Ultrasound is very useful because it allows doctors to see inside the body with out the need to cut it open. Ultra sonic waves are high frequency (30 kHz +), longitudinal waves. They are used in medical scanning medical imaging'. The process works the same way as echo sounding. Ultrasound penetrates the human body well, but some of the original wave is reflected off tissues, bones etc. The returned waves are used to build a picture of inside the body, for example in scans to check on babies while there are still in the mothers' womb pre-natal scan'. The body absorbs some energy, but it is a lot less damaging than other penetrating waves - for example, X-rays. The ultrasonic waves can also be used for a variety of medical uses, such as to study and treat hard-to-reach body areas. Uses for ultra sound were first developed in World War II to locate submerged objects; the technique is now widely used in virtually every branch of medicine. In obstetrics it is used to study the age, sex, and level of development of the fetus and to determine the presence of birth defects or other potential problems. Its use to determine fetal sex has led to the widespread abortion of female fetuses in some countries, such as China and India, where male offspring are more highly valued. Ultrasound is used in cardiology to detect heart damage and in ophthalmology to detect retinal problems. It is also used to heat joints, which relives some arthritic joint pain, and for such procedures as lithotripsy, in which shock waves break up kidney stones, eliminating the need for surgery. Ultrasound is noninvasive, involves no radiation, and avoids the possible hazards "such as bleeding, infection, or reactions to chemicals and this is why its uses is so widespread.
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Animals.
Bats are the classic example of how animals use ultra sound. Bats send out sound waves using their mouth or nose. When the sound hits an object an echo comes back.