The signal velocity of a wave is the speed at which a pulse travels through a medium. The signal velocity is usually defined from the position of half-maximum intensity of the pulse. Jump to: navigation, search A wave is a disturbance that propagates in a periodically repeating fashion, often transfering energy. ... In signal processing, the term pulse has the following meanings: A rapid, transient change in the amplitude of a signal from a baseline value to a higher or lower value, followed by a rapid return to the baseline value. ...
For electromagnetic waves such as light, the signal velocity is identical to the group velocity of the wave except when it is travelling through a medium with an absorption resonance close to the frequency of the wave. In this case, the group velocity vg may exceed the speed of lightc, but the signal velocity vs will always be less than or equal to c. Electromagnetic radiation or EM radiation is a combination (cross product) of oscillating electric and magnetic fields perpendicular to each other, moving through space as a wave, effectively transporting energy and momentum. ... Prism splitting light Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific setting, electromagnetic radiation of any wavelength. ... The group velocity of a wave is the velocity with which the overall shape of the waves amplitude (known as the envelope of the wave) propagates through space. ... Cherenkov effect in a swimming pool nuclear reactor. ...
The phase velocity of a wave is the rate at which the phase of the wave propagates in space. ... Front velocity is the speed at which the first rise of a pulse above zero moves forward. ... In optics, dispersion is a phenomenon that causes the separation of a wave into spectral components with different frequencies, due to a dependence of the waves speed on its frequency. ...
References
Brillouin, Léon. Wave propagation and group velocity. Academic Press Inc., New York (1960).
Velocity pickups have been used as vibration transducers on rotating machines for a very long time, and they are still utilized for a variety of applications today.
Velocity sensors are also susceptible to cross axis vibration, which if great enough may damage a velocity sensor.
Where practical, a velocity sensor should be mounted in the vertical, horizontal, and axial planes to measure vibration in the three directions.
The group velocity of a wave is the velocity with which the variations in the shape of the wave's amplitude (known as the modulation or envelope of the wave) propagates through space.
This "group velocitydispersion" is an important effect in the propagation of signals through optical fibers and in the design of short pulse lasers.
The idea of a group velocity distinct from a wave's phase velocity was first proposed by W.R. Hamilton in 1839, and the first full treatment was by Rayleigh in his "Theory of Sound" in 1877.
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