HARVEY FEIGENBAUM, M.D.
When sound waves attain a frequency above 20,000 cycles/sec, they are regarded as ultrasound. Frequencies this high cannot be detected by the human ear. Although the physical properties of ultrasound are essentially the same as low-frequency sound, the small wave length associated with ultrasound provides some distinct advantages. First of all, with a smaller wave length there is less tendency for the sound to scatter, and the apparatus necessary to focus the sound is much smaller. Thus, it is considerably easier to direct ultrasound in a straight beam. Secondly, the ability of an object to reflect or refract sound waves
FEIGENBAUM H. Diagnostic Ultrasound. Ann Intern Med. ;65:185–189. doi: 10.7326/0003-4819-65-1-185
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Published: Ann Intern Med. 1966;65(1):185-189.
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