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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.
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. Ultrasonic devices operate with frequencies from 20 kHz up to several gigahertz.
For frequencies of ultrasound from 25 to 50 kHz, a guideline of 110 dB had been recommended by Canada, Japan, the USSR, and the International Radiation Protection Agency, and 115 dB by Sweden [24] in the late 1970s to early 1980s, but these were primarily based on subjective effects. The more recent OSHA guidelines above are based on ACGIH ...
Ultrasonic hearing is a recognised auditory effect which allows humans to perceive sounds of a much higher frequency than would ordinarily be audible using the inner ear, usually by stimulation of the base of the cochlea through bone conduction. Normal human hearing is recognised as having an upper bound of 15–28 kHz, [1] depending on the person.
This method of medical ultrasound therapy can be used for various types of pain relief and physical therapy. In physics, the term "ultrasound" [1] applies to all acoustic energy with a frequency above the audible range of human hearing. The audible range of sound is 20 hertz – 20 kilohertz. Ultrasound frequency is greater than 20 kilohertz.
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The ultrasonic devices achieve high directivity by modulating audible sound onto high frequency ultrasound. The higher frequency sound waves have a shorter wavelength and thus don't spread out as rapidly. For this reason, the resulting directivity of these devices is far higher than physically possible with any loudspeaker system. However, they ...