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Rough diagram of sound frequency scale, showing ultrasound and some applications. Date: 28 June 2010, 23:30 (UTC) Source: Ultrasound_range_diagram.png;
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. 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
Ultrasound is sound with frequencies greater than 20 kilohertz. [1] This frequency is the approximate upper audible limit of human hearing in healthy young adults. The physical principles of acoustic waves apply to any frequency range, including ultrasound.
The oceans are fairly transparent to low-frequency acoustics, however. The oceans conduct sound very efficiently, particularly sound at low frequencies, i.e., less than a few hundred hertz. [3] These properties motivated Walter Munk and Carl Wunsch [4] [5] to suggest "acoustic tomography" for ocean measurement in the late 1970s. The advantages ...
Sound from ultrasound is the name given here to the generation of audible sound from modulated ultrasound without using an active receiver. This happens when the modulated ultrasound passes through a nonlinear medium which acts, intentionally or unintentionally, as a demodulator .
The SOFAR channel (short for sound fixing and ranging channel), or deep sound channel (DSC), [1] is a horizontal layer of water in the ocean at which depth the speed of sound is at its minimum. The SOFAR channel acts as a waveguide for sound, and low frequency sound waves within the channel may travel thousands of miles before dissipating.
Both transducer types emit sound waves into the material when excited. Typically these transducers use a predetermined frequency, however certain thickness gauges allow for frequency tuning in order to inspect a wider range of material. A standard frequency used by an ultrasonic thickness gauge is 5 MHz.
Mechanical index (MI) is a unitless ultrasound metric. It is defined as [1] =, where P r is the peak rarefaction pressure of the ultrasound wave , derated by an attenuation factor to account for in-tissue acoustic attenuation; f c is the center frequency of the ultrasound pulse .