Piezoelectricity
NAME: Piezoelectricity
ALTERNATIVE NAME/S:
DETAILS/DSCRIPTION:
In the 1870s, <coined by> Marie Curie* and her husband Pierre experimented with pyroelectricity, which was a form of electricity which could be generated in many crystals.
The structure of these crystals (on which <studied early by> Brewster* had done early work) contained layers of positive and negative atoms. When the crystals were heated, the friction from the movement in the atoms created electricity.
When they were studying the symmetry in crystals, the Curies found that a form of electricity could be created in non-conducting crystals without a centre of symmetry, such as zinc sulfide, sodium chlorate, boracite, tourmaline, quartz, <occurs in> calamine*, topaz, sugar and Rochelle salt.
The Curies’ first thoughts were published in 1880 and a year later, they expanded their knowledge when they found that the atomic layers of two particular crystals, quartz and tourmaline, underwent either contraction or expansion, depending on the direction of an applied electric field. Conversely, the crystals produced electricity or electric polarity, when a mechanical stress was applied. This stress factor was how the name came about, from the Greek ‘piezo’, meaning ‘press’.
An important development from this research was the piezoelectric quartz balance that the Curies designed. This balance produced measurable charges of electricity in direct relation to the stress produced by the weight suspended. Very soon, laboratories working in the field of electricity were using it, Pierre and Marie Curie later using it in their research into radioactivity.
Charles Friedel and Jacques Curie experimented further and discovered that the electric charges came about as a result of the stresses produced due to uneven heating. They found that when the temperature of the crystal remained constant, there was no electrical charge, which made it possible to differentiate between crystals that were pyroelectric and those that were piezoelectric.
For a couple of decades, other than the balance there were few practical applications for piezoelectricity. The outbreak of the 1914-1918 war brought the first industrial use. Piezoelectric quartz was placed in an alternating electrical field and it was discovered that the properties of concentration and expansion resulted in vibration in the crystal.
When the frequencies of the electric field and the natural vibration of the crystal were aligned, it was discovered that the vibration was very strong. Using these findings, the Curies’ assistant, <used by> Langevin* went on to produce the high frequency sound waves which subsequently allowed the development of radar and <basic to> sonar*.
Other applications developed as a result of the work by the Curies and Langevin were electromechanical transducers such as the crystal microphone, the crystal pick-up, and the ultrasonic transducer. Another important application was the radio electromagnetic circuit in which the quartz crystal resonator stabilized oscillations by detecting the electrical effects of stress.
Piezoelectricity plays an important part in the field of medicine too. Piezometers can give very fine measurement of pressure variations and are able very accurately to measure the pulsing of the circulatory system.
In echocardiography, a piezoelectric transducer applied to the chest in conjunction with ultrasound, and produces a projection of the walls and valves of the heart and of their motions on the screen of a cathode ray oscilloscope.
As a result of the pioneering work of the Curie brothers more than a century ago, this technique is of immense value in the diagnosis of cardiac abnormalities and diseases. Today, the demand for piezoelectricity is high and a major spin-off is the manufacture of ‘monocrystals’. These are made in two ways, either hydrothermally, under intense water pressure, or grown in aqueous solutions, providing pure crystals, such as Rochelle salt.
ONELINER: piezoelectricity
EXTRA CONNECTIONS: <investigated by> RJ Hauy* also studied these crystals
BIBLIOGRAPHY:
Encyclopaedia Britannica.
Dictionary of Scientific Biography.