Love‐wave dispersion relations are ...

Surface Waves and Their Application to Transmission Lines

Abstract: In this paper the applicability of non‐radiating surface waves for transmission lines is investigated. Two types of waves are considered. The first one, originally studied by A. Sommerfeld, is guided by a cylindrical conductor of finite conductivity. Although this wave type has (under comparable conditions) much lower attenuation than the waves in coaxial cables or rigid wave guides, its practical application is restricted by the fact that the extension of the field is very large. Efficient excitation and undisturbed propagation of this wave mode are feasible only for very high frequencies. The other wave type considered in this paper has not been treated in the literature. It is guided by a conductor which is coated with a dielectric layer or the surface of which is otherwise modified; for example, by being threaded. The field of this wave type has a structure similar to that of Sommerfeld's wave, but the extension of the field can be controlled by the surface modification. Thus low loss transmission lines on the basis of this wave type become feasible for frequencies above 100 megacycles. The information necessary for the design of such lines is given and the agreement between the theoretically expected transmission losses and the measured transmission losses is checked.