Piezoelectricity, its history and applications

This is the 100th anniversary of the discovery of the piezoelectric effect by the brothers Curie. While this was a scientific curiosity for the next third of a century, with the work of Langevin it produced one of the principal electromechanical transducer effects. Quartz, first used as a transducer, also received wide use in controlling oscillators and in selective wave filters. Quartz was soon replaced by Rochelle salt for transducers. This is a rather unstable crystal, which, however, was the first ferroelectric having an intrinsic polarization between its two Curie temperatures. A theory of this effect was given by the writer. Most crystal transducers have been replaced by ferroelectric ceramics. A material somewhat similar to a ferroelectric is an electret. These have become very useful in transmitters and receivers. Finally, thin films of piezoelectric crystals are useful for producing high frequencies in such devices as the acoustic microscope.