1 August 1972 Acoustic Holographic Scanning Techniques For Imaging Flaws In Thick Metal Sections
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This paper discusses the application of various scanning configurations used in acoustic holography for imaging internal flaws or voids in thick metal sections; i.e., 10 to 25 cm. The following source-receiving scanning configurations were employed: 1. Simultaneous (inclined plane-wave) source and point receiver scan-ning; 2. Simultaneous (focused) source-receiver scanning employing a simulated acoustic off-axis reference; 3. Simultaneous point source-receiver scanning employing a simulated acoustic off-axis reference; and 4. Stationary (plane-wave) source and point receiver scanning employing a simulated acoustic off-axis reference. All of the above mentioned configurations impose a linear diffraction grating on the hologram and provide the necessary conditions for imaging flaws directly in the projected aperture and separation of the reconstruct-ed images. The flaw images appear two-dimensional as a result of the large difference between the construction and reconstruction wavelengths. Longitudinal magnification is much greater than the lateral magnification and the images appear stretched in depth. However, the hologram does contain the complete depth information of the flaws and this is easily observed by focusing on different planes in the metal sections parallel to the hologram plane (i.e., different depths within the metal section are viewed simply bymanipulation of the optical imaging lens in the reconstruction The images of the internal flaws are viewed by adjusting the lens until the image is in focus. The lateral and longitudinal dimensions of the flaws are then calculated using the conventional image location and magnification equations.
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H. Dale Collins, R. Parks Gribble, "Acoustic Holographic Scanning Techniques For Imaging Flaws In Thick Metal Sections", Proc. SPIE 0029, Imaging Techniques for Testing and Inspection, (1 August 1972); doi: 10.1117/12.978151; https://doi.org/10.1117/12.978151


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