A rotating scanning security inspection imaging system

Abstract

The present invention relates to a rotating scanning security inspection imaging system, comprising an antenna arm and a processor; the antenna arm has a fixed rotating shaft, comprising two vertical antenna arms and an arc-shaped antenna arm connecting the two vertical antenna arms; after the processor issues a control instruction to drive the antenna arm to rotate to a preset angle through the rotating shaft, the arc-shaped antenna arm and the vertical antenna arm are controlled to start electric scanning respectively, and after completing the electric scanning of the entire antenna arm at the current angle, the antenna arm is rotated to the next angle and the electric scanning is restarted; data in the electric scanning process is sent to the processor, and the processor processes the data to obtain a three-dimensional imaging result.

Description

Technical Field

[0001] The invention relates to the field of millimeter wave security inspection imaging, and in particular to a millimeter wave security inspection device with an arc-shaped antenna arm. Background Art

[0002] In recent years, traditional security inspection methods have failed to meet the needs of the current security inspection market. Traditional metal detectors can only detect metal contraband, and are powerless against plastic bombs and ceramic knives; although X-ray security inspection equipment can detect all prohibited items, it is not the best security inspection method. Currently, millimeter wave three-dimensional imaging technology is an effective method to replace traditional security inspection methods. The current common cylindrical scanning three-dimensional imaging system uses two vertical antenna arms to rotate and scan to form an image. This device has the problem of not receiving echoes from the top of the human head, shoulders and neck. Summary of the invention

[0003] The technical problem solved by the present invention is to solve the problem that the original millimeter wave security inspection imaging device has poor sensitivity to the angle of the human head and chest, and the obtained image has missing echo information of the top of the head, neck and shoulders, thus resulting in missing security inspection image information.

[0004] The technical solution of the present invention is: a rotating scanning security inspection imaging system, including an antenna arm and a processor; the antenna arm has a fixed rotation axis, including two vertical antenna arms and an arc antenna arm connecting the two vertical antenna arms;

[0005] After the processor issues a control instruction to drive the antenna arm to rotate to a preset angle through the rotating shaft, the arc antenna arm and the vertical antenna arm are controlled to start electrical scanning respectively. After completing the electrical scanning of the entire antenna arm at the current angle, it rotates to the next angle and restarts the electrical scanning. The data during the electrical scanning process is sent to the processor, which processes the data to obtain a three-dimensional imaging result.

[0006] Preferably, the processor controls the arc antenna arm and the vertical antenna arm to start electronic scanning respectively according to the following timing sequence:

[0007] First, the arc antenna arm is controlled to start electronic scanning. A plurality of transmitting antenna units and a plurality of receiving antenna units are arranged on the arc antenna arm. The antenna units arranged on the arc antenna arm adopt a single-transmitting and single-receiving working mode in which only one transmitting antenna unit works at a time from left to right or from right to left, and only one receiving antenna unit works at a time, so that all transmitting units and all receiving units work in sequence;

[0008] After the arc antenna arm completes the electronic scanning, two vertical antenna arms arranged with a plurality of transmitting antenna units and a plurality of receiving antenna units are controlled to start electronic scanning simultaneously or separately; the vertical antenna arms adopt a transmit and receive timing sequence in which only one transmitting antenna unit and one receiving antenna unit work in each column of antenna arms from top to bottom.

[0009] Preferably, the rotation angle ranges from 90° to 140°, and the difference between adjacent rotation angles is from 0.3° to 0.7°, preferably 0.5°.

[0010] Preferably, the processing machine obtains the three-dimensional imaging result by the following method:

[0011] The data obtained by electronic scanning at each angle of the arc antenna arm and the vertical antenna arm are processed respectively, and the imaging results at each angle are coherently added to obtain the spherical imaging result and the cylindrical imaging result respectively, and the spherical imaging result and the cylindrical imaging result of the same imaging area are coherently added to obtain the final three-dimensional imaging result;

[0012] The steps for processing the data obtained by electronically scanning the vertical antenna arm are as follows:

[0013] The cylindrical antenna array echo signal obtained by electronic scanning of the current angle of the vertical antenna arm is subjected to non-uniform Fourier transform in the elevation direction, and then matched filtering is performed to obtain the processed wave number domain data;

[0014] The processed wave number domain data is interpolated in the range direction from non-uniform interpolation to uniform interpolation, and then a two-dimensional inverse Fourier transform is performed to obtain an imaging result of the vertical antenna arm at the current angle;

[0015] The imaging result of the vertical antenna arm at the current angle is used to obtain the cylindrical three-dimensional imaging result by using the angle-dimensional BP algorithm;

[0016] The steps for processing the data obtained by electronically scanning the arc antenna arm are as follows:

[0017] The electronic scanning data at the current angle of the arc antenna arm is sequentially processed through Fourier transform in the distance direction and BP imaging in the azimuth and elevation direction to obtain the arc surface three-dimensional imaging result.

[0018] Preferably, the processing machine obtains the three-dimensional imaging result by the following method:

[0019] The data obtained by electronic scanning at all angles of the arc antenna arm and the vertical antenna arm are processed respectively to obtain arc imaging results and cylindrical imaging results, and the arc imaging results and cylindrical imaging results of the same imaging area are coherently added to obtain the final three-dimensional imaging result;

[0020] The steps for processing the data obtained by electronically scanning the vertical antenna arm are as follows:

[0021] After multiplying the cylindrical antenna array echo signal obtained by electronic scanning of the vertical antenna arm by the data compensation term in the azimuth direction, a non-uniform Fourier transform is performed in the elevation direction, followed by matched filtering to obtain the processed wave number domain data;

[0022] Interpolating the processed wave number domain data in the range direction from non-uniform interpolation to uniform interpolation, and then performing a two-dimensional inverse Fourier transform to obtain an imaging result of the vertical antenna arm;

[0023] The imaging results of the vertical antenna arm are used to obtain the cylindrical imaging results by using the angle-dimensional BP algorithm; the data processing steps for the electronic scanning of the arc antenna arm are as follows:

[0024] The electronic scanning data of the arc antenna arm are sequentially processed through Fourier transform in the distance direction and BP imaging in the azimuth and elevation directions to obtain the arc surface imaging results.

[0025] Preferably, the data compensation term in the azimuth direction is rcosθ; wherein r represents the distance between the antenna array and the center of the cylinder, which is a constant; and θ is the azimuth angle coordinate in the cylindrical coordinate system.

[0026] Preferably, the matched filtering is to multiply the non-uniform Fourier transform result by a matched filtering term, and the matched filtering term is

[0027] In the formula, r represents the distance between the antenna array and the center of the cylinder, which is a constant; k is the working wave number of the system composed of the antenna arm and the processor, k y is the wave number in the y direction of the cylindrical coordinate system.

[0028] Preferably, the distance term interpolation is to obtain the processed wave number domain data after matched filtering. Interpolate to 2k.

[0029] Preferably, a row of transmitting antenna units and a row of receiving antenna units are arranged at certain intervals on the antenna arm, and the distances between the antenna units are selected to be arranged at equal intervals or unequal intervals.

[0030] Preferably, only one transmitting antenna unit and one receiving antenna unit adjacent to it work at a time, and the position difference between the two is ignored, and the positions of the two are represented by the same coordinates.

[0031] Preferably, the arc-shaped antenna arm is a spherical antenna arm, and the echo data is first multiplied by r′cosθ′ before Fourier transform in the range direction to reduce the side lobe height caused by uneven sampling; wherein r′ is the radius of the spherical antenna arm, and θ is defined as span is the angle range of the spherical antenna arm, θ is the θ coordinate of the spherical antenna arm in the spherical coordinate system; θ′ is the angle between the line connecting the antenna unit on the spherical antenna arm to the center of the spherical antenna arm and the line connecting the antenna unit in the middle of the spherical antenna arm to the center of the sphere, and

[0032] Preferably, for the imaging results of the top of the head area, the top of the head area in the cylindrical imaging results and the top of the head area in the arc imaging results are multiplied by different weights K1 and K2 respectively, and then coherently added to obtain the final three-dimensional imaging result of the top of the head area; wherein the value range of K1 is 0 to 0.2; the value range of K2 is 0.5 to 1.

[0033] The beneficial effects of the present invention compared with the prior art are:

[0034] The present invention proposes a rotating scanning 3D imaging device based on an arc-shaped antenna arm, and proposes a rotating scanning 3D imaging algorithm and a timing control method based on an arc-shaped antenna arm. The problem that the original millimeter wave security inspection imaging device has weak echo signals on the top of the head, shoulders and neck of the inspected person, poor imaging effects on the corresponding head, shoulders and neck, and even missing parts of the parts is solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 Schematic diagram of the curved antenna arm;

[0036] Figure 2 Working sequence flow chart of millimeter wave imaging device based on curved antenna arm;

[0037] Figure 3 Millimeter wave security inspection imaging flow chart. DETAILED DESCRIPTION

[0038] The present invention will be further described below in conjunction with the embodiments.

[0039] The current millimeter wave security inspection equipment uses a vertical antenna arm to scan the circumference to obtain three-dimensional echo data. The echo data obtained in this way has the problem that the echo data of the top of the human head, neck and shoulders are missing, resulting in the partial missing of the security inspection image. The present application proposes a method of arc-shaped antenna cantilever, which solves the problem that the original millimeter wave security inspection imaging device has weak echo signals on the top of the head, shoulders and neck of the inspected person, poor imaging effects on the corresponding head, shoulders and neck, and even partial missing parts. The system of the present invention includes an antenna arm and a processor; the antenna arm has a fixed rotation axis, including two vertical antenna arms and an arc-shaped antenna arm connecting the two vertical antenna arms; each antenna arm is arranged with a row of transmitting antenna units and a row of receiving antenna units according to a preset interval; the antenna arm rotates around the rotation axis to a preset angle and starts electronic scanning, and the scanning data is sent to the processor, and the processor obtains the three-dimensional imaging result. The preset interval arrangement of the antenna array can be periodic, that is, the antenna array units are arranged at non-equal intervals in each period, and the entire antenna array consists of several periods. The equivalent phase center of the non-equally spaced arrangement needs to satisfy the Nyquist sampling theorem. The equivalent phase center refers to the center of the line connecting the transmitting antenna element and the corresponding receiving antenna element.

[0040] The schematic diagram of the arc cantilever is as follows Figure 1In order to avoid mutual interference of transmitted signals and save time in scanning and acquiring signals, the transmission and reception timing is Figure 1 A row of transmitting antenna arrays and a row of receiving antenna arrays are arranged at a certain interval on the arc array 201 in the figure, and a single-transmitting and single-receiving working mode is adopted in which only one transmitting unit works at a time and only one receiving unit works at a time from left to right. The single-transmitting and single-receiving means that only one transmitting antenna unit works and only one receiving unit works. Figure 1 The vertical left antenna arm 202 and the vertical right antenna arm 203 adopt a transmission and reception timing from top to bottom, and each column of antennas has only one transmitting antenna unit and one receiving antenna unit working. The control flow chart is as follows Figure 2 As shown. When the servo motor controls the antenna arm to rotate to a fixed angle, the electrical scanning begins. First, the arc-shaped antenna arm is controlled to complete the electrical scanning from left to right, and then the vertical antenna array on the left and the antenna array on the right are controlled to complete the electrical scanning from top to bottom at the same time. The antenna arm is rotated to the next angle, and then the electrical scanning of the antenna arm at this angle is completed. Repeat the above process, complete the electrical scanning process of M angles in sequence, and obtain three-dimensional echo data. M = A / △A, where A is the rotation angle range, with a value of 90° to 140°, and △A is the difference between adjacent rotation angles of 0.3° to 0.7°, preferably 0.5°.

[0041] Compared with the original cylindrical three-dimensional imaging three-dimensional data, the three-dimensional echo data obtained by the arc antenna arm includes upper hemispherical three-dimensional data.

[0042] The imaging algorithm in the processor uses an algorithm that first multiplies the data by the compensation term rcosθ in the azimuth direction, and then performs a combination of non-uniform Fourier transform (NUFFT), BP algorithm and wave number domain algorithm. The imaging algorithm is as follows:

[0043] Assume that the position coordinates of the cylindrical antenna array are (rsinθ, y, rcosθ) and the position of the target is (x i ,y i ,z i ), the target echo signal is in the form of:

[0044]

[0045] Where r is the scanning radius of the antenna array, k is the wave number, f is the operating frequency of the system, c is the speed of light, and θ is the θ coordinate in the cylindrical coordinate system. First, multiply equation (1) by the data compensation term rcosθ in the azimuth direction to obtain:

[0046]

[0047] Perform non-uniform Fourier transform on equation (2) again and get

[0048]

[0049] Multiplying equation (3) by the matched filter term, the matched filter term is

[0050] After matched filtering, the following formula is obtained:

[0051]

[0052] where k y is the wave number in the y direction.

[0053] In formula (4), Interpolate to 2k: (i.e. interpolate the processed wavenumber domain data from non-uniform to uniform)

[0054]

[0055] Perform a two-dimensional inverse Fourier transform on equation (4) to obtain the imaging result of the YZ slice (i.e., the vertical antenna arm at this angle):

[0056]

[0057] where k c is the center wave number.

[0058] The imaging result is obtained by using the one-dimensional angle-dimensional BP algorithm for equation (5):

[0059] s′=δ(zz i )δ(xx i )δ(yy i )

[0060] The arc antenna array can realize three-dimensional imaging by using three-dimensional BP imaging algorithm, or by using Fourier transform in range direction, BP imaging algorithm in azimuth and range direction. The spherical antenna array is a special case of the arc antenna array.

[0061] Assume that the position coordinates of the spherical antenna array are (r n ,θ n ,φ n ), where it is assumed that the transmitting antenna unit and the receiving antenna unit are very close, so the same coordinates can be used to represent their positions. The position of the target is (x i ,y i ,z i ), the target echo signal is in the form of:

[0062]

[0063] The distance from the antenna array to the target is R(r n,θ n ,φ n ,x i ,y i ,z i )for:

[0064] δ i is the target scattering coefficient.

[0065] Then the three-dimensional image s′(x i ,y i ,z i ) can be expressed as:

[0066]

[0067] Echo signal s(r n ,θ n ,φ n ,t) The signal after Fourier transform in the distance direction is s(r n ,θ n ,φ n ,r′), where k is the wave number of the system. A typical form of the arc antenna arm is the spherical antenna arm. In the data processing of the spherical antenna arm, the echo data should be multiplied by r first. n cosθ′ to reduce the sidelobe height caused by uneven sampling. n is the radius of the spherical antenna arm, define θ span is the angle range of the spherical antenna arm, θ is the θ coordinate of the spherical antenna arm in the spherical coordinate system. θ′ is the angle between the line connecting the antenna unit on the spherical antenna arm to the center of the spherical antenna arm and the line connecting the antenna unit in the middle of the spherical antenna arm to the center of the sphere.

[0068]

[0069] The spherical antenna arm echo data is first multiplied by r in the echo data n cosθ′ completes the data compensation in the azimuth angle direction, and then realizes it through the distance dimension Fourier transform and two-dimensional BP algorithm Figure 2 The three-dimensional imaging results of the spherical antenna array obtained by the 201 rotation.

[0070] The cylindrical imaging result and the spherical imaging result in the same imaging area are coherently added to obtain the final three-dimensional imaging result of the arc arm rotation scanning.

[0071] The imaging algorithm flow chart is as follows: Figure 3As shown. For the cylindrical aperture, firstly, after completing data compensation in the azimuth direction, non-uniform Fourier transform is performed in the elevation direction, then matched filtering is performed, and then interpolation is performed in the distance direction. Then, two-dimensional inverse Fourier transform is performed in the elevation and distance directions, and finally, the cylindrical aperture three-dimensional imaging result is obtained by the BP imaging algorithm in the angle direction. For the spherical aperture, data compensation in the azimuth angle direction is completed first, and then the three-dimensional imaging of the hemispherical aperture is realized by Fourier transform in the distance direction and BP imaging in the azimuth elevation direction. The three-dimensional imaging results of the cylindrical aperture and the three-dimensional imaging results of the spherical aperture are summed to obtain the final arc arm rotation scanning three-dimensional imaging result. According to the different emphasis of the cylindrical aperture and the spherical aperture on the imaging area, the interference between each other can be reduced by weighting to improve the quality of the three-dimensional image. For example, the cylindrical aperture mainly images the area below the top of the head. When summing the vectors, a smaller weight K1 needs to be added to the top of the head of the cylindrical aperture three-dimensional imaging result. The arc hole diameter mainly images the area at the top of the head. Therefore, when summing the vectors, a larger weight K2 needs to be added to the three-dimensional imaging result of the top of the head; the value range of K1 is 0 to 0.2; the value range of K2 is 0.5 to 1.

[0072] The sizes of the three-dimensional imaging areas selected for the arc imaging results and the spherical imaging results must be exactly the same to facilitate the final coherent superposition imaging. In order to improve the calculation speed, for the arc imaging results, since the arc antenna array has limited contribution to the imaging of the lower half of the area, we can only calculate the upper half of the imaging area, and then expand the lower half to the same imaging area as the cylindrical imaging result after zero padding, and finally add the vectors to get the final imaging result. Similarly, for the top of the head of the person being examined, the arc antenna array plays a major role in its imaging, and the cylindrical antenna array can image the imaging area below the top of the head, and the part above the head is imaged in three dimensions through the arc antenna array. Then, after the imaging area is padded by zero padding or other operations, the vector addition is completed to get the final imaging result.

[0073] Parts not described in detail in the present invention belong to common knowledge of those skilled in the art.

Claims

1. A rotating scanning security inspection imaging system, characterized in that: The invention comprises an antenna arm and a processor; the antenna arm has a fixed rotation axis, and comprises two vertical antenna arms and an arc-shaped antenna arm connecting the two vertical antenna arms; a plurality of transmitting antenna units and a plurality of receiving antenna units are arranged on the arc-shaped antenna arm; After the processor issues a control instruction to drive the antenna arm to rotate to a preset angle through the rotating shaft, the arc antenna arm and the vertical antenna arm are controlled to start electric scanning respectively. After completing the electric scanning of the entire antenna arm at the current angle, the antenna arm is rotated to the next angle and the electric scanning is restarted. The data during the electric scanning process is sent to the processor, which processes the data to obtain a three-dimensional imaging result. The rotation angle range is 90° to 140°; the difference between adjacent rotation angles is 0.3° to 0.7°; the processor adopts an algorithm combining non-uniform Fourier transform, BP algorithm and wave number domain algorithm to obtain a three-dimensional imaging result; for cylindrical hole diameter, firstly, after completing data compensation in the azimuth direction, non-uniform Fourier transform is performed in the elevation direction, then matched filtering is performed, and then interpolation is performed in the distance direction, and then two-dimensional inverse Fourier transform is performed in the elevation and distance directions, and finally the cylindrical hole diameter three-dimensional imaging result is obtained in the angle direction through the BP imaging algorithm; for spherical hole diameter, firstly, data compensation in the azimuth angle direction is completed, and then the hemispherical hole diameter three-dimensional imaging is realized through Fourier transform in the distance direction and BP imaging in the azimuth elevation direction; the cylindrical hole diameter three-dimensional imaging result and the spherical hole diameter three-dimensional imaging result are summed to obtain the final arc arm rotation scanning three-dimensional imaging result.

2. The system according to claim 1, characterized in that: The processor controls the arc antenna arm and the vertical antenna arm to start electronic scanning respectively according to the following timing sequence: First, the arc antenna arm is controlled to start electronic scanning. The antenna units arranged on the arc antenna arm adopt a single-transmit and single-receive working mode from left to right, or from right to left, in which only one transmitting antenna unit works at a time and only one receiving antenna unit works at a time, and all transmitting units and all receiving units work in sequence; After the arc antenna arm completes the electronic scanning, two vertical antenna arms arranged with a plurality of transmitting antenna units and a plurality of receiving antenna units are controlled to start electronic scanning simultaneously or separately; the vertical antenna arms adopt a transmit and receive timing sequence in which only one transmitting antenna unit and one receiving antenna unit work in each column of antenna arms from top to bottom.

3. The system according to claim 1, characterized in that: The difference between adjacent rotation angles is 0.5°.

4. The system according to claim 1, characterized in that: The processor obtains the three-dimensional imaging result in the following manner: The data obtained by electronic scanning at each angle of the arc antenna arm and the vertical antenna arm are processed respectively, and the imaging results at each angle are coherently added to obtain the spherical imaging result and the cylindrical imaging result respectively, and the spherical imaging result and the cylindrical imaging result of the same imaging area are coherently added to obtain the final three-dimensional imaging result; The steps for processing the data obtained by electronically scanning the vertical antenna arm are as follows: The cylindrical antenna array echo signal obtained by electronic scanning of the current angle of the vertical antenna arm is subjected to non-uniform Fourier transform in the elevation direction, and then matched filtering is performed to obtain the processed wave number domain data; The processed wave number domain data is interpolated in the range direction from non-uniform interpolation to uniform interpolation, and then a two-dimensional inverse Fourier transform is performed to obtain an imaging result of the vertical antenna arm at the current angle; The imaging result of the vertical antenna arm at the current angle is used to obtain the cylindrical three-dimensional imaging result by using the angle-dimensional BP algorithm; The steps for processing the data obtained by electronically scanning the arc antenna arm are as follows: The electronic scanning data at the current angle of the arc antenna arm is sequentially processed through Fourier transform in the distance direction and BP imaging in the azimuth and elevation direction to obtain the arc surface three-dimensional imaging result.

5. The system according to claim 1, characterized in that: The processor obtains the three-dimensional imaging result in the following manner: The data obtained by electronic scanning at all angles of the arc antenna arm and the vertical antenna arm are processed respectively to obtain arc imaging results and cylindrical imaging results, and the arc imaging results and cylindrical imaging results of the same imaging area are coherently added to obtain the final three-dimensional imaging result; The steps for processing the data obtained by electronically scanning the vertical antenna arm are as follows: After the cylindrical antenna array echo signal obtained by electronic scanning of the vertical antenna arm is multiplied by the data compensation term in the azimuth direction, a non-uniform Fourier transform is performed in the elevation direction, followed by matched filtering to obtain the processed wave number domain data; Interpolating the processed wave number domain data in the range direction from non-uniform interpolation to uniform interpolation, and then performing a two-dimensional inverse Fourier transform to obtain an imaging result of the vertical antenna arm; The imaging results of the vertical antenna arm are used to obtain the cylindrical imaging results by using the angle-dimensional BP algorithm; the data processing steps for the electronic scanning of the arc antenna arm are as follows: The electronic scanning data of the arc antenna arm are sequentially processed through Fourier transform in the distance direction and BP imaging in the azimuth and elevation directions to obtain the arc surface imaging results.

6. The system according to claim 4 or 5, characterized in that: The data compensation term in the azimuth direction is rcosθ; wherein r represents the distance between the antenna array and the center of the cylinder, which is a constant; and θ is the azimuth angle coordinate in the cylindrical coordinate system.

7. The system according to claim 4 or 5, characterized in that: The matched filtering is to multiply the non-uniform Fourier transform result by the matched filtering term, and the matched filtering term is In the formula, r represents the distance between the antenna array and the center of the cylinder, which is a constant; k is the working wave number of the system composed of the antenna arm and the processor, k y is the wave number in the y direction of the cylindrical coordinate system.

8. The system according to claim 7, characterized in that: The distance interpolation is to obtain the processed wave number domain data after matched filtering. Interpolate to 2k.

9. The system according to claim 1, characterized in that: A row of transmitting antenna units and a row of receiving antenna units are arranged on the antenna arm at a certain interval, and the distances between the antenna units are selected to be arranged at equal intervals or unequal intervals.

10. The system according to claim 9, characterized in that: Only one transmitting antenna unit and one receiving antenna unit adjacent to it work at a time, and the position difference between the two is ignored, and the positions of the two are represented by the same coordinates.

11. The system according to claim 4 or 5, characterized in that: The arc antenna arm is a spherical antenna arm. Before Fourier transform in the range direction, the echo data is first multiplied by r′cosθ′ to reduce the side lobe height caused by uneven sampling; where r′ is the radius of the spherical antenna arm, and θ is defined as span is the angle range of the spherical antenna arm, θ″ is the coordinate of the spherical antenna arm in the spherical coordinate system; θ′ is the angle between the line connecting the antenna unit on the spherical antenna arm to the center of the spherical antenna arm and the line connecting the antenna unit in the middle of the spherical antenna arm to the center of the sphere, and 12. The system according to claim 5 or 6, characterized in that: For the top of the head imaging result, the top of the head in the cylindrical imaging result and the top of the head in the arc imaging result are multiplied by different weights K1 and K2 respectively, and then coherently added to obtain the final three-dimensional imaging result of the top of the head; The value range of K1 is 0~0.2; The value range of K2 is 0.5~1.

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