A target detection method based on acoustic vortex spatial phase correlation analysis

Abstract

A target detection method based on acoustic vortex spatial phase correlation analysis includes: generating a vortex-like excitation sound field; receiving scattered sound pressure information after the acoustic vortex is incident; extracting the correlation coefficient between the scattered sound field spatial phase and the reference phase matrix, predicting the presence, size and spatial orientation of the target, and realizing the target detection function. The invention can achieve small target detection that breaks through the diffraction limit and can detect the target's spatial position; using acoustic vortices as information carriers, it provides new ideas and technical solutions for the field of target detection.

Description

Technical Field

[0001] The invention belongs to the technical field of sonar detection, and in particular relates to a target detection method based on acoustic vortex spatial phase correlation analysis, which is suitable for acoustic detection of targets underwater and in the air. Background Art

[0002] With the development of detection technology and the demand for practical applications, it is becoming increasingly important to detect small targets, especially targets whose size is close to or smaller than the wavelength. Traditional detection systems have a diffraction limit, which is proportional to λF / D, where λ, F, and D represent the incident wavelength, the focal length of the transducer system, and the aperture scale, respectively. The smaller the diffraction limit, the higher the spatial resolution of the detection system, that is, the resolution is proportional to the aperture of the detection system and inversely proportional to the wavelength. The existence of the diffraction limit limits the minimum spatial scale of objects that can be detected by traditional detection methods. For this reason, effective detection of small targets can only be achieved by increasing the frequency and increasing the caliber. However, whether it is electromagnetic waves commonly used in the air or sound waves commonly used in water, their attenuation increases with the increase of frequency, which limits the detection distance. At the same time, increasing the caliber will face the problems of increased cost and equipment compatibility. Therefore, traditional detection methods are greatly limited in the detection of small targets. With the development trend of the gradual miniaturization and unmanned development of future marine and air equipment, how to effectively detect small targets in the water has become an urgent problem to be solved in the field of hydroacoustic engineering.

[0003] Acoustic vortex is a special kind of sound wave, which has been widely used in the biomedical field. Acoustic vortex carries orbital angular momentum during propagation, and the wavefront twists around its acoustic axis, destructively interfering at the center to form a zero amplitude center. The phase of the acoustic vortex is distributed in a spiral shape about the center, and the phase change on any concentric circle around the vortex center is always 2πl, where l is the topological charge of the acoustic vortex. Therefore, an important feature of the acoustic vortex is that the closer to the vortex center, the more dramatic the phase change, and at the vortex center, the phase "super-oscillation" occurs and a phase singularity is formed. This drastic change in spatial phase information shows different characteristics after being modulated by targets of different materials, shapes and sizes, becoming a new dimension that can be used for target detection. The method of using the spatial phase information of acoustic vortices for target detection is not limited by the diffraction limit of traditional detection methods, and provides a new way to solve the detection problem of small and medium-sized targets. Summary of the invention

[0004] In view of the deficiencies in the prior art, the scattering mechanism of acoustic vortices, and the spatial phase modulation characteristics of acoustic vortices by targets, the present invention proposes a target detection method based on spatial phase correlation analysis of acoustic vortices, which is not restricted by the diffraction limit and can break through the diffraction limit to achieve small target detection.

[0005] The technical solution of the present invention is as follows:

[0006] A target detection method based on acoustic vortex spatial phase correlation analysis, comprising:

[0007] Produce vortex-like excitation sound field;

[0008] Receive scattered sound pressure information after the acoustic vortex incident;

[0009] The correlation coefficient between the spatial phase of the scattered sound field and the reference phase matrix is ​​extracted to predict the presence, size and spatial orientation of the target and realize the target detection function.

[0010] The working principle of the present invention is as follows: the incident acoustic vortex is a type of sound field with a spatial phase singularity. After being scattered by the target, the spatial phase distribution is modulated and changed, which can be used as a new information dimension for target detection. When the acoustic vortex is incident on the target off-axis, the spatial phase correlation spectrum offset is linearly related to the axial spacing and lateral offset distance between the target and the sound source. Combining the linear relationship between the scattered spatial phase information and the correlation spectrum offset, the actual position of the target can be solved, realizing the function of detecting the presence, spatial scale and orientation of the target.

[0011] A target detection method based on acoustic vortex spatial phase correlation analysis specifically comprises the following steps:

[0012] S1. Emitting an acoustic vortex signal to form an acoustic vortex;

[0013] S2. The acoustic vortex field is inspected and calibrated, and a matrix of a certain size centered on a phase singularity is extracted as a reference matrix for cross-correlation analysis;

[0014] S3. transmitting an acoustic vortex signal to the area to be measured;

[0015] S4. Receiving a forward scattered signal and / or a backscattered signal of the measured area;

[0016] S5. Perform correlation analysis on the received scattered signals to predict the presence and size of the target; extract the distribution characteristics of the phase singularity to obtain the linear relationship of the acoustic vortex phase singularity offset;

[0017] S6. Detect and identify the actual position of the target based on the linear relationship of the acoustic vortex phase singularity offset.

[0018] Preferably, the emitted acoustic vortex signal adopts an active acoustic vortex emission system and / or a passive acoustic vortex emission system. The active acoustic vortex emission system can be a transducer array composed of multiple transducer array elements; the passive acoustic vortex emission system includes a finite aperture approximate plane wave incident on a spiral phase modulator (such as an acoustic prism, a circumferential gradient material, a mask plate), and an acoustic vortex is generated after diffraction and propagation.

[0019] Preferably, the inspection and calibration in step S2 refers to comparing the measured results with the calculation results using the angular spectrum method, or judging by referring to the spatial amplitude and phase distribution characteristics of the acoustic vortex.

[0020] Preferably, the correlation analysis in step S5, including spatial phase cross-correlation analysis and phase correlation analysis, refers to placing the target at the acoustic axis and at a certain distance offset from the acoustic axis, emitting and receiving acoustic vortex signals, performing correlation analysis on the received scattered sound pressure phase diagram, and extracting the distribution characteristics of phase singularities; the reference feature matrix of the correlation analysis is the sound pressure information at the phase singularity obtained in step S2; and the linear relationship between the offset distance of the phase singularity and the distance of the target from the acoustic axis and the distance of the target from the sound source plane within a certain range is obtained.

[0021] Preferably, the step S4 receives forward scattered signals and / or backscattered signals of the area to be tested, and uses a spatial sound field receiving system composed of a stepper motor and a hydrophone or a hydrophone linear array or selects a two-dimensional hydrophone array to quickly test the spatial sound pressure information.

[0022] Preferably, the distribution characteristics of the phase singular points in step S5 include the position of the phase singular points when there is only a single singular point, and the position and distribution arrangement of the phase singular points when there are multiple singular points.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The phase information of the acoustic vortex is used as the basis for detection. It is not restricted by the diffraction limit and can detect small targets smaller than the wavelength. The phase information change of the acoustic vortex after being scattered by the target is used to be sensitive to the position of the target, thereby improving the detection accuracy.

[0025] (2) Overcoming the limitation of the diffraction limit of conventional plane wave target detection, a method based on spatial phase information and related technologies under acoustic vortex incidence is proposed, which can achieve small target detection that breaks the diffraction limit and detect the spatial position of the target. Compared with traditional coherent sound sources such as plane waves, spherical waves, and cylindrical waves, the present invention uses acoustic vortices as information carriers, providing new ideas and technical solutions in the field of target detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a flow chart of a target detection method based on acoustic vortex spatial phase correlation analysis of the present invention;

[0027] Figure 2 It is an example of an active acoustic vortex emission system;

[0028] Figure 3 It is a schematic diagram of the forward scattering process;

[0029] Figure 4 It is a schematic diagram of the backscattering process;

[0030] Figure 5 is a linear relationship diagram between the phase singular point offset and the actual position of the target, where a is the relationship diagram between the horizontal offset distance of the phase singular point and the distance from the target to the sound source plane, and b is the relationship diagram between the horizontal offset distance of the phase singular point and the distance from the target horizontal offset acoustic vortex acoustic axis;

[0031] Figure 6 It is the backscattered field sound pressure phase distribution diagram and correlation diagram. DETAILED DESCRIPTION

[0032] The invention scheme of the present invention will be described completely and clearly below in conjunction with the embodiments and drawings, but this should not be used to limit the protection scope of the present invention.

[0033] like Figure 1 As shown, a target detection method based on acoustic vortex spatial phase correlation analysis includes the following contents:

[0034] Generate an acoustic vortex field. The acoustic vortex emission system used in the present invention is as follows: Figure 2 At a certain distance from the transducer plane, after the acoustic vortex field is fully formed, the generated acoustic vortex field is inspected and calibrated to determine the quality of the generated acoustic vortex.

[0035] Acoustic vortex test and calibration. Extract a matrix of a certain size centered on the phase singularity as the reference matrix for cross-correlation analysis. The smaller the matrix, the more accurate the cross-correlation analysis. Figure 6 This is the cross-correlation diagram during backscattering. It can be seen that there is only one point with a correlation coefficient equal to 1, which is the phase singularity, indicating that the cross-correlation accurately extracts the position of the phase singularity.

[0036] The forward scattering process of the target described in the present invention is as follows: Figure 3 As shown in Figure 4 As shown. Initially, the target is placed at a distance d from the sound source plane; set no less than 2 to 4 working conditions with different offset acoustic axis distances, the offset distance is within the radius of the target, and use the acoustic vortex receiving system to scan the sound pressure field signal on the receiving surface. Extract the phase singular point position of each working condition.

[0037] The linear relationship between the distribution of phase singularity and the actual position of the target is obtained. The phase singularity after the characteristic acoustic vortex scattering propagates along the polar direction, so the phase singularity offset distance and the distance between the target and the acoustic vortex sound source plane are linearly related, such as Figure 5 (a) is shown. At the same time, the relationship between the phase singular point offset distance and the actual target offset distance is obtained according to the previous test. The corresponding linear regression equations are fitted respectively to achieve target detection within the linear range.

[0038] The acoustic vortex emission system is used to generate an acoustic vortex signal, including an active acoustic vortex emission system and a passive acoustic vortex emission system. The acoustic vortex signal includes focused and unfocused acoustic vortices.

[0039] The acoustic vortex receiving system is used to receive scattered signals after the acoustic vortex is incident. The scattered signals include forward scattering and / or backscattering.

[0040] The active acoustic vortex emission system is a transducer array composed of a plurality of transducer array elements. Each transducer array element is individually controlled to emit the same signal with equal phase intervals, and the interference between the signals forms an acoustic vortex field.

[0041] The passive acoustic vortex emission system is to inject a plane wave into a specially designed spiral phase modulator (such as an acoustic prism, a circumferential gradient material, a mask plate, etc.), and generate an acoustic vortex after diffraction and propagation.

[0042] The acoustic vortex receiving system can be composed of a stepper motor and a hydrophone or a hydrophone linear array to scan the amplitude and phase information of the sound pressure field on the receiving surface. For forward scattering spatial sound field measurement, a two-dimensional hydrophone array can be used to quickly test the spatial sound pressure information.

[0043] The correlation analysis includes spatial phase cross-correlation analysis and phase correlation analysis.

[0044] The spatial phase correlation analysis technology achieves target detection by obtaining the relationship between the scattering spatial phase correlation spectrum characteristics and the actual position of the target. The method comprises the following steps:

[0045] (1) When there is no target, use the acoustic vortex emission system to emit an acoustic vortex signal. After the acoustic vortex is fully formed at a certain distance from the sound source plane, collect the signal; process the received acoustic vortex signal to obtain the sound pressure field amplitude and phase distribution diagram of the acoustic vortex at the receiving plane, and perform verification and calibration; compare the measured results with the calculation results using the angular spectrum method for verification and calibration.

[0046] (2) When there is no target, observe and record the position of the phase singularity, which reflects the center of the acoustic axis. Record the sound pressure information on the receiving plane as the reference matrix for correlation analysis. When using cross-correlation analysis, the reference matrix is ​​a matrix of a certain size centered on the acoustic axis, that is, centered on the phase singularity. The smaller the matrix, the more accurate the cross-correlation analysis.

[0047] (3) When there is a target, place the target at the acoustic axis and at a certain distance from the acoustic axis, transmit and receive acoustic vortex signals, perform correlation analysis on the received scattered sound pressure phase diagram, and extract the distribution characteristics of the phase singularity; the reference feature matrix of the correlation analysis is the sound pressure information at the phase singularity obtained in step (2); the linear relationship between the offset distance of the phase singularity and the distance of the target from the acoustic axis and the distance of the target from the sound source plane within a certain range is obtained. The distribution characteristics of the phase singularity refer to: when there is only a single singularity, the position of the phase singularity; when there are multiple singularities, the position and distribution arrangement of the phase singularity.

[0048] (4) When there is a target, the target is located at any position. The scattered sound field is also analyzed, and the distribution characteristics of the phase singularity are analyzed. The linear properties of the phase singularity offset are used to determine whether the target exists and the actual position of the target is calculated.

[0049] The target detection method of the acoustic vortex spatial phase correlation analysis used in the present invention uses the phase super-oscillation characteristics of the acoustic vortex and the scattered phase distribution information as the basis for detection. Before and after the acoustic vortex is scattered by the target, the phase singularity is offset, and the offset is linearly related to the distance of the target from the sound source plane and the distance from the sound axis within a certain range. Through this linear relationship, the actual position of the target can be solved from the position of the scattered phase singularity under any working condition to achieve target detection.

[0050] Example

[0051] The following is an embodiment of using acoustic vortex spatial phase correlation analysis to achieve target detection.

[0052] An ideal Bessel sound wave is used as the incident acoustic vortex. The frequency is selected as 14kHz, and the target is a tungsten carbide ball with a diameter of 1 wavelength, surrounded by water medium.

[0053] When there is no target, record the sound pressure field information after the acoustic vortex is fully formed, and select a 5*5 matrix centered on the phase singularity as the reference matrix for cross-correlation analysis. Consider the combined transmission and reception situation, that is, receive the backscattered information of the target at the sound source plane.

[0054] When there is a target, initially, the target is 20 times the wavelength away from the plane of the acoustic vortex source, so that it meets the far-field condition of scattering; thereafter, the target is offset in the horizontal direction, and the spatial distribution diagram of the scattering field phase is obtained when the offset distance is 0.1, 0.2, 0.3 and 0.4 times the wavelength. Cross-correlation is performed with the reference matrix to obtain the exact position of the phase singularity (the correlation coefficient is 1), the offset distance of the phase singularity in the horizontal direction is recorded, and the relationship between the offset distance of the phase singularity and the actual offset distance of the target is obtained, and the corresponding linear regression equation is obtained, such as Figure 5 (b) as shown.

[0055] According to this relationship, it is estimated that the horizontal offset distance of the phase singular point when the target is 32 times the wavelength from the sound vortex sound source plane and the horizontal offset distance is 0.25 times the wavelength is -16.5184 times the wavelength; the correlation diagram at this time is as follows Figure 6 As shown, the actual horizontal offset distance of the phase singularity is -16.5 times the wavelength, which is in good agreement with the above.

[0056] It is explained that in this embodiment, it is possible to detect a target at any position within 0.4 times the wavelength and at any distance from the plane of the acoustic vortex sound source and a horizontal offset distance.

Claims

1. A target detection method based on acoustic vortex spatial phase correlation analysis, characterized in that: include: When there is no target: Emit an acoustic vortex signal, and collect the signal after the acoustic vortex is formed at a certain distance from the sound source plane; Process the received acoustic vortex signal to obtain the acoustic pressure field amplitude and phase distribution diagram of the acoustic vortex at the receiving plane, and perform inspection and calibration; Observe and record the position of the phase singularity, where the position of the phase singularity reflects the center of the acoustic axis; Record the sound pressure information of the receiving plane as a reference matrix for correlation analysis; When using cross-correlation analysis, a matrix of a certain size centered on the acoustic axis, that is, centered on the phase singular point, is selected as the reference matrix; When you have a goal: The target is placed at the acoustic axis and at a certain distance from the acoustic axis, the acoustic vortex signal is emitted and received, and the received scattered sound pressure phase diagram is correlated and analyzed to extract the distribution characteristics of the phase singularity. The sound pressure information at the phase singularity point obtained without a target is used as the reference characteristic matrix for correlation analysis, and the linear relationship between the offset distance of the phase singularity point and the distance of the target from the sound axis within a certain range and the distance of the target from the sound source plane is obtained; When the target is located at any position, its scattered sound field is also correlated and analyzed to analyze the distribution characteristics of the phase singularity. The presence of the target is determined by the linear property of the phase singularity offset, and the actual position of the target is calculated based on the linear relationship.

2. The target detection method based on acoustic vortex spatial phase correlation analysis according to claim 1 is characterized in that: The acoustic vortex signal is emitted using an active acoustic vortex emission system and / or a passive acoustic vortex emission system. The active acoustic vortex emission system can be composed of a transducer array composed of multiple transducer array elements; the passive acoustic vortex emission system includes a finite aperture approximate plane wave incident on a spiral phase modulator, which generates an acoustic vortex after diffraction and propagation.

3. The target detection method based on acoustic vortex spatial phase correlation analysis according to claim 1 is characterized in that: The inspection and calibration refers to comparing the measured results with the calculated results using the angular spectrum method, or judging by referring to the spatial amplitude and phase distribution characteristics of the acoustic vortex.

4. The target detection method based on acoustic vortex spatial phase correlation analysis according to claim 1 is characterized in that: The correlation analysis, including spatial phase cross-correlation analysis and phase correlation analysis, refers to placing the target at the acoustic axis and at a certain distance offset from the acoustic axis, transmitting and receiving acoustic vortex signals, performing correlation analysis on the received scattered sound pressure phase diagram, and extracting the distribution characteristics of phase singularities; The reference characteristic matrix of the correlation analysis is the sound pressure information at the phase singular point obtained in step S2; the linear relationship between the offset distance of the phase singular point and the distance of the target from the sound axis within a certain range and the distance of the target from the sound source plane is obtained.

5. The target detection method based on acoustic vortex spatial phase correlation analysis according to claim 1 is characterized in that: The distribution characteristics of the phase singular points include the position of the phase singular points when there is only a single singular point, and the position and distribution arrangement of the phase singular points when there are multiple singular points.

Images