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Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 k Hz." In air at atmospheric pressure ultrasonic waves have wavelengths of 1.9 cm or less.
Ultrasound devices operate with frequencies from 20 k Hz up to several gigahertz. Ultrasonic devices are used to detect objects and measure distances.
Ultrasound imaging or sonography is often used in medicine.
The Mosquito is an electronic device that uses a high pitched frequency to deter loitering by young people.
Many insects have good ultrasonic hearing and most of these are nocturnal insects listening for echolocating bats.
The first technological application of ultrasound was an attempt to detect submarines by Paul Langevin in 1917.
The piezoelectric effect, discovered by Jacques and Pierre Curie in 1880, was useful in transducers to generate and detect ultrasonic waves in air and water.Polaroid later licensed this ultrasound technology and it became the basis of a variety of ultrasonic products.A common ultrasound application is an automatic door opener, where an ultrasonic sensor detects a person's approach and opens the door.Echolocation in bats was discovered by Lazzaro Spallanzani in 1794, when he demonstrated that bats hunted and navigated by inaudible sound and not vision.Francis Galton in 1893 invented the Galton whistle, an adjustable whistle which produced ultrasound, which he used to measure the hearing range of humans and other animals, demonstrating that many animals could hear sounds above the hearing range of humans.This includes many groups of moths, beetles, praying mantids and lacewings.Upon hearing a bat, some insects will make evasive manoeuvres to escape being caught. In the order Clupeiformes, members of the subfamily Alosinae (shad), have been shown to be able to detect sounds up to 180 k Hz, while the other subfamilies (e.g. An ultrasonic level or sensing system requires no contact with the target.In ihrem Themendienst "Medizin, Ethik, Gesundheit" berichtet die KNA über diese Sachgebiete, auch im Zusammenhang mit Bioethik, Biotechnologie, Euthanasie, Gentechnik, Hospiz, Klonen, Stammzellen und sogenannter Sterbehilfe.Die Agenturtexte werden einzeln per E-Mail übermittelt.Die Zahl der Meldungen hängt von der Intensität der politischen Diskussion ab und liegt monatlich bei rund 100 Texten.Ultrasound is sound waves with frequencies higher than the upper audible limit of human hearing.