A metamaterial-based air-water cross-medium encrypted acoustic holographic communication device, method and equipment

Abstract

The present application relates to the technical field of acoustic secret communication, and relates to an air-water cross-medium encrypted acoustic holographic communication device, method and equipment based on metamaterials. Different image information transmitted through two channels of amplitude and phase is encrypted by a specific encryption super-surface device located at the air-water interface in an initial sound field, an encrypted sound field is formed in an underwater environment, and a key super-surface of the corresponding channel is placed in the encrypted sound field to restore and decrypt the holographic image. The super-surface of the present application can decouple the amplitude and phase of the modulated sound wave, and according to the time reversal symmetry and the superposition principle of the sound wave, the transmitted sound field after super-surface modulation can present a pre-designed amplitude and phase distribution. The present application realizes high communication capacity of acoustic information secret transmission. It is especially suitable for occasions where electromagnetic waves and light waves cannot propagate in air-water cross-medium.

Description

Technical Field

[0001] This invention relates to the field of acoustic secure communication technology, and in particular to an air-water cross-medium encrypted acoustic holographic communication device, method and equipment based on metamaterials. Background Technology

[0002] Underwater wireless communication based on light and electromagnetic waves faces significant limitations, making sound waves a more crucial element in such scenarios. Since human activities primarily occur in the air, sound wave transmission and control across the air-water interface has broader applications than purely underwater acoustic modulation and transmission. However, the significant difference in acoustic impedance between air and water means that only 0.1% of acoustic energy can penetrate the air-water interface, severely limiting cross-medium communication. Under natural conditions, a 0.1% acoustic energy transmission efficiency (i.e., a loss of 30 dB) is equivalent to the loss experienced by underwater sound at 10 kHz over a cumulative propagation distance of over 30 kilometers. Compared to traditional impedance matching techniques, metamaterials for high transmission rates and wavefront manipulation at the air-water interface have become significantly thinner and more practical, laying the foundation for air-to-water acoustic communication. Summary of the Invention

[0003] The purpose of this invention is to address the problems existing in the background technology by proposing a method, device, and equipment for bifacial multi-channel asymmetric encrypted acoustic holographic communication based on metamaterials. This communication technology can greatly expand channel capacity, improve communication security, and has practical application prospects. Amplitude-phase channel encrypted acoustic holographic communication provides a secure acoustic communication framework, which has guiding significance for various acoustic applications, including secure communication and underwater communication.

[0004] The technical solution of the present invention, the first aspect of the present invention proposes an air-water cross-medium encrypted acoustic holographic communication device based on metamaterials, including a transmitter array, a receiver and three metasurfaces; The transmitter array is used to transmit image information in pre-designed amplitude and phase channels; the information in each of the two channels should each contain transmission information of the transmitted field and the reflected field; The receiver is used to receive sound signals in the sound field and to perform sound field scanning and imaging; Among them, the metasurface includes two types: encrypted metasurface and key metasurface. There is one encrypted metasurface and two key metasurfaces, which are the transmitted sound field amplitude key and the transmitted sound field phase key, respectively. The transmitter array is used to transmit different image information that needs to be transmitted in the amplitude channel and the phase channel, respectively; The encrypted metasurface, located at the air-water interface, encrypts the holographic image emitted by the source array in the air medium, generating scrambled information which is then transmitted into the underwater environment. The amplitude key metasurface receives scrambled information at a working position at a specific distance from the encryption metasurface in the underwater encryption field acoustic field. After transmission through the scrambled information, the decrypted and restored amplitude channel acoustic field is obtained. The phase key metasurface receives scrambled information at a working position at a specific distance from the encryption metasurface in the underwater encryption field, and obtains the decrypted and restored phase channel sound field through its transmission.

[0005] The amplitude (phase) key metasurface substrate is a high-strength metal (tungsten) perforated plate with a superhydrophobic coating (PTFE film) on both sides. The hydrophobic properties and the high acoustic impedance difference between the tungsten plate and water are used to avoid the acoustic-structure coupling effect of sound waves in water.

[0006] Preferably, the transmitter array uses pre-designed holographic image information to obtain the transmission parameter matrix through time reversal symmetry, and the image of any channel in the original sound field of the transmission is the image after coupling of the information of two channels.

[0007] Preferably, the encrypted metasurface encrypts the channel-coupled holographic image emitted by the transmitter array by introducing a random number encryption matrix. After encryption, both the amplitude channel and the phase channel in the encrypted sound field produce garbled images that cannot be read.

[0008] Preferably, due to the difference in sound speed between air and water, the hologram itself will be distorted after entering the water. The encrypted metasurface compensates for this distortion by introducing a correction matrix, so that the encrypted image of the encrypted sound field matches the pre-design.

[0009] Preferably, the key metasurface is designed according to the holographic image to be transmitted and the working position as planned. At the working position in the encrypted sound field, the corresponding scrambled information is received, and after transmission through the key metasurface, the decrypted and restored sound field can be obtained. In the encrypted sound field, depending on the type of decryption metasurface, the original holographic image of the corresponding channel can be obtained.

[0010] Preferably, the key metasurface is in the form of a perforated plate, utilizing the nonlocal effect between the vias to modulate the transmitted sound waves and reconstruct the original sound field. The specific positions of the vias are obtained through optimization using a genetic algorithm.

[0011] Preferably, the encrypted metasurface freely and independently modulates the amplitude and phase of the transmitted acoustic wave.

[0012] Preferably, the key metasurface decouples the channel coupling in the original unencrypted sound field when decrypting and restoring information; the key metasurface decouples the channel coupling in the original unencrypted sound field when decrypting and restoring information.

[0013] A second aspect of the present invention proposes a method for encrypted acoustic holographic communication between air and water based on metamaterials, using the aforementioned device for communication, comprising the following specific steps: S1. Pre-design the image information to be transmitted, with the amplitude channel and phase channel transmitting different image information; S2. Determine the emission parameter matrix of the emission source array, including the amplitude matrix and the phase matrix; S3. Arrange the encrypted metasurface at the pre-set location; S4. Arrange the key metasurface at a predetermined position in the encrypted sound field after transmission through the encrypted metasurface; Based on the pre-designed amplitude and phase channel information, each of which should contain the original information to be transmitted to the transmission field and the reflection field, the transmission parameters of the ultrasonic emission source array are obtained through the time reversal method. The ultrasonic emission source array emits ultrasonic waves according to the corresponding emission parameters to form an initial sound field. The amplitude and phase distribution in the initial sound field correspond to the pre-designed amplitude and phase channel image information. After modulation by the air-water interface encrypted metasurface, an encrypted sound field is generated on the transmission side of the metasurface. Directly probing the encrypted sound field image will only yield an unreadable image. After the key metasurface is placed at the corresponding position in the underwater encrypted sound field, the amplitude / phase distribution in the sound field modulated by the key metasurface will reproduce the pre-designed image information.

[0014] Preferably, there is a time-reversal symmetry between the pre-designed transmitted image information and the transmission parameter matrix of the transmitter array, and each transmitter in the transmitter array can be regarded as a point source of an acoustic spherical wave; the wave function of the acoustic spherical wave can be expressed as:

[0015] In the formula, p represents sound pressure level and A represents amplitude. Let r represent the phase, r represent the propagation distance of the spherical wave, and k represent the wave number of the sound wave. i The imaginary unit is used; a holographic image is the superposition of these spherical waves, the amplitude channel is the amplitude of the superimposed sound wave, and the phase channel is the phase of the superimposed sound wave.

[0016] Preferably, the metasurface can arbitrarily modulate the amplitude and phase of the transmitted sound wave. By introducing a random number matrix, the preset image information in the original sound field is destroyed, so that the image information becomes garbled in the encrypted sound field. Different key metasurfaces are designed according to pre-given channel image information and placement positions. They perform amplitude-phase modulation on the received scrambled information and obtain the original image information of the corresponding channel in the decryption sound field transmitted through them.

[0017] A third aspect of the present invention provides an air-water cross-medium encrypted acoustic holographic communication device based on metamaterials, applied to the above-mentioned device, comprising an array of 256 ultrasonic transducers with a diameter of 1 cm, an FPGA controller, a memory and a processor, and a transducer probe for receiving ultrasonic waves.

[0018] Compared with the prior art, the present invention has the following beneficial technical effects: 1. It expands the new acoustic holographic communication channel, and also uses phase information as a channel for communication transmission; 2. It solves the problem of low cross-medium acoustic information transmission efficiency caused by the huge difference in acoustic impedance between air and water; 3. It solves the coupling problem of dual-channel image information transmission. Each channel has a corresponding key, realizing asymmetric encryption of acoustic holography. The decrypted information does not contain the original information of other channels. 4. High image fidelity; the metasurface can independently modulate the amplitude and phase of the transmitted wave. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the workflow of the present invention; Figure 2 This is a schematic diagram of the transmitter array of the present invention; Figure 3 This is a schematic diagram of the coupled image information between the emission source array and the original sound field in this invention; Figure 4 This is a schematic diagram of holographic image distortion caused by a sudden change in the medium in this invention; Figure 5 This is a schematic diagram illustrating the working principle of the encrypted metasurface of the present invention; Figure 6 This is a schematic diagram illustrating the differences between the key metasurface of this invention and traditional metamaterials; Figure 7 This is a schematic diagram showing the structure of the encrypted metasurface of the present invention and the amplitude and phase response of the modulated acoustic wave; Figure 8 This is a simulation result of the encrypted metasurface and an enlarged schematic diagram of the C-layer structure of the present invention. Detailed Implementation

[0020] Example 1 This embodiment provides an air-water cross-medium encrypted acoustic holographic communication device, method, and equipment based on metamaterials, such as... Figure 1 As shown, in this embodiment of the invention, the pre-designed amplitude channel image is represented by the letter A, and the pre-designed phase channel image is represented by the letter M. This is achieved by a transmitter array (40kHz ultrasonic transducer array, such as...). Figure 2 As shown), it is emitted as Figure 3The amplitude channel and phase channel information that can be extracted from the original sound field shown are coupled, that is, A can be seen in the phase channel and M can be seen in the amplitude channel, which causes information leakage.

[0021] like Figure 4 As shown, assuming the original pre-designed pattern only contains the letter A in the amplitude channel and no pre-designed image in the phase channel, the acoustic holographic amplitude image obtained in the air after transmission through the transducer array is the letter A. The pseudo-mask in the figure is a fictitious structure assuming 100% acoustic wave transmittance and no effect on the acoustic wave phase. It is only used to illustrate the image distortion caused by changes in wave velocity and wavelength due to abrupt changes in the medium.

[0022] like Figure 5 As shown, a random number array with elements ranging from 0 to 1 and another random number array with elements ranging from 0 to 2π are constructed, with the number of rows and columns of the matrices matching the number of rows and columns of the cells in the encrypted metamaterial mask. The amplitude of the incident sound wave received by each cell is multiplied by the corresponding element value in the random number matrix (0-1) to obtain the source amplitude matrix in the encrypted sound field. Similarly, the phase value of the incident sound wave received by each cell is added to the corresponding element value in the random number matrix (0-2π) to obtain the source phase matrix in the reflected encrypted sound field. The modulation of the correction matrix also needs to be considered. Whether in water or air, the principle of acoustic holography is based on the superposition and coherence of sound waves. Since the unit size of the metamaterial mask is subwavelength, each unit is considered a point source of spherical waves. The spherical wave equation can be expressed as:

[0023] Here, wave number k = 2 π / λ =2 πf / c ,and k Air / k Water = 4.36, which means that the phase change of sound waves in air is more rapid. To maintain the same sound field distribution, the propagation distance of sound waves in water needs to be approximately 4.36 times that in air, and the size of the holographic planar unit must also be enlarged accordingly based on geometric similarity. However, the encrypted metamaterial mask is in contact with both water and air, making it impossible to simultaneously satisfy the proportional size requirements for both wavelengths. Therefore, two new correction matrices need to be introduced to counteract this effect under the condition of wavelength variation. Assume that the encrypted metamaterial mask is made of... x × y Composed of several units, the encrypted hologram contains... p × q pixels, imaging distance is t Pixels p , q ) and unit (x , y The distance between them can be expressed as:

[0024] The complex sound pressure of an underwater encrypted hologram can be expressed as:

[0025] Therefore, the elements in the amplitude distortion matrix can be represented as:

[0026] The elements in the phase distortion matrix can be represented as:

[0027] At this point, the distortion matrix can be written as a complex matrix in the form of complex sound pressure:

[0028] D pq It is a dimension of p × q The matrices are matrices, while the correction matrices can only be attached to the holographic plane, and their dimensions must be 1. x × y Therefore, only when x = p = y = q That is, when the two dimensions are exactly the same, the problem can be solved analytically; otherwise, it is an underdetermined problem and can only be solved numerically through iterative algorithm optimization.

[0029] For cases with the same dimension, the complex sound pressure of the underwater encrypted hologram needs to be calculated first. p Water (dimension is) x × y Vectorization xy × 1 In vector form, without considering changes in the medium, the complex sound pressure propagating to this point is... The following relationship exists:

[0030] in D xy It is the original x × y Each element is placed in dimension 1. xy × xy On the diagonal of the matrix, therefore D xy It is a diagonal matrix. This is because if D xy off-diagonal elementsD kl ( k ≠ l If ) is not 0, then:

[0031] This means the image surface point k The field was occupied by other points l The fields are mixed, but the distortion matrix should actually describe a comparison of point-to-point distortions in different media. Equation 5.26 can be further written as:

[0032] in It is a complex vector composed of the initial amplitude-phase matrix and the phase matrix of the mask unit after encryption and modulation:

[0033] in The initial amplitude, This is the initial phase. And in Equation 5.28... M xy for:

[0034] The inverse of the above equation can be obtained as follows:

[0035] Among them are

[0036] After transforming the vector into a matrix, we obtain the magnitude correction matrix and the phase correction matrix, respectively. , It should be noted that, because passive metamaterials cannot amplify large amplitudes, for In this case, truncation is required, so that... .

[0037] Experiments were conducted on the above embodiments, and the results are as follows: like Figure 6 As shown, the key metasurface in the form of a perforated plate can avoid the acoustic-structure coupling (fluid-structure coupling) phenomenon that occurs in the internal structure of traditional metamaterials underwater due to its ultrathin characteristics in the thickness direction.

[0038] like Figure 7As shown, all cells of the encrypted metasurface have similar structures, differing only in the values ​​of geometric parameters a and b. Parameter a determines the size of the air-side inlet (layer A) of the encrypted metasurface, which in turn determines the relative acoustic impedance of the metasurface, thus controlling the acoustic transmittance and altering the amplitude of the transmitted wave. Parameter b controls the length of the curved channel in layer B, determining the acoustic path length and thus affecting the phase lag of the transmitted wave. The specific amplitude and phase response simulation results are shown below. Figure 7 As shown.

[0039] like Figure 8 As shown in the figure, the simulation cloud map shows that the phase modulation effect of the encrypted metasurface is good. The hysteresis of the acoustic wave phase is achieved by controlling the length of the air channel in layer B by parameter b. The right figure shows the specific structure and boundary conditions of layer C of the encrypted metasurface.

[0040] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A trans-medium encrypted acoustic holographic communication device based on metamaterials, characterized in that, Includes a transmitter array, a receiver, and three metasurfaces; The transmitter array is used to transmit image information with pre-designed amplitude and phase channels; The receiver is used to receive sound signals in the sound field and to perform sound field scanning and imaging; Among them, the metasurface includes two types: encrypted metasurface and key metasurface. There is one encrypted metasurface and two key metasurfaces, which are the transmitted sound field amplitude key and the transmitted sound field phase key, respectively. The transmitter array is used to transmit different image information that needs to be transmitted in the amplitude channel and the phase channel, respectively; The encrypted metasurface, located at the air-water interface, encrypts the holographic image emitted by the source array in the air medium, generating scrambled information which is then transmitted into the underwater environment. The amplitude key metasurface receives scrambled information at a working position at a specific distance from the encryption metasurface in the underwater encryption field acoustic field. After transmission through the scrambled information, the decrypted and restored amplitude channel acoustic field is obtained. The phase key metasurface receives scrambled information at a working position at a specific distance from the encryption metasurface in the underwater encryption field, and obtains the decrypted and restored phase channel sound field through its transmission.

2. The air-water cross-medium encrypted acoustic holographic communication device based on metamaterials according to claim 1, characterized in that, The transmitter array uses pre-designed holographic image information to obtain the transmission parameter matrix through time reversal symmetry. The image of any channel in the original sound field of the transmission is the image after coupling of information from two channels.

3. The air-water cross-medium encrypted acoustic holographic communication device based on metamaterials according to claim 1, characterized in that, The encrypted metasurface encrypts the channel-coupled holographic image emitted by the transmitter array by introducing a random number encryption matrix.

4. The air-water cross-medium encrypted acoustic holographic communication device based on metamaterials according to claim 1, characterized in that, Encrypted metasurfaces freely and independently modulate the amplitude and phase of transmitted acoustic waves.

5. The air-water cross-medium encrypted acoustic holographic communication device based on metamaterials according to claim 1, characterized in that, A layer of perforated metal plate coated with a hydrophobic layer is set on the key metasurface.

6. The air-water cross-medium encrypted acoustic holographic communication device based on metamaterials according to claim 1, characterized in that, When decrypting and restoring information, the key metasurface decouples the channel coupling in the original unencrypted sound field.

7. A method for encrypted acoustic holographic communication between air and water based on metamaterials, using the device described in any one of claims 1-6 for communication, characterized in that... The specific steps include the following: S1. Pre-design the image information to be transmitted, with the amplitude channel and phase channel transmitting different image information; S2. Determine the emission parameter matrix of the emission source array, including the amplitude matrix and the phase matrix; S3. Arrange the encrypted metasurface at the pre-set location; S4. Arrange the key metasurface at a pre-defined position in the encrypted sound field after transmission through the encrypted metasurface.

8. The air-water cross-medium encrypted acoustic holographic communication method based on metamaterials according to claim 7, characterized in that, There is a time-reversal symmetry between the pre-designed transmitted image information and the transmission parameter matrix of the transmitter array. Each transmitter in the transmitter array can be regarded as a point source of an acoustic spherical wave; the wave function of the acoustic spherical wave can be expressed as: In the formula, p represents sound pressure level, and A represents amplitude. Let r represent the phase, r represent the propagation distance of the spherical wave, and k represent the wave number of the sound wave. i The imaginary unit is used; a holographic image is the superposition of these spherical waves, the amplitude channel is the amplitude of the superimposed sound wave, and the phase channel is the phase of the superimposed sound wave.

9. The air-water cross-medium encrypted acoustic holographic communication method based on metamaterials according to claim 7, characterized in that, Metasurfaces can arbitrarily modulate the amplitude and phase of transmitted sound waves. By introducing a random number matrix, the preset image information in the original sound field is destroyed, causing the image information to become garbled in the encrypted sound field. Different key metasurfaces are designed according to pre-given channel image information and placement positions. They perform amplitude-phase modulation on the received scrambled information and obtain the original image information of the corresponding channel in the decryption sound field transmitted through them.

10. An air-water cross-medium encrypted acoustic holographic communication device based on metamaterials, applied to the apparatus described in any one of claims 1-6, characterized in that, It includes an array of 256 ultrasonic transducers, each 1 cm in diameter, an FPGA controller, a memory and processor, and a transducer probe for receiving ultrasonic waves.

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