Editing Piezoelectricity (section)

===Sensors===

[[File:Piezoelectric pickup1.jpg|thumb|Piezoelectric disk used as a [[guitar pickup]]]]
[[File:RPG-7 detached.jpg|thumb|Many rocket-propelled grenades used a piezoelectric [[wikt:fuse|fuse]]. Pictured, a Russian [[RPG-7]]<ref>{{cite web |last=Speck |first=Shane |date=2004-03-11 |url=http://science.howstuffworks.com/rpg3.htm |title=How Rocket-Propelled Grenades Work by Shane Speck |website=HowStuffWorks.com |access-date=2012-05-04 |url-status=live |archive-url=https://web.archive.org/web/20120429064528/http://science.howstuffworks.com/rpg3.htm |archive-date=2012-04-29 }}</ref>]]
{{main|Piezoelectric sensor}}
The principle of operation of a piezoelectric [[sensor]] is that a physical dimension, transformed into a force, acts on two opposing faces of the sensing element. Depending on the design of a sensor, different "modes" to load the piezoelectric element can be used: longitudinal, transversal and shear.

Detection of pressure variations in the form of sound is the most common sensor application, e.g. piezoelectric [[microphone]]s (sound waves bend the piezoelectric material, creating a changing voltage) and piezoelectric [[Pick up (music technology)|pickups]] for [[acoustic-electric guitar]]s. A piezo sensor attached to the body of an instrument is known as a [[contact microphone]].

Piezoelectric sensors especially are used with high frequency sound in ultrasonic transducers for medical imaging and also industrial [[nondestructive testing]] (NDT).

For many sensing techniques, the sensor can act as both a sensor and an actuator—often the term ''transducer'' is preferred when the device acts in this dual capacity, but most piezo devices have this property of reversibility whether it is used or not. Ultrasonic transducers, for example, can inject ultrasound waves into the body, receive the returned wave, and convert it to an electrical signal (a voltage). Most medical ultrasound transducers are piezoelectric.

In addition to those mentioned above, various sensor and transducer applications include:
* Piezoelectric elements are also used in the detection and generation of sonar waves.
* Piezoelectric materials are used in single-axis and dual-axis tilt sensing.<ref>{{cite journal | last1 = Moubarak | first1 = P. | display-authors = etal | year = 2012 | title = A Self-Calibrating Mathematical Model for the Direct Piezoelectric Effect of a New MEMS Tilt Sensor | journal = IEEE Sensors Journal | volume = 12 | issue = 5| pages = 1033–1042 | doi=10.1109/jsen.2011.2173188| bibcode = 2012ISenJ..12.1033M }}</ref>
* Power monitoring in high power applications (e.g. medical treatment, [[sonochemistry]] and industrial processing).
* [[Piezoelectric microbalance]]s are used as very sensitive chemical and biological sensors.
* Piezoelectrics are sometimes used in [[strain gauge]]s. More commonly however, a [[Piezoresistive effect]] element is used. 
* A piezoelectric transducer was used in the penetrometer instrument on the [[Huygens Probe]].
* Piezoelectric [[transducer]]s are used in [[electronic drum|electronic drum pads]] to detect the impact of the drummer's sticks, and to detect muscle movements in medical [[acceleromyography]].
* Automotive [[Engine Control Unit|engine management systems]] use piezoelectric transducers to detect Engine knock (Knock Sensor, KS), also known as detonation, at certain hertz frequencies. A piezoelectric transducer is also used in fuel injection systems to measure manifold absolute pressure (MAP sensor) to determine engine load, and ultimately the fuel injectors milliseconds of on time.
* Ultrasonic piezo sensors are used in the detection of acoustic emissions in [[acoustic emission testing]].
* Piezoelectric transducers can be used in transit-time [[ultrasonic flow meters]].