<unk>  image (sonogram) of a fetus in the womb, viewed at 12 weeks of pregnancy (bidimensional scan) An<unk> sonic examination Fetal<unk> <unk>  is sound waves with frequencies higher than the upper audible limit of human hearing.<unk>  is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is approximately 20 kilohertz (20,000 hertz) in healthy young adults.<unk>  devices operate with frequencies from 20 kHz up to several gigahertz.<unk>  is<unk> ed in many different fields.<unk> sonic devices are<unk> ed to detect objects and measure distances.<unk>  imaging or sonography is often<unk> ed in medicine. In the nondestructive testing of products and structures,<unk>  is<unk> ed to detect invisible flaws. Industrially,<unk>  is<unk> ed for cleaning, mixing, and accelerating chemical processes. Animals such as bats and porpoises<unk> e<unk>  for locating prey and obstacles.
Ultrasound
Scan
Radiochemistry
Palpation
Physical examination
Radiography
Nuchal scan
Anthropometry