CN113156432B - A Portable Microwave Imaging System - Google Patents

Abstract

The invention discloses a portable microwave imaging system which comprises a handheld active scanner and an information processing terminal. The handheld scanner comprises a radio frequency transceiver, a first attitude sensor, an on-off judging device and a first wireless transceiver module; the information processing terminal comprises an information processor and a second wireless transceiver module and is used for receiving the returned data of the scanner. In the process of one instantaneous sampling, the spatial attitude and echo signals of the scanner are received by an information processing terminal, real-time back projection image reconstruction is carried out, and the reconstructed images are accumulated on the previous image. The invention reconstructs the image by the space coordinates and the angle real-time back projection determined by the gesture sensor, the handheld scanner can be positioned at any position, the device limit of the traditional array imaging is broken, the using flexibility and the coverage angle of the device are greatly improved, the hardware cost is reduced, the real-time imaging can be satisfied, and the detection efficiency is improved.

Description

A Portable Microwave Imaging System

technical field

The invention relates to the technical field of security inspection imaging, in particular to a portable microwave imaging system.

Background technique

The existing main security inspection methods are manual inspection, metal detection equipment and X-ray security inspection machine. The manual inspection method using metal detectors has the problem of low efficiency and there is a certain possibility of infringing on personal privacy due to physical contact, while X-rays cannot directly act on the human body due to ionization characteristics. The millimeter-wave security imaging can not only detect hidden metal objects under the fabric, but also detect dangerous goods such as plastic guns, ceramic knives, explosives, etc., without electromagnetic radiation hazards to the human body. Millimeter wave security inspection can obtain clear image information, which can greatly reduce the false alarm rate, so it has attracted much attention in recent years.

At present, millimeter wave imaging can be divided into millimeter wave focal plane imaging and millimeter wave holographic imaging. Among them, the millimeter wave focal plane imaging system places a two-dimensional array of millimeter wave detectors behind a large lens. The system has relatively low resolution, small aperture, limited field of view, and high cost of 2D arrays. The millimeter-wave holographic imaging system does not need lenses, and uses electronic switches and mechanical scanning, which can greatly reduce the required antenna array elements, and the antenna has a large aperture, and has the characteristics of real-time and high resolution. However, the traditional mechanical transmission structure has high requirements for the detection scene, the object to be measured must be located in a designated area, and the scanning also has a fixed orbit and angle, the flexibility of the equipment is low, and there is a certain scanning dead angle; the detection efficiency of the traditional active imaging method is low. A scan takes too long, and a complete mechanical movement must be completed for image reconstruction, which cannot be imaged in real time; and the movement accuracy and jitter of the mechanical mechanism will cause spatial sampling errors, which are especially obvious at high frequency bands. It brings about various problems of service life and maintenance; finally, even if a mechanical mechanism is used, the cost of a one-dimensional radar array is still very high, let alone a two-dimensional array. This is also the reason why millimeter wave security inspection equipment is currently expensive and not widely used.

Contents of the invention

The purpose of the present invention is to provide a portable microwave imaging system with simple structure and real-time imaging to solve the problems of low equipment flexibility, incapability of real-time imaging, fixed scanning angle and fixed scanning track in the existing security inspection technology.

In order to achieve the above object, the technical scheme adopted in the present invention is as follows:

The invention provides a portable microwave imaging system, comprising: a handheld active scanner and an information processing terminal;

The handheld active scanner includes:

radio frequency transceivers for transmitting electromagnetic waves;

A first attitude sensor for collecting the current spatial coordinates of the handheld active scanner;

An on-off judge for judging whether the object to be detected is within the effective scanning range of the radio frequency transceiver;

as well as,

The first wireless transceiver module for sending the echo signal of the object to be detected received by the radio frequency transceiver and the spatial coordinates of the handheld active scanner collected by the first attitude sensor to the information processing terminal;

The information processing terminal includes:

A second wireless transceiver module for receiving the echo signal of the object to be detected and the spatial coordinates of the active scanner;

A second attitude sensor for constructing a three-dimensional Cartesian coordinate system;

as well as,

The information processor is used for reconstructing the image of the object to be detected according to the echo signal of the object to be detected, the effective scanning range of the radio frequency transceiver, and the spatial coordinates of the active scanner.

Further, the handheld active scanner also includes a battery, a power supply system and a grippable housing.

Further, the first attitude sensor is specifically used for,

acquiring at least two spatial coordinates of the handheld active scanner;

The orientation of the spatial attitude of the handheld active scanner is determined according to the two spatial coordinates.

Further, the on-off judger is specifically used for,

It is judged whether the object to be detected is within the effective scanning range of the radio frequency transceiver, and if so, a working instruction to turn on the radio frequency transceiver is issued.

Further, the on-off judging device is an optical camera or a photosensitive signal sensor or a thermal sensor.

Further, the second attitude sensor is specifically used for,

A three-dimensional Cartesian coordinate system is constructed, at least including a coordinate anchor point, an x-axis unit length anchor point, a y-axis unit length anchor point, and a z-axis unit length anchor point.

Further, the information processor is specifically used to:

Obtain the echo signal s _n (t,τ),

Among them, τ=2r _n /c,

(x _n , y _n , z _n ) are the space coordinates of the active scanner, c is the speed of light, and t is the current time;

The echo signal and the emitted electromagnetic wave are subjected to coherent fast Fourier transformation to obtain the spatial reflectivity function

Among them, r is the linear distance between a point within the effective scanning range and (x _n , y _n , z _n );

Will According to the back projection of the effective scanning range θ, the effective spatial reflectance Φ _n (r, θ′) of each point in the effective scanning range is obtained, that is, the reconstructed image of the object to be detected;

Among them, the effective scanning range θ is determined according to the maximum beam width of the antenna, and r, θ' are polar coordinates after back projection.

Further, the information processing terminal further includes a display device for displaying in real time the image of the object to be detected reconstructed and generated by the information processor.

Further, each time the information processor receives an echo signal, it immediately reconstructs an image and displays it on the display device, and the reconstructed image is added to the previous image.

The beneficial effects of the present invention are:

(1) The present invention reconstructs the image by real-time back-projection of the spatial coordinates and angles determined by the attitude sensor, which can achieve the effect of real-time imaging; (2) The layout of the separation of the scanner and the information processing terminal makes scanning without a fixed radius and angle very easy Greatly increases the flexibility of the system and is easy for operators to use; (3) Introduces an on-off judge to make the system stop working at useless angles, avoiding invalid work and redundant data; (4) Compared with traditional array imaging solutions , the algorithm based on the back projection of the present invention does not need a large number of approximation operations, and more original signal information is reserved; (5) the present invention adopts a single radio frequency transceiver, which greatly reduces the cost compared with the one-dimensional radar array and the two-dimensional radar array, Easy to manufacture and commercialize.

Description of drawings

Fig. 1 is a schematic structural diagram of a portable microwave imaging system of the present invention;

Fig. 2 is a schematic diagram of spatial coordinates in which the imaging target is a corner reflector in an embodiment of the present invention;

Fig. 3 is a schematic diagram of the workflow in the embodiment of the present invention.

Detailed ways

The present invention will be further described below. The following examples are only used to illustrate the technical solution of the present invention more clearly, but not to limit the protection scope of the present invention.

The present invention provides a portable microwave imaging system, as shown in FIG. 1 , which includes: a handheld active scanner 1 and an information processing terminal 2 . The handheld active scanner 1 mainly includes a radio frequency transceiver 3 , a first attitude sensor 4 , an on-off judging device 5 , a first wireless transceiver module 6 , a battery and a power supply system 7 and a grippable housing 8 .

The radio frequency transceiver 3 is used to emit electromagnetic waves, and the radio frequency transceiver is the only emission source of the system.

The first posture sensor 4 is used to collect at least two spatial coordinates of the handheld active scanner 1 and determine the spatial position and spatial posture of the handheld active scanner 1 .

For example, assuming that the scanner is facing one direction, then the first attitude sensor only needs to locate two points on that straight line, and there is a front and back sequence, to know the spatial attitude orientation of the scanner.

The on-off judging device 5 is used to judge whether the object 13 to be detected is directly in front of the radio frequency transceiver antenna radiation direction, that is, the effective scanning range 14, and to control the working state of the radio frequency transceiver.

The first wireless transceiver module 6 is used to send the echo signal of the object to be detected received by the radio frequency transceiver to the information processing terminal; Handle the terminal.

The information processing terminal 2 includes an information processor 9 , a second wireless transceiver module 10 , a second attitude sensor 11 and a display device 12 .

The second wireless transceiver module 10 and the first wireless transceiver module 6 construct the information path between the handheld active scanner 1 and the information processing terminal 2, for receiving the echo signal of the object to be detected and the spatial coordinates and spatial coordinates of the active scanner. Pose, used for subsequent signal processing and image reconstruction.

The second attitude sensor 11 is used to construct a three-dimensional Cartesian coordinate system, which at least needs to include a coordinate anchor point, an x-axis unit length anchor point, a y-axis unit length anchor point, and a z-axis unit length anchor point.

The information processor is used for,

According to the received echo signal S(n) and the space vector attitude P(x _n ,y _n ,z _n ,x _n ′,y′ _n ,z′ _n ) of the handheld active scanner 1, the broadband echo signal Perform backprojection reconstruction. Reconstruction is based on the space vector pose of the handheld active scanner 1

P(x _n ,y _n ,z _n ,x _n ′,y′ _n ,z′ _n ), and the effective scanning range θ _n . (x _n , y _n , z _n ) and (x _n ′, y _n ′, z _n ′) are the coordinates of two points of the active scanner collected by the first attitude sensor. The effective scanning range θ _n is determined according to the maximum beam width of the antenna.

Every time the information processor 9 receives an echo signal, it immediately reconstructs the image and often displays it on the display device 12. The image is superimposed on the previous n-1 images, so as to achieve real-time imaging effect. The more the scanner scans, the more The wider the coverage of the measured object, the clearer the three-dimensional image, which is convenient for the operator to observe the detected object in real time, and n is the current sampling number.

The working process is: when the active scanner is turned on, the built-in on-off judge and the first attitude sensor start to work. The on-off judging device judges whether the object to be detected is directly in front of the radiation direction of the antenna (that is, the effective scanning range). If it is confirmed that the object is within the effective scanning range, the on-off judging device sends a normal working instruction, and the RF transceiver only receives the instruction. It will work, transmit and receive echo data, otherwise it will be in standby state. The on-off judge can avoid invalid work and redundant data of the radio frequency transceiver. The electromagnetic wave is emitted from the antenna of the radio frequency transceiver, and after reaching the surface of the object to be detected, the reflection is attenuated and is received and recorded by the radio frequency transceiver again. The echo signal data is transmitted to the information processing through the information path constructed by the first wireless transceiver module and the second wireless transceiver module At the same time, the information processor also receives the complete space coordinates and space attitude of the active scanner collected by the first attitude sensor. The final information processor uses all the received information to process and reconstruct the imaging in real time, so as to achieve the purpose of real-time imaging.

In the embodiment of the present invention, the on-off judging device 5 may be realized in various manners. For example, an optical camera, which uses image recognition technology to judge whether the object to be detected is within the effective scanning range; or uses the vector attitude information of the first attitude sensor to calculate the radiation angle of the antenna to determine whether the area to be measured is correct; others such as photosensitive Signal sensors, heat sensors, etc. can be used for different actual detection targets or detection scenarios.

In the embodiment of the present invention, the radio frequency transceiver 3 is not limited to a single-station system, and a multi-station single-transmission-single-reception system and a multi-transmission-multiple-reception system can also be used. Compared with the single-station system, the multi-station system can bring higher information processing speed and improve the detection sensitivity and accuracy of the target.

In the embodiment of the present invention, the information processor 9 is generally implemented by a computer, and any device with information processing functions can be used as a processing device such as a single-chip microcomputer, an industrial computer, a portable tablet, a mobile phone, etc., and the processing capacity required by the actual detection scene is required needs to decide.

In the embodiment of the present invention, the final imaging is not limited to a three-dimensional image. For different objects to be detected, you can choose to back-project to a two-dimensional plane to obtain a real-time two-dimensional image, or you can back-project and superimpose or slice from the three-dimensional image to a fixed angle to obtain a two-dimensional image, etc. The final imaging result is determined according to actual needs. A higher-dimensional image will bring more details, but it will also bring higher computational complexity.

Example 1:

Embodiment 1 illustrates the specific working principle of the system. In this embodiment, the test signal is set as a broadband signal with a center frequency of 30 GHz, a bandwidth of 5 GHz, and a sampling rate of 5 MHz. The spatial layout is shown in Figure 2, assuming that the corner reflector to be measured (object to be detected) is located at the origin of the Cartesian coordinate system, and the directions of the three axes are determined. The handheld scanner is located at any position in space, and the object to be detected must be within the effective scanning angle of the scanner, otherwise the on-off judge control system is in a standby state and stops working, so the embodiment defaults that the object to be detected is within the effective angle.

Assuming that the scanner is at (x _n , y _n , z _n ) at the nth sampling, the center point of the scanning angle is (x′ _n , y′ _n , z′ _n ), so the scanning direction vector is ( ), where /> The effective scan angle is fixed at θ. The echo signal received by the scanner in this scan is s _n (t,τ), where τ=2r _n /c,/> c is the speed of light. The spatial reflectance function can be obtained after coherent fast Fourier transformation with the transmitted signal /> where r is the linear distance between a point in the effective scanning range and the scanner, according to the effective scanning range θ, the effective spatial reflectance Φ _n (r, θ′) of each point in the effective scanning range can be obtained by back projection, that is, the three-dimensional image, r , θ' is the polar coordinate after backprojection. At this time, the imaging result can be displayed in real time and displayed on the monitor, which is convenient for the operator to observe.

After multi-scan back projection reconstruction, the signals at the real object are coherently superimposed, while the signals at the virtual shadow gradually tend to zero due to the different phases. Therefore, the more scanning positions and the more imaging times, the clearer the image and the more details. Moreover, due to the inherent concurrency characteristics of back projection, the subsequent addition of concurrent execution algorithms can greatly increase the calculation speed.

Example 2:

This implementation provides a specific operation mode of the portable microwave imaging system, as shown in FIG. 3 . The test signal is set as a broadband signal with a center frequency of 62GHz, a bandwidth of 5GHz, a linear change in frequency, and a sampling rate of 5MHz. The object to be measured is a human body. The operator needs to hold the scanner and make the scanning direction face the human body. Within a scanning interval, the instantaneous position and echo signal of the scanner are obtained and transmitted to the signal processor. Wave signal coherent Fourier transformation, conical area back projection calculation operation, for the first time real-time three-dimensional image can be obtained and displayed on the monitor around the operator.

If the operator continues to scan sensitive parts such as clothes pockets or trousers pockets for a long time, the details of this part will be clearer in the 3D image of the monitor, and the contrast of the reflectivity of the items in the pocket will be higher. The operation method depends on the judgment of the operator. and the actual type of object to be measured. The system supports multiple working frequency bands, and higher bandwidth can bring better resolution.

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made. It should also be regarded as the protection scope of the present invention.

Claims (8)

1. A portable microwave imaging system, comprising: a hand-held active scanner and an information processing terminal;

the hand-held active scanner includes:

a radio frequency transceiver for transmitting electromagnetic waves;

the first attitude sensor is used for acquiring the current space coordinates of the handheld active scanner;

the on-off judging device is used for judging whether the object to be detected is in the effective scanning range of the radio frequency transceiver;

the method comprises the steps of,

the first wireless transceiver module is used for transmitting the echo signal of the object to be detected received by the radio frequency transceiver and the space coordinates of the handheld active scanner acquired by the first attitude sensor to the information processing terminal;

the information processing terminal includes:

the second wireless transceiver module is used for receiving echo signals of the object to be detected and the space coordinates of the active scanner;

the second attitude sensor is used for constructing a three-dimensional rectangular coordinate system;

the method comprises the steps of,

the information processor is used for reconstructing an image of the object to be detected according to the echo signal of the object to be detected, the effective scanning range of the radio frequency transceiver and the space coordinate of the active scanner;

the information processor is particularly adapted to,

acquisition of echo signal s _n (t,τ)，

Wherein τ=2r _n /c，

(x _n ,y _n ,z _n ) The space coordinate of the active scanner is c is the speed of light, and t is the current time;

performing coherent fast Fourier transform on the echo signal and the transmitted electromagnetic wave to obtain a space reflectivity function

Wherein r is a point and (x) in the effective scanning range _n ,y _n ,z _n ) Is a straight line distance of (2);

will beObtaining the effective space reflectivity phi of each point in the effective scanning range according to the effective scanning range theta back projection _n (r, θ'), i.e., a reconstructed image of the object to be detected;

the effective scanning range θ is determined according to the maximum beam width of the antenna, and r, θ' is the post-back-projection polar coordinate.

2. The portable microwave imaging system of claim 1, wherein the handheld active scanner further comprises a battery and power system and a graspable housing.

3. A portable microwave imaging system in accordance with claim 1, wherein the first attitude sensor is configured to,

collecting at least two space coordinates of a handheld active scanner;

and determining the spatial attitude orientation of the handheld active scanner according to the two spatial coordinates.

4. A portable microwave imaging system according to claim 1, wherein the on-off determiner is configured to,

judging whether the object to be detected is in the effective scanning range of the radio frequency transceiver, and if so, sending out a working instruction for starting the radio frequency transceiver.

5. The portable microwave imaging system of claim 4, wherein the on-off determiner is an optical camera or a photosensitive signal sensor or a thermal sensor.

6. A portable microwave imaging system in accordance with claim 1, wherein the second attitude sensor is specifically configured to,

and constructing a three-dimensional rectangular coordinate system, wherein the three-dimensional rectangular coordinate system at least comprises a coordinate anchor point, an x-axis unit length anchor point, a y-axis unit length anchor point and a z-axis unit length anchor point.

7. The portable microwave imaging system according to claim 1, wherein the information processing terminal further comprises a display device for displaying the image of the object to be detected, which is reconstructed by the information processor, in real time.

8. The portable microwave imaging system of claim 7, wherein the information processor reconstructs an image immediately upon receipt of an echo signal and displays the reconstructed image on the display device, and wherein the reconstructed image is accumulated on the previous image.