Complex devices called ultrasonic transducers send ultrasound into liquids and solids, and receive echoes of the ultrasound. These devices convert electric energy into ultrasound and vice versa. Ultrasonic transducers are made of materials, such as quartz and some ceramics, that are piezoelectric (pronounced pee ay zoh ih LEHK trihk). This kind of material vibrates when an electric voltage is applied to it, and produces a voltage when a sound wave causes it to vibrate.

Medical uses of ultrasonic transducers include machines that can detect the heartbeat of fetuses (unborn, developing babies). Other machines produce images of normal and diseased tissue inside the body, and images of fetuses. Physicians can use these machines to detect and evaluate cancer, fetal abnormalities, and other conditions. Instruments that use the Doppler effect can measure the flow of blood in the heart and blood vessels. A lithotripter uses pulses of ultrasound to break up gallstones or kidney stones.

Other uses of ultrasound include burglar alarms, automatic door openers, instruments that detect flaws in metal parts, machines that weld plastic, and tools that cut metal. Underwater sonar devices operate much like radar to measure distances to the ocean floor, detect submarines and other vessels, and even locate schools of fish. Ultrasonic cleaning instruments use sound waves to loosen dust and other contaminants from small, delicate products such as watches and electronic components.

Contributor: Frederick W. Kremkau, Ph.D., Professor and Director, Center for Medical Ultrasound, Wake Forest University School of Medicine.