Liquid Surface Levitation Holography. Part 1. Theoretical Analysis.
NAVAL RESEARCH LAB WASHINGTON DC
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The liquid surface levitation holography system has been analyzed, paralleling analyses by previous investigators but treating several new areas. Depth of focus and depth of field of the acoustic lens system are considered, accounting for differences in the acoustic properties of the imaging and object-tank fluids. The mechanical properties of the minitank membrane are shown to have three significant effects multiple internal reflections of acoustic waves are enhanced in the minitank, which causes the minitank transfer function to become oscillatory for large imaging-fluid depths deformation of the membrane can degrade the focused acoustic image and coupling between motions of the membrane and of the liquid surface occurs at low spatial frequencies. Possible coupling between the acoustic field quantities pressure, density, and velocity and the surface levitation field is shown to be negligible for a typical system. The low-spatial-frequency deformation bulge of the liquid surface is calculated for typical system parameters. The natural frequencies of oscillation of the surface are much less than the rate at which the surface is excited. Consequently the bulge builds up to a steady-state value.
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