Flaw detectors use sophisticated, fully lossless ultrasonic technology that allows sound waves to pass through metals, composites, plastics and ceramics to detect hidden defects that may cause faults, such as cracks, voids and softness. Sound waves work in a highly predictable manner and produce unique echo patterns that can be displayed and recorded by portable instruments, making them very useful.

As an ultrasonic device, a flaw detector USES a transducer to both generate vibration and receive returned echoes. As these vibrations pass through the medium, they pass through the medium at a velocity and velocity specific to the medium in a predictable direction. When a boundary (such as a new medium or defect) is reached, the vibration will echo back to the transducer in a predictable manner. The returned signal is converted into a wave pattern that can be analyzed for inconsistencies.

Ultrasonic flaw detection is a comparative technique. Using appropriate reference standards and knowledge of acoustic propagation and generally accepted test procedures, trained operators can identify specific features, including defects, from the waveforms of the test materials.