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Definition: ultrasound from The Penguin Dictionary of Science

Sound pressure waves of higher frequency than the upper limit of human hearing (i.e. greater than about 20 kHz). Ultrasound is often used where light is unable to penetrate but X-rays would be harmful, for example in the imaging of foetuses.

ultrasound

From The Hutchinson Unabridged Encyclopedia with Atlas and Weather Guide
Pressure waves, known as ultrasonic waves, similar in nature to sound waves but occurring at frequencies above 20,000 Hz (cycles per second), the approximate upper limit of human hearing (15–16 Hz is the lower limit). Ultrasonics is concerned with the study and practical application of these phenomena. Some animals, such as dogs and bats, and insects are able to detect ultrasonic waves. Bats, as well as detecting ultrasonic waves, also emit them. Sound waves reflected from objects allow the bat to estimate the distance of objects, from the time taken for the echo to return. Ultrasound can also be used for cleaning. A material is immersed in water through which ultrasonic waves are passed. The high-frequency vibrations cause dirt particles to be removed. Another use of ultrasound is in developing emulsion-based products in the cosmetics and healthcare industries. High-frequency sounds used in a mixture of oil and water form cavitations (formation of large bubbles). This helps the oil to…
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From The Conversation: An Independent Source of Analysis from Academic Researchers
Editor’s note: Government and academic investigators continue to probe reports from Cuba that, starting in 2016 and continuing through 2017, U.S. and Canadian diplomats and tourists may have been subjected to a “sonic weapon,” damaging their hearing, causing nausea, speech problems and potentially…
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Full text Article Ultrasound

From Encyclopedia of Women's Health
Ultrasound is a specialized diagnostic procedure which allows clinicians to visualize internal body parts or structures. What is the science behind this fascinating tool? Just as a violin string vibrates to produce sound, a solid ceramic “crystal” inside a protected casing (the probe) is set to…
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Full text Article ultrasonics

From The Penguin Dictionary of Physics
The study and application of mechanical vibrations with frequencies beyond the limits of hearing of the human ear, i.e. with frequencies about 20 kilohertz and upwards. There is no theoretical upper limit to the ultrasonic frequency, although ultrasonic applications are usually restricted to about…
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Full text Article ultrasonics

From The Columbia Encyclopedia
study and application of the energy of sound waves vibrating at frequencies greater than 20,000 cycles per second, i.e., beyond the range of human hearing. The application of sound energy in the audible range is limited almost entirely to communications, since increasing the pressure, or intensity, …
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Full text Article ultrasonication

From Dictionary of Microbiology & Molecular Biology
The use of sound waves of frequency ca. 16 kHz or higher (ultrasound) produced by a SONICATOR . Ultrasonication is used, in a liquid medium, e.g. for sphaeroplast lysis, for dispersing the fine particulate matter in centrifuge pellets, and for CELL DISRUPTION . Sphaeroplast lysis requires only a…
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Full text Article Ultrasonic Encephalography

From Gale Encyclopedia of Nursing and Allied Health
Ultrasonic encephalography, or echoencephalography, is the use of ultrasound to produce a noninvasive diagnostic image of the brain and its structures, including the alignment down the midline, the size of ventricles, and the presence of bleeding or tumors. Ultrasonic encephalography is a…
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Full text Article ultrasonic imaging

From The Penguin Dictionary of Physics
ultrasonic imaging
Syn . ultrasonography. The use in medicine of ultrasonic waves ( see ULTRASONICS ) to produce images of soft tissues in the body. (These tissues cannot be imaged by X-rays.) At each tissue interface, some of the incident ultrasonic beam is reflected and can be detected to form the image. The source…
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Full text Article ultrasonics

From Britannica Concise Encyclopedia
Vibrational or stress waves in elastic media that have a frequency above 20 kilohertz, the highest frequency of sound waves that can be detected by the human ear. They can be generated or detected by piezoelectric transducers ( see piezoelectricity ). High-power ultrasonics produce distortion in a…
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Full text Article ultrasonic splicer

From A/V A to Z: An Encyclopedic Dictionary of Media, Entertainment and Other Audiovisual Terms
A device used to splice polyester-base film. Ultrasonic splicers are more complex and expensive than either cement splicers or tape splicers, but are the only way to produce a durable splice in polyester film. Cement splices will not work with polyester-based film stock because the cement is…
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Full text Article ultrasonic inspection

From An Illustrated Dictionary of Aviation
Cathode ray tube indicator corrosion.
A nondestructive test method that employs high-frequency mechanical vibration energy to detect and locate structural discontinuities or differences and to measure the thickness of a variety of materials. Radiation frequency is of the order of 0.1 to 25 MHz. The beam travels unimpeded through large…
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