# group velocity

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## Group velocity

The velocity of propagation of a group of waves forming a wave packet; also, the velocity of energy flow in a traveling wave or wave packet. The pure sine waves used to define phase velocity vp do not ever really exist, for they would require infinite extent. What do exist are groups of waves, wave packets, which are combined disturbances of a group of sine waves having a range of frequencies and wavelengths. Good approximations to pure sine waves exist, provided the extent of the media is very large in comparison with the wavelength of the sine wave. In nondispersive media, pure sine waves of different frequencies all travel at the same speed vp, and any wave packet retains its shape as it propagates. In this case, the group velocity vg is the same as vp. But if there is dispersion, the wave packet changes shape as it moves, because each different frequency which makes up the packet moves with a different phase velocity. If vp is frequency-dependent, then vg is not equal to vp. See Phase velocity, Sine wave, Wave motion

## group velocity

[¦grüp və′läs·əd·ē]
(physics)
The velocity of the envelope of a group of interfering waves having slightly different frequencies and phase velocities.
References in periodicals archive ?
The group velocity vg of the wave packet associated with the electron of rest mass [m.
In this paper, tapered core is used instead of cylindrical core so as to make the light travel with the lesser group velocity and also to stop the light at the fixed position efficiently.
The average group velocity for this path can be obtained as a mean of the group-velocity values calculated for each period.
r] signal at 0[degrees] and 90 mm and it's CWD with superimposed group velocity that this mode is the fundamental anti-symmetric mode F(1,1).
Moreover, the velocity of propagation of the envelope in measurements and in computations based on the Dysthe equation is markedly higher than the linear group velocity as assumed in the NLS equation.
Tarricone, "Negative group velocity in a split ring resonator-coupled microstrip line," Progress In Electromagnetics Research, Vol.
The objective of this work was to investigate performance of the proposed group velocity measurement technique in the case of composite materials.
Where 2[eta] = [square root of ([beta])] the amplitude of microscopic particles, 4[xi]' is related to its group velocity in Equations (39) and (42), and [xi]' is the same as [xi] in Equation (15).
18,19] have investigated the modal propagation characteristics of ternary 1D-PPCs structures and have shown the plasma frequency, plasma width and dielectric constant of dielectric media have influence on band gap, group index, group velocity and phase velocity.
In this case, the quality of the data after passing through the grating is distorted due to delay in the signal which is also called the group velocity dispersion broadening and deformations of the data pulse and Inter Symbol Interference (ISI) in the neighboring and distance time slot.
of Melbourne, Australia) have gathered information from experts in atomic vapor spectroscopy, fiber amplifiers and integrated optics to explain how slow light schemes, or "light propagation in media and structures with reduced group velocity," can be used in applications such as photonic crystal devices, low-loss optical waveguides and microfabrication techniques.
Because the group velocity of Love waves in the earth are nearly constant (4.

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