The physics go back much further of course. It was long known that certain crystals, notably tourmaline, would attract light objects when heated. This was the pyroelectric effect: an electrical polarization caused by heating. The brothers Pierre and P.J. Curie studied this, and discovered the production of electrical polarization when a crystal was strained, in 1880. (They also found the inverse in 1881) NOTE: it is often suggested Pierre's fire Marie was involved as well since she was the one with the physics degree.
FACT: while dying of radiation poisoning, Pierre was trampled to death by horses. Also interesting is that the other man (see below) most responsible for the commercial uses of the pizeoelectric effect also used to date Marie... Was she secretly behind both mens'work?Rochelle salt first became more than a curiosity around 1917, when it was used by Paul Langévin in ultrasonic acoustic transducers for the submarine detection. This was the first practical application for pizeoelectric devices. What we now call sonar was first developed in 1917 in France. Langvin's detector consisted of a transducer, made of thin quartz crystals carefully glued betweentwo steel plates, and a hydrophone to detect the returned echo. By emitting a high-frequency chirp from the transducer, (a ping) and measuring the amount of time it takes to hear an echo from the sound waves bouncingoff an object, one can calculate the distance to that object.