Ultrasonic inspection involves the transmission of ultra-high frequency sound waves through the part being tested and evaluating the reflected waves on a time delay oscilloscope.

It is useful for detecting sub-surface discontinuities, dimensional measurements (thickness) and analyzing material structure. In a typical pulse/echo ultrasonic inspection system, a transducer in contact with the test specimen generates high frequency ultrasonic energy that travels through the test specimen in the form of waves. The waves reflect back to the transducer off the opposite wall of the specimen. Any discontinuity in the path of the waves—a crack or inclusion, for example—will reflect part of the energy back to the transducer. The reflected wave is transformed into an electrical signal by the transducer and displayed on an oscilloscope. Typically, the strength of the reflected signal is plotted against the elapsed time from signal generation (pulse) to the moment the reflected signal (echo) is received. Signal travel times can be converted to the distance traveled, which can yield information on the location, size and orientation of the discontinuity.