CN110806590B - Terahertz active and passive composite imaging quasi-optical scanning system - Google Patents

Abstract

Translated fromChinese

本公开提供一种太赫兹主、被动复合成像准光学扫描系统，包括：主动成像发射线阵，发射第一太赫兹信号；第一反射镜，反射第一太赫兹信号；聚焦透镜，为双曲型平凸聚焦透镜，聚焦第一反射镜反射后的第一太赫兹信号；第二反射镜，将聚焦透镜聚焦后的第一太赫兹信号反射至待成像目标生成回波信号；主动成像接收线阵，接收回波信号并处理得到回波信号的幅度与相位信息；极化线栅，将待成像目标自身辐射出的、经第二反射镜反射进入聚焦透镜聚焦后再经第一反射镜反射后的第二太赫兹信号反射至被动成像辐射计阵列，同时透过回波信号；主动成像发射线阵与接收线阵之间设置有分束器和吸波板实现第一太赫兹信号的收、发隔离；实现太赫兹主、被动复合成像。

The present disclosure provides a terahertz active and passive composite imaging quasi-optical scanning system, comprising: an active imaging emission line array, which emits a first terahertz signal; a first mirror, which reflects the first terahertz signal; and a focusing lens, which is hyperbolic Type plano-convex focusing lens, focusing the first terahertz signal reflected by the first mirror; second reflecting mirror, reflecting the first terahertz signal focused by the focusing lens to the target to be imaged to generate echo signals; active imaging receiving line Array, receive the echo signal and process to obtain the amplitude and phase information of the echo signal; polarization wire grid, radiate from the object to be imaged, reflected by the second mirror into the focusing lens, and then reflected by the first mirror The second terahertz signal is reflected to the passive imaging radiometer array, and the echo signal is transmitted at the same time; a beam splitter and an absorbing plate are arranged between the active imaging transmitting line array and the receiving line array to realize the reception of the first terahertz signal. , hair isolation; realize terahertz active and passive composite imaging.

Description

Terahertz active and passive composite imaging quasi-optical scanning system

Technical Field

The utility model relates to a terahertz imaging technology field especially relates to a terahertz is main, passive compound imaging quasi-optical scanning system now.

Background

The terahertz scientific technology is highly valued by all countries in the world and has important scientific value and application value. Terahertz waves are between microwaves and infrared light, belong to far infrared bands, have the characteristics of wide frequency band, low energy, fingerprint spectrum and the like, and are widely applied to the field of imaging. Terahertz imaging is one of important applications of terahertz wave bands, and compared with microwave imaging, terahertz waves have shorter wavelength and higher resolution; compared with infrared and optical imaging, the terahertz wave has good penetrability on nonpolar materials such as fibers, leather, plastics and the like; compared with X-ray imaging, terahertz photon energy is only one millionth of X-ray photon energy, and loss of living organisms is avoided. By integrating various advantages, the terahertz imaging has great application value in the fields of safety monitoring, biomedicine and the like.

For terahertz imaging technology, there are various classification methods. The terahertz radiation source can be divided into a terahertz active imaging mode and a terahertz passive imaging mode according to whether the terahertz radiation source is used or not. The terahertz imaging in a passive mode is to detect and receive electromagnetic radiation of a target and a background in a detected scene by using a high-sensitivity terahertz radiometer. Different substances have different radiation characteristics, and different objects can be identified according to the difference of the terahertz radiation capability between the scenes of the target and between the parts of the scenes, which is the basic working principle of the terahertz passive imaging mode. The indoor imaging device has the advantages of simple imaging structure, good uniformity of indoor imaging images, no problem of safe radiation, no privacy invasion and small influence of the attitude angle of the target on the imaging effect. However, since the radiation intensity of the target itself is weak and the signal-to-noise ratio is low, the contrast of the imaging result is low and the imaging is not clear enough, as shown in fig. 1 (a). And the passive imaging mode is greatly affected by the environment. For example, the imaging effect in the open space outdoors is much better than the case of other radiators indoors. In the active terahertz imaging system, a terahertz emission source radiates terahertz waves during working, the terahertz emission source irradiates a target through a radiation antenna, coherent signals reflected, scattered or projected by the target are collected and converged by an optical system and enter a detector, and a terahertz image of the target is obtained after the coherent signals are processed by an image processing system, so that the properties and characteristics of the imaged target are analyzed and obtained. The method is characterized by high coherent detection signal-to-noise ratio, less environmental influence on imaging effect and three-dimensional imaging capability, as shown in fig. 1 (b). However, the active imaging mode is also limited, because polar targets such as water have strong absorption to terahertz waves, the targets cannot be imaged, and in addition, active terahertz imaging has multiple reflection artifacts, which are formed by receiving multiple reflection signals of terahertz waves on the surface of a human body by an antenna.

The majority of research at home and abroad aiming at terahertz imaging is independent active imaging or passive imaging, and the respective characteristics of two imaging modes cannot be combined.

BRIEF SUMMARY OF THE PRESENT DISCLOSURE

Technical problem to be solved

Based on the above problems, the present disclosure provides a terahertz active and passive compound imaging quasi-optical scanning system to alleviate technical problems that most of terahertz imaging systems in the prior art are single active imaging or passive imaging, and the respective characteristics of two imaging modes cannot be effectively combined.

(II) technical scheme

The utility model provides a terahertz is initiative now, passive compound imaging quasi-optical scanning system includes:

the active imaging transmitting linear array is used for transmitting a first terahertz signal;

a first mirror for reflecting the first terahertz signal;

the focusing lens is a hyperbolic plano-convex focusing lens and is used for focusing the first terahertz signal reflected by the first reflector;

the second reflector is used for reflecting the first terahertz signal focused by the focusing lens to a target to be imaged to generate an echo signal;

the active imaging receiving linear array is used for receiving echo signals and processing the echo signals to obtain amplitude and phase information of the echo signals;

the polarization wire grating is used for reflecting a second terahertz signal radiated by a target to be imaged, reflected by the second reflector, enters the focusing lens for focusing, is reflected by the first reflector, and then is reflected to the passive imaging radiometer array, and meanwhile, the echo signal is transmitted;

a beam splitter and a wave absorbing plate are arranged between the active imaging transmitting linear array and the receiving linear array to realize the receiving and transmitting isolation of the first terahertz signal; therefore, composite imaging of the terahertz active imaging mode and the passive imaging mode is realized.

In the embodiment of the disclosure, the width of the target to be imaged is width, and the width is more than or equal to 600 and less than or equal to 1000 mm; the height is height, which is more than or equal to 1500mm and less than or equal to 2000 mm; the distance between the target to be imaged and the midpoint of the second reflecting mirror is Z2, and Z2 is more than or equal to 3000mm and less than or equal to 5000 mm.

In the embodiment of the disclosure, in the active imaging mode, the working frequency is F_a340 GHz; the target resolution is not less than 2 rho_aLess than or equal to 6 mm; in the passive imaging mode, the working frequency is F_p220 GHz; the target resolution is equal to or less than 6 rho_p≤10mm。

In the embodiment of the present disclosure, the diameter of the mouth surface of the curved surface of the focusing lens is D, which is expressed as follows:

wherein, T_EEdge power, F, when a Gaussian beam is intercepted for each device in the system_aOperating frequency p for active imaging_aFor target resolution in active imaging, F_pOperating frequency, p, for passive imaging_pFor passive imaging target-specific, Z₂To the object distance to be imaged, C₀Is the speed of light in free space.

In the embodiment of the present disclosure, the focal length of the curved surface of the focusing lens is f, which is expressed as follows:

in the embodiment of the present disclosure, the active imaging transmitting line array includes a plurality of conical horn array elements, a horn mouth surface of each conical horn array element is rectangular, and the dimension of each conical horn array element is a₁×b₁And then:

and the size setting of the array elements in the active imaging receiving linear array is the same as that of the active imaging transmitting linear array.

In the disclosed embodiment, the width of the first reflector is wide_ref1The expression is as follows:

wide_ref1＝max(wide_a1，wide_p1)；

wherein, wide_a1Width of the first reflector required in active mode, wide_p1The width of the first mirror required in the passive mode; wind_a1The expression is as follows:

wherein d is₁For active imaging of the distance between the emitter array and the beam splitter, d₃Distance of the polarizing wire grid from the beam splitter, d₅The distance between the first reflector and the polarized wire grid is taken as height, and the height is the height of an object to be imaged; w is a₀₁A is the gaussian beam waist radius at the active imaging transmitting linear array/active imaging receiving linear array, and is expressed as follows:

w01_ p is the beam waist radius of the Gaussian beam at the antenna aperture of the linear array of the passive imaging radiometer, and the expression is as follows:

wherein Z is_{1_p}The distance of Gaussian beam from the surface of the focusing lens to the linear array at the front end of the radiometer;

length of the first reflectorIs length_ref1, the expression is as follows:

length_ref1＝max(length_a1，length_p1)；

wherein, length_a1Length, of the first mirror required in active mode_p1The width of the first mirror required in the passive mode.

In the embodiment of the disclosure, the width of the second reflector is wide_ref2The expression is as follows:

wide_ref2＝max(wide_a2，wide_p2)；

wherein d is₈The distance between the second reflector and the target to be imaged is defined, and the width is the width of the target to be imaged;

the length of the second reflector is length_ref2The expression is as follows:

length_ref2＝max(length_a2，length_p2)；

in the embodiment of the present disclosure, the width of the polarization wire grid is wide _ d₄The expression is as follows:

the length of the polarization wire grid is length _ d₄The expression is as follows:

in the embodiment of the present disclosure, the width of the beam splitter is wide _ d₁The expression is as follows;

the length of the beam splitter is length _ d₁The expression is as follows;

in the embodiment of the present disclosure, the passive imaging radiometer front-end array includes a plurality of unit antennas, and the size of the horn mouth surface of each unit antenna is as follows; a is₂×b₂The specific expression is as follows:

in the embodiment of the disclosure, the width of the wave absorbing plate is wide _ d₂The expression is as follows:

the length of the wave absorbing plate is length _ d₂The expression is as follows:

(III) advantageous effects

According to the technical scheme, the terahertz active and passive composite imaging quasi-optical scanning system has at least one or part of the following beneficial effects:

(1) the system can realize that the active and passive imaging modes share one set of optical path system;

(2) confocal and pixel-level registration of active and passive imaging is realized, and image fusion is facilitated.

Drawings

FIG. 1 is a schematic diagram of terahertz imaging effect; wherein, fig. 1(a) is a schematic diagram of terahertz imaging effect in a passive mode; fig. 1(b) is a schematic diagram of the terahertz imaging effect in the active mode.

Fig. 2 is a schematic diagram of a working principle of a terahertz active-passive composite imaging quasi-optical scanning system according to an embodiment of the present disclosure.

Fig. 3 is a schematic diagram illustrating a principle that the front end of a passive imaging radiometer and the front end of a receiving and transmitting array for active imaging in the terahertz active and passive composite imaging quasi-optical scanning system according to the embodiment of the present disclosure realize receiving and transmitting isolation and active and passive isolation.

Fig. 4 is a schematic structural diagram of a terahertz active-passive composite imaging quasi-optical scanning system according to an embodiment of the present disclosure.

Detailed Description

The invention provides a terahertz active and passive composite imaging quasi-optical scanning system, which adopts a unique quasi-optical scanning structure, can realize that an active imaging mode and a passive imaging mode share one set of optical path system, realizes confocal and pixel-level registration of active and passive imaging, and is convenient for image fusion; the image fusion technology has outstanding advantages for improving imaging effect and target recognition capability, and in terahertz imaging, composite imaging is carried out on active and passive terahertz imaging modes, so that the imaging effect and the target recognition capability can be further improved.

In order to make the objects, technical solutions and advantages of the present disclosure more clearly apparent, the terahertz active-passive composite imaging quasi-optical scanning system is described in further detail below with reference to the accompanying drawings in combination with specific embodiments.

In an embodiment of the present disclosure, a terahertz active-passive composite imaging quasi-optical scanning system is provided, as shown in fig. 4, the terahertz active-passive composite imaging quasi-optical scanning system includes:

the active imaging transmitting linear array is used for transmitting a first terahertz signal;

a first mirror for reflecting the first terahertz signal;

the focusing lens is a hyperbolic plano-convex focusing lens and is used for focusing the first terahertz signal reflected by the first reflector;

the second reflector is used for reflecting the first terahertz signal focused by the focusing lens to a target to be imaged to generate an echo signal;

the active imaging receiving linear array comprises an active imaging array receiver, and is used for processing amplitude and phase information of the echo signal;

the polarization wire grating is used for reflecting a second terahertz signal radiated by a target to be imaged, reflected by the second reflector, enters the focusing lens for focusing, is reflected by the first reflector, and then is reflected to the passive imaging radiometer array, and meanwhile, the echo signal is transmitted;

a beam splitter and a wave absorbing plate are arranged between the active imaging transmitting linear array and the receiving linear array to realize the receiving and transmitting isolation of the first terahertz signal; therefore, the terahertz active and passive imaging modes are subjected to composite imaging.

The distance (imaging field distance) between the target to be imaged and the midpoint of the second reflector is Z2, and Z2 is more than or equal to 3000mm and less than or equal to 5000 mm;

in bookIn the disclosed embodiment, the distance between the center point of the target to be imaged and the midpoint of the second reflector is d₈3500mm, the coordinates of the center point of the imaging target are (500mm, 0, 3500 mm);

the range of the object to be imaged (also called field of view range, parallel to the XOY plane) is:

the width of an imaging view field (the width of a target to be imaged) is width, and the width is more than or equal to 600 and less than or equal to 1000 mm;

the height of an imaging field (the height of a target to be imaged) is height, and the height is more than or equal to 1500mm and less than or equal to 2000 mm; width × height is 800mm × 1800 mm.

In the active imaging mode, the working frequency is F_a340 GHz; the target resolution is not less than 2 rho_a≤6mm；

In the passive imaging mode, the working frequency is F_p220 GHz; the target resolution is equal to or less than 6 rho_p≤10mm；

The edge power of each device in the quasi-optical structure when intercepting a Gaussian beam is as follows: t is_E＝-15dB；

In the embodiments of the present disclosure, the terahertz wave signal is described as being expressed in a gaussian beam form.

In the embodiment of the present disclosure, the diameter of the mouth surface of the curved surface of the focusing lens is D, which is expressed as follows:

wherein, T_EEdge power, F, when a Gaussian beam is intercepted for each device in the system_aOperating frequency p for active imaging_aFor target resolution in active imaging, F_pOperating frequency, p, for passive imaging_pFor passive imaging target-specific, Z₂To the object distance to be imaged, C₀Is the speed of light in free space.

The focal length of the curved surface of the focusing lens is f and is expressed as follows:

in the embodiment of the present disclosure, in the rectangular coordinate system where the quasi-optical scanning structure is located, the coordinates of the center point of the focusing lens are (0, 0, 0). The relative dielectric constant of the material used for the focusing lens is epsilon_r2.25, that is, the refractive index n is 1.5. The diameter of the mouth surface of the lens is 612.394mm, the focal length is 747.11mm, the thickness of the lens is 106.51mm, and the curved equation of the focusing lens is as follows:

wherein y ∈ [ -D/2, D/2 ].

The active imaging transmitting linear array comprises a plurality of conical horn array elements, the horn mouth surface of each conical horn array element is rectangular, and the size of the horn mouth surface is a₁×b₁And then:

in the embodiment of the disclosure, the active imaging transmitting linear array adopts a 4-element linear array, and the distance between the midpoint of the linear array and the midpoint of the beam splitter is d₁The coordinates of the middle point of the linear array are (-524.47mm, 500.63mm, 0), which is 100 mm. The array element adopts a conical horn antenna with the mouth surface size of a₁×b₁＝3.4579mm×2.5148mm。

In the embodiment of the present disclosure, the size settings of the array elements in the active imaging receiving linear array and the active imaging transmitting linear array are the same. Adopting 4-element linear array, the distance between the middle point of the linear array and the middle point of the beam splitter is d₁The coordinates of the middle point of the linear array are (-624.47mm, 400.63mm, 0), which is 100 mm. The array element adopts a conical horn antenna with the mouth surface size of a₁×b₁＝3.4579mm×2.5148mm。

In the disclosed embodiments, the first inverseWidth of mirror is wide_ref1The expression is as follows:

wide_ref1＝max(wide_a1，wide_p1)；

wherein, wide_a1Width of the first reflector required in active mode, wide_p1The width of the first mirror required in the passive mode; wind_a1The expression is as follows:

wherein d is₁For active imaging of the distance between the emitter array and the beam splitter, d₃Distance of the polarizing wire grid from the beam splitter, d₅The distance between the first reflector and the polarized wire grid is taken as height, and the height is the height of an object to be imaged; w is a₀₁A is the gaussian beam waist radius at the active imaging transmitting linear array/active imaging receiving linear array, and is expressed as follows:

w01_ p is the beam waist radius of the Gaussian beam at the antenna aperture of the linear array of the passive imaging radiometer, and the expression is as follows:

wherein Z is_{1_p}The distance of Gaussian beam from the surface of the focusing lens to the linear array at the front end of the radiometer;

the length of the first reflector is length_ref1The expression is as follows:

length_ref1＝max(length_a1，length_p1)；

wherein, length_a1Length, of the first mirror required in active mode_p1The width of the first mirror required in the passive mode;

in the embodiment of the disclosure, the distance between the center point of the first reflector and the center point of the focusing lens is d₆524.47mm, the coordinates of the center point of the first mirror are (-524.47mm, 0, 0), and the size of the first mirror is wide_ref1×length_ref1＝534.28mm×333.76mm。

The width of the second reflector is wide_ref2The expression is as follows:

wide_ref2＝max(wide_a2，wide_p2)；

wherein d is₈The distance between the second reflector and the target to be imaged is defined, and the width is the width of the target to be imaged;

the length of the second reflector is length_ref2The expression is as follows:

length_ref2＝max(length_a2，length_p2)；

in the embodiment of the present disclosure, the distance between the center point of the second reflector and the center point of the focusing lens is d₇The coordinate of the center point of the second reflector is 500mm, 0, and the size of the second reflector is wide_ref2×length_ref2＝798.62mm×535.88mm。

The width of the polarization wire grid is wide _ d₄The expression is as follows:

the length of the polarization wire grid is length _ d₄The expression is as follows:

in the disclosed embodiment, the distance between the central point of the polarization wire grid and the central point of the first reflector is d₅300 mm. The coordinate of the central point of the polarized wire grid is (-524.47mm, 300mm, 0), and the size of the polarized wire grid is wide _ d₄×length_d₄146.20mm × 103.38 mm. In addition, the wire grid is made of round wires having a radius r₀0.0545mm, adjacent line spacing is g₀＝0.27mm。

The width of the beam splitter is wide _ d₁The expression is as follows;

the length of the beam splitter is length _ d₁The expression is as follows;

in the disclosed embodiment, the distance between the central point of the beam splitter and the central point of the polarization wire grid is d₃100.63 mm. The coordinates of the center point of the beam splitter are (-524.47mm, 400.63mm, 0), and the size of the beam splitter is wide _ d₁×length_d₁＝94.37mm×66.73mm。

The passive imaging radiometer front-end array comprises a plurality of unit antennas, and the size of a horn mouth surface of each unit antenna is as follows; a is₂×b₂The specific expression is as follows:

the radius of the beam waist of the Gaussian beam at the opening of the radiometer linear array antenna is w₀₁_p：

The front-end array of the passive imaging radiometer adopts a 4-element linear array, and the distance between the middle point of the linear array and the middle point of the polarized wire grid is d₄The coordinates of the middle point of the line are (-724.47mm, 300mm, 0), 200 mm. The array element adopts a conical horn antenna with the mouth surface size of a₂×b₂＝6.9030mm×5.0204mm。

The width of the wave absorbing plate is wide _ d₂The expression is as follows:

the length of the wave absorbing plate is length _ d₂The expression is as follows:

in the embodiment of the disclosure, the distance between the central point of the wave absorbing plate and the central point of the beam splitter is d₂The coordinates of the middle point of the wave-absorbing plate are (-424.47mm, 400.63mm, 0). Wave-absorbing materialThe size of the plate is as follows: wide _ d₂×length_d₂＝133.36mm×133.36mm。

In the embodiment of the disclosure, the size of each quasi-optical device in the terahertz active and passive composite imaging quasi-optical scanning system is set based on a gaussian beam method, the target resolution and the view range required by the imaging system are taken as design starting points, the cutoff power of each quasi-optical device on a beam is taken as a constraint condition, and meanwhile, the problem of light path shielding between the quasi-optical devices is considered, and a terahertz wave signal is described as a gaussian beam form below to describe the size parameter, the position parameter and the working principle of each quasi-optical device in the terahertz active and passive composite imaging quasi-optical scanning system.

(1) Depending on the required active imaging mode resolution ρ of the imaging system_aPassive imaging mode resolution ρ_pCalculating the beam waist radius w of the Gaussian beam required by the active working mode and the passive working mode at the imaging target₀₂_a、w₀₂_p：

(2) According to the beam waist radius w at the imaging target₀₂_a、w₀₂P and target distance (Gaussian beam emitting distance) Z₂Calculating the beam radii w _ a, w _ p at the exit surface of the focusing lens and selecting the appropriate cutoff power T_EThis calculates the diameters D _ a, D _ p of the focusing lens in the active mode and in the passive mode:

the maximum value of the desired focusing lens size in two modes is chosen:

D＝max(D_a，D_p)；

in most cases, D _ a > D _ p, so the distance between the receiving and transmitting arrays (i.e. the active imaging receiving and transmitting arrays) and the lens (receiving array) in the active mode is determined first based on the dimension parameter of the active modeThe distance between the transmitting line array and the lens is equal), namely the incident distance Z of the Gaussian beam₁A is 1.3D, notably Z₁The value of a needs to take into account the size and placement of the Mylar beamsplitter, the polarizing wire grid, the first mirror.

(3) In active mode, the beam radius w _ a and the incident distance Z at the surface of the focusing lens are known₁A and working wavelength lam _ a, and can obtain the waist radius w of Gaussian beam at the receiving and transmitting linear array₀₁_a：

The receiving and transmitting arrays both use conical horn as array element, the initial mouth surface size is a₁×b₁：

a₁＝w₀₁_a/0.32；

b₁＝w₀₁_a/0.44；

To obtain a better size of the bell-mouth face, further optimization selection needs to be made on the basis of the initial size.

According to the beam waist radius w of the incident beam₀₁A, incident distance Z₁A, radius of beam waist of outgoing beam w₀₂A, exit distance Z₂Calculating the radius of curvature R of the Gaussian beam at the lens surface before and after the transformation of the lens₁、R₂Obtaining the focal length f of the focusing lens:

(4) since the passive mode and the active mode share the focusing lens, the working wavelength lam _ p and the emitting distance Z in passive imaging need to be determined according to₂And an emergent beam waist w₀₂P, lens focal length f, determining the radius of curvature R of the incident beam in passive mode₁_p。

Then the curvature radius R₁P, beam radius at lens surface w p, simultaneously solving for beam waist radius w of the beam₀₁P, incident distance Z₁_p：

The terahertz passive imaging radiometer linear array element also selects a conical horn antenna, and the initial aperture size is as follows: a is₂×b₂：

(5) The size of a focusing lens, the distance of an imaging target and the size of the horn mouth surface of the receiving and transmitting linear array and the passive radiometer linear array are determined in the first 4 steps. Then, according to the propagation rule of the Gaussian beam, the positions and the sizes of the Mylar beam splitter, the wire grid, the first reflecting mirror, the second reflecting mirror and the wave absorbing plate on the beam propagation path are determined, and meanwhile, the shielding problem among devices is considered.

(6) Mylar beamsplitter position, size. The Mylar beam splitter realizes the receiving and transmitting isolation in the active mode, and the distance between the central point of the Mylar beam splitter and the beam waist position of an incident beam is d₁At an angle of 45 deg. to the beam propagation direction (-y), as shown in figure 4. The size of the Mylar beamsplitter is wide _ d₁×length_d₁：

(7) The position and the size of the wave absorbing plate. The position of the wave absorbing plate is shown in FIG. 4, and the distance from the center of the Mylar beam splitter is d₂Placed perpendicular to the incident beam direction. The size of the wave absorbing plate is wide _ d₂×length_d₂：

(8) Wire grid position, size. The wire grid is placed at a position shown in FIG. 4, and the distance between the center position and the Mylar beam splitter is d₃And the distance between the terahertz passive radiometer and the terahertz passive radiometer is d₄Since the polarization wire grid is mainly responsible for the passive mode, the beam propagation distance d is used₄The wire grid size is calculated. Polarized wire grid size is wide _ d₄×length_d₄：

(9) The first mirror position and size are scanned in a pitching mode. The first reflector is used for realizing the elevation scanning of the beam to the visual field range, and the beam scanning angle is related to the target distance and the visual field range: theta₀＝±tan^-1(height/(2Z₂) ± θ) beam deflection₀The mirror only needs to deflect +/-theta₀/2。

The first reflector is coaxially arranged with the polarization wire grating, the beam splitter and the transmitting linear array (y axis), forms an included angle of 45 degrees with the axis, and has a distance d with the polarization wire grating₅At a distance d from the entrance surface of the focusing lens₆The minimum included angle between the swing process and the incident axis of the wave beam (-y direction) is theta_min＝45°-θ₀/2。

The first reflector has a size of wide_ref1×length_ref1。

Active mode case:

passive mode case:

taking the maximum value between the active mode and the passive mode:

(10) azimuth scans the second mirror position, size. The second reflector is used for realizing azimuth scanning of the beam in the visual field range, and the beam scanning angle is related to the target distance and the visual field range: alpha is alpha₀＝±tan^-1(width/(2Z₂)). Beam deflection ± α₀The mirror only needs to deflect +/-alpha₀/2。

The second reflector is coaxially arranged with the first reflector and the focusing lens (x axis), forms an included angle of 45 degrees with the axis (+ x), and has a distance d with the emergent surface of the focusing lens₇At a distance d from the object to be imaged₈The minimum included angle between the swing and the incident axis (+ x direction) of the wave beam is alpha in the swing process_min＝45-α₀/2。

The second mirror size is: wind_ref2×length_ref2。

Active mode case:

passive mode case:

taking the maximum value between the active mode and the passive mode:

the terahertz active and passive composite imaging quasi-optical scanning system adopts an imaging system combining a transmitting-receiving linear array, quasi-optical focusing and optical machine scanning, and is composed of a terahertz transmitting-receiving linear array, a terahertz radiometer, a focusing lens, a pitching scanning reflector 1(a first reflector), an azimuth scanning reflector 2 (a second reflector) and other quasi-optical devices.

In the embodiment of the present disclosure, as shown in fig. 2, the working principle of the terahertz active and passive compound imaging quasi-optical scanning system is as follows:

taking active imaging as an example, an electronics subsystem in the electronics box is composed of a driving source module, an intermediate frequency processing module, a data acquisition and signal processing module, a servo control module and a comprehensive control module. The two-way linear frequency modulation driving signal generated by the driving source module is respectively used for driving a transmitting frequency multiplication link and a receiving local oscillator frequency multiplication link of the terahertz active imaging receiving and transmitting linear array; the driving source module also generates a microwave phase-locked dot frequency signal for driving a local oscillation frequency doubling link of the terahertz passive imaging radiometer channel. The intermediate frequency output signal of the front end of the active and passive imaging receiver is transmitted to an intermediate frequency processing module of an electronic box for intermediate frequency processing and generating a baseband signal for subsequent signal processing and image reconstruction. On the other hand, the servo control module generates corresponding control signals, and the control signals are transmitted to the quasi-optical box and used for servo motors of the scanning mirror 1(a first reflecting mirror) and the scanning mirror 2 (a second reflecting mirror) to complete rapid scanning of a two-dimensional view field. A first terahertz signal transmitted by the transmitting linear array is reflected by the first reflector and then enters the focusing lens, a beam focused by the focusing lens is reflected by the second reflector and then is emitted from the emergent aperture of the quasi-optical box along the z direction, after reaching a target to be imaged, the reflected signal reversely returns to the confocal receiving linear array along the original path, and the amplitude and phase information of a target echo signal is obtained through the processing of the active imaging array receiver. The field of view information within the band on the imaging plane can be obtained by rapidly swinging (fast swinging) the first mirror around the z-axis. The width of the strip corresponds to the number of the array elements of the transmitting linear array, and the more the number of the array elements is, the wider the strip is. And then the second reflector synchronously swings around the y axis at a specific speed (the second reflector is matched and provided with the electrode 2), so that a plurality of dark stripes can be formed and seamlessly spliced along the x direction, and the fast scanning of the two-dimensional field of view in the x-y direction is realized. For the z direction, distance direction high resolution is realized by transmitting a terahertz broadband frequency modulation continuous wave signal and performing pulse compression, so that target three-dimensional imaging is completed.

For passive imaging, a second terahertz signal radiated by the target passes through the second reflector, the focusing lens, the first reflector and the polarization wire grid, and then enters the passive imaging radiometer array. The passive imaging and the active imaging share a quasi-optical focusing lens, a scanning first reflecting mirror and a scanning second reflecting mirror, so that confocal and pixel-level registration of the active imaging and the passive imaging is realized.

The active imaging and passive imaging in the terahertz active and passive composite imaging quasi-optical scanning system are isolated:

the terahertz transmitting-receiving linear array comprises a transmitting-receiving linear array for active imaging and a front-end array for a passive imaging radiometer. The different linear arrays share the quasi-optical confocal device and the beam scanning device through the quasi-optical isolation technology.

The front end of the passive imaging radiometer and the front end of the receiving and transmitting array of the active imaging adopt a novel quasi-optical isolation network to simultaneously realize receiving and transmitting isolation and active and passive isolation.

The specific implementation is shown in fig. 3: the active receiving and transmitting feed source arrays are isolated by using a Mylar beam splitter and a wave absorbing plate; polarization isolation is realized between the active feed source array and the passive feed source array by adopting a polarization separator (a polarization wire grid), wherein the passive feed source is polarized along the z direction, and the active emission feed source is polarized along the x direction. The polarized wire grid is drawn along the z direction, and for the echo polarized in the z direction, the polarized wire grid is reflected to the passive radiometer array, and for the echo polarized in the x direction, the echo is reflected to the receiver array for active imaging after being transmitted by the wire grid.

In addition, different working frequency bands (active-340GHz and passive-220GHz) are adopted for active and passive imaging in the imaging system, so that even if polarization rotation is caused by target scattering, the passive receiver is not influenced.

So far, the embodiments of the present disclosure have been described in detail with reference to the accompanying drawings. It is to be noted that, in the attached drawings or in the description, the implementation modes not shown or described are all the modes known by the ordinary skilled person in the field of technology, and are not described in detail. Further, the above definitions of the various elements and methods are not limited to the various specific structures, shapes or arrangements of parts mentioned in the examples, which may be easily modified or substituted by those of ordinary skill in the art.

From the above description, those skilled in the art should clearly recognize that the terahertz active-passive composite imaging quasi-optical scanning system of the present disclosure.

In summary, the present disclosure provides a terahertz active and passive compound imaging quasi-optical scanning system, which uses a unique quasi-optical scanning structure, and can realize that an active imaging mode and a passive imaging mode share one set of optical path system, thereby realizing confocal and pixel-level registration of active and passive imaging, completing compound imaging, and further improving imaging effect and target identification capability.

It should also be noted that directional terms, such as "upper", "lower", "front", "rear", "left", "right", and the like, used in the embodiments are only directions referring to the drawings, and are not intended to limit the scope of the present disclosure. Throughout the drawings, like elements are represented by like or similar reference numerals. Conventional structures or constructions will be omitted when they may obscure the understanding of the present disclosure.

And the shapes and sizes of the respective components in the drawings do not reflect actual sizes and proportions, but merely illustrate the contents of the embodiments of the present disclosure. Furthermore, in the claims, any reference signs placed between parentheses shall not be construed as limiting the claim.

Unless otherwise indicated, the numerical parameters set forth in the specification and attached claims are approximations that can vary depending upon the desired properties sought to be obtained by the present disclosure. In particular, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Generally, the expression is meant to encompass variations of ± 10% in some embodiments, 5% in some embodiments, 1% in some embodiments, 0.5% in some embodiments by the specified amount.

Furthermore, the word "comprising" does not exclude the presence of elements or steps not listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements.

The use of ordinal numbers such as "first," "second," "third," etc., in the specification and claims to modify a corresponding element does not by itself connote any ordinal number of the element or any ordering of one element from another or the order of manufacture, and the use of the ordinal numbers is only used to distinguish one element having a certain name from another element having a same name.

In addition, unless steps are specifically described or must occur in sequence, the order of the steps is not limited to that listed above and may be changed or rearranged as desired by the desired design. The embodiments described above may be mixed and matched with each other or with other embodiments based on design and reliability considerations, i.e., technical features in different embodiments may be freely combined to form further embodiments.

Those skilled in the art will appreciate that the modules in the device in an embodiment may be adaptively changed and disposed in one or more devices different from the embodiment. The modules or units or components of the embodiments may be combined into one module or unit or component, and furthermore they may be divided into a plurality of sub-modules or sub-units or sub-components. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and all of the processes or elements of any method or apparatus so disclosed, may be combined in any combination, except combinations where at least some of such features and/or processes or elements are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Also in the unit claims enumerating several means, several of these means may be embodied by one and the same item of hardware.

Similarly, it should be appreciated that in the foregoing description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various disclosed aspects. However, the disclosed method should not be interpreted as reflecting an intention that: that is, the claimed disclosure requires more features than are expressly recited in each claim. Rather, as the following claims reflect, disclosed aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this disclosure.

The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.

Claims (10)

Translated fromChinese

1.一种太赫兹主、被动复合成像准光学扫描系统，包括：1. A terahertz active and passive composite imaging quasi-optical scanning system, comprising:主动成像发射线阵，用于发射第一太赫兹信号；Active imaging transmission line array for transmitting the first terahertz signal;第一反射镜，用于反射所述第一太赫兹信号；a first reflector for reflecting the first terahertz signal;聚焦透镜，为双曲型平凸聚焦透镜，用于聚焦所述第一反射镜反射后的第一太赫兹信号；a focusing lens, which is a hyperbolic plano-convex focusing lens, used for focusing the first terahertz signal reflected by the first reflecting mirror;第二反射镜，用于将聚焦透镜聚焦后的第一太赫兹信号反射至待成像目标生成回波信号；a second reflector, configured to reflect the first terahertz signal focused by the focusing lens to the target to be imaged to generate an echo signal;主动成像接收线阵，用于接收回波信号并处理得到所述回波信号的幅度与相位信息；an active imaging receiving line array for receiving echo signals and processing to obtain amplitude and phase information of the echo signals;极化线栅，用于将待成像目标自身辐射出的、经第二反射镜反射进入聚焦透镜聚焦后再经第一反射镜反射后的第二太赫兹信号反射至被动成像辐射计阵列，同时透过所述回波信号；The polarization wire grid is used to reflect the second terahertz signal radiated by the target to be imaged, reflected by the second mirror into the focusing lens, and then reflected by the first mirror to the passive imaging radiometer array, and at the same time through the echo signal;所述主动成像发射线阵与接收线阵之间设置有分束器和吸波板实现第一太赫兹信号的收、发隔离；从而实现对太赫兹主动成像模式和被动成像模式进行复合成像；A beam splitter and a wave absorbing plate are arranged between the active imaging transmitting line array and the receiving line array to realize the isolation of the first terahertz signal reception and transmission; thereby realizing the composite imaging of the terahertz active imaging mode and the passive imaging mode;所述第一反射镜的宽为wide_ref1，表达式如下：The width of the first reflector is wide_ref1 , and the expression is as follows:wide_ref1＝max(wide_a1，wide_p1)；wide_ref1 = max(wide_a1 , wide_p1 );其中，wide_a1为主动模式下所需第一反射镜的宽度，wide_p1为被动模式下所需第一反射镜的宽度；wide_a1表达式如下：Among them, wide_a1 is the width of the first mirror required in the active mode, and wide_p1 is the width of the first mirror required in the passive mode; the expression of wide_a1 is as follows:

其中，w₀₁_a为主动成像发射线阵/主动成像接收线阵处的高斯波束束腰半径，表达如下：Among them, w₀₁ _a is the beam waist radius of the Gaussian beam at the active imaging transmitting line array/active imaging receiving line array, which is expressed as follows:

w₀₁_p为被动成像辐射计线阵天线口面处高斯波束的束腰半径，表达式如下：w₀₁ _p is the beam waist radius of the Gaussian beam at the mouth of the passive imaging radiometer linear array antenna, and the expression is as follows:

其中，Z_{1_p}为高斯波束从聚焦透镜表面到辐射计前端线阵所传播的距离；Among them, Z_{1_p} is the distance that the Gaussian beam propagates from the surface of the focusing lens to the front-end linear array of the radiometer;所述第一反射镜的长为length_ref1，其表达式如下：The length of the first reflecting mirror is length_ref1 , and its expression is as follows:length_ref1＝max(length_a1，length_p1)；length_ref1 =max(length_a1 , length_p1 );

其中，length_a1为主动模式下所需第一反射镜的长度，length_p1为被动模式下所需第一反射镜的长度；Wherein, length_a1 is the length of the first reflector required in the active mode, and length_p1 is the length of the first reflector required in the passive mode;所述第二反射镜的宽为wide_ref2，表达式如下：The width of the second mirror is wide_ref2 , and the expression is as follows:wide_ref2＝max(wide_a2，wide_p2)；wide_ref2 = max(wide_a2 , wide_p2 );

其中d₈为第二反射镜与待成像目标之间的距离，width为待成像目标宽度；wide_a2为主动模式下所需第二反射镜的宽度，wide_p2为被动模式下所需第二反射镜的宽度；where_d8 is the distance between the second mirror and the target to be imaged, width is the width of the target to be imaged; wide_a2 is the width of the second mirror required in active mode, wide_p2 is the second reflection required in passive mode the width of the mirror;所述第二反射镜的长度为length_ref2，其表达式如下：The length of the second mirror is length_ref2 , and its expression is as follows:length_ref2＝max(length_a2，length_p2)；length_ref2 = max(length_a2 , length_p2 );length_a2为主动模式下所需第二反射镜的长度，length_p2为被动模式下所需第二反射镜的长度；length_a2 is the length of the second mirror required in the active mode, and length_p2 is the length of the second mirror required in the passive mode;

其中，T_E为系统中各器件截获高斯波束时的边缘功率，F_a为主动成像时工作频率ρ_a为主动成像时目标分辨率，F_p为被动成像时工作频率，ρ_p为被动成像时目标分辨率，Z₂为待成像目标距离第二反射镜中点距离，C₀为自由空间中的光速，d₁为主动成像发射线阵与分束器之间的距离，d₃为极化线栅与分束器的距离，d₄为被动成像辐射计前端阵列线阵中点与极化线栅中点之间的距离，d₅为第一反射镜与极化线栅之间的距离，height为待成像目标的高度。Among them, TE is the edge power of each device in the system when the Gaussian beam is intercepted, F_a is the working frequency during active imaging, ρ_a is the target resolution during active imaging, F_p is the working frequency during passive imaging, and_{ρ pis} during passive imaging. Target resolution, Z₂ is the distance between the target to be imaged and the midpoint of the second mirror, C₀ is the speed of light in free space, d₁ is the distance between the active imaging emission line array and the beam splitter, and d₃ is the polarization The distance between the wire grid and the beam splitter, d₄ is the distance between the center point of the front-end array line array of the passive imaging radiometer and the mid point of the polarization wire grid, and d₅ is the distance between the first mirror and the polarization wire grid , height is the height of the target to be imaged.2.根据权利要求1所述的太赫兹主、被动复合成像准光学扫描系统，其中，600≤width≤1000mm；1500mm≤height≤2000mm；3000mm≤Z2≤5000mm。2. The terahertz active-passive composite imaging quasi-optical scanning system according to claim 1, wherein 600≤width≤1000mm; 1500mm≤height≤2000mm; 3000mm≤Z2≤5000mm.3.根据权利要求1所述的太赫兹主、被动复合成像准光学扫描系统，主动成像模式下，工作频率为F_a＝340GHz；目标分辨率为2≤ρ_a≤6mm；被动成像模式下，工作频率为F_p＝220GHz；目标分辨率为6≤ρ_p≤10mm。3. The terahertz active and passive composite imaging quasi-optical scanning system according to claim 1, in the active imaging mode, the working frequency is F_a =340GHz; the target resolution is_{2≤ρa≤6mm} ; under the passive imaging mode, The working frequency is F_p =220GHz; the target resolution is_{6≤ρp≤10mm} .4.根据权利要求1所述的太赫兹主、被动复合成像准光学扫描系统，所述聚焦透镜曲面的口面直径为D，表达如下：4. The terahertz active and passive composite imaging quasi-optical scanning system according to claim 1, the diameter of the aperture of the focusing lens curved surface is D, and is expressed as follows:

。

.5.根据权利要求4所述的太赫兹主、被动复合成像准光学扫描系统，所述聚焦透镜曲面的焦距为f，表达如下：5. The terahertz active and passive composite imaging quasi-optical scanning system according to claim 4, wherein the focal length of the focusing lens curved surface is f, which is expressed as follows:

6.根据权利要求1所述的太赫兹主、被动复合成像准光学扫描系统，所述主动成像发射线阵，包括多个锥形喇叭阵元，每个锥形喇叭阵元的喇叭口面为矩形，其尺寸为a₁×b₁，则：6. The terahertz active and passive composite imaging quasi-optical scanning system according to claim 1, the active imaging emission line array comprises a plurality of conical horn array elements, and the bell mouth surface of each conical horn array element is A rectangle whose dimensions are a₁ ×b₁ , then:

所述主动成像接收线阵与所述主动成像发射线阵中阵元尺寸设置相同。The size of the array elements in the active imaging receiving line array is the same as that of the active imaging transmitting line array.7.根据权利要求1所述的太赫兹主、被动复合成像准光学扫描系统，7. The terahertz active and passive composite imaging quasi-optical scanning system according to claim 1,所述极化线栅的宽度为wide_d₄，表达式如下：The width of the polarized wire grid is wide_d₄ , and the expression is as follows:

所述极化线栅的长度为length_d₄，表达式如下：The length of the polarized wire grid is length_d₄ , and the expression is as follows:

8.根据权利要求1所述的太赫兹主、被动复合成像准光学扫描系统，所述分束器的宽度为wide_d₁，表达式如下；8. The terahertz active and passive composite imaging quasi-optical scanning system according to claim 1, wherein the width of the beam splitter is wide_d₁ , and the expression is as follows;

所述分束器的长度为length_d₁，表达式如下；The length of the beam splitter is length_d₁ , and the expression is as follows;

9.根据权利要求1所述的太赫兹主、被动复合成像准光学扫描系统，所述被动成像的辐射计前端阵列，包括多个单元天线，单元天线的喇叭口面尺寸为；a₂×b₂，具体表达式如下：9. The terahertz active-passive composite imaging quasi-optical scanning system according to claim 1, the passive imaging radiometer front-end array comprises a plurality of unit antennas, and the size of the horn mouth of the unit antennas is: a₂ × b₂ , the specific expression is as follows:

10.根据权利要求1所述的太赫兹主、被动复合成像准光学扫描系统，所述吸波板的宽度为wide_d₂，其表达式如下：10. The terahertz active and passive composite imaging quasi-optical scanning system according to claim 1, the width of the wave absorbing plate is wide_d₂ , and its expression is as follows:

所述吸波板的长度为length_d₂，其表达式如下：The length of the absorber is length_d₂ , and its expression is as follows:

d₂为吸波板中心点与分束器中点距离。d₂ is the distance between the center point of the absorber and the center point of the beam splitter.

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