Detection, characterization and studying of flaws in work by acoustic imaging

摘要

In detecting, characterizing or studying flaws in work whose surface is irregular by acoustic imaging in which a holographic pattern is produced the irregular surface is scanned by acoustic energy focussed on or near the irregular surface and the reception of the acoustic energy resulting from echoes from flaws is controlled for each scanned elemental area so as to reduce to a negligible magnitude the effects or variations in the acoustical path caused by the irregularties at different elemental areas in accordance with the irregularity at that area. The control may be effected by filling in the depressions in the irregular surface with an acoustic energy absorbing material such as butyl rubber or with a material, such as wax, which is not wetted by the liquid through which the acoustic energy is propagated to the surface. The control may also be effected by introducing a phase-shift correction into the reference frequency signal, the electrical analog of an acoustical reference wave, which cooperatively with the signal derived from the received acoustic energy produces the interference pattern on the hologram.