RU2515133C1 - Spherical hydroacoustic antenna - Google Patents

Abstract

FIELD: physics, acoustics.SUBSTANCE: invention relates to hydroacoustic engineering. The antenna has a thin-walled hollow spherical casing, piezoelectric transducers and a support for mounting the antenna to a carrier. The spherical casing is acoustically transparent and is made of plastic with uniformly arranged openings for filling the casing with water when the antenna is immersed in water. The piezoelectric transducers are mounted on the inner surface of the spherical casing. The transducers are omnidirectional in the operating wavelength range of the antenna and are arranged in twelve groups such that the centres of the groups are located at the vertices of the icosahedron inscribed in the sphere at distances less than or equal to 1.5 times the wavelength of the maximum frequency of the band of the received signal; each of the twelve groups is formed by three transducers such that the acoustic centre of each transducer of the group is located on the vertex of an equilateral triangle with side length equal to half the wavelength of the maximum frequency of the band of the received signal. The transducers are arranged such that the axis of the antenna support lies perpendicular to one of the edges of the icosahedron and passes through the centre of the equilateral triangle formed by that edge.EFFECT: protecting piezoelectric transducers from external mechanical action, low weight of the antenna, possibility of determining the direction of hydroacoustic signal sources with high accuracy and resolution with small dimensions of the antenna aperture.2 dwg

Description

The invention relates to the field of sonar and can be used mainly as a direction-finding antenna for sonar underwater navigation systems with an ultrashort base.

When developing sonar systems with an ultrashort base, which determine the location of the navigation object by angular direction measurements to the sonar beacon from one point where the direction-finding antenna of small wave sizes is installed, the main task is to achieve the greatest accuracy of angular measurements when striving to reduce weight, dimensions and complexity of the antenna.

As a way to increase the accuracy of estimating the horizontal and vertical angles of arrival of a navigation signal, superresolution methods can be used (Ratinsky MV Adaptation and superresolution in antenna arrays. - M.: Radio and Communications, 2003), which make it possible to estimate directions to signal sources with angular resolution , greater than the width of the main lobe of the antenna pattern, and consisting in the application of spectral methods for analyzing the correlation matrix of signals received by the antenna converters. One of the methods of superresolution is the MUSIC method (Multiple Signal Classification) - a multi-signal classification method that allows you to evaluate the directions to several signal sources received by the antenna at the same time. The result of the work of this method is a direction finding relief (G. Malyshkin. Optimal and adaptive methods for processing hydroacoustic signals. - St. Petersburg: JSC Concern TsNII Elektropribor, 2011) - a function of two variables (in the case of determining the direction in space): horizontal and vertical angles of direction to the signal source, having maxima corresponding to the direction to signal sources.

However, the application of these methods of analysis of the multidimensional signal received by the antenna leads to the necessity of arranging the receiving transducers on the surface of the antenna with distances between adjacent transducers as close as possible to half the wavelength of the received signal. If the transducers in the antenna are at distances greater than those indicated, false maxima appear in the direction-finding relief that do not correspond to the directions to the signal sources, which can lead to an incorrect determination of the direction to the signal source. At the same time, to reduce the interaction of antenna elements across the field, it is necessary to use transducers and structural elements having small wave sizes, the distances between the centers of adjacent elements should be greater than the wavelength (Smaryshev M.D., Dobrovolsky Yu.Yu. Hydroacoustic antennas. - L .: Shipbuilding, 1984). However, a compromise may be reached in an effort to reduce the number of transducers and obtain a directional relief without false maxima. This compromise is the selection of such a sparse placement of the transducers, which gives an acceptable ratio of the levels of true and false maxima of the directional relief or antenna pattern.

For sonar navigation systems with an ultrashort base, the greatest possible coverage of the possible directions of the arrival of the navigation signal from the transponder beacon is required. Even if the navigation object and the transponder beacon have a close immersion depth, due to hydroacoustic refraction and reflections from the bottom and surface of the water (Urik R.J. Fundamentals of hydroacoustics. - L .: Sudostroenie, 1978) a navigation signal can come to the antenna under a significant angle in the vertical plane. Therefore, an antenna is required that can cover the entire range of angles, not only in the horizontal, but also in the vertical plane, while the directivity of the antenna should be constant for all directions of signal arrival. All of the above requirements are best met by a spherical antenna.

Known spherical hydroacoustic antenna of the noise path, containing a spherical frame, which is applied soundproof coating with evenly placed on it and rigidly fastened by a frame hydroacoustic receivers, the number of which reaches several thousand (see the description of the invention to US patent No. 4207621, IPC G01S 3/80, publication 06/10/1980).

A disadvantage of the known antenna is the dependence of the sensitivity of the receivers on changes in hydrostatic pressure. In addition, the manufacture of such an antenna is technologically difficult, since it requires fixing a large number of receiving elements on the frame.

Known spherical sonar antenna having a spherical body, covered with plates, on which hydrophones are located. The plates are in the form of isosceles trapezoids and are located in strips parallel to the equator of the spherical antenna body. The antenna is attached to the hull of the vessel and has a technological cutout intended for mounting the mounting device and devoid of converters. Also, the part of the spherical body diametrically opposite to the technological cut-out is devoid of converters (see the description of the invention to French patent No. 2709909, IPC H04R 1/44, publication March 17, 1995).

A disadvantage of the known antenna is the high level of the lateral field and the uneven directional characteristics in planes perpendicular to the equator of the spherical antenna body.

Known spherical diffraction sonar antenna containing a thin-walled hollow spherical shell made of metal and six piezoelectric transducers located externally on the surface of the spherical shell, uniformly spaced from each other along its surface and attached to it with glue along three mutually perpendicular axes with simultaneous obtaining of a three-dimensional measurement space and the ability to obtain a bearing with a minimum of sensors - piezoelectric transducers (see the description of the certificate of the Russian Federation for utility model No. 4863, IPC H01Q 1/04, publication 16.08.1997).

The disadvantages of the known antenna is the inability to distinguish the directions of arrival of signals from several sources acting on the antenna simultaneously in the same frequency range, as well as the deterioration of the characteristics of the multipath propagation of hydroacoustic, in addition, the use of glue for attaching piezoelectric transducers outside the antenna body can lead to loss transducer during external mechanical influences or temperature differences during immersion of the antenna in water.

A spherical sonar antenna for a sonar is known, comprising a spherical body having a circular hole for attachment to a sonar carrier, on which piezoelectric transducers are mounted in a spiral, twisted clockwise and starting from the point of intersection with an axis passing through the center of the round hole and the center of the spherical body, its outer surface, and the first in order piezoelectric transducer is located near point A (see description of the invention to RF patent No. 2460092, IPC G 01S 15/00, publication 08/27/2012).

A disadvantage of the known antenna adopted as a prototype from the point of view of its angular resolution is that in the reception mode when forming a fan of the radiation patterns only a part of the antenna converters are used, and the width of the main lobe of the fan is determined by the size of the flat aperture equivalent to that involved in the reception of the surface of the sphere directivity characteristics, therefore, in order to achieve high angular resolution, it is necessary to increase the size of the antenna, and therefore use in Anna design a large number of transducers, thereby increasing the constructive complexity of the antenna and its mass.

The objective of the invention is the creation of a spherical sonar antenna, the design of which allows to protect the piezoelectric transducers from external mechanical stress with a small mass of the antenna and to obtain a direction-finding characteristic that allows you to determine the direction to the source of the sonar signal with high accuracy at small sizes of the antenna aperture.

The essence of the claimed invention is as follows.

The spherical hydroacoustic antenna contains a thin-walled hollow spherical shell, piezoelectric transducers, a support for attaching the antenna to the carrier. The spherical shell is made of acoustically transparent plastic with evenly spaced openings for filling the shell with water when the antenna is immersed in water, piezoelectric transducers are installed on the inner surface of the spherical shell.

The transducers are omnidirectional in the working range of the antenna wavelengths and are arranged in twelve groups so that the centers of the groups are located at the vertices of the icosahedron inscribed in the sphere at distances less than or equal to 1.5 wavelengths of the maximum frequency of the received signal band, each of the twelve groups is formed by three transducers so that the acoustic center of each group transducer is located at the apex of an equilateral triangle with a side length equal to half the wavelength of the maximum frequency n received signal strength. The transducers are located in such a way that the axis of the antenna support is perpendicular to one of the faces of the icosahedron and passes through the center of an equilateral triangle formed by this face.

This allows you to protect the piezoelectric transducers from external mechanical stress, reduce the weight of the antenna, determine the directions to the sources of hydroacoustic signals with high accuracy and resolution with small sizes of the antenna aperture.

Protection of piezoelectric transducers from external mechanical stress is achieved thanks to the claimed arrangement of sonar transducers inside the antenna shell. Placing the transducers inside the spherical shell allows the shell to be used as a radome around the antenna. The use of an acoustically transparent sheath allows one to get rid of the shading by the sheath of the transducers located on the side of the antenna opposite to the signal source, and thereby, when receiving a signal from any direction, use all the antenna converters. The location of the centers of the groups of transducers at the vertices of the icosahedron makes it possible to arrange the groups so that the neighboring groups of transducers are on the surface of the spherical shell at equal distances, which allows to obtain a uniform directivity characteristic. The location of the transducers in such groups that within each group the acoustic centers of the transducers are at the vertices of equilateral triangles with a side length equal to half the wavelength of the maximum frequency of the band of the received signal, and the distance between adjacent centers of the groups does not exceed 1.5 wavelengths of the maximum frequency of the band of the received signal, allows to prevent false maxima in the direction finding relief at low signal-to-noise ratios. The location of the antenna converters in such a way that the axis of the antenna support is perpendicular to one of the faces of the icosahedron, and passes through the center of an equilateral triangle formed by this face, coinciding with the axis of the antenna, which is the diagonal of the cube on which the icosahedron is built, allows for mounting the support to the spherical body of the antenna Do not remove the transducers that interfere with the mounting of the support to the shell, and ensure that the directivity of the antenna is uniform. The acoustic transparency of the antenna and the claimed arrangement of the transducers make it possible to effectively use the MUSIC method to analyze the signals received by the antenna, and thereby determine the directions to the sources of hydroacoustic signals with high accuracy and resolution.

The essence of the claimed invention is illustrated by drawings, where Fig. 1 shows a design image of the claimed antenna with a sphere diameter of 160 mm, an icosahedron rib length of 84.1 mm, and distances between the acoustic centers of piezoelectric transducers equal to 25 mm, which corresponds to half the wavelength of the acoustic signal at a frequency of 30 kHz at a speed of sound propagation in water equal to 1500 m / s, the shell is shown translucent for clarity, the edges of the icosahedron, at the vertices of which a cent s groups of transducers, wherein the numeral 1 denotes a hollow thin-walled spherical shell filled by an acoustically transparent water; 2 - cylindrical piezoelectric transducers; 3 - holes for filling the antenna with water; 4 - support for mounting the antenna to the carrier; 5 - a group of transducers whose acoustic centers are located at the vertices of an equilateral triangle;

figure 2 shows the directional relief constructed using the MUSIC method (Multiple Signal Classification) of signals simultaneously received by the model of the claimed antenna from three sources having the same radiation power in the band 25-30 kHz under the influence of spatially isotropic interference in the form of white Gaussian noise with a signal-to-noise ratio of -10 dB in the frequency band of useful signals, where the number 6 denotes the local maximum corresponding to the signal source with angular coordinates of 40 ° in the horizontal plane and -50 ° in the vertical oskosti; 7 is a local maximum corresponding to a signal source with angular coordinates of 120 ° in the horizontal plane and 40 ° in the vertical plane; 8 is a local maximum corresponding to a signal source with angular coordinates of 300 ° in the horizontal plane and 10 ° in the vertical plane.

A spherical hydroacoustic antenna contains: a hollow thin-walled spherical acoustically transparent shell filled with water 1, piezoelectric transducers 2, holes 3 for filling the housing with water, a support 4 for attaching the antenna to the carrier.

The antenna works as follows: sound waves from M signal sources excite mechanical vibrations N = 36 of the piezoelectric transducers 2 antennas, at the outputs of which electrical signals arise. Due to the acoustic transparency of the spherical body 1 of the antenna, all antenna converters participate in the formation of electrical signals containing information about the direction to a specific source of the acoustic signal.

$$$$

сигналов, принятых антенной, путем усреднения по поступающим блокам по следующей формуле:Due to the spatial diversity of the converters, the signals of the associated antenna channels have phase delays, based on which the directions to the signal sources are estimated, for which the signals of the antenna converters are amplified, digitized, their complex envelope is calculated and stored in the computer memory in blocks from each block of digitized converter signals form an Xf _r matrix of size N × L, where N is the number of converters in the antenna, L is the length of the block with the signal, and a selective estimate of relational matrix $${\hat{R}}_{XX}$$

$$$$

signals received by the antenna by averaging over incoming blocks according to the following formula:

$${\hat{R}}_{XX}=\frac{\mathrm{one}}{K_{fr}}{\displaystyle \sum _{fr=\mathrm{one}}^{N_{fr}}{X}_{fr}{X}_{fr}^H},$$

where fr is the block number, K _fr is the number of signal blocks involved in averaging.

A three-dimensional rectangular coordinate system OXYZ is connected to the antenna, oriented in such a way that its center O is aligned with the center of the spherical antenna, the axis OZ is directed downward. The direction to each signal source is set by the horizontal and vertical angles α and ε, respectively. The horizontal angle α is counted from the positive direction of the OX axis clockwise when viewed from the OXY plane. The vertical angle 8 is counted down from the OXY plane.

сигналов, принятых антенной. На основе N-M - наименьших собственных значений матрицы Λ из матрицы U формируют матрицу U_N собственных векторов, задающих подпространство помехи. На основе полученной таким образом матрицы U_N строят пеленгационный рельеф методом MUSIC, вычисляя следующую функцию по всем пространственным направлениям, задаваемым горизонтальным углом α и вертикальным углом ε:Assuming that the interference is spatially isotropic and is white Gaussian noise with zero mean, the matrix of eigenvectors U and the matrix of eigenvalues Λ of the estimated correlation matrix are calculated $${\hat{R}}_{XX}$$

signals received by the antenna. Based on NM, the smallest eigenvalues of the matrix Λ, a matrix U _{N of} eigenvectors defining the interference subspace is formed from the matrix U. Based on the matrix U _N thus obtained, the direction-finding relief is constructed by the MUSIC method, calculating the following function in all spatial directions defined by the horizontal angle α and vertical angle ε:

$$P(\alpha ,\epsilon )=\mathrm{one}/|\; |\; |D^H(\alpha ,\epsilon )U_H{U}_N^{H}D(\alpha ,\epsilon )|\; |\; |,$$

- направляющая матрица антенныWhere $$D(\alpha ,\epsilon )=\left[s{\nu }_{\mathrm{one}}({\alpha }_{\mathrm{one}},{\epsilon }_{\mathrm{one}})\cdots s{\nu }_M({\alpha }_M,{\epsilon }_M)\right]$$

- antenna guide matrix

for M - sources of signals having horizontal and vertical angles of direction in space: α ₁ , ε ₁ , ..., α _M , ε _M , H - Hermite symbol of conjugation of a complex-valued matrix,

$$s\nu (\alpha ,\epsilon )=\left[\begin{array}{l}\exp \left(j\frac{2\pi f_0}{c}(\cos (\epsilon )\cos (\alpha )x_i+\cos (\epsilon )\sin (\alpha )y_i+\sin (\alpha )z_i\right)\\ \exp \left(j\frac{2\pi f_0}{c}(\cos (\epsilon )\cos (\alpha )x_N+\cos (\epsilon )y_N+\sin (\alpha )z_N\right)\end{array}\right]$$

- the antenna direction vector characterizing the effect of a single source signal at a carrier frequency f ₀ from the direction specified by the horizontal angle α and vertical angle ε on N antenna converters.

To confirm the operability of the claimed antenna by the indicated method, a direction-finding relief was constructed for signals simultaneously received by the model of the claimed antenna from three sources having the same radiation power in the band 25-30 kHz. The first signal source with angular coordinates α = 40 ° in the horizontal plane and ε = -50 ° in the vertical plane; a second signal source with angular coordinates α = 120 ° in the horizontal plane and ε = 40 ° in the vertical plane; the third signal source with angular coordinates α = 300 ° in the horizontal plane and ε = 10 ° in the vertical plane. The signals were received under the influence of spatially isotropic interference in the form of white Gaussian noise with a signal-to-noise ratio of 10 dB in the frequency band of useful signals. The simulation result is shown in figure 2, where the number 6 denotes the local maximum corresponding to the first signal source, 7-local maximum corresponding to the second signal source, 8-local maximum corresponding to the third signal source. According to the graph in figure 2 it can be seen that the direction-finding relief has no false maxima, local maxima exactly correspond to the directions to the signal sources.

Thus, the objective of the invention can be considered solved.

The claimed invention allows to protect piezoelectric transducers from external mechanical stress, reduce the weight of the antenna, determine the directions to the sources of hydroacoustic signals with high accuracy and resolution with small sizes of the antenna aperture.

Claims (1)

Spherical hydroacoustic antenna containing a thin-walled hollow spherical acoustically transparent shell made of plastic with evenly spaced holes for filling the shell with water when the antenna is immersed in water, piezoelectric transducers mounted on the inner surface of the spherical shell, omnidirectional, mounted on the inner surface of the spherical shell, a support for mounting the antenna to the carrier, characterized in that the transducers are arranged in twelve groups so that the centers of the groups located at the vertices of the icosahedron inscribed in the sphere at distances shorter than or equal to 1.5 wavelengths of the maximum frequency of the band of the received signal, each of the twelve groups is formed by three transducers so that the acoustic center of each transducer of the group is at the top of an equilateral triangle with a side length equal to half the wavelength of the maximum frequency of the band of the received signal, the axis of the antenna support is perpendicular to one of the faces of the icosahedron and passes through the center of an equilateral triangle olnik formed by this face.

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