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Nov 1976

Volume 60, Issue S1, pp. S1-S125

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back to top Session I. Physical Acoustics II: Acoustic Levitation
Invited Papers
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Radiation pressure—the history of mislabeled tensor (A)

Robert T. Beyer

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S21-S21 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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The acoustic radiation pressure has found practical application in recent years in instruments measuring sound intensity and in experiments on acoustic levitation. A historical review of the concept would therefore seem appropriate. The history of light radiation pressure goes back more than 200 years, beginning with Leonhard Euler and including such worthies as Maxwell, Boltzmann, and Lebedev. The concept of acoustic radiation pressure dates back some 100 Years, and its history features the names of Rayleigh, Poynting, Langevin, and Brillouin among many others. It was pointed out by Brillouin that what we call radiation pressure is not a pressure at all, but a diagonal tensor, all the diagonal terms of which are not identical. The size of the effect is small and the values obtained for the radiation pressure are very sensitive to boundary conditions and to approximations. In addition, although the phenomenon is one of nonlinear acoustics, it can be observed down to the lowest sound intensities under certain conditions. Thus, the Rayleigh radiation pressure vanishes for the linear case but the Langevin pressure doe not. It might be said that radiation pressure is a phenomenon that the observer thinks he understands—for short intervals and only every now and then. [Work supported in part by the Office of Naval Research.]
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Acoustic levitation and manipulation for space application (A)

Taylor G. Wang

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S21-S21 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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The acoustics in space, apart from the obvious function of communication has branched out into many other areas of applications. The acoustical positioning device developed at JPL for manipulating and controlling liquid systems in a 0‐g environment has the potential of becoming one of the most versatile tools for space research and applications. For example, in order to study the liquid drop systems originated from the Newton—Cassini controversy experimentally, we need a free suspended liquid drop without any dense medium surrounding it. Hence, both the 0‐g environment and the acoustic manipulation chamber appear to be necessary. In order to carry out many of the processes for Material Science Laboratory in Space the melt is to be positioned and formed within a container but without making contact with the container walls. Electromagnetic methods of positioning and forming are limited to melts which are electrically conducting. The acoustical method is useful in the control of any moltem material including material that is electrically nonconducting. In this presentation, I will describe the principle of operation of this apparatus and the results of tests both in our laboratory and in the 0‐g environment provided by the Johnson Space Center aircraft flights.
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Acoustic levitation—a useful experimental technique (A)

L. A. Crum

J. Acoust. Soc. Am. Volume 60, Issue S1, pp. S21-S21 (1976); (1 page)

Online Publication Date: 11 Aug 2005

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The nonzero, time‐averaged acoustic force exerted by a sound field on a local inhomogeneity allows liquid, solid, and gaseous particles to be suspended in a fluid medium relatively free of physical restraints. This splendid isolation allows studies to be made of radiation pressure, rectified diffusion, damping constants, acoustic streaming, surface waves, and physical parameters of metastable states, as well as many other phenomena, that would be nearly impossible without it. A review will be given of the general technique, and of various ways it can be utilized to obtain experimental data. [Work supported by ONR.]
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