Real-Time Acoustical Holography Systems.
ARMY MISSILE RESEARCH AND DEVELOPMENT COMMAND REDSTONE ARSENAL AL TECHNOLOGY LAB
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The existing system for Acoustical Real Time Holographic Image Reproduction is described, together with operating instructions. Its novel features include 1 large diameter approximately 4 in. ultrasonic beam and correspondingly large image area 2 high intensity of the ultrasonic beam and therefore improved penetrability for thick test objects and 3 excellent damping in the water tanks and therefore less background noise during real time viewing. Preliminary nondestructive testing measurements indicate that the system resolution is close to the theoretical diffraction limit for the acoustical wavelengths in the water medium of 0.3, 0.5, and 1.5 mm. For discerning flaws in samples with high internal scattering, the real-time feature is necessary. For highly reflecting test objects, an improvement in penetration has been demonstrated using a coating to reduce the reflection coefficient of the test object. Preliminary data are presented using 3-MHz beams through ceramic and foam test plates with the images recorded photographically. The Acoustical Real Time Holographic Image Reproduction system is ready to be tested as a nondestructive testing method for flaws in silica radomes. Author