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Twitches and Sparks
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11466 |
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Section : |
NATURAL SCIENCE
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| Issue
Date : |
4 / 1994 |
2,551 Words |
| Author
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Lawrence H. Berlow
Lawrence H. Berlow is a free-lance writer and researcher based
in Suffern, New York. His recent projects include several
contributions to How Products Are Made (Gale Research, 1993). |
More than one million Allied troops were on the ground in Europe within one month of the Normandy Invasion (D-day). Although no single aspect of this campaign can be pointed to as the reason for its success, a vital factor was the soldiers' ability to communicate with one another. If it had not been possible for each of thousands of transmitters to operate without jamming the others, the Allied effort might have been a tragic failure. Nestled in the heart of each transmitter was a small crystal whose vibrations in response to an electronic signal held the key to maintaining the transmitter on its assigned frequency. Walter Cady, who is credited with having done much of the research required for making quartz oscillators practical, estimated that 75 million piezoelectric crystals (quartz oscillators) were produced for the U.S. military in World War II.
Fifty years after D-day, piezoelectric crystals are not the costly devices they were at that time. If they were expensive, perhaps we would know how special they are. But unless we know about crystals from our work or hobbies, most of us are blithely unaware that these now-common devices are essential to our everyday lives.
Discovery
In 1881, Pierre Curie, with his brother Jacques, discovered that if pressure is applied to a piece of quartz, the quartz produces a voltage. They named this phenomenon piezoelectricity, the root piezo coming from the Greek verb "to squeeze." Conversely, if a voltage is applied to quartz, the quartz deforms mechanically in a phenomenon called electrostriction (pressure through electricity). Though the brothers may have sensed that piezoelectricity was much more than an amusing laboratory phenomenon, they could not have foretold its applications as the world prepares to move into the twenty-first century. The use of piezoelectricity is so widespread that it is a unique, defining characteristic of our age.
Piezoelectricity is a property of several types of crystals, although quartz is generally preferred because of its frequency stability. Basically, a crystal is a very regular structure characterized by up to five geometric symmetries. There are 32 categories of crystals; the combination or lack of certain of the symmetries makes piezoelectric crystals respond to pressure and electricity the way they do.
Piezoelectric crystals play vital roles in timekeeping and radio communication. Both realms are surprisingly broad and deeply embedded in the fabric of
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