The reflection coefficient is used in physics and electrical engineering when wave propagation in a medium containing discontinuities is considered. A reflection coefficient describes either the amplitude or the intensity of a reflected wave relative to an incident wave. The reflection coefficient is closely related to the transmission coefficient.
Different specialties have different applications for the term.
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Telecommunications
In telecommunications, the reflection coefficient is the ratio of the amplitude of the reflected wave to the amplitude of the incident wave. In particular, at a discontinuity in a transmission line, it is the complex ratio of the electric field strength of the reflected wave (E ^{−} ) to that of the incident wave (E ^{+} ). This is typically represented with a Γ (capital gamma) and can be written as:
The reflection coefficient may also be established using other field or circuit quantities.
The reflection coefficient can be given by the equations below, where Z_{S} is the impedance toward the source, Z_{L} is the impedance toward the load:
Notice that a negative reflection coefficient means that the reflected wave receives a 180°, or π, phase shift.
The absolute magnitude (designated by vertical bars) of the reflection coefficient can be calculated from the standing wave ratio, SWR:
The reflection coefficient is displayed graphically using a Smith chart.
Seismology
Reflection coefficent is used in feeder testing for reliability of medium.
Optics
In optics, intensity and amplitude reflection coefficients are used. Typically, the former are represented by a capital R, while the latter are represented by a lowercase r.
Semipermeable membranes
The reflection coefficient in semipermeable membranes relates to how such a membrane can reflect solute particles from passing through. A value of zero results in all particles passing through. A value of one is such that no particle can pass. It is used in the Starling equation.
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