Methods Used With Basic Ultrasonic Instruments.
The principle of this method is shown in Figure 5-68. Delaminations in either skin, unbonds between skin and core, and
core damage prevent the transmission of sound to the receiving search unit. The minimum size flaw that can be
detected is proportional to the size of the receiving search units. The received signal does not have to disappear
completely to indicate a flaw. Any flaw large enough to lower the received signal noticeably can be detected. Care
must be taken to move both transducers in tandem; otherwise, misaligned transducers will generate false indications.
Figure 5-68. Through-Transmission Method.