Phase Velocity


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Phase velocity

The velocity of propagation of a pure sine wave of infinite extent. In one dimension, for example, the form of the disturbance for such a wave is given by y(x, t) = A sin [2π(x/λ - t/T)]. Here x is the position at which the disturbance y(x, t) exists at time t, λ is the wavelength, T is the period which is related to the wave frequency by T = 1/f, and A is the disturbance amplitude. The argument of the sine function is called the phase. The phase velocity is the speed with which a point of constant phase can be said to move. Thus x/λ - ft = constant, so the phase velocity vp is given by dx/dt = vp = λf. This is the basic relationship connecting phase velocity, wavelength, and frequency. See Phase (periodic phenomena), Sine wave, Wave motion

The phase velocity for waves in a medium is determined in part by intrinsic properties of the medium. For all mechanical waves in elastic media, the square of the phase velocity is proportional to the ratio of the appropriate elastic property of the medium to the appropriate inertia property. The phase velocity of electromagnetic waves depends upon the medium as well. In vacuum, the phase velocity c is given by c2 = l/ε0μ0 ≈ 9 × 1016 m2/s2, where ε0 and μ0 are respectively the permittivity and permeability of the vacuum. Phase velocity may also depend upon the mode of wave propagation—in general, upon the frequency of the wave. Waves of different frequencies will travel at different speeds, resulting in a phenomenon called dispersion. See Electromagnetic radiation, Light, Wave equation

Phase Velocity

 

(phase speed), the velocity of propagation of the phase of a harmonic wave. The phase velocity c can be expressed in terms of the frequency f and the wavelength λ or in terms of the angular frequency ω = 2πf and the wave number k = 2π/λ: c = fλ = ω/k.

The concept of phase velocity is valid if the harmonic wave is propagated with constant wave form; this condition is always satisfied in linear media. Velocity dispersion occurs if the phase velocity is dependent on frequency or, stated differently, on wavelength. In the absence of dispersion any wave will propagate, without changing its wave form, at a velocity equal to the phase velocity. If dispersion occurs, nonharmonic waves change their wave form, and the conventional concept of velocity no longer applies. In such cases the concepts of group velocity and wave-front velocity become important. The phase velocity for a given frequency can be found experimentally by determining the wavelength in interference experiments. The ratio of phase velocities in two different media can be determined from the refraction of a plane wave at the interface surface of the media, because the refractive index is equal to the ratio of the phase velocities.

M. A. ISAKOVICH

phase velocity

[′fāz və‚läs·əd·ē]
(physics)
The velocity of a point that moves with a wave at constant phase. Also known as celerity; phase speed; wave celerity; wave speed; wave velocity.
References in periodicals archive ?
The wave phase velocity (in vacuum) can be expressed as w = [c.
Similar direction, but weak relationships were observed between step phase velocity with hop contact time and jump contact time (r=0.
1] = 146 [micro]m, which is equal to the wavelength of the Scholte wave propagating at the silicon--water interface with 1460 m/s phase velocity [10].
The rectangular irregularity at the interface of layered half-space affected the phase velocity of Love-type waves.
Using the phase velocity (6) and adding the interaction terms with the gauge field, we can identify the full Lagrangian density as
From these time domain responses, the dispersion curve, giving the explicit dependence of phase velocity on frequency, has been calculated and is shown in Figure 1(b).
p] are the parameter s and the phase velocity C respectively of the spectral component at the spectral peak frequency [f.
1]] and [omega] = kc, k is the wave number and c is the phase velocity.
Firstly, phase velocity was expressed in terms of pseudo energy and power flow.
The main applications of negative index metamaterials (or left-handed materials (LHM)) are connected with a remarkable property: the direction of the energy flow and the direction of the phase velocity are opposite in NIM that results unusual properties of electromagnetic waves propagating in these mediums.
Here, in order to highlight the advantages of the double-slotted helix SWS, the high-frequency characteristics of the conventional helix SWS and the three-slotted helix SWS are also calculated under the condition of the same normalized phase velocity at 30 GHz.