Randy Spalding, age 16, of Dothan, Ala., for his question:
WHAT IS ULTRASONIC?
Ultrasonics is the branch of physics dealing with high frequency sound waves, usually in the range above 20,000 hertz. In contrast with supersonics, which deals with phenomena arising when the velocity of a solid body exceeds the speed of sound, ultrasonics involves acoustical sound waves too high pitched to be heard.
The two words were formerly used interchangeably.
Modern ultrasonic generators can produce frequencies up to about 500 kilohertz by transforming alternating electronic currents into mechanical oscillations. Detection and measuring of ultrasonic waves is accomplished mainly through the use of a piezoelectric receiver or by optical means, because ultrasonic waves are rendered visible by the diffraction of light.
The science of ultrasonics has many applications in technology, and various fields including physics, chemistry and technology. Applied originally after World War I as a means of underwater signaling, ultrasonic waves were later used for detection and communication devices called sonar, of great importance in present day navigation, and especially in submarine warfare.
Applications of ultrasonics in physics include the determination of such properties of matter as compressibility, specific heat ratios and elasticity.
Ultrasonics is employed in producing emulsions, such as homogenized milk and photographic film, and for detecting flaws in industrial materials. Strong screen illumination in television is accomplished by using ultrasonic waves modulated by light diffraction.
In medicine, ultrasonics is used as a diagnostic tool, to destroy diseased tissue and to repair damaged tissue.
Ultrasonic waves have been used to treat bursitis, various types of rheumatoid arthritis, gout and muscular injuries and to destroy kidney stones. As a diagnostic tool, ultrasonics is often more revealing than X rays.
Scientists say that ultrasonics is often more revealing than X rays because X rays do not prove as useful in detecting the subtle density differences found in certain forms of cancer.
When ultrasonic waves pass through a tissue, the waves are reflected in varying degrees, depending on the density and elasticity of the tissue. Analysis of the echoes tells much about the nature of the tissue. .
Ultrasonic waves of greater intensity are used to destroy or to repair tissue in a small area. Using an ultrasonic "scalpel," a surgeon can make an incision finer than with a conventional surgical knife. Such techniques have been used in delicate surgery on the brain and on the ear.
Diathermic devices in which ultrasonic waves are used to produce heat internally as s result of tissue resistance have been used successfully in physical therapy.