Acoustic propagation

If we suppose the medium is composed of a known part (the background) identified by the density po and the celerity co, and an unknown part (the perturbation) identified by p and c, the equation that describes acoustic propagation/diffiision phenomena in the medium (including the boundary and Sommerfeld conditions) result from the Pekeris equation and is given, for weak-scattering (pc poCo), by ... 

T is the acoustic propagation time from the combustion region to the measurement point r... 

Time scale for observation The response of the acoustic effect is limited by the acoustic propagation between the fringe distance and that time constant is rac = A/v. Therefore, in 0 < t rac, the density contribution is small and fast response of the population grating can be easily observed (although the Temp.G signal could contribute to the signal even in this time scale). In principle, even rather slow dynamics of the population, which is not disturbed by the thermal... 

Biot, M.A., 1962. Mechanics of deformation and acoustic propagation in porous media. Journal of Applied Physics 33 pp. 1482-1498. 

QCM can be described as a thickness-shear mode resonator, since weight change is measured on the base of the resonance frequency change. The acoustic wave propagates in a direction perpendicular to the crystal surface. The quartz crystal plate has to be cut to a specific orientation with respect to the ciystal axis to attain this acoustic propagation properties. AT-cut crystals are typically used for piezoelectric crystal resonators[7]. The use of quartz crystal microbalances as chemical sensors has its origins in the work of Sauerbrey[8] and King [9] who... 

Figure 2 Modes of acoustic propagation (A) longitudinal or compressional wave (B) transverse or shear wave (C) surface or Rayleigh wave and (D) plate or Lamb wave (symmetric mode).

Forest L, Gibiat V, Woignier T (1998) Biot s theory of acoustic propagation in porous media applied to aerogels and alcogels. J Non-Cryst Solids 225 287-292... 

De Leo R (2008) Long-term operational experience with the HERMES aerogel RICH detector. Nuclear Instruments Methods Phys Res A Accelerators, Spectrometers, Detectors, and Associated Equipment 595 19-22 Forest L, Gibiat V, Woignier T (1998) Biot s theory of acoustic propagation in porous media applied to aerogels and alcogels. J Non-Cryst SoUds 225 287-292... 

Acoustic propagation parameters are determined from observation of the position and half peak widths of the resonances of the cavity. The thermal stability of the cavity must be of the order of 0,01 C or better to give a 2 accuracy in the absorption coefficient. 

Figure 25 Effects of local thermal differences on the acoustic propagation of sound...

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