Development of Underwater Acoustic Transducer in Underwater Detection Application

The underwater acoustic transducer is the main tool that uses sound waves to detect, identify and locate underwater targets, or to communicate and send reports underwater. The transducer is used to emit sound waves is called a transmitter. When the transducer is in the emitting state, it converts electrical energy into mechanical energy and then into acoustic energy. At present, conventional transducer array elements designed with piezoelectric materials, especially low-frequency transducers, have a large volume and weight due to their structural characteristics, which not only increase the cost of manufacturing, use and maintenance, but also propose special features for the platform. Requirements and limits the scale and form of formation, thereby restricting tactics and technical indicators. How to solve the problem of the size and form of the acoustic array, how to unify the structural design of the low-frequency and high-frequency sonar arrays, and on the basis of the new array element structure, by combining large-scale conformal arrays to improve the sound The various technical indicators of the Naji Array are undoubtedly an urgent need to give play to the combat performance of the platform and underwater weapons and improve the underwater combat capabilities of our army.

1 New type of piezoelectric composite transducer

Figure 3.1 Array element and cross-sectional view of the moon bud piezoelectric composite transducer

Figure 3.2 Array element and cross-section view of the cymbal transducer

Moonbud type piezoelectric underwater acoustic transducer (Figure 3.1) and cymbal type piezoelectric composite transducer (Figure 3.2) are the most representative flextensional transducers currently focused on abroad. The piezoelectric composite transducers of these two structures are named after the shape of their metal end caps. The metal end cap cavity of the moon bud structure is a moon bud type, while the metal end cap cavity of the cymbal structure is a cymbal type, and the cavity is air. They are all made of a composite of metal and piezoelectric ceramics. Metal-piezoelectric ceramic composite materials are combined with piezoelectric ceramics through plate-shaped, shell-shaped and cap-shaped metals to change the stress distribution inside the ceramics, thereby improving the performance of piezoelectric materials. Its main features are simple design, easy processing and low cost. The moon bud piezoelectric composite transducer and the cymbal piezoelectric composite transducer show good piezoelectric performance. This structure changes the stress distribution of the ceramic interface through the stress conversion between the cap-shaped metal and the ceramic interface, and makes the composite material The longitudinal piezoelectric performance and the transverse piezoelectric performance produce an additive effect, thereby greatly improving the piezoelectric coupling performance dh of the material. Among them, the dh of the moon bud structure composite material is 10-20 times higher than that of the piezoelectric ceramics. The cap structure can be 30-40 times higher than piezoelectric ceramics. The performance comparison of moon bud and cap-shaped metal-piezoelectric ceramic composites and piezoelectric ceramics is shown in Table 3.1.

2 Cymbal transducer

Figure 4.1 Sectional view of the basic structure of the cymbal transducer array element

Figure 4.2 The radial displacement of the ceramic chip of the cymbal array element is transformed into the displacement in the thickness direction of the metal cap

Array element structure: The basic structure of the array element is shown in Figure 4.1. It is formed by bonding two pieces of metal sheet stamped into a cymbal shape and a piezoelectric ceramic sheet. The material of the metal sheet can be titanium alloy, brass, alloy steel, etc. The use of titanium alloy as the metal sheet material can make the cymbal element have greater resistance to water pressure. For the element diameter dp=10mm, the cymbal underwater acoustic transducer can withstand the pressure at a depth of 600 meters. However, titanium alloy materials are more expensive than brass and alloy steel materials. Therefore, titanium alloy materials are relatively limited when the water depth is not considered. Compared with alloy steel materials, brass cymbal array elements have better piezoelectric properties when they are simultaneously applied to cymbal array elements. The materials of piezoelectric ceramics also mainly include PZT-4, PZT-8 and PZT-5. When cymbal transducers are used as transmitting transducers, PZT-4 and PZT-8 piezoelectric ceramics are commonly used as receiving transducers. When used, PZT-5 piezoelectric ceramics are commonly used. Working principle: When voltage is applied to the two poles of the cymbal array element, the piezoelectric ceramic will produce longitudinal and lateral vibration. The longitudinal vibration of the piezoelectric ceramic makes the two metal plates of the array element directly produce longitudinal displacement; The lateral displacement causes the metal sheet to compress or expand in the radial direction. Due to the special shape of the cymbal, this also causes the longitudinal displacement of the top of the metal sheet, as shown in Figure 4.2. Both the longitudinal and radial displacement of the piezoelectric ceramic will cause the metal end cap to produce a longitudinal displacement, and the result of the superposition of the two displacements is the displacement of the metal end cap, which results in the amplification of the displacement of the metal end cap.

3 Characteristics and application prospects of cymbal piezoelectric underwater acoustic transducer

3.1 Features of cymbal piezoelectric transducer

1) The array element is small in size, high in static pressure and piezoelectric coefficient, easy to match with the water medium, and has a very large bandwidth; among them, the concave array element design and the special hydrostatic balance design are used to break through the working depth limit of the basic array.

2) Provide a type of comprehensively applicable acoustic sensors and arrays for underwater platforms and underwater weapons. This type of acoustic array is small in size, light in weight, and has a wide range of applications. Claim.

3) Due to the small and light characteristics of the new cymbal array, it can be assembled on a large scale.

4) Use cymbal array element design theory and special software to unify the array structure of each frequency band into a cymbal structure of various scales, so that each frequency band can be optimized and developed

It also avoids unnecessary and tedious tests and forms a fast and unified new cymbal array design and development method. Using this method, in addition to developing products with similar operating frequencies, new low-frequency, high-frequency array elements and basic arrays that work in different frequency bands will also be developed.

3.2 Application prospects

1) Underwater communication: Because the cymbal sonar transducer has the characteristics of small size, light weight, easy deployment, high sensitivity, etc., the cymbal sonar array elements can be formed into a linear array for underwater communication, or as a The underwater communication system unit establishes an underwater communication network to realize large-area and long-distance underwater communication, and can instantly change the underwater defense position according to combat needs, making underwater communication fast and flexible.

2) Used for torpedo guidance: Cymbal sonar has high receiving sensitivity. Cymbal sonar can be applied to passive torpedoes to realize torpedo tracking and guidance.

3) Used for submarine receiving sonar: the cymbal sonar array elements can be formed into a common array, which can be arranged on the head or side of the submarine to perform the functions of detection and positioning.

4) Others: can be used as towing sonar, mine avoidance sonar, dipping sonar, etc.