Terahertz encryption superstructure surface based on incident angle and exit angle correlation regulation

Abstract

The present application relates to the technical field of terahertz communication, and more particularly to a terahertz encryption superstructure based on incident angle and exit angle correlation regulation and control. The superstructure comprises a high-resistance silicon substrate, a polyimide dielectric layer, and an asymmetric gold film superunit array, each unit encoding the nonlinear mapping relationship between the incident angle and the exit angle through a specific rotation angle; only when the incident angle and the exit angle match the preset function, a strong reflection response accompanied by characteristic polarization conversion is generated, otherwise the signal is significantly suppressed. Further integration of angle perception feedback and PIN diode suppression circuit can verify the incident legality in real time and block illegal detection; some embodiments introduce a graphene gate control layer to support online reconfiguration of the mapping function. The structure realizes high-security terahertz encryption with physical unclonable and multi-dimensional feature binding, and is suitable for anti-counterfeiting labels and PUF devices.

Description

Technical Field

[0001] This invention relates to the field of terahertz communication technology, and more specifically to a terahertz encryption metasurface based on the correlation between incident angle and exit angle. Background Technology

[0002] Terahertz waves have significant application prospects in fields such as communication, imaging, and security detection. Metasurfaces, as artificial electromagnetic materials, can flexibly control the phase, amplitude, and polarization state of terahertz waves at the subwavelength scale, providing possibilities for the development of novel terahertz functional devices, especially physical layer information security devices (such as anti-counterfeiting tags and encryption carriers).

[0003] Currently, metasurface design for encryption applications primarily relies on responses to dimensions such as frequency, polarization, or external electronically controlled signals. For example, some solutions achieve efficient anomalous beam deflection or holographic imaging under fixed perpendicular incidence conditions through precisely designed unit structures; others achieve dynamic function switching under electronic control by integrating tunable materials or semiconductor devices. However, these existing technologies generally share a common limitation: they fail to incorporate the inherent spatial physical parameters of the incident and exit angles of electromagnetic waves into a highly secure encryption dimension.

[0004] Existing design paradigms often treat the incident angle as an interference factor to be overcome or an optimization goal for achieving stable operation over a wide range of angles, rather than a usable "key." Their encryption responses lack a strict, non-linear binding relationship with specific angle combinations. This means that attackers can theoretically obtain valid authentication signals by simply traversing the incident angles, resulting in a relatively weak practical security boundary for the system. Therefore, breaking through traditional design thinking and creating a novel metasurface that uniquely and strongly correlates the incident and exit angles, activating the target response only when a preset strict angle mapping relationship is met, has become a key challenge in realizing high-security terahertz physical encryption devices. Summary of the Invention

[0005] The purpose of this invention is to provide a terahertz dynamic holographic encryption and security sensing system based on a programmable metasurface, so as to solve the technical contradiction in the prior art that dynamic encryption and high-sensitivity sensing functions are difficult to deeply integrate and coordinately optimize on the same programmable hardware platform.

[0006] To achieve the above objectives, in one aspect, the present invention provides a terahertz encryption metasurface based on the correlation between the incident angle and the exit angle, comprising:

[0007] The system comprises a substrate layer, a dielectric spacer layer, and a top metacell array. The substrate layer is made of high-resistivity silicon with a resistivity of at least 10 kΩ·cm and a thickness of 500 μm. The dielectric spacer layer is composed of a polyimide film with a dielectric constant of 3.2, a loss tangent of less than 0.002, and a thickness of 30 μm. The top metacell array consists of periodically arranged asymmetric metallic resonant structures, each metacell having a lateral dimension of 60 μm × 60 μm and a periodic spacing of 70 μm, operating in the 0.3 THz to 0.8 THz frequency band. Each metacell consists of a first metal arm, a second metal arm, and a central coupling bridge. The first metal arm extends along the x-axis with a length of 45 μm and a width of 8 μm. The second metal arm extends along the y-axis with a length of 32 μm and a width of 6 μm. The central coupling bridge connects the two arms at their intersection in a cross shape, with a width of 4 μm and a length of 10 μm. μm; all metal structures are formed by gold film deposition with a thickness of 200 nm and a surface roughness RMS of less than 2 nm. The first and second metal arms are not spatially coplanar and are electrically isolated by micro-vias beneath the dielectric spacer layer, ensuring independent excitation paths for incident electromagnetic waves under different polarization components;

[0008] The meta-unit array is arranged according to a preset two-dimensional coding matrix, which consists of N×M unit positions, each position corresponding to a unique structural rotation angle. ,in , , The value range is from 0° to 359°, with a step accuracy of 1°; the rotation angle Instead of random allocation, it is designed in reverse based on the preset mapping function β = f(α) between the incident angle α and the exit angle β; specifically, for each target exit direction The system calculates its corresponding angle of incidence. And based on this, determine the phase gradient required for that position unit. Then, the structural rotation angle that satisfies the phase gradient is obtained through full-wave electromagnetic simulation. Ultimately, the structural arrangement of the entire array is this mapping function. The physical realization carrier; the phase gradient Determined by the generalized Snell's law: ,in The wavelength is in free space; in this invention, Fixed at 600 μm (corresponding to 0.5 THz), therefore = The phase gradient is obtained by rotating the unit by an angle. The modulation of the local equivalent refractive index is achieved through a physical mechanism derived from the azimuth-dependent inductor-capacitor resonance mode generated by the asymmetric metal arm under oblique incidence conditions.

[0009] Furthermore, when the metasurface is incident perpendicularly (α=0°), all units exhibit a weak resonant response due to the broken structural symmetry, with a reflectivity below -15 dB; when the incident angle deviates to a preset value... At that time, only when the direction of launch is exactly the same At this time, the overall phase distribution of the array satisfies the coherent superposition condition, and the reflection intensity suddenly increases to above -3 dB, accompanied by a change in polarization state from linear polarization to elliptic polarization. This polarization conversion characteristic is caused by the birefringence effect introduced by the length difference between the first and second metal arms within the unit cell, and its fast and slow axis directions follow... Dynamic rotation allows for the formation of detectable polarized fingerprints under specific angular combinations.

[0010] In a preferred embodiment of the present invention, the metacell array is divided into multiple functional sub-regions, each sub-region corresponding to a set of independent incident-out incident angle pairs. , The sub-regions are used to carry different encrypted information bits; sub-region A is configured to be activated only when α=30° and β=45°, outputting a resonance peak at 0.52 THz; sub-region B is configured to be activated only when α=−20° and β=−35°, outputting a transmission valley at 0.48 THz; each sub-region is separated by an electromagnetic isolation trench with a depth of 1.5 times the thickness of the dielectric spacer layer, a width of 15 μm, and a filling material of silicon dioxide with a dielectric constant of 3.9 to suppress cross-region crosstalk.

[0011] The electromagnetic isolation trenches continuously surround the boundaries of the unit array, forming a closed electromagnetic barrier. The sidewalls are etched by ion beams, and the surface tilt angle is 85° to ensure that terahertz waves cannot penetrate into adjacent areas even under grazing incidence conditions. In addition, a grounding metal layer is embedded at the bottom of the trench. This metal layer is interconnected with the coplanar grounding plane on the back of the substrate through silicon vias. The silicon vias have a diameter of 10 μm, a spacing of 50 μm, and are filled with copper, achieving full-band electromagnetic shielding.

[0012] Furthermore, the metasurface described in this invention integrates an angle sensing feedback module, which consists of four miniature pyroelectric detectors located at the four edges of the metasurface for real-time monitoring of the spatial distribution of the incident beam. Each detector has an effective photosensitive area of ​​1 mm², a response band covering 0.1 THz to 1.0 THz, and a time constant of 10 ms. The detector output signal is conditioned by a low-noise transimpedance amplifier and then sent to a field-programmable gate array (FPGA) for angle calculation. The FPGA has a built-in lookup table algorithm that maps the intensity ratios of the four paths to the precise value of the current incident angle α and performs matching verification with a pre-stored set of valid angles. Only when the matching is successful will the system allow reading the electromagnetic response signal of the metasurface; otherwise, the signal suppression circuit will be automatically activated to cut off the output channel.

[0013] The signal suppression circuit consists of a PIN diode switch array integrated inside the dielectric spacer layer. The anode of each PIN diode is connected to the end of the metal arm of the metacell, the cathode is grounded, and the control terminal is connected to the GPIO pin of the programmable gate array. When the programmable gate array determines that the incident angle is illegal, it outputs a high level to turn on the PIN diode, short-circuiting the metacell to ground, thus forcibly destroying its resonant characteristics and attenuating the reflected signal by more than 20 dB. This suppression mechanism completes its response within 100 ns, ensuring that illegal probes cannot obtain valid information.

[0014] In another embodiment of the present invention, the meta-unit adopts a multi-layer stacked structure, including an upper gold film resonator, an intermediate graphene control layer, and a lower ITO transparent electrode. The graphene layer is grown on a polyimide medium by chemical vapor deposition, and the carrier concentration can be continuously adjusted in the range of 1×10¹² cm⁻² to 5×10¹³ cm⁻² by applying an external gate voltage. The ITO electrode has a thickness of 150 nm and a sheet resistance of 10 Ω / □, serving as a common gate. By applying different gate voltages, the conductivity of the graphene can be dynamically changed, thereby modulating the equivalent impedance of the meta-unit and realizing the online reconfiguration of the incident-outgoing angle mapping function f(·). This reconfiguration process does not change the physical structure, but can switch to another set of preset encryption keys, which is suitable for dynamic key distribution scenarios.

[0015] The gate voltage is provided by a CMOS driving circuit integrated on the back of the substrate, which includes a 12-bit digital-to-analog converter, a voltage buffer, and an electrostatic discharge (ESD) protection diode. The digital-to-analog converter has an output range of 0 V to 5 V and a resolution of 1.22 mV. It is connected to the ITO electrode via gold-gold thermocompression bonding. The ESD protection diode adopts a bidirectional TVS structure with a breakdown voltage of ±8 V to ensure circuit safety in terahertz strong field environments.

[0016] Compared with the prior art, the beneficial effects of the present invention are:

[0017] This invention creatively uses the preset mapping relationship β=f(α) between the incident angle α and the exit angle β as the core key, and solidifies it through a physical structure of meta-unit rotation encoding. Only when the detection optical path simultaneously satisfies this unique angle pair can an effective response be triggered. This fundamentally changes the paradigm of traditional encrypted meta-surfaces that rely on fixed patterns or a single external key, elevating the security dimension from "conditional verification" to "path authorization," and significantly enhancing the system's anti-cracking capability.

[0018] Through precise phase gradient design, this invention enables the metasurface to coherently superimpose only under specific angle combinations that satisfy the mapping relationship, generating a strong reflection signal; while for any other incident-out incident angle combination, the response is strongly suppressed. This characteristic effectively resists attacks that brute-force scan by traversing angles, resolving the inherent contradiction in existing technologies where security is sacrificed in pursuit of wide-angle operation.

[0019] The encryption response of this invention is not a single strength change, but rather a collaborative binding of multiple physical features such as angle, polarization, and frequency. This simultaneous verification of multi-dimensional features greatly increases the difficulty of illegal counterfeiting and copying, providing a unique "physical fingerprint" for identity authentication.

[0020] By integrating angle sensing and active suppression circuits, or introducing tunable material layers such as graphene, it can be upgraded into an intelligent security system with real-time legitimacy judgment, active anti-probing, or online reconfiguration of encryption rules, meeting multi-level application needs from static anti-counterfeiting to dynamic key distribution. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the metasurface in this invention. Figure 2 This is a schematic diagram of the planar geometric configuration of the superstructure unit in this invention and its rotational arrangement in the array. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0023] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” and “described” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the described features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0024] This invention provides a terahertz dynamic holographic encryption and security sensing system based on a programmable metasurface. Its overall structure consists of three layers: a substrate layer, a dielectric spacer layer, and a top-layer metacellular array. The substrate layer uses a high-resistivity silicon wafer with a resistivity of no less than 10 kΩ·cm and a thickness of 500 μm to ensure extremely low dielectric loss and good mechanical support performance in the 0.3 THz to 0.8 THz frequency band. The dielectric spacer layer, disposed above the substrate layer, is composed of a polyimide film with a dielectric constant of 3.2, a loss tangent of less than 0.002, and a precisely controlled thickness of 30 μm. It isolates parasitic coupling between the top-layer metal structure and the substrate conductive layer and serves as a dielectric platform for subsequent microvia and through-silicon via (TSV) interconnect processes. The top-level meta-unit array consists of periodically arranged asymmetric metallic resonant structures. Each meta-unit has a lateral dimension of 60 μm × 60 μm and a center-to-center spacing of 70 μm, ensuring that subwavelength conditions are met within the operating frequency band and avoiding the excitation of higher-order diffraction modes.

[0025] Each metaunit is integrally formed from three parts: a first metal arm, a second metal arm, and a central coupling bridge. The first metal arm extends along the x-axis, with a length of 45 μm and a width of 8 μm; the second metal arm extends along the y-axis, with a length of 32 μm and a width of 6 μm. They are orthogonally arranged in space but not coplanar, and their vertical spacing is determined by the thickness of the dielectric spacer layer. The central coupling bridge, located at the intersection of the two arms, is cross-shaped, with a width of 4 μm and a length of 10 μm, and is used to achieve near-field coupling between the two arms under electromagnetic excitation. All metal structures are formed by gold film deposition with a thickness of 200 nm and a surface roughness RMS of less than 2 nm to reduce ohmic loss and improve the quality factor in the terahertz band. The first and second metal arms are electrically isolated through a micro-via beneath the dielectric spacer layer. This micro-via has a diameter of 5 μm and penetrates the polyimide layer. It is filled with insulating material to ensure independent response paths for the two arms under different polarization components, thereby supporting the decoupled excitation of the x and y components in the linearly polarized incident wave.

[0026] The meta-unit array is spatially arranged according to a preset two-dimensional encoding matrix, which consists of N×M unit positions, where N and M are the number of units in the array along the x and y directions, respectively, with typical values ​​of N=128 and M=128. Each position (i,j) corresponds to a unique structural rotation angle. , The value ranges from 0° to 359°, with a step precision of 1°. This rotation angle is not randomly assigned, but rather based on a preset mapping function between the incident angle α and the exit angle β. Perform reverse engineering.

[0027] For each target launch direction The system first calculates the required phase gradient according to the generalized Snell's law. : in The free-space wavelength is fixed at 600 μm in this embodiment (corresponding to a center frequency of 0.5 THz). Subsequently, the reflection phase of a single metaunit at different rotation angles is parametrically scanned using full-wave electromagnetic simulation software (CST Studio Suite or Ansys HFSS) to establish... Mapping database. Based on this database, the phase gradient satisfying the target is retrieved. Required local element rotation angle Ultimately, the structural arrangement of the entire array is the mapping function. The physical carrier for implementation, such that only when the incident angle is And the direction of launch is At this time, the overall phase distribution of the array satisfies the coherent superposition condition, generating a strong reflected signal.

[0028] Furthermore, under perpendicular incidence (α=0°) conditions, the metasurface, due to the asymmetric geometric topology of all its unit structures, disrupts the mirror symmetry of the traditional dipole resonator, resulting in its inability to effectively excite the current loop under normal excitation, leading to a reflectivity below -15 dB. When the incident angle deviates to a certain preset value... At that time, only when the observation direction is exactly the same At this time, the local phase delay generated by each element of the array forms a linear gradient distribution along the emission direction, satisfying the momentum matching condition, and the reflection intensity suddenly increases to above -3 dB. Simultaneously, due to the birefringence effect introduced by the length difference between the first and second metal arms (45 μm vs. 32 μm), the polarization state of the reflected wave changes from linear polarization to elliptic polarization, with an ellipticity not less than 0.6. The fast and slow axes change with the element rotation angle. The dynamic changes form a "polarization fingerprint" that can be recognized by polarization-sensitive detectors.

[0029] In a preferred embodiment of the present invention, the metacell array is divided into multiple functional sub-regions, each sub-region being independently configured to respond to a specific set of incident-exit angle pairs. , The array contains different encrypted information bits. For example, sub-region A occupies a 32×32 cell in the upper left corner of the array and is configured to be activated only when α=30° and β=45°, producing a sharp reflection peak at 0.52 THz; sub-region B occupies a 32×32 cell in the lower right corner and is configured to be activated only when α=−20° and β=−35°, exhibiting a transmission valley at 0.48 THz. The sub-regions are separated by electromagnetic isolation trenches with a depth of 45 μm (1.5 times the thickness of the 30 μm dielectric spacer layer) and a width of 15 μm. The trenches are filled with silicon dioxide, which has a dielectric constant of 3.9, creating a dielectric contrast with polyimide and effectively suppressing surface wave propagation and cross-region electromagnetic crosstalk.

[0030] The electromagnetic isolation trenches continuously encircle the boundaries of each sub-region, forming a closed electromagnetic barrier. Their sidewalls are treated with ion beam etching, resulting in a near-vertical 85° surface tilt angle to prevent terahertz waves from diffracting and penetrating along the trench sidewalls under grazing incidence conditions. A 200 nm thick gold grounding layer is embedded at the bottom of the trench. This layer is electrically connected to the coplanar grounding plane on the back of the substrate through through-silicon vias (TSVs). The TSVs are 10 μm in diameter, spaced 50 μm apart, and arranged in a checkerboard pattern. They are filled with high-purity copper, and after electroplating and annealing, their resistivity is less than 2 μΩ·cm, ensuring good grounding performance from DC to 1 THz, thus constructing a full-band electromagnetic shielding environment.

[0031] Furthermore, the metasurface described in this invention integrates an angle sensing feedback module for real-time verification of the legality of the incident angle. This module consists of four miniature pyroelectric detectors, each mounted in a dedicated groove along the perimeter of the metasurface. Each detector has an effective photosensitive area of ​​1 mm², a response band covering 0.1 THz to 1.0 THz, and a time constant of 10 ms, enabling rapid response to the spatial energy distribution of the incident beam. The weak current signal output by the detector is amplified by a low-noise transimpedance amplifier (gain of 10). 6 After conditioning (V / A, input noise density <5 pA / √Hz), the signal is converted into a voltage signal and fed into the programmable gate array (PLA). The PLA contains a built-in lookup table algorithm and pre-stores a database of normalized intensity ratios for the four detectors at different incident angles. By comparing the current ratios of the four signals with valid entries in the database in real time, the PLA can calculate the precise value of the incident angle α (accuracy ±0.2°) within 1 ms and verify it against the pre-stored set of valid angles (e.g., {25.3°, 30°, −20°}).

[0032] Only when a match is successful does the programmable gate array (PGA) output an enable signal, allowing subsequent readings of the electromagnetic response of the metasurface; otherwise, the PGA automatically activates a signal suppression circuit. This signal suppression circuit consists of a PIN diode switch array integrated within the dielectric spacer layer. The anode of each PIN diode is connected to the end of the first or second metal arm of the corresponding metasurface unit via a metal lead, and the cathode is connected to the ground metal layer. The control terminal is connected to the GPIO pin of the PGA. When the PGA determines that the incident angle is illegal, it outputs a high level (+3.3 V) to turn on the PIN diodes, short-circuiting the metasurface unit to ground and forcibly disrupting its LC resonant circuit, causing the reflected signal to attenuate by more than 20 dB. The response time of this suppression mechanism is less than 100 ns, much faster than the duration of a terahertz pulse (typically >1 ps), ensuring that illegal probes cannot obtain valid information.

[0033] Example 1:

[0034] This embodiment provides a terahertz encryption metasurface for physically cloning-resistant anti-counterfeiting. The metasurface comprises, from top to bottom, a top-layer metacell array, a dielectric spacer layer, and a substrate layer. The substrate layer is a high-resistivity silicon wafer with a resistivity of not less than 10 kΩ·cm and a thickness of 500 μm. The dielectric spacer layer is composed of a polyimide film with a dielectric constant of 3.2, a loss tangent of less than 0.002, and a precisely controlled thickness of 30 μm. The top-layer metacell array consists of asymmetric golden cross-shaped resonant units with a period of 70 μm, each unit having a lateral dimension of 60 μm × 60 μm.

[0035] The specific configuration of the metaunit is as follows: the first metal arm extends along the x-axis with a length of 45 μm and a width of 8 μm; the second metal arm extends along the y-axis with a length of 32 μm and a width of 6 μm; the two arms are connected by a cross-shaped central coupling bridge with a width of 4 μm and a length of 10 μm. All metal structures are made of a 200 nm thick gold film with a surface roughness RMS of less than 2 nm. The first and second metal arms are spatially separated and electrically isolated in the vertical direction by a dielectric spacer layer.

[0036] The arrangement of the meta-unit array is reverse-engineered based on a preset encryption mapping function. This function is set as β = arcsin(1.5 × sinα), where α is the incident angle and β is the uniquely valid outgoing observation angle. A set of valid keys is selected as (α0, β0) = (25.0°, 39.0°). To achieve this function, the required phase gradient is first calculated according to the generalized Snell's law. Then, the Gerchberg-Saxton iterative algorithm is used, with the target encrypted image (such as a specific logo) as the target for the outgoing field strength distribution, to inversely derive the required reflection phase φᵢⱼ for each position (i, j) in the array. A database of the relationship between the unit rotation angle θ and the reflection phase φ is established through full-wave electromagnetic simulation, and a unique and precise rotation angle θᵢⱼ is assigned to each unit, thereby physically encoding the mapping function and the encrypted image.

[0037] During verification, a terahertz time-domain spectroscopy system was used for testing. When irradiated at a legal incident angle of α = 25.0°, a clear image of the preset logo was received only in the exit direction of β = 39.0°, and the reflected wave exhibited a right-handed elliptically polarized state with an ellipticity of not less than 0.65. If the incident angle deviated from ±1.5° or the observation direction deviated from the legal direction, the image contrast dropped sharply by more than 90%, and the signal-to-noise ratio fell below -20 dB, achieving a high-security encryption effect of "narrow-domain activation and wide-domain suppression." Due to microscopic process deviations during manufacturing, different batches or different samples within the same batch have unique precise activation angles and subtle image features, constituting a physically unclonable function.

[0038] Example 2:

[0039] An encrypted metasurface supporting dynamic key reconfiguration, wherein the metasurface unit adopts a multi-layer stacked reconfigurable design, comprising, from top to bottom: an asymmetric gold cross-shaped resonator, a 30 nm thick atomic layer deposited Al2O3 dielectric isolation layer, a chemical vapor deposition grown monolayer graphene control layer, a 150 nm thick ITO transparent common gate layer, a polyimide dielectric layer and a high-resistivity silicon substrate.

[0040] To enable dynamic reconfiguration, a CMOS driver circuit, including a 12-bit digital-to-analog converter, is integrated on the back side of the silicon substrate. This circuit is electrically connected to the ITO gate via gold wire bonding and can receive external commands and output gate voltages of 0 V, 40 V, or 80 V to the graphene layer. By changing the gate voltage Vg, the carrier concentration and surface conductivity of the graphene can be continuously adjusted, thereby changing the equivalent electromagnetic parameters of the metacell.

[0041] This embodiment encodes two independent encryption mapping functions, each corresponding to a different gate voltage state. When a gate voltage Vg = 0 V is applied, the system is in "Mode A", with the mapping function β = arcsin(0.8 × sinα + 0.15), the valid key pair being (α1, β1) = (15.0°, 26.5°), and the corresponding decryption image being the digit "1". When a gate voltage Vg = 40 V is applied, the system switches to "Mode B", the mapping function becomes β = -arcsin(1.2 × sinα), the valid key pair is (α2, β2) = (-20.0°, 24.3°), and the corresponding decryption image becomes the letter "A". When Vg = 80 V is applied, the graphene is in a high-loss state, the entire metasurface has no encryption response, and it enters a globally off state.

[0042] The array's encoding matrix was obtained through multi-objective optimization design, enabling the same physical structure to approximate the two different phase distributions required for "Mode A" and "Mode B" under two different gate voltages. The fabrication process, based on Example 1, added key steps such as graphene transfer, atomic layer deposition of ultrathin dielectric, and ITO gate fabrication.

[0043] In the dynamic encryption demonstration, the system is initialized in a shutdown state with Vg=80V. When authorized user A requests verification, the drive circuit switches the gate voltage to 0V. At this time, user A must use their proprietary key (15.0°, 26.5°) to probe and correctly read the digit "1". After verification, the system switches the gate voltage to 40V, and user A's key immediately becomes invalid. Subsequently, authorized user B uses their proprietary key (-20.0°, 24.3°) to probe and can read the letter "A". Tests show that the response time for encryption function switching is less than 10 milliseconds, and the signal isolation between different modes is better than 18 dB. This embodiment realizes dynamic and reversible rewriting of encryption rules at the physical layer, suitable for high-security scenarios with multi-user time-sharing authentication or periodic key updates.

[0044] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely preferred examples and are not intended to limit the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A terahertz-encrypted metasurface based on the correlation between incident angle and exit angle, characterized in that, include: basal layer; A dielectric spacer layer is disposed on the substrate layer; The top-level metacell array is composed of asymmetric metal resonant structures arranged periodically on the dielectric spacer layer. The asymmetric metal resonant structures include a first metal arm and a second metal arm of different lengths, and the first metal arm and the second metal arm have different spatial orientations. Each metaunit in the metaunit array has a rotation angle θ uniquely determined according to a preset mapping function β=f(α) between the incident angle α and the exit angle β. The spatial arrangement of the metaunit array is configured such that: when the incident angle α and the exit angle β satisfy the preset mapping function β=f(α), the reflection response in the direction of the exit angle β is coherently superimposed, and the reflection intensity is higher than a first threshold; for any combination of incident angle and exit angle that does not satisfy the mapping function, its reflection response is significantly suppressed to below a second threshold. The rotation angle θ is configured such that the reflection phase provided by each metaunit satisfies a gradient distribution, where the phase gradient is... The relationship with the mapping function is as follows: ； in, The free-space wavelength is the operating frequency.

2. The terahertz encrypted metasurface according to claim 1, characterized in that, The first metal arm and the second metal arm are electrically isolated in space by a dielectric spacer layer.

3. The terahertz encrypted metasurface according to claim 1, characterized in that, When the incident angle is α and the outgoing direction is β=f(α), the polarization state of the reflected wave from the metasurface changes relative to the incident wave, and the ellipticity is greater than 0.

6.

4. The terahertz encrypted metasurface according to claim 1, characterized in that, The supercell array is divided into multiple functional sub-regions, each corresponding to a different mapping function.

5. The terahertz encryption metasurface according to claim 4, characterized in that, An electromagnetic isolation structure is provided between adjacent functional sub-regions.

6. The terahertz encrypted metasurface according to claim 1, characterized in that, It also includes an angle sensing module and a signal suppression module; the angle sensing module is used to detect the incident angle α' in real time and compare it with the set of legal incident angles; the signal suppression module is used to actively reduce the electromagnetic response intensity of the metasurface when α' does not belong to the set of legal angles.

7. The terahertz encrypted metasurface according to claim 1, characterized in that, The meta-unit includes a tunable material layer whose electromagnetic parameters can be controlled by an external signal to change the mapping function β=f(α).

8. The terahertz encryption metasurface according to claim 7, characterized in that, The adjustable material layer is a graphene layer, and the external signal is a gate voltage applied to the graphene layer.

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