The underwater acoustic transducer uses the piezoelectric effect of crystal (quartz or potassium sodium tartrate) piezoelectric ceramics (barium titanate and lead zirconate titanate, etc.) or the magnetostrictive effect of iron-nickel alloys to work. The so-called piezoelectric effect is to cut the crystal into thin slices in a certain direction, and apply pressure on the crystal thin slices, which will generate positive and negative charges on both ends of it. On the contrary, when a tensile force is applied to the crystal sheet, the opposite charge will be generated on its two end faces. Contrary to the piezoelectric effect, the electrostrictive effect, that is, when an alternating voltage is applied to the two end faces of the crystal, the crystal will produce corresponding mechanical deformation. We use electrostrictive effect and piezoelectric effect to generate and receive ultrasonic waves.
When the sonar emits ultrasonic waves, the ultrasonic oscillating voltage is applied to the two end faces of the crystal sheet. Then the thickness of the crystal will change with the ultrasonic oscillation voltage, generating ultrasonic vibration. The vibration of the crystals pushes the surrounding water to produce ultrasonic radiation.