CN210465706U

CN210465706U - Security check equipment

Info

Publication number: CN210465706U
Application number: CN201822275787.9U
Authority: CN
Inventors: 陈志强; 游�燕; 赵自然; 马旭明; 武剑; 黄士卫
Original assignee: Tsinghua University; Nuctech Co Ltd
Current assignee: Tsinghua University; Nuctech Co Ltd
Priority date: 2018-12-29
Filing date: 2018-12-29
Publication date: 2020-05-05
Anticipated expiration: 2028-12-29

Abstract

The present disclosure provides a security inspection apparatus, the security inspection apparatus including: the device comprises a device body, wherein a detection space is arranged on the device body and used for accommodating an article to be detected; the 1D MIMO device is a one-dimensional multi-transmitting and multi-receiving device and is arranged in the detection space and used for transmitting a detection signal to an article to be detected in the detection space and receiving an echo signal from the article to be detected; and the processor is connected with the 1D MIMO device and used for reconstructing an image of the object to be detected according to the echo signals received by the ID MIMO device. The embodiment of the disclosure can improve the detection accuracy and the detection efficiency.

Description

Security check equipment

Technical Field

The disclosure relates to the technical field of safety detection, in particular to safety inspection equipment.

Background

At present, most mail inspection mechanisms for small mails such as letters and registered small bags only use manual inspection, but the manual inspection only can use factors such as simple information on a bill, the weight of packages, the names and the regions from the country and the region, and the like, and the inspection personnel can sample and open the packages for inspection according to the experience of the inspection personnel, and the manual inspection is limited by various human factors, so that the working efficiency and the inspection accuracy are low. Part of the mail inspection mechanism can also extract part of small mails to be inspected by an X-ray machine, but the machine-passing imaging effect is poor. The number of the small mails is large, the traditional inspection mode causes more missed inspection, and hidden troubles are brought to inspection and quarantine work.

Disclosure of Invention

According to an aspect of the present disclosure, there is provided a security inspection apparatus including:

the device comprises a device body, wherein a detection space is arranged on the device body and used for accommodating an article to be detected;

the 1D MIMO device is a one-dimensional multi-transmitting and multi-receiving device and is arranged in the detection space and used for transmitting a detection signal to an article to be detected in the detection space and receiving an echo signal from the article to be detected; and

and the processor is connected with the 1D MIMO device and used for reconstructing an image of the object to be detected according to the echo signals received by the ID MIMO device.

In some embodiments, the 1D MIMO device comprises:

a 1D MIMO antenna array disposed in the detection space, including a plurality of transmitting antennas arranged in a first row and a plurality of receiving antennas arranged in a second row, equivalent phase centers formed by the plurality of transmitting antennas and the plurality of antennas being arranged in a third row and being spaced apart at an equal interval of one-half of a detection signal wavelength, wherein the first, second and third rows are parallel to each other; and

and the control circuit is used for controlling the plurality of transmitting antennas to transmit the detection signals according to a preset sequence and controlling the plurality of receiving antennas to receive the echo signals.

In some embodiments, the plurality of transmitting antennas are equally spaced apart, the plurality of receiving antennas are equally spaced apart, and a distance between two adjacent transmitting antennas is an integer multiple of a distance between two adjacent receiving antennas.

In some embodiments, the plurality of transmit antennas comprises a plurality of transmit antenna groups spaced apart at equal intervals, the plurality of receive antennas are spaced apart at equal intervals, and a distance between two adjacent transmit antenna groups is greater than a distance between two adjacent receive antennas.

In some embodiments, each transmit antenna group includes two transmit antennas, and the distance between the two transmit antennas is an integer multiple of the wavelength of the detection signal.

In some embodiments, the 1D MIMO antenna array is a periodic sparse co-prime array having an array period, the plurality of transmit antennas are equally spaced, the plurality of receive antennas are equally spaced, a distance between two adjacent transmit antennas is greater than a distance between two adjacent receive antennas, and the number of transmit antennas and the number of receive antennas are co-prime within the array period.

In some embodiments, a distance between the first and second rows is less than 10% of an imaging distance of the 1D MIMO antenna array.

In some embodiments, the security check device further comprises: a translation device mounted on the apparatus body for translating the 1D MIMO antenna array along a direction perpendicular to the first, second and third rows within a plane in which the 1D MIMO antenna array is located.

In some embodiments, the security check device further comprises: and the lifting device is arranged on the equipment body and used for controlling the 1D MIMO antenna array to be far away from or close to the object to be detected to move.

In some embodiments, the security check device further comprises: the back plate is arranged in the detection space and located below the object to be detected and used for reflecting a detection signal which penetrates through the object to be detected to the back plate back to the 1D MIMO device.

In some embodiments, the backing plate comprises a metal plate or a plate with a metal coating.

In some embodiments, the detection space is configured as a groove structure, and has a first sidewall and a second sidewall parallel to each other, and a third sidewall perpendicular to the first sidewall and the second sidewall, the 1D MIMO device is located on the first sidewall, and the second sidewall is used for placing an object to be tested.

In some embodiments, the security check device further comprises: and the conveying device is arranged to penetrate through the detection space and is used for conveying the object to be detected so as to enable the object to be detected to enter or leave the detection space.

In some embodiments, the security check device further comprises: and the display device is connected with the processor and used for presenting the reconstructed image of the object to be measured to a user.

In some embodiments, the security inspection equipment further comprises an alarm device, and the processor is further configured to determine whether the object to be detected may contain dangerous goods based on a preset standard according to the reconstructed image of the object to be detected, and if so, control the alarm device to alarm.

In some embodiments, the detection signal is a millimeter wave.

According to another aspect of the present disclosure, there is provided a control method of the security inspection apparatus, including:

controlling the 1D MIMO device to send a detection signal to an article to be detected and receive an echo signal from the article to be detected; and

and reconstructing an image of the object to be detected according to the received echo signals.

In some embodiments, the reconstructing the image of the item under test includes reconstructing the image of the item under test based on a holographic reconstruction algorithm or a back projection algorithm.

Drawings

Fig. 1A shows a schematic structural diagram of a security inspection apparatus according to an embodiment of the present disclosure.

FIG. 1B shows a schematic circuit diagram of the security device of FIG. 1A.

Fig. 2A shows a schematic structural diagram of a security inspection apparatus according to another embodiment of the present disclosure.

Fig. 2B shows a schematic circuit diagram of the security device of fig. 2A.

Fig. 3A shows a schematic structural diagram of a security inspection apparatus according to another embodiment of the present disclosure.

Fig. 3B shows a schematic circuit diagram of the security device of fig. 3A.

Fig. 4A shows a schematic structural diagram of a security inspection apparatus according to another embodiment of the present disclosure.

Fig. 4B shows a schematic circuit diagram of the security device of fig. 4A.

Fig. 5 shows a schematic diagram of the operation of a 1D MIMO antenna array.

Fig. 6A, 6B show structural schematic diagrams of a 1D MIMO antenna array according to an embodiment of the present disclosure.

Fig. 7A and 7B are schematic structural diagrams of a 1D MIMO antenna array according to another embodiment of the present disclosure.

Fig. 8A and 8B are schematic structural diagrams of a 1D MIMO antenna array according to another embodiment of the present disclosure.

Fig. 9A and 9B are schematic structural diagrams of a 1D MIMO antenna array according to another embodiment of the present disclosure.

Fig. 10A and 10B are schematic structural diagrams of a 1D MIMO antenna array according to another embodiment of the present disclosure.

Fig. 11 shows a schematic structural diagram of a 1D MIMO antenna array according to another embodiment of the present disclosure.

Fig. 12 shows a schematic flowchart of a control method of a security inspection apparatus according to an embodiment of the present disclosure.

Fig. 13 shows a schematic flowchart of a control method of a security inspection apparatus according to another embodiment of the present disclosure.

Detailed Description

While the present disclosure will be fully described with reference to the accompanying drawings, which contain preferred embodiments of the disclosure, it should be understood before this description that one of ordinary skill in the art can modify the disclosure described herein while obtaining the technical effects of the present disclosure. Therefore, it should be understood that the foregoing description is a broad disclosure directed to persons of ordinary skill in the art, and that there is no intent to limit the exemplary embodiments described in this disclosure.

Furthermore, in the following detailed description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the disclosure. It may be evident, however, that one or more embodiments may be practiced without these specific details. In other instances, well-known structures and devices are shown in schematic form in order to simplify the drawing.

Fig. 1A shows a schematic structural diagram of a security inspection apparatus according to an embodiment of the present disclosure. FIG. 1B shows a schematic circuit diagram of the security device of FIG. 1A. As shown in fig. 1A and 1B (hereinafter, referred to as fig. 1), the security inspection apparatus 100 includes an apparatus body 10, a one-dimensional Multiple-Input Multiple-Output (1D MIMO, 1-dimensional Multiple-Input Multiple-Output) device 20, and a processor 30.

The equipment body 10 is provided with a detection space 11, and the detection space 11 is used for accommodating an object 12 to be detected. The detection space 11 may be provided in a groove structure as shown in fig. 1A, having first and

second sidewalls

111 and 112 parallel to each other and a third sidewall 113 perpendicular to the first and

second sidewalls

111 and 112. The first sidewall 111 may have the 1D MIMO device 20 mounted thereon, and the second sidewall 112 may have the object 12 placed thereon. In the present embodiment, the security inspection apparatus 100 can be applied to small mail pieces such as letters and registered small bags, and the structure and size of the inspection space 11 can be set according to the shape and size of the small mail pieces, for example, the distance between the first side wall 111 and the second side wall 112 can be set to be in the range of 20cm-100cm, for example, about 30cm, so that most of the small mail pieces at present can be accommodated substantially, while ensuring a sufficient imaging distance between the 1D MIMO device 20 and the object 12 to be inspected. However, the embodiments of the present disclosure are not limited thereto, and the structure and size of the apparatus body 10 and the detection space 11 may be selected according to needs, for example, the detection space 11 may be provided in a tunnel structure, a combined structure of a tray and a ceiling, or any other suitable structure, and the size of the detection space 11 may be adjusted according to the type of the object to be detected.

The 1D MIMO device 20 is disposed in the detection space 11, and is configured to transmit a detection signal to the object to be detected 12 and receive an echo signal from the object to be detected. The 1D MIMO device 20 includes a 1D MIMO antenna array 21 and a control circuit 22. The 1D MIMO antenna array 21 is disposed in the detection space 10, for example, on the first sidewall 111 of the detection space 10 in the example of fig. 1A, so as to transmit a detection signal to the opposite object 12 to be detected, and an echo signal generated after the detection signal passes through the object 12 to be detected is received by the 1D MIMO antenna array 21. The control circuit 22 may be located in the device body 10, or may be disposed at another suitable position as needed, and the control circuit 22 is connected to the 1D MIMO antenna array 21 to control the 1D MIMO antenna array 21 to transmit the detection signal and receive the echo signal. The detection signal may be an electromagnetic wave, such as a millimeter wave, specifically a millimeter wave terahertz wave. In some embodiments, the 1D MIMO device 20 may be implemented by a 76-81GHz chip, which has the advantages of high array integration level, low cost, and the like.

The processor 30 is connected to the 1D MIMO device 20 and is configured to reconstruct an image of the object to be measured according to the received echo signals. After a detection signal (for example, millimeter waves) transmitted to the object 12 to be tested by the transmitting antenna in the 1D MIMO antenna array 21 reaches the object 12 to be tested, the detection signal may penetrate through contents in the object 12 to be tested, so as to generate an echo signal, and the echo signal is received by the receiving antenna in the 1D MIMO antenna array 21. Processor 30 may reconstruct an image of the item under test by processing the received echo signals, the image including information about the contents of item under test 12. The staff can judge whether dangerous goods are possibly contained according to the shape, the density and the like of the objects in the image, so that unpacking inspection is further performed, and the detection efficiency and the detection accuracy are improved. For example, the object 12 to be tested in fig. 1A is shown as a letter containing prohibited seeds, after the electromagnetic wave scanning of the object 12 to be tested is performed by the 1d mimo device 20 and the image reconstruction is performed by the processor 30, the reconstructed image is displayed on the display device 50, and information related to the content in the letter, such as contour, density, etc., is shown in the image, and the staff member can determine whether the letter is prohibited seeds.

In some embodiments, the security inspection apparatus 100 may further include a back plate 40, the back plate 40 being disposed in the inspection space 11 below the object 12 to be inspected, including but not limited to a metal plate or a plate with a metal coating, including but not limited to aluminum. After the detection signal reaches the object to be detected 12, a part of the detection signal may pass through the object to be detected 12, which is particularly obvious in the case of using millimeter waves as the detection signal, for example, by providing the back plate 40, the detection signal that passes through the object to be detected 12 and reaches the back plate 30 can be reflected back to the 1D MIMO device 20 again, so that the echo signal from the object to be detected 12 is enhanced, and the quality of the reconstructed image is improved.

In some embodiments, the security check device 100 may further include a display device 50. A display device 50 is connected to the processor 30 for presenting the reconstructed image of the item under test to a user. The display device 50 may include any suitable type of display to enable an inspector to view the reconstructed image of the item under test through the display to determine whether the item under test may contain hazardous materials.

In some embodiments, the processor 30 may further determine whether the object to be tested may contain dangerous goods based on a preset standard according to the reconstructed image of the object to be tested after reconstructing the image. For example, a characteristic template of dangerous goods such as forbidden seeds, drugs, and external harmful organisms may be stored in advance, whether the object to be tested may contain dangerous goods may be determined by comparing the reconstructed image with the template, and the type and amount of dangerous goods that may be contained, the probability that the dangerous goods may be contained, and the like may be further determined. After detecting that the object 12 to be tested contains a dangerous article, the processor 30 may control the display device 50 to present prompt information, for example, the prompt information may indicate the type of the dangerous article, the probability of containing the dangerous article, and the like, so as to help the staff make further judgment and, if necessary, open a package for inspection.

In addition, the security inspection apparatus 100 may further include an alarm device 60, and the processor 30 may control the alarm device 60 to alarm after detecting that the object 12 to be tested may contain dangerous goods. The alarm device 60 may be implemented in various forms including, but not limited to, devices that sound an alarm such as a speaker, vibrator, alarm, etc., by audio, vibration, and various other means. An alarm level may also be set, for example, when the probability of containing a dangerous article is low, an alarm may be given by a lower volume of sound or a weaker vibration, and when the probability of containing a dangerous article is high, an alarm may be given by a higher volume of sound or a stronger vibration.

In fig. 1, the security inspection apparatus 100 may further include a translation device 70, where the translation device 70 is installed on the apparatus body 10, and may translate the 1D MIMO antenna array 21 in the plane where the 1D MIMO antenna array 21 is located, for example, the translation device 90 may translate the 1D MIMO antenna array 21 according to a preset path, so that each time the 1D MIMO antenna array 21 completes a scanning task (i.e., each time all transmitting antennas in the 1D MIMO antenna array 21 complete transmission of a detection signal and a corresponding receiving antenna completes reception of an echo signal), the 1D MIMO antenna array 21 is translated to a next position, so that the 1D MIMO antenna array 21 restarts a next scanning round, and so on, so that a scanning effect of one 1D MIMO antenna array 21 on multiple 1D MIMO antenna arrays 21 can be utilized to complete scanning of a two-dimensional plane, thereby providing a more comprehensive scan result. This will be described in further detail below.

The translation device 70 may be implemented in various forms, for example as a manual translation device and/or an automatic translation device. For example, the translation device 70 may include, as shown in fig. 1A, a translation rail on the apparatus body 10 (e.g., the first sidewall 111) on which the security inspection apparatus 100 is provided, the 1D MIMO antenna array 21 being mounted on and slidable along the translation rail, in which case the 1D MIMO antenna array 21 may be moved along the translation rail by a manual manner. In another example, the translation device 70 may further include a translation controller, the translation controller may move the 1D MIMO antenna array 21 along the translation track according to a preset standard, for example, move the 1D MIMO antenna array 21 by a preset distance at a preset time, and the translation controller may also translate the 1D MIMO antenna array 21 along the translation track under the control of the processor 30 as shown in fig. 1B, for example, the processor 30 controls the translation controller to translate the 1D MIMO antenna array 21 by a preset distance each time the 1D MIMO antenna array 21 completes scanning.

Fig. 2A shows a schematic structural diagram of a security inspection apparatus according to another embodiment of the present disclosure. Fig. 2B shows a schematic circuit diagram of the security device of fig. 2A. The security apparatus of fig. 2A and 2B (hereinafter referred to as fig. 2) is similar to the security apparatus 100 of fig. 1, except that at least the security apparatus 200 of fig. 2 further includes a lifting device 80. For the sake of brevity, the following mainly describes the distinctive parts in detail.

As shown in fig. 2A and 2B, the lifting device 80 may be installed on the apparatus body 10, and may control the array of 1D MIMO antennas 21 to move away from or close to the object 12 to be measured, so as to adjust a distance between the 1D MIMO antennas 21 and the object to be measured, that is, an imaging distance.

The lifting device 80 may be implemented in various forms, for example as a manual and/or automatic lifting device. As an example, the lifting device 80 may include a plurality of position limiting parts arranged in a direction perpendicular to the object to be measured, and the distance between the 1D MIMO antenna 21 and the object to be measured may be adjusted by mounting the translation device 70 or the 1D MIMO antenna 21 on different position limiting parts. As another example, the lifting device 80 may include a lifting rail extending perpendicular to the direction of the object to be measured, the 1D MIMO antenna 21 may be designed to be movable on and fixed to the lifting rail in addition to the translation rail, or the translation device 70 may be designed to be movable along and fixed to the lifting rail, and the 1D MIMO antenna 21 may be manually moved along the lifting rail and fixed at a desired position, thereby adjusting the imaging distance. As another example, the security inspection apparatus 100 may include a plurality of translation devices 70 arranged in a direction perpendicular to the object to be measured, the elevating device 80 may be connected to and fix the plurality of translation devices, and the 1D MIMO antenna 21 may be designed to be detachable from one translation device 70 and mounted to another translation device 70, thereby adjusting the imaging distance by mounting the 1D MIMO antenna 21 on a different translation device 70.

In the example of fig. 2B, the lifting device 80 may be designed to include a lifting controller that may adjust a lifting distance according to a preset standard in addition to the above-described lifting rail, or may move the 1D MIMO antenna array 21 along the lifting rail under the control of the processor 30 as shown in fig. 2B. For example, a sensor may be utilized to measure the height of the item 12 to be tested, and the processor 30 controls the elevator 80 to adjust the imaging distance based on the height of the item 12 to be tested. For example, when the distance between the 1D MIMO antenna array 21 and the object 12 is smaller than the preset value, the processor 30 controls the lifting controller to move the 1D MIMO antenna array 21 away from the object 12, and when the distance is larger than the preset value, the 1D MIMO antenna array 21 is moved close to the object 12. In some embodiments, the imaging distance may also be adjusted as follows: when the height of the object to be detected falls within the first threshold range, judging that the object to be detected belongs to a letter class object, and adjusting the distance between the 1D MIMO antenna array 21 and the object to be detected 12 to enable the imaging distance to be 10cm-40 cm; and when the height of the object to be detected falls within the second threshold range, judging that the object to be detected belongs to the small express package, and adjusting the distance between the 1D MIMO antenna array 21 and the object to be detected 12 to enable the imaging distance to be 20-100 cm.

Fig. 3A shows a schematic structural diagram of a security inspection apparatus according to another embodiment of the present disclosure. Fig. 3B shows a schematic circuit diagram of the security device of fig. 3A. The security apparatus 300 of fig. 3A and 3B (hereinafter referred to as fig. 3) is similar to the security apparatus 100 of fig. 1, except at least that the security apparatus 300 of fig. 3 further includes a conveyor 90. For the sake of brevity, the following mainly describes the distinctive parts in detail.

The conveyor 90 passes through the inspection space 11, and can convey the object to be inspected to enter or leave the inspection space 11. For example, the conveying device 90 may include a conveying belt 91 and a conveying control unit 92 (not shown), and the conveying control unit 92 may control the conveying belt 91 to convey according to a preset manner, or may control the conveying belt 91 to convey under the control of the processor 30 as shown in fig. 3B, so that the time for the to-be-tested object 12 to stay under the 1D MIMO device 20 allows the 1D MIMO device 20 to complete at least one scan. The conveying manner may be selected according to needs, and for example, may be set to convey at a preset speed, may be set to stop for a preset time each time the object 12 to be tested is conveyed below the 1D MIMO device 20, and the like.

As an example, the 1D MIMO antenna array 21 may be controlled to start acquiring data when the object 12 to be measured enters the imaging area along with the conveyor belt 91, and the 1D MIMO antenna array 21 may be controlled to stop acquiring data when the object to be measured leaves the imaging area.

Assuming that the moving speed of the conveyor belt 91 is v and the time interval of data acquisition is t, the following relationship can be satisfied: vt ═ λ_c/2

Wherein λ is_cMay be the center operating wavelength of the 1D MIMO antenna array 21, e.g., the wavelength corresponding to the center frequency of the detection signal.

The security inspection apparatus 300 may not include the translation device 70 if the transmission device 90 is included, as long as the object 12 to be measured can be translated with respect to the 1D MIMO device 20. In the process of translating the object 12 to be measured relative to the 1D MIMO device 20, the 1D MIMO device 20 may complete multiple scans, so as to complete scanning of a two-dimensional plane by using a one-dimensional antenna array.

Fig. 4A shows a schematic structural diagram of a security inspection apparatus according to another embodiment of the present disclosure. Fig. 4B shows a schematic circuit diagram of the security device of fig. 4A. Security apparatus 400 of fig. 4A and 4B (hereinafter referred to as fig. 4) is similar to security apparatus 300 of fig. 3, except at least that security apparatus 300 of fig. 4 further includes a lifting device 80. For the sake of brevity, the following mainly describes the distinctive parts in detail.

Similar to the above, the lifting device 80 may be installed on the apparatus body 10, and may control the array of 1D MIMO antennas 21 to move away from or close to the object 12 to be measured, so as to adjust a distance between the 1D MIMO antennas 21 and the object to be measured, i.e., an imaging distance.

The lifting device 80 may be implemented in various forms, for example as a manual and/or automatic lifting device. As an example, the lifting device 80 may include a plurality of position limiting parts arranged in a direction perpendicular to the object to be measured, and the distance between the 1D MIMO antenna 21 and the object to be measured may be adjusted by mounting the 1D MIMO antenna 21 on different position limiting parts. As another example, the lifting device 80 may include a lifting rail extending perpendicular to the direction of the object to be measured, the 1D MIMO antenna 21 may be designed to be movable and fixed on the lifting rail, and the 1D MIMO antenna 21 may be manually moved and fixed at a desired position along the lifting rail, thereby adjusting the imaging distance. In the example of fig. 4B, the lifting device 80 may be designed to include a lifting controller that may adjust the imaging distance according to a preset standard in addition to the above-described lifting rail, and may also move the 1D MIMO antenna array 21 along the lifting rail under the control of the processor 30 as shown in fig. 1B. For example, a sensor may be utilized to measure the height of the item 12 to be tested, and the processor 30 controls the elevator 80 to adjust the imaging distance based on the height of the item 12 to be tested. For example, when the distance between the 1D MIMO antenna array 21 and the object 12 is smaller than the preset value, the processor 30 controls the lifting controller to move the 1D MIMO antenna array 21 away from the object 12, and when the distance is larger than the preset value, the 1D MIMO antenna array 21 is moved close to the object 12. In some embodiments, the imaging distance may also be adjusted as follows: when the height of the object to be detected falls within the first threshold range, judging that the object to be detected belongs to a letter class object, and adjusting the distance between the 1D MIMO antenna array 21 and the object to be detected 12 to enable the imaging distance to be 10cm-40 cm; and when the height of the object to be detected falls within the second threshold range, judging that the object to be detected belongs to the small express package, and adjusting the distance between the 1D MIMO antenna array 21 and the object to be detected 12 to enable the imaging distance to be 20-100 cm.

A 1D MIMO antenna array according to an embodiment of the present disclosure is described below with reference to fig. 5 to 10.

For clarity of explanation, the working principle of a 1D MIMO antenna array is first described with reference to fig. 5. Fig. 5 shows a schematic diagram of the operation of a 1d mimo antenna array. In FIG. 5, X-A Y coordinate system, a plurality of transceiving combinations set on the x axis, each transceiving combination comprising a transmitting antenna and a receiving antenna, and a_r(x_t，y_r) And A_r(x_r，y_r) Respectively representing a transmitting antenna and a receiving antenna of a transceiving combination, wherein x_tAnd y_tDenotes the coordinates, x, of the transmitting antenna_rAnd y_rIndicating the coordinates of the receiving antenna.

I(x_n，y_n) Representing a point object within the object region, defining I (x)_n，y_n) And a transmitting antenna A_tA distance of R_t，n，I(x_n，y_n) And a receiving antenna A_rAt a distance of R_r，n，R₀Is the vertical distance between the center of the target area and the 1D MIMO antenna array, i.e., the imaging distance.

The echo signal after scattering by the point target can be expressed as

S_n(x_t，y_t；x_r，y_r；k_ω)＝σ(x_n，y_n)exp[-jK_ω(R_t，n+R_r，n)]

Where σ (x, y) is the scattering coefficient of the object to be measured, K_ωJ is the spatial frequency of the frequency stepped signal and is in units of imaginary numbers.

For a transceiving combination A_tA_rThe echo signals received from the target area are:

where D is the imaging area.

The equivalent location of the transmitted and received signals may be by dayThe phase center of the line indicates that the location is the physical center of two independent antennas or apertures. In a multiple-input multiple-output system, where a transmitting antenna corresponds to multiple receiving antennas, and where the receiving antennas and the transmitting antennas are not co-located, this spatially separated system of transmitting and receiving antennas can be modeled using a virtual system in which a virtual location is added between each set of transmitting and receiving antennas, this location being referred to as the equivalent phase center. The echo data collected by the transmitting-receiving antenna combination can be equivalent to an equivalent phase center A thereof_e(x_e,y_e) The position of the antenna is the echo collected by the self-transmitting and self-receiving antenna. In this embodiment, a midpoint of a connection line between each transmitting antenna and a corresponding receiving antenna may be taken as an equivalent phase center, and a position of the equivalent phase center may be represented as:

using the principle of equivalent phase centers, the equivalent echo signal can be expressed as:

the structure of a 1D MIMO array according to an embodiment of the present disclosure is described below with reference to fig. 6 to 10. A 1D MIMO array according to an embodiment of the present disclosure may include a plurality of transmission antennas arranged in a first row and a plurality of reception antennas arranged in a second row, equivalent phase centers formed by the plurality of transmission antennas and the plurality of antennas being arranged in a third row and spaced apart at an equal interval of half a wavelength of a detection signal, wherein the first, second, and third rows are parallel to each other. The length of the 1D MIMO array according to the embodiments of the present disclosure may be determined according to the size of the object, for example, the length of the 1D MIMO array may be in the range of 30-50 cm; the translatable distance (e.g., the distance of mechanical scanning or movement) of the 1D MIMO array may be determined according to the size of the object, for example, in the range of 30-50 cm. The vertical distance dtr between the first row of transmit antennas and the second row of receive antennas in a 1D MIMO array according to an embodiment of the present disclosure may be set to dtr/z0 < 10%, where z0 is the imaging distance.

Fig. 6A and 6B (collectively fig. 6) show schematic structural diagrams of a 1D MIMO antenna array according to an embodiment of the present disclosure, where a square represents a transmitting antenna T, a circle represents a receiving antenna R, and a triangle represents an equivalent phase center.

As shown in fig. 6A, the 1D MIMO antenna array includes a plurality of transmission antennas T arranged in a first row and a plurality of reception antennas R arranged in a second row, one transmission antenna corresponding to 8 reception antennas. The plurality of transmitting antennas T are equally spaced apart by a distance of 4 λ, the plurality of receiving antennas R are equally spaced apart by a distance λ, the transmitting antenna T at the head of the first row is aligned with the receiving antenna R at the head of the second row such that the line therebetween is perpendicular to the direction of the first row and the second row, the second transmitting antenna T of the first row is aligned with the fifth transmitting antenna R of the second row, and so on. The equivalent phase centers are arranged in a third row, located between the first and second rows, equally spaced apart by a distance λ/2. According to the embodiments of the present disclosure, the distance separating the group of transmitting antennas in the first row from the group of receiving antennas in the second row may be arbitrary, however, it is advantageous that the distance separating the group of transmitting antennas in the first row from the group of receiving antennas in the second row is as small as possible, because the equivalent phase center condition is not satisfied due to the too large distance; however, in practical applications, too short a distance causes problems of difficult implementation, crosstalk and spatial arrangement. In one embodiment, the set of transmit antennas in the first row is spaced apart from the set of receive antennas in the second row by less than 10% of the imaging distance.

As an example, the length of the 1D MIMO antenna array of fig. 6A may be 30cm, the length of the mechanical scan (i.e., the maximum distance that can be translated) may be 40cm, the number of transmit antennas may be Nt-20, the number of receive antennas may be Nr-76, and the number of steps of the mechanical scan may be 201.

When the antenna works, the first transmitting antenna performs difference on the front 4 receiving antennas; the second to Nt-1 transmitting antennas are respectively corresponding to 8 receiving antennas for difference; and the Nt transmitting antenna performs difference on the last 4 receiving antennas, so that equivalent phase center distribution with equal interval of 0.5 lambda is obtained, and finally equivalent phase center distribution meeting the Nyquist sampling law requirement is obtained. Each transmitting antenna can be switched in turn to complete one scan. The antenna array is then translated in the array orthogonal direction (i.e., a synthetic aperture scan is performed) to complete the scan of the two-dimensional aperture. Based on the scanning result, the fast reconstruction can be realized according to the synthetic aperture holographic algorithm based on the fast Fourier change, and the imaging test is completed.

The 1D MIMO antenna array of fig. 6B is similar to fig. 6A, except at least that the first and second rows are staggered in head in fig. 6B. For simplicity of description, the following mainly describes the difference in detail. As shown in fig. 6B, the transmitting antenna T at the head of the first row and the receiving antenna R at the head of the second row are staggered so that the connecting line of the two antennas is not perpendicular to the directions of the first row and the second row, the second transmitting antenna T of the first row is aligned with the fourth transmitting antenna R of the second row so that the connecting line of the two antennas is perpendicular to the directions of the first row and the second row, and so on, the last transmitting antenna T of the first row is aligned with the last receiving antenna R of the second row. In fig. 6B, the transmitting antenna T at the head of the first row is offset from the receiving antenna at the head of the second row by a distance λ, however, the embodiment of the present disclosure is not limited thereto, and the distance may be set as needed, and may be any value in the range of [ -5 λ, 5 λ ], for example.

The 1D MIMO antenna array of fig. 6 may be designed as follows: the method comprises the steps of determining the number N and the interval d of equivalent units required according to imaging index parameters such as working frequency (wavelength lambda is long, antenna array length, namely antenna aperture Lap and the like), arranging actual antenna units according to a transceiving split mode, wherein transmitting antennas/receiving antennas are respectively distributed according to two parallel straight lines, the interval is dtr, then designing the arrangement of the transmitting antenna units, the total number Nt of the transmitting antennas is any number and is determined by the antenna aperture Lap, the interval of each transmitting antenna is 4 lambda, and then designing the arrangement of the receiving antenna units, the total number Nr of the receiving antennas is any number, the receiving antennas are distributed at equal intervals, and the interval is lambda.

As an example, the number and the spacing of the equivalent units required can be determined according to the imaging index parameter requirements, such as imaging resolution, side lobe level, and the like, that is, the distribution of the equivalent virtual array can be determined. The spacing of the equivalent array elements needs to be at most slightly greater than or equal to half the operating wavelength. Then, the actual antenna units are arranged according to a receiving and transmitting split mode, the transmitting antennas/receiving antennas are respectively distributed according to two parallel straight lines, the distance between the straight lines can be any value, but is as small as possible (the lambda receiving antennas can be respectively arranged according to the two parallel straight lines), the actual design antenna unit size and the array size design requirement are reasonably selected, and the array size is designed to be 1 m. Then, the arrangement of the transmitting antennas is designed, and the total number of the transmitting antennas is 4 spreading. Next, the arrangement of the receiving antenna units is designed, the specific number is determined by factors such as imaging resolution, imaging range, and the like, and the distance between each receiving antenna is λ.

Fig. 7A and 7B (collectively fig. 7) are schematic diagrams illustrating a structure of a 1D MIMO antenna array according to another embodiment of the present disclosure, where a first transmitting antenna and a first receiving antenna in fig. 7A are aligned, and the first transmitting antenna and the first receiving antenna in fig. 7B are staggered by λ. The 1D MIMO antenna array of fig. 7 is similar to that of fig. 6, except that at least the distance between adjacent transmit antennas T is 3 λ, and for simplicity of description, the following description mainly deals with the difference. In the example of fig. 7, the transmit antennas T are equally spaced apart by a distance 3 λ and the receive antennas are equally spaced apart by a distance λ, one transmit antenna for each of the 6 receive antennas. As an example, the length of the 1D MIMO antenna array of fig. 7 may be 30cm, the length of the mechanical scan (i.e., the maximum distance that can be translated) may be 40cm, the number of transmit antennas may be Nt-20, the number of receive antennas may be Nr-76, and the number of steps of the mechanical scan may be 201.

Fig. 8A and 8B (collectively fig. 8) are schematic diagrams illustrating a structure of a 1D MIMO antenna array according to another embodiment of the present disclosure, where a first transmitting antenna and a first receiving antenna in fig. 8A are aligned, and the first transmitting antenna and the first receiving antenna in fig. 8B are staggered by a λ. The 1D MIMO antenna array of fig. 8 is similar to that of fig. 6, except at least that the distance between adjacent transmit antennas T is 2 λ. The 1D MIMO antenna array of fig. 8 is similar to that of fig. 6, except that at least the distance between adjacent transmit antennas T is 2 λ, and for simplicity of description, the following description mainly deals with the difference. In the example of fig. 8, the transmit antennas T are equally spaced apart by a distance 2 λ and the receive antennas are equally spaced apart by a distance λ, one transmit antenna for each of the 4 receive antennas. As an example, the length of the 1d mimo antenna array of fig. 8 may be 30cm, the length of the mechanical scan (i.e., the maximum distance that can be translated) may be 40cm, the number of transmit antennas may be Nt-39, the number of receive antennas may be Nr-76, and the number of steps of the mechanical scan may be 201.

Fig. 9A and 9B (collectively fig. 9) show schematic structural diagrams of a 1D MIMO antenna array according to another embodiment of the present disclosure, where a first transmitting antenna and a first receiving antenna are aligned in fig. 9A, and the first transmitting antenna and the first receiving antenna are staggered by one λ in fig. 9B. The 1D MIMO antenna array of fig. 9 is similar to that of fig. 6, except at least that the distance between adjacent transmit antennas T is 5 λ. For simplicity of description, the following description mainly describes the difference portion. In the example of fig. 8, the transmit antennas T are equally spaced apart by a distance 2 λ and the receive antennas are equally spaced apart by a distance λ, one transmit antenna for each of the 10 receive antennas. As an example, the length of the 1D MIMO antenna array of fig. 9 may be 30cm, the length of the mechanical scan (i.e., the maximum distance that can be translated) may be 40cm, the number of transmit antennas may be Nt-16, the number of receive antennas may be Nr-76, and the number of steps of the mechanical scan may be 201.

In the above embodiments, at least one transmitting antenna and at least one receiving antenna are aligned such that a line between the two is perpendicular to the direction of the row of the group of transmitting antennas or the group of receiving antennas, however, embodiments of the present disclosure are not limited thereto. In another embodiment, a line connecting any one of the transmitting antennas and any one of the receiving antennas is not perpendicular to the row direction of the group of transmitting antennas or the group of receiving antennas. This may be advantageous in that the space between the transmit antenna and the nearby receive antenna may be efficiently utilized without bringing a pair of transmit antennas too close to the receive antenna.

Fig. 10A and 10B (collectively fig. 10) show structural schematic diagrams of a 1D MIMO antenna array according to another embodiment of the present disclosure. The 1D MIMO array of fig. 10 is similar to fig. 6-9 described above, except at least that the transmit antennas of fig. 10 are grouped into groups, one group of transmit antennas corresponding to one group of receive antennas. For clarity of description, the following description mainly describes the difference portion.

As shown in fig. 10A, one transmit antenna corresponds to 8 receive antennas, receive antennas r1, r 2.., r 8.. are equally spaced apart by a distance of 2 λ, the transmit antennas are equally spaced in a group of two, specifically, transmit antennas t1 and t2 are in a group, t3 and t4 are in a group, and so on. The spacing between the groups of transmit antennas (e.g., the distance between transmit antennas t1 and t 3) is 8 λ, the spacing between two transmit antennas in a group (e.g., the distance between t1 and t2, the distance between t3 and t4) is λ, and the equivalent phase centers are equally spaced by a distance of λ/2. Two transmit antennas (e.g., t3 and t4) in the same group both correspond to the same group of receive antennas (e.g., transmit antenna t3 corresponds to receive antennas r1 through r8, and transmit antenna t4 also corresponds to receive antennas r1 through r 8). In fig. 10A, the length of the 1D MIMO antenna array may be 30cm, the length of the mechanical scan (i.e., the maximum distance that can be translated) may be 40cm, the number of transmit antennas may be Nt-22, the number of receive antennas may be Nr-76, and the number of steps of the mechanical scan may be 201.

The 1D MIMO antenna array of fig. 10B is similar to that of fig. 10A, except at least for the spacing of the transmit and receive antennas. For simplicity of description, the following description mainly describes the difference portion. As shown in fig. 10B, the receive antennas r1, r 2.,. r 8.. are equally spaced apart by a distance 2 λ, the transmit antennas are equally spaced in groups of two, specifically the transmit antennas t1 and t2, t3 and t4, and so on. The spacing between the groups of transmit antennas (e.g., the distance between transmit antennas t1 and t 3) is 6.5 λ, the spacing between two transmit antennas in a group (e.g., the distance between t1 and t2, the distance between t3 and t4) is 1.5 λ, and the distance between equivalent phase centers is λ/2 (excluding beginning and end). Two transmit antennas (e.g., t1 and t2) in the same group both correspond to the same group of receive antennas (e.g., transmit antenna t1 corresponds to receive antennas r1 through r8, and transmit antenna t2 also corresponds to receive antennas r1 through r 8). In fig. 10B, one transmitting antenna corresponds to 8 receiving antennas, the length of the 1D MIMO antenna array may be 30cm, the length of the mechanical scanning (i.e., the maximum distance that can be translated) may be 40cm, the number of transmitting antennas Nt is 22, the number of receiving antennas Nr is 76, and the number of steps of the mechanical scanning is 201.

As shown in fig. 10A and 10B, since the two transmitting antennas in the same group both correspond to the same group of receiving antennas, so that the equivalent phase centers of the two transmitting antennas in the same group are alternately arranged, the problem of the crossing can be solved by sequentially correcting the data before reconstruction. For example, electromagnetic wave signals transmitted by a transmitting antenna may be encoded such that signals received by a receiving antenna intended to receive the signals thereof may be identified and decoded for use in generating an image. A method of correcting the sequence will be described below with reference to fig. 10B.

As shown in fig. 10B, each transmitting antenna corresponds to the equivalent phase center number (i.e., the number from left to right in the figure) generated by the antenna as follows:

the transmit antenna t1 corresponds to the equivalent phase centers 1, 2, 4, 6, 8, 10, 12, 14;

the transmitting antenna t2 corresponds to the equivalent phase centers 3, 5, 7, 9, 11, 13, 15, 17;

the transmit antenna t3 corresponds to the equivalent phase centers 16, 18, 20, 22, 24, 26, 28, 30;

the transmit antenna t4 corresponds to the equivalent phase centers 19, 21, 23, 25, 27, 29, 31, 33.

However, when receiving the echo signal, the receiving antenna receives the echo signal in the order of the transmitting antennas t1, t2, t3, and t4, and does not match the above correspondence, and therefore, the correction can be performed as follows.

for it＝1∶

id＝1∶8＝(it×8-7)∶it×8

for it＝2：

id＝9∶16＝(it×8-7)∶it×8

for it＝3：

id＝17∶24＝(it×8-7)∶it×8

for it＝4：

id＝25∶32＝(it×8-7)∶it×8

Wherein it represents the number of the transmitting antenna, and it is 1 to represent the transmitting antenna t1, and it is 2 to represent the transmitting antenna t2, and so on; id denotes the actual number of the received data, and the relationship between it and it satisfies id (it × 8-7): it × 8, for example, id 1: 8 for it, 9: 16 for it 2, and so on; idr denotes the corrected number of the received data.

The above formula shows that:

in the first period, the echo signals corresponding to the detection signals transmitted by the transmitting antenna t1 are received by the receiving antennas r1 to r8, so that the received data are numbered in the order of 1 to 8, that is, the actual number id is 1: 8, and the corrected number idr is 1, 2, 4, 6, 8, 10, 12, 14, which is consistent with the above correct number. The differences between the corrected numbers and the actual numbers are [0, 0, 1, 2, 3, 4, 5, 6], respectively.

In the second time period, the echo signals corresponding to the detection signals transmitted by the transmitting antenna t2 are received by the receiving antennas r1 to r8, so that the received data are numbered in the order of 9 to 16, that is, the actual number id is 9: 16, and the corrected number idr is 3, 5, 7, 9, 11, 13, 15, 17, which is consistent with the above correct number. The difference between the corrected number and the actual number is [ -6, -5, -4, -3, -2, -1, 0, 1], respectively.

In the third time period, the echo signals corresponding to the detection signals transmitted by the transmitting antenna t3 are received by the receiving antennas R5 to R12, so that the received data are numbered in the order of 17 to 24, that is, the actual number id is 17: 24, and the corrected number idr is 16, 18, 20, 22, 24, 26, 28, 30, which is consistent with the above correct number. The differences between the corrected numbers and the actual numbers are [ -1, 0, 1, 2, 3, 4, 5, 6], respectively.

In the fourth period, the echo signals corresponding to the detection signals transmitted by the transmitting antenna t4 are received by the receiving antennas R5 to R12, so that the received data are numbered in the order of 25 to 32, i.e., the actual number id is 25: 32, whereas the correct number idr is 19, 21, 23, 25, 27, 29, 31, 33 as described above, which is consistent with the above correct number. The difference between the corrected number and the actual number is [ -6, -5, -4, -3, -2, -1, 0, 1], respectively.

It can be seen that when it is an odd number, idr ═ id + j, where j ∈ [ -1, 0, 1, 2, 3, 4, 5, 6], except when id ═ 1 (when id ═ 1, idr ═ 1); when it is an even number, idr ═ id + k, where k ∈ [ -6, -5, -4, -3, -2, -1, 0, 1], and so on, corrections to the data numbering can be achieved.

Fig. 11 shows a schematic structural diagram of a 1D MIMO antenna array according to another embodiment of the present disclosure. The 1D MIMO antenna array of fig. 11 is similar to the above-described antennas of fig. 6 to 9, except that at least the 1D MIMO antenna array of fig. 11 is a periodic sparse co-prime array having an array period, the number of transmitting antennas and the number of receiving antennas in the array period are co-prime, and a midpoint of a connecting line between a transmitting antenna and a corresponding receiving antenna is regarded as a position of a single transceiving array, thereby obtaining a uniform line array of an equivalent phase center.

Suppose the number of transmit antennas T in an array period is N₁The number of receiving antennas R is N₂To obtain an evenly sampled equivalent array, N is required₁And N₂Is not equal to N₁And N₂Without common divisor, usually N₂＞N₁. Assuming that the length of the array antenna is D in one array period, the distance between the transmitting antennas T in the array period is D/N₁The distance between the receiving antennas R is D/N₂One transmit antenna will correspond to 2N₂An equivalent phase center, then one periodThe total number of equivalent phase centers in the phase-locked loop is 2N₁N₂. Assuming that the number of periodic array periods of the array is M, the total number of equivalent phase centers is 2MN₁N₂. The distance dtr between the first row of transmitting antennas T and the second row of receiving antennas R is greater than 10% of the imaging distance.

As an example, the length of the 1D MIMO antenna array of fig. 11 may be 30cm, the length of the mechanical scan (i.e., the maximum distance that can be translated) may be 40cm, the number of array periods M is 20, and the number of transmit antennas within an array period may be N₁The number of receive antennas may be N ═ 2₂The total number of transmit antennas of the 1D MIMO antenna array may be Nt-40, the total number of receive antennas may be Nr-60, and the number of mechanical scanning steps may be 201.

The 1D MIMO antenna array proposed in the present disclosure is based on a single-station equivalent principle, that is, the array is designed to be equivalent by a single station and combined with the control of a control circuit (e.g., a control switch), so that the finally formed equivalent phase center (also referred to as an equivalent unit or an equivalent antenna unit in the present disclosure) satisfies the nyquist sampling law, that is, the pitch of the equivalent antenna units formed by the transceiving antenna array is greater than or equal to half of the wavelength of the detection signal (e.g., the wavelength corresponding to the central operating frequency of the antenna). In order to reduce the number of transmitting antennas and receiving antennas and generally avoid overlapping of equivalent phase centers, the distance between adjacent equivalent phase centers is half or slightly larger than half of the wavelength of the radiated wave, for example, the distance between adjacent equivalent phase centers is 0.3 to 0.7 times the wavelength of the radiated wave, which may suffice to finally constitute a clear image. According to the principle, the short wavelength of the millimeter waves in the high-frequency band is considered, the engineering realizability is considered, meanwhile, the array sparsity design and the array switch control technology are adopted, and finally the requirement of the distribution of the half-wavelength-distance equivalent antenna units is met.

Fig. 12 shows a schematic flowchart of a control method of a security check device according to an embodiment of the present disclosure.

In step S101, the 1D MIMO device is controlled to transmit a detection signal to an object to be measured and receive an echo signal from the object to be measured. For example, the control circuit 22 may be used to control the 1D MIMO antenna array 21 to transmit detection signals to the opposite object 12 to be tested and receive echo signals. The detection signal may be an electromagnetic wave, such as a millimeter wave, specifically a millimeter wave terahertz wave. The detection signal, upon reaching the item under test 12, passes through the item under test 12, thereby generating an echo signal that carries information about the contents of the item under test 12. The 1D MIMO device may be controlled in an electronic scanning manner or a combination of electronic scanning and mechanical scanning as described above, so as to obtain scattering data of a plurality of different viewing angles of the object to be measured. For example, the plurality of transmitting antennas in the first row may be controlled to transmit the detection signal one by one/step from left to right (i.e., from one transmitting antenna at one end), and the corresponding plurality of receiving antennas (e.g., 6 or 8 receiving antennas closest to the transmitting antenna) receive the echo signals (the interval between the equivalent phase centers is ensured to be half wavelength), until all transmitting antennas finish transmitting the detection signal, i.e., one scan is finished. In some embodiments, the multiple transmitting antennas in the first row may be controlled to simultaneously transmit mutually orthogonal detection signals, and the multiple receiving antennas in the second row may receive echo signals, so as to complete a scan, wherein the detection signals are orthogonally encoded, and the echo signals received by the receiving antennas are decoded for image reconstruction. In one embodiment, the plurality of transmitting antennas in the first row transmit the detection signal one by one/step from left to right (i.e., starting from the transmitting antenna at one end), and the corresponding plurality of receiving antennas receive the echo signal, wherein the frequency of the detection signal gradually increases until all transmitting antennas finish transmitting the detection signal, i.e., one scanning is finished. In some embodiments, for example in case of having the translation means 70 or the transmission means 90, the 1D MIMO antenna array may be translated by a preset distance, for example along a direction perpendicular to the first and second rows, and scanned again (for example at a different frequency than the last time), and so on, each time the 1D MIMO antenna array completes one scan, so that the two-dimensional scanning effect of one 1D MIMO antenna array 21 may be utilized.

In step S103, an image of the object to be measured is reconstructed from the received echo signals. For example, a global reconstruction algorithm or a back projection algorithm may be used to reconstruct an image of the object under test.

The holographic reconstruction algorithm can realize the real-time reconstruction of the image of the object to be detected.

For example, the control circuit may be used to control the 1D MIMO antenna array to transmit and receive signals, for example, the group of transmit antennas may be controlled to sequentially transmit radiation waves to complete scanning of the group of transmit antennas, and the two-dimensional scanning is gradually completed by displacement along a direction orthogonal to the direction of the row of the group of transmit antennas; and completing imaging by using a synthetic aperture holographic algorithm based on Fourier transform. As shown in fig. 8A, a millimeter-scale radiation wave is emitted from the first transmitting antenna on the left side, the receiving antenna receives the return signal, and then the second transmitting antenna emits the radiation wave, which are sequentially operated to complete one scan. The scan is then repeated again moving a step distance in an upward or downward direction across the page.

Taking the 1D MIMO antenna array received at one transmitting end 8 of fig. 6A as an example, in operation, the control circuit may control the plurality of transmitting antennas to sequentially transmit the radiated wave. When the 1 st transmitting antenna works, the 1 st to 4 th receiving antennas collect echo data; when the 2 nd transmitting antenna works, the 1 st to 8 th receiving antennas collect echo data; when the 3 rd transmitting antenna works, the 5 th to the 12 th receiving antennas collect echo data; in turn, each transmitting antenna corresponds to 8 receiving antennas to collect data; until the last transmit antenna, the Nt-th transmit antenna, and the last 4 receive antennas collect data.

And after all the transmitting antennas transmit in sequence, completing one time of transverse data acquisition, and finally obtaining (Nt-1) line-based echo data. These echo data may be equivalent to (Nt-1) echo data acquired according to the equivalent phase center principle described above. The interval between these equivalent phases is 0.5 λ, and the distribution of equivalent elements satisfies the nyquist sampling law.

Then synthetic aperture scanning, namely mechanical scanning, is carried out in the orthogonal direction of the array to complete the scanning of the two-dimensional aperture, the scanning step length also satisfies the theorem,i.e., half wavelength 0.5 array. After the two-dimensional aperture scan is completed, the acquired echo data can be represented as S (x)_t，y_t；x_r，y_r；K_ω)。

And finally, combining a synthetic aperture holographic algorithm based on fast Fourier change to realize fast reconstruction and finish imaging.

The imaging algorithm aims to invert the characteristics of the object to be measured from the echo expression, such as the scattering coefficient σ (x, y) of the object to be measured, and the imaging formula is as follows:

where σ (x, y) is the scattering coefficient of the object to be measured, R₀Is the imaging distance, FT_2DIn order to perform a two-dimensional fourier transform,

is two-dimensional inverse Fourier transform, j is an imaginary unit, k is a propagation constant, k_x、k_yAre the spatial propagation constants, respectively;

receiving echo signals of a human body for a pair of transmitting antenna-receiving antenna combination; k_ωIs the spatial frequency of the frequency stepped signal.

Backprojection originated from computed tomography technology, an accurate imaging algorithm based on time-domain signal processing. The basic idea is that for each imaging point in the imaging area, the time delay between the point to the receiving antenna and the transmitting antenna is calculated, and the contributions of all the echoes to the point are coherently superposed to obtain the corresponding pixel value of the point in the image, so that the coherent superposition processing is performed on the whole imaging area point by point, and the image of the imaging area can be obtained. The back projection algorithm is naturally easy to implement parallel computation, and therefore, is suitable for the case where the receiving antennas in a plurality of sub-arrays receive the reflected electromagnetic waves at the same time. Although reconstruction is required for each point in the whole imaging interval, if the hardware in the processing system adopts GPU or FPGA technology, the reconstruction time can be greatly reduced, and even real-time reconstruction is realized. The reconstruction formula can be expressed as,

wherein the content of the first and second substances,

is the scattering coefficient of the object to be measured, and (x, y, z) represents the coordinate of the object to be measured, wherein z represents the distance between the 1D MIMO array panel and a certain fault of the object to be measured, and z represents the distance between the 1D MIMO array panel and the certain fault of the object to be measured_aIs the imaging distance, j is the unit of imaginary number, k is the propagation constant, s (x)_t，y_r，x_r，y_rK) is the echo signal of the object to be measured received by a pair of transmitting antenna-receiving antenna combination, (x)_t，y_t) As the transmitting antenna coordinate, (x)_r，y_r) The coordinates of the receiving antenna.

In step S201, the height of the object to be measured is detected. For example, the height of the object to be detected may be automatically detected by using a sensor provided on the security inspection apparatus, but the height of the object to be detected may also be detected in other manners, for example, manually.

In step S202, a distance between the 1D MIMO device and the object to be measured is adjusted. For example, when the height of the object to be measured is low, such as a letter-type object, the imaging distance between the 1D MIMO antenna array 21 and the object to be measured 12 may be adjusted to 10cm to 40cm by using the lifting device 80; when the object to be measured is high, for example, a small express parcel, the imaging distance between the 1D MIMO antenna array 21 and the object to be measured 12 may be adjusted to 20cm to 100 cm.

In step S203, the 1D MIMO device is controlled to transmit a detection signal to the object to be tested and receive an echo signal from the object to be tested. In this embodiment, a scanning mode combining an electronic scanning and a mechanical scanning is adopted, and in this step, the 1d mimo device performs an electronic scanning at the current position.

In step S204, it is determined whether the 1D MIMO device completes scanning, if so, it indicates that the scanning of the current position is completed, and the process proceeds to step S205, otherwise, the process returns to step S203 to continue the scanning of the current position.

In step S205, it is determined whether the translation path is completed, if so, it indicates that the 1D MIMO device has completed scanning at all positions on the path, and therefore, the scanning of the current object to be measured is completed, and step S206 is performed to reconstruct an image, otherwise, step S207 is performed to translate to the next position for scanning.

In step S206, an image of the object to be measured is reconstructed using the obtained echo signals. The reconstruction algorithm includes, but is not limited to, the above-described ensemble reconstruction algorithm and the backprojection algorithm.

In step S207, the 1D MIMO device is translated, and returns to step S203 to perform scan detection again at a new position. For example, the 1D MIMO antenna array may be translated by a preset distance relative to the object to be measured by using the translation device 70 or the conveying device, so as to implement mechanical scanning.

In some embodiments, steps S208 to 209 may also be performed after step S206.

In step S208, the reconstructed image of the object to be tested is analyzed to determine whether the object to be tested may contain dangerous goods, if yes, step S209 is executed, otherwise, the security detection of the current object to be tested is ended. For example, the reconstructed image of the object to be tested may be compared with a pre-stored template, and if the degree of matching with the feature template of a certain dangerous article is greater than a preset threshold, it is determined that the dangerous article is likely to be contained, otherwise, it is determined that the dangerous article is not contained. In some embodiments, the probability of containing dangerous goods may also be determined according to the degree of matching, for example, a higher degree of matching indicates a higher probability of containing dangerous goods, and a lower degree of matching indicates a lower probability of containing dangerous goods.

In step S209, the alarm device is controlled to alarm. Ways of alerting include, but are not limited to, visual display, audio alert, vibration alert, and the like. An alarm level may also be set, for example, when the probability of containing a dangerous article is low, an alarm may be given by a lower volume of sound or a weaker vibration, and when the probability of containing a dangerous article is high, an alarm may be given by a higher volume of sound or a stronger vibration.

In this embodiment, the image of the object to be tested reconstructed in step S206 and/or the determination result in step S208 may also be presented to the user, for example, the reconstructed image may be displayed by using a display screen after the image is reconstructed in step S206, and the determination result in step S208 may also be presented on the display screen after step S208; after the comparison in step S208 is completed, the reconstructed image in step S206 and the determination result in step S208 may be displayed on the display screen. The presentation mode of the determination result (for example, which dangerous goods may be contained or the probability of containing the dangerous goods) in step S208 may be selected as needed, and in addition to the above presentation in the form of a screen on the display screen, the determination result may be presented in other modes such as audio and vibration, for example, the determination result may be played in the form of voice, or the determination result may be indicated by using the alarm volume or the vibration intensity of the alarm, for example, the alarm with high volume indicates that the dangerous goods are contained more likely, and the alarm with low volume indicates that the dangerous goods are contained less likely.

The embodiment of the disclosure can realize automatic safety inspection of small mails such as letters and registered small bags by utilizing the 1D MIMO device for scanning detection in the safety inspection equipment, and can improve the safety inspection efficiency and accuracy compared with the traditional manual inspection and X-ray machine inspection.

The embodiment of the disclosure can select 1D MIMO antenna arrays with various structures according to requirements, and has high use flexibility. Through adopting the millimeter wave as detected signal, can pierce through the article formation of image that awaits measuring to when replacing the X-ray machine to reach safety inspection's purpose, provide higher detection quality and higher security.

The embodiment of the disclosure can reflect the detection signal passing through the object to be detected back to the 1D MIMO device by arranging the back plate below the object to be detected, thereby enhancing the contrast between the echo signal from the object to be detected and other echo signals and improving the detection precision.

The imaging distance can be adjusted according to the height of the object to be measured, so that the optimal imaging distance is found, and high-resolution imaging is realized. In some cases, a sufficiently small imaging distance may even achieve a resolution of one-fourth.

The 1D MIMO device of the embodiment of the disclosure can greatly improve the data acquisition speed and the utilization rate of the antenna unit through the multiple-input multiple-output array sparse design and control technology. The embodiment of the disclosure supports a full electronic scanning mode and a scanning mode combining electronic scanning and mechanical scanning. The scanning speed is high in a full electronic scanning mode (namely, the antennas are controlled to work one by one through a switch or the antennas are controlled to use frequency scanning one by one through the switch), and real-time imaging can be realized by combining a three-dimensional holographic algorithm based on Fast Fourier Transform (FFT). The scanning mode combining electronic scanning and mechanical scanning can realize scanning of a larger imaging area by using a smaller antenna array, thereby reducing the complexity of antenna design and saving cost.

The embodiment of the disclosure can provide automatic threat detection by automatically analyzing the reconstructed image of the object to be detected, greatly improves the detection efficiency and reduces the omission factor compared with the traditional mode.

The security inspection equipment of the embodiment of the disclosure has the advantages of simple structure, portability, firmness, small volume, high sensitivity, portability, and capability of being installed in offices, transceiving rooms and other places and being safer for human bodies compared with the traditional X-ray machine.

It will be appreciated by those skilled in the art that the embodiments described above are exemplary and can be modified by those skilled in the art, and that the structures described in the various embodiments can be freely combined without conflict in structure or principle.

Having described preferred embodiments of the present disclosure in detail, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the scope and spirit of the appended claims, and the disclosure is not limited to the exemplary embodiments set forth herein.

Claims

1. A security device comprising:

the detection device comprises an equipment body, wherein a detection space is arranged on the equipment body and used for accommodating an article to be detected, the detection space is arranged to be of a groove structure and is provided with a first side wall, a second side wall and a third side wall, the first side wall and the second side wall are parallel to each other, the third side wall is perpendicular to the first side wall and the second side wall, and the second side wall is used for placing the article to be detected;

a 1D MIMO device, namely a one-dimensional multiple-input multiple-output device, which is arranged in the detection space and is positioned on the first side wall of the detection space and used for transmitting detection signals to an object to be detected in the detection space and receiving echo signals from the object to be detected, wherein the 1D MIMO device is provided with a 1D MIMO antenna array with the length in the range of 30-50 cm; and

2. The security inspection apparatus of claim 1, wherein the 1D MIMO device comprises:

the 1D MIMO antenna array is arranged in the detection space and comprises a plurality of transmitting antennas arranged in a first row and a plurality of receiving antennas arranged in a second row, equivalent phase centers formed by the plurality of transmitting antennas and the plurality of antennas are arranged in a third row and are separated by half of the wavelength of a detection signal at equal intervals, wherein the first row, the second row and the third row are parallel to each other; and

3. The security inspection device of claim 2, wherein the plurality of transmit antennas are equally spaced apart and the plurality of receive antennas are equally spaced apart, the distance between two adjacent transmit antennas being an integer multiple of the distance between two adjacent receive antennas.

4. The security inspection device of claim 2, wherein the plurality of transmit antennas comprises a plurality of transmit antenna groups spaced at equal intervals, the plurality of receive antennas are spaced at equal intervals, and a distance between two adjacent transmit antenna groups is greater than a distance between two adjacent receive antennas.

5. The security inspection device of claim 4, wherein each set of transmit antennas comprises two transmit antennas, the distance between the two transmit antennas being an integer multiple of the wavelength of the detection signal.

6. The security inspection device of claim 2, wherein the 1D MIMO antenna array is a periodic sparse co-prime array having an array period, the plurality of transmit antennas are equally spaced, the plurality of receive antennas are equally spaced, a distance between two adjacent transmit antennas is greater than a distance between two adjacent receive antennas, and the number of transmit antennas is co-prime to the number of receive antennas within the array period.

7. The security device of claim 2, wherein the distance between the first and second rows is less than 10% of the imaging distance of the 1d evimo antenna array.

8. The security check device of claim 2, further comprising: a translation device mounted on the apparatus body for translating the 1D MIMO antenna array along a direction perpendicular to the first, second and third rows within a plane in which the 1D MIMO antenna array is located.

9. The security check device of claim 2, further comprising: and the lifting device is arranged on the equipment body and used for controlling the 1D MIMO antenna array to be far away from or close to the object to be detected to move.

10. The security device of any one of claims 1 to 9, further comprising: the back plate is arranged in the detection space and positioned below the object to be detected and used for reflecting a detection signal which penetrates through the object to be detected and reaches the back plate back to the 1DMIMO device.

11. The security inspection apparatus of claim 10, wherein the back plate comprises a metal plate or a plate with a metal coating.

12. The security device of any one of claims 1 to 9, further comprising: and the conveying device is arranged to penetrate through the detection space and is used for conveying the object to be detected so as to enable the object to be detected to enter or leave the detection space.

13. The security device of any one of claims 1 to 9, further comprising: and the display device is connected with the processor and used for presenting the reconstructed image of the object to be measured to a user.

14. A security device according to any one of claims 1 to 9, wherein the detection signal is a millimetre wave.