CN107942328A - Terahertz aperture coding three-dimensional target scanning imaging method - Google Patents

Abstract

The current two-dimensional imaging technology under the aperture coding imaging system is no longer suitable for three-dimensional targets. To address the above-mentioned defects in the prior art, the present invention provides a terahertz aperture coding three-dimensional target scanning imaging method. The present invention evenly divides the entire 3D imaging area where the 3D target is located into 3D imaging units of the same size, and for each 3D imaging unit, calculates and updates the lens phase modulation factor according to the position of a single 3D imaging unit, which can realize the three-dimensional imaging unit Complete coverage of the 3D imaging area is achieved. The present invention can realize forward-looking high-resolution imaging for short-distance three-dimensional targets, effectively improve the imaging range and speed of terahertz aperture coding imaging, improve imaging efficiency, and reduce computer memory configuration requirements, and can be applied to security inspection and anti-terrorism, target detection and Identify isometric imaging fields.

Description

A terahertz aperture-coded three-dimensional object scanning imaging method

technical field

The invention belongs to the technical field of three-dimensional target block scanning, in particular to a three-dimensional target block scanning method based on terahertz aperture coding imaging.

Background technique

With the development of society, radar high-resolution imaging plays an increasingly important role in ensuring national strategic security and promoting national economic development. Optical radar can provide forward-looking imaging, with short wavelength, high resolution and fast imaging speed, but it relies on target radiation, has poor penetration ability to smoke, dust, fog and obstacles, and is easily affected by environmental factors. Microwave radar can actively detect and has strong penetrating ability. However, due to the low microwave frequency, long wavelength, and low angular resolution, and due to the limitation of the imaging principle, imaging accumulation time is required, and high frame rate and high resolution imaging cannot be achieved. Among them, although synthetic aperture radar (SAR) and inverse synthetic aperture radar (ISAR) imaging can obtain high resolution in the lateral direction through synthetic aperture, both rely on the relative motion between the radar and the target, and cannot look forward to imaging. Array radars and phased array radars require a large number of array elements, complex structures, and high construction and maintenance costs. Microwave correlation imaging technology can realize high-resolution imaging under forward-looking and staring conditions. It constructs a time-uncorrelated and space-orthogonal array signal as the transmitting signal, calculates and deduces the detection signal in the area where the target is located, and obtains target information through the correlation processing between the detection signal and the target echo signal. However, this method needs to construct a large-scale antenna array at the transmitting end, and it is difficult to achieve effective real-time beam pointing control.

Terahertz aperture coded imaging draws on the idea of microwave correlation imaging, and replaces the radar array in microwave correlation imaging by real-time modulation of the array coded aperture on the terahertz beam, thereby forming a time-space two-dimensional randomly distributed radiation field, and finally using the detection echo And the radiation field reference signal matrix realizes high-resolution, forward-looking and staring imaging by solving matrix equations, which makes up for the deficiency that synthetic aperture high-resolution imaging relies on target movement, and realizes more complex and diverse spatial wave modulation. Compared with traditional radars, terahertz waves have higher frequencies and shorter wavelengths, enabling terahertz radars to provide greater absolute bandwidth. Combining aperture coding technology under the same aperture antenna conditions, it is easier to generate diverse illumination patterns and faster The more diverse the irradiation mode, the higher the degree of freedom, the richer the target information carried in the echo, and the greater the potential for high-resolution imaging of the target using the echo. At the same time, the transmission and reception link of the system is single-transmitting and single-receiving, which is easy to realize miniaturization. At present, the 3D target imaging method under this system is seldom studied. It is mainly for 2D target imaging. High-resolution large-scale two-dimensional targets can be scanned and stitched into blocks. Figure 1 is a schematic diagram of a high-resolution scanning imaging scheme for two-dimensional targets in the y direction based on the terahertz aperture coding imaging system. The capital letters A-D in figure 1 represent the terahertz transceiver antenna, array coded aperture, two-dimensional imaging plane and focal plane, respectively.

The array coded aperture has P array elements evenly distributed in the vertical direction, and the array coded aperture has Q array elements evenly distributed in the horizontal direction, and the entire array coded aperture includes P×Q array elements. Considering that the working modes of the imaging system in the horizontal and vertical directions are symmetrical, the vertical direction is taken as an example for illustration. In the vertical direction, the p-th element of the array coding aperture is loaded with the lens phase modulation factor of formula (1) to control the terahertz beam to illuminate the n-th target scanning area:

Among them, f _y is the focal length of the lens, k=2πf _c /c, f _c is the center frequency of the terahertz wave, c is the speed of light, and y _p is the ordinate of the center point of the pth array element in the vertical direction of the array coding aperture , p=1,2...P, is the ordinate at the phase center position of the lens phase modulation factor on the array encoding aperture. The focal plane of two-dimensional imaging is parallel to the imaging plane, and the focal length of the lens can be determined by the terahertz transceiver antenna and the array coded aperture, and the relative position between the array coded aperture and the focal plane. During the scanning process, the focal length of the lens in the lens phase modulation factor is fixed, and the scanning area of the terahertz beam can be changed by changing the position of the phase center. As shown in the figure, by loading N different phase modulation factors, the terahertz beam can be scanned N times on the imaging plane, and the size of each scanning area is exactly the same. Seamless stitching between adjacent scanning areas, such as scanning areas 1 and 2 in Figure 1.

However, the scan stitching method in 2D imaging is not completely suitable for 3D target imaging. Transplant the 2D target high-resolution scanning imaging scheme based on the terahertz aperture coding imaging system in Figure 1 into 3D target imaging. In the process of 3D block scanning, the right side of the entire 3D imaging area is regarded as a 2D imaging plane , by loading the same lens phase modulation factor as in the two-dimensional target high-resolution block scanning imaging scheme, seamless traversal scanning of the right side of the entire three-dimensional imaging area can be achieved, but this method has drawbacks. As shown in Figure 2, Figure 2 is a schematic diagram illustrating the problem of high-resolution block scanning imaging of terahertz aperture coded three-dimensional targets in the Y direction. In the terahertz aperture coding imaging system, the size of the radiation field reference signal matrix is affected by the number of grid cells, and the number of grid cells is determined by the size of the grid cells and the target three-dimensional imaging range. Therefore, in order to reduce the requirements of the imaging system for computer memory configuration, the imaging resolution is first determined according to the parameters of the terahertz aperture coding imaging system, and then the 3D imaging area is evenly divided into M×N three-dimensional The imaging unit is divided into N three-dimensional imaging units in the y direction of the three-dimensional imaging area, and M three-dimensional imaging units in the x direction. The number of three-dimensional imaging units in the entire three-dimensional imaging area is M×N. When the terahertz beam irradiates the 3D imaging unit n, it can irradiate the whole unit; but when the terahertz beam irradiates the 3D imaging units 1, 2 and N, the blank area in the target scanning unit is not irradiated, so the echo The target information for this scan area in . Similarly, if the left side of the 3D imaging area is used as the plane of 2D imaging, the 2D block scanning scheme also cannot completely cover some 3D imaging units.

Similar to the grid division of 2D imaging plane, in microwave correlation imaging, it is proposed to divide the 3D imaging area into grid along the horizontal, vertical and distance directions, then construct the reference signal matrix, and then perform correlation imaging processing. Also suitable for terahertz aperture-encoded imaging. However, this method is aimed at low-resolution imaging in the microwave region, the grid division is relatively sparse, and the scale of the reference signal matrix is relatively small. For high-resolution imaging of relatively large-volume 3D targets, such as the human body in security inspection imaging, the scale of the reference signal matrix that needs to be constructed is doubled. On the one hand, the radiation field reference matrix for the entire human target is huge, and the imaging process requires too much computer memory. Therefore, there is an urgent need for a new 3D object imaging method based on the aperture-encoded imaging system.

Contents of the invention

The 2D imaging technology under the current aperture coding imaging system is no longer suitable for 3D targets. In addition, the currently available 3D imaging technology has low imaging resolution, narrow imaging range, and high requirements for computer system memory. In view of the above defects in the prior art, the present invention provides a terahertz aperture coded three-dimensional object scanning imaging method. The present invention evenly divides the entire 3D imaging area where the 3D target is located into 3D imaging units of the same size, performs scanning and imaging for each 3D imaging unit, and then stitches the imaging results of all 3D imaging units to form the entire 3D imaging result. The invention can realize forward-looking high-resolution imaging of short-distance three-dimensional targets, and can be applied to the fields of short-distance imaging such as security inspection and anti-terrorism, target detection and identification, and the like. The invention can improve the resolution of three-dimensional imaging, expand the range of three-dimensional imaging, reduce the memory configuration requirements of the computer, and improve the operating efficiency of the computer.

For realizing the above object, technical scheme of the present invention is:

A terahertz aperture coded three-dimensional object scanning imaging method, comprising the following steps:

The first step is to determine the parameters of the terahertz aperture coding imaging system and divide the three-dimensional imaging area;

The known parameters of the terahertz aperture coding imaging system are as follows: the vertical height of the array coding aperture in the y direction is h, the horizontal length of the array coding aperture in the x direction v; the distance between the terahertz transceiver antenna and the array coding aperture is a, The distance between the array coding aperture and the left side of the three-dimensional imaging area is b, and the thickness of the three-dimensional imaging area is c.

According to the imaging resolution of the terahertz aperture coding imaging system and the size of the 3D target, the 3D imaging area is evenly divided into M×N 3D imaging units, and the 3D imaging area is divided into N 3D imaging units in the y direction. The x-direction is divided into M three-dimensional imaging units, and the number of three-dimensional imaging units in the entire three-dimensional imaging area is M×N. This step is the same as the subdivision method in the background art.

In the second step, the right side of the 3D imaging area is used as the 2D imaging plane to perform terahertz aperture coded 2D target block scanning imaging, and for each 3D imaging unit on the 3D imaging area, its y direction (vertical direction) is preliminarily solved. ) lens phase modulation factor and x-direction (horizontal direction) lens phase modulation factor, including y-direction digital lens focal length f _{y, mn} and y-direction phase center position And the focal length of the digital lens in the x direction f _{x, mn} and the phase center position in the x direction Where m and n represent the three-dimensional imaging units in the mth row and nth column of the three-dimensional imaging area, m=1, 2...M, n=1, 2...N.

The third step is to determine whether the lens phase modulation factors corresponding to the three-dimensional imaging units in the three-dimensional imaging area need to be corrected;

In the fourth step, it is determined in the third step that the three-dimensional imaging unit that needs to be corrected for the lens phase modulation factor is solved for the correction of the lens phase modulation factor in the y direction (vertical direction) and the solution for the correction of the lens phase modulation factor in the x direction (horizontal direction), Determine its corrected digital lens focal length f _y ′ _,mn in the y direction and the corrected phase center position in the y direction And the corrected digital lens focal length f′ _x,mn in the x direction and the corrected phase center position in the x direction

Step 5: Comprehensive correction of lens phase modulation factor

In order to make the 3D imaging unit completely covered by the terahertz beam in the x direction and the y direction, compare the corrected digital lens focal length f′ _x,mn in the x direction with the corrected digital lens focal length f′ _y,mn in the y direction, Choose the larger one as the digital lens focal length:

f'=max(f' _x,mn ,f' _y,mn ) (14)

When the terahertz aperture coding imaging system scans the three-dimensional imaging area in blocks, the pth row and the qth column of the array coding aperture in the terahertz aperture coding imaging system are loaded with the lens phase modulation factor F _{pq of formula (15), mn} to control the terahertz beam to irradiate the 3D imaging unit in the mth row and nth column of the 3D imaging area:

Where: p=1,2...P, q=1,2...Q, k=2πf _c /c, f _c is the center frequency of the terahertz wave, and c is the speed of light. The array coded aperture is evenly distributed with P array elements in the vertical direction, that is, the y direction, and the array coded aperture is evenly distributed with Q array elements in the horizontal direction, that is, the x direction. The entire array coded aperture contains P×Q array elements . (x _pq , y _pq ) is the coordinate position of the center point of the array element in row p and column q of the array coding aperture, p=1,2...P.

In the second step of the present invention, for each three-dimensional imaging unit on the three-dimensional imaging area, such as the three-dimensional imaging unit in the mth row and the nth column, the phase modulation factor of the lens in the y direction (vertical direction) is initially solved, including the focal length of the digital lens in the y direction f _{y, mn} and y direction phase center position Methods as below:

2.1 Preliminary calculation of the digital lens focal length f _y,mn in the y direction

Use the right side of the 3D imaging area as the 2D imaging plane to scan and image the terahertz aperture-coded 2D target block in the y direction, and determine the terahertz beam emitted by the terahertz transceiver antenna in the terahertz aperture-coded imaging system. Coverage _Sh of the right side of the imaging unit.

Calculate the distance between the right side of each 3D imaging unit and the focal plane under the 2D imaging system (that is, the corresponding focal plane when the right side of the 3D imaging area is used as the 2D imaging plane for terahertz aperture coding 2D imaging) according to the triangle similarity relationship. The distance d:

Then, according to the lens imaging formula, when the right side of the three-dimensional imaging area is used as the two-dimensional imaging plane to scan and image the terahertz aperture coded two-dimensional target block in the y direction, the y direction of the three-dimensional imaging unit in the mth row and nth column The focal length f _y,mn of the digital lens that needs to be loaded:

2.2 Preliminary solution to the phase center position in the y direction

When the right side of the 3D imaging area is used as the 2D imaging plane for terahertz aperture coded 2D target block scanning imaging in the y direction, in order to realize the seamless stitching between the scanning areas during the 2D target block scanning imaging process , the phase center position step length of the lens phase modulation factor to be loaded between adjacent 3D imaging units for:

According to step length It can calculate the phase center position to be loaded in the y direction of the 3D imaging unit in the mth row and nth column of the 3D imaging area

The imaging mechanism of the terahertz aperture coding imaging system works in the same mode in the x direction (ie, the horizontal direction) and the y direction (ie, the vertical direction). For each 3D imaging unit on the 3D imaging area, the same method as in 2.1 and 2.2 The same method is used to complete the initial calculation of the lens phase modulation factor in the x direction (horizontal direction), including the digital lens focal length f _{x, mn} in the x direction and the phase center position in the x direction

In the third step of the present invention, the method for judging whether the lens phase modulation factor corresponding to each three-dimensional imaging unit in the three-dimensional imaging area needs to be corrected is as follows:

Before judging whether the phase modulation factor of the lens corresponding to each three-dimensional imaging unit needs to be corrected, a gray area is determined first: suppose a parallel beam is emitted from the entire array coding aperture along the z-axis direction, the gray area is the coverage of the parallel beam, and the gray area y The vertical height of the direction is the vertical height h of the y direction of the array coding aperture, the horizontal length of the x direction of the gray area is the horizontal length of the x direction of the array coding aperture, and the length of the z direction of the gray area is the array coding aperture to The distance between the right side of the three-dimensional imaging area (that is, the sum of the distance b between the array coding aperture and the left side of the three-dimensional imaging area and the thickness c of the three-dimensional imaging area);

When the three-dimensional imaging unit is completely in the gray area, the lens phase modulation factor that needs to be loaded on the array coded aperture does not need to be corrected, the lens phase modulation factor that needs to be loaded on the array coded aperture is the same as the two-dimensional target imaging, and the focal plane is still the same as the three-dimensional imaging area parallel vertical planes.

When there are 3D imaging units that are not completely in the gray area, the lens phase modulation factor under the 2D scanning imaging system cannot completely cover the 3D imaging area, and the lens phase modulation factor needs to be corrected so that the terahertz beam irradiates the entire 3D imaging area.

In the fourth step of the present invention, for the three-dimensional imaging unit that needs to be corrected for the lens phase modulation factor in the third step (that is, there is a three-dimensional imaging unit that is not completely in the gray area), such as the mth row and the nth column on the three-dimensional imaging area If a three-dimensional imaging unit is not completely in the gray area, the lens phase modulation factor of the three-dimensional imaging unit is corrected, wherein the correction of the lens phase modulation factor includes the correction of the focal length of the digital lens in the y direction, and the phase center position in the y direction The correction of the digital lens focal length in the x direction and the correction of the phase center position in the x direction determine the corrected digital lens focal length f′ _y,mn in the y direction and the corrected phase center position in the y direction And the corrected digital lens focal length f′ _x,mn in the x direction and the corrected phase center position in the x direction The three-dimensional imaging units discussed in the fourth step of the present invention all refer to three-dimensional imaging units that are not completely in the gray area. For any three-dimensional imaging unit that is not completely in the gray area, such as the three-dimensional imaging unit in the mth row and the nth column, use The following steps correct its lens phase modulation factor.

4.1 Correct the focal length of the digital lens in the y direction for the 3D imaging unit that is not completely in the gray area in the 3D imaging area, and calculate the corrected focal length of the digital lens in the y direction f′ _y,mn .

Considering the left side of the entire 3D imaging area as a 2D imaging plane, perform terahertz aperture coded 2D target block scanning imaging in the y direction. The three-dimensional imaging unit in the mth row and nth column that is completely in the gray area, the terahertz beam emitted by the terahertz transceiver antenna in the terahertz aperture coding imaging system is in the three-dimensional imaging unit that is not completely in the gray area (not completely in the gray area) The coverage area on the right side of the 3D imaging unit in the mth row, nth column) of the area is _Sh , and the coverage area of the terahertz beam on the left side of the mth row nth column of the 3D imaging unit that is not completely in the gray area for s _h ;

Assuming that the coverage of the left side of the three-dimensional imaging unit obtained after lens phase modulation factor correction is s″ _h , there is a relationship s″ _h = _s′h +Δs, and Δs can be solved according to the following formula:

where h _mn is the focal point before correction (that is, before the correction of the lens phase modulation factor, the right side of the three-dimensional imaging area is used as the two-dimensional imaging plane to perform terahertz aperture coded two-dimensional target block scanning imaging on the three-dimensional imaging area. The y-axis coordinates of the focal point obtained by the three-dimensional imaging unit in the nth column of m row) can be obtained according to the triangle similarity relationship:

Combining formulas (6), (7) and (8), s″ _h can be obtained.

Calculate the distance from the focal point to the right side of the 3D imaging area when the terahertz aperture coded 2D target is scanned and imaged in blocks by using the right side of the 3D imaging area as the 2D imaging plane after the correction of the lens phase modulation factor is obtained from the triangle similarity relationship distance d'

Calculate the corrected digital lens focal length f′ _y,mn in the y direction according to the lens imaging formula

4.2 For the correction of the phase center position in the y direction, solve the corrected phase center position in the y direction

The shortest vertical distances between the intersection points of the terahertz beams before and after the correction and the top of the left side surface of the three-dimensional imaging unit in the mth row and nth column not completely in the gray area and the gray area are h ₁ and h′ ₁ respectively, Similar to s′ _h and s″ _h , there is a relationship h′ ₁ =h ₁ +Δs, where Δs can be determined by formula (7). In addition, h ₁ can be obtained by the following formula:

After the lens phase modulation factor is corrected, the right side of the 3D imaging area is used as the 2D imaging plane, and the focal point obtained by the 3D imaging unit in the mth row and nth column of the 3D imaging area when the terahertz aperture coded 2D target is scanned and imaged in blocks The y-axis coordinate h′ _mn is

According to the triangle similarity relationship, the corrected phase center position in the y direction can be obtained

4.3 The imaging system of the terahertz aperture-encoded imaging system works in the same mode in the x direction (that is, the horizontal direction) and the y direction (that is, the vertical direction), and the correction of the lens phase modulation factor is required for each of the three-dimensional imaging areas Using the same method as 4.1 and 4.2 to correct the digital lens focal length in the x direction and correct the phase center position in the x direction, determine the corrected digital lens focal length f′ _x,mn and phase in the x direction Central location

Furthermore, during the three-dimensional block scanning process of the present invention, while the target three-dimensional imaging unit is completely covered, the adjacent non-target three-dimensional imaging unit will also be irradiated by the terahertz beam, and the echo information obtained in this way is redundant. of. The echo information can be reconstructed by constructing a radiation field reference signal matrix that includes redundant information, and then the redundant information can be removed to reconstruct the target three-dimensional imaging unit, so that the reconstruction result of each unit does not contain redundant information , and finally combine the reconstruction results of all units to obtain complete target information.

The beneficial technical effect of the present invention is:

The present invention aims at terahertz aperture coded three-dimensional target imaging, and proposes a block scanning and splicing system. Block scanning can reduce the requirements for computer memory configuration for imaging calculations. In addition, the imaging process of each three-dimensional imaging unit can be processed in parallel, and finally splicing can be performed. Under the premise of high resolution, the imaging range and speed of terahertz aperture coding imaging are effectively improved, the imaging efficiency is improved, the requirements for computer memory configuration are reduced, and the operating efficiency of the computer is effectively improved.

In the process of block scanning, the present invention is different from the general two-dimensional block scanning method. According to the position of a single three-dimensional imaging unit, the phase modulation factor of the lens is calculated and updated, which can realize the complete coverage of the three-dimensional imaging unit and realize the three-dimensional imaging A full scan of the area.

The present invention aims at the problem of information redundancy in the reconstruction process of the three-dimensional imaging unit, appropriately expands the scale of the radiation field reference signal matrix, and then combines the echo vector to first reconstruct and then eliminate the redundant information to obtain pure three-dimensional imaging unit information, reducing the The impact of redundant information on the 3D reconstruction process is investigated.

Description of drawings

Figure 1 is a schematic diagram of a two-dimensional target high-resolution scanning imaging scheme based on a terahertz aperture coding imaging system.

Figure 2 is a schematic diagram illustrating the problem of high-resolution block scanning imaging of terahertz aperture-coded three-dimensional targets.

Fig. 3 is a schematic diagram in the y direction of the high-resolution sub-block scanning imaging scheme of the terahertz aperture coded three-dimensional target of the present invention.

Fig. 4 is a schematic diagram in the x direction of the high-resolution block-by-block scanning imaging scheme of a terahertz aperture coded three-dimensional target according to the present invention.

Fig. 5 is a flowchart of a specific embodiment provided by the present invention.

Detailed ways

In order to make the technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described here are only used to explain the present invention, not to limit the present invention.

Referring to FIG. 3 , FIG. 3 is a schematic diagram in the y direction of the high-resolution block-by-block scanning imaging scheme of a terahertz aperture coded three-dimensional target according to the present invention. The height of the y-direction of the gray area in Fig. 3 is the vertical height of the y-direction of the array coded aperture is h, and the length of the z-direction of the gray area is the distance between the array coded aperture and the right side of the three-dimensional imaging area (that is, the array coded aperture and the three-dimensional The sum of the distance b from the left side of the imaging area and the thickness c of the three-dimensional imaging area). The distance between the terahertz transceiver antenna and the array coded aperture is a, the distance between the array coded aperture and the left side of the 3D imaging area is b, the thickness of the 3D imaging area is c, the right side of the 3D imaging area and the 2D imaging system The distance of the focal plane is d. When the 3D imaging units are distributed in the gray area, the y-direction lens phase modulation factor that needs to be loaded on the array coded aperture is the same as that of the 2D target imaging, and the focal plane is still a vertical plane parallel to the 3D imaging area. When the upper end of a certain 3D imaging unit is higher or lower than the gray area (that is, when the 3D imaging unit is not completely in the gray area), the lens phase modulation factor in the y direction under the loading of the 2D scanning imaging system cannot be within y If the direction completely covers the three-dimensional imaging unit, the phase modulation factor of the lens needs to be corrected so that the terahertz beam can completely irradiate the three-dimensional imaging unit in the y direction. As shown in Figure 3, before the lens phase modulation factor in the y direction is corrected, the coverage area of the terahertz beam on the right side of the 3D imaging unit that is not completely in the gray area is _Sh , while the coverage area on the left side of the terahertz beam is is s′ _h . After the lens phase modulation factor in the y direction of the three-dimensional imaging unit is corrected, the beam coverage on the left side of the three-dimensional imaging unit is s″ _h , so that the terahertz wave can irradiate the entire three-dimensional imaging unit in the y direction, and the correction The distance between the focal point after correction and the right side of the 3D imaging unit is d′. h _mn , h′ _mn are the y-axis coordinates of the focal point before and after correction, respectively. h ₁ , h′ ₁ are the terahertz frequencies before and after correction, respectively. The minimum vertical distance between the intersection point of the beam and the left side of the three-dimensional imaging unit that is not completely in the gray area and the gray area. Figure 3 provides the situation that the upper end of the three-dimensional imaging unit is higher than the gray area.

Referring to FIG. 4 , FIG. 4 is a schematic diagram in the x direction of the high-resolution block scanning imaging scheme of a terahertz aperture coded three-dimensional target according to the present invention. The x-direction length of the gray area in Fig. 4 is the lateral length v of the x-direction of the array coding aperture, and the length of the z-direction of the gray area is the distance between the array coding aperture and the right side of the three-dimensional imaging area (that is, the array coding aperture and the three-dimensional imaging The sum of the distance b on the left side of the area and the thickness c of the three-dimensional imaging area). The distance between the terahertz transceiver antenna and the array coded aperture is a, the distance between the array coded aperture and the left side of the 3D imaging area is b, the thickness of the 3D imaging area is c, the right side of the 3D imaging area and the 2D imaging system The distance of the focal plane is d. When the 3D imaging units are distributed in the gray area, the lens phase modulation factor in the x direction that needs to be loaded by the array coded aperture is the same as that of the 2D target imaging, and the focal plane is still a vertical plane parallel to the 3D imaging area. When a 3D imaging unit is not completely in the gray area, the lens phase modulation factor in the x direction under the 2D scanning imaging system cannot completely cover the 3D imaging unit in the x direction, and the lens phase modulation factor needs to be corrected so that the terahertz The beam can completely irradiate the three-dimensional imaging unit. As shown in Figure 4, before the lens phase modulation factor in the x direction is corrected, the coverage of the terahertz beam on the right side of the 3D imaging unit that is not completely in the gray area is S _v , while the coverage of the left side of the terahertz beam is is s′ _v . After the lens phase modulation factor in the x direction of the three-dimensional imaging unit is corrected, the beam coverage on the left side of the three-dimensional imaging unit is s″ _v , so that the terahertz wave in the x direction can irradiate the entire three-dimensional imaging unit, The distance between the corrected focus and the right side of the three-dimensional imaging unit is d'. v _mn and v' _mn are the z-axis coordinates of the focus before and after correction respectively. v ₁ and v' ₁ are the coordinates of the focus before and after correction respectively. The minimum horizontal distance between the intersection point of the Hertz beam and the left side of the 3D imaging unit not completely in the gray area and the gray area. Figure 4 shows the situation where the upper end of the 3D imaging unit is higher than the gray area.

The lens phase modulation factor is determined by the loaded digital lens focal length and phase center position, so the core is to find out the corrected digital lens focal length and phase center position.

With reference to Fig. 5, be flow chart of the present invention, comprise the following steps:

The first step is to determine the parameters of the terahertz aperture coding imaging system and divide the three-dimensional imaging area;

The known parameters of the terahertz aperture coding imaging system are as follows: the vertical height of the array coding aperture in the y direction is h, the horizontal length of the array coding aperture in the x direction v; the distance between the terahertz transceiver antenna and the array coding aperture is a, The distance between the array coding aperture and the left side of the three-dimensional imaging area is b, and the thickness of the three-dimensional imaging area is c.

According to the imaging resolution of the terahertz aperture coding imaging system and the size of the 3D target, the 3D imaging area is evenly divided into M×N 3D imaging units, and the 3D imaging area is divided into N 3D imaging units in the y direction. The x-direction is divided into M three-dimensional imaging units, and the number of three-dimensional imaging units in the entire three-dimensional imaging area is M×N. This step is the same as the subdivision method in the background art.

In the second step, the right side of the 3D imaging area is used as the 2D imaging plane to perform terahertz aperture coded 2D target block scanning imaging, and for each 3D imaging unit on the 3D imaging area, its y direction (vertical direction) is preliminarily solved. ) lens phase modulation factor and x-direction (horizontal direction) lens phase modulation factor, including y-direction digital lens focal length f _{y, mn} and y-direction phase center position And the focal length of the digital lens in the x direction f _{x, mn} and the phase center position in the x direction Where m and n represent the three-dimensional imaging units in the mth row and nth column of the three-dimensional imaging area, m=1, 2...M, n=1, 2...N.

The working modes of the imaging mechanism of the terahertz aperture coding imaging system in the x direction (ie, the horizontal direction) and the y direction (ie, the vertical direction) are the same. Therefore, the preliminary calculation of the lens phase modulation factor in the y direction (vertical direction) is the same as the preliminary calculation of the lens phase modulation factor in the x direction (horizontal direction). The following takes the preliminary solution of the y-direction (vertical direction) lens phase modulation factor as an example to illustrate its specific solution process:

For any 3D imaging unit in the 3D imaging area, such as the 3D imaging unit in the mth row and the nth column, initially solve the y-direction (vertical direction) lens phase modulation factor, including the y-direction digital lens focal length f _{y, mn} and the y-direction phase Central location Methods as below:

2.1 Preliminary calculation of the digital lens focal length f _y,mn in the y direction

Use the right side of the 3D imaging area as the 2D imaging plane to scan and image the terahertz aperture-coded 2D target block in the y direction, and determine the terahertz beam emitted by the terahertz transceiver antenna in the terahertz aperture-coded imaging system. Coverage _Sh of the right side of the imaging unit.

Calculate the distance between the right side of each 3D imaging unit and the focal plane under the 2D imaging system (that is, the corresponding focal plane when the right side of the 3D imaging area is used as the 2D imaging plane for terahertz aperture coding 2D imaging) according to the triangle similarity relationship. The distance d:

Then, according to the lens imaging formula, when the right side of the three-dimensional imaging area is used as the two-dimensional imaging plane to scan and image the terahertz aperture coded two-dimensional target block in the y direction, the y direction of the three-dimensional imaging unit in the mth row and nth column The focal length f _y,mn of the digital lens that needs to be loaded:

2.2 Preliminary solution to the phase center position in the y direction

When the right side of the 3D imaging area is used as the 2D imaging plane for terahertz aperture coded 2D target block scanning imaging in the y direction, in order to realize the seamless stitching between the scanning areas during the 2D target block scanning imaging process , the phase center position step length of the lens phase modulation factor to be loaded between adjacent 3D imaging units for:

According to step length It can calculate the phase center position to be loaded in the y direction of the 3D imaging unit in the mth row and nth column of the 3D imaging area

For each 3D imaging unit on the 3D imaging area, the same method as 2.1 and 2.2 can be used to complete the initial calculation of its x-direction (horizontal direction) lens phase modulation factor, including the digital lens focal length f _{x, mn} in the x direction and the x-direction Phase center position

In the third step, it is determined whether the lens phase modulation factors corresponding to the three-dimensional imaging units in the three-dimensional imaging area need to be corrected.

Before judging whether the phase modulation factor of the lens corresponding to each three-dimensional imaging unit needs to be corrected, a gray area is determined first: suppose a parallel beam is emitted from the entire array coding aperture along the z-axis direction, the gray area is the coverage of the parallel beam, and the gray area y The vertical height of the direction is the vertical height h of the y direction of the array coding aperture, the horizontal length of the x direction of the gray area is the horizontal length of the x direction of the array coding aperture, and the length of the z direction of the gray area is the array coding aperture to The distance between the right side of the three-dimensional imaging area (that is, the sum of the distance b between the array coding aperture and the left side of the three-dimensional imaging area and the thickness c of the three-dimensional imaging area);

When the three-dimensional imaging unit is completely in the gray area, the lens phase modulation factor that needs to be loaded on the array coded aperture does not need to be corrected, the lens phase modulation factor that needs to be loaded on the array coded aperture is the same as the two-dimensional target imaging, and the focal plane is still the same as the three-dimensional imaging area parallel vertical planes.

When there are 3D imaging units that are not completely in the gray area, the lens phase modulation factor under the 2D scanning imaging system cannot completely cover the 3D imaging area, and the lens phase modulation factor needs to be corrected so that the terahertz beam irradiates the entire 3D imaging area.

In the fourth step, it is determined in the third step that the three-dimensional imaging unit that needs to be corrected for the lens phase modulation factor is solved for the correction of the lens phase modulation factor in the y direction (vertical direction) and the solution for the correction of the lens phase modulation factor in the x direction (horizontal direction), Determine its corrected digital lens focal length f′ _y,mn in the y direction and the corrected phase center position in the y direction And the corrected digital lens focal length f′ _x,mn in the x direction and the corrected phase center position in the x direction

For the 3D imaging unit that needs to be corrected for the lens phase modulation factor in the third step (that is, there are 3D imaging units that are not completely in the gray area), for example, the 3D imaging unit in the mth row and nth column of the 3D imaging area is not completely in the In the gray area, the lens phase modulation factor of the three-dimensional imaging unit is corrected, wherein the correction of the lens phase modulation factor includes the correction of the focal length of the digital lens in the y direction, the correction of the phase center position in the y direction, and the correction of the phase center position in the x direction. The correction of the focal length of the digital lens and the correction of the phase center position in the x direction, determine the corrected digital lens focal length f′ _y,mn in the y direction and the corrected phase center position in the y direction And the corrected digital lens focal length f′ _x,mn in the x direction and the corrected phase center position in the x direction

4.1 Correct the focal length of the digital lens in the y direction for the 3D imaging unit that is not completely in the gray area in the 3D imaging area, and calculate the corrected focal length of the digital lens in the y direction f′ _y,mn .

Considering the left side of the entire 3D imaging area as a 2D imaging plane, perform terahertz aperture coded 2D target block scanning imaging in the y direction. The 3D imaging unit in row m and column n that is completely in the gray area, the coverage of the terahertz beam emitted by the terahertz transceiver antenna in the terahertz aperture coding imaging system on the right side of the 3D imaging unit that is not completely in the gray area The range is S _h , and the coverage area of the terahertz beam on the left side of the three-dimensional imaging unit in the mth row and nth column that is not completely in the gray area is s′ _h ;

Assuming that the coverage of the left side of the three-dimensional imaging area obtained after lens phase modulation factor correction is s″ _h , there is a relationship s″ _h = _s′h +Δs, and Δs can be solved according to the following formula:

where h _mn is the focal point before correction (that is, before the correction of the lens phase modulation factor, the right side of the three-dimensional imaging area is used as the two-dimensional imaging plane to perform terahertz aperture coded two-dimensional target block scanning imaging on the three-dimensional imaging area. The y-axis coordinates of the initial focus obtained by the 3D imaging unit in the nth column of row m) can be obtained according to the triangle similarity relationship:

Combining formulas (6), (7) and (8), s″ _h can be obtained.

Calculate the distance from the focal point to the right side of the 3D imaging area when the terahertz aperture coded 2D target is scanned and imaged in blocks by using the right side of the 3D imaging area as the 2D imaging plane after the correction of the lens phase modulation factor is obtained from the triangle similarity relationship distance d'

Calculate the corrected digital lens focal length f′ _y,mn in the y direction according to the lens imaging formula

4.2 For the correction of the phase center position in the y direction, solve the corrected phase center position in the y direction

The shortest vertical distances between the intersection points of the terahertz beams before and after the correction and the top of the left side surface of the three-dimensional imaging unit in the mth row and nth column not completely in the gray area and the gray area are h ₁ and h′ ₁ respectively, Similar to s′ _h and s″ _h , there is a relationship h′ ₁ =h ₁ +Δs, where Δs can be determined by formula (7). In addition, h ₁ can be obtained by the following formula:

After the lens phase modulation factor is corrected, the right side of the 3D imaging area is used as the 2D imaging plane, and the focal point obtained by the 3D imaging unit in the mth row and nth column of the 3D imaging area when the terahertz aperture coded 2D target is scanned and imaged in blocks The y-axis coordinate h′ _mn is

According to the triangle similarity relationship, the corrected phase center position in the y direction can be obtained

The imaging system of the terahertz aperture coding imaging system works in the same mode in the x direction (ie, the horizontal direction) and the y direction (ie, the vertical direction). For the three-dimensional imaging unit, use the same method as 4.1 and 4.2 to correct the focal length of the digital lens in the x direction and correct the position of the phase center in the x direction, and determine the corrected digital lens focal length f′ _x,mn and phase center in the x direction Location

Step 5: Comprehensive correction of lens phase modulation factor

In order to make the 3D imaging unit completely covered by the terahertz beam in the x direction and the y direction, compare the corrected digital lens focal length f′ _x,mn in the x direction with the corrected digital lens focal length f′ _y,mn in the y direction, Choose the larger one as the digital lens focal length:

f'=max(f' _x,mn ,f' _y,mn ) (14)

When the terahertz aperture coding imaging system scans the three-dimensional imaging area in blocks, the pth row and the qth column of the array coding aperture in the terahertz aperture coding imaging system are loaded with the lens phase modulation factor F _{pq of formula (15), mn} to control the terahertz beam to irradiate the 3D imaging unit in the mth row and nth column of the 3D imaging area:

Where: p=1,2...P, q=1,2...Q, k=2πf _c /c, f _c is the center frequency of the terahertz wave, and c is the speed of light. The array coded aperture is evenly distributed with P array elements in the vertical direction, that is, the y direction, and the array coded aperture is evenly distributed with Q array elements in the horizontal direction, that is, the x direction. The entire array coded aperture contains P×Q array elements . (x _pq , y _pq ) is the coordinate position of the center point of the array element in row p and column q of the array coding aperture, p=1,2...P.

Furthermore, during the three-dimensional block scanning process of the present invention, while the target three-dimensional imaging unit is completely covered, the adjacent non-target three-dimensional imaging unit will also be irradiated by the terahertz beam, and the echo information obtained in this way is redundant. of. The echo information can be reconstructed by constructing a radiation field reference signal matrix that includes redundant information, and then the redundant information can be removed to reconstruct the target three-dimensional imaging unit, so that the reconstruction result of each unit does not contain redundant information , and finally combine the reconstruction results of all units to obtain complete target information.

In the following, for the terahertz aperture coding imaging system, given the system parameters, the core parameters of the lens phase modulation factor in the present invention are obtained through calculation and simulation, and the practicability of the method of the present invention is verified.

Determine the height h=0.50m in the vertical direction of the array coding aperture, and the width in the horizontal direction is also 0.5m. The vertical direction contains 25 rows of array elements, and the horizontal direction contains 25 rows of array elements, with a total of 625 array elements. The horizontal distance between the terahertz transceiver antenna and the array coding aperture is a=0.25m, the distance between the array coding aperture and the left side of the three-dimensional imaging area is b=0.75m, the thickness of the three-dimensional imaging area is c=0.25m, and the three-dimensional imaging area is on the xoy plane The projection range on is 1.8m×1.8m, and the size of the right side of the three-dimensional imaging unit is set to s=0.1m.

The Prime Minister divides the three-dimensional imaging area into 18×18=324 three-dimensional imaging units along the horizontal and vertical directions, and for the three-dimensional imaging units of the ninth row and the tenth column, the method of the present invention determines its lens phase modulation factor core parameter digital lens focal length and Phase center position. Judging that the three-dimensional imaging unit is in the gray area, the focal length and phase center position of the digital lens can be obtained by direct calculation as 0.2065m and (-0.0109m, 0.0109m) respectively.

For the 3D imaging unit in the 4th row and 5th column, it can be judged that the 3D imaging unit is not in the gray area, and the focal length and phase center position of the digital lens in the x direction and y direction are respectively calculated to obtain f′ _x = 0.2127m, f′ _y = 0.2153m and (0.0978m, 0.1196m). According to step 2, select a larger lens focal length to determine the corrected digital lens focal length and phase center position as 0.2153m and (0.0978m, 0.1196m).

According to the above method provided by the present invention, the lens phase modulation factors corresponding to each three-dimensional imaging unit can be calculated separately, and after the block scanning is completed, redundant information can be removed according to the method proposed by the present invention, and a complete three-dimensional imaging target can be spliced.

In summary, although the present invention has been disclosed above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make various modifications without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims (5)

1. A terahertz aperture coding three-dimensional object scanning imaging method, is characterized in that, comprises the following steps: The first step is to determine the parameters of the terahertz aperture coding imaging system and divide the three-dimensional imaging area; The second step is to use the right side of the 3D imaging area as the 2D imaging plane to scan and image the 2D target with terahertz aperture coding, and to calculate the phase modulation factor of the lens in the y direction for each 3D imaging unit in the 3D imaging area. And the lens phase modulation factor in the x direction, including the focal length of the digital lens in the y direction f _y,mn and the phase center position in the y direction And the focal length of the digital lens in the x direction f _{x, mn} and the phase center position in the x direction Where m and n represent the three-dimensional imaging unit in the mth row and nth column of the three-dimensional imaging area, m=1,2...M, n=1,2...N; The third step is to determine whether the lens phase modulation factors corresponding to the three-dimensional imaging units in the three-dimensional imaging area need to be corrected; Step 4: For the three-dimensional imaging unit that needs to be corrected for the lens phase modulation factor in the third step, the lens phase modulation factor correction solution in the y direction and the lens phase modulation factor correction solution in the x direction are determined, and the corrected number in the y direction is determined. Lens focal length f′ _y,mn and the corrected phase center position in the y direction And the corrected digital lens focal length f′ _x,mn in the x direction and the corrected phase center position in the x direction The fifth step, comprehensive correction of the lens phase modulation factor; In order to make the 3D imaging unit completely covered by the terahertz beam in the x direction and the y direction, compare the corrected digital lens focal length f′ _x,mn in the x direction with the corrected digital lens focal length f′ _y,mn in the y direction, Choose the larger one as the digital lens focal length: f'=max(f' _x,mn ,f' _y,mn ) (14) When the terahertz aperture coding imaging system scans the three-dimensional imaging area in blocks, the pth row and the qth column of the array coding aperture in the terahertz aperture coding imaging system are loaded with the lens phase modulation factor F _{pq of formula (15), mn} to control the terahertz beam to irradiate the 3D imaging unit in the mth row and nth column of the 3D imaging area: <mrow><msub><mi>F</mi><mrow><mi>p</mi><mi>q</mi><mo>,</mo><mi>m</mi><mi>n</mi></mrow></msub><mo>=</mo><msup><mi>e</mi><mrow><mo>-</mo><mi>i</mi><mfrac><mi>k</mi><mrow><mn>2</mn><msup><mi>f</mi><mo>&amp;prime;</mo></msup></mrow></mfrac><mo>&amp;lsqb;</mo><msup><mrow><mo>(</mo><msub><mi>x</mi><mrow><mi>p</mi><mi>q</mi></mrow></msub><mo>-</mo><msubsup><mover><mi>x</mi><mo>^</mo></mover><mrow><mi>m</mi><mi>n</mi></mrow><mo>&amp;prime;</mo></msubsup><mo>)</mo></mrow><mn>2</mn></msup><mo>+</mo><msup><mrow><mo>(</mo><msub><mi>y</mi><mrow><mi>p</mi><mi>q</mi></mrow></msub><mo>-</mo><msubsup><mover><mi>y</mi><mo>^</mo></mover><mrow><mi>m</mi><mi>n</mi></mrow><mo>&amp;prime;</mo></msubsup><mo>)</mo></mrow><mn>2</mn></msup><mo>&amp;rsqb;</mo></mrow></msup><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>15</mn><mo>)</mo></mrow></mrow> Among them: p=1,2...P, q=1,2...Q, k=2πf _c /c, f _c is the center frequency of the terahertz wave, c is the speed of light; the array coding aperture is in the vertical direction, that is, the y direction P array elements are evenly distributed on the array coding aperture, and Q array elements are evenly distributed in the horizontal direction, that is, in the x direction, and the entire array coding aperture contains P×Q array elements; (x _pq ,y _pq ) is the array coding The coordinate position of the center point of the array element in the pth row and the qth column of the aperture, p=1,2...P. 2. The terahertz aperture coded three-dimensional object scanning imaging method according to claim 1, characterized in that: in the first step: the known parameters of the terahertz aperture coded imaging system are as follows: the vertical height of the y-direction of the array coded aperture is h, the lateral length of the array coding aperture in the x direction; the distance between the terahertz transceiver antenna and the array coding aperture is a, the distance between the array coding aperture and the left side of the three-dimensional imaging area is b, and the thickness of the three-dimensional imaging area is c; According to the imaging resolution of the terahertz aperture coding imaging system and the size of the 3D target, the 3D imaging area is evenly divided into M×N 3D imaging units, and the 3D imaging area is divided into N 3D imaging units in the y direction. The x-direction is divided into M three-dimensional imaging units, and the number of three-dimensional imaging units in the entire three-dimensional imaging area is M×N. 3. The terahertz aperture coded three-dimensional object scanning imaging method according to claim 2, characterized in that: in the second step, for each three-dimensional imaging unit on the three-dimensional imaging area, such as the three-dimensional imaging unit in the mth row and the nth column, Preliminary solution of its y-direction lens phase modulation factor, including y-direction digital lens focal length f _{y, mn} and y-direction phase center position Methods as below: 2.1 Preliminary calculation of the digital lens focal length f _y,mn in the y direction Use the right side of the 3D imaging area as the 2D imaging plane to scan and image the terahertz aperture-coded 2D target block in the y direction, and determine the terahertz beam emitted by the terahertz transceiver antenna in the terahertz aperture-coded imaging system. Coverage _Sh on the right side of the imaging unit; Calculate the distance d between the right side of each three-dimensional imaging unit and the focal plane under the two-dimensional imaging system according to the triangle similarity relationship: <mrow><mi>d</mi><mo>=</mo><mfrac><mrow><msub><mi>s</mi><mi>h</mi></msub><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>)</mo>mo></mrow></mrow><mrow><mi>h</mi><mo>-</mo><msub><mi>s</mi><mi>h</mi></msub></mrow></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>2</mn><mo>)</mo></mrow></mrow> Then, according to the lens imaging formula, when the right side of the three-dimensional imaging area is used as the two-dimensional imaging plane to scan and image the terahertz aperture coded two-dimensional target block in the y direction, the y direction of the three-dimensional imaging unit in the mth row and nth column The focal length f _y,mn of the digital lens that needs to be loaded: <mrow><msub><mi>f</mi><mrow><mi>y</mi><mo>,</mo><mi>m</mi><mi>n</mi></mrow></msub><mo>=</mo><mfrac><mrow><mi>a</mi><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><mi>d</mi><mo>)</mo></mrow></mrow><mrow><mi>a</mi><mo>+</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><mi>d</mi></mrow></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>3</mn><mo>)</mo></mrow></mrow> 2.2 Preliminary solution to the phase center position in the y direction When the right side of the 3D imaging area is used as the 2D imaging plane for terahertz aperture coded 2D target block scanning imaging in the y direction, in order to realize the seamless stitching between the scanning areas during the 2D target block scanning imaging process , the phase center position step length of the lens phase modulation factor to be loaded between adjacent three-dimensional imaging units for: <mrow><mi>&amp;Delta;</mi><mover><mi>y</mi><mo>^</mo></mover><mo>=</mo><mfrac><mrow><mi>a</mi><mo>&amp;CenterDot;</mo><mi>s</mi><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><mi>d</mi><mo>)</mo></mrow></mrow><mrow><mo>(</mo><mi>a</mi><mo>+</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><mi>d</mi><mo>)</mo><mo>&amp;CenterDot;</mo><mo>(</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>)</mo></mrow></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>4</mn><mo>)</mo></mrow></mrow> According to step length It can calculate the phase center position to be loaded in the y direction of the 3D imaging unit in the mth row and nth column of the 3D imaging area <mrow><msub><mover><mi>y</mi><mo>^</mo></mover><mrow><mi>m</mi><mi>n</mi></mrow></msub><mo>=</mo><mfrac><mrow><mi>N</mi><mo>+</mo><mn>1</mn><mo>-</mo><mn>2</mn><mi>n</mi></mrow><mn>2</mn></mfrac><mo>&amp;CenterDot;</mo><mi>&amp;Delta;</mi><mover><mi>y</mi><mo>^</mo></mover><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>5</mn><mo>)</mo></mrow></mrow> The imaging system of the terahertz aperture coding imaging system has the same working mode in the x direction and the y direction. For each 3D imaging unit in the 3D imaging area, the same method as 2.1 and 2.2 is used to complete the preliminary calculation of the lens phase in the x direction. Modulation factor, including the digital lens focal length f _x,mn in the x direction and the phase center position in the x direction 4. The terahertz aperture coding three-dimensional object scanning imaging method according to claim 3, characterized in that: in the third step, the method for judging whether the lens phase modulation factor corresponding to each three-dimensional imaging unit in the three-dimensional imaging area needs to be corrected is as follows: Before judging whether the phase modulation factor of the lens corresponding to each three-dimensional imaging unit needs to be corrected, a gray area is determined first: suppose a parallel beam is emitted from the entire array coding aperture along the z-axis direction, the gray area is the coverage of the parallel beam, and the gray area y The vertical height of the direction is the vertical height h of the y direction of the array coding aperture, the horizontal length of the x direction of the gray area is the horizontal length of the x direction of the array coding aperture, and the length of the z direction of the gray area is the array coding aperture to The distance between the right sides of the 3D imaging area; When the three-dimensional imaging unit is completely in the gray area, the lens phase modulation factor that needs to be loaded on the array coded aperture does not need to be corrected, and the lens phase modulation factor that needs to be loaded on the array coded aperture is the same as the two-dimensional target imaging; When there are 3D imaging units that are not completely in the gray area, the lens phase modulation factor under the 2D scanning imaging system cannot completely cover the 3D imaging area, and the lens phase modulation factor needs to be corrected so that the terahertz beam irradiates the entire 3D imaging area. 5. The terahertz aperture coded three-dimensional target scanning imaging method according to claim 4, characterized in that: in the third step, any part that needs to be corrected for the lens phase modulation factor in the third step is not completely in the gray area The three-dimensional imaging unit of is such as the three-dimensional imaging unit in the mth row and the nth column, and the following steps are used to correct its lens phase modulation factor: 4.1 Correct the focal length of the digital lens in the y direction for the 3D imaging unit that is not completely in the gray area on the 3D imaging area, and solve the focal length f′ _y,mn of the digital lens in the corrected y direction; Consider the left side of the entire 3D imaging area as a 2D imaging plane to perform terahertz aperture coded 2D target block scanning imaging in the y direction. For any 3D imaging unit that is not completely in the gray area on the 3D imaging area, such as the m In the nth column of 3D imaging unit, the coverage of the terahertz beam emitted by the terahertz transceiver antenna in the terahertz aperture coding imaging system on the right side of the 3D imaging unit that is not completely in the gray area is S _h , the terahertz beam The coverage area on the left side of the three-dimensional imaging unit in the mth row and nth column that is not completely in the gray area is s _h '; <mrow><msubsup><mi>s</mi><mi>h</mi><mo>&amp;prime;</mo></msubsup><mo>=</mo><mfrac><mrow><mo>(</mo><mi>c</mi><mo>+</mo><mi>d</mi><mo>)</mo><mo>&amp;CenterDot;</mo><msub><mi>s</mi><mi>h</mi></msub></mrow><mi>d</mi></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>6</mn><mo>)</mo></mrow></mrow> Assuming that the coverage area of the left side of the three-dimensional imaging unit obtained after lens phase modulation factor correction is s _h ″, there is a relationship s _h ″=s _h ′+Δs, and Δs is solved according to the following formula: <mrow><mi>&amp;Delta;</mi><mi>s</mi><mo>=</mo><mfrac><mrow><mi>c</mi><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mo>|</mo><msub><mi>h</mi><mrow><mi>m</mi><mi>n</mi></mrow></msub><mo>|</mo><mo>-</mo><mi>h</mi><mo>/</mo><mn>2</mn><mo>)</mo></mrow></mrow><mrow><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><mi>d</mi></mrow></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>7</mn><mo>)</mo></mrow></mrow> Where h _mn is the y-axis coordinate of the focus before correction, which can be obtained according to the triangle similarity relationship: <mrow><msub><mi>h</mi><mrow><mi>m</mi><mi>n</mi></mrow></msub><mo>=</mo><mfrac><mrow><msub><mover><mi>y</mi><mo>^</mo></mover><mrow><mi>m</mi><mi>n</mi></mrow></msub><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mi>a</mi><mo>+</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><mi>d</mi><mo>)</mo></mrow></mi>mrow><mi>a</mi></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>8</mn><mo>)</mo></mrow></mrow> Comprehensive formula (6), (7) and (8), obtain s″ _h ; Calculate the distance from the focal point to the right side of the 3D imaging area when the terahertz aperture coded 2D target is scanned and imaged in blocks by using the right side of the 3D imaging area as the 2D imaging plane after the correction of the lens phase modulation factor is obtained from the triangle similarity relationship distance d' <mrow><msup><mi>d</mi><mo>&amp;prime;</mo></msup><mo>=</mo><mfrac><mrow><msubsup><mi>s</mi><mi>h</mi><mrow><mo>&amp;prime;</mo><mo>&amp;prime;</mo></mrow></msubsup><mo>&amp;CenterDot;</mo><mi>b</mi><mo>+</mo><msubsup><mi>s</mi><mi>h</mi><mrow><mo>&amp;prime;</mo><mo>&amp;prime;</mo></mrow></msubsup><mo>&amp;CenterDot;</mo><mi>c</mi><mo>-</mo><mi>h</mi><mo>&amp;CenterDot;</mo><mi>c</mi></mrow><mrow><mi>h</mi><mo>-</mo><msubsup><mi>s</mi><mi>h</mi><mrow><mo>&amp;prime;</mo><mo>&amp;prime;</mo></mrow></msubsup></mrow></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>9</mn><mo>)</mo></mrow></mrow> Calculate the corrected digital lens focal length f _y ′ _,mn in the y direction according to the lens imaging formula <mrow><msubsup><mi>f</mi><mrow><mi>y</mi><mo>,</mo><mi>m</mi><mi>n</mi></mrow><mo>&amp;prime;</mo></msubsup><mo>=</mo><mfrac><mrow><mi>a</mi><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><msup><mi>d</mi><mo>&amp;prime;</mo></msup><mo>)</mo></mrow></mrow><mrow><mi>a</mi><mo>+</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><msup><mi>d</mi><mo>&amp;prime;</mo></msup></mrow></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>10</mn><mo>)</mo></mrow></mrow> 4.2 For the correction of the phase center position in the y direction, solve the corrected phase center position in the y direction The shortest vertical distances between the intersection points of the terahertz beams before and after the correction and the upper left side surface of the three-dimensional imaging unit in the mth row and nth column not completely in the gray area and the gray area are h ₁ and h ₁ ′ respectively, Similar to s _h ′ and s _h ″, there is a relationship h ₁ ′=h ₁ +Δs, where Δs can be determined by formula (7); in addition, h ₁ can be obtained by the following formula: <mrow><msub><mi>h</mi><mn>1</mn></msub><mo>=</mo><mfrac><mrow><mi>b</mi><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mo>|</mo><msub><mi>h</mi><mrow><mi>m</mi><mi>n</mi></mrow></msub><mo>|</mo><mo>-</mo><mi>h</mi><mo>/</mo><mn>2</mn><mo>)</mo></mrow></mrow><mrow><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><mi>d</mi></mrow></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>11</mn><mo>)</mo></mrow></mrow> After the lens phase modulation factor is corrected, the right side of the 3D imaging area is used as the 2D imaging plane, and the focal point obtained by the 3D imaging unit in the mth row and nth column of the 3D imaging area when the terahertz aperture coded 2D target is scanned and imaged in blocks The y-axis coordinate h′ _mn is <mrow><msubsup><mi>h</mi><mrow><mi>m</mi><mi>n</mi></mrow><mo>&amp;prime;</mo></msubsup><mo>=</mo><mfenced open = "{" close = ""><mtable><mtr><mtd><mrow><mfrac><mrow><msubsup><mi>h</mi><mn>1</mn><mo>&amp;prime;</mo></msubsup><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mrow><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><msup><mi>d</mi><mo>&amp;prime;</mo></msup></mrow><mo>)</mo></mrow></mrow><mi>b</mi></mfrac><mo>+</mo><mi>h</mi><mo>/</mo><mn>2</mn></mrow></mtd><mtd><mrow><msub><mover><mi>y</mi><mo>^</mo></mover><mi>n</mi></msub><mo>&gt;</mo><mn>0</mn></mrow></mtd></mtr><mtr><mtd><mrow><mo>-</mo><mfrac><mrow><msubsup><mi>h</mi><mn>1</mn><mo>&amp;prime;</mo></msubsup><mo>&amp;CenterDot;</mo><mrow><mo>(</mo><mrow><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><msup><mi>d</mi><mo>&amp;prime;</mo></msup></mrow><mo>)</mo></mrow></mrow><mi>b</mi></mfrac><mo>-</mo><mi>h</mi><mo>/</mo><mn>2</mn></mrow></mtd><mtd><mrow><msub><mover><mi>y</mi><mo>^</mo></mover><mi>n</mi></msub><mo>&gt;</mo><mn>0</mn></mrow></mtd></mtr></mtable></mfenced><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>12</mn><mo>)</mo></mrow></mrow> According to the triangle similarity relationship, the corrected phase center position in the y direction can be obtained <mrow><msubsup><mover><mi>y</mi><mo>^</mo></mover><mrow><mi>m</mi><mi>n</mi></mrow><mo>&amp;prime;</mo></msubsup><mo>=</mo><mfrac><mrow><mi>a</mi><mo>&amp;CenterDot;</mo><msubsup><mi>h</mi><mrow><mi>m</mi><mi>n</mi></mrow><mo>&amp;prime;</mo></msubsup></mrow><mrow><mi>a</mi><mo>+</mo><mi>b</mi><mo>+</mo><mi>c</mi><mo>+</mo><msup><mi>d</mi><mo>&amp;prime;</mo></msup></mrow></mfrac><mo>-</mo><mo>-</mo><mo>-</mo><mrow><mo>(</mo><mn>13</mn><mo>)</mo></mrow></mrow> 4.3 The imaging system of the terahertz aperture coded imaging system has the same working mode in the x direction and the y direction. For each 3D imaging unit that needs to correct the lens phase modulation factor in the 3D imaging area, the same method as 4.1 and 4.2 is used. The method corrects the focal length of the digital lens in the x direction and corrects the phase center position in the x direction, and determines the corrected digital lens focal length f _x ′ _{, mn} and the phase center position in the x direction