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Shortwave (1.6 to 30 MHz) diathermy (where EM waves are used to produce heat) can be used as a therapeutic technique for its analgesic effect and deep muscle relaxation, but has largely been replaced by ultrasound. Temperatures in muscles can increase by 4–6 °C, and subcutaneous fat by 15 °C.
Ultrasound is defined by the American National Standards Institute as "sound at frequencies greater than 20 kHz". In air at atmospheric pressure, ultrasonic waves have wavelengths of 1.9 cm or less. Ultrasound can be generated at very high frequencies; ultrasound is used for sonochemistry at frequencies up to multiple hundreds of kilohertz.
Ultrasound energy, simply known as ultrasound, is a type of mechanical energy called sound characterized by vibrating or moving particles within a medium. Ultrasound is distinguished by vibrations with a frequency greater than 20,000 Hz, compared to audible sounds that humans typically hear with frequencies between 20 and 20,000 Hz.
Sound waves propagating through a liquid at ultrasonic frequencies have wavelengths many times longer than the molecular dimensions or the bond length between atoms in the molecule. Therefore, the sound wave cannot directly affect the vibrational energy of the bond, and can therefore not directly increase the internal energy of a molecule.
This is an accepted version of this page This is the latest accepted revision, reviewed on 23 January 2025. Claimed sensitivity to electromagnetic fields This article is about a pseudomedical diagnosis. For the recognized effects of electromagnetic radiation on human health, see Electromagnetic radiation and health. Electromagnetic hypersensitivity Idiopathic environmental intolerance ...
[34] [35] It is not known for sure that this is the cause; some have suggested that it may have been the influence of electromagnetic waves, and not of infrasonic waves, that prompted these animals to flee. [36] Research in 2013 by Jon Hagstrum of the US Geological Survey suggests that homing pigeons use low-frequency infrasound to navigate. [37]
There are contradictions in Oohashi's results. [3] [12]No effect was detected on listeners in the Oohashi study when only the ultrasonic (frequencies higher than 24 kHz) portion of the test material was played for test subjects.
When ultrasonic waves are generated in a liquid in a rectangular vessel, the wave can be reflected from the walls of the vessel. These reflected waves are called echoes. The direct and reflected waves are superimposed, forming a standing wave. The density of the liquid at a node is more than the density at an antinode.