Attenuation of sound

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. 

The attenuation of sound intensity / follows Eq. (4-29), which is analogous to Beer s law. 

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... 

In each case the attenuation of sound can be formally represented by defining a complex wavenumber, where the sound attenuation coefficient is the imaginary part of the wavenumber. The complex wavenumber also leads to the definition of a complex sound speed and a complex dynamic elastic modulus. 

Both the total sound level, and the attenuation of sound, are often expressed in a dimensionless unit, the decibel, where the sound level (SL) in decibels is,... 

In many practical applications of anechoic materials the specifications demand not only high attenuation of sound, but also good performance over a range of temperatures and pressures. The extent to which these demands can be simultaneously realized is limited by some general relations which govern the behavior of linear damped systems. These relations, known as the... 

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. 

The speed and attenuation of sound in a food material are of no practical value in themselves but only as they relate to other relevant material properties. Fundamentally, wavenumber is related to material properties via the Wood equation (5) ... 

ASTM C 522 covers the measurement of airflow resistance and the related measurements of specific airflow resistance and airflow resistivity of porous materials that can be used for the absorption and attenuation of sound. The method describes how to measure a steady flow of air through a test specimen, how to measure the air-pressure difference across the specimen, and how to measure the volume velocity of airflow through the specimen. The airflow resistance, R, the specific airflow resistance, r, and the airflow resistivity, rQ, may be calculated from the measurements. The apparatus includes a suction generator or positive air supply arranged to draw or force air at a uniform rate through the specimen. A flowmeter is used to measure the volume velocity of airflow through the specimen, and a differential-pressure-measuring device measures the static-pressure difference between the two faces of the specimen with respect to atmosphere. 

Steady attenuation of sound indicates constant composition in the product... 

Hovem J.M., Ingram G.D., 1979. Viscous attenuation of sound in saturated sand. Journal of the Acoustical Society of America 66 1807-1812... 

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%. 

TA Strout. Attenuation of Sound in High Concentration Suspensions Development and Application of an Oscillatory Cell Model. Thesis. The University of Maine, 1991. 

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

Attenuation of Sound at a Given Distance from a Source... 

Tallon S, Davies CE. Attenuation of sound in beds of particulate materials and application to measurement of flow rate. In Fan LS, Knowlton TM, eds. Fluidization IX. New York Engineering Foundation, 1998, pp 597-604. 

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

The Argonne National Laboratory project (LeSage and OTallon, 1977) is developing a meter dependent on the attenuation of sound by the particles suspended in a gas. The path length, frequency, and power level of the acoustic are essential parameters to be set. 

AUegra, J.R. and Hawley, S.A. (1972) Attenuation of sound in suspensions and emulsions theory and experiments. 

---