Theory of Acoustic Shaping in Microgravity

      The phenomenon of acoustic levitation has been demonstrated in several applications. Intense sound fields created inside confined spaces exert forces which can move small particles. The particles move to stable locations with the least potential. The stable locations of the particles constitute a balance between gravity, drag, surface forces, and acoustic pressure.  As an example, we may consider particles being moved using beat patterns of sound waves, and induced to deposit along surfaces which join nodes of the acoustic field. In a microgravity environment, this offers tremendous potential for intricate fabrication technology.  With the dominant gravitational force removed, fine control can be exerted on the acoustic field and the resulting movement and deposition patterns of the particles. The particles can be solid or liquid. Thus, for example, we can induce resins to harden along carefully-specified, intricate surfaces inside a structure, with no need for access or machining.
      Sound propagation is described by the wave equation,and the spatial geometry of standing wave patterns formed by multiple waves is described by the Helmholtz equation. Solution techniques are well-known for these equations, and solution surfaces can be determined and tailored to obtain desired surface shapes. From these solutions, the fluid velocity and pressure field can also be determined. Particle mechanics in this field can also be computed. This poses some uncertainties, especially in the microgravity environment, which requires experimental validation. The data recovered from our flight-tests abroad NASA's KC-135 will enable us to remove such unknowns and advance the theory of acoustic levitation to acousticmanufacturing.

REFERENCES

Pierce, A.D., "Acoustics". McGraw-Hill, 1980.

Landau, L.D., Lifshitz, E.M., "Fluid Mechanics".Course on Theoretical Physics, Volume 6, Pergamon Press, 1987, p. 305-307.

Wanis, S.S., Sercovich,A.H., Komerath, N.M., "Acoustic Shaping in Microgravity: Higher Order SurfaceShapes", AIAA Paper 99-0954, 37th Aerospace Sciences Meeting & Exhibit,Reno, NV, January 1999.