Technological Innovation in the Development of Underwater Acoustic Transducers(1)

Technological Innovation in the Development of Underwater Acoustic Transducers

 

 

70.8% of the earth’s surface area is the ocean. The vast ocean is the largest treasure house of resources on the earth, and the ocean is also an important position for international military struggles. The research, development and utilization of the ocean are inseparable from sound waves. Sound waves are the only information carrier that can travel long distances in the ocean. The exploration and development of marine resources, underwater communication transducer and navigation of ships, underwater target detection and recognition, environmental monitoring, and natural disaster forecasting and so on all rely on underwater acoustic technology to achieve. The development of underwater acoustic technology requires the support of all kinds of underwater acoustic transducers. The mission of underwater acoustic transducers is to transmit and receive sound waves underwater, so it is called “eyes and ears of underwater acoustic equipment”, which can be said to be underwater acoustic transducers. The birth of ”H” marks the beginning of the development of hydroacoustic technology. The technical progress of hydroacoustic transducers is an important prerequisite and foundation for the rapid development of hydroacoustic technology(1)

 

The underwater acoustic transducer is not a simple isolated subject, but a multi-disciplinary technical field. The closely related subjects mainly include: physics, materials science, mathematics, mechanics, electronics, chemistry, mechanical science, etc., so underwater acoustics Although the transducer has only a history of more than a hundred years of development, it has now become a vibrant subject field. The urgent need from the field of hydroacoustic technology is the direct driving force for the development of hydroacoustic transducers, and the development of functional materials and technological progress are the most important material basis for the development of hydroacoustic transducers. Throughout the development history of hydroacoustic transducers, in order to meet the ever-increasing technical requirements in the field of hydroacoustics to the greatest extent, the corresponding functional materials are constantly being updated. People have carried out special application research around the characteristics of various functional materials and designed new technologies and new structures have been proposed, which have improved and enhanced the comprehensive technical performance of the transducer, which has enabled an endless stream of innovative research results on the transducer. The author selects some typical research examples of launch transducers, analyzes and summarizes the innovative ideas of these research work from several different angles, and hopes to provide young scholars with certain guidance and enlightenment, and actively explore the profound aspects of classic research work.

 

1. Technical innovation of underwater acoustic transducer based on functional materials

 

In 1915, Paul Langevin of France and others used a capacitor transmitter and a carbon particle receiver to conduct underwater acoustic experiments. These two transmitting and receiving devices should be primitive underwater acoustic transducers; 1917～1918 Langevin Zhiwan designed and improved the quartz transducer. Its vibrator is composed of several piezoelectric quartz plates sandwiched between two thick steel plates. This structure is called Langzhiwan transducer. Since natural quartz cannot meet the ever-increasing demand, it was found that the water-soluble synthetic piezoelectric crystal Rochelle salt has a stronger piezoelectric effect than quartz, but its stability problem limits the scope of application, and the piezoelectricity is slightly inferior. Ammonium Dihydrogen Phosphate (ADP) crystals, due to their relatively stable properties, were widely used in World War II. In 1920, the magnetostrictive effect was applied in underwater acoustic transducers; in 1925, nickel magnetostrictive transducers were designed and applied; in 1931, the in-depth study of thin nickel sheets led to the rapid development of magnetostrictive transducers. And gradually replaced piezoelectric crystal transducers; in 1944, it was discovered that barium titanate ceramics have strong piezoelectricity after polarization, and its loss is much smaller than that of magnetostrictive materials. Later, barium titanate piezoelectric ceramics transducers It has developed rapidly; the polarized lead zirconate titanate ceramic (PZT) discovered in 1954 has stronger piezoelectricity. To this day, PZT piezoelectric ceramics are still the main functional materials of underwater acoustic transducers.

 

In the 1970s, Dr. Clark AE in the United States developed the rare earth giant magnetostrictive ternary alloy Terfenol-D. Since the 1990s, the relaxation ferroelectric single crystal materials PZN-PT and PMN with high voltage electrical properties and high energy density -PT has been discovered one after another, and new breakthroughs have been made in the application research of these three materials. This section will focus on the research results of these new functional material transducers.

 

⒈A new generation of magnetostrictive materials and their transducers

The new generation of magnetostrictive materials includes rare earth alloy materials and rare metal alloy materials. The giant magnetostrictive effect of rare earth alloy materials was first discovered under low temperature conditions. The highest magnetostrictive strain of the Tb0.6Dy0.4 material at 77K is 0.65%, and the highest magnetostrictive strain of Terfenol-D at room temperature is 0.25%. There are documents showing that a magnetostrictive dual-piston longitudinal transducer driven by a superconducting coil has been developed. The rare-earth (terbium-dysprosium) alloy magnetostrictive rod is placed in an air-conditioning room (temperature 50-60K), and the cooling tower is circulated and cooled by the cooling tower of the refrigerator. In the room, a superconducting material coil provides a DC bias magnetic field and an excitation magnetic field to excite the magnetostrictive rod to generate stretching vibration and transmit it to the piston-type radiating surface through the mechanical transition piece. The piston-type radiating surface pushes the water medium to generate pressure waves for radiation. A vacuum chamber is designed in the structure to isolate heat conduction. The outer wall of the vacuum chamber is a dome-shaped pressure-resistant cover, which can withstand a pressure of 10 atmospheres. The main technical parameters are as follows: the resonance frequency is 430Hz, the maximum sound source level is 181.4dB, and the efficiency is about 25%. This underwater hydrophone transducer complicates the manufacturing process in order to obtain low-temperature working conditions. In recent years, people are willing to use the Terfenol-D material that works at room temperature to simplify the manufacturing process, while achieving excellent radiation performance with a new structure.

 

It is the Terfenol-D driven octagonal transmitter transducer completed by Butler equal to 1980. 16 rare earth rods are arranged in two layers, and 8 rare earth rods in each layer are connected into an octagon through a wedge-shaped transition block and form a closed Magnetic circuit, the transition block is connected with the radiating surface of a part of the cylinder (close to the 45° central angle), and the rare earth rod is prestressed through high-strength stress wires between the transition blocks. The internal prestress of the rare earth rod is about 13.8MPa, and the resonant frequency of the transducer in water At 775Hz, the non-linear driving under the DC bias magnetic field condition and the unbiased field condition were compared, and the sound source level 189.8dB under the DC bias magnetic field condition and 196.2dB under the non-biased nonlinear drive condition were realized respectively.