Ultrasonics use transmission of high-frequency sound waves into a material to detect imperfections or to locate changes in material properties. The most commonly used ultrasonic testing technique is pulse echo, wherein sound is introduced into a test object and reflections (echoes) are returned to a receiver from internal imperfections or from the part's geometrical surfaces.
Ultrasonic inspection is most often performed on steels and metals. It can be used on other nonmetallic materials with success. This form of nondestructive testing is widely used many industries including aerospace, automotive, pressure vessel, and the welding fabrication industry. It can locate subsurface discontinuities in weldments when access to only one side is possible. It has many advantages such as; high penetrating power for going thru very thick parts, high sensitivity for the detection of small discontinuities, only one surface need be accessible, non hazardous to the operator or to nearby personnel, and it is highly portable