What is Ultrasound?

Some sounds are too high pitched for people to hear. Most people can't hear frequencies greater than 20,000 Hz. Sounds above the range of human hearing are called ultrasound. Even though you can't hear ultrasound, it has many important medical and commercial uses. You may have experienced ultrasound without being aware of it.
Scientists produce ultrasound by changing electric or magnetic energy into mechanical energy. They use a device called an ultrasonic transducer. The transducer has a quartz or ceramic disk that can be charged with electricity. When charged, the disk vibrates very rapidly. The high-frequency vibration produces ultra­sonic waves.

Medical Uses

 Doctors use ultrasound to observe soft tissues in the human body. Soft tissues, such as those that make up the liver, are almost invisible on an X-ray picture. However, ultrasonic waves reflect off soft tis­sues. A computer transforms the reflected waves into a picture on a computer screen. The picture is called a sonogram. Using a sonogram, a surgeon can detect a tumor or examine valves in the heart. Pregnant women routinely have sonograms to determine the development of the fetus.
Other medical professionals also use ultrasonic devices. Physicians use ultrasonic vibrations to get rid of stones that form in the kidney and gall bladder. The ultrasonic vibrations break the stones into very small pieces so they can pass out of the body naturally. Dental hygienists use high-frequency vibrations to loosen plaque deposits on teeth. Physical therapists use ultra­sound to produce a deep-heating effect for muscle spasms and sprains.

Commercial Uses
 Ultrasound is used to clean small, intricate metal items, such as jewelry and small machine parts. The item to be cleaned is placed in a liquid bath. Ultrasonic vibrations travel through the liquid bath to loosen and remove dirt and corrosion. Ultrasound makes it easy to clean cracks and crevices that can't be reached by hand-polishing methods.