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Limits to the Detection of Small Internal Voids in Solids with Holographic Techniques.
GRUMMAN AEROSPACE CORP BETHPAGE N Y RESEARCH DEPT
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The ability to find small voids in acoustically excited solid specimens using coherent optical detection methods is limited by three factors available ultrasonic power levels, acoustical and optical noise elements, and nonlinear properties of the working materials. Constraints on the detection sensitivity due to ultrasonic power limitations are established in this memorandum. A void embedded in an elastic halfspace is used as a physical model. Deformations of the free surface due to void-scattered ultrasonic waves are derived and illustrated for several void sizes and depth locations. Properties of the liquid layer that influence the magnitude of signal amplification and sources of systematic distortions due to nonlinearities are determined from the fundamental fluid dynamic equations. Several holographic techniques to observe the liquid surface profile are discussed. Author
APPROVED FOR PUBLIC RELEASE