Overview of the development of deep-water low-frequency transmitting underwater acoustic transducers

With the development of ocean research, there is a wide range of demand for transducers that can work in deep water. Deep-water transducers are mostly mounted on various types of self-contained underwater platforms, the

platform can accommodate limited volume and weight as well as power supply capacity, low frequency transducer is required to meet the characteristics of small size, low weight, high efficiency and high hydrostatic pressure resistance.

This paper introduces the research progress of low-frequency deep-water transducers at home and abroad, including the common types of the transducers, their characteristics and development problems, for reference of researchers in

related fields.196dB and the weight is 2800kg; 65Hz very low frequency sound The maximum source level of the source is 203dB and the weight is 1900Kg. Its main disadvantage is that it is limited by the structural characteristics of the curved disc, and the working depth is difficult to reach 1000 meters.

 

2.2 Janus-Helmholtz transducer

The Janus-Helmholtz transducer can also be attributed to the Helmholtz transducer type. Its typical form is that a double-ended longitudinal vibrator excites rigid cylindrical shells at both ends, using the liquid cavity frequency and the radial vibration frequency to form a double resonance peak. The main part is a longitudinal vibration transducer that can radiate on both sides (called Janus transducer). A pair of cylindrical shell cavities are placed on the outside of the radiation head of the Janus transducer, and the space enclosed by the cavity and the Janus transducer The Helmholtz resonant cavity is formed, which works under the excitation of the longitudinal vibration of the Janus transducer. Its structure can work in deeper water without the use of pressure compensation devices. , Utilizing the coupling of the liquid cavity resonance mode and the longitudinal vibration mode, it has low frequency, broadband, high power characteristics, and at the same time has a relatively small size, which is suitable for use as a deep-sea low-frequency sound source. IXBLUE has developed a variety of full-depth Janus-Helmholtz transducers JH250-6000, JH650-6000, etc. The working frequency band of the JH250-6000 transducer is 200Hz-1050Hz, the overall size is Φ72*112cm, the weight is 450kg, and the sound source The level is greater than 196dB; the working frequency band of JH650-6000 transducer is 580Hz-2020Hz, the external dimension is Φ45*61cm, and the weight is 90kg. The sound source level is greater than 196dB; its shortcomings are large fluctuations in the band.

 

Many domestic units have also carried out related researches on Janus-Helmholtz transducers. This type of transducer has a relatively small size and weight to obtain a low-frequency working effect, and theoretically, the performance of the transducer does not change with depth, and has a good application prospect. The main problem is that the liquid cavity resonance mode has a high Q value, which leads to sharp conductance and response curves near the resonance peak of the liquid cavity, which is not conducive to the design of the matching network and has a certain impact on the broadband operation. Hangzhou Institute of Applied Acoustics has conducted research on the problems of JH transducers, and effectively improved the two resonant mode coupling problems of traditional Janus-Helmholtz transducers, and improved the bandwidth and working frequency band of the transducer. The flatness of the transmit voltage response. The produced prototype transducer has a working frequency range of 400~700Hz, a liquid cavity peak of 480Hz, a transmission voltage response bandwidth (6dB) greater than 200Hz, and a maximum sound source level 205dB. The relatively high-frequency prototype working frequency range is 700~1400Hz, the liquid cavity peak is 760Hz, the transmission voltage response bandwidth (6dB) is greater than 500Hz, and the maximum sound source level is 200dB.

 

2.3 Janus-Hammer Bell transducer

 

In 2013,deep-water transducer, which is quite different from the traditional JH transducer. It specifically includes a bidirectional radiating longitudinal vibration transducer and a rigid cylindrical shell, which is mounted on a rigid cylinder. On the medium mass. The mechanism lies in the coupling of the double-ended longitudinal vibration mode and the toroidal mode (two aluminum rings). The longitudinal vibration drives the liquid in the cavity to vibrate, causing the rigid cylindrical shell to resonate. The longitudinal mode is coupled with the radial mode of the shell. To achieve broadband radiation, the in-band level is basically non-directional. Use this transducer to carry out the long-distance sound propagation experiment. The JHB transducer is placed on the channel axis (about 1000m), and the 20-yuan vertical receiving array is used to receive the 1000km signal successfully.

2.4 Overflow ring transducer

 

The overflow ring transducer is a common type of deep-water transducers in the middle and low frequency bands. The inner and outer surfaces of the ceramic ring are sealed with watertight materials (polyurethane or vulcanized rubber). The hydrostatic pressure on the structure is self-balanced, and theoretically the working depth is not limited by the water depth. At the same time, reasonable design of the liquid cavity size of the toroidal transducer can excite the low-frequency liquid cavity resonance peak and combine with the radial resonance of the toroid itself to achieve multi-mode broadband working effects. Generally work in the frequency range of 1kHz~10kHz. For frequency bands below 1kHz, large-size mosaic rings need to be made, which requires high assembly technology. The overflow ring transducer reported abroad has a working frequency band of 250Hz-1kHz and a sound source. The level is 197dB, the diameter is 1m, the height is 1.6m, and the weight is about 800kg.

lan "deep-sea acoustic tomography latent standard", and has achieved preliminary results, but there is still room for further improvement. The working frequency range of the device is 400Hz~550Hz, the maximum transmission voltage response is 132dB, and the maximum sound source level is 182dB. Based on the two sets of deep-sea acoustic tomographic submarine targets of this transducer, low-frequency (500Hz), deep water (1000m channel axis depth), Long-term (3 months on-duty time) acoustic signal emission and acoustic signal reception on the vertical profile at a depth of 300m~1500m. In the utility model patent for the overflow flex-tension transducer applied , rigid foam plastic is used as the pressure-resistant material, the resonance frequency is 2.4kHz, and the transmission voltage response is 126dB. Harbin Engineering University proposed in the patent "A phase-inverted deep-sea flextensional underwater acoustic transducer". By installing half-wavelength inverted tubes at both ends of the IV type flextensional transducer, the internal radiation of the overflow type flextensional transducer is radiated. The sound pressure phase is inverted by 180 degrees, which adjusts the sound pressure phase inside the flexural radiating shell, so that the sound pressure radiated from the inner side at the nozzle of the inverted tube is in the same phase as the sound pressure radiated from the outside of the vibrating shell, overcoming the traditional The problem of low radiation efficiency of the overflow type flextensional transducer. Through this design, the transducer has three in-phase radiating surfaces, namely the elliptical plane piston radiating surface at both ends and the shell radiating surface of the flextensional transducer, forming a ternary in-phase matrix mode, which enables flextensional transduction. The device forms a figure-of-eight directivity, which makes it have the characteristics of directional emission.

2.6 Gas-compensated low-frequency transducer

 

The U.S. Alliant Techsystems company developed the ultra-low frequency high-power underwater acoustic transducer HX-554 for the 1993-1994 Acoustic Thermometry of Ocean Climate (ATOC). The transducer consists of 10 piezoelectric crystal stacks with length 1085mm, width 119mm and thickness 53mm (each crystal stack is made of 92 piezoelectric ceramic square plates bonded together, and a section of passive material is added in the middle of the crystal stack) into a bucket. Shaped structure, with an inflatable bag inside to balance the hydrostatic pressure, and the working depth can reach 1000 meters. The transducer uses piezoelectric stack bending vibration to emit horizontal non-directional sound waves. The resonance frequency is 75Hz, the working bandwidth is 57-92Hz, and the maximum sound source level is 197dB (sound power 420W, CW pulse); the overall size of the transducer is 2.06 long. m, 0.94m in diameter, 2300kg in air, 770kg in water, plus supporting structure and inflation system, the total weight is 5500kg.

 

2.7 Hydrodynamic sound source

The fluid-powered sound source uses hydraulic drive to generate vibration, and has the characteristics of ultra-low frequency emission, wide working frequency, long working stroke and large thrust. The HLF-1 hydraulic sound source developed by Hydroacoustics has a working frequency range of 20Hz-2kHz, the sound source level can reach 196dB at 260Hz resonance, and its maximum size is 1m. The developed HLF-4 hydraulic sound source has a single sound source with a sound source level of 206dB at a resonance frequency of 57Hz and a bandwidth of 14Hz. 5 sound sources are used to form a matrix, and the sound source level has reached 221dB. It is famous in 1991 This transducer was used in the Heard Island ocean temperature measurement test, and the acoustic signal has a propagation distance of 18,000km.

 

3 Conclusion

Different types of deep-water low-frequency transmitting transducers have great differences in size, weight, and deep acoustic characteristics. It is impossible to meet the needs of various types of sonar equipment with one transducer. For example, the overflow ring transducer has good performance. Deep water stability, full-space coverage directivity, better broadband effect, but the corresponding size and weight are relatively large; JH transducer achieves low-frequency and broadband operation in a relatively small volume, but its directivity changes more with frequency. Large, and there are often deep "valleys" in the frequency band, which has a certain impact on the actual use effect. According to the actual needs of the project, comprehensive consideration should be given to the requirements of suitability, sound source level, directivity, broadband operation, etc., and the appropriate type of deep-water low-frequency transmitting transducer should be selected.