CN110637516B - Nonlinear active sonar multi-beam scanning method - Google Patents
Nonlinear active sonar multi-beam scanning method Download PDFInfo
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Abstract
The invention relates to a nonlinear active sonar multi-beam scanning method, which utilizes the influence of a downward shifting ratio on the difference frequency sound source level of nonlinear sonar, reduces the downward shifting ratio to improve the difference frequency sound source level in a large angle of nonlinear sonar beam scanning, thereby improving the observation range of the nonlinear sonar. One of the advantages of the invention is that the observation range problem of the nonlinear sonar is solved by beam scanning.
Description
Technical Field
The invention relates to the technical field of underwater detection, in particular to a multi-beam scanning method of active nonlinear sonar.
Background
In the sixties of the last century, when 2 high-energy sound waves with close frequencies are found to propagate in water, due to the nonlinear effect of an aqueous medium, a difference frequency component of the two frequencies is generated, and the difference frequency component continues to propagate forwards in a narrow beam of the original high-frequency sound wave, namely the beam width of a difference frequency signal is equivalent to that of an original frequency signal. If the conventional technology is adopted, if the beam width of the difference frequency signal is the same as that of the original frequency signal, the sonar array is large, and the requirement on suitability for installation is difficult to meet in engineering. For example, 2 coaxial acoustic matrixes generate 2 high-frequency signals with strong acoustic energy of 100kHz and 110kHz respectively, seawater in a narrow wave beam is excited simultaneously, a difference frequency signal of 10kHz can be obtained by utilizing the nonlinear effect of the seawater, the wave beam width of the difference frequency signal is equivalent to the original frequency, if the conventional technology is adopted, the area of the difference frequency matrix is 100 times larger than that of the original frequency matrix, and the absorption attenuation of the difference frequency signal in water is much smaller than that of the original frequency signal, so that the propagation distance of the difference frequency signal is far longer than that of the original frequency signal. The nonlinear active sonar is characterized in that active detection signals of low-frequency narrow beams are obtained under the condition of a small-size array, and long-distance detection can be well realized on small-size targets such as UUV, frogman and mine mines even under the condition of moderate turbid water.
Generally, the transmitting beam of the active sonar has no directivity or very wide directivity (for example, 120 °), and beam scanning is not required, but the original frequency transmitting signal of the nonlinear active sonar needs a large sound source level, which is impossible to be achieved by increasing the transmitting power alone, so that the array gain of the transmitting matrix needs to be used to increase the transmitting sound source level. In order to obtain higher directional gain, the transmission beam width of the nonlinear active sonar is generally narrower, so that the observation range of a single beam of the nonlinear active sonar is smaller, and in order to ensure a larger observation range of the sonar, transmission beam scanning is required.
According to the product theorem, the beam directivity of the sonar is determined by the directivity of a single transmitting element and the formation of a transmitting array, and when the single element has the directivity, the beam level of a transmitting sound is reduced when the beam scans a large-angle direction because the directivity of the single element is generally the largest in the positive transverse direction and smaller on two sides. The sound source level of the original frequency signal has a large influence on the sound source level of the difference frequency signal, and the reduction of the sound source level of the original frequency signal can cause the rapid reduction of the sound source level of the difference frequency signal, so that when the wave beam scans to a large angle, the original frequency sound source level can be reduced due to the directivity of a single element, and at the moment, the difference frequency sound source level can be greatly reduced, and the observation range of the nonlinear active sonar is directly reduced.
In previous researches, the nonlinear sonar is generally single-beam transmission, and the range of beam scanning is very small even if the beam is multi-beam, which severely limits the application of the nonlinear sonar.
The invention content is as follows:
the technical problem to be solved by the invention is that the nonlinear active sonar wave beam cannot be scanned or the wave beam scanning range is very small. In order to solve the above technical problem, the present invention provides a multi-beam scanning method of an active nonlinear sonar.
Obtained according to the theoretical formula of nonlinear sonar, the difference frequency sound source level SLdAnd original frequency sound source level SL0Primary frequency f0Differential frequency fdAnd the medium parameter isWherein R is0The Rayleigh distance of the primary beam, r 'is the coordinate of the parametric array source, the integration is carried out on the coordinates of each point of the parametric virtual source array, and T (r') is the amplitude gradient function of the primary beam, namely the amplitude attenuation function of the primary beam along with rα0Is the average absorption attenuation coefficient of the primary wave, and x represents the Rayleigh distance R0The ratio of the distance formed by the plane wave impact. From the theoretical formula of nonlinear sonar, it can be seen that the difference frequency sound source level SLdIs SL0Andα0R0and chi three dimensionless parameters,is the ratio of the original frequency to the difference frequency, called the downshifting ratio. When the beam of the nonlinear sonar is scanned, alpha0R0χ is approximately constant, due to the directivity of the matrix array elements, when the beam is swept over a large angle, the SL is0Will become smaller, which will cause the SL to become smallerdAnd rapidly becomes smaller. From the above formula, it can be seen that the difference frequency sound source level SL is constant when other parameters are not changeddAnd ratio of downshiftingThe relationship of (1) is that the lower the downshifting ratio is, the smaller the SLdThe larger, the difference frequency sound source level SL can therefore be solved by changing the downshifting ratiodThe problem becomes smaller. When the beam is scanned, the difference frequency is required to be constant, so that the original frequency f can be reduced0To reduce the downshifting ratio and thereby increase the difference frequency sound source level, i.e. a higher f can be used in the 0 degree direction of the beam and in the vicinity thereof0Frequency, when the beam is swept to a large angle, f can be reduced0Thus in the non-linear sonar observation range, SLdThe fluctuation of the sound wave can meet the using requirement of the sonar.
The invention comprises the following steps:
step 1, beam control is carried out on each element emission signal of the nonlinear active sonar, so that a beam is formed at a specified angle in an observation range:
xi(t)＝x0(t-τi)
wherein xi(t) is the signal of the ith primitive, x0(t) is the signal of the reference cell, τiThe delay of the ith base element relative to the signal of the reference element is shown.
And 2, measuring the original frequency beam directivity and the difference frequency beam directivity, and judging whether the descending amplitude of the difference frequency sound source level meets the application requirements of the nonlinear active sonar or not, but not performing the step 3.
Step 3, reducing the original frequency f within the range of the original frequency working frequency band0And (3) continuing the steps 1 and 2 until the descending amplitude of the difference frequency sound source level meets the application requirement of the nonlinear active sonar.
In the step 1, the delay amount τ of the signaliAccording to different matrix array shapes, its and element spacing, waveBeam steering angle, speed of sound, etc.;
when f is decreased in the above step 30Not only does the downshifting ratio decrease, the corresponding SL0Also becomes larger, further suppressing SLdReduction of (d);
in the above step 3, in practical application, the difference frequency f can be changeddTo change the downward shift ratio and improve the difference frequency sound source level SL under large angledThereby meeting the observation range requirement of the nonlinear active sonar.
Compared with the prior art, the invention has the advantages that:
(1) the difference frequency sound source level SL at large angles is improved by utilizing the downshifting ratio, namely by reducing the original frequency at large anglesdThe nonlinear active sonar is enabled to scan from a small range to a large range from a single beam to a multi-beam. The problem that the observation range of the nonlinear sonar is small is solved, the use efficiency of the nonlinear active sonar is improved, the application range of the nonlinear active sonar is widened, and the development of the nonlinear active sonar has a better application prospect.
(2) In practical application, according to application conditions, the difference frequency can be changed, the beam angles of the nonlinear active sonar are distinguished through different frequencies in different beams, the problem of wide beam angle caused by wide beam receiving is solved, and the angle resolution of the nonlinear active sonar is improved.
Description of the drawings:
FIG. 1 is a beat frequency beam scan pattern without the present invention
FIG. 2 is a beat frequency beam scan of an embodiment of the present invention
The specific implementation mode is as follows:
the present embodiment is directed to actual beam scanning of a 46-element plate array of nonlinear sonar, using the nonlinear active sonar multi-beam scanning method of the present invention.
In the specific embodiment, the array elements are spaced by 0.75 wavelength, the original frequency center frequency is 80kHz, the difference frequency is 20kHz, and the sound velocity is 1500 m/s. Within the whole observation range of the nonlinear sonar +/-30 degrees, a beam is transmitted every 5 degrees.
The result of nonlinear beam scanning using a general beam scanning method is shown in fig. 1, and it can be seen from fig. 1 that when the beam is scanned to ± 30 °, the sound source level is 10dB smaller than the sound source level in the direction of 0 °, or the beam angle range which is 3dB lower than the sound source level in the direction of 0 ° is ± 20 °, which cannot satisfy the requirement of the observation range of the nonlinear active sonar of ± 30 °.
FIG. 2 shows the results of this example. It can be seen from figure 2 that the drop in the difference frequency source level is around 2.5dB over the viewing range of 30.
Claims (4)
1. A nonlinear active sonar multi-beam scanning method is characterized by comprising the following steps:
step 1, beam control is carried out on each element emission signal of the nonlinear active sonar, so that a beam is formed at a specified angle in an observation range, and the formula is as follows:
xi(t)＝x0(t-τi)
wherein xi(t) is the signal of the ith primitive, x0(t) is the signal of the reference cell, τiTime delay of the ith road base element relative to the reference element signal is obtained;
step 2, measuring the original frequency wave beam directivity and the difference frequency wave beam directivity, and judging whether the descending amplitude of the difference frequency sound source level meets the application requirements of the nonlinear active sonar or not, but not performing the step 3;
step 3, reducing the original frequency f within the range of the original frequency working frequency band0And (3) continuing the steps 1 and 2 until the descending amplitude of the difference frequency sound source level meets the application requirement of the nonlinear active sonar.
2. The scanning method according to claim 1, wherein in step 1, the time delay τ of the signal is determinediAccording to different array shapes, the array shape is related to element spacing, beam steering angle and sound velocity.
3. The scanning method according to claim 1, characterized in that in step 3 f is reduced0While not only moving downReducing, correspondingly, the original audio source level SL0Also becomes larger, further suppressing the difference frequency sound source level SLdIs reduced.
4. Scanning method according to claim 3, characterized in that the difference frequency sound source level SLdAnd original frequency sound source level SL0Primary frequency f0Differential frequency fdAnd the medium parameter isBy varying the downshifting ratioTo change SLdIn which R is0The Rayleigh distance of the primary beam, r 'is the coordinate of the parametric array source, T (r') is the gradient function of the amplitude of the primary beam, and χ represents the ratio of the Rayleigh distance to the plane wave impact forming distance.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110736976A (en) * | 2019-10-25 | 2020-01-31 | 海鹰企业集团有限责任公司 | sonar beam former performance estimation method of arbitrary array |
| CN112198515A (en) * | 2020-10-13 | 2021-01-08 | 湖南国天电子科技有限公司 | Parametric array shallow-section difference frequency conversion performance optimization method |
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Cited By (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN110736976A (en) * | 2019-10-25 | 2020-01-31 | 海鹰企业集团有限责任公司 | sonar beam former performance estimation method of arbitrary array |
| CN112198515A (en) * | 2020-10-13 | 2021-01-08 | 湖南国天电子科技有限公司 | Parametric array shallow-section difference frequency conversion performance optimization method |
| CN112198515B (en) * | 2020-10-13 | 2021-06-29 | 湖南国天电子科技有限公司 | Parametric array shallow-section difference frequency conversion performance optimization method |
| US11237258B1 (en) | 2020-10-13 | 2022-02-01 | Hunan Guotian Electronic Technology Co., Ltd. | Method for optimization of a parametric array shallow profile difference frequency conversion performance |
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