Hydroacoustic transducers sensor work with the piezoelectric effect of crystals (quartz or potassium sodium tartrate) piezoelectric ceramics (barium titanate and lead zirconate titanate) or the magnetostrictive effect of iron-nickel alloys. The so-called piezoelectric effect is to cut the crystal in a certain direction into thin slices, and apply pressure on the crystal flakes. Positive and negative charges are generated on both ends of the crystal. In contrast, when a tensile force is applied to the crystal flakes, opposite charges are generated on both ends of the crystal flakes. When the piezoelectric effect is reversed, the electrostrictive effect, that is, the alternating voltage is applied to both ends of the crystal, the crystal will produce a corresponding mechanical deformation. We use electrostrictive and piezoelectric effects to generate and receive ultrasound waves.
Ultrasonic oscillating voltages are applied to both end faces of the crystal flakes when the sonar emits ultrasonic waves. The thickness of the crystal then changes with the ultrasonic oscillating voltage and generates ultrasonic vibration. The crystal vibrates the ultrasonic radiation that pushes the surrounding water.
When the ultrasonic wave reaches the target, it will produce reflection. The echo acts on the crystal of the hydroacoustic transducer, and electrical signals may be obtained on both ends of the hydroacoustic transducer due to the piezoelectric effect. Like radar antennas, underwater acoustic transducers not only emit and receive ultrasonic signals, but also have sharp directionality. Only in this way can the orientation of the target be determined. Sonar devices use many piezoelectric crystals to form a transducer array to achieve sharp directionality. Therefore, sonar hydroacoustic transducers are relatively large and are generally installed in the underwater part of the naval vessel.
A device that converts sound energy and electric energy (or two different forms of energy) to each other is called a transducer. Most of the underwater acoustic equipment use electro-acoustic conversion; because this conversion method is most convenient for manual control. The underwater transducers are called underwater acoustic transducers.
An electrical signal generated by the electronic oscillator excites the transducer to generate a mechanical vibration, and thus a transducer that drives the water medium to emit sound waves into the water is called a transmission transducer. Conversely, transducers that vibrate under the excitation of sound waves to convert sound energy into electrical energy are called receiving transducers or hydrophones.
The transducers have different classifications due to their different uses and applications. For example, the underwater acoustic transducers are classified as ultrasonic transducers in many countries.