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New developments piezo ceramics used in the underwater sonar transducers(2)

Views:6     Author:Site Editor     Publish Time: 2019-09-18      Origin:Site

Composite vector hydrophone

In order to improve the detection performance of passive sonar, research has developed a vector hydrophone that can receive and utilize scalar parameters (sound pressure) and vector parameters (vibration speed) in the sound field, making full use of the information in the sound field. Vector hydrophones and their corresponding signal processing technologies are among the new technologies that are currently being developed internationally. the application of vector hydrophones in the SURTASS system solves the problem of the left and right side blur.it is used the vector hydrophone drag line array to systematically study the attitude, drag speed and flow noise of the vector hydrophone to detect the vector hydrophone. The development of vector hydrophones has basically achieved structural serialization and functional utility which can meet different engineering requirements. A number of units have begun research in this area. After a decade of research and technology introduction, they have also begun to move toward the practical stage of engineering. In terms of structural form, the sound pressure gradient hydrophone is also called a vibration speed hydrophone, and can be divided into a double sound pressure hydrophone, a differential pressure type and a homogenizing spherical type.The double-sound hydrophone type is directly composed of two sound pressure hydrophones, and the fixed-shell type sound pressure gradient hydrophone has a fixed casing, and the double laminated piezoelectric hemisphere piezo ceramics are fixed on the outer casing, and the pressure is fixed. The electric plate is subjected to bending vibration under the action of a sound pressure gradient in the thickness direction thereof. The sensitive components are placed in three orthogonal directions and have the same phase center, which constitutes a three-dimensional vector hydrophone. After the sound pressure hydrophone and the vector hydrophone are structurally integrated, the whole is spherical, and the buoyancy in the sea water is zero. The same-vibration composite vector hydrophone (hereinafter referred to as a vector hydrophone) is constructed, and the output signals of the two are processed. The co-vibration vector hydrophone does not touch the water, and the sensor responds to the overall pulsation of the sensor, requiring free installation. For example, vector hydrophone with an operating frequency range of 20Hz to 6000Hz and Mp =-180dB. In addition to the co-vibration vector hydrophone, there is also a differential pressure type. The differential pressure vector hydrophone contacts the medium water and responds not to the overall movement of the sensor, but also to the high frequency range. The directionality of the vector hydrophone is cosine shaped. Unidirectional directional beam sharpening and electronic rotation of the beam can be achieved to achieve orientation. The operating frequency of the vector hydrophone can range from a few hundred hertz to several tens of kilohertz. After the signal processing, the sound energy flow can suppress the noise by 10-20dB compared with the sound pressure signal energy. The single vector hydrophone has an orientation accuracy of ±2° and can be up to 1° after special treatment.

Piezoelectric ceramics transducer

As early as 1978, it is proposed a piezo ceramic phase and a polymer phase bonded structural material. This material has a particularly high hydrostatic piezoelectric coefficient compared to piezoelectric ceramics and is much larger than PZT piezoelectric ceramics, making it ideal for deep water applications. Its characteristic impedance is small, it is easy to match with water, frequency bandwidth, and its characteristics can also be adjusted by changing the proportion of piezo ceramics. So far, dozens of composite piezoelectric materials have been developed. Among them, the 222, 123 and 023, 321 two-phase composite materials are generally considered to be the most promising future sonar conversion.The 023 composite material, which is made of ceramic powder material and rubber, it is called piezoelectric rubber. It has the softness and flexibility of rubber, which is 20 times that of ordinary piezoelectric ceramics, which is equivalent to PVDF. These advantages make it suitable for surface hydrophones. Piezoelectric rubber is easy to make a few millimeters thick, which is its advantage over PVDF. Research on nanostructured composite piezoelectric materials has also been carried out. It is a process in which piezoelectric ceramics are processed and then infused into composite piezoelectric materials. Another method is to process piezoelectric ceramics into  powders. It is then sintered and formed with other materials. This subject area is currently under study. Materials Systems has successfully developed a large-scale composite hydrophone module with a standard size of 250 × 250 mm. It has also developed a model 123 piezoelectric composite transducer array for use in new lightweight electric torpedo collection and vocal bases.It has also developed a 123-connected piezo ceramic column and epoxy composite surface element hydrophone module, the size is 100 × 180mm, and constitutes a 18-element wide-face line array with a matrix length of 1. 9m and a width of 200mm at 60KHz. The following wideband sensitivity is higher than -190dB and the fluctuation is less than 2dB. Both theory and experiment prove that the composite material can increase the emission response and receiving sensitivity by 3dB~5dB due to the supercharging effect of the polymer material. After adding the hard cover, the effect is more obvious and can be improved by 10dB.

low frequency large area PVDF hydrophone and (PVDF2TrFE) piezoelectric film hydrophone

In order to improve the turbulence noise interference capability of the shipboard side array sonar anti-ship surface, a large-area hydrophone is used in the shipboard side array sonar according to the characteristics of the noise-related radius. PVDF piezoelectric film is an ideal piezoelectric material for making large-area hydrophones. It is light in texture, flexible, and easy to make a curved shape. A large-area hydrophone has been produced with a PVDF film of an area of 200 × 300 × 0.2 mm, and the sensitivity is about -200 dB in the frequency range of several hundred hertz to 4 kHz. In addition to PVDF piezoelectric films, in the 1990s, a new piezoelectric film material PVDF-TrFE (VF2) was developed. which is a ferroelectric polymer copolymer formed of polyvinylidene fluoride (PVDF) and polytrifluoroethylene (TrFE), and is electronically radiation modification. This new material has the potential to solve the temperature and pressure stability problems of PVDF piezoelectric films and lateral mode problems, and the sensitivity is also slightly improved.

High performance electrostrictive piezoceramic material (relaxed single crystal ferroelectric material)

From 1997 to 2000, Institute of Ceramics and Xi'an Jiaotong University successively developed a kind of relaxed iron voltage electric single crystal material, referred to as PMN2PT and PZN2PT. This material has a greater improvement in energy storage density, electromechanical coupling coefficient, dielectric constant and the like than ordinary piezoelectric ceramics, and has residual polarization, and does not require a DC bias. The performance parameters of PMN2PT are given. It has been rated as a rare and exciting breakthrough in the decade since the advent of piezoelectric ceramics in the 1950s by magazines such as SCIENCE and NATURE. However, there are still shortcomings such as low mechanical tensile strength and various complexities with temperature, frequency and electric field , and the cost is too high. It is made a type IV bent low frequency high power transducer, which is 5 dB higher than the transducer with the same structure made of PZT28 material. A part of the ferroelectric body of PMN2X needs a DC-polarized electric field to be used as a high-power emitting material.

The underwater acoustic transducer has been active and rapid in recent years, and its power is mainly driven by the strong demand for military and the overall progress of science and technology. In recent decades, stealth technology has been widely used in targets such as ships and torpedoes, and target detection has become increasingly difficult. In order to overcome the difficulties that the target stealth technology brings to the detection target and improve the active and passive detection performance of various targets, the transducer has higher requirements in terms of transmission power, conversion efficiency and sensitivity; The emergence of materials and new concepts has broadened the research field of transducers and opened up an effective way for improving the performance of transducers. The rapid development of computer technology, using multi-physics finite element software for computer simulation, indicating the vibration system, natural frequency, vibration mode, modal stiffness, transducer directionality, etc., which changed the design method of the transducer; the further improvement and improvement of the transducer processing technology provided a powerful guarantee for the development of the transducer. All of this has driven the development of underwater acoustic transducers. It is foreseeable that the above aspects will still be the hotspot of transducer research. The development of future transducers will inevitably improve the conversion efficiency, increasing the rated power and the operating frequency band has low frequency performance, and reduce the weight by continuously developing new materials, broadening the research field, perfecting the design method, and improving the processing technology. Enhancing the anti-jamming capability and providing more information to further improve the performance of the sonar transducer is the key to improving the performance of the entire sonar system.

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