阅读说明：本技术 一种被动毫米波三维成像系统及其成像方法 (Passive millimeter wave three-dimensional imaging system and imaging method thereof ) 是由 王鹏程 王楠楠 邱景辉 马翰驰 于 2021-09-10 设计创作，主要内容包括：本发明是一种被动毫米波三维成像系统及其成像方法。所述系统包括：主介质透镜,子介质透镜阵列,辐射计接收机阵列,数字采集电路和计算机；场内物体辐射的电磁波经过主介质透镜汇聚至子透镜阵列平面,再经过不同的子透镜聚焦至辐射计接收机阵列平面,辐射计接收机阵列上的接收天线接收到电磁波,将信号顺次输出至毫米波段低噪放,高灵敏度平方律检波器,低通滤波器,低频放大器,低频放大器输出端与数字采集电路的输入端连接,数字采集电路将采样信号传输至计算机进行数据处理。(The invention discloses a passive millimeter wave three-dimensional imaging system and an imaging method thereof. The system comprises: the radiometer comprises a main dielectric lens, a sub-dielectric lens array, a radiometer receiver array, a digital acquisition circuit and a computer; electromagnetic waves radiated by objects in a field are converged to a sub-lens array plane through a main dielectric lens and focused to a radiometer receiver array plane through different sub-lenses, a receiving antenna on the radiometer receiver array receives the electromagnetic waves, signals are sequentially output to a millimeter wave band low-noise amplifier, a high-sensitivity square law detector, a low-pass filter and a low-frequency amplifier, the output end of the low-frequency amplifier is connected with the input end of a digital acquisition circuit, and the digital acquisition circuit transmits sampling signals to a computer for data processing.)

1. A passive millimeter wave three-dimensional imaging system is characterized in that: the system comprises: the radiometer comprises a main dielectric lens, a sub-dielectric lens array, a radiometer receiver array, a digital acquisition circuit and a computer;

electromagnetic waves radiated by objects in a field are converged to a sub-lens array plane through a main dielectric lens and focused to a radiometer receiver array plane through different sub-lenses, a receiving antenna on the radiometer receiver array receives the electromagnetic waves, and signals are sequentially output to a millimeter wave band low-noise amplifier, a high-sensitivity square law detector, a low-pass filter and a low-frequency amplifier, wherein the output end of the low-frequency amplifier is connected with the input end of a digital acquisition circuit, and the digital acquisition circuit transmits sampling signals to a computer for data processing;

a group of radiometer receivers which are arranged at equal intervals in two dimensions are arranged on the focal plane of each sub-dielectric lens, the distances between the phase center of a receiving antenna of each radiometer receiver and the central point of the bright surface of the corresponding sub-dielectric lens are the same, and all the radiometer receivers jointly form a radiometer receiver array;

and step 3: flywheel speed optimization during imaging is performed.

2. The passive millimeter wave three-dimensional imaging system of claim 1, wherein: the sub-medium lens array is composed of a plurality of sub-medium lenses which are arranged at equal intervals in a two-dimensional mode, and the centers of the sub-medium lens array and the main medium lens are on the same axis.

3. A passive millimeter wave three-dimensional imaging method based on a passive millimeter wave three-dimensional imaging system according to claim 1, characterized in that: the method comprises the following steps:

step 1: extracting radiation field information, and recording a four-dimensional function of the radiation field;

step 2: determining the radiation field intensity on the plane of the radiometer according to the distance between the plane of the radiometer array and the plane of the sub-lens;

and step 3: millimeter wave radiation power corresponding to a series of plane sampling points with different depths of field is obtained, namely three-dimensional millimeter wave radiation field data corresponding to three-dimensional space sampling points one to one are obtained, and millimeter wave three-dimensional radiation field detection is achieved.

4. The passive millimeter wave three-dimensional imaging method according to claim 3, wherein: the step 1 specifically comprises the following steps:

a radiation field from a certain point in the field of view of the imaging system is focused by the main lens and then received by a plurality of radiometer receivers behind the plurality of sub-lenses; each radiometer receiver receives millimeter wave radiation from a plurality of range, multi-azimuth targets; coordinates corresponding to the radiation path are expressed by intersection coordinates of the sub-lens plane and the radiometer array plane;

coordinates (x, y) of the plane of the radiometer represent the azimuth information of the target, the connection line of the coordinates (x, y) with the coordinates (x ', y') on the plane of the sub-lens represents the radiation direction, the recorded radiation field, passes through P_F(x ', y', x, y) represents a four-dimensional function of the radiation field.

5. The passive millimeter wave three-dimensional imaging method according to claim 4, wherein: the step 2 specifically comprises the following steps: the distance between the plane of the radiometer array and the plane of the sub-lenses is f, and the intensity of the radiation field at point (x, y) on the radiometer plane is:

6. the passive millimeter wave three-dimensional imaging method according to claim 5, wherein: the step 3 specifically comprises the following steps:

the method comprises the steps of measuring scene depth, target geometric form and scene shielding relation information lost in a traditional passive millimeter wave focal plane array imaging mode through a passive millimeter wave three-dimensional imaging system, and obtaining millimeter wave radiation power corresponding to a series of plane sampling points with different depths of field through representing the mapping relation between the radiation intensity of a target point and the azimuth and distance information of the target point, namely obtaining three-dimensional millimeter wave radiation field data corresponding to three-dimensional space sampling points one by one, and realizing millimeter wave three-dimensional radiation field detection.

7. The passive millimeter wave three-dimensional imaging method according to claim 6, wherein: the millimeter wave three-dimensional radiation field detection is realized through the following steps:

the distance between the new imaging plane and the sub-lens plane is f ', and f' is beta f, and beta is a virtual imaging depth scale factor; when the plane of the sub-lens and the plane of the sensor are infinite, when the sub-lens array is focused at different depths, the distance between the plane of the sub-lens and the imaging plane changes, and the integral track of the calculated focused image in the space shifts, so that the focal length agility is realized by applying space domain integral projection;

according to the similar triangle theorem, after the focal length is changed quickly, the coordinate of the intersection point formed by the electromagnetic wave and the plane of the radiometer isThe resulting radiation field strength at the radiation plane is therefore expressed as:

after the focal length is obtained, the radiation intensity of the plane of the radiometer is as follows:

on the basis of the collected four-dimensional (x ', y', x, y) matrix radiation field data, determining corresponding beta values by transforming different virtual focusing image planes, determining a sub-lens corresponding to the position of a pixel on a radiometer according to the beta values, and obtaining the mapping relation of the radiation field at different depth distances, thereby realizing the information extraction of the three-dimensional radiation field;

through a sensitive target depth of field extraction algorithm and a focus agility image inversion algorithm, the focus of the imaging system focus plane is agilely changed to the plane of the target of interest in the system field of view by changing the virtual depth of field conversion factor to perform coordinate conversion, and therefore a two-dimensional or three-dimensional gray image of the target is inverted according to a passive millimeter wave imaging algorithm.

8. The passive millimeter wave three-dimensional imaging method according to claim 7, wherein: the aperture and the focal length of the main lens and the sub lens need to be systematically integrated with the requirements on the imaging distance, the field range and the volume of the main lens and the sub lens; the number of the system imaging pixel points is determined by the number and the arrangement of the sub-lens arrangement and the number and the arrangement of the radiometer receivers, when the sub-lens arrangement is m1 × m2 and the radiometer receivers are n1 × n2, the system imaging pixel points are (m1 × n1) × (m2 × n 2).

Technical Field

The invention relates to the technical field of three-dimensional imaging, in particular to a passive millimeter wave three-dimensional imaging system and an imaging method thereof.

Background

The millimeter wave is electromagnetic wave with the frequency range from 30GHz to 300GHz, the millimeter wave band covers a plurality of atmospheric windows (35GHz, 94GHz, 140GHz, 220GHz and the like), can penetrate cloud, fog and smoke dust, and the radiation measurement is not influenced by weather and environment; therefore, the millimeter wave radiation field measurement technology has important application in the fields of military and national defense, remote sensing detection and the like. In addition, because millimeter waves have good penetration characteristics to clothes, millimeter wave radiation field detection also has important application in the field of human body security inspection imaging for detecting concealed dangerous goods. In millimeter wave band, especially W wave band, the difference between the radiation of hidden object and human body is large, which is beneficial to radiation field detection and passive imaging.

The conventional millimeter wave radiation field measurement and passive millimeter wave imaging are usually limited to detecting two-dimensional information, only position information passed by an electromagnetic wave radiation path can be recorded, and angle information highly coupled with scene depth, target geometric form, scene shielding relation and the like is lost, which means that the conventional millimeter wave radiation field detection cannot adjust the detection and imaging focal depth to focus an imaging plane on a plane where an object which is interested is located, and cannot obtain three-dimensional information of a radiation field, so that the functions and application scenes of the millimeter wave radiation field measurement and passive millimeter wave imaging are greatly limited.

The millimeter wave focal plane system is the mainstream technology of passive millimeter wave detection imaging at present, and the structure of the system is that a view field plane is positioned on a focal plane of a dark surface of a lens, and a receiver array is arranged on a bright focal plane of the lens, so that the problem that the resolution of an imaging space and the depth of field of the imaging are mutually contradictory exists. The spatial resolution refers to the size of a focal spot formed by a feed source beam on an imaging plane, and the smaller the focal spot is, the higher the spatial resolution is, and the higher the imaging precision is. Depth of field refers to the distance of axial movement of the focal plane allowed by the focal spot distortion to a certain extent, and the larger the focal depth, the larger the working range of the system imaging, the more effective the scanning of the object with surface relief [1 ]. It is desirable that the spatial resolution of the imaging system be high and the depth of field be large. The spatial resolution δ and the depth of field Δ u are related as follows:

as shown in fig. 1, if the imaging spatial resolution is increased, the imaging depth of field is reduced; if the depth of field is increased, the imaging spatial resolution is reduced. Therefore, the conventional focal plane array passive millimeter wave imaging system with a fixed focal depth has the problem of small imaging depth of field, which results in the reduced resolving power of the imaging system during scanning of a rotating or moving target, especially during axial movement, and the poor capability of detecting surface spoofs.

Disclosure of Invention

The invention provides a passive millimeter wave three-dimensional imaging system and an imaging method thereof for solving the problems in the prior art, and the invention provides the following technical scheme:

a passive millimeter wave three-dimensional imaging system, the system comprising: the radiometer comprises a main dielectric lens, a sub-dielectric lens array, a radiometer receiver array, a digital acquisition circuit and a computer;

electromagnetic waves radiated by objects in a field are converged to a sub-lens array plane through a main dielectric lens and focused to a radiometer receiver array plane through different sub-lenses, a receiving antenna on the radiometer receiver array receives the electromagnetic waves, and signals are sequentially output to a millimeter wave band low-noise amplifier, a high-sensitivity square law detector, a low-pass filter and a low-frequency amplifier, wherein the output end of the low-frequency amplifier is connected with the input end of a digital acquisition circuit, and the digital acquisition circuit transmits sampling signals to a computer for data processing;

a group of radiometer receivers which are arranged at equal intervals in two dimensions are arranged on the focal plane of each sub-dielectric lens, the distances between the phase center of a receiving antenna of each radiometer receiver and the central point of the bright surface of the corresponding sub-dielectric lens are the same, and all the radiometer receivers jointly form a radiometer receiver array;

and step 3: flywheel speed optimization during imaging is performed.

Preferably, the sub-medium lens array is composed of a plurality of sub-medium lenses which are arranged in a two-dimensional equal interval mode, and the centers of the sub-medium lenses and the main medium lens are on the same axis.

A passive millimeter wave three-dimensional imaging method comprises the following steps:

step 1: extracting radiation field information, and recording a four-dimensional function of the radiation field;

step 2: determining the radiation field intensity on the plane of the radiometer according to the distance between the plane of the radiometer array and the plane of the sub-lens;

and step 3: millimeter wave radiation power corresponding to a series of plane sampling points with different depths of field is obtained, namely three-dimensional millimeter wave radiation field data corresponding to three-dimensional space sampling points one to one are obtained, and millimeter wave three-dimensional radiation field detection is achieved.

Preferably, the step 1 specifically comprises:

a radiation field from a certain point in the field of view of the imaging system is focused by the main lens and then received by a plurality of radiometer receivers behind the plurality of sub-lenses; each radiometer receiver receives millimeter wave radiation from a plurality of range, multi-azimuth targets; coordinates corresponding to the radiation path are expressed by intersection coordinates of the sub-lens plane and the radiometer array plane;

coordinates (x, y) of the radiometer plane represent the position information of the target, a connection line of the coordinates (x, y) with coordinates (x ', y') on the sub-lens plane represents the radiation direction, the recorded radiation field, and a four-dimensional function of the radiation field is represented by PF (x ', y', x, y).

Preferably, the step 2 specifically comprises: the distance between the plane of the radiometer array and the plane of the sub-lenses is f, and the intensity of the radiation field at point (x, y) on the radiometer plane is:

preferably, the step 3 specifically comprises:

the method comprises the steps of measuring scene depth, target geometric form and scene shielding relation information lost in a traditional passive millimeter wave focal plane array imaging mode through a passive millimeter wave three-dimensional imaging system, and obtaining millimeter wave radiation power corresponding to a series of plane sampling points with different depths of field through representing the mapping relation between the radiation intensity of a target point and the azimuth and distance information of the target point, namely obtaining three-dimensional millimeter wave radiation field data corresponding to three-dimensional space sampling points one by one, and realizing millimeter wave three-dimensional radiation field detection.

Preferably, the millimeter wave three-dimensional radiation field detection is realized by the following steps:

the distance between the new imaging plane and the sub-lens plane is f ', and f' is beta f, and beta is a virtual imaging depth scale factor; when the plane of the sub-lens and the plane of the sensor are infinite, when the sub-lens array is focused at different depths, the distance between the plane of the sub-lens and the imaging plane changes, and the integral track of the calculated focused image in the space shifts, so that the focal length agility is realized by applying space domain integral projection;

according to the similar triangle theorem, after the focal length is changed quickly, the coordinate of the intersection point formed by the electromagnetic wave and the plane of the radiometer isThe resulting radiation field strength at the radiation plane is therefore expressed as:

after the focal length is obtained, the radiation intensity of the plane of the radiometer is as follows:

on the basis of the collected four-dimensional (x ', y', x, y) matrix radiation field data, determining corresponding beta values by transforming different virtual focusing image planes, determining a sub-lens corresponding to the position of a pixel on a radiometer according to the beta values, and obtaining the mapping relation of the radiation field at different depth distances, thereby realizing the information extraction of the three-dimensional radiation field;

through a sensitive target depth of field extraction algorithm and a focus agility image inversion algorithm, the focus of the imaging system focus plane is agilely changed to the plane of the target of interest in the system field of view by changing the virtual depth of field conversion factor to perform coordinate conversion, and therefore a two-dimensional or three-dimensional gray image of the target is inverted according to a passive millimeter wave imaging algorithm.

Preferably, the aperture and the focal length of the main lens and the sub lens need to be systematically integrated with the requirements of the imaging distance, the field range and the volume of the main lens and the sub lens; the number of the system imaging pixel points is determined by the number and the arrangement of the sub-lens arrangement and the number and the arrangement of the radiometer receivers, when the sub-lens arrangement is m1 × m2 and the radiometer receivers are n1 × n2, the system imaging pixel points are (m1 × n1) × (m2 × n 2).

Has the advantages that:

the passive millimeter wave three-dimensional imaging method and the passive millimeter wave three-dimensional imaging system realize the introduction of millimeter wave radiation field measurement by inserting the sub-lens array between the main focusing antenna and the radiometer receiver array, can measure the information such as scene depth, target geometric form, scene shielding relation and the like lost in the traditional passive millimeter wave focal plane array imaging mode, and obtain millimeter wave radiation power corresponding to a series of plane sampling points with different depths of field by representing the mapping relation between the radiation intensity of a target point and the azimuth and distance information of the target point, namely obtain three-dimensional millimeter wave radiation field data corresponding to three-dimensional space sampling points one by one. The method and the system can realize the detection of the three-dimensional millimeter wave radiation field of the environment (leaf clusters, cloud fog and smoke dust) under all-weather complex shielding conditions all day long, and realize the three-dimensional perspective of the environment. The system can realize large-depth-of-field imaging, thereby meeting the requirements of non-fit type, quick and convenient security inspection imaging. The system realizes plane focusing imaging of any depth of field in the field range of the system through focus agility, and realizes two-dimensional or three-dimensional imaging of sensitive objects in scenes such as human body security inspection and the like through a sensitive target depth of field extraction algorithm and a focus agility image inversion algorithm.

Drawings

FIG. 1 is a schematic view of depth of field versus spatial resolution;

FIG. 2 is a block diagram of a passive millimeter wave three-dimensional imaging system;

FIG. 3 is a schematic diagram of a passive millimeter wave three-dimensional imaging system;

FIG. 4 is a perspective view of a passive millimeter wave three-dimensional imaging system;

FIG. 5 is a schematic diagram of a point source radiation path;

FIG. 6 is a schematic diagram of spatial domain focus agility;

fig. 7 is a schematic diagram of an imaging algorithm based on focus agility.

Detailed Description

The present invention will be described in detail with reference to specific examples.

The first embodiment is as follows:

as shown in fig. 2 to 7, the specific optimized technical solution adopted to solve the above technical problems of the present invention is: the three-dimensional structure of the system is shown in figure 4. The millimeter wave three-dimensional radiation field measuring system comprises a main dielectric lens 1, a sub-dielectric lens array 2, a radiometer receiver array 3, a digital acquisition circuit 4 and a computer 5. Electromagnetic waves radiated by an object in a system field of view are converged to a plane of a sub-lens array 2 through a main dielectric lens 1, and are focused to a plane of a radiometer receiver array 3 through different sub-lenses, a receiving antenna 3-1 on the radiometer receiver receives the electromagnetic waves, signals are sequentially output to a millimeter wave band low-noise amplifier 3-2, a high-sensitivity square law detector 3-3, a low-pass filter 3-4 and a low-frequency amplifier 3-5, the output end of the low-frequency amplifier 3-5 is connected with the input end of a digital acquisition circuit 4, and the digital acquisition circuit 4 transmits sampling signals to a computer 5 for data processing. The method is characterized in that: the sub dielectric lens array 2 is composed of two-dimensional sub dielectric lenses arranged at equal intervals, and the centers of the sub dielectric lens array 2 and the main dielectric lens 1 are on the same axis. A group of radiometer receivers which are arranged at equal intervals in two dimensions are arranged on the focal plane of each sub-dielectric lens, the distances between the phase center of the receiving antenna of each radiometer receiver and the central point of the bright surface of the corresponding sub-dielectric lens are the same, and all the radiometer receivers jointly form a radiometer receiver array.

The main medium lens is made of Polytetrafluoroethylene (PTFE); the sub-medium lens is made of Polytetrafluoroethylene (PTFE), the propagation path of electromagnetic waves in the main medium lens and the sub-medium lens is simulated by a ray tracing method in combination with the requirements of the imaging distance (1000mm) and the field range of the system, and the propagation path of the electromagnetic waves between the feed source and the lens is simulated by a Gaussian beam method; determining the aperture of the main lens to be 300mm, the focusing focal lengths of the bright surface and the dark surface to be 1000mm, the aperture of the sub-lens to be 10mm, the focal lengths of the bright surface and the dark surface to be 1000mm and 12mm respectively, and the arrangement to be 10 x 10; the radiometer receiver consists of a receiving antenna, a millimeter wave band low-noise amplifier, a high-sensitivity square law detector, a low-pass filter, a low-frequency amplifier and a low-frequency amplifier, and the number and the arrangement are (10 multiplied by 10) multiplied by (3 multiplied by 3); the main dielectric lens and the sub-dielectric lens are arranged in a matrix, and the radiometer receiver array is fixed on the metal support frame. Electromagnetic waves radiated by an object in a system field of view are converged to a sub-lens array plane through a main dielectric lens and focused to a radiometer receiver array plane through different sub-lenses, the output end of a radiometer receiver is connected with the input end of a digital acquisition circuit, and the output end of the digital acquisition circuit is connected with the input end of a computer.

In the embodiment, the digital acquisition circuit adopts and codes the analog signal output by the radiometer receiver and transmits the analog signal to the computer for data processing, so that three-dimensional information of a radiation field in a system view field range can be obtained, and two-dimensional or three-dimensional imaging of a sensitive target can be realized through a focal-length-edge-based imaging algorithm discussed in the principle.

The embodiment adopts a mode of combining mechanical scanning with a one-dimensional radiometer array, reduces the number of radiometer receivers for constructing the system, and saves the system cost.

A passive millimeter wave three-dimensional imaging method comprises the following steps:

step 1: extracting radiation field information, and recording a four-dimensional function of the radiation field;

the step 1 specifically comprises the following steps:

a radiation field from a certain point in the field of view of the imaging system is focused by the main lens and then received by a plurality of radiometer receivers behind the plurality of sub-lenses; each radiometer receiver receives millimeter wave radiation from a plurality of range, multi-azimuth targets; coordinates corresponding to the radiation path are expressed by intersection coordinates of the sub-lens plane and the radiometer array plane;

coordinates (x, y) of the plane of the radiometer represent the azimuth information of the target, the connection line of the coordinates (x, y) with the coordinates (x ', y') on the plane of the sub-lens represents the radiation direction, the recorded radiation field, passes through P_F(x ', y', x, y) represents a four-dimensional function of the radiation field.

Step 2: determining the radiation field intensity on the plane of the radiometer according to the distance between the plane of the radiometer array and the plane of the sub-lens;

the step 2 specifically comprises the following steps: the distance between the plane of the radiometer array and the plane of the sub-lenses is f, and the intensity of the radiation field at point (x, y) on the radiometer plane is:

and step 3: millimeter wave radiation power corresponding to a series of plane sampling points with different depths of field is obtained, namely three-dimensional millimeter wave radiation field data corresponding to three-dimensional space sampling points one to one are obtained, and millimeter wave three-dimensional radiation field detection is achieved.

The step 3 specifically comprises the following steps:

the method comprises the steps of measuring scene depth, target geometric form and scene shielding relation information lost in a traditional passive millimeter wave focal plane array imaging mode through a passive millimeter wave three-dimensional imaging system, and obtaining millimeter wave radiation power corresponding to a series of plane sampling points with different depths of field through representing the mapping relation between the radiation intensity of a target point and the azimuth and distance information of the target point, namely obtaining three-dimensional millimeter wave radiation field data corresponding to three-dimensional space sampling points one by one, and realizing millimeter wave three-dimensional radiation field detection.

The millimeter wave three-dimensional radiation field detection is realized through the following steps:

the distance between the new imaging plane and the sub-lens plane is f ', and f' is beta f, and beta is a virtual imaging depth scale factor; when the plane of the sub-lens and the plane of the sensor are infinite, when the sub-lens array is focused at different depths, the distance between the plane of the sub-lens and the imaging plane changes, and the integral track of the calculated focused image in the space shifts, so that the focal length agility is realized by applying space domain integral projection;

according to the similar triangle theorem, after the focal length is changed quickly, the coordinate of the intersection point formed by the electromagnetic wave and the plane of the radiometer isThe resulting radiation field strength at the radiation plane is therefore expressed as:

after the focal length is obtained, the radiation intensity of the plane of the radiometer is as follows:

on the basis of the collected four-dimensional (x ', y', x, y) matrix radiation field data, determining corresponding beta values by transforming different virtual focusing image planes, determining a sub-lens corresponding to the position of a pixel on a radiometer according to the beta values, and obtaining the mapping relation of the radiation field at different depth distances, thereby realizing the information extraction of the three-dimensional radiation field;

through a sensitive target depth of field extraction algorithm and a focus agility image inversion algorithm, the focus of the imaging system focus plane is agilely changed to the plane of the target of interest in the system field of view by changing the virtual depth of field conversion factor to perform coordinate conversion, and therefore a two-dimensional or three-dimensional gray image of the target is inverted according to a passive millimeter wave imaging algorithm.

The aperture and the focal length of the main lens and the sub lens need to be systematically integrated with the requirements on the imaging distance, the field range and the volume of the main lens and the sub lens; the number of the system imaging pixel points is determined by the number and the arrangement of the sub-lens arrangement and the number and the arrangement of the radiometer receivers, when the sub-lens arrangement is m1 × m2 and the radiometer receivers are n1 × n2, the system imaging pixel points are (m1 × n1) × (m2 × n 2).

The above description is only a preferred embodiment of the passive millimeter wave three-dimensional imaging system and the imaging method thereof, and the protection scope of the passive millimeter wave three-dimensional imaging system and the imaging method thereof is not limited to the above embodiments, and all technical solutions belonging to the idea belong to the protection scope of the present invention. It should be noted that modifications and variations which do not depart from the gist of the invention will be those skilled in the art to which the invention pertains and which are intended to be within the scope of the invention.