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The Mosquito is an electronic device that uses a high pitched frequency to deter loitering by young people.
In the nondestructive testing of products and structures, ultrasound is used to detect invisible flaws.
Industrially, ultrasound is used for cleaning, mixing, and to accelerate chemical processes.
Ultrasound is no different from 'normal' (audible) sound in its physical properties, except in that humans cannot hear it.
This limit varies from person to person and is approximately 20 kilohertz (20,000 hertz) in healthy, young adults.
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.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.For many processes in the medical, pharmaceutical, military and general industries this is an advantage over inline sensors that may contaminate the liquids inside a vessel or tube or that may be clogged by the product. The principle behind a pulsed-ultrasonic technology is that the transmit signal consists of short bursts of ultrasonic energy.After each burst, the electronics looks for a return signal within a small window of time corresponding to the time it takes for the energy to pass through the vessel.In rheology, an acoustic rheometer relies on the principle of ultrasound.In fluid mechanics, fluid flow can be measured using an ultrasonic flow meter.Only a signal received during this window will qualify for additional signal processing.A popular consumer application of ultrasonic ranging was the Polaroid SX-70 camera which included a light-weight transducer system to focus the camera automatically.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.