A terahertz material structure imaging device and method based on multi-band splicing

Abstract

The application provides a terahertz substance structure imaging device and method based on multi-band splicing, and relates to the field of terahertz substance structure imaging.The device comprises an ultra-wideband microwave signal generation module, a terahertz transceiving module, a terahertz quasi-light module, a multi-channel synchronous acquisition module, a mechanical motion device and a host computer, wherein the terahertz transceiving module comprises an odd-frequency-band terahertz transceiving module and an even-frequency-band terahertz transceiving module, which are used for realizing the generation and reception of terahertz signals of each frequency band; the terahertz quasi-light module is used for realizing the branching and combining of terahertz beams of each frequency band, and ensuring that each transceiving module only receives signals of the corresponding frequency band.The application realizes the splicing and fusion of multiple adjacent frequency bands, solves the problem that the imaging bandwidth of a single terahertz frequency band is limited, and effectively improves the imaging resolution; by referring to the frequency division multiplexing technology, each frequency band works simultaneously and synchronously acquires, thereby effectively improving the test efficiency of each frequency band.

Description

Technical Field

[0001] This invention relates to the field of terahertz matter structure imaging, and specifically to a terahertz matter structure imaging device and method based on multi-band stitching. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] Terahertz waves typically refer to electromagnetic radiation with frequencies between 0.1 and 10 THz and wavelengths between 3 mm and 30 μm, falling between microwaves and infrared. Electronically based terahertz imaging technology holds significant promise for non-destructive testing of materials due to its advantages such as strong penetration, high resolution, non-contact operation, and wide dynamic range. Electronically based terahertz signal generation methods typically generate terahertz signals by using a frequency multiplication and amplification link to generate low-frequency broadband microwave signals. Currently, there are two main methods for generating low-frequency broadband microwave signals: one is a stepped-frequency system, which can achieve frequency resolution on the order of Hz, but sacrifices sweep time and testing efficiency; the other is a linear frequency modulation system, which is simple to implement in hardware, has low environmental requirements, and offers high testing efficiency. In the field of terahertz material structure imaging, terahertz imaging technology based on linear frequency modulation has taken the lead in non-destructive testing applications. Its application scope has covered different material targets such as foam, composite materials, ceramics, and coatings. Its application in industrial production, maintenance and inspection and other fields is constantly expanding and developing towards higher frequencies, wider bandwidths and faster speeds. The resolution of non-destructive testing imaging is also constantly improving.

[0004] Currently, when using terahertz frequencies for material structure imaging, whether single-point mechanical scanning or array scanning, most methods employ a single frequency band. This creates a contradiction between imaging resolution and penetration depth. Higher operating frequencies result in higher imaging resolution but lower penetration, while lower operating frequencies offer stronger penetration but lower resolution. The limited imaging bandwidth of a single terahertz band restricts imaging resolution. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a terahertz material structure imaging device and method based on multi-band stitching, which realizes the stitching and fusion of multiple adjacent frequency bands, with each frequency band working and acquiring data simultaneously to improve imaging resolution.

[0006] To achieve the above objectives, according to some embodiments, a first aspect of the present invention provides a terahertz material structure imaging device based on multi-band stitching, including an ultra-wideband microwave signal generation module, a terahertz transceiver module, a terahertz quasi-optical module, a multi-channel synchronous acquisition module, a mechanical motion device, and a main control computer.

[0007] The ultra-wideband microwave signal generation module is used to generate microwave radio frequency and local oscillator signals required by transceiver modules covering each terahertz frequency band. One signal generation generates microwave radio frequency and local oscillator signals required for all operating frequency bands.

[0008] The terahertz transceiver module includes an odd-band terahertz transceiver module and an even-band terahertz transceiver module, which are used to generate and receive terahertz signals in each band.

[0009] The terahertz quasi-optical module is used to split and combine terahertz beams of various frequency bands, ensuring that each transceiver module only receives signals of the corresponding frequency band.

[0010] The multi-channel synchronous acquisition module is used to synchronously acquire the test intermediate frequency or reference intermediate frequency signals obtained by the terahertz transceiver modules of each frequency band, and transmit the acquired data to the main control computer.

[0011] Mechanical motion equipment used to carry the material being measured in two-dimensional motion;

[0012] The main control computer is connected to the ultra-wideband microwave signal generation module, the terahertz transceiver module, the terahertz quasi-optical module, the multi-channel synchronous acquisition module, and the mechanical motion equipment, respectively. It is used to coordinate the control of each component module to complete the acquisition of the target scattered echo signal, and to perform error calibration and three-dimensional imaging processing on the acquired data.

[0013] Preferably, the terahertz quasi-optical module includes a terahertz reflecting surface, a terahertz filter, and a terahertz polarization grid, wherein the terahertz filter is a high-pass filter.

[0014] Preferably, the frequency bands are separated into horizontal and vertical polarization. The frequency bands transmitted and received by the odd-numbered frequency band terahertz transceiver module are transmitted and received using horizontal polarization, while the frequency bands transmitted and received by the even-numbered frequency band terahertz transceiver module are transmitted and received using vertical polarization.

[0015] Preferably, the terahertz signal is divided into eight frequency bands, which are designated as the first, second, third, fourth, fifth, sixth, seventh, and eighth frequency bands according to their frequency from smallest to largest. The first, third, fifth, and seventh frequency bands use horizontal polarization for transmission and reception, while the second, fourth, sixth, and eighth frequency bands use vertical polarization for transmission and reception.

[0016] Preferably, the first-band terahertz signal emitted by the first-band terahertz transceiver module is reflected by the first terahertz high-pass filter, the second terahertz high-pass filter, the first terahertz reflector, the terahertz polarization grating, and the second terahertz reflector, and then focused by the third terahertz reflector.

[0017] The third-band terahertz signal emitted by the third-band terahertz transceiver module is transmitted through the first terahertz high-pass filter, reflected by the second terahertz high-pass filter, reflected by the first terahertz reflector, reflected by the terahertz polarization grating, reflected by the second terahertz reflector, and then focused by the third terahertz reflector.

[0018] Preferably, the fifth-band terahertz signal emitted by the fifth-band terahertz transceiver module is reflected by the third terahertz high-pass filter, the fourth terahertz reflector, the second terahertz high-pass filter, the first terahertz reflector, the terahertz polarization grating, and the second terahertz reflector before being focused by the third terahertz reflector.

[0019] The terahertz signal emitted by the terahertz transceiver module passes through the third terahertz high-pass filter, the fourth terahertz reflector, the second terahertz high-pass filter, the first terahertz reflector, the terahertz polarization grating, and the second terahertz reflector before being focused by the third terahertz reflector.

[0020] Preferably, the second-band terahertz signal emitted by the second-band terahertz transceiver module is reflected by the fourth terahertz high-pass filter, reflected by the fifth terahertz reflector, transmitted by the fifth terahertz high-pass filter, transmitted by the terahertz polarization grating, and reflected by the second terahertz reflector, and then focused by the third terahertz reflector to complete the terahertz signal beam.

[0021] The fourth-band terahertz signal emitted by the fourth-band terahertz transceiver module is transmitted through the fourth terahertz high-pass filter, reflected by the fifth terahertz reflector, transmitted through the fifth terahertz high-pass filter, transmitted through the terahertz polarization grid, reflected by the second terahertz reflector, and then focused by the third terahertz reflector.

[0022] Preferably, the terahertz signal emitted by the sixth-band terahertz transceiver module passes through the sixth terahertz high-pass filter for transmission, the fifth terahertz high-pass filter for reflection, the terahertz polarization grid for transmission, and the second terahertz reflector for reflection, and then passes through the third terahertz reflector to complete the focusing of the terahertz signal beam.

[0023] The terahertz signal emitted by the terahertz transceiver module passes through the sixth terahertz high-pass filter, the fifth terahertz high-pass filter, the terahertz polarization grating, and the second terahertz reflector before being focused by the third terahertz reflector.

[0024] Preferably, the signal after error calibration by the main control computer. for:

[0025]

[0026] in, This is a background measurement without the material being tested being placed on it. For calibration of metal plate test data, This is the vertical distance from the center of the last-stage terahertz reflector to the material being measured. The operating frequency corresponding to the m-th frequency band is... This is the target scattered echo signal received in the m-th frequency band.

[0027] A second aspect of the present invention provides a terahertz matter structure imaging method based on multi-band stitching, the method being based on the aforementioned terahertz matter structure imaging device based on multi-band stitching, comprising:

[0028] Set imaging parameters;

[0029] Start the imaging device and control the mechanical motion equipment to scan according to the set scanning path;

[0030] Background measurements were performed without the material being measured being placed on the surface.

[0031] Calibration measurements are performed when the calibration metal plate is placed.

[0032] Place the substance to be measured for target measurement;

[0033] Data preprocessing, error calibration, and 3D imaging processing are performed on background measurement data, calibration measurement data, and target measurement data.

[0034] Compared with the prior art, the beneficial effects of the present invention are:

[0035] This invention provides a terahertz material structure imaging device and method based on multi-band stitching, which realizes the stitching and fusion of multiple adjacent frequency bands, solving the problem of limited imaging bandwidth in a single terahertz frequency band and effectively improving imaging resolution. Terahertz material structure imaging focuses on imaging efficiency and imaging resolution. This invention draws on frequency division multiplexing technology, allowing each frequency band to work simultaneously and acquire data synchronously. Compared with existing time-division control methods, this effectively improves the testing efficiency of each frequency band.

[0036] In designing the terahertz quasi-optical path, this invention emphasizes that each imaging frequency band can work simultaneously without affecting the signal transmission of other frequency bands. In addition, the design of the terahertz quasi-optical path is also to ensure high imaging resolution and multi-polarization information fusion.

[0037] This invention employs ultra-wideband microwave signal generation technology to generate local oscillator and radio frequency microwave signals required to cover various terahertz frequency bands. It utilizes a multi-channel synchronous receiver to achieve synchronous acquisition of intermediate frequency signals for testing in each frequency band, and uses an error compensation method to achieve simultaneous connection of each frequency band, thereby improving imaging bandwidth and balancing imaging resolution and penetration depth.

[0038] This invention employs a terahertz signal transceiver scheme based on linear frequency modulation, which features fast frequency sweep speed and millimeter-level scanning time for a single location point, thus ensuring high-speed scanning imaging. It acquires three-dimensional structural images of the tested substance through planar scanning.

[0039] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0040] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0041] Figure 1 A schematic diagram of a terahertz matter structure imaging device based on multi-band stitching provided in an embodiment of the present invention;

[0042] Figure 2 A schematic diagram of the quasi-optical path design in a terahertz quasi-optical module;

[0043] Among them, 1. First terahertz high-pass filter, 2. Second terahertz high-pass filter, 3. First terahertz reflector, 4. Terahertz polarization grid, 5. Second terahertz reflector, 6. Third terahertz reflector, 7. Third terahertz high-pass filter, 8. Fourth terahertz reflector, 9. Fourth terahertz high-pass filter, 10. Fifth terahertz reflector, 11. Fifth terahertz high-pass filter, 12. Sixth terahertz high-pass filter. Detailed Implementation

[0044] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0045] Example 1

[0046] like Figure 1 As shown, Embodiment 1 of the present invention provides a terahertz matter structure imaging device based on multi-band stitching, including an ultra-wideband microwave signal generation module, a terahertz transceiver module, a terahertz quasi-optical module, a multi-channel synchronous acquisition module, a mechanical motion device, and a main control computer; wherein:

[0047] The ultra-wideband microwave signal generation module is used to generate microwave radio frequency and local oscillator signals required by transceiver modules covering various terahertz frequency bands. A single signal generation generates microwave radio frequency and local oscillator signals required for all operating frequency bands.

[0048] The terahertz transceiver module includes odd-band and even-band terahertz transceiver modules, used to generate and receive terahertz signals in each band.

[0049] Terahertz quasi-optical modules are used to split and combine terahertz beams of various frequency bands, and to ensure that each transceiver module only receives signals of the corresponding frequency band.

[0050] The multi-channel synchronous acquisition module is used to synchronously acquire the test intermediate frequency or reference intermediate frequency signals obtained by the terahertz transceiver modules of each frequency band, and transmit the acquired data to the main control computer after digital filtering and decimation.

[0051] Mechanical motion equipment is used to carry the material under test in two-dimensional motion to realize planar scanning test of the material under test, and then realize three-dimensional imaging of the material under test;

[0052] The main control computer is connected to the ultra-wideband microwave signal generation module, the terahertz transceiver module, the terahertz quasi-optical module, the multi-channel synchronous acquisition module, and the mechanical motion equipment, respectively. It is used to coordinate the control of each component module to complete the acquisition of the target scattered echo signal, and to perform error calibration and three-dimensional imaging processing on the acquired data.

[0053] Based on the frequency multiplication used in the conventional terahertz band, the ultra-wideband microwave signal generation module needs to generate ultra-wideband microwave radio frequency (RF) and local oscillator (LO) signals with operating frequencies covering 9 GHz to 18 GHz. To generate these ultra-wideband signals, two methods are employed: One method uses a stepped frequency sweep system to generate ultra-wideband signals. Specifically, a voltage-controlled oscillator (VCO) and a phase-locked loop (PLL) are used to achieve high-purity and low-phase-noise microwave RF and LO signals. The operating frequencies of the microwave RF and LO signals have a frequency difference of several MHz, which is used for subsequent intermediate frequency (IF) processing. The second method uses direct digital signal generation (DDM) technology to generate ultra-wideband microwave RF and LO signals based on linear frequency modulation (LFM). Since DDM can only generate a 1 GHz signal, a frequency multiplication and downmixing scheme is used to generate the required operating frequency. That is, after achieving a 9 GHz operating bandwidth through multiple frequency multiplication stages, the signal center frequency typically operates in the millimeter-wave band. Therefore, downmixing is used to achieve ultra-wideband microwave RF and LO signals covering 9 GHz to 18 GHz based on LFM. Considering the imaging efficiency of material structures, this invention adopts an ultra-wideband microwave radio frequency (RF) and local oscillator (LO) signal generation scheme based on linear frequency modulation (LFM). To cover the 75GHz–1500GHz operating frequency band, eight terahertz operating frequency bands are required. Each band requires one RF signal and one LO signal, thus requiring a total of eight RF signals and eight LO signals. To improve integration and reduce cost, the eight RF and LO signals can be expanded by generating one RF signal and one LO signal, followed by a power divider and amplifier.

[0054] The terahertz transmitting module in the terahertz transceiver module receives the microwave radio frequency signal generated by the microwave ultra-wideband microwave signal generation module, amplifies it through multiple stages of frequency multiplication, and then generates the required terahertz signal. For the stepped-frequency system, the terahertz receiving module in the terahertz transceiver module includes two terahertz receiving links: one for testing and the other for reference to obtain coherent phase information. Both terahertz receiving links receive the microwave local oscillator signal generated by the microwave ultra-wideband microwave signal generation unit, amplify it through multiple stages of frequency multiplication, and then generate the terahertz local oscillator signal required by the mixer. The test link is mixed with the received scattered echo signal from the target under test to generate eight corresponding test intermediate frequency signals. The reference link is mixed with the terahertz reference signal coupled to the terahertz transmitting module to generate eight corresponding reference intermediate frequency signals. For the linear frequency modulation system, the eight microwave radio frequency signals and eight microwave local oscillator signals generated by the ultra-wideband signal generation module are coherent. Therefore, compared to the stepped-frequency system, no reference link is needed, and only eight test intermediate frequency signals are obtained.

[0055] In a terahertz quasi-optical module, the splitting and combining of terahertz beams across various frequency bands is achieved through the rational arrangement of terahertz reflectors, terahertz filters, and terahertz polarization grids. The terahertz reflectors primarily function to deflect or focus the terahertz beams. The terahertz filters are high-pass filters, allowing terahertz frequencies above the cutoff frequency to pass through while reflecting frequencies below the cutoff frequency. The terahertz polarization grids enable the transmission or reflection of terahertz signals with different polarizations. To simplify the design of the terahertz quasi-optical devices and improve the isolation between frequency bands, horizontal and vertical polarization are separated for each band; odd-numbered bands use horizontal polarization for transmission and reception, while even-numbered bands use vertical polarization. Referring to the frequency division multiplexing concept in communications, terahertz signals from eight frequency bands are transmitted and received simultaneously. Through the rational arrangement of the terahertz devices in the terahertz quasi-optical module, each frequency band receiver receives only the terahertz signal corresponding to its designated frequency band. Furthermore, since a zero-IF receiving system based on linear frequency modulation is adopted, the IF signal frequencies of the mixed reception in each frequency band are different. Therefore, the FPGA in the multi-channel synchronous acquisition module further filters the acquired data to remove background interference signals from other frequency bands introduced by the insufficient isolation of the terahertz quasi-optical device itself.

[0056] like Figure 2 As shown, in this embodiment, the terahertz signal is divided into eight frequency bands, which are, in ascending order of frequency, the first band (75GHz-110GHz), the second band (110GHz-170GHz), the third band (170GHz-220GHz), the fourth band (220GHz-330GHz), the fifth band (330GHz-500GHz), the sixth band (500GHz-750GHz), the seventh band (750GHz-1100GHz), and the eighth band (1100GHz-1500GHz). Odd-numbered frequency bands, namely the first, third, fifth, and seventh bands, use horizontal polarization for transmission and reception, while even-numbered frequency bands, namely the second, fourth, sixth, and eighth bands, use vertical polarization for transmission and reception.

[0057] The first-band terahertz transceiver module emits a first-band (75GHz-110GHz) terahertz signal. The first terahertz high-pass filter 1 cuts off terahertz signals below 110GHz. The first-band terahertz signal, after passing through the first terahertz high-pass filter 1, is reflected and transmitted to the second terahertz high-pass filter 2. The second terahertz high-pass filter 2 cuts off terahertz signals below 220GHz. The first-band terahertz signal reflected from the first terahertz high-pass filter 1 is then filtered by the second terahertz high-pass filter... The signal is reflected by reflector 2 to the first terahertz reflector 3, and then reflected by the first terahertz reflector 3 to the terahertz polarization grating 4. Since the polarization direction of the first-band terahertz signal is inconsistent with that of the terahertz polarization grating 4, the first-band terahertz signal reflected by the first terahertz reflector 3 is reflected by the terahertz polarization grating 4 to the second terahertz reflector 5. The first-band terahertz signal is then beam-adjusted by the second terahertz reflector 5 and transmitted to the third terahertz reflector 6, where the beam is focused. The echo signal reflected from the target is transmitted along the original path and received by the first-band terahertz transceiver module.

[0058] A third-band terahertz signal (170GHz-220GHz) is generated by the third-band terahertz transceiver module. This signal is transmitted through a first terahertz high-pass filter 1 to a second terahertz high-pass filter 2, and then reflected by the second terahertz high-pass filter 2 to a first terahertz reflecting surface 3. The signal is then reflected by the first terahertz reflecting surface 3 to a terahertz polarization grating 4. Because the polarization direction of the third-band terahertz signal is inconsistent with that of the terahertz polarization grating 4, the third-band terahertz signal reflected by the first terahertz reflecting surface 3 is reflected by the terahertz polarization grating 4 to a second terahertz reflecting surface 5. The third-band terahertz signal is then beam-adjusted by the second terahertz reflecting surface 5 and transmitted to a third terahertz reflecting surface 6, where the beam is focused. The echo signal reflected from the target is transmitted along the original path and received by the third-band terahertz transceiver module.

[0059] The fifth-band terahertz transceiver module generates a fifth-band (330GHz-500GHz) terahertz signal. The third terahertz high-pass filter 7 cuts off terahertz signals below 500GHz. The fifth-band terahertz signal generated by the fifth-band terahertz transceiver module is reflected by the third terahertz high-pass filter 7 and transmitted to the fourth terahertz reflector 8. It is then reflected by the fourth terahertz reflector 8 and transmitted to the second terahertz high-pass filter 2. Finally, it is transmitted through the second terahertz high-pass filter 2 to the first terahertz band. The signal is reflected by the first terahertz reflector 3 and transmitted to the terahertz polarization grating 4. Since the polarization direction of the fifth-band terahertz signal is inconsistent with that of the terahertz polarization grating 4, the fifth-band terahertz signal reflected by the first terahertz reflector 3 is reflected by the terahertz polarization grating 4 and transmitted to the second terahertz reflector 5. The fifth-band terahertz signal is then beam-adjusted by the second terahertz reflector 5 and transmitted to the third terahertz reflector 6, where the fifth-band terahertz signal beam is focused. The echo signal reflected from the target is transmitted along the original path and received by the fifth-band terahertz transceiver module.

[0060] The seventh-band terahertz signal (750GHz-1100GHz) generated by the seventh-band terahertz transceiver module is transmitted through the third terahertz high-pass filter 7 to the fourth terahertz reflector 8, reflected by the fourth terahertz reflector 8 to the second terahertz high-pass filter 2, transmitted through the second terahertz high-pass filter 2 to the first terahertz reflector 3, reflected by the first terahertz reflector 3 to the terahertz polarization grid 4. Since the polarization direction of the seventh-band terahertz signal is inconsistent with the terahertz polarization grid 4, the seventh-band terahertz signal reflected by the first terahertz reflector 3 is reflected by the terahertz polarization grid 4 to the second terahertz reflector 5. The seventh-band terahertz signal is then transmitted through the second terahertz reflector 5 with its beam adjusted to the third terahertz reflector 6, where the beam of the seventh-band terahertz signal is focused. The echo signal reflected from the target is transmitted along the original path and received by the seventh-band terahertz transceiver module.

[0061] The transmission of terahertz signals in the second band (110GHz-170GHz), the fourth band (220GHz-330GHz), the sixth band (500GHz-750GHz), and the eighth band (1100GHz-1500GHz) is the same as that in the odd-numbered bands. The main difference is that the polarization direction of the terahertz signal in the even-numbered bands is consistent with that of the terahertz polarization grid 4. Therefore, the terahertz signal in the even-numbered bands is transmitted through the terahertz polarization grid 4.

[0062] The second-band terahertz signal emitted by the second-band terahertz transceiver module is reflected by the fourth terahertz high-pass filter 9, reflected by the fifth terahertz reflector 10, transmitted by the fifth terahertz high-pass filter 11, transmitted by the terahertz polarization grid 4, and reflected by the second terahertz reflector 5. Finally, it is focused by the third terahertz reflector 6.

[0063] The fourth-band terahertz signal emitted by the fourth-band terahertz transceiver module is transmitted through the fourth terahertz high-pass filter 9, reflected by the fifth terahertz reflector 10, transmitted through the fifth terahertz high-pass filter 11, transmitted through the terahertz polarization grid 4, reflected by the second terahertz reflector 5, and then focused by the third terahertz reflector 6.

[0064] The terahertz signal emitted by the sixth-band terahertz transceiver module is transmitted through the sixth terahertz high-pass filter 12, reflected by the fifth terahertz high-pass filter 11, transmitted through the terahertz polarization grid 4, reflected by the second terahertz reflecting surface 5, and then focused by the third terahertz reflecting surface 6.

[0065] The terahertz signal emitted by the terahertz transceiver module is reflected by the sixth terahertz high-pass filter 12, the fifth terahertz high-pass filter 11, transmitted by the terahertz polarization grid 4, and reflected by the second terahertz reflector 5. Finally, it is focused by the third terahertz reflector 6.

[0066] The echo signal reflected from the target is transmitted along the original path and received by the corresponding terahertz transceiver module.

[0067] The multi-channel synchronous acquisition module simultaneously acquires intermediate frequency signals received by the terahertz transceiver module in eight frequency bands. Since the bandwidth of each frequency band is inconsistent, data is acquired according to the maximum sampling rate required by the largest frequency band. After acquisition, the data is filtered and extracted by the internal FPGA to generate useful and clean signal data for subsequent processing.

[0068] The main control computer is responsible for the measurement and control of the entire device, and performs data preprocessing, error calibration, and 3D imaging processing on the measurement data obtained from the multi-channel synchronous acquisition module. Error calibration is mainly used to calibrate the nonlinearity and splicing / fusion amplitude and phase errors of each frequency band. The method used is an air interface calibration method based on a metal plate, defining the target scattered echo signal received in the m-th (m=1, 2...8) frequency band as... calibrated signal for:

[0069]

[0070] in, This is a background measurement without the material being tested being placed on it. For calibration of metal plate test data, This is the vertical distance from the center of the last-stage terahertz reflector to the material being measured. This is the work corresponding to the m-th frequency band.

[0071] This embodiment employs frequency division multiplexing to achieve the splicing and fusion of up to eight terahertz frequency bands. Each band operates simultaneously and acquires data synchronously, effectively improving the testing efficiency of each band. Furthermore, it provides a quasi-optical splicing approach for terahertz bands. By rationally configuring terahertz optical devices, it achieves the combining and splitting of terahertz beams from each frequency band, ensuring that each terahertz transceiver module can only process the target scattering signal of its corresponding frequency band.

[0072] This embodiment achieves the stitching and fusion of multiple adjacent frequency bands, solving the problem of limited imaging bandwidth in a single terahertz band and effectively improving imaging resolution. By drawing on frequency division multiplexing technology, each frequency band operates simultaneously and acquires data synchronously, effectively improving the testing efficiency of each frequency band compared to existing time-division control methods. Furthermore, this invention employs ultra-wideband microwave signal generation technology based on linear frequency modulation to generate local oscillator and radio frequency microwave signals required to cover all terahertz frequency bands. A multi-channel synchronous receiver is used to achieve synchronous acquisition of intermediate frequency signals for testing each frequency band, and an error compensation method is used to achieve simultaneous connection of each frequency band, improving imaging bandwidth and thus balancing imaging resolution and penetration depth.

[0073] Example 2

[0074] This embodiment, based on the terahertz matter structure imaging device based on multi-band stitching provided in Embodiment 1, further provides a terahertz matter structure imaging method based on multi-band stitching, specifically including the following steps:

[0075] Step 1: The main control computer sends parameter setting instructions, including: setting the radio frequency and local oscillator signals of the microwave signal source according to the corresponding parameter values ​​such as frequency range and sweep time; setting the mechanical motion equipment according to the corresponding parameter values ​​such as scanning range, scanning step and scanning speed; and setting the multi-channel synchronous acquisition module according to the corresponding parameter values ​​such as the number of acquisition channels, sampling rate and sampling time.

[0076] Step 2: After setting the parameters, the main control computer starts the imaging test and controls the mechanical motion equipment to scan according to the set scanning path;

[0077] Step 3: Perform background measurement without placing the test material. The mechanical motion device moves to the scanning center position and sends a pulse trigger signal to the microwave signal source to generate linear frequency modulated radio frequency and local oscillator signals. Simultaneously, the microwave signal source generates a pulse trigger signal to the multi-channel synchronous acquisition module for synchronous acquisition of data from each channel. After acquisition, the data is digitally filtered and extracted by the FPGA inside the multi-channel synchronous acquisition module. The digital filter removes background interference signals, and the data extraction removes useless data from each frequency band, reducing the pressure on subsequent data storage. The processed data is cached in the internal storage space of the multi-channel synchronous acquisition module and then transmitted to the main control computer. The test data is recorded as follows: ;

[0078] Step 4: Perform calibration measurements while placing the calibration metal plate. The measurement process is the same as in Step 3, and the test data is recorded as follows. ;

[0079] Step 5: Place the test material for target measurement. After the mechanical motion device reaches a certain position, complete the same testing process as in Step 3. The mechanical motion device sequentially completes the target measurement at each scanning position, and the test data is recorded. ;

[0080] Step 6: The main control computer performs data preprocessing, error calibration, and 3D imaging processing on the background measurement data, calibration measurement data, and target measurement data.

[0081] Data preprocessing involves converting real data into complex data using the Hilbert transform. This process sacrifices half the data volume. Therefore, data acquisition is set according to the frequency band with the largest bandwidth. For example, band 8 has a bandwidth of 400 GHz, which is the largest among the eight bands. To meet the 0.1 GHz step interval, 4000... For the acquisition of 2=8000 effective data points, the maximum sampling rate required to meet the above data acquisition volume is determined based on the frequency sweep time, and data acquisition is performed in other frequency bands according to this frequency band.

[0082] Error calibration is mainly used to calibrate the nonlinearity and splicing / fusion amplitude and phase errors of each frequency band. The method employed is an air interface calibration method based on a metal plate. The target scattered echo signal received in the m-th (m=1, 2...8) frequency band is defined as... calibrated signal for:

[0083]

[0084] in, This is a background measurement without the material being tested being placed on it. For calibration of metal plate test data, This is the vertical distance from the center of the last-stage terahertz reflector to the material being measured. This is the work corresponding to the m-th frequency band.

[0085] Three-dimensional imaging processing is used to achieve three-dimensional structural imaging of the measured material. The method involves performing one-dimensional complex interpolation on the data after error calibration at each scanning position to ensure consistent frequency spacing across frequency bands. For example, if the frequency is set to 0.1 GHz, the number of interpolated frequency points for band 1 is (110-75) / 0.1 = 351, and for band 2 it is (170-110) / 0.1 = 601, and so on for other frequency bands. After interpolation, the data from each frequency band are stitched together to achieve a continuous flow from 75 GHz to 1100 GHz, with a total number of sampling points. Then, a Fourier transform is used to convert the frequency domain to the time domain, generating a one-dimensional range image. These one-dimensional range images from all positions are combined to form a three-dimensional array, which is the three-dimensional structural image of the measured material. This image can be displayed using a volumetric data display tool.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A terahertz matter structure imaging device based on multi-band stitching, characterized in that, include: It includes an ultra-wideband microwave signal generation module, a terahertz transceiver module, a terahertz quasi-optical module, a multi-channel synchronous acquisition module, mechanical motion equipment, and a main control computer; The ultra-wideband microwave signal generation module is used to generate microwave radio frequency and local oscillator signals required by transceiver modules covering each terahertz frequency band. One signal generation generates microwave radio frequency and local oscillator signals required for all operating frequency bands. The terahertz transceiver module includes an odd-band terahertz transceiver module and an even-band terahertz transceiver module, which are used to generate and receive terahertz signals in each band. The terahertz quasi-optical module is used to split and combine terahertz beams of various frequency bands, ensuring that each transceiver module only receives signals of the corresponding frequency band. The terahertz signal is divided into eight frequency bands, which are numbered from smallest to largest as follows: band 1, band 2, band 3, band 4, band 5, band 6, band 7, and band 8. Bands 1, 3, 5, and 7 use horizontal polarization for transmission and reception, while bands 2, 4, 6, and 8 use vertical polarization for transmission and reception. The first-band terahertz signal emitted by the first-band terahertz transceiver module is reflected by the first terahertz high-pass filter, the second terahertz high-pass filter, the first terahertz reflector, the terahertz polarization grating, and the second terahertz reflector before being focused by the third terahertz reflector. The third-band terahertz signal emitted by the third-band terahertz transceiver module is transmitted through the first terahertz high-pass filter, reflected by the second terahertz high-pass filter, reflected by the first terahertz reflecting surface, reflected by the terahertz polarization grid, reflected by the second terahertz reflecting surface, and then focused by the third terahertz reflecting surface. The fifth-band terahertz signal emitted by the fifth-band terahertz transceiver module is reflected by the third terahertz high-pass filter, the fourth terahertz reflector, the second terahertz high-pass filter, the first terahertz reflector, the terahertz polarization grid, and the second terahertz reflector before being focused by the third terahertz reflector. The terahertz signal emitted by the terahertz transceiver module passes through the third terahertz high-pass filter, the fourth terahertz reflector, the second terahertz high-pass filter, the first terahertz reflector, the terahertz polarization grating, and the second terahertz reflector before being focused by the third terahertz reflector. The second-band terahertz signal emitted by the second-band terahertz transceiver module is reflected by the fourth terahertz high-pass filter, reflected by the fifth terahertz reflector, transmitted through the fifth terahertz high-pass filter, transmitted through the terahertz polarization grating, and reflected by the second terahertz reflector. Finally, it is focused by the third terahertz reflector. The fourth-band terahertz signal emitted by the fourth-band terahertz transceiver module is transmitted through the fourth terahertz high-pass filter, reflected by the fifth terahertz reflector, transmitted through the fifth terahertz high-pass filter, transmitted through the terahertz polarization grid, reflected by the second terahertz reflector, and then focused by the third terahertz reflector. The terahertz signal emitted by the sixth-band terahertz transceiver module is transmitted through the sixth terahertz high-pass filter, reflected by the fifth terahertz high-pass filter, transmitted through the terahertz polarization grid, reflected by the second terahertz reflector, and then focused by the third terahertz reflector. The terahertz signal emitted by the terahertz transceiver module passes through the sixth terahertz high-pass filter, the fifth terahertz high-pass filter, the terahertz polarization grid, and the second terahertz reflector before being focused by the third terahertz reflector. The multi-channel synchronous acquisition module is used to synchronously acquire the test intermediate frequency or reference intermediate frequency signals obtained by the terahertz transceiver modules of each frequency band, and transmit the acquired data to the main control computer. Mechanical motion equipment used to carry the material being measured in two-dimensional motion; The main control computer is connected to the ultra-wideband microwave signal generation module, the terahertz transceiver module, the terahertz quasi-optical module, the multi-channel synchronous acquisition module, and the mechanical motion equipment, respectively. It is used to coordinate the control of each component module to complete the acquisition of the target scattered echo signal, and to perform error calibration and three-dimensional imaging processing on the acquired data.

2. The terahertz matter structure imaging device based on multi-band stitching as described in claim 1, characterized in that, The terahertz quasi-optical module includes a terahertz reflector, a terahertz filter, and a terahertz polarization grid, wherein the terahertz filter is a high-pass filter.

3. The terahertz matter structure imaging device based on multi-band stitching as described in claim 2, characterized in that, The frequency bands are separated into horizontal and vertical polarization. The frequency bands transmitted and received by the odd-numbered terahertz transceiver modules are transmitted and received using horizontal polarization, while the frequency bands transmitted and received by the even-numbered terahertz transceiver modules are transmitted and received using vertical polarization.

4. The terahertz matter structure imaging device based on multi-band stitching as described in claim 1, characterized in that, Signal after error calibration by the main control computer for: in, This is a background measurement without the material being tested being placed on it. For calibration of metal plate test data, This is the vertical distance from the center of the last-stage terahertz reflector to the material being measured. The operating frequency corresponding to the m-th frequency band is... This is the target scattered echo signal received in the m-th frequency band.

5. A terahertz matter structure imaging method based on multi-band stitching, characterized in that, The apparatus according to any one of claims 1-4 comprises: Set imaging parameters; Start the imaging device and control the mechanical motion equipment to scan according to the set scanning path; Background measurements were performed without the material being measured being placed on the surface. Calibration measurements are performed when the calibration metal plate is placed. Place the substance to be measured for target measurement; Data preprocessing, error calibration, and 3D imaging processing are performed on background measurement data, calibration measurement data, and target measurement data.

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