Ultrasonic inspection is defined as a non-destructive mechanical inspection procedure, which is based on acoustic impedance, which is manifested as the product of the maximum speed of sound propagation and the density of the material. One of its main characteristics is its high cost. When this procedure was invented, the decrease in acoustic energy intensity was measured when supersonic waves were made to travel through a material, requiring the use of an emitter and a receiver. Currently, a single device is used that functions as an emitter and receiver, based on the characteristic property of sound of being reflected when reaching an acoustic interface.

The ultrasound equipment currently used allows detecting superficial, subsurface and internal discontinuities, depending on the type of probe used and the frequencies "Frequency (physical)") that are selected within a range that goes from 0.25 to 25 MHz. Ultrasonic waves are generated by a piezoelectric crystal or ceramic called a transducer and which has the property of transforming electrical energy into mechanical energy and vice versa. When electrically excited the transducer vibrates at high frequencies generating ultrasound. The vibrations generated are received by the material to be inspected, and during the journey the intensity of the sonic energy attenuates exponentially with the distance of the journey. Upon reaching the boundary of the material, the sonic beam is reflected, and the echo is received by another (or the same) transducer. Its signal is filtered and increased to be sent to an oscilloscope.

• - Herbert Krautkrämer, Josef Krautkrämer, und Otto Rüdiger: Ein Ueberschallgerät zur zerstörungsfreien Werkstoffprüfung, Verlag Stahleisen, 1949.

• - Josef Krautkrämer: Ultraschallprüfung im Dienste der Unfallverhütung, 1957.

• - Josef Krautkrämer: Fehlergrössenermittlung mit Ultraschall in: Bericht des Werkstoffausschusses des Vereins Deutscher Eisenhüttenleute Nr. 1211, Verlag Stahleisen, 1959.

• - Josef Krautkrämer, Herbert Krautkrämer: Werkstoffprüfung mit Ultraschall,Springer, Berlin, 5. Aufl., 1986, ISBN 3-540-15754-9.

• - Josef Krautkrämer, Herbert Krautkrämer: Ultrasonic Testing of Materials, Springer, Berlin 4th edition, 1990, ISBN 978-3-540-51231-8, or also New York: Springer-Verlag, 1990. ISBN 3-540-51231-4.

• - Albert S. Birks, Robert E. Green, Jr., technical editors; Paul McIntire, editor. , 2nd ed. Columbus, OH: American Society for Nondestructive Testing, 1991. ISBN 0-931403-04-9.