Attenuation of sound waves

Ultrasonic Spectroscopy. Information on size distribution maybe obtained from the attenuation of sound waves traveling through a particle dispersion. Two distinct approaches are being used to extract particle size data from the attenuation spectmm an empirical approach based on the Bouguer-Lambert-Beerlaw (63) and a more fundamental or first-principle approach (64—66). The first-principle approach implies that no caHbration is required, but certain physical constants of both phases, ie, speed of sound, density, thermal coefficient of expansion, heat capacity, thermal conductivity. 

Acoustic spectroscopy measures the speed and attenuation of sound waves interacting with a colloidal suspension. When a sound wave in the range of 1 to 100 MHz interacts with a colloidal suspension, the measured acoustic attenuation and... 

Acoustic methods Measures the attenuation of sound waves as a means of determining size through the fitting of physically relevant equations... 

Sound absorption The attenuation of sound waves on impingement upon soundabsorbing interfaces, due to friction and conversion into heat. 

It is obvious from the above review that a wide variety of composite materials and composite structures have been developed for attenuation of sound. Nevertheless, there is a continuing need and opportunity for new concepts for attenuation of air-borne and water-borne sound waves, and to reduce structural vibrations. In particular there is a continuing need for coatings which operate over a wide range of frequencies, over a range of temperatures, and in some cases over a range of pressures. 

Many problems in ultrasonic visualization, nondestructive evaluation, materials design, geophysics, medical physics and underwater acoustics involve wave propagation in inhomogeneous media containing bubbles and particulate matter. A knowledge of the effect of voids or inclusions on the attenuation and velocity of sound waves is necessary in order to properly model the often complex, multilayered systems. 

Because the energy state of a Jahn-Teller complex depends on the local lattice distortions, the macroscopic long-distant strain that produces an ultrasonic wave should influence it as well. The cross effect is initiated by the Jahn-Teller complexes (1) the dispersion (i.e., frequency-dependent variation of phase velocity) and (2) attenuation of the wave. In terms of the elastic moduli it sounds as appearance (or account) of the Jahn-Teller contribution to the real and imaginary parts of the elastic moduli. For a small-amplitude wave it is a summand Ac. Obviously, interaction between the Jahn-Teller system and the ultrasonic wave takes place only if the wave, while its propagation in a crystal, produces the lattice distortions corresponding to one of the vibronic modes. 

To obtain the absolute sound attenuation in the coal slurry, the diffraction loss, the acoustic mismatch loss, the attenuation due to the Teflon window, and the oil coupling must be calculated. Thus, it is difficult to accurately determine the absolute attenuation. In practice, one measures the relative attenuation with respect to a standard. The attenuation of ultrasonic waves in a solid suspension is attributed to three major factors, namely, scattering, viscosity, and thermal effects. Although the presence of particles affects the fluid viscosity and thermal conductivity, the primary source of attenuation may be due to particle scattering. Hence, one may define the relative attenuation of the HYGAS coal slurry by comparing the slurry attenuation with that of the carrier fluid, i.e., the toluene/benzene mixture. This can be expressed by the equation... 

More recendy, Matec has introduced their AcoustoSizer, which measures electrokinetic sonic amplitude as a function of frequency (dififusion wave spectroscopy). Rather large samples (400 ml) are required in the concentradon range 1-40 vol%. The particle size range is 0.1-10 pm. The Pen Kem AcoustoPhor 8000 is based on the measuimient of attenuation of sound as it passes through the dispersion. It is claimed to have a range of 0.1 -10 pm plus, requires a sample volume of 1(K) ml and is applicable to dispersions greater than 40 voI%. 

Ultrasonic absorption is used in the investigation of fast reactions in solution. If a system is at equilibrium and the equilibrium is disturbed in a very short time (of the order of 10"seconds) then it takes a finite time for the system to recover its equilibrium condition. This is called a relaxation process. When a system in solution is caused to relax using ultrasonics, the relaxation lime of the equilibrium can be related to the attenuation of the sound wave. Relaxation times of 10" to 10 seconds have been measured using this method and the rates of formation of many mono-, di-and tripositive metal complexes with a range of anions have been determined. 

With nondestructive ultrasonic test back and forth scanning of a specimen is accomplished with ultrasonics. This NDT can be used to find voids, delaminations, defects in fiber distribution, etc. In ultrasonic testing the sound waves from a high frequency ultrasonic transducer are beamed into a material. Discontinuities in the material interrupt the sound beam and reflect the energy back to the transducer, providing data that can be used to detect and characterize flaws. It can locate internal flaws or structural discontinuities by the use of high frequency reflection or attenuation (ultrasonic beam). 

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