Ka-band scattering electromagnetic tags and scattering methods based on time-controlled metasurfaces

Abstract

This application discloses a Ka-band scattering electromagnetic tag based on a time-controlled metasurface and a scattering method. The scattering electromagnetic tag includes a time-controlled metasurface for receiving point-frequency signals or incident radar waves; its scattering state is controlled by applying different voltage values; when the FPGA control module generates corresponding high and low level control signals according to pre-stored time modulation codes, the state of the electromagnetic tag metasurface array changes accordingly, thereby modulating the information onto the radar scattered wave and completing the modulation of the scattered echo; the FPGA control module is used to change the voltage amplitude output of different channels in the time-controlled metasurface according to pre-stored time modulation code information to control the reflection phase of the time-controlled metasurface and thus change the scattering state of the time-controlled metasurface. Compared with traditional designs, this application has the characteristics of small size and low power consumption, effectively improving the cooperative scattering capability of the target in the Ka-band.

Description

Technical Field

[0001] This application relates to the field of electromagnetic functional materials technology, and in particular to a Ka-band scattering electromagnetic tag based on a time-controlled metasurface and a scattering method. Background Technology

[0002] In modern complex electromagnetic environments, scattering technology is a research area of ​​continuous interest. Due to the advantages of high-frequency radar over low-frequency radar—low cost, small size, and high precision—current research on radar scatterers mainly focuses on the high-frequency band, such as DDS-based high-frequency radar scatterers and all-digital high-frequency radar scatterers. However, current high-frequency radar scatterers all face challenges such as receiver phase calibration, delay control, and the accuracy of target echo simulation. In this context, electromagnetic metasurfaces, with their unique ability to manipulate spatial electromagnetic waves and their low complexity and low cost, offer a potential solution for modern scattering technology, making research on metasurface-based electromagnetic tags undoubtedly of great significance.

[0003] C. Hilton and JA Nanzer, “NarrowbandPassive RF Tags for Frequency-Selective Harmonic Doppler Radar Tracking,” IEEE Trans. Antennas Propagat (vol. 71, no. 2, pp. 1216–1222, Feb. 2023) proposed a frequency-selective radio frequency harmonic tag for harmonic Doppler radar tracking. The tag integrates a circular antenna, a dipole antenna, and a diode. It utilizes the narrowband operation of the circular antenna to perform narrowband filtering on the received signal, and then uses the nonlinear characteristics of the diode to generate a second-order harmonic signal, which is radiated by the dipole antenna, thereby achieving harmonic scattering of a specific frequency signal. However, since this design can only generate second-order harmonic signals, it has the disadvantage of a single scattering form. The patent application CN202311286344.9 proposes a passive intelligent scattering system and method based on amplitude-coded metasurfaces in the Ka band. This system can determine whether the received signal is a friendly signal, thereby giving the radar echo signal different characteristics and achieving scattering or electromagnetic stealth. Although it has relatively complete functions, it has the disadvantages of high system complexity and large volume due to the need to receive and process the signal, which leads to the addition of a post-processing system structure, thus limiting its application scenarios. Summary of the Invention

[0004] The purpose of this application is to provide a Ka-band scattering electromagnetic tag and scattering method based on a time-controlled metasurface. The scattering encoding combined with pseudo-random encoding technology can realize the cooperative scattering function. The tag storage encoding can be updated by the host computer. By combining phase and spectral encoding scattering methods, cooperative passive scattering with multiple encodings can be achieved in complex electromagnetic environments.

[0005] This application discloses a Ka-band scattering electromagnetic tag based on a time-controlled metasurface, which includes an electromagnetic tag metasurface array with electrically tunable scattering state and an FPGA control module that adjusts the time-controlled metasurface according to the time modulation encoding sequence; the electromagnetic tag metasurface array is composed of multiple time-controlled metasurfaces.

[0006] The time-controlled metasurface is used to receive incident radar waves from the detection radar in the form of point frequency signals or linear frequency modulated pulse signals; its scattering state is controlled by applying different voltage values; when the FPGA control module generates corresponding high and low level control signals according to the pre-stored time modulation code, the state of the electromagnetic tag metasurface array will change accordingly, thereby modulating the information on the radar scattered wave and completing the regulation of the scattered echo.

[0007] The FPGA control module is used to change the voltage amplitude of different channels output in the time-controlled metasurface according to the pre-stored time modulation coding information, so as to control the reflection phase of the time-controlled metasurface and realize the change of the scattering state of the time-controlled metasurface.

[0008] Furthermore, the FPGA control module includes an encoding storage module, an encoding reading module, and a voltage output module;

[0009] The encoding storage module is used to store an encoding file containing the multi-channel encoding order and the set symbol frequencies; the encoding file includes scattering information, pseudo-random encoding, and channel encoding;

[0010] The encoding reading module is used to read the time modulation encoding information in the encoding storage module and control the voltage output module to output high and low levels according to the encoding information;

[0011] The voltage output module is controlled by the encoding and reading module and is used to convert the time modulation encoding information of different channels into corresponding time-varying high and low levels, adjust the voltage amplitude of the multi-channel electromagnetic tag metasurface array, and thus control the reflection phase of the electromagnetic tag metasurface array.

[0012] Furthermore, the electromagnetic tag metasurface array is composed of multiple time-controlled metasurface basic units arranged periodically;

[0013] The FPGA control module is used to control the on / off state of the PIN diodes loaded in the basic unit of the electromagnetic tag metasurface array by outputting high and low levels through multiple channels and using voltage values, thereby controlling the phase of the scattered wave and making the scattering state of the electromagnetic tag metasurface array change with time according to a preset time modulation code.

[0014] Furthermore, the electromagnetic tag metasurface array includes a basic unit layer, a dielectric substrate, and a metal ground layer arranged sequentially from top to bottom;

[0015] The basic unit consists of parallel metal strip patches and semiconductor devices loaded between the parallel metal strip patches. By changing the voltage loaded across the semiconductor devices, the on / off state of the semiconductor devices is changed, thereby switching the scattering state of the electromagnetic tag metasurface array; the metal ground layer provides grounding for the semiconductor devices.

[0016] Furthermore, each basic unit in the electromagnetic tag metasurface array extends along the long side of the metal strip patch to form a column, and each column of basic units forms a subarray. The subarrays are periodically arranged along the short side of the metal strip patch to form the electromagnetic tag metasurface array.

[0017] The voltage output module is a multi-channel output, with each channel corresponding to a subarray in the electromagnetic tag metasurface array. By adjusting the input voltage of each subarray, the semiconductor device can be switched between different states. By switching the on and off states of the semiconductor device, each subarray can achieve two scattering states: 0° phase and 180° phase.

[0018] This application also discloses a scattering method for a Ka-band scattering electromagnetic tag based on a time-controlled metasurface, applicable to the aforementioned Ka-band scattering electromagnetic tag based on a time-controlled metasurface, comprising:

[0019] Step 1: The encoding storage module stores the encoding file containing the multi-channel encoding order and the set symbol frequencies; the encoding file includes scattering information, pseudo-random encoding, and channel encoding.

[0020] Step 2: The encoding reading module reads the time modulation encoding information in the encoding storage module and controls the voltage output module to output high and low levels according to the encoding information;

[0021] Step 3: The voltage output module is controlled by the encoding and reading module to convert the time modulation encoding information of different channels into corresponding time-varying high and low levels, and adjust the voltage amplitude of the multi-channel electromagnetic tag metasurface array, thereby controlling the reflection phase of the electromagnetic tag metasurface array.

[0022] Step 4: The adjusted output voltage changes the scattering state of the electromagnetic tag metasurface array, modulating the time modulation coding information onto the radar scattering echo, thereby realizing the electromagnetic tag's control over the radar signal's scattering echo.

[0023] Further, step 4 includes:

[0024] When the electromagnetic waves emitted by the radar are incident on the timing-controlled metasurface, the metasurface is divided into N columns of modulation units. When the electromagnetic waves emitted by the radar are point-frequency signals, the time modulation coding uses phase coding to control the scattered echo, obtaining the time-domain signal of the scattered coded echo received by the radar. By bandpass filtering the time-domain signal of the scattered coded echo, the phase scattering coded signal can be recovered. This enables the modulation of the scattered echo of the point frequency signal.

[0025] Furthermore, in step 4:

[0026] Assume the electromagnetic tag metasurface array is divided into N columns of modulation units in the x-direction, with a unit spacing of d, and each column extends along the y-direction, meaning it has the same response in the y-direction. The electromagnetic wave emitted by the radar has a center frequency of... Angle of incidence The modulation frequency of the electromagnetic tag metasurface array is irradiated onto the time-controlled metasurface. far below The scattered electromagnetic waves of the electromagnetic tag metasurface array are then represented as:

[0027] (1)

[0028] in, It is a scattered electromagnetic wave. Phase encoding of scattering information, Time modulation encoding for the nth column cell, It is a pseudo-random code. and All modulation units of the electromagnetic tag metasurface array are identical. For electromagnetic wave number, , c Let t be the speed of light, and t be time. This indicates the observation angle of a single radar station.

[0029] Furthermore, step 4 specifically includes:

[0030] If the time modulation sequences of each column are the same, then ;

[0031] When a radar receives a point-frequency incident signal, it uses phase-coded scattering. It appears as a binary coded sequence. This is time modulation coding, and the timing sequence of time modulation coding is as follows:

[0032] (2)

[0033] in, Represents the i-th time modulation period , ,right Perform a Fourier transform to obtain Where h represents the harmonic order, The corresponding harmonic coefficients; Indicates the i-th time modulation frequency;

[0034] Because the ±1st harmonic amplitude is the highest, therefore, ignoring the influence of higher-order harmonics, i.e. At that time, the time-domain signal of the scatter-coded echo received by our own radar is:

[0035] (3)

[0036] in, The scattering-encoded echo time-domain signal; , These are the ±1st harmonic amplitudes, respectively;

[0037] If there is interference signal , To represent the amplitude of the interference signal, the time signal of our own radar after pseudo-random demodulation is expressed as:

[0038] (4)

[0039] in, The time signal is after pseudo-random demodulation;

[0040] Through the By performing bandpass filtering, the phase encoding of the scattering information can be recovered. This enables the scattering of point frequency signals.

[0041] Further, step 4 includes:

[0042] The electromagnetic waves emitted by the radar are incident on the electromagnetic tag metasurface array, which is divided into N columns of modulation units. When the electromagnetic waves emitted by the radar are linear frequency modulated pulse signals... hour,

[0043] (5)

[0044] Where t is time, Indicates the pulse width. For frequency modulation slope and , For signal bandwidth, The center frequency; It is a rectangular window function, in The value is 1 within the specified time range and 0 elsewhere;

[0045] The electromagnetic tag metasurface array uses spectral coding for scattering, directly scattering time-modulated signals. Multiple frequency codes are used, and their spectral characteristics are used as scattering codes to de-skew the reflected waves of the linear frequency modulated wave emitted by the radar on the time-controlled supersurface, recover the phase of the coded signal, and then perform pseudo-random demodulation. The spectrum of the demodulated signal is the scattering coded spectrum, thereby realizing the scattering of the linear frequency modulated signal.

[0046] Furthermore, step 4 specifically includes:

[0047] Time modulation coding Multiple frequency codes are employed, and their spectral characteristics are used as scattering codes. for:

[0048] (6)

[0049] in, Indicates the first n A single-cycle modulated signal, total N Seed; Set The modulus of all values ​​is 1, and pseudo-random coding is introduced. The scattered echo of the linear frequency modulated pulse signal emitted by the radar on the metasurface array of the electromagnetic tag can be represented as N single-period modulated signals; after modulating the linear frequency modulated signal, the sum of the corresponding infinite order harmonics is generated:

[0050] (7)

[0051] in, It is the reflected wave, that is, the sum of infinite order harmonics. Let be the amplitude of the h-th harmonic of the n-th modulation signal. It is a rectangular window function, in The value is 1 within the specified time range and 0 elsewhere. Let n be the modulation frequency of the nth modulation signal. Let B be the frequency modulation slope of the linear frequency modulated pulse signal, and let B be the bandwidth of the linear frequency modulated pulse signal. The pulse width of a linear frequency modulated pulse signal, where h is the order of the harmonics;

[0052] After introducing pseudo-random coding, the scattered echo is de-skewing to recover the phase of the coded signal. Then, pseudo-random demodulation is performed, and the Fourier transform of the demodulated signal yields the scattering spectrum. Its spectral characteristics constitute the spectral coding. The scattering spectrum is expressed as:

[0053] (8)

[0054] in, The scattering spectrum, For Fourier transform, The conjugate of the linear frequency modulated signal, Fourier transform of a single-cycle modulated signal;

[0055] The spectral encoding is obtained from the scattered echo, thereby enabling the scattering control of the linear frequency modulated signal.

[0056] Due to the adoption of the above technical solution, this application has the following advantages:

[0057] (1) The scattering tag is a passive scattering system. The overall module has been integrated, which has the advantages of lower power consumption, smaller size and more flexible application scenarios compared with the secondary scattering system.

[0058] (2) When scattering tags are combined with the air-conditioned metasurface, a variety of complex codes can be achieved. The scattering methods include phase scattering and spectral scattering. Combined with pseudo-random coding technology, the cooperating party can identify the scattering coded signal, while the non-cooperating party cannot obtain the scattering coded signal, thus having the characteristics of cooperative work. Attached Figure Description

[0059] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments recorded in the embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings.

[0060] Figure 1 This is a block diagram illustrating the overall principle of the Ka-band scattering electromagnetic tag based on a time-controlled metasurface in this application embodiment.

[0061] Figure 2 This is a schematic diagram of the array structure of the time-cooled metasurface in an embodiment of this application;

[0062] Figure 3 This is a schematic diagram of the unit structure of the time-cooled metasurface in the embodiments of this application;

[0063] Figure 4This is a graph showing the reflection coefficient of the air conditioning metasurface unit in the embodiment of this application as a function of frequency when the PIN diode is conducting under high and low voltage levels.

[0064] Figure 5 These are the measured results of the reflection coefficient of the air-conditioning metasurface in the embodiments of this application;

[0065] Figure 6(a) is the test result of the electromagnetic tag encoding and scattering of the external point frequency incident signal in the embodiment of this application - the signal spectrum obtained by measured demodulation;

[0066] Figure 6(b) shows the test results of the electromagnetic tag encoding and scattering of external point frequency incident signals in the embodiments of this application - the measured recovered time-domain phase diagram;

[0067] Figure 7(a) is the test result of the electromagnetic tag encoding and scattering of the external linear frequency modulated incident signal in the embodiment of this application - the measured spectrum distribution of spectrum scattering encoding one;

[0068] Figure 7(b) is the test result of the electromagnetic tag encoding and scattering of the external linear frequency modulated incident signal in the embodiment of this application - the measured spectrum distribution of spectrum scattering encoding two. Detailed Implementation

[0069] The present application will be further described in conjunction with the accompanying drawings and embodiments. The described embodiments are only some, not all, of the embodiments of the present application. All other embodiments obtained by those skilled in the art should fall within the protection scope of the embodiments of the present application.

[0070] See Figure 1 As shown, this application provides an embodiment of a Ka-band scattering electromagnetic tag based on a time-controlled metasurface, which includes an electromagnetic tag metasurface array with electrically adjustable scattering state and an FPGA control module that adjusts the time-controlled metasurface according to the time modulation coding timing; the electromagnetic tag metasurface array is composed of multiple time-controlled metasurfaces;

[0071] The time-controlled metasurface is used to receive incident radar waves from the detection radar in the form of point frequency signals or linear frequency modulated pulse signals; its scattering state is controlled by applying different voltage values; when the FPGA control module generates corresponding high and low level control signals according to the pre-stored time modulation code, the state of the electromagnetic tag metasurface array will change accordingly, thereby modulating the information on the radar scattered wave and completing the regulation of the scattered echo.

[0072] The FPGA control module is used to change the voltage amplitude of different channels output in the time-controlled metasurface according to the pre-stored time modulation coding information, so as to control the reflection phase of the time-controlled metasurface and realize the change of the scattering state of the time-controlled metasurface.

[0073] Optionally, the FPGA control module includes an encoding storage module, an encoding reading module, and a voltage output module;

[0074] The encoding storage module is used to store an encoding file containing the multi-channel encoding order and the set symbol frequencies; the encoding file includes scattering information, pseudo-random encoding, and channel encoding;

[0075] The encoding reading module is used to read the time modulation encoding information in the encoding storage module and control the voltage output module to output high and low levels according to the encoding information;

[0076] The voltage output module is controlled by the encoding and reading module and is used to convert the time modulation encoding information of different channels into corresponding time-varying high and low levels, adjust the voltage amplitude of the multi-channel electromagnetic tag metasurface array, and thus control the reflection phase of the electromagnetic tag metasurface array.

[0077] Optionally, see Figure 2 and Figure 3 The electromagnetic tag metasurface array is composed of multiple time-controlled metasurface basic units arranged periodically.

[0078] The FPGA control module is used to control the on / off state of the PIN diodes loaded in the basic unit of the electromagnetic tag metasurface array by outputting high and low levels through multiple channels and using voltage values, thereby controlling the phase of the scattered wave and making the scattering state of the electromagnetic tag metasurface array change with time according to a preset time modulation code.

[0079] Optionally, the electromagnetic tag metasurface array includes a basic unit layer, a dielectric substrate, and a metal ground layer arranged sequentially from top to bottom;

[0080] The basic unit consists of parallel metal strip patches and semiconductor devices loaded between the parallel metal strip patches. By changing the voltage loaded across the semiconductor devices, the on / off state of the semiconductor devices is changed, thereby switching the scattering state of the electromagnetic tag metasurface array; the metal ground layer provides grounding for the semiconductor devices.

[0081] Optionally, each basic unit in the electromagnetic tag metasurface array extends along the long side of the metal strip patch to form a column, each column of basic units forms a subarray, and the subarrays are periodically arranged along the short side of the metal strip patch to form the electromagnetic tag metasurface array.

[0082] The voltage output module is a multi-channel output, with each channel corresponding to a subarray in the electromagnetic tag metasurface array. By adjusting the input voltage of each subarray, the semiconductor device can be switched between different states. By switching the on and off states of the semiconductor device, each subarray can achieve two scattering states: 0° phase and 180° phase.

[0083] This application also provides an embodiment of a scattering method for a Ka-band scattering electromagnetic tag based on a time-controlled metasurface, applicable to the Ka-band scattering electromagnetic tag based on a time-controlled metasurface described in the above embodiment, comprising:

[0084] S1, the encoding storage module stores the encoding file containing the multi-channel encoding order and the set symbol frequencies; the encoding file includes scattering information, pseudo-random encoding, and channel encoding;

[0085] S2. The encoding reading module reads the time modulation encoding information in the encoding storage module and controls the voltage output module to output high and low levels according to the encoding information;

[0086] S3. The voltage output module is controlled by the encoding and reading module, which converts the time modulation encoding information of different channels into corresponding time-varying high and low levels, and regulates the voltage amplitude of the multi-channel electromagnetic tag metasurface array, thereby controlling the reflection phase of the electromagnetic tag metasurface array.

[0087] S4. The adjusted output voltage changes the scattering state of the electromagnetic tag's metasurface array, modulating the time-modulated coding information onto the radar scattering echo, thereby realizing the electromagnetic tag's control over the radar signal's scattering echo.

[0088] Optionally, S4 includes:

[0089] When the electromagnetic waves emitted by the radar are incident on the timing-controlled metasurface, the metasurface is divided into N columns of modulation units. When the electromagnetic waves emitted by the radar are point-frequency signals, the time modulation coding uses phase coding to control the scattered echo, obtaining the time-domain signal of the scattered coded echo received by the radar. By bandpass filtering the time-domain signal of the scattered coded echo, the phase scattering coded signal can be recovered. This enables the modulation of the scattered echo of the point frequency signal.

[0090] Optionally, in S4:

[0091] Assume the electromagnetic tag metasurface array is divided into N columns of modulation units in the x-direction, with a unit spacing of d, and each column extends along the y-direction, meaning it has the same response in the y-direction. The electromagnetic wave emitted by the radar has a center frequency of... Angle of incidence The modulation frequency of the electromagnetic tag metasurface array is irradiated onto the time-controlled metasurface. far below The scattered electromagnetic waves of the electromagnetic tag metasurface array are then represented as:

[0092] (1)

[0093] in, It is a scattered electromagnetic wave. Phase encoding of scattering information, Time modulation encoding for the nth column cell, It is a pseudo-random code. and All modulation units of the electromagnetic tag metasurface array are identical. For electromagnetic wave number, , c Let t be the speed of light, and t be time. This indicates the observation angle of a single radar station.

[0094] Optionally, S4 specifically includes:

[0095] If the time modulation sequences of each column are the same, then ;

[0096] When a radar receives a point-frequency incident signal, it uses phase-coded scattering. It appears as a binary coded sequence. This is time modulation coding, and the timing sequence of time modulation coding is as follows:

[0097] (2)

[0098] in, Represents the i-th time modulation period , ,right Perform a Fourier transform to obtain Where h represents the harmonic order, The corresponding harmonic coefficients; Indicates the i-th time modulation frequency;

[0099] Because the ±1st harmonic amplitude is the highest, therefore, ignoring the influence of higher-order harmonics, i.e. At that time, the time-domain signal of the scatter-coded echo received by our own radar is:

[0100] (3)

[0101] in, The scattering-encoded echo time-domain signal; , These are the ±1st harmonic amplitudes, respectively;

[0102] If there is interference signal , To represent the amplitude of the interference signal, the time signal of our own radar after pseudo-random demodulation is expressed as:

[0103] (4)

[0104] in, The time signal is after pseudo-random demodulation;

[0105] Through the By performing bandpass filtering, the phase encoding of the scattering information can be recovered. This enables the scattering of point frequency signals.

[0106] Optionally, S4 includes:

[0107] The electromagnetic waves emitted by the radar are incident on the electromagnetic tag metasurface array, which is divided into N columns of modulation units. When the electromagnetic waves emitted by the radar are linear frequency modulated pulse signals... hour,

[0108] (5)

[0109] Where t is time, Indicates the pulse width. For frequency modulation slope and , For signal bandwidth, The center frequency; It is a rectangular window function, in The value is 1 within the specified time range and 0 elsewhere;

[0110] The electromagnetic tag metasurface array uses spectral coding for scattering, directly scattering time-modulated signals. Multiple frequency codes are used, and their spectral characteristics are used as scattering codes to de-skew the reflected waves of the linear frequency modulated wave emitted by the radar on the time-controlled supersurface, recover the phase of the coded signal, and then perform pseudo-random demodulation. The spectrum of the demodulated signal is the scattering coded spectrum, thereby realizing the scattering of the linear frequency modulated signal.

[0111] Optionally, S4 specifically includes:

[0112] Time modulation coding Multiple frequency codes are employed, and their spectral characteristics are used as scattering codes. for:

[0113] (6)

[0114] in, Indicates the first n A single-cycle modulated signal, total N Seed; Set The modulus of all values ​​is 1, and pseudo-random coding is introduced. The scattered echo of the linear frequency modulated pulse signal emitted by the radar on the metasurface array of the electromagnetic tag can be represented as N single-period modulated signals; after modulating the linear frequency modulated signal, the sum of the corresponding infinite order harmonics is generated:

[0115] (7)

[0116] in, It is the reflected wave, that is, the sum of infinite order harmonics. Let be the amplitude of the h-th harmonic of the n-th modulation signal. It is a rectangular window function, in The value is 1 within the specified time range and 0 elsewhere. Let n be the modulation frequency of the nth modulation signal. Let B be the frequency modulation slope of the linear frequency modulated pulse signal, and let B be the bandwidth of the linear frequency modulated pulse signal. The pulse width of a linear frequency modulated pulse signal, where h is the order of the harmonics;

[0117] After introducing pseudo-random coding, the scattered echo is de-skewing to recover the phase of the coded signal. Then, pseudo-random demodulation is performed, and the Fourier transform of the demodulated signal yields the scattering spectrum. Its spectral characteristics constitute the spectral coding. The scattering spectrum is expressed as:

[0118] (8)

[0119] in, The scattering spectrum, For Fourier transform, The conjugate of the linear frequency modulated signal, Fourier transform of a single-cycle modulated signal;

[0120] The spectral encoding is obtained from the scattered echo, thereby enabling the scattering control of the linear frequency modulated signal.

[0121] Figure 4 This is a graph showing the reflection coefficient of the air conditioning metasurface unit in the embodiment of this application as a function of frequency when the PIN diode is conducting under high and low voltage levels. Figure 5Figure 6(a) shows the measured reflection coefficient of the time-controlled metasurface in this embodiment of the application; Figure 6(b) shows the measured demodulated signal spectrum of the electromagnetic tag performing encoded scattering of the external point-frequency incident signal in this embodiment of the application; Figure 7(a) shows the measured spectrum distribution of the electromagnetic tag performing encoded scattering of the external point-frequency incident signal in this embodiment of the application; Figure 7(b) shows the measured spectrum distribution of the electromagnetic tag performing encoded scattering of the external linear frequency modulated incident signal in this embodiment of the application; Figure 7(b) shows the measured spectrum distribution of the electromagnetic tag performing encoded scattering of the external linear frequency modulated incident signal in this embodiment of the application.

[0122] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and not to limit them. Although this application has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of this application. Any modifications or equivalent substitutions that do not depart from the spirit and scope of this application should be covered within the protection scope of the claims of this application.

Claims

1. A Ka-band scattering electromagnetic tag based on a time-controlled metasurface, characterized in that, It includes an electromagnetic tag metasurface array with electrically tunable scattering state and an FPGA control module that controls the time-controlled metasurface according to the time modulation encoding sequence; the electromagnetic tag metasurface array is composed of multiple time-controlled metasurfaces; The time-controlled metasurface is used to receive incident radar waves from the detection radar in the form of point frequency signals or linear frequency modulated pulse signals; Its scattering state is controlled by applying different voltage values; when the FPGA control module generates corresponding high and low level control signals according to the pre-stored time modulation code, the state of the electromagnetic tag metasurface array will change accordingly, thereby modulating the information on the radar's scattered echo and completing the regulation of the scattered echo. The FPGA control module is used to change the voltage amplitude of different channels output in the time-controlled metasurface according to the pre-stored time modulation coding information, so as to control the reflection phase of the time-controlled metasurface and realize the change of the scattering state of the time-controlled metasurface. The FPGA control module includes an encoding storage module, an encoding reading module, and a voltage output module; The encoding storage module is used to store an encoding file containing the multi-channel encoding order and the set symbol frequencies; the encoding file includes scattering information, pseudo-random encoding, and channel encoding; The encoding reading module is used to read the time modulation encoding information in the encoding storage module and control the voltage output module to output high and low levels according to the time modulation encoding information; The voltage output module is controlled by the encoding and reading module and is used to convert the time modulation encoding information of different channels into corresponding time-varying high and low levels, regulate the voltage amplitude of the multi-channel electromagnetic tag metasurface array, thereby controlling the reflection phase of the electromagnetic tag metasurface array. The electromagnetic tag metasurface array is composed of multiple time-controlled metasurface basic units arranged periodically. The FPGA control module is used to control the on / off state of the PIN diodes loaded in the basic unit of the electromagnetic tag metasurface array by outputting high and low levels through multiple channels and using voltage values, thereby controlling the phase of the scattered echo and making the scattering state of the electromagnetic tag metasurface array change with time according to a preset time modulation code.

2. The Ka-band scattering electromagnetic tag based on a time-controlled metasurface according to claim 1, characterized in that, The electromagnetic tag metasurface array includes a basic unit layer, a dielectric substrate, and a metal ground layer arranged sequentially from top to bottom. The basic unit layer consists of parallel metal strip patches and semiconductor devices loaded between the parallel metal strip patches. By changing the voltage loaded across the semiconductor devices, the on / off state of the semiconductor devices is changed, thereby switching the scattering state of the electromagnetic tag metasurface array; the metal ground layer provides grounding for the semiconductor devices.

3. The Ka-band scattering electromagnetic tag based on a time-controlled metasurface according to claim 1, characterized in that, The time-controlled metasurface basic units in the electromagnetic tag metasurface array are extended in a column along the long side of the metal strip patch. Each column of time-controlled metasurface basic units forms a subarray. The subarrays are periodically arranged along the short side of the metal strip patch to form the electromagnetic tag metasurface array. The voltage output module is a multi-channel output, with each channel corresponding to a subarray in the electromagnetic tag metasurface array. By adjusting the input voltage of each subarray, the semiconductor device can be switched between different states. By switching the on and off states of the semiconductor device, each subarray can achieve two scattering states: 0° phase and 180° phase.

4. A scattering method for a Ka-band scattering electromagnetic tag based on a time-controlled metasurface, applicable to the Ka-band scattering electromagnetic tag based on a time-controlled metasurface as described in any one of claims 1-3, characterized in that, include: Step 1: The encoding storage module stores the encoding file containing the multi-channel encoding order and the set symbol frequencies; The encoded file includes scattering information, pseudo-random coding, and channel coding; Step 2: The encoding reading module reads the time modulation encoding information in the encoding storage module and controls the voltage output module to output high and low levels according to the time modulation encoding information; Step 3: The voltage output module is controlled by the encoding and reading module to convert the time modulation encoding information of different channels into corresponding time-varying high and low levels, and adjust the voltage amplitude of the multi-channel electromagnetic tag metasurface array, thereby controlling the reflection phase of the electromagnetic tag metasurface array. Step 4: The output voltage is adjusted to change the scattering state of the electromagnetic tag metasurface array, and the time modulation coding information is modulated onto the radar's scattered echo, thereby realizing the control of the radar's scattered echo.

5. The scattering method for Ka-band scattering electromagnetic tags based on time-controlled metasurfaces according to claim 4, characterized in that, Step 4 includes: The incident radar wave from the detection radar is incident on the timing-controlled metasurface, which is divided into N columns of modulation units. When the incident radar wave is a point-frequency signal, the time modulation coding uses phase coding to modulate the scattered echo, obtaining the time-domain signal of the scattered coded echo received by the radar. By bandpass filtering the time-domain signal of the scattered coded echo, the phase scattering coded signal can be recovered. This enables the modulation of the scattered echo of the point frequency signal.

6. The scattering method for Ka-band scattering electromagnetic tags based on time-controlled metasurfaces according to claim 5, characterized in that, In step 4: Assume the electromagnetic tag metasurface array is divided into N columns of modulation units in the x-direction, with a spacing of d between the modulation units. Each column of modulation units extends along the y-direction, meaning they have the same response in the y-direction. The incident radar wave of the detection radar has a center frequency of... Angle of incidence The modulation frequency of the electromagnetic tag metasurface array is irradiated onto the time-controlled metasurface. Below The scattered electromagnetic waves of the electromagnetic tag metasurface array are then represented as: (1) in, It is a scattered electromagnetic wave. Phase encoding of scattering information, The time modulation code for the nth column modulation unit, It is a pseudo-random code. and All modulation units of the electromagnetic tag metasurface array are identical. For electromagnetic wave number, , c Let t be the speed of light, and t be time. This indicates the observation angle of a single radar station.

7. The scattering method for Ka-band scattering electromagnetic tags based on time-controlled metasurfaces according to claim 6, characterized in that, Step 4 specifically includes: If the time modulation sequences of all modulation units are the same, then ; When a radar receives a point-frequency incident signal, it uses phase-coded scattering. It appears as a binary coded sequence. This is time modulation coding, and the timing sequence of time modulation coding is as follows: (2) in, Represents the i-th time modulation period , ,right Perform a Fourier transform to obtain Where h represents the harmonic order, The corresponding harmonic coefficients; Indicates the i-th time modulation frequency; Because the ±1st harmonic amplitude is the highest, therefore, ignoring the influence of higher-order harmonics, i.e. At that time, the time-domain signal of the scatter-coded echo received by our own radar is: (3) in, The scattering-encoded echo time-domain signal; , These are the ±1st harmonic amplitudes, respectively; If there is interference signal , To represent the amplitude of the interference signal, the time signal of our own radar after pseudo-random demodulation is expressed as: (4) in, The time signal is after pseudo-random demodulation; Through the By performing bandpass filtering, the phase encoding of the scattering information can be recovered. This enables the scattering of point frequency signals.

8. The scattering method for Ka-band scattering electromagnetic tags based on time-controlled metasurfaces according to claim 6, characterized in that, Step 4 includes: The incident radar wave from the detection radar is incident on the electromagnetic tag metasurface array, which is divided into N columns of modulation units. When the incident radar wave from the detection radar is a linear frequency modulated pulse signal... hour, (5) Where t is time, Indicates the pulse width. For frequency modulation slope and , For signal bandwidth, The center frequency; It is a rectangular window function, in The value is 1 within the specified time range and 0 elsewhere; The electromagnetic tag metasurface array uses spectral coding for scattering, directly scattering time-modulated signals. Multiple frequency codes are used, and their spectral characteristics are used as scattering codes to de-skew the reflected waves of the linear frequency modulated pulse signal emitted by the radar on the time-controlled supersurface, recover the phase of the coded signal, and then perform pseudo-random demodulation. The spectrum of the demodulated signal is the scattering coded spectrum, thereby realizing the scattering of the linear frequency modulated pulse signal.

9. The scattering method for Ka-band scattering electromagnetic tags based on time-controlled metasurfaces according to claim 8, characterized in that, Step 4 specifically includes: Time modulation coding Multiple frequency codes are employed, and their spectral characteristics are used as scattering codes. for: (6) in, Indicates the first n A single-cycle modulated signal, total N Seed; Set The modulus of all values ​​is 1, and pseudo-random coding is introduced. The scattered echo of the linear frequency modulated pulse signal emitted by the radar on the metasurface array of the electromagnetic tag can be represented as N single-period modulation signals; after modulating the linear frequency modulated pulse signal, the sum of the corresponding infinite order harmonics is generated: (7) in, It is the reflected wave, that is, the sum of infinite order harmonics. Let be the amplitude of the h-th harmonic of the n-th modulation signal. It is a rectangular window function, in The value is 1 within the specified time range and 0 elsewhere. Let n be the modulation frequency of the nth modulation signal. Let B be the frequency modulation slope of the linear frequency modulated pulse signal, and let B be the bandwidth of the linear frequency modulated pulse signal. The pulse width of a linear frequency modulated pulse signal, where h is the order of the harmonics; After introducing pseudo-random coding, the scattered echo is de-skewing to recover the phase of the coded signal. Then, pseudo-random demodulation is performed, and the Fourier transform of the demodulated signal yields the scattering spectrum. Its spectral characteristics constitute the spectral coding. The scattering spectrum is expressed as: (8) in, The scattering spectrum, For Fourier transform, The conjugate of the linear frequency modulated pulse signal. Fourier transform of a single-cycle modulated signal; The spectral encoding is obtained from the scattered echo, thereby enabling the scattering control of linear frequency modulated pulse signals.

Images