Editing Piezoelectricity (section)

===World War I and inter-war years===
The first practical application for piezoelectric devices was [[sonar]], first developed during [[World War I]]. The superior performance of piezoelectric devices, operating at ultrasonic frequencies, superseded the earlier [[Fessenden oscillator]]. In [[France]] in 1917, [[Paul Langevin]] and his coworkers developed an [[ultrasound|ultrasonic]] [[submarine]] detector.<ref>{{cite journal |title= Who knew piezoelectricity? Rutherford and Langevin on submarine detection and the invention of sonar |last= Katzir |first= S. |journal= Notes Rec. R. Soc. |date= 2012 |volume= 66 |issue= 2 |pages= 141–157 |doi= 10.1098/rsnr.2011.0049 |doi-access= free }}</ref> The detector consisted of a [[transducer]], made of thin quartz crystals carefully glued between two steel plates, and a [[hydrophone]] to detect the returned [[Echo (phenomenon)|echo]]. By emitting a high-frequency pulse from the transducer, and measuring the amount of time it takes to hear an echo from the sound waves bouncing off an object, one can calculate the distance to that object.

Piezoelectric devices found homes in many fields. Ceramic [[phonograph]] cartridges simplified player design, were cheap and accurate, and made record players cheaper to maintain and easier to build. The development of the [[ultrasonic transducer]] allowed for easy measurement of viscosity and elasticity in fluids and solids, resulting in huge advances in materials research. Ultrasonic [[time-domain reflectometer]]s (which send an ultrasonic pulse through a material and measure reflections from discontinuities) could find flaws inside cast metal and stone objects, improving structural safety.