HyperPhysics***** Condensed Matter ***** Electricity and Magnetism This effect, called magnetostriction, is responsible for the familiar hum of transformers and other AC devices containing iron cores. There is a magnetic analog where ferromagnetic materials respond mechanically to magnetic fields. The effect known as piezoelectricity was discovered by brothers Pierre and Jacques Curie when they were 21 and 24 years old in 1880. Piezoelectric ceramic materials have found use in producing motions on the order of nanometers in the control of scanning tunneling microscopes. The standard piezoelectric material for medical imaging processes has been lead zirconate titanate (PZT). If an electrical oscillation is applied to such ceramic wafers, they will respond with mechanical vibrations which provide the ultrasonic sound source. Barium titanate, lead zirconate, and lead titanate are ceramic materials which exhibit piezoelectricity and are used in ultrasonic transducers as well as microphones. Rochelle salt produces a comparatively large voltage upon compression and was used in early crystal microphones. Quartz crystals are used for watch crystals and for precise frequency reference crystals for radio transmitters. Quartz demonstrates this property and is extremely stable. This provides a convenient transducer effect between electrical and mechanical oscillations. Crystals which acquire a charge when compressed, twisted or distorted are said to be piezoelectric.
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