Acoustic dispersion is the phenomenon of a sound wave separating into its component frequencies as it passes through a material

Transmission medium

A transmission medium is a material substance that can propagate energy waves...

. The phase velocity

Phase velocity

The phase velocity of a wave is the rate at which the phase of the wave propagates in space. This is the speed at which the phase of any one frequency component of the wave travels. For such a component, any given phase of the wave will appear to travel at the phase velocity...

 of the sound wave is viewed as a function of frequency. Hence, separation of component frequencies is measured by the rate of change in phase velocities as the radiated waves pass through a given medium.

Broadband transmission method

A widely used technique for determining acoustic dispersion is a broadband transmission method. This technique was originally introduced in 1978 and has been employed to study the dispersion properties of metal

Metal

A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

 (1978), epoxy resin (1986), paper materials

Paper

Paper is a thin material mainly used for writing upon, printing upon, drawing or for packaging. It is produced by pressing together moist fibers, typically cellulose pulp derived from wood, rags or grasses, and drying them into flexible sheets....

 (1993) ultra-sound contrast agent (1998), In 1990 and 1993 this method confirmed the Kramers–Kronig relation for acoustic wave

Acoustic wave

Acoustic waves are a type of longitudinal waves that propagate by means of adiabatic compression and decompression. Longitudinal waves are waves that have the same direction of vibration as their direction of travel. Important quantities for describing acoustic waves are sound pressure, particle...

s.

Application of this method to requires the measurements of a reference velocity to obtain values for the acoustic dispersion. This is accomplished by determining (usually) the speed of the sound in water, the thickness of the specimen, and the phase spectrum of each of the two transmitted ultrasound

Ultrasound

Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...

pulses.