What Is It Used In?
During World War I, Megacycle quartz were developed into resonators to stabilize the frequency of vacuum-tube oscillators, which increased its stability by a factor of 10. A new class of testing material methods were designed on the propagation of ultrasonic waves. This was the first time elastic and viscous properties of liquids and gasses could be determined with ease. A new range of transient pressure measurments were opened. This gave way to being able to study explosives and internal combustion engines.
Again, in World War II, piezo materials were utilized. More powerful sonar were developed, ceramic phono cartridges were made that simplified circuit design, and allowed for new ignition systems. Alot of other applications consists of mostly listening devices.
Today they are used in a majority of technologies that are based on sound, accelerometrs,ultrasonic ransducers, office hardwear, and much others.