Construction of Acoustic Dipole and Its Performance Verification Test in Shallow Water

The complex underwater noise field is formed in the process of the ship's constant volume sound source sailing. Due to the large number of machinery and equipment on the ship, and the navigation state of the ship on the sea is easy to change, these factors make it difficult to obtain the low-frequency radiated noise characteristics of the ship in a stable state. Therefore, it is an effective way to understand and master the characteristics of low-frequency underwater radiated noise field by using directional sound source in controllable state. Dipole transducer is a typical directional sound source with horizontal or vertical octagonal directivity, which is widely used in seismic and logging research. However, few dipole transducers are used in underwater acoustic research. The reason is: the directional emission of underwater acoustic low-frequency transducer is a big problem in the current transducer design. The directional emission technology of low-frequency dipole transducer is related to the distance / wavelength of the radiation surface. Because the position relationship of the radiation surface is fixed, it can only form the ideal directivity at a specific frequency. This brings great inconvenience to the application of underwater acoustic low- frequency dipole transducer. Firstly, the mathematical model of sound field radiated by acoustic dipole is established; then, the common non-directional low-frequency sound source is used to construct an acoustic dipole source. By adjusting the distance between two low-frequency sound sources, low-frequency dipole signals with different frequencies can be emitted. The lake test results show that the maximum difference of horizontal directivity of dipole source is less than 0.5dB and the depth of concave point is more than 21dB; finally, the test scheme in shallow water is designed, and the low-frequency narrow-band signals of 63Hz and 80Hz are emitted by the acoustic dipole source in uniform towing state, and the received signals of the bottom mounted hydrophone are analyzed and processed. The results of marine test show that the horizontal directivity of the dipole sound source constructed by two low-frequency sound sources can meet the requirements of acoustic test at multiple frequencies. The dipole transducer constructed in this paper has the advantages of simple structure, convenient equipment connection and wide signal frequency band, which can be applied in the study of underwater acoustic field characteristics of ships. Using the dipole sound source constructed in this paper, the sound propagation characteristics of underwater directional sound sources such as ships in the far field can be studied.