A terahertz continuous wave three-dimensional tomography method

Abstract

The present invention discloses a terahertz continuous wave three-dimensional tomography device and method, the device mainly includes: a terahertz wave transceiver module, including: a dual-channel microwave source, a synchronous acquisition unit, a frequency doubling module and a transceiver antenna, which are used to generate, detect and analyze terahertz wave signals; a terahertz wave optical path scanning module, including: an off-axis parabola, which is used to form a terahertz optical path and focus the terahertz wave radiated by the antenna into a Gaussian beam. A three-dimensional object-carrying mobile platform is used to simulate the traditional tomography scanning mode and move the imaging target; a main control host module, including a main control computer and a single-chip microcomputer, is used to control the terahertz wave transceiver module and the terahertz wave optical path scanning module to scan the imaging target object, and the obtained terahertz wave transmission object data is subjected to data inversion imaging by using filtered back projection or joint algebraic reconstruction method to obtain a three-dimensional internal structure diagram of the imaging target object.

Description

Technical Field

[0001] The invention belongs to the technical field of terahertz imaging, and in particular relates to a terahertz continuous wave three-dimensional tomography method. Background Art

[0002] The terahertz band is an electromagnetic wave with a frequency higher than that of millimeter waves and lower than that of infrared waves. It is generally believed that its frequency is between 100GHz and 10THz, and the corresponding wavelength is from 3mm to 30μm. Since this band is a transitional band between electronics and optics, it has some unique properties. The vibration frequencies and rotational energy levels of many macromolecular substances fall in the terahertz band, so these substances have some absorption peaks for terahertz waves, which means that these substances can be detected using the terahertz TDS system. At the same time, for non-polar materials, terahertz waves have stronger penetration than microwaves, smaller scattering fields, and lower photon energy than X-rays. It will not cause ionization effects on materials and human bodies, making it safer. Therefore, under the same tomography principle, the imaging resolution is higher than microwave imaging, and the penetration is stronger than infrared waves. Compared with X-rays, terahertz waves have higher contrast for low-density materials, and the low photon energy of terahertz waves will not cause ionization of materials, so non-destructive imaging can be achieved. Therefore, terahertz imaging can be used as an important supplement to existing imaging technology and applied to non-destructive testing, biomedicine and other fields. Now terahertz imaging technology has developed many imaging modes, such as active and passive, continuous wave and TDS imaging, reflection and transmission imaging, etc.

[0003] Among the current terahertz three-dimensional imaging technologies, the more mature technology is terahertz wave computer-aided tomography (CT). However, the propagation process of X-rays in matter is very different from that of terahertz waves. X-rays propagate in a straight line. However, terahertz waves will cause the movement of electric charges, so when they are obliquely incident on the interface of different materials, reflection and refraction will occur. The higher the dielectric contrast of the material, the more serious the reflection and refraction will be. At present, most terahertz tomography systems emit terahertz waves through a terahertz source, focus the terahertz beam with a lens or parabola, scan the sample to be tested, and then focus it and receive it with a terahertz detector. This system can only obtain a single-frequency emission amplitude-frequency information and a received amplitude information. The amount of information is single. If you want to obtain the spectrum information, you need to modulate it with a chopper. The limitation of the chopper modulation signal is also relatively large. When the terahertz source is unstable, the measured received amplitude will have errors. Moreover, the imaging speed of this system is very slow because it needs to scan and record data point by point, and the system has a small dynamic range and lacks other reference data to optimize the result data volume. Summary of the invention

[0004] In order to solve the above-mentioned deficiencies in the existing technology, the present invention provides a terahertz continuous wave three-dimensional tomography device and method. The device adopts a terahertz continuous wave transceiver integrated equipment to achieve rapid scanning of the imaging target; records the data after the terahertz continuous wave transmits the object, and then uses filtered back projection and a joint algebraic reconstruction algorithm to image the internal structure of the imaging target, thereby achieving non-destructive flaw detection of the target.

[0005] According to one aspect of the present invention, a technical solution of a terahertz continuous wave three-dimensional tomography device is provided:

[0006] A terahertz continuous wave three-dimensional tomography device, the device comprising a terahertz transceiver module, a terahertz optical path scanning module and a main control host module;

[0007] The terahertz transceiver module includes a dual-channel microwave source, a synchronous acquisition unit, a frequency doubling module and a transceiver antenna, integrating the transceiver module. The dual-channel microwave source is used to generate a microwave signal and a reference signal; the synchronous acquisition unit is used to synchronously acquire the received and transmitted signals; the frequency doubling module is used to multiply the microwave signal of the microwave source to the terahertz band, and to down-convert the received terahertz wave signal to the microwave band; the transceiver antenna is used to transmit and receive terahertz waves.

[0008] The terahertz optical path scanning module includes an off-axis parabolic mirror and a three-dimensional object turntable. The function of the off-axis parabolic reflector is to focus the terahertz wave emitted by the antenna into a terahertz Gaussian beam with strong penetrating power, thereby transmitting the imaging target, and converge the terahertz wave diverged after transmission to the receiving antenna to form a terahertz scanning optical path; the three-dimensional object moving platform can move in three dimensions: horizontally, vertically and rotationally, and is used to enable the single-transmitter and single-receiver imaging system to simulate the traditional CT imaging mode and perform three-dimensional movement of the imaging target.

[0009] The main control host module includes a main control host and a single-chip microcomputer. The function of the main control host is to connect to the terahertz transceiver module to read the scanning data and use filtered back projection or joint algebraic reconstruction method to process the data to perform three-dimensional structural imaging of the imaging target object; the function of the single-chip microcomputer is to connect to the three-dimensional carrier mobile platform with the main control host and control the movement of the three-dimensional carrier mobile platform.

[0010] Another aspect of the present invention provides a method for controlling a terahertz continuous wave three-dimensional tomography device.

[0011] A method for controlling a terahertz continuous wave three-dimensional tomography device, the method comprising the following steps:

[0012] S1. Set the output frequency, scanning mode, scanning points and scanning time of the terahertz transceiver module;

[0013] S2. According to the imaging target, set the 3D scanning range, scanning step length, and scanning time;

[0014] S3. Place the imaging target on the three-dimensional carrier moving platform and set the three-dimensional carrier moving platform to the initial position;

[0015] S4. While the three-dimensional object-carrying mobile platform moves horizontally to a preset range, the vector network analyzer transmits a terahertz continuous wave from the transmitting antenna, and the receiving antenna records the transmission wave data passing through the imaging target object, and then records the data in the first column of a two-dimensional array, and then the three-dimensional object-carrying mobile platform rotates an angle step in the plane;

[0016] S5. Repeat the step of S4, and record the transmission wave data of the next angle into the next column of the two-dimensional array, and so on, until the rotation angle completes the scanning of all angles in the preset range. The transmission wave data recorded by the array is stored in the main control host module, and recorded as the plane scanning data of the cross-sectional imaging target object at the current height, and then the two-dimensional tomogram is inverted and reconstructed using filtered back projection or joint algebraic method to obtain the internal structure image of the imaging target object in the changed cross section;

[0017] S6. Raise the three-dimensional object-carrying mobile platform by a step distance in the vertical direction, repeat the steps of S4 and S5, and obtain the two-dimensional tomographic image of the imaging target object in the vertical direction; and so on, until the three-dimensional turntable rises to the preset height. Complete the step scans in all vertical directions and the corresponding two-dimensional tomographic images. Finally, perform three-dimensional stacking and reconstruction of the two-dimensional tomographic images of all cross sections in the vertical direction to obtain the three-dimensional structure diagram of the imaging target object. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a structural diagram of a terahertz continuous wave three-dimensional tomography device according to an embodiment of the present invention.

[0019] Figure 2 This is a flow chart of a control method of a terahertz continuous wave three-dimensional tomography device according to an embodiment of the present invention.

[0020] FIG. 3 is a diagram of an imaging result of a cross section of an object measured by the device of the present invention according to an embodiment of the present invention. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0022] like Figure 1 According to one aspect of the present invention, a technical solution of a terahertz continuous wave three-dimensional tomography device is provided:

[0023] A terahertz continuous wave three-dimensional tomography device comprises a terahertz transceiver module 1, a terahertz optical path scanning module 2 and a main control host module 3.

[0024] The terahertz transceiver module includes a dual-channel microwave source, a synchronous acquisition unit, a frequency doubling module and a transceiver antenna, integrating the transceiver module. The dual-channel microwave source is used to generate a microwave signal and a reference signal; the synchronous acquisition unit is used to synchronously acquire the received and transmitted signals; the frequency doubling module is used to multiply the microwave signal of the microwave source to the terahertz band, and to down-convert the received terahertz wave signal to the microwave band; the transceiver antenna is used to transmit and receive terahertz waves.

[0025] In this embodiment, the method for generating signals by the dual-path microwave source includes:

[0026] Only by using general test instruments such as vector network analyzers can the continuous wave microwave signal of step or electrical frequency be obtained;

[0027] Alternatively, frequency synthesis technology is used to generate a continuous microwave signal.

[0028] The terahertz optical path scanning module includes an off-axis parabolic mirror and a three-dimensional object turntable. The function of the off-axis parabolic reflector is to focus the terahertz wave emitted by the antenna into a terahertz Gaussian beam with strong penetration, thereby transmitting the imaging target, and converge the terahertz wave diverged after transmission to the receiving antenna to form a terahertz scanning optical path; the three-dimensional object moving platform is driven by a stepper motor and can move in three dimensions: horizontally, vertically and rotationally, so that the single-transmitting and single-receiving imaging system can simulate the traditional CT imaging mode and perform three-dimensional movement of the imaging target.

[0029] The main control host module includes a main control host and a single-chip microcomputer. The function of the main control host is to connect to the terahertz transceiver module to read the scanning data and use filtered back projection or joint algebraic reconstruction method to process the data to perform three-dimensional structural imaging of the imaging target object; the function of the single-chip microcomputer is to connect to the main control host, output pulse signals to control the motor to drive the three-dimensional carrier moving platform, and maintain the movement of the three-dimensional carrier moving platform.

[0030] The present invention also provides an embodiment, a terahertz continuous wave three-dimensional tomography device control method, such as Figure 2 The method shown comprises the following steps:

[0031] S1. Input the focus position (x, y), input the X, Z axis scanning step and range, input the rotation angle θ and range, and the displacement scanning settings to determine the center position and size of the object to be measured. According to the above data, input the appropriate focus position (x, y) in the control program, input the X, Z axis scanning step and range, input the rotation angle and range, and the time interval of the measurement data corresponds to the time interval of the recording data of the terahertz transceiver module;

[0032] S2. Initialize the three-dimensional object-carrying mobile platform, manually adjust the Y axis, and configure the relevant parameters of the terahertz transceiver module;

[0033] S3. Move the three-dimensional object moving platform to the starting point of the scan;

[0034] S4. The X-axis moving stage moves horizontally to a preset value, and at the same time, the synchronous acquisition unit in the terahertz transceiver module records the data after the terahertz wave transmits the imaging target object, and records the data into the first column of a two-dimensional array, and then the three-dimensional turntable rotates an angle;

[0035] S5. Repeat the steps of step S4 and record the data in the next column of the two-dimensional array until the rotation angle θ reaches the preset θ. The recorded data of the array is stored in the control host as the cross-sectional scanning data of the current height z, and the structure imaging of the cross-section is performed using filtered back projection or joint algebraic method.

[0036] S6. Then the three-dimensional object-carrying moving platform rises one step on the Z axis, repeats steps S4 to S5, and scans each cross-sectional structure diagram corresponding to the Z axis position z until the position z reaches the preset value Z.

[0037] S7. Overlay the structural layers of all cross sections to obtain a three-dimensional structural image of the imaging target.

[0038] A typical embodiment is shown in FIG3 , in which FIG3( a ) shows a metal wrench with a diameter of 0.11 cm placed in a paper cup with a diameter of 7 cm. The combination is placed on the three-dimensional object moving platform of the system, and the cross-sectional data of the paper cup at a height of 5 cm is measured using the device disclosed in the present invention.

[0039] Use the main control host to set the parameters of the terahertz transceiver module and the three-dimensional object-carrying mobile platform. The main parameter settings of the terahertz transceiver module are as follows:

[0040] 1. Start frequency and end frequency: 110GHz;

[0041] 2. Scanning points: 50;

[0042] 3. Scanning interval: 1ms;

[0043] The step size of the 3D turntable is set as follows:

[0044] 1.X-axis step length: 2mm;

[0045] 2. X-axis range: 10cm;

[0046] 3. Rotation axis step size: 5°;

[0047] 4. Rotation axis range: 180°;

[0048] 5. Z-axis height: 5cm;

[0049] Figure 3(b)-(c) are the results of reconstructing the collected cross-sectional data using the filtered back-projection algorithm and the joint algebraic reconstruction method, respectively. From the figures, we can see the location of the cup edge and the metal, and realize the imaging of the internal structure of the object.

[0050] Although the above describes the specific implementation methods of the present disclosure in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present disclosure. Technical personnel in the relevant field should understand that various modifications or variations that can be made by technical personnel in this field without creative work are within the scope of protection of the present disclosure.

Claims

1. A terahertz continuous wave three-dimensional tomography method, characterized in that: include: The terahertz wave transceiver module is used to generate and receive terahertz signals, and directly analyze the transmitted and received terahertz waves to obtain data after the terahertz waves pass through the imaging target object; the terahertz wave transceiver module includes: a dual-channel microwave source, used to generate two baseband signals, one signal is used to generate microwave signals, and the other signal is used as a reference signal; a frequency doubling module, used to multiply the baseband signal generated by the dual-channel microwave source to the terahertz band, and to reduce the received terahertz wave to the original frequency band; a synchronous acquisition unit, used to synchronously acquire the signals transmitted and received by the terahertz transceiver module; a transceiver antenna, used to transmit and receive terahertz continuous waves; A terahertz wave optical path scanning module is used to focus the terahertz wave radiated by the transmitting antenna in the terahertz transceiver module into a Gaussian beam, wherein the three-dimensional object-carrying mobile platform moves the object to perform three-dimensional scanning, and focuses the beam diverged after scanning to the receiving antenna in the terahertz transceiver module; the terahertz optical path scanning module includes: an off-axis parabolic reflector, which is used to focus the terahertz wave emitted by the antenna into a terahertz Gaussian beam with strong penetrating power, thereby transmitting the imaging target, and converge the terahertz wave diverged after transmission to the receiving antenna to form a terahertz scanning optical path; a three-dimensional object-carrying mobile platform, which uses a stepping motor to drive the platform to move, and is used to enable the single-transmitting and single-receiving imaging system to simulate the traditional CT imaging mode and perform three-dimensional rotation and movement scanning on the imaging target; A main control host module is used to control the terahertz wave transceiver module to transmit and receive terahertz waves, and control the terahertz wave optical path scanning module to move the imaging target object in three dimensions, and use filtered back projection or joint algebraic reconstruction method to reconstruct the internal structure image of the imaging target for the scanning data; the main control host module includes a main control host and a single-chip microcomputer; The method comprises the following steps: S1. Set the terahertz wave output frequency, scanning mode, scanning points and scanning time of the terahertz transceiver module; S2. According to the imaging target, set the three-dimensional scanning range, scanning step length, and scanning time of the terahertz optical path scanning module; S3. Place the imaging target on the three-dimensional carrier moving platform and set the three-dimensional carrier moving platform to the initial position; S4. The terahertz wave transceiver module transmits a terahertz wave while the three-dimensional object-carrying mobile platform moves horizontally to a preset range, and receives and records the transmission wave data of the terahertz wave after passing through the target object, and then records the data in the first column of a two-dimensional array, and then the three-dimensional object-carrying mobile platform rotates an angle step in the plane where it is located; S5. Repeat the step of S4, record the transmission wave data of the next angle into the next column of the two-dimensional array, and so on, until the rotation angle completes the scanning of all angles in the preset range; the data recorded by the array is stored in the main control host module, recorded as the plane scanning data of the cross-sectional imaging target object at the current height, and then use the filtered back projection method or the joint algebraic method to invert and reconstruct the two-dimensional tomographic image to obtain the internal structure image of the imaging target object in the cross section; S6. Move the three-dimensional object-carrying moving platform up and down in the vertical direction by a step distance, and repeat steps S4 and S5 to obtain a two-dimensional tomographic image of the imaging target object in the vertical direction; and so on, until the three-dimensional turntable rises to a preset height, completing all the step scans in the vertical direction and the corresponding two-dimensional tomographic images; finally, the two-dimensional tomographic images of all cross sections are three-dimensionally stacked and reconstructed in the vertical direction to obtain a three-dimensional structural diagram of the imaging target object.

2. A terahertz continuous wave three-dimensional tomography method according to claim 1, characterized in that: The method for generating signals by the dual-path microwave source comprises: Using a test instrument to generate a continuous wave microwave signal with a point frequency or a step frequency; Alternatively, frequency synthesis technology is used to generate a continuous microwave signal.

3. The terahertz continuous wave three-dimensional tomography method according to claim 1, characterized in that: The main control host uses filtered back projection or joint algebraic iteration algorithm to process the terahertz continuous wave transmission imaging target object data to obtain a three-dimensional internal structure diagram of the imaging target.

4. The terahertz continuous wave three-dimensional tomography method according to claim 1, characterized in that: The main control host is connected to the synchronous acquisition unit in the terahertz transceiver module, and is also connected to the single-chip microcomputer to control the three-dimensional object-carrying mobile platform in the terahertz wave optical path scanning module; the frequency of the terahertz wave of the terahertz transceiver module and the moving mode of the three-dimensional object-carrying mobile platform are set, the three-dimensional movement of the imaging target object and the emission and reception of the terahertz continuous wave are synchronized, and the data after the terahertz continuous wave transmits the imaging target object is recorded.

5. The terahertz continuous wave three-dimensional tomography method according to claim 1, characterized in that: The single chip microcomputer outputs a pulse signal to drive the motor of the three-dimensional object carrying mobile platform, thereby controlling the movement of the three-dimensional object carrying mobile platform.

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