Dual-band terahertz frequency-modulated continuous wave imaging system and method

Abstract

The embodiment of the present disclosure provides a dual-band terahertz frequency-modulated continuous wave imaging system and method. The system comprises a signal transmission device and a host computer, the signal transmission device comprises a first frequency band unit, a second frequency band unit, a polarization grating, a focusing lens and a sample moving stage, wherein the host computer is connected with the first frequency band unit and the second frequency band unit respectively. Each first echo signal and second echo signal of different preset positions of the sample to be measured is obtained through the signal transmission device, wherein the polarization directions of the first echo signal and the second echo signal corresponding to the same preset position are different, each group of the first echo signal and the second echo signal is fused into a target signal corresponding to the preset position through the host computer, and an image corresponding to the sample to be measured is formed based on the target signal corresponding to each preset position of the sample to be measured. The echo signals of the sample to be measured under different polarizations are fused to improve the bandwidth, and the distance resolution of the imaging system can be greatly improved.

Description

Technical Field

[0001] This application relates to the field of radar imaging, and in particular to a dual-band terahertz frequency-modulated continuous wave imaging system and method. Background Technology

[0002] Due to the unique penetrating and non-ionizing properties of terahertz waves, terahertz non-destructive testing technology has been successfully applied in fields such as art preservation, industrial product quality control, and packaged integrated circuit testing. Terahertz frequency-modulated continuous wave imaging technology, with its advantages of high power, miniaturization, low cost, and fast scanning speed, has attracted widespread attention in the field of terahertz non-destructive testing.

[0003] However, due to the limitations of microwave devices, the bandwidth of the signal is greatly restricted, which limits the range resolution.

[0004] Therefore, existing terahertz nondestructive testing technologies suffer from low range resolution due to limited signal bandwidth. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides a dual-band terahertz frequency-modulated continuous wave imaging system and method, the specific solution of which is as follows:

[0006] In a first aspect, embodiments of this application provide a dual-band terahertz frequency-modulated continuous wave imaging system, the dual-band terahertz frequency-modulated continuous wave imaging system including a signal transmission device and a host computer, the signal transmission device including a first frequency band unit, a second frequency band unit, a polarization grid, a focusing lens and a sample moving stage, wherein the host computer is connected to the first frequency band unit and the second frequency band unit respectively;

[0007] The first frequency band unit is used to radiate a vertically polarized terahertz beam of the first frequency band, and to focus the terahertz beam of the first frequency band onto the sample to be tested disposed on the sample moving stage via the polarization grid and the focusing lens in sequence, and to receive first echo signals corresponding to different preset positions of the sample to be tested. The polarization grid is used to reflect the terahertz beams of different polarization directions to the same focusing lens. The polarization direction includes vertical polarization and horizontal polarization.

[0008] The second frequency band unit is used to radiate a horizontally polarized terahertz beam of the second frequency band, and to focus the terahertz beam of the second frequency band sequentially through the polarization grid and the focusing lens onto the same sample to be tested on the sample moving stage, and to receive each second echo signal corresponding to different preset positions of the sample to be tested.

[0009] The host computer is used to fuse the first echo signal and the second echo signal corresponding to the same preset position of the sample under test into a target signal corresponding to the preset position, and to form an image corresponding to the sample under test based on the target signals corresponding to each preset position of the sample under test.

[0010] According to a specific embodiment disclosed in this application, the first frequency band unit includes a first transmitting antenna, a collimating lens, a first beam splitter, and a first receiving antenna;

[0011] The first transmitting antenna is used to radiate a vertically polarized terahertz beam in the first frequency band, wherein the collimating lens, the first beam splitter, the polarization grid, the focusing lens, and the sample moving stage are all arranged in the optical path of the terahertz beam in the first frequency band.

[0012] The collimating lens is used to collimate the terahertz beam of the first frequency band into a parallel beam, and the parallel beam is focused onto the sample to be tested on the sample moving stage in sequence by the first beam splitter, the polarization grid and the focusing lens.

[0013] The first beam splitter is also used to reflect the first echo signal, which propagates sequentially through the focusing lens and the polarization grid, to the first receiving antenna.

[0014] According to a specific embodiment disclosed in this application, the second frequency band unit includes a second transmitting antenna, a second beam splitter, and a second receiving antenna;

[0015] The second transmitting antenna is used to radiate a horizontally polarized terahertz beam in the second frequency band, and focuses the terahertz beam in the second frequency band sequentially through the second beam splitter, the polarization grid and the focusing lens onto the sample to be tested disposed on the sample moving stage;

[0016] The second beam splitter reflects the second echo signal, which propagates sequentially through the focusing lens and the polarization grid, to the second receiving antenna.

[0017] In a second aspect, embodiments of this application provide a dual-band terahertz frequency-modulated continuous wave imaging method, applied to the dual-band terahertz frequency-modulated continuous wave imaging system described in any one of the first aspects, the dual-band terahertz frequency-modulated continuous wave imaging method comprising:

[0018] The first frequency band unit radiates a vertically polarized terahertz beam of the first frequency band, and focuses the terahertz beam of the first frequency band onto the sample to be tested on the sample moving stage in sequence via a polarization grid and a focusing lens, and receives first echo signals corresponding to different preset positions of the sample to be tested. The polarization grid is used to reflect the terahertz beams of different polarization directions to the same focusing lens. The polarization directions include vertical polarization and horizontal polarization.

[0019] The second frequency band unit radiates a horizontally polarized terahertz beam of the second frequency band, and focuses the terahertz beam of the second frequency band sequentially through the polarization grid and the focusing lens onto the same sample to be tested on the sample moving stage, and receives the second echo signals corresponding to different preset positions of the sample to be tested.

[0020] The host computer fuses the first echo signal and the second echo signal corresponding to the same preset position of the sample under test into a target signal corresponding to the preset position, and forms an image corresponding to the sample under test based on the target signals corresponding to each preset position of the sample under test.

[0021] According to a specific embodiment disclosed in this application, the first frequency band unit includes a first transmitting antenna, a collimating lens, a first beam splitter, and a first receiving antenna;

[0022] The first transmitting antenna radiates a vertically polarized terahertz beam in the first frequency band, wherein the collimating lens, the first beam splitter, the polarization grating, the focusing lens, and the sample moving stage are all arranged in the optical path of the terahertz beam in the first frequency band.

[0023] The collimating lens collimates the terahertz beam of the first frequency band into a parallel beam, and the parallel beam is focused onto the sample to be tested on the sample moving stage by the first beam splitter, the polarization grid and the focusing lens in sequence.

[0024] The first beam splitter reflects the first echo signal, which propagates sequentially through the focusing lens and the polarization grid, to the first receiving antenna.

[0025] According to a specific embodiment disclosed in this application, the second frequency band unit includes a second transmitting antenna, a second beam splitter, and a second receiving antenna;

[0026] The second transmitting antenna radiates a horizontally polarized terahertz beam in the second frequency band, and focuses the terahertz beam in the second frequency band sequentially through the second beam splitter, the polarization grid and the focusing lens onto the sample to be tested disposed on the sample moving stage;

[0027] The second beam splitter reflects the second echo signal, which propagates sequentially through the focusing lens and the polarization grid, to the second receiving antenna.

[0028] According to a specific embodiment disclosed in this application, the step of fusing the first echo signal and the second echo signal corresponding to the same preset position of the sample to be tested into a target signal corresponding to the preset position by the host computer includes:

[0029] Acquire the first echo signal and the second echo signal at each preset position of the sample to be tested.

[0030] The first and second echo signals of each group are de-modulated to obtain the corresponding first and second initial intermediate frequency signals.

[0031] The second initial intermediate frequency signal is sequentially subjected to gain adjustment, frequency shift, time shift and phase compensation to obtain the second target intermediate frequency signal;

[0032] The target signal corresponding to the preset position is obtained by time-domain splicing of the first initial intermediate frequency signal and the second target intermediate frequency signal corresponding to the same preset position.

[0033] According to a specific embodiment disclosed in this application, the step of forming an image corresponding to the sample under test based on target signals corresponding to each preset position of the sample under test includes:

[0034] A sub-image corresponding to the preset position is generated based on the target signal;

[0035] All the sub-images corresponding to the preset positions are fused into the target detection image corresponding to the sample to be tested.

[0036] According to a specific embodiment disclosed in this application, the step of sequentially performing gain adjustment, frequency shift, time shift, and phase compensation on the second initial intermediate frequency signal to obtain the second target intermediate frequency signal includes:

[0037] The second initial intermediate frequency signal is subjected to gain adjustment and frequency shifting to obtain the second frequency-shifted signal;

[0038] The second frequency-shifted signal is time-shifted to obtain a second time-shifted signal;

[0039] Phase compensation is performed on the second time-shifted signal to obtain the second target intermediate frequency signal.

[0040] Thirdly, this application provides a signal transmission device applied to the dual-band terahertz frequency-modulated continuous wave imaging system described in any one of the first aspects. The signal transmission device includes a first frequency band unit, a second frequency band unit, a polarization grid, a focusing lens, and a sample moving stage. Both the first frequency band unit and the second frequency band unit are connected to a host computer.

[0041] The first frequency band unit is used to radiate a vertically polarized terahertz beam of the first frequency band, and to focus the terahertz beam of the first frequency band onto the sample to be tested disposed on the sample moving stage in sequence via the polarization grid and the focusing lens. It receives first echo signals corresponding to different preset positions of the sample to be tested and transmits each first echo signal to the host computer. The polarization grid is used to reflect the terahertz beams of different polarization directions to the same focusing lens. The polarization direction includes vertical polarization and horizontal polarization.

[0042] The second frequency band unit is used to radiate a horizontally polarized terahertz beam of the second frequency band, and to focus the terahertz beam of the second frequency band sequentially through the polarization grid and the focusing lens onto the same sample to be tested on the sample moving stage, to receive each second echo signal corresponding to different preset positions of the sample to be tested, and to transmit each second echo signal to the host computer.

[0043] Fourthly, this application provides a host computer for use in the dual-band terahertz frequency-modulated continuous wave imaging system described in any one of the first aspects, wherein the host computer is connected to the first frequency band unit and the second frequency band unit respectively;

[0044] The host computer is used to receive first echo signals and second echo signals corresponding to different preset positions of the sample under test, fuse the first echo signals and second echo signals corresponding to the same preset position of the sample under test into a target signal corresponding to the preset position, and form an image corresponding to the sample under test based on the target signals corresponding to each preset position of the sample under test.

[0045] Compared with the prior art, this application has the following beneficial effects:

[0046] This application acquires first echo signals and second echo signals from different preset positions of the sample under test using a signal transmission device. The first echo signals and second echo signals corresponding to the same preset position have different polarization directions. A host computer fuses the first echo signals and second echo signals into a target signal corresponding to the preset position, and forms an image of the sample under test based on the target signal corresponding to each preset position. This application improves bandwidth by fusing echo signals of the sample under test under different polarizations, which can significantly improve the range resolution of the imaging system. Attached Figure Description

[0047] To more clearly illustrate the technical solutions of the embodiments of this disclosure, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this disclosure. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0048] Figure 1 This is one of the schematic diagrams of a dual-band terahertz frequency-modulated continuous wave imaging system provided in an embodiment of this application;

[0049] Figure 2 This is a second schematic diagram of the composition of a dual-band terahertz frequency-modulated continuous wave imaging system provided in an embodiment of this application;

[0050] Figure 3 This is one of the flowcharts of a dual-band terahertz frequency-modulated continuous wave imaging method provided in an embodiment of this application;

[0051] Figure 4 This is the second schematic flowchart of a dual-band terahertz frequency-modulated continuous wave imaging method provided in this application embodiment. Detailed Implementation

[0052] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0053] The components of the embodiments of the invention described and illustrated herein can typically be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0054] In the following, the terms “comprising,” “having,” and their cognates, which may be used in various embodiments of the invention, are intended only to indicate a particular feature, number, step, operation, element, component, or combination thereof, and should not be construed as excluding, firstly, the presence of one or more other features, numbers, steps, operations, elements, components, or combinations thereof, or adding the possibility of one or more features, numbers, steps, operations, elements, components, or combinations thereof.

[0055] Furthermore, the terms "first," "second," and "third" are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0056] Unless otherwise specified, all terms used herein (including technical and scientific terms) shall have the same meaning as commonly understood by one of ordinary skill in the art to which the various embodiments of the invention pertain. Terms (such as those defined in commonly used dictionaries) shall be interpreted as having the same meaning as in their contextual meaning in the relevant technical field and shall not be interpreted as having an idealized or overly formal meaning, unless clearly defined in the various embodiments of the invention.

[0057] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the following embodiments and features can be combined with each other.

[0058] See Figure 1 , Figure 1 This is one of the schematic diagrams of a dual-band terahertz frequency-modulated continuous wave imaging system provided in an embodiment of this application.

[0059] The dual-band terahertz frequency-modulated continuous wave imaging system 10 includes a signal transmission device 11 and a host computer 12. The signal transmission device 11 includes a first frequency band unit 111, a second frequency band unit 112, a polarization grid 113, a focusing lens 114, and a sample moving stage 115. The host computer 12 is connected to the first frequency band unit 111 and the second frequency band unit 112 respectively.

[0060] The first frequency band unit 111 is used to radiate a vertically polarized terahertz beam of the first frequency band, and to focus the terahertz beam of the first frequency band sequentially through the polarization grid 113 and the focusing lens 114 onto the sample to be tested disposed on the sample moving stage 115, and to receive first echo signals corresponding to different preset positions of the sample to be tested. The polarization grid 113 is used to reflect the terahertz beams of different polarization directions to the same focusing lens 114, and the polarization direction includes vertical polarization and horizontal polarization.

[0061] Radiation is a type of wave propagation. Electromagnetic waves do not rely on any elastic medium for propagation; they propagate through the principle that a changing electric field generates a changing magnetic field, and a changing magnetic field generates a changing electric field. When the frequency of electromagnetic waves is low, they need to be transmitted through a tangible conductor. As the frequency gradually increases, the electromagnetic waves overflow outside the conductor. At this point, energy can be transferred outward without a medium; this form of propagation is called radiation. Polarization refers to the direction of the electric field strength formed during radiation. When the direction of the electric field strength is perpendicular to the ground, the wave is called a vertically polarized wave; when the direction of the electric field strength is parallel to the ground, the wave is called a horizontally polarized wave.

[0062] The first frequency band unit 111 includes a first transmitting antenna 1111, a collimating lens 1112, a first beam splitter 1113, and a first receiving antenna 1114;

[0063] The first transmitting antenna 1111 is used to radiate a vertically polarized terahertz beam in the first frequency band, wherein the collimating lens 1112, the first beam splitter 1113, the polarization grid 113, the focusing lens 114 and the sample moving stage 115 are all arranged in the optical path of the terahertz beam in the first frequency band.

[0064] The collimating lens 1112 is used to collimate the terahertz beam of the first frequency band into a parallel beam, and the parallel beam is focused onto the sample to be tested on the sample moving stage 115 by the first beam splitter 1113, the polarization grid 113 and the focusing lens 114 in sequence.

[0065] The first beam splitter 1113 is also used to reflect the first echo signal, which propagates sequentially through the focusing lens 114 and the polarization grid 113, to the first receiving antenna 1114.

[0066] The second frequency band unit 112 is used to radiate a horizontally polarized terahertz beam of the second frequency band, and to focus the terahertz beam of the second frequency band sequentially through the polarization grid 113 and the focusing lens 114 onto the same sample to be tested disposed on the sample moving stage 115, and to receive each second echo signal corresponding to different preset positions of the sample to be tested.

[0067] The second frequency band unit 112 includes a second transmitting antenna 1121, a second beam splitter 1122, and a second receiving antenna 1123;

[0068] The second transmitting antenna 1121 is used to radiate a horizontally polarized terahertz beam in the second frequency band, and focuses the terahertz beam in the second frequency band sequentially through the second beam splitter 1122, the polarization grid 113 and the focusing lens 114 onto the sample to be tested disposed on the sample moving stage 115.

[0069] The second beam splitter 1122 reflects the second echo signal, which propagates sequentially through the focusing lens 114 and the polarization grid 113, to the second receiving antenna 1123.

[0070] In specific implementation, the first transmitting antenna 1111 and the second transmitting antenna 1121 can be terahertz transmitting links and horn antennas, used to radiate terahertz linear frequency modulated signals, while the first receiving antenna 1114 and the second receiving antenna 1123 can be terahertz receiving links and horn antennas. The first beam splitter 1113 and the second beam splitter 1122 are used to split the beams of the transmitting and receiving links, and the polarization grid 113 is used to split beams with different polarization directions. The sample moving stage 115 is used to load the sample to be tested and moves under the control of the host computer 12, so that the terahertz beam of the first frequency band radiated by the first transmitting antenna 1111 and the terahertz beam of the second frequency band radiated by the first transmitting antenna 1111 can be focused on different preset positions of the sample to be tested for omnidirectional scanning. Specifically, the sample moving stage 115 can be a two-dimensional translation stage or a three-dimensional translation stage, controlling the two-dimensional or three-dimensional movement of the sample to be tested.

[0071] The specific range of values ​​for the first and second frequency bands can be customized according to the user's actual usage needs, specific application scenarios, or historical experience values. For example, the first frequency band can be 110-170GHz, and the second frequency band can be 150-220GHz. No further restrictions are imposed here.

[0072] Preferably, the horn antenna can be a diagonal horn or a conical horn antenna to ensure the symmetry of the antenna radiation pattern in the E and H planes and high radiation efficiency. The polarization grid 113 can be a tungsten filament metal grid, placed at 45° in the optical path. The polarization grid 113 can transmit or reflect according to the polarization characteristics of the incident beam, minimizing terahertz beam power loss compared to the first beam splitter 1113 and the second beam splitter 1122. The first beam splitter 1113 and the second beam splitter 1122 can be made of high-resistivity silicon material, with a transmission-to-reflection energy ratio of 54%:46%, and are placed at 45° in the optical path. Specifically, the transmitting optical path utilizes the transmission characteristics of the first beam splitter 1113 and the second beam splitter 1122, while the receiving optical path utilizes the reflection characteristics of the first beam splitter 1113 and the second beam splitter 1122.

[0073] The host computer 12 is used to fuse the first echo signal and the second echo signal corresponding to the same preset position of the sample under test into a target signal corresponding to the preset position, and to form an image corresponding to the sample under test based on the target signals corresponding to each preset position of the sample under test.

[0074] The preset position can be the position corresponding to the focal point of the terahertz beam on the sample under test via the focusing lens 114.

[0075] In specific implementations, if the first receiving antenna 1114 is not located within the beam-splitting range of the first beam splitter 1113, and / or the second receiving antenna 1123 is not located within the reflection range of the second beam splitter 1122, a reflective device can be added to the dual-band terahertz frequency-modulated continuous wave imaging system 10 to ensure that the first echo signal can accurately propagate to the first receiving antenna 1114, and that the second echo signal can accurately propagate to the second receiving antenna 1123. See also... Figure 2 , Figure 2 This is a second schematic diagram of the composition of a dual-band terahertz frequency-modulated continuous wave imaging system 10 provided in this application embodiment. The dual-band terahertz frequency-modulated continuous wave imaging system 10 further includes a first parabolic mirror 1115 and a second parabolic mirror 1124.

[0076] The vertically polarized (parallel to the plane of the paper) terahertz beam of the first frequency band radiated by the first transmitting antenna 1111 is collimated into a parallel beam by the collimating lens 1112. The phase center of the first transmitting antenna 1111 is located at the focal point of the collimating lens 1112. The parallel beam is sequentially focused onto the sample under test by the first beam splitter 1113, the polarization grating 113, and the focusing lens 114. The first echo signals obtained by scanning at different preset positions by the two-dimensional translation stage are sequentially reflected by the focusing lens 114, the polarization grating 113, and the first beam splitter 1113 to the first parabolic reflector and focused onto the phase center of the first receiving antenna 1114.

[0077] The horizontally polarized (perpendicular to the paper and inward) terahertz beam of the first frequency band radiated by the second transmitting antenna 1121 is reflected by the second beam splitter 1122 and collimated into a parallel beam by the second parabolic mirror 1124. The phase center of the second transmitting antenna 1121 is located at the focal point of the second parabolic mirror 1124. After reflection by the polarization grating 113 and focusing by the focusing lens 114 onto the sample under test, the second echo signals from different preset positions of the sample under test, obtained by scanning with a two-dimensional translation stage, are sequentially reflected by the focusing lens 114 and the polarization grating 113 to the second parabolic mirror and the second beam splitter 1122, and then focused onto the phase center of the second receiving antenna 1123. By adding the first parabolic mirror 1115 and the second parabolic mirror 1124, the first receiving antenna 1114 and the second receiving antenna 1123 can be positioned at any position in dual-band terahertz frequency-modulated continuous wave imaging, greatly reducing the limitations of device layout.

[0078] This application acquires first echo signals and second echo signals from different preset positions of the sample under test using a signal transmission device. The first echo signals and second echo signals corresponding to the same preset position have different polarization directions, enabling the host computer to fuse the various sets of first echo signals and second echo signals into a target signal for the corresponding preset position. Based on the target signal corresponding to each preset position of the sample under test, an image corresponding to the sample under test is formed. By acquiring and fusing echo signals of the sample under test under different polarizations, this application can improve bandwidth and significantly enhance the range resolution of the imaging system.

[0079] Corresponding to the above system embodiments, see [link to relevant documentation]. Figure 3 , Figure 3 This is one of the flowcharts illustrating a dual-band terahertz frequency-modulated continuous wave imaging method provided in this application embodiment. The dual-band terahertz frequency-modulated continuous wave imaging method includes:

[0080] Step S301: The first frequency band unit radiates a vertically polarized terahertz beam of the first frequency band, and focuses the terahertz beam of the first frequency band onto the sample to be tested on the sample moving stage via a polarization grid and a focusing lens in sequence, and receives first echo signals corresponding to different preset positions of the sample to be tested. The polarization grid is used to reflect the terahertz beams of different polarization directions to the same focusing lens. The polarization directions include vertical polarization and horizontal polarization.

[0081] In specific implementation, the first frequency band unit includes a first transmitting antenna, a collimating lens, a first beam splitter, and a first receiving antenna. The first transmitting antenna radiates a vertically polarized terahertz beam in the first frequency band, wherein the collimating lens, the first beam splitter, the polarization grating, the focusing lens, and the sample moving stage are all arranged in the optical path of the terahertz beam in the first frequency band. The collimating lens collimates the terahertz beam in the first frequency band into a parallel beam, which is then focused sequentially by the first beam splitter, the polarization grating, and the focusing lens onto the sample to be tested disposed on the sample moving stage. The first beam splitter reflects the first echo signal, which propagates sequentially through the focusing lens and the polarization grating, back to the first receiving antenna.

[0082] Step S302: The second frequency band unit radiates a horizontally polarized terahertz beam of the second frequency band, and focuses the terahertz beam of the second frequency band sequentially through the polarization grid and the focusing lens onto the same sample to be tested on the sample moving stage, and receives the second echo signals corresponding to different preset positions of the sample to be tested.

[0083] In specific implementation, the second frequency band unit includes a second transmitting antenna and a second receiving antenna. The second transmitting antenna radiates a horizontally polarized terahertz beam of the second frequency band, and focuses the terahertz beam of the second frequency band sequentially through the polarization grating and the focusing lens onto the sample to be tested disposed on the sample moving stage. The second receiving antenna receives the second echo signal that propagates sequentially through the focusing lens and the polarization grating.

[0084] The specific implementation process of steps S301-S302 can be found in the specific implementation process of the dual-band terahertz frequency-modulated continuous wave imaging system provided in the above embodiments, and will not be repeated here.

[0085] In step S303, the host computer fuses the first echo signal and the second echo signal corresponding to the same preset position of the sample under test into a target signal corresponding to the preset position, and forms an image corresponding to the sample under test based on the target signals corresponding to each preset position of the sample under test.

[0086] The step of the host computer fusing the first echo signal and the second echo signal corresponding to the same preset position of the sample to be tested into a target signal corresponding to the preset position includes:

[0087] Acquire the first echo signal and the second echo signal at each preset position of the sample to be tested.

[0088] The first and second echo signals of each group are de-modulated to obtain the corresponding first and second initial intermediate frequency signals.

[0089] The second initial intermediate frequency signal is sequentially subjected to gain adjustment, frequency shift, time shift and phase compensation to obtain the second target intermediate frequency signal;

[0090] The target signal corresponding to the preset position is obtained by time-domain splicing of the first initial intermediate frequency signal and the second target intermediate frequency signal corresponding to the same preset position.

[0091] The step of sequentially performing gain adjustment, frequency shift, time shift, and phase compensation on the second initial intermediate frequency signal to obtain the second target intermediate frequency signal includes:

[0092] The second initial intermediate frequency signal is subjected to gain adjustment and frequency shifting to obtain the second frequency-shifted signal;

[0093] The second frequency-shifted signal is time-shifted to obtain a second time-shifted signal;

[0094] Phase compensation is performed on the second time-shifted signal to obtain the second target intermediate frequency signal.

[0095] See Figure 4 , Figure 4 This is a second schematic flowchart illustrating a dual-band terahertz frequency-modulated continuous wave imaging method provided in this application embodiment. In specific implementation, the terahertz beam in the first frequency band radiated by the first transmitting antenna, or the terahertz beam in the second frequency band radiated by the second transmitting antenna, is actually a linear frequency-modulated continuous wave, and the corresponding transmitted signal form is: S T (t)=exp[j2π(f0t+1 / 2Kt 2 The received signal, i.e., the first echo signal or the second echo signal, takes the form of: S RF (t)=exp[j2π(f0(t-τ)+1 / 2K(t-τ) 2 Where f0 is the carrier frequency, t is the time variation within the pulse repetition interval T, K is the sweep rate, which is equal to the ratio of the signal bandwidth B to the pulse repetition period T, and τ = 2R / c is the target time delay, where c is the speed of light.

[0096] After de-modulation processing or mixing and filtering, the first and second echo signals are obtained in the following signal forms:

[0097] S ZF1 (t)=A1 exp[j2π(f1t1+Ktτ1-1 / 2Kτ1 2 )],

[0098] S ZF2 (t)=A2 exp[j2π(f2t2+Ktτ2-1 / 2Kτ2 2 )).

[0099] Where f1 is the starting frequency corresponding to the first echo signal, f2 is the starting frequency corresponding to the second echo signal, τ1 is the echo delay corresponding to the first echo signal, and τ2 is the echo delay corresponding to the second echo signal.

[0100] In practice, due to the differences in RF devices in the first and second frequency band units, the RF link exhibits differences in transmit power, conversion loss, and antenna gain. Therefore, the gain of the second initial intermediate frequency signal needs to be adjusted, i.e., A2*A c =A1, so that the echo amplitudes of the two frequency bands are approximately equal. Furthermore, due to the difference in RF line length and optical path difference between the first and second initial intermediate frequency signals, the echo delays of the first and second initial intermediate frequency signals are different (Δτ = τ1 - τ2 is a constant), and because τ1 and τ2 are very small (10... -7 (order of magnitude), quadratic term and Both can be ignored. The first initial intermediate frequency (IF) signal is frequency-shifted, and the frequency-shifted first IF signal and the frequency-shifted second IF signal are as follows:

[0101] S ZF1 (t)=A1·exp[j2π(f1τ1+Ktτ1)],

[0102] S ZF2-C (t)=A2A c ·exp[j2π(f2(τ1-Δτ)+Kt(τ2+Δτ))]

[0103] =A1·exp[j2π(f2τ1+Ktτ1-f2Δτ)].

[0104] From the expression for the second frequency-shifted signal, it can be seen that since Δτ is a constant and f2Δτ is a constant phase, the intermediate frequency signals of the two frequency bands differ only in phase. Therefore, this phase difference needs to be compensated for in the second frequency-shifted signal. This is achieved using a time-shift term Δf / K, where Δf / K = (f2 - f1) / K is a constant. The resulting second time-shifted signal is:

[0105]

[0106] From the expressions of the first initial intermediate frequency signal and the second frequency-shifted signal after frequency shift, it can be seen that the two signals only have a constant phase difference f2Δτ. Therefore, as long as the constant phase is compensated for in the second time-shifted signal to obtain the second target intermediate frequency signal, the first initial intermediate frequency signal and the second target intermediate frequency signal are spliced ​​in the time domain to complete the dual-band data fusion, increase the bandwidth and improve the range resolution of the dual-band terahertz frequency-modulated continuous wave imaging system.

[0107] The step of forming an image of the sample under test based on the target signals corresponding to each preset position of the sample under test includes:

[0108] A sub-image corresponding to the preset position is generated based on the target signal;

[0109] All the sub-images corresponding to the preset positions are fused into the target detection image corresponding to the sample to be tested.

[0110] In practice, the host computer can generate sub-images corresponding to the preset positions of the sample under test based on the target signals at each preset position. Then, according to the fusion command input by the user, all sub-images before receiving the fusion command are fused to obtain the target detection image corresponding to the sample under test at the current moment. Depending on the moment the fusion command is received, the target detection image may be complete or it may only be a partial image of the sample under test. In addition, the host computer can also perform image fusion after determining that it has obtained the target signals corresponding to all preset positions of the sample under test. The specific fusion command can be customized according to user needs and specific application scenarios, and no further limitations are made here.

[0111] The dual-band terahertz frequency-modulated continuous wave imaging method provided in this application acquires first echo signals and second echo signals from different preset positions of the sample under test through a signal transmission device. The first echo signals and second echo signals corresponding to the same preset position have different polarization directions, allowing the host computer to fuse the various sets of first echo signals and second echo signals into a target signal corresponding to the preset position. Based on the target signal corresponding to each preset position of the sample under test, an image corresponding to the sample under test is formed. By acquiring and fusing echo signals of the sample under test under different polarizations, this application can improve bandwidth and significantly enhance the range resolution of the imaging system.

[0112] In addition, a signal transmission device is provided for use in the above-mentioned dual-band terahertz frequency-modulated continuous wave imaging system. The signal transmission device includes a first frequency band unit, a second frequency band unit, a polarization grid, a focusing lens, and a sample moving stage. Both the first frequency band unit and the second frequency band unit are connected to a host computer.

[0113] The first frequency band unit is used to radiate a vertically polarized terahertz beam of the first frequency band, and to focus the terahertz beam of the first frequency band onto the sample to be tested disposed on the sample moving stage in sequence via the polarization grid and the focusing lens. It receives first echo signals corresponding to different preset positions of the sample to be tested and transmits each first echo signal to the host computer. The polarization grid is used to reflect the terahertz beams of different polarization directions to the same focusing lens. The polarization direction includes vertical polarization and horizontal polarization.

[0114] The second frequency band unit is used to radiate a horizontally polarized terahertz beam of the second frequency band, and to focus the terahertz beam of the second frequency band sequentially through the polarization grid and the focusing lens onto the same sample to be tested on the sample moving stage, to receive each second echo signal corresponding to different preset positions of the sample to be tested, and to transmit each second echo signal to the host computer.

[0115] In addition, a host computer is provided for use in the above-mentioned dual-band terahertz frequency-modulated continuous wave imaging system, wherein the host computer is connected to the first frequency band unit and the second frequency band unit respectively;

[0116] The host computer is used to receive first echo signals and second echo signals corresponding to different preset positions of the sample under test, fuse the first echo signals and second echo signals corresponding to the same preset position of the sample under test into a target signal corresponding to the preset position, and form an image corresponding to the sample under test based on the target signals corresponding to each preset position of the sample under test.

[0117] The specific implementation process of the signal transmission equipment and host computer provided in this application can be found in the specific implementation process of the dual-band terahertz frequency-modulated continuous wave imaging method provided in the above embodiments, and will not be repeated here.

[0118] The signal transmission device and host computer provided in this application can improve bandwidth and significantly enhance the range resolution of the imaging system by acquiring and fusing the echo signals of the sample under different polarizations.

[0119] In the several embodiments provided in this application, it should be understood that the disclosed apparatus and methods can also be implemented in other ways. The apparatus embodiments described above are merely illustrative; for example, the flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of apparatus, methods, and computer program products according to various embodiments of the present invention. In this regard, each block in a flowchart or block diagram may represent a module, segment, or portion of code containing one or more executable instructions for implementing a specified logical function. It should also be noted that, as an alternative implementation, the functions marked in the blocks may occur in a different order than those marked in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, and they may sometimes be executed in reverse order, depending on the functions involved. It should also be noted that each block in the block diagram and / or flowchart, and combinations of blocks in the block diagram and / or flowchart, can be implemented using a dedicated hardware-based system that performs the specified function or action, or using a combination of dedicated hardware and computer instructions.

[0120] In addition, the functional modules or units in the various embodiments of the present invention can be integrated together to form an independent part, or each module can exist independently, or two or more modules can be integrated to form an independent part.

[0121] If the aforementioned functions are implemented as software functional modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a smartphone, personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0122] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A dual-band terahertz frequency-modulated continuous wave imaging system, characterized in that, The dual-band terahertz frequency-modulated continuous wave imaging system includes a signal transmission device and a host computer. The signal transmission device includes a first frequency band unit, a second frequency band unit, a polarization grid, a focusing lens, and a sample moving stage. The host computer is connected to the first frequency band unit and the second frequency band unit respectively. The first frequency band unit is used to radiate a vertically polarized terahertz beam of the first frequency band, and to focus the terahertz beam of the first frequency band onto the sample to be tested disposed on the sample moving stage via the polarization grid and the focusing lens in sequence, and to receive first echo signals corresponding to different preset positions of the sample to be tested. The polarization grid is used to reflect the terahertz beams of different polarization directions to the same focusing lens. The polarization direction includes vertical polarization and horizontal polarization. The second frequency band unit is used to radiate a horizontally polarized terahertz beam of the second frequency band, and to focus the terahertz beam of the second frequency band sequentially through the polarization grid and the focusing lens onto the same sample to be tested on the sample moving stage, and to receive each second echo signal corresponding to different preset positions of the sample to be tested. The host computer is used to fuse the first echo signal and the second echo signal corresponding to the same preset position of the sample under test into a target signal corresponding to the preset position, and to form an image corresponding to the sample under test based on the target signals corresponding to each preset position of the sample under test. It also includes a collimating lens, which is used to collimate the terahertz beam of the first frequency band into a parallel beam. The parallel beam is focused onto the sample to be tested on the sample moving stage by passing through the first beam splitter, the polarization grid and the focusing lens in sequence.

2. The dual-band terahertz frequency-modulated continuous wave imaging system according to claim 1, characterized in that, The first frequency band unit includes a first transmitting antenna, a first beam splitter, and a first receiving antenna; The first transmitting antenna is used to radiate a vertically polarized terahertz beam in the first frequency band, wherein the collimating lens, the first beam splitter, the polarization grid, the focusing lens, and the sample moving stage are all arranged in the optical path of the terahertz beam in the first frequency band. The first beam splitter is also used to reflect the first echo signal, which propagates sequentially through the focusing lens and the polarization grid, to the first receiving antenna.

3. The dual-band terahertz frequency-modulated continuous wave imaging system according to claim 2, characterized in that, The second frequency band unit includes a second transmitting antenna, a second beam splitter, and a second receiving antenna; The second transmitting antenna is used to radiate a horizontally polarized terahertz beam in the second frequency band, and focuses the terahertz beam in the second frequency band sequentially through the second beam splitter, the polarization grid and the focusing lens onto the sample to be tested disposed on the sample moving stage; The second receiving antenna is used to receive the second echo signal that propagates sequentially through the focusing lens, the polarization grid and the second beam splitter.

4. A dual-band terahertz frequency-modulated continuous wave imaging method, characterized in that, The dual-band terahertz frequency-modulated continuous wave imaging system, applicable to any one of claims 1 to 3, comprises: The first frequency band unit radiates a vertically polarized terahertz beam of the first frequency band, and focuses the terahertz beam of the first frequency band onto the sample to be tested on the sample moving stage in sequence via a polarization grid and a focusing lens, and receives first echo signals corresponding to different preset positions of the sample to be tested. The polarization grid is used to reflect the terahertz beams of different polarization directions to the same focusing lens. The polarization directions include vertical polarization and horizontal polarization. The second frequency band unit radiates a horizontally polarized terahertz beam of the second frequency band, and focuses the terahertz beam of the second frequency band sequentially through the polarization grid and the focusing lens onto the same sample to be tested on the sample moving stage, and receives the second echo signals corresponding to different preset positions of the sample to be tested. The host computer fuses the first echo signal and the second echo signal corresponding to the same preset position of the sample under test into a target signal corresponding to the preset position, and forms an image corresponding to the sample under test based on the target signals corresponding to each preset position of the sample under test.

5. The dual-band terahertz frequency-modulated continuous wave imaging method according to claim 4, characterized in that, The first frequency band unit includes a first transmitting antenna, a collimating lens, a first beam splitter, and a first receiving antenna; The first transmitting antenna radiates a vertically polarized terahertz beam in the first frequency band, wherein the collimating lens, the first beam splitter, the polarization grating, the focusing lens, and the sample moving stage are all arranged in the optical path of the terahertz beam in the first frequency band. The collimating lens collimates the terahertz beam of the first frequency band into a parallel beam, and the parallel beam is focused onto the sample to be tested on the sample moving stage by the first beam splitter, the polarization grid and the focusing lens in sequence. The first beam splitter reflects the first echo signal, which propagates sequentially through the focusing lens and the polarization grid, to the first receiving antenna.

6. The dual-band terahertz frequency-modulated continuous wave imaging method according to claim 4, characterized in that, The second frequency band unit includes a second transmitting antenna, a second beam splitter, and a second receiving antenna; The second transmitting antenna radiates a horizontally polarized terahertz beam in the second frequency band, and focuses the terahertz beam in the second frequency band sequentially through the second beam splitter, the polarization grid and the focusing lens onto the sample to be tested disposed on the sample moving stage; The second beam splitter reflects the second echo signal, which propagates sequentially through the focusing lens and the polarization grid, to the second receiving antenna.

7. The dual-band terahertz frequency-modulated continuous wave imaging method according to claim 4, characterized in that, The step of the host computer fusing the first echo signal and the second echo signal corresponding to the same preset position of the sample to be tested into a target signal corresponding to the preset position includes: Acquire the first echo signal and the second echo signal at each preset position of the sample to be tested. The first and second echo signals of each group are de-modulated to obtain the corresponding first and second initial intermediate frequency signals. The second initial intermediate frequency signal is sequentially subjected to gain adjustment, frequency shift, time shift and phase compensation to obtain the second target intermediate frequency signal; The target signal corresponding to the preset position is obtained by time-domain splicing of the first initial intermediate frequency signal and the second target intermediate frequency signal corresponding to the same preset position.

8. The dual-band terahertz frequency-modulated continuous wave imaging method according to claim 4, characterized in that, The step of forming an image of the sample under test based on the target signals corresponding to each preset position of the sample under test includes: A sub-image corresponding to the preset position is generated based on the target signal; All the sub-images corresponding to the preset positions are fused into the target detection image corresponding to the sample to be tested.

9. The dual-band terahertz frequency-modulated continuous wave imaging method according to claim 7, characterized in that, The steps of sequentially performing gain adjustment, frequency shift, time shift, and phase compensation on the second initial intermediate frequency signal to obtain the second target intermediate frequency signal include: The second initial intermediate frequency signal is subjected to gain adjustment and frequency shifting to obtain the second frequency-shifted signal; The second frequency-shifted signal is time-shifted to obtain a second time-shifted signal; Phase compensation is performed on the second time-shifted signal to obtain the second target intermediate frequency signal.

10. A signal transmission device, characterized in that, The dual-band terahertz frequency-modulated continuous wave imaging system according to any one of claims 1 to 3, wherein the signal transmission device includes a first frequency band unit, a second frequency band unit, a polarization grid, a focusing lens and a sample moving stage, and both the first frequency band unit and the second frequency band unit are connected to a host computer; The first frequency band unit is used to radiate a vertically polarized terahertz beam of the first frequency band, and to focus the terahertz beam of the first frequency band onto the sample to be tested disposed on the sample moving stage in sequence via the polarization grid and the focusing lens. It receives first echo signals corresponding to different preset positions of the sample to be tested and transmits each first echo signal to the host computer. The polarization grid is used to reflect the terahertz beams of different polarization directions to the same focusing lens. The polarization direction includes vertical polarization and horizontal polarization. The second frequency band unit is used to radiate a horizontally polarized terahertz beam of the second frequency band, and to focus the terahertz beam of the second frequency band sequentially through the polarization grid and the focusing lens onto the same sample to be tested on the sample moving stage, to receive each second echo signal corresponding to different preset positions of the sample to be tested, and to transmit each second echo signal to the host computer.

11. A host computer, characterized in that, The dual-band terahertz frequency-modulated continuous wave imaging system according to any one of claims 1 to 3, wherein the host computer is respectively connected to the first frequency band unit and the second frequency band unit; The host computer is used to receive first echo signals and second echo signals corresponding to different preset positions of the sample under test, fuse the first echo signals and second echo signals corresponding to the same preset position of the sample under test into a target signal corresponding to the preset position, and form an image corresponding to the sample under test based on the target signals corresponding to each preset position of the sample under test.

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