Reflection coefficient

Résumé

In physics and electrical engineering the reflection coefficient is a parameter that describes how much of a wave is reflected by an impedance discontinuity in the transmission medium. It is equal to the ratio of the amplitude of the reflected wave to the incident wave, with each expressed as phasors. For example, it is used in optics to calculate the amount of light that is reflected from a surface with a different index of refraction, such as a glass surface, or in an electrical transmission line to calculate how much of the electromagnetic wave is reflected by an impedance discontinuity. The reflection coefficient is closely related to the transmission coefficient. The reflectance of a system is also sometimes called a "reflection coefficient". Different specialties have different applications for the term. Transmission lines Reflections of signals on conducting lines and Signal reflection In telecommunications and transmission line theory, the reflection coeffic

Source officielle

https://en.wikipedia.org/wiki/Reflection_coefficient

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Effect of vertically extended strike object on the distribution of current along the lightning channel

José-Luis Bermudez

On the basis of a distributed-source representation of the lightning channel, the mathematical formulations of the so-called engineering lightning return stroke models are generalized to take into account the presence of a vertically extended strike object. The strike object is modeled as a lossless uniform transmission line, and the reflection coefficients are all assumed to be constant. The distribution of current along the lightning channel for each model is expressed in terms of the "undisturbed" current, object height, and current reflection coefficients at the top and the bottom of the object. The undisturbed current is defined as the current that would flow in the channel if the current reflection coefficients at the extremities of the strike object were equal to zero, that is, the characteristic impedances of the lightning channel and the strike object were equal to each other and equal to the grounding impedance of the strike object. The distributed-source representation of the lightning channel adopted in this study allows for a more general and straightforward formulations of the generalized return-stroke models than the traditional representations implying a lumped current source at the bottom of the channel, including a self-consistent treatment of the impedance discontinuity at the tower top

2002

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In this paper, we propose a method based on genetic algorithms to extract primary lightning return stroke current parameters from currents measured using instrumented towers, including the possibility of contamination by multiple reflections occuring along the tower. The algorithm allows additionally the evaluation of reflection coefficients at the top and at the bottom of the tower. The proposed method is validated using first theoretically-generated current waveforms and then, using experimental data of lightning current measured at Peissenberg tower

2002

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A MATLAB-based tool for visualizing the plane wave propagation in multilayer structures containing metamaterials

Juan Ramon Mosig

The paper reports on a graphical user interface developed in MATLAB to aid the visualization of the plane wave impinging from a lossless half-space onto a multilayer structure. Individual layers are assumed to be homogeneous and isotropic with electric permittivity (∊) and magnetic permeability (μ) taking arbitrary complex values. Double-positive, single-negative and double-negative media (real parts of ∊ and μ) as well as lossless, dissipative and amplifying media (imaginary parts of ∊ and μ) are allowed. 2D field distribution, transmission and reflection coefficients, and the wave vectors' z-component locations in the complex plane are presented to the user.

2012

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