Single-directional circular hydrophone sensor

Introduction

The circular hydrophone is a commonly used type of hydrophone, which is generally used in low frequency bands. It has the characteristics of flat frequency response, small size, low acceleration sensitivity, non-directivity and good consistency. The unidirectional circular hydrophone sensor introduced in this article is made of a dipole ceramic tube and a monopole ceramic tube. The signal received by the dipole is phase shifted and amplified, and then the signal is received with the monopole synthesize to form a heart-shaped directivity. The unidirectional circular hydrophone is small in size and light in weight. As the piezo element of a large receiving array, it can effectively reduce the weight of the array. Especially when used in a conformal array, it can function as a virtual sound baffle and realize detection. The port and port are distinguished.

1 Theoretical analysis

The schematic diagram of the unidirectional circular hydrophone is shown in Figure 1. It can be seen that the unidirectional circular tube hydrophone uses the natural directivity of the dipole and the omnidirectional directivity of the monopole to synthesize the cardioid directivity.

In the low frequency band, the phase difference between the monopole vibration mode and the dipole vibration mode of the piezo ceramic tube of the same size is 90°, so the dipole piezo ceramic tube can be compensated for 90°phase. At the same time, there is a difference in the magnitude of the received signal between the two, so the amplitude of the dipole should be amplified so that the incident sound waves in the 180°direction cancel each other out, and the directivity of the hydrophone is heart-shaped.

2 Finite element simulation of unidirectional hydrophone

Use ANSYS finite element simulation software to build a hydrophone model. As shown in Figure 2, the blue is a dipole, the red is a monopole, and the pink is a water area. The use of symmetrical boundaries can simplify the model, and only need to build 1/2 model. The piezoelectric ceramic material is PZT-5, the size isφ20mm×φ18mm×10mm, its resonance frequency is at 48kHz.

According to the theoretical analysis, first calculate the phase and the receiving sensitivity of the monopole and dipole receiving signals respectively, and the results are shown in Figure 3 and Figure 4. It can be seen that in the low frequency band, the phase difference between monopole and dipole radiation is about 90°, with fluctuations of 2.5°. Sensitivity difference change curve .The line has a minimum slope around 6kHz. According to this, the center operating frequency can be set around 6kHz, the dipole phase shift is 90 degrees, and the amplitude compensation is 10 times.

According to the phase shift and amplitude compensation calculated above, the unidirectional circular tube is simulated and calculated, and the directivity diagram is shown in Figure 5. It can be seen that the hydrophone has the best heart-shaped directivity at 6kHz. In the range of 4kHz~12kHz, the difference in radiation before and after the hydrophone Above 10dB, it can be considered that the hydrophone has unidirectionality and can distinguish front and back.

3 Making and testing of unidirectional circular tube hydrophone

According to the results of the simulation calculation, the actual picture of a unidirectional circular tube hydrophone is shown in 6.

Measure in the anechoic pool, use the acquisition board for data acquisition, and use Matlab to process the obtained data according to the phase shift and amplitude compensation obtained by the simulation. The directivity diagram obtained is shown in 7.

The measured 4kHz~12kHz directional graph data of the unidirectional circular tube is basically consistent with the simulation, but the front and rear radiation difference is slightly smaller than the simulation result, which is caused by the large and small dipole figure-of-eight directivity. This test verifies that the unidirectional circular tube hydrophone sensor has wide-band unidirectional performance. As a receiving array element, it has the ability to distinguish between starboard and starboard.

4 Conclusion

In this paper, a unidirectional circular tube is designed. Using the principle of monopole and dipole directivity synthesis, phase compensation and amplitude amplification are performed on the dipole, and the unidirectionality in the frequency band of 4kHz~12kHz can be obtained. Finally, it passes the test. The possibility of this kind of hydrophone is verified, and it has a certain practical prospect. The next step is to improve the production of the dipole tube, optimize the sensitivity of the hydrophone, and broaden the working frequency band.