Acceleration is the piezoelectric device, but they operate at much lower frequency (typically tens or hundreds of Hz instead of hundreds of kHz). Both the AE acceleration sensor is used to sense movement. However, perceived motion accelerometer has a wavelength of the order of tens to hundreds of feet. Therefore, the measure the movement of the structure as a whole and not sensitive to small points disorders. The AE sensor test part of the local structure, and is very sensitive to the disorder..