1. The Georgia Tech student team used an air-filled rectangular box in microgravity flight tests in 1997 and '98. The chamber was made of % inch plexi-glass`four speakers were mounted flush to the sides of the chamber as seen in Figure 1. Three video cameras were mounted to the sides of the chamber to capture the response of solid particles to various sound parameters.
2. In the 1997 flights very good results were obtained using Styrofoam pieces of arbitrary shape. They formed large walls that extended the full height of the chamber. At low amplifier gain settings (later determined to produce 150dB in the resonant chamber) they formed stable walls and did not show any rotation. All walls formed were one pellet thick. An example is shown in Figure 2.
3. The Georgia Tech Microgravity student flight team PI, as discussed above, developed Acoustic Shaping technology to form complex shapes using large numbers of solid particles in air, in a rectangular chamber. The particles used had random shape in one case (Styrofoam pieces), and quasi-ellipsoidal shape in the other (Kellogg's Rice Crispies Cereal). Comparing with the bulk of the work in the literature shows some differences: The frequencies used in these experiments are very low: 800 to 3000Hz, as compared to the 50KHz to 1MHz ultrasonic frequencies generally used (See [7j1.Thechamberdimensionsaresuchthatthemodesstudied are the lowest: (100) and up, so that details of particle behavior at various points in the standing wave are seen. Also, in this case, the acoustic streaming is expected to form only a few cells in the chamber. Thermal effects are negligible, since the speakers operate in the audible range. The power input to the speakers is relatively low (settings 3 to 7 on the volume dial of a home stereo system) The resonant field pressure amplitude is moderate: 150dB to 159dB. The particles used in the 1997 experiments had low density: Styrofoam specific gravity is 0.025.