Acoustic levitation at high temperatures in the microgravity of space

Acoustic levitation of a small specimen is obtained in the energy well produced by a single axis arrangement consisting of a sound source and a small acoustic reflector. At high temperatures, the acoustic forces are generally insufficient to levitate a specimen except in the microgravity environment available in space. A single axis acoustic levitator (SAAL) has been built to levitate a specimen inside a high-temperature furnace where it may be heated, melted, cooled, and solidified while being positioned without physical contact. The acoustic field configuration in such a containerless processing device has been analyzed and the expected levitation or positioning forces are calculated for the specific case of the NASA-SAAL experimental hardware as flown on the Space Shuttle on the STS-61A mission. This experiment successfully levitated and processed three samples at temperatures from 600 °C to 1550 °C. Experimental data are presented and the results compared with those predicted. [Work supported by NASA.]