Compact reflective terahertz imaging method and system based on transflective metasurface

Abstract

The invention relates to the technical field of terahertz imaging, and discloses a compact reflective terahertz imaging method and system based on a transflective metasurface. The method comprises the following steps: acquiring an imaging parameter set; constructing a geometric optical path constraint; constructing a transflective integrated metasurface unit constraint set; a metasurface target phase matrix is calculated, and transmission and reflection integrated metasurface structure parameters are obtained through mapping according to the geometric phase regulation and control principle; and outputting a two-dimensional or three-dimensional image of the target object. The technical problems of large system size, complex optical path, high energy loss and insufficient stability caused by dependence on quasi-optical devices such as a discrete beam splitter, a focusing lens and an off-axis reflector in the prior art are solved. By integrating transmission, reflection beam splitting and wavefront regulation and control mechanisms in a single plane metasurface structure, common aperture focusing, integrated regulation and control and polarization isolation of a transmission and reflection light path in a reflection type terahertz imaging system are realized, system noise is reduced, and energy utilization efficiency and imaging stability are improved.

Description

Technical Field

[0001] This invention relates to the field of terahertz imaging technology, and in particular to a compact reflective terahertz imaging method and system based on a transflective metasurface. Background Technology

[0002] Currently, terahertz imaging technology has been widely used in industrial non-destructive testing, security inspection, and materials characterization. Among these, reflective terahertz imaging, because it does not require transmission through the object under test, is applicable to opaque or thick targets, thus possessing high engineering application value. To obtain information such as the amplitude, phase, and distance of the target object, existing reflective terahertz imaging systems typically employ heterodyne interferometry imaging, achieving high-sensitivity detection through frequency mixing of the echo signal.

[0003] However, due to the long wavelength and significant diffraction effect of terahertz waves, existing reflective terahertz imaging systems generally rely on discretely configured quasi-optical devices such as beam splitters, focusing lenses, or off-axis mirrors to achieve separation of the transmitting and receiving optical paths and wavefront focusing control. For example, common schemes use silicon wafers or semi-reflective mirrors for beam splitting, followed by focusing and collimation using large-aperture lenses or off-axis parabolic mirrors. While these structures can meet basic imaging requirements, they often result in large system size, complex optical path layout, and high requirements for assembly accuracy and system stability.

[0004] Meanwhile, existing discrete beam splitters and multi-stage optical devices inevitably introduce additional absorption and reflection losses in the terahertz band, reducing the system's energy utilization efficiency. In reflective heterodyne interferometry imaging scenarios, the stacking of multiple devices can easily cause optical path inconsistencies and phase error accumulation, thereby affecting imaging consistency and stability. Especially in applications requiring system miniaturization, integration, or sensitivity to environmental vibrations, existing technologies struggle to balance system compactness and energy efficiency while ensuring imaging performance.

[0005] Therefore, there is an urgent need for a compact reflective terahertz imaging method based on a transmissive-reflective metasurface that can still achieve coordinated control of the transmission and reflection optical paths and precise wavefront control in reflective terahertz imaging without relying on multi-level discrete quasi-optical devices, so as to reduce system complexity and energy loss and improve the overall stability and engineering applicability of the reflective terahertz imaging system. Summary of the Invention

[0006] To address the aforementioned technical shortcomings, the purpose of this invention is to propose a compact reflective terahertz imaging method based on a transflective metasurface. This method aims to solve the technical problems of existing reflective terahertz imaging technologies, which rely on discrete beam splitters, focusing lenses, and off-axis mirrors, resulting in large system size, complex optical paths, high energy loss, and insufficient stability.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: The present invention provides a compact reflective terahertz imaging method based on a transmissive-reflective metasurface.

[0008] The compact reflective terahertz imaging method based on a transmissive-reflective metasurface includes: Step S10: Obtain the preset imaging parameter set of the reflective terahertz imaging system, and perform equivalent optical path constraint modeling based on the Fermat principle of optical path consistency in reflective imaging, and output the geometric constraint parameter set. ; Step S20: Based on the geometric constraint parameter set A physical beam-splitting mechanism based on the coordinated constraint of transmission and reflection amplitudes of anisotropic resonant elements is employed to perform the task of constructing beam-splitting conditions for integrated transmissive and reflective metasurface elements, outputting a set of metasurface element constraints. ; Step S30: Based on the metasurface element constraint set A phase modulation mechanism based on dual-path equivalent optical path superposition is used to perform the phase distribution calculation task of the integrated transmissive and reflective metasurface, and the target phase matrix of the metasurface is output. ; Step S40: For the target phase matrix of the metasurface Perform metasurface rotation angle mapping to output the structural parameters of the transmissive and reflective metasurface. ; Step S50: Based on the reflective terahertz heterodyne interferometry imaging process, feedback is applied to the integrated transmissive and reflective metasurface structure parameters in the reflective terahertz imaging system. Output the imaging results of the target object.

[0009] Preferably, in step S10, the imaging parameter set includes the spatial position parameters of the transmitting antenna. Receiver antenna spatial location parameters Target object surface expected focus position parameters Terahertz operating wavelength With free space wavenumber ;in, The position coordinates of the transmitting antenna along the x-axis in the reflective terahertz imaging system; The position coordinates of the transmitting antenna along the y-axis in the reflective terahertz imaging system; The position coordinates of the transmitting antenna along the z-axis in the reflective terahertz imaging system; The position coordinates of the receiving antenna along the x-axis in the reflective terahertz imaging system; The position coordinates of the receiving antenna along the y-axis in the reflective terahertz imaging system; The position coordinates of the receiving antenna along the z-axis in the reflective terahertz imaging system; The position coordinates of the target object's surface along the x-axis in the reflective terahertz imaging system; The position coordinates of the target object's surface along the y-axis in the reflective terahertz imaging system; The coordinates of the target object's surface along the z-axis in the reflective terahertz imaging system.

[0010] Preferably, in step S20, based on the geometric constraint parameter set A physical beam-splitting mechanism based on the coordinated constraint of transmission and reflection amplitudes of anisotropic resonant elements is employed to perform the task of constructing beam-splitting conditions for integrated transmissive and reflective metasurface elements, outputting a set of metasurface element constraints. The steps specifically include: Step S201: Based on the geometric constraint parameter set An anisotropic resonant metasurface structure model for the terahertz operating frequency band is constructed. The anisotropic resonant metasurface structure model includes the geometric dimension parameters of the metal resonant pattern, the orientation parameters in the metasurface plane, and the material parameters and thickness parameters of the dielectric substrate. Step S202: Adjust the geometric dimensions of the metal resonant pattern and the thickness of the dielectric substrate in the anisotropic resonant metasurface structure model using electromagnetic simulation software, and collect the reflection coefficient amplitude of the reflection channel in the anisotropic resonant metasurface structure model in real time. and the amplitude of the transmission coefficient of the transmission channel ; Step S203: Regarding the amplitude of the reflection coefficient Calculate the reflection amplitude deviation error relative to the preset target reflection amplitude value. For the amplitude of the transmission coefficient of the transmission channel Calculate the transmission amplitude deviation error relative to the preset target transmission amplitude value. Only the reflection amplitude deviation error is retained. and transmission amplitude deviation error Simultaneously satisfying the preset tolerance range of the metal resonator geometric dimensions, metasurface in-plane orientation parameters, and dielectric substrate material and thickness parameters, the output metasurface element constraint set is generated. The preset tolerance range is -3dB to +3dB.

[0011] Preferably, in step S30, the metasurface target phase matrix The formula for calculating the phase of any metasurface target is as follows: ; in, For the set of constraints with metasurface elements In the corresponding transmissive and reflective integrated metasurface array, the first Line number The metasurface units of the column are along the coordinate system of the reflective terahertz imaging system. The coordinates of the element center position along the axial direction; For metasurface elements along the coordinate system of a reflective terahertz imaging system The coordinates of the element center position along the axial direction; For metasurface elements along the coordinate system of a reflective terahertz imaging system The coordinates of the element center position along the axial direction; Phase matrix of the metasurface target Any metasurface target phase; These are preset equivalent focal length parameters used for unified reference translation of the dual-path equivalent path.

[0012] Preferably, in step S10, the free space wavenumber The formula is expressed as: .

[0013] Preferably, in step S40, the parameters of the integrated transmissive and reflective metasurface structure are... This includes the phase modulation results of transmitted terahertz waves and the phase modulation results of reflected terahertz waves.

[0014] Preferably, in step S50, based on the reflective terahertz heterodyne interferometry imaging process, the integrated transmissive and reflective metasurface structure parameters are fed back into the reflective terahertz imaging system. The steps for outputting the imaging results of the target object specifically include: Step S501: In the reflective terahertz imaging system, the parameters of the transmissive-reflective integrated metasurface structure are... The corresponding transflective metasurface structure is arranged at the optical axis position; Step S502: The transmitting antenna transmits a linearly polarized terahertz wave, and the transmissive and reflective integrated metasurface structure arranged at the optical axis position splits the linearly polarized terahertz wave into a transmitted wave and a first reflected wave; wherein, the first reflected wave is reflected twice by the transmissive and reflective integrated metasurface structure to form a second reflected wave; Step S503: The transmitted wave is used as the local oscillator signal, the second reflected wave is used as the echo signal, and heterodyne interference mixing is performed based on the local oscillator signal and the echo signal to obtain the corresponding intermediate frequency signal; wherein, the intermediate frequency signal carries amplitude modulation information and phase modulation information related to the target object, which are used to characterize the reflection characteristics and spatial position information of the target object. Step S504: Extract the intensity information, phase information and distance information of the target object based on the intermediate frequency signal, and then generate the target object imaging result, which includes the two-dimensional imaging result and the three-dimensional imaging result of the target object.

[0015] This invention also provides a compact reflective terahertz imaging system based on a transmissive-reflective metasurface, comprising: The geometric optical path constraint modeling module is used to acquire a preset set of imaging parameters for a reflective terahertz imaging system, and based on this set, performs equivalent optical path constraint modeling using Fermat's principle based on the optical path consistency of reflective imaging, outputting a set of geometric constraint parameters. ; The integrated transmissive and reflective metasurface unit beam-splitting constraint construction module is used for constructing beams based on geometric constraint parameter sets. A physical beam-splitting mechanism based on the coordinated constraint of transmission and reflection amplitudes of anisotropic resonant elements is employed to perform the task of constructing beam-splitting conditions for integrated transmissive and reflective metasurface elements, outputting a set of metasurface element constraints. ; The integrated transflection and reflection metasurface phase distribution calculation module is used for calculating phase distribution based on metasurface element constraint sets. A phase modulation mechanism based on dual-path equivalent optical path superposition is used to perform the phase distribution calculation task of the integrated transmissive and reflective metasurface, and the target phase matrix of the metasurface is output. ; The metasurface structure parameter mapping module is used for mapping the phase matrix of a target metasurface. Perform metasurface rotation angle mapping to output the structural parameters of the transmissive and reflective metasurface. ; The reflective terahertz heterodyne imaging execution module is used to feed back and apply integrated transmissive and reflective metasurface structure parameters in a reflective terahertz imaging system based on a reflective terahertz heterodyne interferometric imaging process. Output the imaging results of the target object.

[0016] The present invention also provides a compact reflective terahertz imaging device based on a transflective-reflective metasurface, comprising: a memory, a processor, and a compact reflective terahertz imaging program based on a transflective-reflective metasurface stored in the memory and executable on the processor. When the compact reflective terahertz imaging program based on a transflective-reflective metasurface is executed by the processor, a compact reflective terahertz imaging method based on a transflective-reflective metasurface is implemented.

[0017] The present invention also provides a computer program product, including a compact reflective terahertz imaging program based on a transflective metasurface, wherein the compact reflective terahertz imaging program based on a transflective metasurface implements the compact reflective terahertz imaging method based on a transflective metasurface when executed by a processor.

[0018] The beneficial effects of this invention are as follows: By integrating transmission beam splitting, reflection beam splitting, and wavefront modulation functions into a single transmissive-reflective metasurface structure, this invention replaces the traditionally discrete beam splitters and focusing optics in reflective terahertz imaging systems. While ensuring the optical path consistency required for reflective heterodyne interferometry imaging, it effectively reduces the complexity of the optical path and the number of devices, and improves the compactness and overall stability of the system structure.

[0019] This invention constructs optical path constraints for reflective imaging based on Fermat's principle, and combines a phase modulation mechanism of dual-path equivalent optical path superposition with a metasurface unit design method of transmission and reflection amplitude coordination constraints. This enables the transmitted and reflected waves to be coordinated and controlled in the same planar structure, thereby reducing the energy loss of terahertz waves during multiple transmissions through discrete optical devices and improving the energy utilization efficiency and imaging consistency of the reflective terahertz imaging system. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1 This is a schematic flowchart of the first embodiment of a compact reflective terahertz imaging method based on a transflective metasurface according to the present invention.

[0022] Figure 2 This is a schematic diagram of the original system optical path of the first embodiment of the compact reflective terahertz imaging method based on a transflective metasurface according to the present invention.

[0023] Figure 3 This is a schematic diagram of the optical path after metasurface replacement, representing a first embodiment of a compact reflective terahertz imaging method based on an integrated transmissive and reflective metasurface according to the present invention.

[0024] Figure 4 This is a schematic diagram of the transmission and reflection propagation process of the integrated metasurface based on a compact reflective terahertz imaging method according to the first embodiment of the present invention.

[0025] Figure 5 This is a diagram showing the electric field intensity distribution at the transmission focal plane of the integrated transmissive-reflective metasurface, which is the first embodiment of the compact reflective terahertz imaging method based on the integrated transmissive-reflective metasurface of the present invention.

[0026] Figure 6This is a diagram showing the electric field intensity distribution at the reflective focal plane of the integrated transflective metasurface, which is the first embodiment of the compact reflective terahertz imaging method based on an integrated transflective metasurface according to the present invention.

[0027] Figure 7 This is a side view of the multi-frequency electric field distribution in the interference optical path after the metasurface is replaced, according to a first embodiment of the compact reflective terahertz imaging method based on a transmissive metasurface of the present invention.

[0028] Figure 8 This is a schematic diagram of the focal plane electric field distribution at the multi-frequency receiver of the interference optical path after the metasurface is replaced by a first embodiment of the compact reflective terahertz imaging method based on a transmissive-reflective metasurface according to the present invention.

[0029] Figure 9 This is a schematic diagram of a compact reflective terahertz imaging method based on a transflective metasurface according to the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] Example 1: As Figure 1 The diagram shown is a flowchart of the first embodiment of the compact reflective terahertz imaging method based on a transflective metasurface according to the present invention. The first embodiment of the compact reflective terahertz imaging method based on a transflective metasurface according to the present invention is presented.

[0032] In the first embodiment, the compact reflective terahertz imaging method based on a transmissive-reflective metasurface includes: Step S10: Obtain the preset imaging parameter set of the reflective terahertz imaging system, and perform equivalent optical path constraint modeling based on the Fermat principle of optical path consistency in reflective imaging, and output the geometric constraint parameter set. ; It should be noted that the set of imaging parameters obtained in this step is used to describe the spatial geometric relationship between the transmitting antenna, receiving antenna, transmissive-reflective metasurface, and target object in the reflective terahertz imaging system. This set of imaging parameters provides a unified geometric reference basis for the subsequent construction of metasurface unit beam splitting conditions and phase distribution calculation.

[0033] It is understandable that modeling the equivalent optical path constraint based on Fermat's principle of optical path consistency in reflective imaging essentially involves describing the emission path and the echo path in the same coordinate system, so that different propagation paths have consistent or equivalent optical path lengths when the imaging conditions are met, thereby ensuring the physical consistency of wavefront modulation in reflective terahertz imaging.

[0034] Step S20: Based on the geometric constraint parameter set A physical beam-splitting mechanism based on the coordinated constraint of transmission and reflection amplitudes of anisotropic resonant elements is employed to perform the task of constructing beam-splitting conditions for integrated transmissive and reflective metasurface elements, outputting a set of metasurface element constraints. ; It should be noted that the metasurface unit constraint set constructed in this step is intended to pre-limit the transmission and reflection response of the metasurface unit from a physical perspective, so that the subsequent phase distribution calculation is only performed within the unit set that meets the preset beam splitting conditions, thereby avoiding the problem of inconsistency between the phase control design and the actual physical beam splitting capability.

[0035] It is understandable that the physical beam splitting mechanism based on the coordinated constraint of the transmission and reflection amplitudes of anisotropic resonant units is achieved by co-designing the geometric parameters of the metasurface unit and the parameters of the dielectric substrate, so that a single metasurface unit can simultaneously have controllable transmission and reflection channel responses in the target terahertz operating frequency band, and achieve the expected beam splitting ratio requirements at the amplitude level.

[0036] It should be understood that the physical beam splitting mechanism does not rely on traditional discrete beam splitters or semi-reflective and semi-transparent optical elements. Instead, it achieves the simultaneous generation of transmitted and reflected waves through the electromagnetic response characteristics of anisotropic resonant units in a single planar metasurface structure. Therefore, it can simplify and reconstruct the optical path structure of the system without changing the basic imaging mechanism of reflective terahertz imaging.

[0037] For example, such as Figure 2 As shown, the original optical path of the system, namely the reflective terahertz imaging system, usually requires the sequential placement of multiple quasi-optical devices such as beam splitters, focusing lenses, and reflectors to achieve separation of the transmitting and receiving optical paths and wavefront focusing control. The overall optical path is relatively complex and the system size is large.

[0038] And such Figure 3As shown, by placing an integrated transmissive-reflective metasurface at the optical axis of the system, transmission beam splitting, reflection beam splitting, and wavefront modulation functions can be simultaneously achieved in a single planar structure. This allows a single metasurface structure to replace the beam splitter and focusing optics in the original system, enabling the transmitted and reflected waves to propagate along symmetrical paths, significantly simplifying the system's optical path layout. It is evident that, under preset beam splitting conditions, the integrated transmissive-reflective metasurface can generate a stable energy distribution and spatially consistent electromagnetic field response in both the transmission and reflection channels. The transmitted wave forms a clear focused spot on the target object's surface, while the reflected wave effectively guides the echo signal to the receiving antenna, thereby reducing system energy loss and improving overall stability while ensuring imaging performance.

[0039] Step S30: Based on the metasurface element constraint set A phase modulation mechanism based on dual-path equivalent optical path superposition is used to perform the phase distribution calculation task of the integrated transmissive and reflective metasurface, and the target phase matrix of the metasurface is output. ; It is understandable that the phase modulation mechanism based on the superposition of dual-path equivalent optical path is to superimpose the optical path of the propagation path from the transmitting antenna to the metasurface unit and the optical path of the propagation path from the metasurface unit to the expected focusing position of the target object, and based on Fermat's principle, convert the equivalent optical path difference corresponding to different metasurface units into a phase difference, thereby ensuring that the transmitted wave and the reflected wave meet the equivalent optical path consistency requirements under the reflection imaging condition.

[0040] Step S40: For the target phase matrix of the metasurface Perform metasurface rotation angle mapping to output the structural parameters of the transmissive and reflective metasurface. ; It should be noted that metasurface rotation angle mapping refers to utilizing the geometric phase effect introduced when anisotropic resonant metasurface units rotate in a plane to convert the phase information in the target phase matrix of the metasurface calculated in the previous steps into rotation angle parameters of each metasurface unit at the physical structure level. This rotation angle mapping includes determining the rotation direction and amplitude of the unit based on the target phase value, and outputting the rotation angle, along with the geometric dimensions and spatial arrangement parameters of the metasurface units, as structural parameters of the integrated transmissive and reflective metasurface to guide the actual design and fabrication of the metasurface.

[0041] It is understood that, through the aforementioned rotation angle mapping method, this invention can accurately load complex phase distribution information into a single-layer transmissive-reflective integrated metasurface structure without introducing additional active modulation or multi-layer complex structures. This allows the transmission and reflection channels to simultaneously achieve the desired wavefront modulation effect within the same planar structure. This method enables the metasurface to achieve precise control of the terahertz wavefront while maintaining structural simplicity, which is beneficial for improving the consistency and stability of wavefront modulation in reflective terahertz imaging systems.

[0042] It should be understood that, compared to traditional reflective terahertz imaging systems that rely on discrete lenses, mirrors, or multi-stage phase plates for wavefront modulation, this invention achieves phase loading through rotational angle mapping, significantly reducing the number of optical components and optical path adjustment steps, thus lowering system assembly complexity and environmental sensitivity. Furthermore, since phase modulation is directly achieved through the geometric orientation of the metasurface unit, it avoids the phase error accumulation problem caused by the stacking of multiple components in traditional methods, contributing to improved stability of the imaging system during long-term operation or under vibration.

[0043] Step S50: Based on the reflective terahertz heterodyne interferometry imaging process, feedback is applied to the integrated transmissive and reflective metasurface structure parameters in the reflective terahertz imaging system. Output the imaging results of the target object.

[0044] It should be noted that "feedback application of integrated transmissive and reflective metasurface structure parameters" in this step refers to arranging the integrated transmissive and reflective metasurface structure determined in step S40 as an actual device at the optical axis position of the reflective terahertz imaging system, so that it participates in both the illumination process of the emitted wave and the reception process of the target echo during operation, thereby verifying the effectiveness of the preceding metasurface design and phase modulation scheme in the actual imaging process.

[0045] It should be noted that in optical imaging systems, the shape of the point spread function is a key physical quantity for evaluating its imaging quality. A light spot that is close to the diffraction limit and has highly concentrated energy signifies that the system possesses excellent aberration correction and a high spatial bandwidth product, thus enabling the achievement of high-resolution, high-fidelity images. Therefore, light spot quality is considered a core performance indicator of an imaging system.

[0046] It is understandable that by introducing a transflective metasurface structure into the reflective terahertz heterodyne interferometry imaging process, this invention can achieve coordinated control of the transmitted wave and the echo wavefront without changing the basic working principle of heterodyne interferometry imaging. It maintains good optical path consistency and wavefront matching relationship in each stage of illumination, echo transmission and signal acquisition, which is beneficial to improving the stability of intermediate frequency signals and the consistency of imaging results.

[0047] It should be understood that the integrated beam splitting and focusing function of the transmissive and reflective metasurface of this invention is extremely suitable for interference optical paths, especially for interference optical imaging, such as Michelson interferometers, Mach-Zehnder interferometers, etc. Here, only heterodyne interferometer systems are used as examples.

[0048] For example, combining Figure 4 The side-view distribution of the transmission and reflection electric field intensity of the metasurface shown reveals that the transmitted and reflected beams exhibit significant energy convergence along their respective propagation directions. The focal point positions are consistent with the design expectations, and the beams are axially symmetrically distributed along the tangent direction of the metasurface, indicating that the transmission / reflection channel possesses good wavefront control during actual propagation. Furthermore, Figure 5 and Figure 6 The electric field intensity distributions at the transmission and reflection focal planes are shown, indicating that the incident wave is split by the integrated transmissive-reflective metasurface and can be effectively focused to the transmission focal plane after transmission / reflection. The energy distribution of the transmission focal spot exhibits a clear Gaussian distribution, indicating high spot quality. These results collectively demonstrate that the integrated transmissive-reflective metasurface can simultaneously guarantee beam splitting and high-quality transmission / reflection focusing under spherical wave incident conditions. This provides a stable signal foundation for subsequent heterodyne mixing and imaging information extraction, ultimately resulting in clear and reliable imaging of the target object.

[0049] In addition, such as Figure 7 As shown, the side-view distribution of the electric field in the interference optical path after replacing traditional discrete quasi-optical devices with an integrated transmissive-reflective metasurface is obtained under different operating frequency conditions (e.g., 160 GHz, 165 GHz, and 170 GHz). Terahertz waves are incident from above. It can be observed that at multiple operating frequencies, the terahertz electromagnetic waves are first reflected by the metasurface to the target object (represented by a small copper plate in the simulation). The echo from the target object is then transmitted and converged to the receiving antenna by the same metasurface. This indicates that the integrated transmissive-reflective metasurface can stably perform beam splitting, phase modulation, and wavefront shaping functions across a wide frequency band, maintaining good geometric consistency and optical path matching between the transmission and reflection paths in space. Furthermore, it can be seen that… Figure 7 The side-view distribution of the electric field under different frequency conditions remains highly similar overall, with only minor variations in energy distribution details that occur with frequency. This indicates that the integrated transmissive and reflective metasurface does not only function at a single frequency point, but also possesses stable wavefront modulation capabilities within a certain bandwidth. The bandwidth determines the axial resolution of the system, and a large bandwidth implies the possibility of three-dimensional imaging.

[0050] like Figure 8As shown, the final electric field distribution of the transmission focal plane under corresponding frequency conditions and its intensity curves along the transverse and longitudinal directions are presented. From the two-dimensional electric field distribution of the focal plane, it can be clearly seen that at different frequencies such as 160 GHz, 165 GHz, and 170 GHz, a focused spot with a single dominant main lobe and concentrated energy is formed at the focal plane, and the center position of the spot is stable, without significant shift or multifocal splitting. This indicates that the integrated transmissive and reflective metasurface can effectively maintain the expected focusing position and focusing shape over a wide frequency band. Furthermore, from... Figure 8 The corresponding transverse and longitudinal intensity profile curves show that the electric field intensity at the focal plane exhibits a smooth and continuous variation trend within the main lobe region, while the side lobe levels are relatively low, with energy mainly concentrated within the main lobe region. This result indicates that the metasurface, while achieving beam splitting and focusing functions, does not introduce significant aberration accumulation or higher-order scattering interference, which is beneficial for improving the concentration of the system's point spread function and imaging contrast.

[0051] Figure 7 and Figure 8 The wideband stable focusing and energy convergence characteristics reflected directly verify the effectiveness of the equivalent optical path constraint modeling, unit amplitude cooperative constraint, and phase modulation design established in this invention in the real imaging process. By applying the integrated transmissive and reflective metasurface structure parameters in a reflective terahertz heterodyne interferometry imaging system, this invention can simultaneously ensure the illumination wavefront quality and echo reception efficiency over a wide bandwidth, thus providing a stable and reliable physical basis for subsequent heterodyne mixing, intermediate frequency signal extraction, and three-dimensional imaging of the target object.

[0052] Example 2: Furthermore, the present invention provides a compact reflective terahertz imaging system based on a transflective integrated metasurface, employing a compact reflective terahertz imaging method based on a transflective integrated metasurface as described in the above embodiments, which can solve the technical problem of compact reflective terahertz imaging based on a transflective integrated metasurface. Compared with the prior art, the beneficial effects of the compact reflective terahertz imaging system based on a transflective integrated metasurface provided by the present invention are the same as the beneficial effects of the compact reflective terahertz imaging method based on a transflective integrated metasurface provided in the above embodiments, and other technical features of the compact reflective terahertz imaging system based on a transflective integrated metasurface are the same as those disclosed in the methods of the above embodiments, and will not be repeated here.

[0053] Example 3: This invention provides a compact reflective terahertz imaging device based on a transmissive-reflective metasurface. Please refer to... Figure 9A compact reflective terahertz imaging device based on a transflective-reflective metasurface includes: at least one processor; and a memory communicatively connected to the at least one processor; wherein the memory stores instructions executable by the at least one processor, which, when executed by the at least one processor, enable the at least one processor to perform the compact reflective terahertz imaging method based on a transflective-reflective metasurface as described in Embodiment 1 above. The compact reflective terahertz imaging device based on a transflective-reflective metasurface in this embodiment of the invention may include, but is not limited to, mobile terminals such as mobile phones, laptops, digital radio receivers, PDAs (Personal Digital Assistants), PADs (Portable Application Description), PMPs (Portable Media Players), and in-vehicle terminals (e.g., in-vehicle navigation terminals), as well as fixed terminals such as digital TVs and desktop computers. This compact reflective terahertz imaging device based on a transflective-reflective metasurface is merely an example and should not impose any limitations on the functionality and scope of use of the embodiments of the invention. A compact reflective terahertz imaging device based on a transflective metasurface may include a processing unit 1001 (e.g., a central processing unit, a graphics processing unit, etc.) that can perform various appropriate actions and processes according to a program stored in a read-only memory 1002 or a program loaded from a storage device 1003 into a random access memory 1004. The random access memory 1004 also stores various programs and data required for the operation of the compact reflective terahertz imaging device based on a transflective metasurface. The processing unit 1001, the read-only memory 1002, and the random access memory 1004 are interconnected via a bus 1005. An I / O interface 1006 is also connected to the bus. Typically, the following systems can be connected to I / O interface 1006: input devices 1007 including, for example, touchscreens, touchpads, keyboards, mice, image sensors, microphones, accelerometers, gyroscopes, etc.; output devices 1008 including, for example, liquid crystal displays (LCDs), speakers, vibrators, etc.; storage devices 1003 including, for example, magnetic tapes, hard disks, etc.; and communication devices 1009. Communication device 1009 allows a compact reflective terahertz imaging device based on a transflective metasurface to wirelessly or wiredly communicate with other devices to exchange data. Although a compact reflective terahertz imaging device based on a transflective metasurface with various systems is shown in the figures, it should be understood that it is not required to implement or possess all the systems shown. More or fewer systems may be implemented alternatively.

[0054] Example 4: This invention also provides a computer program product, including a computer program that, when executed by a processor, implements the steps of the compact reflective terahertz imaging method based on a transflective integrated metasurface as described above. The computer program product provided by this invention can solve the technical problem of compact reflective terahertz imaging based on a transflective integrated metasurface. Compared with the prior art, the beneficial effects of the computer program product provided by this invention are the same as those of the compact reflective terahertz imaging method based on a transflective integrated metasurface provided in the above embodiments, and will not be repeated here.

[0055] In particular, according to the embodiments disclosed in this invention, the processes described above with reference to the flowcharts can be implemented as computer software programs. For example, embodiments of this invention include a computer program product comprising a computer program carried on a computer-readable medium, the computer program containing program code for performing the methods shown in the flowcharts. In such embodiments, the computer program can be downloaded and installed from a network via a communication device, or installed from storage device 1003, or installed from read-only memory 1002. When the computer program is executed by processing device 1001, it performs the functions defined in the methods of the embodiments disclosed in this invention.

[0056] It should be understood that the various parts disclosed in this invention can be implemented using hardware, software, firmware, or a combination thereof. In the description of the above embodiments, specific features, structures, materials, or characteristics can be combined in any suitable manner in one or more embodiments or examples.

[0057] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A compact reflective terahertz imaging method based on a transmissive-reflective metasurface, characterized in that, The methods include: Step S10: Obtain the preset imaging parameter set of the reflective terahertz imaging system, and perform equivalent optical path constraint modeling based on the Fermat principle of optical path consistency in reflective imaging, and output the geometric constraint parameter set. ; Step S20: Based on the geometric constraint parameter set A physical beam-splitting mechanism based on the coordinated constraint of transmission and reflection amplitudes of anisotropic resonant elements is employed to perform the task of constructing beam-splitting conditions for integrated transmissive and reflective metasurface elements, outputting a set of metasurface element constraints. ; Step S30: Based on the metasurface element constraint set A phase modulation mechanism based on dual-path equivalent optical path superposition is used to perform the phase distribution calculation task of the integrated transmissive and reflective metasurface, and the target phase matrix of the metasurface is output. ; Step S40: For the target phase matrix of the metasurface Perform metasurface rotation angle mapping to output the structural parameters of the transmissive and reflective metasurface. ; Step S50: Based on the reflective terahertz heterodyne interferometry imaging process, feedback is applied to the integrated transmissive and reflective metasurface structure parameters in the reflective terahertz imaging system. Output the imaging results of the target object.

2. The compact reflective terahertz imaging method based on a transmissive-reflective metasurface as described in claim 1, characterized in that, In step S10, the imaging parameter set includes the spatial position parameters of the transmitting antenna. Receiver antenna spatial location parameters Target object surface expected focus position parameters Terahertz operating wavelength With free space wavenumber ;in, The position coordinates of the transmitting antenna along the x-axis in the reflective terahertz imaging system; The position coordinates of the transmitting antenna along the y-axis in the reflective terahertz imaging system; The position coordinates of the transmitting antenna along the z-axis in the reflective terahertz imaging system; The position coordinates of the receiving antenna along the x-axis in the reflective terahertz imaging system; The position coordinates of the receiving antenna along the y-axis in the reflective terahertz imaging system; The position coordinates of the receiving antenna along the z-axis in the reflective terahertz imaging system; The position coordinates of the target object's surface along the x-axis in the reflective terahertz imaging system; The position coordinates of the target object's surface along the y-axis in the reflective terahertz imaging system; The coordinates of the target object's surface along the z-axis in the reflective terahertz imaging system.

3. The compact reflective terahertz imaging method based on a transmissive-reflective metasurface as described in claim 1, characterized in that, In step S20, based on the geometric constraint parameter set A physical beam-splitting mechanism based on the coordinated constraint of transmission and reflection amplitudes of anisotropic resonant elements is employed to perform the task of constructing beam-splitting conditions for integrated transmissive and reflective metasurface elements, outputting a set of metasurface element constraints. The steps specifically include: Step S201: Based on the geometric constraint parameter set An anisotropic resonant metasurface structure model for the terahertz operating frequency band is constructed. The anisotropic resonant metasurface structure model includes the geometric dimension parameters of the metal resonant pattern, the orientation parameters in the metasurface plane, and the material parameters and thickness parameters of the dielectric substrate. Step S202: Adjust the geometric dimensions of the metal resonant pattern and the thickness of the dielectric substrate in the anisotropic resonant metasurface structure model using electromagnetic simulation software, and collect the reflection coefficient amplitude of the reflection channel in the anisotropic resonant metasurface structure model in real time. and the amplitude of the transmission coefficient of the transmission channel ; Step S203: Regarding the amplitude of the reflection coefficient Calculate the reflection amplitude deviation error relative to the preset target reflection amplitude value. For the amplitude of the transmission coefficient of the transmission channel Calculate the transmission amplitude deviation error relative to the preset target transmission amplitude value. Only the reflection amplitude deviation error is retained. and transmission amplitude deviation error Simultaneously satisfying the preset tolerance range of the metal resonator geometric dimensions, metasurface in-plane orientation parameters, and dielectric substrate material and thickness parameters, the output metasurface element constraint set is generated. The preset tolerance range is -3dB to +3dB.

4. The compact reflective terahertz imaging method based on a transmissive-reflective metasurface as described in claim 2, characterized in that, In step S30, the metasurface target phase matrix The formula for calculating the phase of any metasurface target is as follows: ; in, For the set of constraints with metasurface elements In the corresponding transmissive and reflective integrated metasurface array, the first Line number The metasurface units of the column are along the coordinate system of the reflective terahertz imaging system. The coordinates of the element center position along the axial direction; For metasurface elements along the coordinate system of a reflective terahertz imaging system The coordinates of the element center position along the axial direction; For metasurface elements along the coordinate system of a reflective terahertz imaging system The coordinates of the element center position along the axial direction; Phase matrix of the metasurface target Any metasurface target phase; These are preset equivalent focal length parameters used for unified reference translation of the dual-path equivalent path.

5. A compact reflective terahertz imaging method based on a transmissive-reflective metasurface as described in claim 2, characterized in that, In step S10, the free space wavenumber The formula is expressed as: .

6. The compact reflective terahertz imaging method based on a transmissive-reflective metasurface as described in claim 1, characterized in that, In step S40, the parameters of the integrated transmissive and reflective metasurface structure are... This includes the phase modulation results of transmitted terahertz waves and the phase modulation results of reflected terahertz waves.

7. The compact reflective terahertz imaging method based on a transmissive-reflective metasurface as described in claim 1, characterized in that, In step S50, based on the reflective terahertz heterodyne interferometry imaging process, the parameters of the integrated transmissive and reflective metasurface structure are fed back into the reflective terahertz imaging system. The steps for outputting the imaging results of the target object specifically include: Step S501: In the reflective terahertz imaging system, the parameters of the transmissive-reflective integrated metasurface structure are... The corresponding transflective metasurface structure is arranged at the optical axis position; Step S502: The transmitting antenna transmits a linearly polarized terahertz wave, and the transmissive and reflective integrated metasurface structure arranged at the optical axis position splits the linearly polarized terahertz wave into a transmitted wave and a first reflected wave; wherein, the first reflected wave is reflected twice by the transmissive and reflective integrated metasurface structure to form a second reflected wave; Step S503: The transmitted wave is used as the local oscillator signal, the second reflected wave is used as the echo signal, and heterodyne interference mixing is performed based on the local oscillator signal and the echo signal to obtain the corresponding intermediate frequency signal; wherein, the intermediate frequency signal carries amplitude modulation information and phase modulation information related to the target object, which are used to characterize the reflection characteristics and spatial position information of the target object. Step S504: Extract the intensity information, phase information and distance information of the target object based on the intermediate frequency signal, and then generate the target object imaging result, which includes the two-dimensional imaging result and the three-dimensional imaging result of the target object.

8. A compact reflective terahertz imaging system based on a transflective metasurface, applied to the compact reflective terahertz imaging method based on a transflective metasurface as described in any one of claims 1 to 7, characterized in that, The compact reflective terahertz imaging system based on a transmissive-reflective metasurface includes: The geometric optical path constraint modeling module is used to acquire a preset set of imaging parameters for a reflective terahertz imaging system, and based on this set, performs equivalent optical path constraint modeling using Fermat's principle based on the optical path consistency of reflective imaging, outputting a set of geometric constraint parameters. ; The integrated transmissive and reflective metasurface unit beam-splitting constraint construction module is used for constructing beams based on geometric constraint parameter sets. A physical beam-splitting mechanism based on the coordinated constraint of transmission and reflection amplitudes of anisotropic resonant elements is employed to perform the task of constructing beam-splitting conditions for integrated transmissive and reflective metasurface elements, outputting a set of metasurface element constraints. ; The integrated transflection and reflection metasurface phase distribution calculation module is used for calculating phase distribution based on metasurface element constraint sets. A phase modulation mechanism based on dual-path equivalent optical path superposition is used to perform the phase distribution calculation task of the integrated transmissive and reflective metasurface, and the target phase matrix of the metasurface is output. ; The metasurface structure parameter mapping module is used for mapping the phase matrix of a target metasurface. Perform metasurface rotation angle mapping to output the structural parameters of the transmissive and reflective metasurface. ; The reflective terahertz heterodyne imaging execution module is used to feed back and apply integrated transmissive and reflective metasurface structure parameters in a reflective terahertz imaging system based on a reflective terahertz heterodyne interferometric imaging process. Output the imaging results of the target object.

9. A compact reflective terahertz imaging device based on a transflective metasurface, characterized in that, The compact reflective terahertz imaging device based on a transflective-reflective metasurface includes: a memory, a processor, and a compact reflective terahertz imaging program based on a transflective-reflective metasurface stored in the memory and executable on the processor. When the processor executes the compact reflective terahertz imaging program based on a transflective-reflective metasurface, it implements a compact reflective terahertz imaging method based on a transflective-reflective metasurface as described in any one of claims 1 to 7.

10. A computer program product, characterized in that, The computer program product includes a compact reflective terahertz imaging program based on a transflective metasurface, which, when executed by a processor, implements a compact reflective terahertz imaging method based on any one of claims 1 to 7.

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