Present and Future Capabilities of Acoustic Levitation and Positioning Devices
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PRESENT AND FUTURE CAPABILITIES OF ACOUSTIC LEVITATION AND POSITIONING DEVICES CHARLES A. REY, ROY R. WHYMARK, THOMAS J. DANLEY AND DENNIS R. MERKLEY, Intersonics, Incorporated, 425 Huehl Road, Northbook, IL 60062 ABSTRACT The techniques of acoustic positioning without the use of resonant cavities have been explored and developed over a number of years and the currently available capabilities are reviewed. The performance and characteristics of these nonresonant acoustic systems are described in regard to containerless processing with emphasis on the low-g environment. This includes manipulation and mixing of liquid drops, super-cooling phenomena, heating to temperatures of 1600 C or higher, rapid cooling solidification, and surface shape control. Some possible applications are measurements of physical properties of substances at high temperatures or of highly reactive specimens, and the formation of unique glasses and alloys of new compositions. 1.
INTRODUCTION
Nonresonant acoustic levitation systems have been demonstrated successfully in low-g environments during the past several years. (1) The nonresonant levitator, sometimes referred to as the interference levitator , is especially useful for specimen positioning at high temperatures, but also finds uses in medium and room temperature applications. 2.
INTERFERENCE LEVITATOR
The interference levitator apparatus is shown diagramatically in Figure 1. (2) The sound source points at a reflector rod of small diameter. Furnace wall reflections are made as diffuse as possible. Immediately below the small reflector there exists a strongly coherent sound field, as illustrated in Figure 2. Other small energy wells may exist below the primary energy well but by proper design these secondary wells can be made small enough that they do not interfere with the single primary well located a distance slightly greater than one-quarter wavelength from the reflector. A force distribution through an energy well is plotted in Figure 3 for an interference levitator operating at a temperature of 16000 C. The specimen size was 1 cm in diameter. The data in Figure 3 was obtained by suspending the 1 cm specimen in the heated furnace on a compliant pendulum and measuring the deflection of the pendulum under the action of the levitation forces. Integration of the curve in Figure 3 leads to the characteristic potential energy distribution shown in Figure 4. Objects levitate in the trough of the potential energy well. The spatial definition of the acoustic energy well is dependent upon careful selection of a series of design parameters. Gas absorption at the operating temperature, furnace cavity size and acoustic path lengths, and the nature and shaping of reflecting surfaces must all be considered in the levitator design. (3) If the gas absorption is too high the energy well may be too
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REFLECTOR
Energy Well
Figure 2
Figure 1
Local Interference Energy Well
Interference Levitator
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Distance From Reflector (cm) Figure 3
Axial Force Distribution
Figure 4
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