CN116224328A - Millimeter wave edge imaging system for target multi-angle scanning and imaging method thereof - Google Patents
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Abstract
The invention discloses a millimeter wave edge imaging system for target multi-angle scanning and an imaging method thereof, comprising a front millimeter wave scanning platform, a rear millimeter wave scanning platform, a MIMO scanning module, an FPGA edge computing module and a display terminal, wherein the millimeter wave scanning platform is vertically arranged at the bottom; each scanning platform can realize equivalent half-wavelength uniform sampling in a two-dimensional synthetic aperture through a specially designed MIMO scanning module, and high-speed imaging and synchronous display of three scanning platforms are realized through an FPGA edge computing module. Aiming at the designed MIMO scanning array, the invention provides a corresponding high-efficiency and high-resolution rapid three-dimensional imaging method, and an imaging algorithm accelerator integrated in an FPGA edge calculation module. The imaging system has the advantages of simple and compact structure, low cost, small volume, low power consumption, high stability and high imaging speed, and can effectively and synchronously complete the detection of hidden dangerous objects on the front, the back and the bottom of a detected object.
Description
Technical Field
The invention belongs to the technical field of millimeter wave imaging, and relates to a millimeter wave edge imaging system capable of realizing synchronous scanning detection of front and back surfaces and bottom of a target at multiple angles and an imaging method thereof.
Background
The global terrorist activities are frequent, serious in casualties and huge in loss, and have characteristics which are quite different from those of the traditional terrorist attacks, and nonmetal hidden forbidden articles such as plastic explosives, nonmetal cutters, liquid dangerous goods and the like become main weapons of terrorists, so that the harm of the terrorist attacks is remarkably aggravated by the inadvisable suicide meat bombs. Therefore, it is particularly important to perform security inspection on personnel in special occasions. And people also put higher and higher demands on the safety, the high efficiency and the intelligence of security inspection equipment, especially equipment for human body detection. The traditional safety inspection means has seriously lagged the requirements of the comprehensive rail transit system, civil aviation system and important occasions on the aspects of reliability, rapidness, intellectualization, comfort and the like of personnel safety inspection. The conventional metal detector universal for personnel security inspection can only judge whether the metal contraband is present or not and can not accurately identify the metal contraband, and is more incapable of non-metal contraband and serious in security hole. The touch manual security check mode of beating, touching, pressing and pressing is low in efficiency, privacy of checked personnel cannot be respected, and more importantly, the security check practitioner cannot guarantee the self security. Other security inspection means for various personnel have the defects of safety, efficiency, cost, volume, detection capability and the like, such as police dogs and people in the biological security inspection technology are only suitable for special occasions, the service period is short, the skill training and maintenance cost is high, and the sustainability is not realized; the infrared detection technology images the surface temperature of an object, and can not image clearly under the condition that clothes are shielded; although various rays such as X rays have strong penetrating power, the rays can cause ionizing radiation injury to tested personnel and operators, and the hazard effect of the ionizing radiation on targets has a cumulative effect, so that even a low-dose X ray machine is still not easily accepted by the public.
Millimeter waves have strong penetrability, can penetrate common clothes, textiles, packaging paper and the like, have high resolution, good directivity and strong anti-interference capability, and do not have ionizing radiation harm to detected targets, especially human bodies, so the millimeter waves are widely regarded as key technologies in the fields of security inspection, nondestructive inspection and the like of new-generation personnel, and are primary choices for replacing the existing low-efficiency metal detection and combining manual search. In recent years, along with the continuous growth of millimeter wave imaging technology research teams, a great deal of scientific research results emerge. The most successful commercial application direction of the millimeter wave imaging technology at present is a security gate facing the application of human body security, such as Provision series products of L3 company in the United states, and thousands of products are sold in the world; some millimeter wave human body security inspection products in Germany R & S company and China are mature day by day and form part of sales. The existing active millimeter wave human body security gate generally adopts a holographic imaging system, the phase of the reflected millimeter wave signal is directly measured through heterodyne mixing, and then the human body surface image is obtained based on inversion of phase information. The technology adopts synthetic aperture imaging, has high resolution, can reach half wavelength magnitude, reflects reflection information of the body surface of the human body, can clearly see the surface details of articles carried by the human body, and has high differentiation of different types of articles.
Although millimeter wave imaging technology is rapidly developed, numerous scientific research institutions and related enterprises at home and abroad have achieved remarkable results, the existing millimeter wave security inspection imaging technology is still far immature, and the research and development of the millimeter wave imaging technology with low cost, high reliability and high resolution still face great challenges. For example, in the imaging system of planar scanning, in order to ensure high resolution of imaging, the sampling interval must reach half a wavelength or less, and thus a large number of transceiver antenna units are required. In the most extreme case of pure electric scanning without mechanical scanning, a two-dimensional full array would be able to achieve real-time gaze scanning, with the scanning speed reaching the fastest, but the cost of the transceiver units in this case and the complexity of the switching network controlling the operation of the array would also be extremely great. In addition, the existing millimeter wave security inspection imaging products almost completely adopt each side to scan and detect independently when scanning the front and back sides of a human body, then turn around and then detect the other side, or adopt columnar spiral scanning and detect, and few products are found to realize the security inspection products which can realize the whole body comprehensive synchronous scanning of the front and back sides of the human body and the soles. However, in actual security inspection, considering the conflict emotion of the person to be inspected on the inspection, the front and rear sides and the sole are inspected one by one for multiple times, which is very easy to cause dissatisfaction of the person to be inspected, and more cases of hiding poison, knife, gun and the like of the sole attempt to hide forbidden objects in the sole. Under the condition, only the shoes taking and searching measures can be taken for the detected personnel, so that the privacy of the detected personnel cannot be respected, the safety of security check practitioners cannot be guaranteed, the missed detection risk is increased remarkably, and if an attack event is caused, the consequences cannot be assumed. Therefore, there is a need for a millimeter wave imaging system for multi-angle synchronous scanning of targets.
In order to balance the complexity and the scanning efficiency of the security imaging system, the most widely applied technical scheme at present is to realize two-dimensional plane scanning by utilizing a linear array electric scanning and machine scanning mode. However, with the commercialized popularization of millimeter wave security inspection systems, the cost of the transceiver unit required by the linear full array at half-wavelength scanning intervals is quite huge, so that research on how to further reduce the hardware cost is significant. The linear multi-transmitting multi-receiving MIMO sparse array technology can just solve the problem, the number of the antennas is reduced by sparse array, the antennas with larger calibers are allowed to be used for more convenient installation, fewer mutual interference is generated between the receiving and transmitting antennas, the isolation is larger, and the array performance is improved. Simultaneously, the synchronous scanning of the front side, the rear side and the bottom side is considered. According to the invention, array sparsity and multi-angle synchronous scanning are comprehensively considered, a novel MIMO sparse array arrangement mode is provided, namely, the problem of sampling leakage and repeated sampling is avoided while the array is uniformly sampled at equal intervals according to half wavelength, the maximum distance of a receiving and transmitting antenna is moderate, the corresponding equivalent phase center error is smaller, accurate calibration can be performed in the imaging algorithm process, and finally, the more ideal imaging effect is obtained.
Disclosure of Invention
The present invention is directed to solving the above problems of the prior art. A millimeter wave edge imaging system and an imaging method for multi-angle scanning of a target are provided. The technical scheme of the invention is as follows:
a millimeter wave edge imaging system for multi-angle scanning of a target, comprising:
the device comprises a front millimeter wave scanning platform, a rear millimeter wave scanning platform, a MIMO scanning module, an FPGA edge computing module and a display terminal, wherein the front millimeter wave scanning platform and the rear millimeter wave scanning platform are vertically arranged; wherein,
the three scanning platforms are respectively provided with an MIMO scanning module and an FPGA edge computing module;
the MIMO scanning module performs mechanical scanning on the corresponding scanning platform according to vertical up-and-down movement and horizontal left-and-right movement, so that synchronous detection of the front, the back and the bottom of a detected target is realized;
the MIMO scanning module comprises an MIMO scanning array, a receiving and transmitting module and a data acquisition module, wherein the MIMO scanning array is used for realizing uniform sampling of equivalent half-wavelength intervals; the receiving and transmitting module is used for generating millimeter wave signals for transmitting and echo signals for receiving, mixing the echo signals with the intrinsic signals, obtaining intermediate frequency echo signals and transmitting the intermediate frequency echo signals to the data acquisition module; the data acquisition module acquires the obtained intermediate frequency signals and transmits the intermediate frequency signals to the FPGA edge calculation module through an LVDS interface;
the FPGA edge calculation module processes the intermediate frequency echo signals and performs target reconstruction; and the display terminal is connected with the FPGA module through HDMI and synchronously displays imaging results of the three scanning platforms.
Further, the FPGA edge calculation module comprises an imaging algorithm accelerator, an AI target recognition and enhancement module and a display driving module. The imaging algorithm accelerator comprises echo data phase compensation, a fast Fourier transform unit, an interpolation unit, an inverse Fourier transform unit and the like, can realize the acceleration of the imaging algorithm according to unit splitting calculation of a three-dimensional imaging algorithm aiming at the MIMO system, can effectively reduce the time for reading and writing high-latitude data and calculating the radar imaging algorithm while meeting the requirement of high-precision imaging, realizes that the time consumption for calculating is several times less than that of a CPU, and meets the requirement of real-time display. The AI target recognition and enhancement module comprises a neural network inference module and a non-maximum suppression (NMS) post-processing module which are respectively used for dangerous object detection classification and post-frame processing, a deep learning processing unit (DPU) of the FPGA is utilized on hardware, a software part uses VitisAI development software to quantize, prune and compile a trained model, and then the model is deployed into an FPGA edge calculation module to infer an edge end in real time. The display driving module includes three parts: the first display time sequence driving module (VGA_driver) can flexibly configure the resolution and refresh rate of the display, and provides pixel address information for displaying pictures; secondly, an image display driving module (sar_2d_disp) requests an algorithm acceleration calculation result after data acquisition is completed, and performs pixel conversion on the result, and a corlomap function is added in the module to enhance the display effect due to poor display effect of a gray level picture so as to obtain a clearer target outline, and finally the module outputs display enhancement pixels carrying image information; third, the display interface driving module (rgb2dvi, vgaddrv_conv_rgbd 2 dvi) inputs the displayed timing information and the pixel information of the picture, and finally connects to the external display through HMDI or VGA.
Further, the MIMO scanning array is configured to implement uniform sampling of equivalent half-wavelength intervals, and specifically includes: the MIMO array consists of Nc MIMO units, wherein each MIMO unit comprises N transmitting antennas and M receiving antennas; the MIMO unit realizes the equal and uniform sampling of half-wavelength interval in the array direction by configuring the working state of the receiving and transmitting antenna at each moment, and realizes the equal and uniform sampling of half-wavelength interval in the area with the scanning length L in the array direction;
furthermore, the transmitting antennas in each MIMO unit sequentially work according to the sequence numbers, all M receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit can obtain NM equivalent sampling points, and the scanning length of the covered array direction is (NM-1) lambda/2; the alignment mode of N transmitting antennas and M receiving antennas in each MIMO unit is not limited, and the N transmitting antennas and the M receiving antennas can be aligned or not aligned;
two adjacent MIMO units are rotationally symmetrical at 180 degrees, and the interval between the receiving and transmitting antennas closest to each other in the two adjacent MIMO units is half-wavelength lambda/2; and (3) obtaining NcNM equivalent sampling points in total by the MIMO scanning array formed by Nc MIMO units, wherein the scanning length of the covered array direction is L= (NcNM-1) lambda/2.
An imaging method based on the system of any one of the above claims, comprising the steps of:
Further, the step 201 designs an arrangement mode of the millimeter wave MIMO array with equivalent half-wavelength uniform sampling, and specifically includes:
the M receiving antennas are uniformly distributed, and the interval is 1 time of wavelength lambda; the N transmitting antennas are also uniformly distributed, and the interval is M times of wavelength (M lambda);
the transmitting antennas in each MIMO unit sequentially work according to the sequence numbers, all M receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit can obtain NM equivalent sampling points, and the scanning length of the covered array direction is (NM-1) lambda/2;
two adjacent MIMO units are rotationally symmetrical at 180 degrees, and the interval between the nearest receiving and transmitting antennas in the two adjacent MIMO units is half-wavelength (lambda/2); and (3) obtaining NcNM equivalent sampling points in total by the MIMO scanning array formed by Nc MIMO units, wherein the scanning length of the covered array direction is L= (NcNM-1) lambda/2.
Further, the step 202, the step of synthesizing a two-dimensional aperture scan by the MIMO array specifically includes:
the two vertical scanning platforms are respectively positioned in front of and behind the target to be detected, so that synchronous scanning of the front and the rear of the target is realized; in the direction of the MIMO array, after receiving a scanning start command, the MIMO scanning array is sequentially turned on and off according to a specified sequence to realize horizontal scanning, but the scanning directions of the arrays on the front and back sides are just opposite, namely when the front array is scanned from left to right, the rear array is scanned from right to left; in the direction perpendicular to the MIMO array, the scanning direction is also opposite, i.e. when the front array is swept down from top to bottom, the rear array is swept down to top; the bottom MIMO scanning array is not limited by the scanning directions of the front and back MIMO scanning arrays, and can synchronously and reciprocally scan with the front and back surfaces.
Further, the step 203 of designing an imaging method corresponding to MIMO array scanning specifically includes:
(1) Each scanning platform scans by utilizing a millimeter wave MIMO array with equivalent half-wavelength uniform sampling to obtain echo data s (x, y, k) with the size of NcNMXH XF; wherein F is the sampling point number in the broadband frequency sweeping process of each sampling position, H is the number of times of movement at half wavelength intervals in the vertical direction, (x, y) represents the position of a receiving antenna, and k is the wave number;
(2) Calculating the phase center approximation error e of the MIMO array -jkΔR ：
Phase error factor generated by phase center equivalence
Wherein R represents the distance from the equivalent phase center of the receiving and transmitting antenna to the target center, R to 、R or Respectively represent the distance from the transmitting antenna to the target and the distance from the target to the receiving antenna, d l The distance difference of the first channel transceiver antenna in the array direction, namely the x direction is shown; when the target is reconstructed by utilizing the echo obtained by MIMO array scanning, the receiving and transmitting antenna separation mode is approximated to be a single-station mode at the equivalent phase center position, and the delta R can obtain the target to be complementedThe compensated phase center approximation error is e -jkΔR ；
(3) Compensating the echo signal by using the phase center approximation error to obtain a compensated echo signal s c (x,y,k)：
Sigma target reflectivity, r o ＝(x o ,y o ,z o ) Respectively representing the spatial position of the target region.
(4) For the compensated echo signal s c (x, y, k) performing azimuthal two-dimensional Fourier transform to obtain S (k) x ,k y ,k)：
S(k x ,k y ,k)＝∫∫s c (x,y,k)exp(-jk x x-jk y y)dxdy
wherein ,kx ,k y ,k z Components of the spatial wave number in three coordinate directions are respectively represented;
(5) For S (k) x ,k y K) resampling to obtain a sample in (k) x ,k y ,k z ) Data for a uniform distribution of domains:
(6) Obtaining a three-dimensional reconstruction result of the target by utilizing three-dimensional inverse Fourier transform:
wherein ,
representing an inverse three-dimensional fourier transform. />
The invention has the advantages and beneficial effects as follows:
the millimeter wave edge imaging system for multi-angle scanning of the target provided by the invention has the advantages of simple and compact structure, low cost, small volume, low power consumption, high stability and high imaging speed, performs two-dimensional scanning aperture synthesis based on the MIMO sparse linear array through a plurality of angles, realizes synchronous imaging of the front surface, the rear surface and the bottom of the target to be detected on the FPGA edge computing module by utilizing a corresponding three-dimensional imaging method, and greatly improves the detection efficiency. The three advantages and beneficial effects to be described are respectively:
1. compared with the traditional detection system, the detection system only generally detects front and rear sides, or can increase metal detection functions on soles in the system for human body security inspection, and can not comprehensively detect nonmetallic detected targets.
2. Compared with the traditional upper computer CPU or GPU calculation, the imaging system has the advantages that all calculation is completed only by an FPGA edge calculation module, the smart technology is utilized to accelerate the integration of the whole process of using the calculation resources of the FPGA for the imaging algorithm and the AI target identification and enhancement, the display drive is further used for directly displaying the result outwards, the additional arrangement of a computer or a server and other upper computer terminal platforms for calculation, imaging and display is avoided, the cost is greatly saved, and the imaging system is lighter and more miniaturized and is convenient to transport and disassemble.
3. The millimeter wave MIMO linear array arrangement mode with uniform and equivalent half-wavelength sampling provided by the invention has universality, the number of receiving and transmitting antennas of the MIMO array, the array length and other parameters are adjustable, the equivalent half-wavelength sampling is realized by utilizing the effective multiplexing of the receiving and transmitting antennas by utilizing the arrangement mode, and the leakage sampling and repeated sampling of any equivalent sampling point are avoided, but the number of receiving and transmitting antennas required by full-array half-wavelength sampling is greatly reduced. Step 201 designs an arrangement manner of the millimeter wave MIMO array with equivalent half-wavelength uniform sampling, that is, the specific arrangement manner of the MIMO array described in claims 3 and 4 is not easily conceivable: the number of the receiving antennas in the MIMO unit is arbitrarily adjustable, on the premise that the receiving antennas are uniformly spaced by one time of wavelength, the number of the receiving antennas determines the interval between the transmitting antennas, and then the number of the transmitting antennas can be better set (the same situation that the functions of the receiving antennas are interchanged is the same), so that the arrangement mode is very ingenious and is not easy to think; in addition, when the array is formed by the MIMO units, 180-degree rotation symmetry and the like of two adjacent units are also very ingenious. As the MIMO array parameters are adjustable, the arrangement mode of the MIMO array is equivalent to that of a type of MIMO array, and half-wavelength uniform equivalent sampling can be realized. And a corresponding high-efficiency high-resolution three-dimensional reconstruction method is provided for the MIMO sparse arrangement mode, namely 8 in the claims, and the method has strong universality.
Drawings
Fig. 1 is a block diagram of the overall structure of a preferred embodiment provided by the present invention.
FIG. 2 is a schematic diagram of a system architecture according to the present invention.
FIG. 3 is a schematic view of a bottom horizontal scanning platform according to the present invention.
Fig. 4 is a schematic diagram of a MIMO scanning array according to the present invention.
Fig. 5 is a schematic diagram of a MIMO scanning array given specific parameters in accordance with a preferred embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and specifically described below with reference to the drawings in the embodiments of the present invention. The described embodiments are only a few embodiments of the present invention.
The technical scheme for solving the technical problems is as follows:
referring to fig. 1, 2, 3 and 4, the invention discloses a millimeter wave edge imaging system for multi-angle scanning of a target, which comprises a scanning platform 1, a MIMO scanning module 2, an FPGA edge computing module 3, a display terminal 4 and the like. (in the specification, reference numerals are not used in parentheses)
Referring to fig. 2, the scanning platform 1 includes two vertically installed millimeter wave scanning platforms 1-1 and 1-2, and one millimeter wave scanning platform 1-3 installed at the bottom.
And the three scanning platforms are respectively provided with a MIMO scanning module 2 and an FPGA edge computing module 3, and the two-dimensional synthetic aperture scanning is respectively carried out by moving up and down in the vertical direction and moving left and right in the horizontal direction, so that the front, rear and bottom synchronous detection of a detected target is realized.
Referring to fig. 1, the MIMO scanning module 2 includes a MIMO scanning array 201, a transceiver module 202, and a data acquisition module 203. Uniform sampling of equivalent half-wavelength intervals is achieved by the MIMO scanning array 201; the transceiver module 202 is configured to generate a millimeter wave signal and receive an echo signal, the millimeter wave signal transmission link is configured to generate a millimeter wave source and transmit the millimeter wave source to the transmitting antenna, and the millimeter wave signal reception link is configured to receive the echo signal and mix the echo signal with an intrinsic signal, so as to obtain an analog intermediate frequency signal and transmit the analog intermediate frequency signal to the data acquisition module 203; the data acquisition module 203 acquires the obtained analog intermediate frequency signal, and the obtained digital intermediate frequency signal is transmitted to the FPGA edge calculation module 3 through the LVDS interface.
The FPGA edge computation module 3 includes an imaging algorithm accelerator 301, an AI target recognition and enhancement module 302, a display driving module 303, and the like. The imaging algorithm accelerator 301 comprises an echo data phase compensation unit, a fast fourier transform unit, an interpolation unit, an inverse fourier transform unit and the like, can realize the acceleration of the imaging algorithm by splitting the three-dimensional imaging algorithm aiming at the MIMO system according to the unit, can effectively reduce the time for reading and writing high-latitude data and calculating the imaging algorithm while meeting the requirement of high-precision imaging, and realizes that the time consumption for calculating is several times less than that of a CPU (central processing unit), thereby meeting the requirement of real-time display. The AI target recognition and enhancement module 302 includes a neural network inference module and a non-maximum suppression (NMS) post-processing module, which are respectively used for dangerous object detection classification and post-frame processing, and uses a deep learning processing unit (DPU) of the FPGA on hardware, and uses the Vitisai development software to quantize, prune, compile and deploy the trained model into the FPGA edge calculation module, so as to infer the edge in real time. The display driving module 303 includes three parts: the first display time sequence driving module (VGA_driver) can flexibly configure the resolution and refresh rate of the display, and provides pixel address information for displaying pictures; secondly, an image display driving module (sar_2d_disp) requests an algorithm acceleration calculation result after data acquisition is completed, and performs pixel conversion on the result, and a corlomap function is added in the module to enhance the display effect due to poor display effect of a gray level picture so as to obtain a clearer target outline, and finally the module outputs display enhancement pixels carrying image information; third, the display interface driving module (rgb2dvi, vgaddrv_conv_rgbd 2 dvi) inputs the displayed timing information and the pixel information of the picture, and finally connects to the external display through HMDI or VGA.
The display terminal 4 is connected with the FPGA edge calculation module 3 through HDMI, and synchronously displays imaging results of the three scanning platforms.
Referring to fig. 3, a MIMO scanning array 201 on each scanning platform of the millimeter wave edge imaging system for target multi-angle scanning is equivalent half-wavelength uniform sampling, and the steps of scanning and imaging by using the MIMO array include the following steps:
referring to fig. 4, the step 1 of designing an arrangement mode of the millimeter wave MIMO array with equivalent half-wavelength uniform sampling specifically includes:
each MIMO unit forming the MIMO scanning array comprises N transmitting antennas and M receiving antennas, wherein the M receiving antennas are uniformly distributed, and the interval is 1 time of wavelength lambda; the N transmitting antennas are also uniformly distributed, and the interval is M times of wavelength (M lambda); the transmitting antennas in each MIMO unit sequentially work according to the sequence numbers, all M receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit can obtain NM equivalent sampling points, and the scanning length of the covered array direction is (NM-1) lambda/2; the alignment mode of N transmitting antennas and M receiving antennas in each MIMO unit is not limited, and the N transmitting antennas and the M receiving antennas can be aligned or not aligned.
Two adjacent MIMO units are rotationally symmetrical at 180 degrees, and the interval between the nearest receiving and transmitting antennas in the two adjacent MIMO units is half-wavelength (lambda/2); and (3) obtaining NcNM equivalent sampling points in total by the MIMO scanning array formed by Nc MIMO units, wherein the scanning length of the covered array direction is L= (NcNM-1) lambda/2.
The arrangement mode of the MIMO scanning array for realizing the equivalent half-wavelength uniform sampling comprises a plurality of variable parameters, such as the number Nc of MIMO units, the number N of transmitting antennas in each MIMO unit, the number M of receiving antennas, the wavelength lambda, the row spacing h of receiving and transmitting antennas and the like. For better understanding, FIG. 4 shows an array layout for N, M values of 3, 4. In practical application, the value of N and M can be freely defined according to the situation.
The method comprises the steps that a target scene is scanned by using an MIMO array, half-wavelength interval equivalent uniform sampling is realized by controlling the working state of a receiving and transmitting antenna in an array at each moment in an area with a scanning length L in the array direction, the MIMO array is uniformly moved at half-wavelength intervals after the electronic scanning in the array direction is completed each time in the vertical array direction, the number of times H of movement in the vertical direction is determined by the actual scanning scene size, and NcNM multiplied by H sampling positions on a two-dimensional scanning plane can be obtained in the mode; the sampling point number of the broadband sweep process at each sampling position is F, and the size of the complete echo data s for completing one target sweep is NcNM multiplied by H multiplied by F.
Aiming at the designed scanning mode of the MIMO scanning array 201, the invention provides a corresponding high-efficiency and high-resolution rapid three-dimensional imaging method, and an imaging algorithm accelerator 301 integrated in an FPGA edge computing module 3, namely the steps of the imaging method designed in the step 3 and corresponding to the MIMO array scanning, specifically comprise the following steps:
(1) Each scanning platform scans by utilizing a millimeter wave MIMO array with equivalent half-wavelength uniform sampling to obtain echo data s (x, y, k) with the size of NcNMXH XF; wherein (x, y) represents the position of the receiving antenna, k is the wave number;
(2) Calculating the phase center approximation error e of the MIMO array -jkΔR ：
Phase error factor generated by phase center equivalence
Wherein the distance from the equivalent phase center of the R receiving and transmitting antenna to the target center, d l The distance difference of the first channel transceiver antenna in the array direction, namely the x direction is shown; when the target is reconstructed by utilizing the echo obtained by MIMO array scanning, the receiving and transmitting antenna separation mode is approximated to be a single-station mode at the equivalent phase center position, and the phase center approximation error to be compensated is obtained by delta R and is e -jkΔR 。
(1) Compensating the echo signal by using the phase center approximation error to obtain a compensated echo signal s c (x,y,k)：
(3) For the compensated echo signal s c (x, y, k) performing azimuthal two-dimensional Fourier transform to obtain S (k) x ,k y ,k)：
S(k x ,k y ,k)＝∫∫s c (x,y,k)exp(-jk x x-jk y y)dxdy
wherein ,kx ,k y ,k z Representing the components of the spatial wavenumber in three coordinate directions, respectively.
(4) For S (k) x ,k y K) resampling to obtain a sample in (k) x ,k y ,k z ) Data for a uniform distribution of domains:
(5) Obtaining a three-dimensional reconstruction result of the target by utilizing three-dimensional inverse Fourier transform:
wherein ,
representing an inverse three-dimensional fourier transform.
Further, the imaging method corresponding to MIMO array scanning designed in step 3 is fully integrated into the imaging algorithm accelerator 301 of the FPGA edge computing module 3.
The present invention will be further illustrated by the following examples, with the understanding that the present invention is more fully understood.
Embodiment one:
referring to fig. 5, a MIMO array layout is performed, n=3, m=4, nc=30, the equivalent sampling point number ncnm=360, the total number of transmit-receive antennas is (n+m) nc=210, the total number of transmit-receive antennas required for the corresponding half-wavelength full array is 720, and the total number of transmit-receive antennas required in this embodiment is 7/24 of the total number of transmit-receive antennas required for the corresponding full array. The row spacing h=10mm of the receiving and transmitting antenna, the frequency range of the millimeter wave broadband linear frequency modulation signal is 60-64GHz, the frequency dimension sampling point number F=64, the half wavelength lambda/2=2.5mm is obtained by taking the initial frequency of 60GHz as an example, the equivalent sampling length (NM-1) lambda/2=27.5mm of the MIMO unit, and the coverage length (NcNM-1) lambda/2=897.5 mm of the MIMO scanning array. Scanning a human body target at the position 0.35m in front, wherein the imaging size of the front surface and the rear surface is 0.9m multiplied by 1.8m, and the number of times of repeated movement in the vertical array direction with half wavelength is H=720; for bottom detection, nc=10 is only required, i.e. the coverage length of the MIMO scanning arrayThe degree (NcNM-1) λ/2=297.5 mm, and the direction perpendicular to the MIMO array is just like to scan around 300mm, i.e. h=120. Echo data s (r) is obtained from the front and back surfaces of the human body target to be detected r The data size of k is ncnm×h×f=360×720×64, and the sole scan obtains echo data s (r r The data size of k is ncnm×h×f=120×120×64. Finally, the echo data of the front surface, the rear surface and the sole are processed and imaged respectively by using the imaging method of the embodiment, and are synchronously displayed on the display terminal.
In summary, the millimeter wave edge imaging system for multi-angle scanning of the target provided by the invention takes the cost and imaging time of the system into consideration, and utilizes three scanning platforms to work simultaneously, each scanning platform adopts a one-dimensional electric scanning and another-dimensional mechanical scanning mode to realize the front and back surfaces and the bottom of the detected target for one-time scanning detection, millimeter wave echo signals scattered by the target are subjected to all data processing, imaging and displaying processes in the FPGA edge computing module, and finally millimeter wave images of the front, back and sole of the target are synchronously obtained, and no external computer or server and other upper computer terminals are needed.
The system, apparatus, module or unit set forth in the above embodiments may be implemented in particular by a computer chip or entity, or by a product having a certain function.
It should also be noted that the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in a process, method, article or apparatus that comprises the element.
The above examples should be understood as illustrative only and not limiting the scope of the invention. Various changes and modifications to the present invention may be made by one skilled in the art after reading the teachings herein, and such equivalent changes and modifications are intended to fall within the scope of the invention as defined in the appended claims.
Claims (8)
1. A millimeter wave edge imaging system for multi-angle scanning of a target, comprising:
the device comprises a front millimeter wave scanning platform, a rear millimeter wave scanning platform, a MIMO scanning module, an FPGA edge computing module and a display terminal, wherein the front millimeter wave scanning platform and the rear millimeter wave scanning platform are vertically arranged; wherein,
the three scanning platforms are respectively provided with an MIMO scanning module and an FPGA edge computing module;
the MIMO scanning module performs mechanical scanning on the corresponding scanning platform according to vertical up-and-down movement and horizontal left-and-right movement, so that synchronous detection of the front, the back and the bottom of a detected target is realized;
the MIMO scanning module comprises an MIMO scanning array, a receiving and transmitting module and a data acquisition module, wherein the MIMO scanning array is used for realizing uniform sampling of equivalent half-wavelength intervals; the receiving and transmitting module is used for generating millimeter wave signals for transmitting and echo signals for receiving, mixing the echo signals with the intrinsic signals, obtaining intermediate frequency signals and transmitting the intermediate frequency signals to the data acquisition module; the data acquisition module acquires the obtained intermediate frequency signals and transmits the intermediate frequency signals to the FPGA edge calculation module through an LVDS interface;
the FPGA edge calculation module processes the intermediate frequency echo signals, completes target reconstruction, identification and enhancement, and performs display driving; and the display terminal is connected with the FPGA module through an HDMI data line and synchronously displays imaging results of the three scanning platforms.
2. The millimeter wave edge imaging system for multi-angle scanning of the target according to claim 1, wherein the FPGA edge computing module comprises an imaging algorithm accelerator, an AI target recognition and enhancement module and a display driving module, wherein the imaging algorithm accelerator comprises an echo data phase compensation unit, a fast Fourier transform unit, an interpolation unit and an inverse Fourier transform unit, a three-dimensional imaging algorithm aiming at the MIMO system can be split and computed according to the units to realize the acceleration of the imaging algorithm, high-precision imaging is met, the time for reading, writing high-latitude data and computing the imaging algorithm can be effectively reduced, the time consumed by computing of a plurality of times of CPU is reduced, and the requirement for real-time display is met; the AI target recognition and enhancement module comprises a neural network inference module and a non-maximum suppression (NMS) post-processing module which are respectively used for dangerous object detection classification and post-stage frame processing, a deep learning processing unit (DPU) of an FPGA is utilized on hardware, a software part uses Vitisai development software to quantize, prune and compile a trained model, and then the model is deployed into an FPGA edge calculation module for real-time inference of an edge; the display driving module includes three parts: the first display time sequence driving module (VGA_driver) can flexibly configure the resolution and refresh rate of the display, and provides pixel address information for displaying pictures; secondly, an image display driving module (sar_2d_disp) requests an algorithm acceleration calculation result after data acquisition is completed, and performs pixel conversion on the result, and a corlomap function is added in the module to enhance the display effect due to poor display effect of a gray level picture so as to obtain a clearer target outline, and finally the module outputs display enhancement pixels carrying image information; third, the display interface driving module (rgb2dvi, vgaddrv_conv_rgbd 2 dvi) inputs the displayed timing information and the pixel information of the picture, and finally connects to the external display through HMDI or VGA.
3. The millimeter wave edge imaging system for target multi-angle scanning of claim 1, wherein said MIMO scanning array is configured to achieve uniform sampling of equivalent half-wavelength intervals, and specifically comprises: the MIMO array consists of Nc MIMO units, wherein each MIMO unit comprises N transmitting antennas and M receiving antennas; the MIMO unit realizes the equivalent and uniform sampling of half wavelength interval in the array direction by configuring the working state of the receiving and transmitting antenna at each moment, and realizes the equivalent and uniform sampling of half wavelength interval in the area with the scanning length L in the array direction.
4. The millimeter wave edge imaging system for target multi-angle scanning according to claim 3, wherein the transmitting antennas in each MIMO unit sequentially work according to sequence numbers, all M receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit can obtain NM equivalent sampling points, and the scanning length of the covered array direction is (NM-1) lambda/2; the alignment mode of N transmitting antennas and M receiving antennas in each MIMO unit is not limited, and the N transmitting antennas and the M receiving antennas can be aligned or not aligned;
two adjacent MIMO units are rotationally symmetrical at 180 degrees, and the interval between the receiving and transmitting antennas closest to each other in the two adjacent MIMO units is half-wavelength lambda/2; and (3) obtaining NcNM equivalent sampling points in total by the MIMO scanning array formed by Nc MIMO units, wherein the scanning length of the covered array direction is L= (NcNM-1) lambda/2.
5. A method of imaging based on the system of any one of claims 1-4, comprising the steps of:
step 201, designing an arrangement mode of a millimeter wave MIMO array with equivalent half-wavelength uniform sampling; the millimeter wave MIMO array with the equivalent half wavelength being uniformly sampled consists of Nc MIMO units, wherein each MIMO unit comprises N transmitting antennas and M receiving antennas; the MIMO unit realizes the equal and uniform sampling of half-wavelength interval in the array direction by configuring the working state of the receiving and transmitting antenna at each moment, and realizes the equal and uniform sampling of half-wavelength interval in the area with the scanning length L in the array direction;
step 202, a step of synthesizing two-dimensional aperture scanning by the MIMO array: forming equivalent sampling points in a direction perpendicular to the MIMO array by mechanically moving the MIMO array, wherein each time of movement of half wavelength, the movement times H are determined by the aperture length in the direction;
step 203, designing an imaging method corresponding to the MIMO array scanning; and performing millimeter wave image three-dimensional reconstruction of the target on the FPGA edge calculation module by utilizing the received target area echo signal.
6. The imaging method according to claim 5, wherein the step 201 designs an arrangement mode of the millimeter wave MIMO array with equivalent half-wavelength uniform sampling, specifically includes:
the M receiving antennas are uniformly distributed, and the interval is 1 time of wavelength lambda; the N transmitting antennas are also uniformly distributed, and the interval is M times of wavelength (M lambda);
the transmitting antennas in each MIMO unit sequentially work according to the sequence numbers, all M receiving antennas simultaneously receive echo signals when each transmitting antenna works, the MIMO unit can obtain NM equivalent sampling points, and the scanning length of the covered array direction is (NM-1) lambda/2;
two adjacent MIMO units are rotationally symmetrical at 180 degrees, and the interval between the nearest receiving and transmitting antennas in the two adjacent MIMO units is half-wavelength (lambda/2); and (3) obtaining NcNM equivalent sampling points in total by the MIMO scanning array formed by Nc MIMO units, wherein the scanning length of the covered array direction is L= (NcNM-1) lambda/2.
7. The imaging method according to claim 5, wherein the step 202, the step of MIMO array synthesis two-dimensional aperture scanning, specifically comprises:
the two vertical scanning platforms are respectively positioned in front of and behind the target to be detected, so that synchronous scanning of the front and the rear of the target is realized; in the direction of the MIMO array, after receiving a scanning start command, the MIMO scanning array is sequentially turned on and off according to a specified sequence to realize horizontal scanning, but the scanning directions of the arrays on the front and back sides are just opposite, namely when the front array is scanned from left to right, the rear array is scanned from right to left; in the direction perpendicular to the MIMO array, the scanning direction is also opposite, i.e. when the front array is swept down from top to bottom, the rear array is swept down to top; the bottom MIMO scanning array is not limited by the scanning directions of the front and back MIMO scanning arrays, and can synchronously and reciprocally scan with the front and back surfaces.
8. The imaging method according to claim 5, wherein the step 203 of designing an imaging method corresponding to MIMO array scanning specifically comprises:
(1) Each scanning platform scans by utilizing a millimeter wave MIMO array with equivalent half-wavelength uniform sampling to obtain echo data s (x, y, k) with the size of NcNMXH XF; wherein F is the sampling point number in the broadband frequency sweeping process of each sampling position, H is the number of times of movement at half wavelength intervals in the vertical direction, (x, y) represents the position of a receiving antenna, and k is the wave number;
(2) Calculating the phase center approximation error e of the MIMO array -jkΔR ：
Phase error factor generated by phase center equivalence
Wherein R represents the distance from the equivalent phase center of the receiving and transmitting antenna to the target center, R to 、R or Respectively represent the distance from the transmitting antenna to the target and the distance from the target to the receiving antenna, d l The distance difference of the first channel transceiver antenna in the array direction, namely the x direction is shown; when the target is reconstructed by utilizing the echo obtained by MIMO array scanning, the receiving and transmitting antenna separation mode is approximated to be a single-station mode at the equivalent phase center position, and the phase center approximation error to be compensated is obtained by delta R and is e -jkΔR ；
(3) Compensating the echo signal by using the phase center approximation error to obtain a compensated echo signal
s c (x,y,k)：
Sigma target reflectivity, r o ＝(x o ,y o ,z o ) Respectively representing the spatial positions of the target areas;
(4) For the compensated echo signal s c (x, y, k) performing azimuthal two-dimensional Fourier transform to obtain S (k) x ,k y ,k)：
S(k x ,k y ,k)＝∫∫s c (x,y,k)exp(-jk x x-jk y y)dxdy
wherein ,kx ,k y ,k z Components of the spatial wave number in three coordinate directions are respectively represented;
(5) For S (k) x ,k y K) resampling to obtain a sample in (k) x ,k y ,k z ) Data for a uniform distribution of domains:
(6) Obtaining a three-dimensional reconstruction result of the target by utilizing three-dimensional inverse Fourier transform:
wherein ,
representing an inverse three-dimensional fourier transform. />
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