Use of Time-Averaged Optical Holographic Interferometry for Visualization of Standing Acoustic Waves

The technique of time-averaged optical holographic interferometry is useful in investigating three-dimensional acoustic fields, since it provides a graphic three-dimensional record of the geometry of the nodal patterns of standing waves. This technique was used to obtain interferograms of longitudinal standing waves in a duct of square cross section. The three-dimensional fringe patterns clearly indicate the locations of the antinodal planes. Photographs of the hologram reconstructions of the virtual images illustrate the effects of acoustic wave frequency and amplitude on the fringe pattern.