ultrasonic sensor - wikipedia, the free encyclopedia
TRANSCRIPT
12/15/13 Ultrasonic sensor - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/Ultrasonic_transducer 1/3
Sound field of a non focusing 4 MHz
ultrasonic transducer with a near field
length of N = 67 mm in water. The
plot shows the sound pressure at a
logarithmic db-scale.
Ultrasonic sensorFrom Wikipedia, the free encyclopedia
(Redirected from Ultrasonic transducer)
Ultrasonic sensors (also known as transceivers when they both send and receive, but more generally calledtransducers) work on a principle similar to radar or sonar which evaluate attributes of a target by interpretingthe echoes from radio or sound waves respectively. Ultrasonic sensors generate high frequency sound wavesand evaluate the echo which is received back by the sensor. Sensors calculate the time interval between sendingthe signal and receiving the echo to determine the distance to an object.
This technology can be used for measuring wind speed and direction (anemometer), tank or channel level, andspeed through air or water. For measuring speed or direction a device uses multiple detectors and calculates thespeed from the relative distances to particulates in the air or water. To measure tank or channel level, the sensormeasures the distance to the surface of the fluid. Further applications include: humidifiers, sonar, medicalultrasonography, burglar alarms and non-destructive testing.
Systems typically use a transducer which generates sound waves in the ultrasonic range, above 18,000 hertz, byturning electrical energy into sound, then upon receiving the echo turn the sound waves into electrical energywhich can be measured and displayed.
The technology is limited by the shapes of surfaces and the density or consistency of the material. Foam, in
particular, can distort surface level readings.[1]
Contents
1 Transducers
2 Use in medicine3 Use in industry
4 References5 External links
Transducers
An ultrasonic transducer is a device that converts energy intoultrasound, or sound waves above the normal range of human hearing.While technically a dog whistle is an ultrasonic transducer thatconverts mechanical energy in the form of air pressure into ultrasonicsound waves, the term is more apt to be used to refer to piezoelectrictransducers that convert electrical energy into sound. Piezoelectriccrystals have the property of changing size when a voltage is applied,thus applying an alternating current (AC) across them causes them tooscillate at very high frequencies, thus producing very high frequencysound waves.
The location at which a transducer focuses the sound can be determined by the active transducer area andshape, the ultrasound frequency, and the sound velocity of the propagation medium.
12/15/13 Ultrasonic sensor - Wikipedia, the free encyclopedia
en.wikipedia.org/wiki/Ultrasonic_transducer 2/3
Sound pressure field of the same
ultrasonic transducer (4 MHz,
N = 67 mm) with the transducer
surface having a spherical curvature
with the curvature radius R = 30 mm
The example shows the sound fields of an unfocused and a focusingultrasonic transducer in water.
Since piezoelectric crystals generate a voltage when force is appliedto them, the same crystal can be used as an ultrasonic detector. Somesystems use separate transmitter and receiver components whileothers combine both in a single piezoelectric transceiver.
Non-piezoelectric principles are also used in construction ofultrasound transmitters. Magnetostrictive materials slightly change sizewhen exposed to a magnetic field; such materials can be used to make transducers. A capacitor microphoneuses a thin plate which moves in response to ultrasound waves; changes in the electric field around the plateconvert sound signals to electric currents, which can be amplified.
Use in medicine
Medical ultrasonic transducers (probes) come in a variety of different shapes and sizes for use in makingpictures of different parts of the body. The transducer may be passed over the surface of the body or insertedinto a body opening such as the rectum or vagina. Clinicians who perform ultrasound-guided procedures oftenuse a probe positioning system to hold the ultrasonic transducer.
Air detection sensors are used in various roles. Non-invasive air detection capabilities in the most criticalapplications where the safety of a patient is mandatory. Many of the variables, which can affect performance ofamplitude or continuous wave based sensing systems, are eliminated or greatly reduced, thus yielding accurateand repeatable detection. The principle behind the technology is that the transmit signal consists of short burstsof ultrasonic energy. After each burst, the electronics looks for a return signal within a small window of timecorresponding to the time it takes for the energy to pass through the vessel. Only signals received during thisperiod will qualify for additional signal processing.
Use in industry
Ultrasonic sensors are used to detect movement of targets and to measure the distance to targets in manyautomated factories and process plants. Sensors with an on or off digital output are available for detecting themovement of objects, and sensors with an analog output which varies proportionally to the sensor to targetseparation distance are commercially available. They can be used to sense the edge of material as part of a webguiding system
Ultrasonic sensors are gaining popularity in a number of uses including ultrasonic people detection and assistingin autonomous UAV navigation.
Because ultrasonic sensors use sound rather than light for detection, they work in applications where
photoelectric sensors may not. Ultrasonics are a great solution for clear object detection, clear label detection[2]
and for liquid level measurement, applications that photoelectrics struggle with because of target translucence.Target color and/or reflectivity don't affect ultrasonic sensors which can operate reliably in high-glare
environments.[3]
Other types of transducers are used in commercially available ultrasonic cleaning devices. An ultrasonictransducer is affixed to a stainless steel pan which is filled with a solvent (frequently water or isopropanol) and asquare wave is applied to it, imparting vibrational energy on the liquid.
Nowadays Ultrasonic sensors are widely used in automotive applications for park assist technology.
12/15/13 Ultrasonic sensor - Wikipedia, the free encyclopedia
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References
1. ^ Ultrasonic Flow Meters and Foam (http://www.openchannelflow.com/blog/article/the-heady-problem-of-foam-in-flumes-and-weirs), Openchannelflow.com
2. ^ LabelSensors.com (http://www.labelsensors.com/choose/labelSensorTypes.html)
3. ^ Ultrasonics Basics (Banner Engineering) (http://www.bannerengineering.com/training/faq.php?faqID=34&div=1)
External links
Ultrasonic Acoustic Sensing (http://www.cs.brown.edu/people/tld/courses/cs148/02/sonar.html) Brown
UniversityLaser Ultrasonic Sensor Streamlines Papermaking Process (http://www.lbl.gov/Science-
Articles/Archive/EETD-papersensor-Ridgway.html), Lawrence Berkeley Lab, Dan KrotzUltrasonic Flaw Detection for Technicians
(http://www.silverwinguk.com/en/technical%20pdfs/ultrasonics_vol1.htm), Chapter 2, 3rd ed., 2004 byJ. C. Drury (~5 pages)
Measure distance using the ultrasonic sensor (http://www.emant.com/index.php?tid=100011)Ultra Technology (http://www.ultratechnology.se) More uniform fibre distribution in paper with
ultrasonics in the paper machine wet end.Ultrasound transducer (http://www.cancer.gov/dictionary?CdrID=367430) entry in the public domainNCI Dictionary of Cancer Terms
United ultrasonic (http://www.united-ultrasonic.com)Ultrasonic Transmitter and Receiver circuit diagram
(http://www.explorecircuits.com/circuit/cir_ultrasonic_transmitter_receiver.htm)Ultrasonic Sensors for Industry (http://www.bannerengineering.com/en-
US/products/8/Sensors/30/Ultrasonic)Siemens Ultrasonic Level Measurement (http://www.automation.siemens.com/w1/process-
instrumentation-ultrasonic-4930.htm)Ultrasonic Transducer Technical Info (http://www.bjultrasonic.com/ultrasonic-technical-info/ultrasonic-transducer-technical/)
Transducer for cleaning (http://ultrasonic-cleaners.org/ultrasonic-transducer-for-cleaning.html)
Choosing an Ultrasonic Sensor for Proximity or Distance Measurement(http://www.sensorsmag.com/sensors/acoustic-ultrasound/choosing-ultrasonic-sensor-proximity-or-
distance-measurement-825) Sensors Magazine.
Transducer Info Center (http://www.transducer.co.nz).
Outdoor Ultrasonic Sensors (http://www.maxbotix.com)
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Categories: Ultrasound Sensors
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