Joseph Scorcio, age 12, of Spokane, Washington, for his question:

What are ultrasonic waves?

Sonic equipment copes with sounds and a sonic boom delivers a resounding bang. "Ultra" adds something extra to a word. "Ultrarapid" is faster than normal and "ultrawise" means super sensible. "Ultrasonic" refers to sounds that are so high that they are above the range of normal human hearing.
Sound, as you know,  is a form of energy that vibrates at speeds through solids, liquids or gases. Its different qualities are governed different by variations in its vibra¬tions. Sound waves rise and fall in cycles, and they are measured by frequency    so many pulsing cycles of sound per second. The lowest note on a piano has a frequency of 27. An organ may utter a deep throaty note of 15 sound vibrations per second, while the highest note on a piano is 4,000 vibrations per second. Normal human hearing equipment can sense and interpret the variations within a frequency range from 20 to 20,000 vibra¬tions per second. We hear the highest of these wave lengths as thin, very high pitched sounds.

But sound waves are not limited to our range of hearing, and ours are not the best ears in the world. Maybe you call your dog home to dinner by blowing into what seems to be a noiseless little whistle. Actually the whistle utters a note that is too high for your ears to hear. Most dogs have super hearing equipment that can detect shorter sound waves than we can. Waves of such high frequency are called ultrasonic waves. This range of super sound begins with about 20,000 cycles per second. Its lowest notes may be just within the capabilities of a well tuned human ear.

Bats, dolphins and many other members of the animal kingdom have astonishing bio¬logical equipment for using ultrasonic waves. Scientists have borrowed these ideas to build all sorts of mechanical ultrasonic equipment. Ultrasonic waves can be fed into a microphone and then into an electronic oscilloscope, which transposes them into shadowy images for viewing on a special fluorescent screen. The high frequency sounds can thus be seen.

    Ultrasonics, like audible sound waves, bounce and echo back from solid objects in the air and water. Ultrasonic beams are directed to scan underwater and report echoes from enemy submarines. Distance is estimated from the time that the sound waves take to reach the target and echo back. This echolocation is sonar    Sound Navigation and Rang¬ing. Similar devices are used to chart the floor of the ocean. Ultrasonic waves also are used for many other purposes, such as detecting flaws in metals and drilling tooth cavities, pasteurizing milk and sterilizing surgical instruments. The somascope is a super X ray machine. It uses ultrasonic echolocation to reveal nerves and muscle within the body. And we expect many more amazing new uses for inaudible supersonic waves.

Much of our information in this field has been gathered from studies of how the little brown bat uses ultrasonics to echolocate his way around obstacles. His built in receiving equipment can interpret sound waves up to 50,000 cycles per second, almost three times higher than frequencies we can hear. The porpoise can do even better. He can in¬terpret frequencies of 150,000    seven times above the human range. Certain whales now being studied may be able to do even better.