Editing Ultrasound (section)

==Detection and ranging==

===Non-contact sensor===
An ultrasonic level or sensing system requires no contact with the target.  For many processes in the medical, pharmaceutical, military and general industries this is an advantage over inline sensors that may contaminate the liquids inside a vessel or tube or that may be clogged by the product.

Both continuous wave and pulsed systems are used. The principle behind a pulsed-ultrasonic technology is that the transmit signal consists of short bursts of ultrasonic energy. After each burst, the electronics looks for a return signal within a small window of time corresponding to the time it takes for the energy to pass through the vessel. Only a signal received during this window will qualify for additional signal processing.

A popular consumer application of ultrasonic ranging was the [[Polaroid SX-70]] camera, which included a lightweight transducer system to focus the camera automatically. Polaroid later licensed this ultrasound technology and it became the basis of a variety of ultrasonic products.

===Motion sensors and flow measurement===
A common ultrasound application is an automatic door opener, where an ultrasonic sensor detects a person's approach and opens the door. Ultrasonic sensors are also used to detect intruders; the ultrasound can cover a wide area from a single point. The flow in pipes or open channels can be measured by ultrasonic flowmeters, which measure the average velocity of flowing liquid.  In [[rheology]], an [[acoustic rheometer]] relies on the principle of ultrasound. In [[fluid mechanics]], fluid flow can be measured using an [[ultrasonic flow meter]].

===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.

===Ultrasonic range finding===
[[File:Sonar Principle EN.svg|thumb|400px|Principle of an active sonar]]
{{Main|Sonar}}
A common use of ultrasound is in underwater [[range finding]]; this use is also called [[sonar]]. An ultrasonic pulse is generated in a particular direction. If there is an object in the path of this pulse, part or all of the pulse will be reflected back to the transmitter as an [[Echo (phenomenon)|echo]] and can be detected through the receiver path. By measuring the difference in time between the pulse being transmitted and the echo being received, it is possible to determine the distance.

The measured travel time of Sonar pulses in water is strongly dependent on the temperature and the salinity of the water. Ultrasonic ranging is also applied for measurement in air and for short distances. For example, hand-held ultrasonic measuring tools can rapidly measure the layout of rooms.

Although range finding underwater is performed at both sub-audible and audible frequencies for great distances (1 to several kilometers), ultrasonic range finding is used when distances are shorter and the accuracy of the distance measurement is desired to be finer. Ultrasonic measurements may be limited through barrier layers with large salinity, temperature or vortex differentials. Ranging in water varies from about hundreds to thousands of meters, but can be performed with centimeters to meters accuracy

===Ultrasound Identification (USID)===
[[Ultrasound Identification]] (USID) is a [[Real-time locating system|Real-Time Locating System]] (RTLS) or [[Indoor Positioning System]] (IPS) technology used to automatically track and identify the location of objects in real time using simple, inexpensive nodes (badges/tags) attached to or embedded in objects and devices, which then transmit an ultrasound signal to communicate their location to microphone sensors.