Single-pixel visual dynamic encryption and decryption system and method based on reconfigurable metasurface

Abstract

The application provides a single-pixel visual dynamic encryption and decryption system and method based on a reconfigurable metasurface. The system realizes dynamic coding of secret information through an integrated field programmable gate array, converts the secret information into a visual key, and restores the original content under the pixel-level position superposition condition by using the electromagnetic wave superposition effect. The system takes each 2*2 pixel unit as an independent encryption unit, realizes fine control of the encryption process and real-time reconstruction of the visual key, simulates the encryption principle of the one-time password book, and can effectively resist brute force cracking, machine learning attacks and replay attacks. The pixel-level coding technology is adopted, the limitation of low resolution of traditional visual secret sharing is overcome, and high-fidelity coding and decryption can be performed on complex contents such as alphanumeric texts and high-resolution images. The application has self-adaptability and high security, is suitable for wireless communication, remote sensing imaging and security information processing fields, and provides an expandable security implementation scheme for electromagnetic cryptography.

Description

Technical Field

[0001] This invention relates to the fields of information security and electromagnetic control technology, specifically to a single-pixel visual dynamic encryption and decryption system and method based on a reconfigurable metasurface. Background Technology

[0002] With the rapid development of wireless communication, remote sensing imaging, and other fields, the demand for secure information transmission continues to rise. Meanwhile, increasingly complex security threats such as network attacks and eavesdropping place higher demands on the security, dynamic adaptability, and anti-interference capabilities of information encryption technologies. Currently, most digital encryption algorithms are based on large integer factorization or discrete logarithm problems. However, with the rapid development of quantum computing, these algorithms are quantum vulnerable to being quickly cracked, making them unsuitable for high-security information transmission requirements. Physical layer security mechanisms, on the other hand, often rely on fixed electromagnetic properties or preset encoding methods, lacking the ability to dynamically and precisely control the amplitude and phase of electromagnetic waves. This makes them vulnerable to complex and ever-changing physical layer attacks and channel hijacking, resulting in significant deficiencies in anti-interference capabilities, dynamic encryption capabilities, and information theory security.

[0003] Reconfigurable metasurfaces are two-dimensional artificial structures whose electromagnetic response can be adjusted in real time through external control. They enable dynamic manipulation of electromagnetic wave propagation characteristics and are gradually being applied to the field of information encryption. Numerous research results have been achieved in related technologies.

[0004] A search of patent literature revealed invention patent CN206401526U, which discloses a microwave-programmable 1-bit anisotropic metasurface. This metasurface achieves [the desired effect] by controlling the on / off state of two mutually perpendicular switching diodes loaded in the middle and upper layers of the coding unit. x polarization and y Independent reflection phases at 0° and 180° polarization under perpendicular incidence support dynamic switching between different functions. Unlike the patent, the programmable metasurface proposed in this application has the same phase under different polarizations. Furthermore, this application primarily focuses on constructing a novel information encryption framework based on the programmable metasurface and a visual secret sharing scheme. This framework enables flexible adjustment of encryption methods, dynamic updating of key patterns, and higher-precision secure information transmission, thereby improving the system's security, confidentiality, and adaptability. Patent CN104078771A discloses a digitally programmable metasurface, composed of a digital control unit and an artificial electromagnetic surface with integrated switching diodes. It achieves unit state switching through different bias voltages and supports dynamic reconfiguration of various electromagnetic functions. Unlike this patent, this application uses an integrated field-programmable gate array (FPGA) to dynamically encode secret information, converting it into a visual key similar to noise, and utilizing electromagnetic superposition effects to reveal the content under specific conditions.

[0005] The invention patent with patent number CN104714218A discloses a terahertz coded metasurface with wideband radar cross-section reduction. By designing four unit structures (00, 01, 10, and 11), it achieves broadband diffuse reflection, reducing the radar cross-section by more than 10 dBsm in the 0.66-1.26 THz range. Unlike this patent, this application proposes a 1-bit coded metasurface, combining Visual Secret Sharing (VSS) with physical layer holographic encoding to achieve highly secure, pixel-level programmable encryption information hiding and recovery.

[0006] Patent CN108683408A discloses a time-domain encoded metasurface with independently adjustable harmonic amplitude and phase. This metasurface achieves independent harmonic amplitude and phase control by changing the frequency, amplitude, and delay of the control signal. Unlike that patent, this application achieves 1-bit phase control by controlling the switching on and off of a switching diode instead of the voltage of a varactor diode. Furthermore, it combines a programmable metasurface with single-pixel visual secret sharing technology to construct a novel information encryption framework.

[0007] Patent CN105161858A discloses a circularly polarized rotation controller based on an tunable metasurface and its design method. The proposed circularly polarized rotation controller consists of an upper microstrip conduction layer (containing a circular ELC structure, bias circuit, and PIN diode), a middle dielectric substrate, and a lower metal ground plane. Switching between rotation conversion and rotation retention functions is achieved by controlling the on / off state of the PIN diode. Unlike this patent, this application primarily designs a novel programmable metasurface unit, mainly for application in the field of information encryption. It combines a reconfigurable metasurface with single-pixel visual secret sharing to construct a novel encryption framework. This overcomes problems such as fixed keys, low resolution, and poor dynamic adaptability, achieving flexible encryption adjustment, dynamic key updates, and high-precision secure transmission, significantly improving system security, confidentiality, and adaptability.

[0008] Patent CN105303124A discloses a master-child key encryption method for physical tape libraries, comprising a pair of mutually redundant encryption devices: a master key USB hard drive and a child key USB hard drive. The encryption key generated by the master key is synchronized to the child key USB hard drive via the physical tape library, achieving data encryption and decryption. Unlike that patent, this application primarily uses a programmable metasurface to transmit secret information. To improve the security of the secret information, it combines visual secret sharing with physical layer holographic encoding to achieve highly secure, pixel-level programmable encrypted information hiding.

[0009] The existing patents and literature mentioned above have failed to achieve high-security, pixel-level programmable encryption information hiding and recovery. Therefore, researching a single-pixel visual dynamic encryption and decryption system and method based on reconfigurable metasurfaces has become a key task that urgently needs to be solved. Summary of the Invention

[0010] To address the shortcomings of existing technologies, the purpose of this invention is to provide a single-pixel visual dynamic encryption and decryption system and method based on reconfigurable metasurfaces.

[0011] A single-pixel visual dynamic encryption / decryption system based on a reconfigurable metasurface, provided by the present invention, includes: The encryption encoding module is used to convert the original information to be transmitted into a pixel matrix, decompose the pixel matrix into two key images according to the (2,2) threshold visual secret sharing algorithm, and map the pixel information of each key image into phase modulation state code. The reconfigurable metasurface control module consists of multiple reconfigurable metasurface units arranged in a periodic square grid, with each metasurface unit integrating multiple PIN diodes. The programmable control module is used to control the on / off state of the PIN diodes of each metasurface unit according to the phase modulation state encoding, so that each metasurface unit independently and programmably modulates the phase of the incident electromagnetic wave according to the preset or dynamically generated encryption key, thereby enabling the reconfigurable metasurface control module to generate a wavefront distribution corresponding to the key image under electromagnetic wave irradiation. The decryption module receives electromagnetic signals modulated by two key images. Based on the principle of electromagnetic wave superposition, when the two key images are superimposed at pixel level, the original information is recovered through superposition operations.

[0012] Preferably, the encryption encoding module includes: The digital encoding unit is used to binarize or multi-level grayscale the original information to be transmitted to form a corresponding pixel matrix. The visual secret sharing unit is used to decompose the pixel matrix into two independent key images according to the (2,2) threshold visual secret sharing algorithm. The (2,2) threshold visual secret sharing algorithm includes: expanding each pixel in the pixel matrix into a 2×2 sub-pixel block, and randomly generating the distribution of black sub-pixels and white sub-pixels through the encoding function, so that each key image presents a statistical noise distribution separately. The phase mapping unit is used to map the pixel information of each key image to phase modulation state code, where black sub-pixels correspond to 180° phase and white sub-pixels correspond to 0° phase.

[0013] Preferably, each metasurface unit integrates two PIN diodes, namely PIN diode I and PIN diode II; the structure of the metasurface unit includes four alternating metal layers and three dielectric layers, which are arranged from top to bottom as follows: PIN diode I and PIN diode II, metal radiation layer and coupling feed structure, upper dielectric substrate, bias control layer, prepreg adhesive sheet, metal ground plane, lower dielectric substrate, and feed network layer.

[0014] Preferably, the relative permittivity and thickness of the upper dielectric substrate are εr1 = 3.55 and h1 = 3.048 mm, respectively; the relative permittivity and thickness of the semi-cured adhesive sheet are εr2 = 3.52 and h2 = 0.404 mm, respectively; and the relative permittivity and thickness of the lower dielectric substrate are εr3 = 3.55 and h3 = 3.048 mm, respectively.

[0015] Preferably, the metal radiating layer consists of two coaxial annular patches, with PIN diode I and PIN diode II integrated at the connection point; the outer elliptical annular patch is connected to the ground plane through two symmetrically distributed metallized vias on the horizontal center line, forming electromagnetic boundary conditions and a reference ground; the inner patch is designed with a Φ-shaped structure and is electrically connected to the feed network layer below through a metallized via penetrating the ground plane at the center, realizing signal injection and modulation.

[0016] Preferably, the bias control layer is connected to the metallized feed probe, and the bias control layer includes symmetrically arranged zigzag distributed inductors and fan-shaped distributed capacitors to filter out radio frequency signals in the bias DC circuit.

[0017] By applying a preset bias voltage to PIN diodes I and II through a bias control layer, a stable 180° phase difference in space is achieved by utilizing the forward and reverse directions of the excitation current. This allows the reconfigurable metasurface unit bundle to exhibit two different phases: 0 degrees and 180 degrees, corresponding to unit codes "0" and "1," respectively. When the unit code is "1," PIN diode I is in the on state and PIN diode II is in the off state; when the unit code is "0," PIN diode I is in the off state and PIN diode II is in the on state.

[0018] Preferably, the reconfigurable metasurface control module is fed through a power divider network, which is one or more of a microstrip power divider network, a waveguide power divider network, a substrate integrated waveguide power divider network, or a gap waveguide power divider network.

[0019] Preferably, the programmable control module is a field-programmable gate array (FPGA) used to apply different bias voltages to control the on / off state of the PIN diodes of each metasurface unit in the reconfigurable metasurface control module, so that each metasurface unit is in a different digitally encoded state.

[0020] This invention also provides a single-pixel visual dynamic encryption and decryption method based on a reconfigurable metasurface, employing the aforementioned single-pixel visual dynamic encryption and decryption system based on a reconfigurable metasurface, comprising the following steps: Encryption process: Step S1: Convert the original information to be transmitted into a pixel matrix through the encryption encoding module, decompose the pixel matrix into two key images according to the (2,2) threshold visual secret sharing algorithm, and map the pixel information of each key image into phase modulation state code. Step S2: The programmable control module controls the on / off state of the PIN diodes of each metasurface unit in the reconfigurable metasurface control module according to the phase modulation state encoding, so that each metasurface unit independently and programmably modulates the phase of the incident electromagnetic wave according to the preset or dynamically generated encryption key, thereby enabling the reconfigurable metasurface control module to generate a wavefront distribution corresponding to the key image under electromagnetic wave irradiation. Decryption process: Step S3: Receive two sets of key image modulated electromagnetic signals through the decryption module, and spatially superimpose the two received electromagnetic signals based on the principle of electromagnetic wave superposition. Step S4: The superimposed signal is decrypted by the decryption module according to the (2,2) threshold visual secret sharing algorithm to restore the original information.

[0021] Preferably, step S1 includes: Step S1.1: The original information to be transmitted is binarized or multi-level grayscale processed by the digital encoding unit to form the corresponding pixel matrix; Step S1.2: The pixel matrix is ​​decomposed into two independent key images by the visual secret sharing unit according to the (2,2) threshold visual secret sharing algorithm. The (2,2) threshold visual secret sharing algorithm includes: expanding each pixel in the pixel matrix into a 2×2 sub-pixel block, and randomly generating the distribution of black sub-pixels and white sub-pixels through the encoding function, so that each key image presents a statistical noise distribution separately. Step S1.3: The pixel information of each key image is mapped to phase modulation state code through the phase mapping unit, where black sub-pixels correspond to 180° phase and white sub-pixels correspond to 0° phase.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention combines reconfigurable metasurfaces with single-pixel visual secret sharing technology to construct a novel single-pixel visual dynamic encryption and decryption framework. By setting 2×2 pixel units as independent encryption units and using field-programmable gate arrays to achieve real-time reconstruction of visual keys, it solves the problems of fixed keys, low resolution, and difficulty in adapting to dynamic security requirements in traditional static information encryption systems. It realizes flexible adjustment of encryption methods and dynamic updating of key patterns, improving the accuracy of information transmission and the security and confidentiality performance of the system.

[0023] 2. This invention generates a unique visual key pair in each encryption cycle through a field-programmable gate array, simulating the one-time key book principle. This eliminates the statistical correlation between encryption cycles, avoids statistical vulnerabilities from a technical perspective, and can effectively resist brute-force attacks, machine learning attacks, and replay attacks, ensuring the information theory security of the system. At the same time, the design of independent encryption units of 2×2 pixels breaks through the technical limitations of the coarse resolution of traditional visual secret sharing, and supports high-fidelity encoding of alphanumeric text, multi-level grayscale images, and high-resolution scenes.

[0024] 3. The reconfigurable metasurface unit of the present invention integrates two PIN diodes and achieves a stable 180-degree phase difference between the two encoding states through the current reversal principle. The unit has a simple structure design and phase modulation can be achieved by controlling the on and off of the PIN diodes through the bias voltage. The bias control is easy to operate and highly controllable.

[0025] 4. The reconfigurable metasurface control module of the present invention does not require an additional spatial excitation feed source, but is directly fed through a power divider network, which effectively reduces the profile and volume of the encryption and decryption system and meets the design requirements of easy conformal and integration of the system; at the same time, it avoids the energy exposure problem caused by spatial excitation feeding and improves the overall imaging resolution of the system. 5. The single-pixel visual dynamic encryption and decryption system based on reconfigurable metasurface of the present invention has been experimentally verified to have a tolerance of up to 65% for phase noise. Even when the hologram is partially damaged, the original information can still be reliably decrypted. The anti-interference ability and robustness of the system are significantly improved, and the encryption and decryption effectiveness can still be guaranteed in complex electromagnetic environments. Attached Figure Description

[0026] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings: Figure 1 This is a schematic diagram of a visual shared key scheme based on reconfigurable metasurface-driven single-pixel visual dynamic encryption technology in an embodiment of the present invention.

[0027] Figure 2These are diagrams illustrating encryption and decryption schemes for four different encrypted information based on reconfigurable metasurface-driven single-pixel visual dynamic encryption technology in embodiments of the present invention.

[0028] Figure 3 This is an S-parameter characteristic diagram of a reconfigurable metasurface in an embodiment of the present invention, representing the two encoding states of digital “1” and digital “0”.

[0029] Figure 4 This is a schematic diagram of the structure of a 16×16-element reconfigurable metasurface array in an embodiment of the present invention.

[0030] Figure 5 This is a cell coding distribution diagram corresponding to the 16×16-element reconfigurable metasurface system in this embodiment of the invention when generating a high-gain single beam.

[0031] Figure 6 This is the spatial three-dimensional radiation pattern corresponding to the 16×16-element reconfigurable metasurface system in this embodiment of the invention when generating a high-gain single beam.

[0032] Figure 7 This is a cell encoding distribution diagram corresponding to the 16×16-element reconfigurable metasurface system in the embodiment of the present invention when it is excited to generate symmetric highly directional dual beams.

[0033] Figure 8 This is the spatial three-dimensional radiation pattern of the 16×16 reconfigurable metasurface system in this embodiment of the invention when it is excited to generate symmetrical highly directional dual beams.

[0034] Figure 9 These are simulation results of six different visual keys based on reconfigurable metasurface-driven single-pixel visual dynamic encryption technology in this embodiment of the invention.

[0035] Figure 10 This is a schematic diagram of a single-pixel visual password based on reconfigurable metasurface-driven letter NPU information encoding in an embodiment of the present invention.

[0036] Figure 11 This is a schematic diagram of a single-pixel visual cryptography based on reconfigurable metasurface driven arbitrary information encoding in an embodiment of the present invention.

[0037] Figure 12 This is a robustness analysis diagram of the single-pixel visual dynamic encryption technology based on reconfigurable metasurface driven in an embodiment of the present invention. Detailed Implementation

[0038] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several changes and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0039] This invention discloses a single-pixel visual dynamic encryption and decryption system and method based on a reconfigurable metasurface. The system integrates a field-programmable gate array (FPGA) to dynamically encode secret information, converting it into a visual key with a noise-like distribution. It then utilizes the electromagnetic wave superposition effect to reconstruct the original content under pixel-level positional superposition conditions. The system treats each 2×2 pixel unit as an independent encryption unit, enabling fine-grained control of the encryption process and real-time reconstruction of the visual key. Simulating the encryption principle of a one-time key, it effectively resists brute-force attacks, machine learning attacks, and replay attacks. Employing pixel-level encoding technology, it overcomes the low resolution limitations of traditional Visual Secret Sharing (VSS), enabling high-fidelity encoding and decryption of complex content such as alphanumeric text and high-resolution images. Experimental results show that this invention has a tolerance of up to 65% for phase noise and can still achieve reliable decryption even with partial hologram damage. Simultaneously, it eliminates statistical correlations between encryption cycles, ensuring information-theoretic security and outperforming existing VSS technologies in resisting partial key interception attacks. This invention possesses adaptability and high security, making it suitable for fields such as wireless communication, remote sensing imaging, and secure information processing, and can provide a scalable and secure implementation scheme for electromagnetic cryptography.

[0040] Example 1: This embodiment provides a single-pixel visual dynamic encryption and decryption system based on a reconfigurable metasurface, including an encryption encoding module, a reconfigurable metasurface control module, a programmable control module, and a decryption module.

[0041] The encryption encoding module is used to convert the original information to be transmitted into a pixel matrix, decompose the pixel matrix into two key images according to the (2,2) threshold visual secret sharing algorithm, and map the pixel information of each key image into a phase modulation state code. The key image refers to an image that presents a statistical noise distribution on its own and requires two copies to be superimposed to recover the original information.

[0042] Please see Figure 1 and Figure 2 The encryption and encoding module includes: The digital encoding unit is used to binarize or multi-level grayscale the original information to be transmitted to form a corresponding pixel matrix. The visual secret sharing unit is used to decompose the pixel matrix into two independent key images according to the (2,2) threshold visual secret sharing algorithm. Specifically, the (2,2) threshold visual secret sharing algorithm includes: expanding each pixel in the pixel matrix into a 2×2 sub-pixel block, and randomly generating the distribution of black sub-pixels and white sub-pixels through an encoding function, so that each key image presents a statistical noise distribution separately, and the original information cannot be restored separately.

[0043] The phase mapping unit is used to map the pixel information of each key image to phase modulation state code, so as to realize fine control and real-time reconstruction of the key, thereby simulating the encryption principle of "one-time codebook"; specifically, black sub-pixels correspond to 180° phase and white sub-pixels correspond to 0° phase.

[0044] In this embodiment, the overall design concept of the encryption encoding module is a visual key design rule, aiming to map the key information required for encryption into the spatial control state of the reconfigurable metasurface control module in the form of a visible pattern. Combined with single-pixel visual secret sharing technology, it achieves highly secure information hiding and dynamic key updates. Specifically, the spatial resolution and phase / amplitude encoding scheme of the key are first determined based on the complexity and transmission accuracy requirements of the information to be encrypted. Then, the key pattern is decomposed into multiple incomplete encoded sub-images (i.e., secret sharing shares). These sub-images cannot be viewed individually to obtain the original information; only after meeting spatial alignment conditions and being superimposed by the metasurface under specific control states can the identifiable information image corresponding to the key be recovered. The entire process can be summarized as follows: ① Input the original key information; ② Design the corresponding spatial encoding pattern (phase or amplitude distribution); ③ Perform secret sharing segmentation of the encoding result to generate multiple sub-images; ④ Load different control units of the reconfigurable metasurface control module according to the sub-images; ⑤ At the receiving end, the decryption module performs spatial superposition and information reconstruction of the sub-images; ⑥ Output identifiable key information to achieve secure decryption.

[0045] The digital encoding unit binarizes the raw information to be transmitted (such as the letters "NPU") to form a corresponding pixel matrix, where each pixel has a value of 0 or 1, representing black or white respectively.

[0046] To verify the feasibility of this concept, this invention employs a (2,2)-order Visualized Secret Sharing (VSS) encryption scheme, using binarized letter information (such as N, W, P, U) as the target encrypted image, and utilizing a programmable metasurface to achieve information hiding and reconstruction. As shown in Figure 1, based on the (2,2) VSS encoding mechanism, each pixel of the pixel matrix is ​​encoded by an encoding function. It is decomposed into four sub-pixels (2×2 array) containing black / white coded blocks (i.e., black sub-pixels and white sub-pixels) in two shared units. For white pixels (pi = 1) and black pixels (p i = 0), and randomly selects and combines them from the corresponding six encoding matrices. Each secret pixel corresponds to one of the six encoding matrices, which improves the security of encryption (all six pixel encoding modes are shown in Figure 1). Due to the random selection of the basic shared unit during the encryption process, adjacent pixels will present different encoding formats, thus ensuring that the secret information cannot be recovered whether the shared key SK1 or SK2 is used alone, and that each key image presents a statistical noise distribution separately. Based on this, Figure 2 uses the (2, 2) VSS scheme to encode the letter information "NPU" into two random dot matrix images (VKn and VKn′) without leaking any information. The original image can be recovered by superposition, thereby realizing the secure encryption and decryption of the secret information. Subsequently, the six sets of shared pixel information are encoded into the reconfigurable metasurface control module.

[0047] The phase mapping unit maps the pixel information of each key image to phase modulation state codes, where black sub-pixels correspond to 180° phase (digit "1") and white sub-pixels correspond to 0° phase (digit "0"). Subsequently, the six sets of shared pixel information are encoded into the reconfigurable metasurface control module.

[0048] Through the processing of the encryption and encoding module described above, the original information is converted into a phase modulation state code that can be executed by the reconfigurable metasurface control module, laying the foundation for subsequent wavefront generation and decryption recovery.

[0049] The reconfigurable metasurface control module consists of multiple reconfigurable metasurface units arranged in a periodic square grid. Each metasurface unit integrates multiple PIN diodes and is fed through a power divider network.

[0050] In this embodiment, the reconfigurable metasurface control module is spatially divided into multiple independent 2×2 pixel encryption units, each corresponding to an original pixel in the pixel matrix. By performing independent phase encoding on the four metasurface units within each 2×2 pixel encryption unit, fine-grained control and real-time key reconstruction are achieved, thereby simulating the encryption principle of a "one-time codebook" at the physical level and ensuring that no single encryption unit can leak the original information.

[0051] In this embodiment, each metasurface unit integrates two PIN diodes, namely PIN diode I and PIN diode II. The structure of the metasurface unit includes four alternating metal layers and three dielectric layers, which are arranged from top to bottom as follows: PIN diode I and PIN diode II (to realize digital reconstruction of the unit phase), metal radiating layer and coupling feed structure, upper dielectric substrate, bias control layer, prepreg adhesive sheet, metal ground plane, lower dielectric substrate, and feed network layer.

[0052] The relative permittivity and thickness of the upper dielectric substrate are εr1 = 3.55 and h1 = 3.048 mm, respectively; the relative permittivity and thickness of the semi-cured adhesive sheet are εr2 = 3.52 and h2 = 0.404 mm, respectively; and the relative permittivity and thickness of the lower dielectric substrate are εr3 = 3.55 and h3 = 3.048 mm, respectively.

[0053] The metal radiating layer consists of two coaxial circular patch panels, with PIN diode I and PIN diode II integrated at the connection point. The outer elliptical ring patch is connected to the ground plane through two symmetrically distributed metallized vias on the horizontal center line, forming a stable electromagnetic boundary condition and reference ground. The inner patch is designed with a Φ-shaped structure and is electrically connected to the feed network layer below through a metallized via penetrating the ground plane at the center, realizing signal injection and modulation.

[0054] The bias control layer is connected to the metallized feed probes and includes symmetrically arranged zigzag distributed inductors and fan-shaped distributed capacitors to filter out RF signals in the bias DC circuit. The bias control network uses high-impedance narrow-band lines and is very close to the metal ground plane, effectively reducing the influence of the control lines on the top-level radiation structure.

[0055] In practical applications, a preset bias voltage is applied to PIN diodes I and II through a bias control layer. The opposing directions of the excitation current achieve a stable 180° phase difference, causing the metasurface element (the radiated wave of the digital antenna element) to exhibit two different phases: 0 degrees and 180 degrees, corresponding to element codes "0" and "1," respectively. When element code "1," PIN diode I is in the on state and PIN diode II is in the off state; when element code "0," PIN diode I is in the off state and PIN diode II is in the on state. When the PIN diodes are forward-biased and conducting, their effective parameters can be equivalent to a series resistor. When the PIN diode is closed under negative voltage, its effective parameters can be equivalent to a parallel capacitor. .

[0056] Figure 3 The S-parameters, element amplitude, and phase characteristics of the metasurface element for characterizing two digital states, "1" and "0," are presented. Figure 3 As can be seen, the frequency range covers 6.543–7.115 GHz. The reflection coefficients of both states are below -10 dB in the overlapping frequency band (especially between 6.6 GHz and 6.95 GHz). Specifically, the 0 state reaches a minimum of approximately -22 dB at 6.75 GHz, while the π state achieves a minimum of approximately -16 dB at 6.68 GHz.

[0057] Please see Figure 4 and Figure 5 In this embodiment, the metasurface unit is arranged in a 16×16 periodic square grid array, with an overall size of 352mm×352mm, and is fed by a power divider network. For its detailed structure, please refer to [reference needed]. Figure 4 .

[0058] In this embodiment, an equal-amplitude, in-phase feeding network is preferred. Drawing inspiration from Wilkinson power dividers and impedance transformation principles, energy is uniformly distributed to each unit through a step-by-step equal-division method. This structural design is relatively simple, and the metasurface coding strategy is straightforward, making it suitable for systems requiring low cost and rapid deployment. The power divider network can be one or more of the following: microstrip power divider network, waveguide power divider network, substrate-integrated waveguide power divider network, or gapped waveguide power divider network.

[0059] The programmable control module is used to control the on / off state of the PIN diodes of each metasurface unit according to the phase modulation state encoding, so that each metasurface unit independently and programmably modulates the phase of the incident electromagnetic wave according to a preset or dynamically generated encryption key. This enables the reconfigurable metasurface control module to generate a wavefront distribution corresponding to the key image under electromagnetic wave irradiation, so that the receiver cannot obtain effective information without another key image.

[0060] Specifically, the programmable control module employs a field-programmable gate array (FPGA) to control the on / off state of the PIN diodes in each metasurface unit of the reconfigurable metasurface control module by applying different bias voltages according to the phase modulation state code, thereby placing each metasurface unit in a different digitally encoded state. In this embodiment, by controlling the encoding distribution of the units on the reconfigurable metasurface control module, different numbers of highly directional radiation beams can be achieved. For details, please refer to [reference needed]. Figure 5 .

[0061] First, the coding distribution of the metasurface elements is controlled to generate a high-gain single beam. At this point, the coding distribution of each element on the array is as follows: Figure 5 As shown, the obtained three-dimensional spatial radiation pattern is as follows: Figure 6 As shown, the maximum gain of a single beam is 25.8 dB at this point. Next, the effect of multi-beam radiation is further verified by controlling the coding distribution of the metasurface units as follows... Figure 7 As shown, the obtained three-dimensional spatial radiation pattern of the dual-beam radiation is as follows: Figure 8As shown, the excitation generates two symmetrically distributed, highly directional dual-radiation beams, both with a maximum gain of 23.2 dB. This verifies that the programmable control module controls the on / off state of the PIN diodes of each metasurface unit according to the phase modulation state code, enabling each metasurface unit to independently programmably modulate the phase of the incident electromagnetic wave according to a preset or dynamically generated encryption key. This, in turn, allows the reconfigurable metasurface control module to generate a wavefront distribution corresponding to the key image under electromagnetic wave illumination.

[0062] This embodiment integrates visual cryptography and computational holography, and achieves single-pixel visual encryption through a reconfigurable metasurface control module.

[0063] The decryption module receives electromagnetic signals modulated by two key images. Based on the principle of electromagnetic wave superposition, when the two key images are precisely superimposed at the pixel level, the original information is recovered through superposition operations. Specifically, when the two electromagnetic wavefronts are precisely aligned in space and their phases match, the superposition result recovers the encoding pattern of the original 2×2 sub-pixel block.

[0064] In this embodiment, based on the reconfigurable metasurface control module, the key image generated by the encryption encoding module is used to simulate and verify six different VK pixels. (See...) Figure 9 As shown in the figure, each key has a specific phase modulation pattern with a different spatial distribution, and each key corresponds to a metasurface phase code. By adjusting the phase of the metasurface, different encryption effects can be achieved in different regions. Based on this, the present invention will reconstruct VK1 and VK2 information corresponding to different secret messages based on six different VK pixels.

[0065] Figure 10 The different secret messages in the simulation and experiment are clearly explained, showing the decryption results of the generated VK1, VK2, and their superposition. Obviously, a single VK1 or VK2, such as... Figure 10 The simulation and experimental results in the leftmost column show that only meaningless random patterns can be decrypted. In stark contrast, the secret information can only be successfully reconstructed by combining and superimposing the two sets of information (i.e., VK1 and VK2 or their corresponding experimental versions). This is in... Figure 10 This is clearly demonstrated in the rightmost column. This phenomenon highlights the fundamental principle of using metasurface VK pixels for secure information processing: individual components do not carry interpretable data, but their collaborative superposition unlocks hidden content. This is precisely the manifestation of the decryption module recovering the original information based on the principle of electromagnetic wave superposition.

[0066] System robustness verification experiment: In general, an efficient encryption / decryption system must possess excellent robustness to resist malicious noise attacks and attempts to compromise the integrity of ciphertext. This invention proposes a single-pixel visual dynamic encryption / decryption system based on reconfigurable metasurfaces, which integrates the advantages of visual cryptography and computational holography, achieving enhanced robustness while ensuring high security. To comprehensively evaluate the robustness of this system, theoretical research was conducted to verify its ability to recover original information under malicious attacks, including tolerance analysis for various noise modes and resistance analysis to plaintext destruction attacks.

[0067] Considering that individual shared pixels need to be integrated into different VKs, a weighted averaging method is used to analyze overall secret robustness. Noise attacks are applied to six shared pixels, extending to VK and dual-VK overlay decryption analysis. Figure 12 As shown, the noise in the recovered image decreases with increasing noise correlation, maintaining high quality over a wide noise range until the image becomes unrecognizable, highlighting the system's strong noise resistance. Experimental results show that the robustness coefficient Co gradually decreases as the noise correlation increases from 0 to 1, validating the system's tolerance to 65% noise.

[0068] Example 2: Example 1 presents a single-pixel visual dynamic encryption and decryption system for simple letters based on reconfigurable metasurfaces. Furthermore, the encryption encoding module proposed in this example is not limited to letter information, but can be extended to any information type, such as animal shapes and buildings.

[0069] Figure 11 Several sets of complex images are given, each serving as the raw information to be transmitted. First, a digital encoding unit converts the image into a pixel matrix, then a visual secret sharing unit encodes it into two shared keys. The sub-pixel array size is optimized based on image complexity: 30×30 (pedestrians, low complexity), 50×50 (umbrellas, medium complexity), 200×200 (zebras, high complexity), and 300×300 (buildings, very high complexity). This scaling directly corresponds to the complexity of the target image, ensuring that complex details (such as zebra stripes and building facades) are preserved during encryption-decryption. A phase mapping unit maps the pixel information of each key image to phase modulation state codes, where black sub-pixels correspond to 180° phase and white sub-pixels correspond to 0° phase.

[0070] The shared keys generated by the classic VSS algorithm individually exhibit a seemingly random pattern (not providing meaningful decryption), but their superposition reconstructs the original image. Figure 11 The simulation results demonstrate the programmable and tunable capabilities of the metasurface, showcasing its effective encoding of complex visual information. Figure 11Enlarged experimental illustrations reveal subpixel encoding gradients, such as zebra stripes and building windows. Notably, the number of shared pixels required for high-fidelity reconstruction increases exponentially with image complexity (from pedestrians to buildings) (from 30×30 to 300×300), highlighting the scalability of the scheme and its adaptability to rich details.

[0071] Example 3: This embodiment provides a single-pixel visual dynamic encryption and decryption method based on a reconfigurable metasurface. It is implemented on top of the single-pixel visual dynamic encryption and decryption system based on a reconfigurable metasurface described in the above embodiment. That is, those skilled in the art can understand the single-pixel visual dynamic encryption and decryption method based on a reconfigurable metasurface as the operation mode of the single-pixel visual dynamic encryption and decryption system based on a reconfigurable metasurface.

[0072] Specifically, the single-pixel visual dynamic encryption and decryption method based on reconfigurable metasurfaces, using the single-pixel visual dynamic encryption and decryption system based on reconfigurable metasurfaces of Example 1, includes the following steps: Encryption process: Step S1: The original information to be transmitted is converted into a pixel matrix through the encryption encoding module. The pixel matrix is ​​decomposed into two independent key images according to the (2,2) threshold visual secret sharing algorithm, and the pixel information of each key image is mapped to phase modulation state code.

[0073] Specifically, step S1 includes: Step S1.1: The original information to be transmitted is binarized or multi-level grayscale processed by the digital encoding unit to form the corresponding pixel matrix; Step S1.2: The pixel matrix is ​​decomposed into two independent key images by the visual secret sharing unit according to the (2,2) threshold visual secret sharing algorithm. The (2,2) threshold visual secret sharing algorithm includes: expanding each pixel in the pixel matrix into a 2×2 sub-pixel block, and randomly generating the distribution of black sub-pixels and white sub-pixels through the encoding function, so that each key image presents a statistical noise distribution separately. Step S1.3: The pixel information of each key image is mapped to phase modulation state code through the phase mapping unit, where black sub-pixels correspond to 180° phase and white sub-pixels correspond to 0° phase.

[0074] Step S2: The programmable control module controls the on / off state of the PIN diodes of each metasurface unit in the reconfigurable metasurface control module according to the phase modulation state encoding, so that each metasurface unit independently programmably modulates the phase of the incident electromagnetic wave according to the preset or dynamically generated encryption key, thereby enabling the reconfigurable metasurface control module to generate a wavefront distribution corresponding to the key image under electromagnetic wave irradiation.

[0075] Decryption process: Step S3: The decryption module receives two sets of key image modulated electromagnetic signals and spatially superimposes the two sets of electromagnetic signals based on the superposition principle of electromagnetic waves.

[0076] Step S4: The decryption module decrypts the superimposed signal according to the (2,2) threshold visual secret sharing algorithm to recover the original information.

[0077] Those skilled in the art will understand that, besides implementing the system and its various devices, modules, and units provided by this invention in the form of purely computer-readable program code, the same functions can be achieved entirely through logical programming of the method steps, making the system and its various devices, modules, and units of this invention function in the form of logic gates, switches, application-specific integrated circuits, programmable logic controllers, and embedded microcontrollers. Therefore, the system and its various devices, modules, and units provided by this invention can be considered as a hardware component, and the devices, modules, and units included therein for implementing various functions can also be considered as structures within the hardware component; alternatively, the devices, modules, and units for implementing various functions can be considered as both software modules implementing the method and structures within the hardware component.

[0078] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various changes or modifications within the scope of the claims, which do not affect the essence of the present invention. Unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

Claims

1. A single-pixel visual dynamic encryption and decryption system based on reconfigurable metasurface, characterized in that, include: The encryption encoding module is used to convert the original information to be transmitted into a pixel matrix, decompose the pixel matrix into two key images according to the (2,2) threshold visual secret sharing algorithm, and map the pixel information of each key image into phase modulation state code. The reconfigurable metasurface control module consists of multiple reconfigurable metasurface units arranged in a periodic square grid, with each metasurface unit integrating multiple PIN diodes. The programmable control module is used to control the on / off state of the PIN diodes of each metasurface unit according to the phase modulation state encoding, so that each metasurface unit independently programmably modulates the phase of the incident electromagnetic wave according to a preset or dynamically generated encryption key, thereby enabling the reconfigurable metasurface control module to generate a wavefront distribution corresponding to the key image under electromagnetic wave irradiation. The decryption module receives electromagnetic signals modulated by two key images. Based on the principle of electromagnetic wave superposition, when the two key images are superimposed at pixel level, the original information is recovered through superposition operations.

2. The single-pixel visual dynamic encryption / decryption system based on reconfigurable metasurface of claim 1, wherein, The encryption encoding module includes: The digital encoding unit is used to binarize or multi-level grayscale the original information to be transmitted to form a corresponding pixel matrix. The visual secret sharing unit is used to decompose the pixel matrix into two independent key images according to the (2,2) threshold visual secret sharing algorithm. The (2,2) threshold visual secret sharing algorithm includes: expanding each pixel in the pixel matrix into a 2×2 sub-pixel block, and randomly generating the distribution of black sub-pixels and white sub-pixels through an encoding function, so that each key image presents a statistical noise distribution separately. The phase mapping unit is used to map the pixel information of each key image into a phase modulation state code, where black sub-pixels correspond to 180° phase and white sub-pixels correspond to 0° phase.

3. The single-pixel visual dynamic encryption / decryption system based on reconfigurable metasurface of claim 1, wherein, Each metasurface unit integrates two PIN diodes, namely PIN diode I and PIN diode II. The structure of the metasurface unit includes four alternating metal layers and three dielectric layers, which are arranged from top to bottom as follows: PIN diode I and PIN diode II, metal radiation layer and coupling feed structure, upper dielectric substrate, bias control layer, prepreg adhesive sheet, metal ground plane, lower dielectric substrate, and feed network layer.

4. The single-pixel visual dynamic encryption and decryption system based on a reconfigurable metasurface according to claim 3, characterized in that, The relative permittivity and thickness of the upper dielectric substrate are εr1 = 3.55 and h1 = 3.048 mm, respectively; the relative permittivity and thickness of the semi-cured adhesive sheet are εr2 = 3.52 and h2 = 0.404 mm, respectively; and the relative permittivity and thickness of the lower dielectric substrate are εr3 = 3.55 and h3 = 3.048 mm, respectively.

5. The single-pixel visual dynamic encryption and decryption system based on a reconfigurable metasurface according to claim 4, characterized in that, The metal radiating layer consists of two coaxial annular patches, with PIN diode I and PIN diode II integrated at the connection point. The outer elliptical annular patch is connected to the ground plane through two symmetrically distributed metallized vias on the horizontal center line, forming electromagnetic boundary conditions and a reference ground. The inner patch is designed with a Φ-shaped structure and is electrically connected to the feed network layer below through a metallized via penetrating the ground plane at the center, realizing signal injection and modulation.

6. The single-pixel visual dynamic encryption / decryption system based on a reconfigurable metasurface according to claim 4, characterized in that, The bias control layer is connected to the metallized feed probe, and the bias control layer includes symmetrically arranged zigzag distributed inductors and fan-shaped distributed capacitors to filter out radio frequency signals in the bias DC circuit. By applying a preset bias voltage to PIN diodes I and II through a bias control layer, a stable 180° phase difference in space is achieved by utilizing the forward and reverse directions of the excitation current. This allows the reconfigurable metasurface unit bundle to exhibit two different phases: 0 degrees and 180 degrees, corresponding to unit codes "0" and "1," respectively. When the unit code is "1," PIN diode I is in the on state and PIN diode II is in the off state; when the unit code is "0," PIN diode I is in the off state and PIN diode II is in the on state.

7. The single-pixel visual dynamic encryption and decryption system based on a reconfigurable metasurface according to claim 2, characterized in that, The reconfigurable metasurface control module is fed through a power divider network, which is one or more of a microstrip power divider network, a waveguide power divider network, a substrate integrated waveguide power divider network, or a gap waveguide power divider network.

8. The single-pixel visual dynamic encryption / decryption system based on a reconfigurable metasurface according to claim 1, characterized in that, The programmable control module is a field-programmable gate array, used to apply different bias voltages to control the conduction and closing states of the PIN diodes of each metasurface unit in the reconfigurable metasurface control module, so that each metasurface unit is in a different digital encoding state.

9. A single-pixel visual dynamic encryption / decryption method based on a reconfigurable metasurface, characterized in that, The single-pixel visual dynamic encryption and decryption system based on a reconfigurable metasurface as described in any one of claims 1 to 8 includes the following steps: Encryption process: Step S1: The original information to be transmitted is converted into a pixel matrix by the encryption encoding module. The pixel matrix is ​​decomposed into two key images according to the (2,2) threshold visual secret sharing algorithm, and the pixel information of each key image is mapped to phase modulation state code. Step S2: The programmable control module controls the on / off state of the PIN diodes of each metasurface unit in the reconfigurable metasurface control module according to the phase modulation state encoding, so that each metasurface unit independently programmably modulates the phase of the incident electromagnetic wave according to a preset or dynamically generated encryption key, thereby enabling the reconfigurable metasurface control module to generate a wavefront distribution corresponding to the key image under electromagnetic wave irradiation. Decryption process: Step S3: The decryption module receives two electromagnetic signals modulated by the key image and spatially superimposes the two received electromagnetic signals based on the superposition principle of electromagnetic waves. Step S4: The decryption module decrypts the superimposed signal according to the (2,2) threshold visual secret sharing algorithm to recover the original information.

10. The single-pixel visual dynamic encryption / decryption method based on a reconfigurable metasurface according to claim 9, characterized in that, Step S1 includes: Step S1.1: The original information to be transmitted is binarized or multi-level grayscale processed by the digital encoding unit to form the corresponding pixel matrix; Step S1.2: The pixel matrix is ​​decomposed into two independent key images by the visual secret sharing unit according to the (2,2) threshold visual secret sharing algorithm. The (2,2) threshold visual secret sharing algorithm includes: expanding each pixel in the pixel matrix into a 2×2 sub-pixel block, and randomly generating the distribution of black sub-pixels and white sub-pixels through the encoding function, so that each key image presents a statistical noise distribution separately. Step S1.3: The pixel information of each key image is mapped to phase modulation state code through the phase mapping unit, where black sub-pixels correspond to 180° phase and white sub-pixels correspond to 0° phase.

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