Editing Ultrasound (section)

===Nondestructive testing===
{{See also|Macrosonics|Ultrasonic testing}}
[[File:UT principe.svg|thumb|right| Principle of flaw detection with ultrasound. A void in the solid material reflects some energy back to the transducer, which is detected and displayed.]]

[[Ultrasonic testing]] is a type of [[nondestructive testing]] commonly used to find flaws in materials and to measure the thickness of objects. Frequencies of 2 to 10&nbsp;MHz are common, but for special purposes other frequencies are used. Inspection may be manual or automated and is an essential part of modern manufacturing processes. Most metals can be inspected as well as plastics and [[aerospace]] [[Composite material|composites]]. Lower frequency ultrasound (50–500&nbsp;kHz) can also be used to inspect less dense materials such as wood, [[concrete]] and [[cement]].

Ultrasound inspection of welded joints has been an alternative to [[radiography]] for nondestructive testing since the 1960s.  Ultrasonic inspection eliminates the use of ionizing radiation, with safety and cost benefits. Ultrasound can also provide additional information such as the depth of flaws in a welded joint. Ultrasonic inspection has progressed from manual methods to computerized systems that automate much of the process. An ultrasonic test of a joint can identify the existence of flaws, measure their size, and identify their location.  Not all welded materials are equally amenable to ultrasonic inspection; some materials have a large grain size that produces a high level of background noise in measurements.<ref>{{cite book | veditors = Buschow KH, etal | title = Encyclopedia of Materials | publisher = Elsevier | date = 2001 | isbn = 978-0-08-043152-9 | page = 5990 }}</ref>
[[File:Swing shaft spline cracking.png|thumb|right|Non-destructive testing of a swing shaft showing [[Spline (mechanical)|spline]] cracking]]

[[Ultrasonic thickness measurement]] is one technique used to monitor quality of welds.