Non-Contact Ultrasound
Encyclopedia
Non-Contact Ultrasound is a method of non-destructive testing where ultrasound is generated and used to test materials without the generating sensor making direct or indirect contact with the test material or test subject. Historically this has been difficult to do, as a typical transducer
is very inefficient in air. Therefore most conventional ultrasound
methods require the use of some type of acoustic
coupling medium in order to efficiently transmit the energy from the sensor to the test material. Couplant materials can range from gels or jets of water to direct solder bonds. However in non-contact ultrasound, ambient air is the only acoustic coupling medium.
An electromagnetic acoustic transducer (EMAT), is a type of non-contact ultrasound that generates an ultrasonic pulse which reflects off the sample and induces an electric current in the receiver. This is interpreted by software and provides clues about the internal structure of the sample such as cracks or faults.
Research is continuing to improve traditional transducers by applying different plastics, elastomers, and other materials. The sensitivity of these devices continues to improve; a newly developed piezoelectric transducer can produce frequencies in the MHz that can easily propagate through even high acoustic impedance materials such as steel and dense ceramics.
Non-contact ultrasound allows some materials to be inspected which otherwise can’t be inspected due to fear of contamination from couplants or water. In general non-contact ultrasound would facilitate testing of materials or components that are continuously rolled on a production line, in extremely hot environments, coated, oxidized, or otherwise difficult to physically contact.
Transducer
A transducer is a device that converts one type of energy to another. Energy types include electrical, mechanical, electromagnetic , chemical, acoustic or thermal energy. While the term transducer commonly implies the use of a sensor/detector, any device which converts energy can be considered a...
is very inefficient in air. Therefore most conventional ultrasound
Ultrasound
Ultrasound is cyclic sound pressure with a frequency greater than the upper limit of human hearing. Ultrasound is thus not separated from "normal" sound based on differences in physical properties, only the fact that humans cannot hear it. Although this limit varies from person to person, it is...
methods require the use of some type of acoustic
Acoustics
Acoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...
coupling medium in order to efficiently transmit the energy from the sensor to the test material. Couplant materials can range from gels or jets of water to direct solder bonds. However in non-contact ultrasound, ambient air is the only acoustic coupling medium.
An electromagnetic acoustic transducer (EMAT), is a type of non-contact ultrasound that generates an ultrasonic pulse which reflects off the sample and induces an electric current in the receiver. This is interpreted by software and provides clues about the internal structure of the sample such as cracks or faults.
Research is continuing to improve traditional transducers by applying different plastics, elastomers, and other materials. The sensitivity of these devices continues to improve; a newly developed piezoelectric transducer can produce frequencies in the MHz that can easily propagate through even high acoustic impedance materials such as steel and dense ceramics.
Non-contact ultrasound allows some materials to be inspected which otherwise can’t be inspected due to fear of contamination from couplants or water. In general non-contact ultrasound would facilitate testing of materials or components that are continuously rolled on a production line, in extremely hot environments, coated, oxidized, or otherwise difficult to physically contact.