Radio frequency identification tag time-frequency feature generation method, device, equipment and medium

Abstract

The present application relates to a radio frequency identification tag time-frequency feature generation method, device, equipment and medium. The method comprises: constructing an equivalent time interval pulse function based on a variable period sequence; determining a metasurface time modulation function according to the time interval pulse function; constructing a metasurface modulated echo signal model according to the metasurface time modulation function; based on the echo signal model, unfolding the echo signal of the metasurface array unit to obtain a time domain echo signal; performing frequency domain transformation on the time domain echo signal to obtain the frequency feature of the echo signal; and performing short-time Fourier transform on the time domain echo signal to obtain the time-frequency feature of the echo signal. The present application can improve the signal anti-interference ability and the stability of moving target recognition.

Description

Technical Field

[0001] This invention relates to the field of radio frequency identification (RFID) tag technology, and in particular to a method, apparatus, device, and medium for generating time-frequency characteristics of RFID tags. Background Technology

[0002] Radio Frequency Identification (RFID) technology is a non-contact automatic identification technology that automatically identifies target objects and acquires relevant data through radio frequency signals. Due to its advantages such as requiring no human intervention, enabling batch identification, and being able to operate in harsh environments, it has been widely used in various fields such as logistics management, supply chain tracking, and access control systems.

[0003] With the continuous evolution of technology, radio frequency identification (RFID) tags have achieved precise control over changes in light beams in space by utilizing the changes in the radar cross section (RCS) of hypersurfaces with time-varying codes, while also controlling the harmonics generated by the modulated signal.

[0004] However, research on RFID tags mainly relies on harmonic distribution and correlation for identification. This spectrum-based method has significant limitations. In complex electromagnetic environments, it is susceptible to interference, leading to harmonic peak distortion, affecting identification accuracy, and exhibiting poor anti-interference capabilities. Furthermore, when a target is in motion, the resulting Doppler shift disrupts the static spectral characteristics, rendering existing technologies ineffective in identifying moving targets. Summary of the Invention

[0005] Therefore, it is necessary to provide a method, apparatus, device, and medium for generating time-frequency features of radio frequency identification tags that can solve problems such as poor anti-interference capability and unstable recognition of moving targets, in order to address the above-mentioned technical problems.

[0006] A method for generating time-frequency features of radio frequency identification (RFID) tags, the method comprising: Based on the variable periodic sequence, an equivalent time interval pulse function is constructed; according to the time interval pulse function, the metasurface time modulation function is determined. Based on the metasurface time modulation function, an echo signal model modulated by the metasurface is constructed; Based on the echo signal model, the echo signal of the metasurface array unit is expanded to obtain the time-domain echo signal; The time-domain echo signal is subjected to frequency domain transformation to obtain the frequency characteristics of the echo signal; the time-domain echo signal is subjected to short-time Fourier transform to obtain the time-frequency characteristics of the echo signal.

[0007] On the other hand, a time-frequency feature generation device for radio frequency identification tags is also provided, comprising: The time interval pulse function construction module is used to construct equivalent time interval pulse functions based on variable period sequences. The metasurface time modulation function determination module is used to determine the metasurface time modulation function based on the time interval pulse function; The echo signal model construction module is used to construct an echo signal model modulated by the metasurface based on the metasurface time modulation function. The time-domain echo signal calculation module is used to expand the echo signal of the metasurface array unit based on the echo signal model to obtain the time-domain echo signal. The frequency feature generation module is used to perform frequency domain transformation on the time-domain echo signal to obtain the frequency features of the echo signal. The time-frequency feature generation module is used to perform a short-time Fourier transform on the time-domain echo signal to obtain the time-frequency features of the echo signal.

[0008] In another aspect, a computer device is also provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps of the above-described method for generating the time-frequency characteristics of radio frequency identification tags.

[0009] Furthermore, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed by a processor, implements the steps of the above-described method for generating the time-frequency characteristics of radio frequency identification tags.

[0010] Compared with existing technologies, the time-frequency feature generation method, apparatus, device, and medium for RFID tags provided by this invention have the following advantages: 1. By constructing an equivalent time interval pulse function through a variable period sequence, the modulation period parameter can be dynamically adjusted to achieve adaptive configuration of the timing signal; at the same time, due to the persistence of the time-frequency characteristics, the recognition capability can be maintained under strong interference, thus improving the signal's anti-interference capability.

[0011] 2. By designing variable periodic sequences, the time-frequency characteristics of metasurfaces can be freely designed, allowing for precise control of the metasurface's time modulation function, generating distinguishable time-frequency ridge shapes, ensuring signal uniqueness, and thus achieving more accurate resolution and high-precision time-domain control of echo signals.

[0012] 3. By combining row short-time Fourier transform with dynamic compensation of metasurface modulation parameters, dynamic tracking of time-frequency features can be achieved, thereby improving the stability of moving target recognition.

[0013] 4. The method proposed in this invention has multi-scenario compatibility and is applicable to various scenarios such as passive RFID and backscatter communication. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings required in the embodiments will be briefly described below. It should be understood that the following drawings only show some embodiments of the present invention, and those skilled in the art can obtain other related drawings based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart illustrating the method for generating time-frequency features of an RFID tag provided in Example 1. Figure 2 This is a schematic diagram of a time-modulated radar signal based on a metasurface provided in Example 1, wherein, Figure 2 (a) is a schematic diagram of periodic modulation. Figure 2 (b) is a schematic diagram of variable period modulation; Figure 3 A schematic diagram of the spectrum of time-modulated sequence 1 and sequence 2 provided in Example 1; wherein, Figure 3 (a) is a schematic diagram of the spectrum of sequence 1. Figure 3 (b) is a schematic diagram of the spectrum of sequence 2; Figure 4 A time-spectral diagram of time-modulated sequence 1 and sequence 2 provided in Example 1; wherein, Figure 4 (a) is a schematic diagram of the time spectrum of sequence 1. Figure 4 (b) is a schematic diagram of the time spectrum of sequence 2; Figure 5 This is a schematic diagram of the spectrum of different time modulation sequences provided in Example 1; wherein, Figure 5 (a) is a schematic diagram of the spectrum of sequence 3. Figure 5 (b) is a schematic diagram of the spectrum of sequence 4; Figure 6 This is a time-spectral diagram of different time-modulated sequences provided in Example 1; wherein, Figure 6 (a) is a schematic diagram of the time spectrum of sequence 4. Figure 6 (b) is a schematic diagram of the time spectrum of sequence 4; Figure 7 This is a structural block diagram of the time-frequency feature generation device for the radio frequency identification tag provided in Example 2; Figure 8 This is an internal structural diagram of the computer device provided in Example 3.

[0016] The objectives, features, and advantages of this invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0018] It is understood that the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0019] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0020] Example 1 like Figure 1 As shown, the method for generating time-frequency features of RFID tags provided in this embodiment includes the following steps: Step 201: Construct an equivalent time interval pulse function based on the variable periodic sequence.

[0021] Step 202: Determine the metasurface time modulation function based on the time interval pulse function.

[0022] Step 203: Construct an echo signal model modulated by the metasurface based on the metasurface time modulation function.

[0023] Step 204: Based on the echo signal model, expand the echo signal of the metasurface array unit to obtain the time-domain echo signal.

[0024] Step 205: Perform frequency domain transformation on the time-domain echo signal to obtain the frequency characteristics of the echo signal; perform short-time Fourier transform on the time-domain echo signal to obtain the time-frequency characteristics of the echo signal.

[0025] It is understood that in this embodiment, by constructing an equivalent time interval pulse function through a variable period sequence, the period parameter can be dynamically adjusted in complex electromagnetic environments to avoid interference frequency bands, thereby improving the signal's anti-interference capability and enabling the modulation process to adapt to the timing requirements of different scenarios. Compared to traditional fixed-period modulation, determining the metasurface time modulation function based on the time interval pulse function can generate richer time-frequency features through time-varying parameters, thus achieving high-precision time-domain control of the echo signal. The constructed echo signal model combines the electromagnetic modulation characteristics of the metasurface, which can accurately describe the echo characteristics of RFID tags under different conditions and reduce the probability of collisions. The method provided by this invention can improve the signal's anti-interference capability and enhance the stability of moving target recognition; at the same time, by encoding through joint time-frequency features, it expands the coding space, breaks through spectrum limitations, increases data capacity, and has strong robustness and adaptability.

[0026] In the specific implementation of steps 201 and 202, the metasurface modulates the radar signal by changing the unit reflection state, thereby changing the amplitude and phase of the incident signal without delay. For example... Figure 2 The diagram shows a radar signal modulated by a metasurface. The signal is modulated by the metasurface, and the initial model expression for the echo signal is: (1) In the formula, Indicates the radar's transmitted signal; This indicates time modulation of the metasurface.

[0027] For a time-modulated metasurface, its reflection state can be defined as a combination of a series of time intervals within a linear period. Therefore, the expression for the metasurface time modulation function is: (2) In the formula, This indicates time modulation of the metasurface; This represents the reflectivity amplitude and reflection phase within a time interval; This represents a time interval pulse function that changes over time. This represents the length of the time-modulated sequence within a variable period; Indicates the first A time interval; This indicates the modulation period of the coded sequence.

[0028] Due to hardware limitations of FPGAs, they cannot continuously change unit phase in the time domain. The control signal for a 1-bit surface consists of a series of square wave signals. Variable period sequences differ from square waves because the length of each period is unequal. Therefore, based on the variable period sequence, an equivalent time interval pulse function is constructed, expressed as: (3) In the formula, Represents a time interval pulse function; Indicates the first The end time of each time interval; Indicates the first The total time of each time interval.

[0029] When the control signal changes non-periodically over time, it can be expanded into a Fourier series form using the continuous-time Fourier transform (CTFT): (4) In the formula, yes Fourier series coefficients; Indicates frequency as The complex sine wave.

[0030] Based on this, in formula (2) It can also be expanded into a Fourier series. The expression is: (5) In the formula, Indicates the first Second harmonics; Indicates the first The modulation period of a pulse modulation function; The modulation frequency represents a non-uniform time interval; This represents the reflectivity amplitude and reflection phase within a time interval; This represents the phase. The time interval length is also included. Modulation frequency of non-uniform time interval related.

[0031] As can be seen from the above analysis, the influence of the variable period sequence manifests in the frequency domain as a series of harmonic components with variable period frequency step size offset. The following analysis will incorporate the transmitted and received signals.

[0032] In the specific implementation of step 203, because linear frequency modulation (LFM) signals have a large time-bandwidth product, they are widely used in radar systems. Therefore, the expression for the LFM signal transmitted by the pulse radar is: (6) In the formula, Indicates the frequency modulation rate. Indicates signal bandwidth. Indicates the duration of pulse duration; Indicates the carrier frequency.

[0033] Based on this, according to the initial model of the echo signal in formula (1), the echo signal model of the metasurface modulation is obtained, and the expression of the echo signal model is: (7) In the formula, This represents the echo signal modulated by the metasurface; This indicates metasurface time modulation after echo delay; This represents the received signal after the echo delay; This indicates the echo delay of the hypersurface; This indicates the effect of Doppler frequency shift on the phase; This indicates Doppler frequency shift.

[0034] In the specific implementation of step 204, based on the echo signal model, the echo signal of the metasurface array unit is expanded to obtain the time-domain echo signal. The process expression is as follows: (8) In the formula, Represents the time-domain echo signal; This represents the echo signal modulated by the metasurface; Indicates the conjugate of the transmitted signal; The control signal represents the unit cell; Indicates time; Indicates echo delay; Indicates phase change; Indicates spatial phase; Indicates the number of rows in the cell array; Indicates the number of column cells in the cell array; Represents the rows of a cell array; Represents the columns of a cell array.

[0035] In the specific implementation of step 205, the time-domain echo signal is transformed in the frequency domain to obtain the frequency characteristics of the echo signal. The process expression is as follows: (9) Performing a short-time Fourier transform (STFT) on the time-domain echo signal yields the time-frequency characteristics of the echo signal. The process expression is as follows: (10) In the formula, Represents window functions, Indicates a time window; Indicates the correction frequency.

[0036] Since the time modulation rate is typically below milliseconds, the position and Doppler shift of a traditional target can be considered invariant, allowing... Then the frequency characteristics can be simplified as: ; The time-frequency characteristics can be simplified as follows: ; In the formula, This represents the time-frequency characteristics of the echo signal; Indicates the first OK The spectrum of the unit time modulation of the column; Represents a constant; Indicates phase change; Indicates spatial phase Indicates the frequency characteristics of the echo signal; Indicates frequency; Indicates the correction frequency; This indicates a phase change.

[0037] In one embodiment, the time-frequency ridge shape is extracted using a short-time Fourier transform (STFT) based on the time-frequency and frequency features generated in this embodiment. For example... Figure 3 and Figure 4 As shown, Sequence 1 is a conventional square wave signal with a fixed periodic modulation frequency of 60 kHz, which maintains a constant modulation frequency in different time slots. Sequence 2 is a variable periodic sequence with a modulation frequency that varies over time. The frequency of Sequence 2 gradually increases from 90 kHz to 120 kHz, then gradually decreases to 60 kHz, and finally rises to 90 kHz within one cycle.

[0038] The generation mechanism of time-frequency features of metasurfaces under radar excitation was systematically studied. The radar parameters were set as follows: LFM signal carrier frequency of 1 GHz, bandwidth of 8 MHz, and pulse width of 1 ms. Figure 3 (a) and Figure 3 In (b), the red line shows the frequency distribution of different modulation sequences in the spectral dimension, and the blue line shows the unmodulated result for comparison. Figure 3 (a) and Figure 3 As shown in (b), the fixed-period encoding (sequence 1) produces a uniform 60 kHz harmonic, while the variable-period encoding (sequence 2) produces a dynamically distributed harmonic across a bandwidth of 60-120 kHz.

[0039] By specifying an appropriate window length and moving it in one direction, the temporal variation pattern of the encoded sequence can be obtained. Figure 4 (a) and Figure 4 (b) shows the time-frequency spectrum of the metasurface. Can you see that the resulting time-frequency characteristics are significant differences in frequency variation? Figure 4 In (a), the frequency of sequence 1 remains constant over time. For example... Figure 4As shown in (b), the frequency of sequence 2 varies triangularly over time, gradually increasing from 90 kHz to 120 kHz, then gradually decreasing to 60 kHz, and finally rising back to 90 kHz. This perfectly matches the coded variation pattern. In the time-frequency domain, there is a significant difference between the variable-period sequence and the conventional sequence, and the time-frequency information can be easily identified using a simple time-frequency ridge estimation comparator. Therefore, to obtain more accurate resolution, the time-frequency characteristics of the metasurface can be freely designed by designing a variable-period sequence as needed.

[0040] To demonstrate the superiority of the method proposed in this invention, diverse time-frequency spectra can be designed. Figure 5 (a) and Figure 5 In (b), the frequency components of the two signal sequences are mainly between 60 kHz and 120 kHz. Their spectral distribution and energy intensity are consistent. It can be seen that these two sequences cannot be distinguished solely by their spectral characteristics. Figure 6 (a) and Figure 6 (b) shows the time-frequency characteristics. Figure 6 In (a), the frequency of sequence 3 shows a trapezoidal change over time. The frequency gradually increases from 90 kHz to 120 kHz and remains stable for a period of time. In Figure [missing information]... Figure 6 In (b), the temporal spectrum trend shows a pattern of first trapezoidal transformation and then triangular transformation.

[0041] As can be seen from the above analysis, the present invention utilizes the morphological persistence of time-frequency features to maintain recognition capability in strong interference environments, and its anti-interference capability is far superior to traditional spectrum methods. Through dynamic modulation period, time-frequency ridge shape tracking can be achieved, decoupling the influence of Doppler frequency shift on coding features and improving the stability of moving target recognition. In addition, the diversity of time-frequency morphology (such as triangular waves and trapezoidal waves) supports more distinguishable sequences, expands the coding space, and breaks through spectrum limitations.

[0042] It is worth noting that, in addition to the metasurface mentioned in this embodiment, multi-bit metasurfaces can also be used to further improve modulation flexibility; or a hybrid coding system combining time-frequency coding and spatial coding can be used to further improve data capacity.

[0043] It should be understood that, although this embodiment Figure 1 The steps are shown sequentially as indicated by the arrows, but they are not necessarily executed in the order indicated by the arrows. Unless otherwise specified in this document, there is no strict order in which these steps are performed; they can be executed in other orders. Figure 1At least some of the steps in the process may include multiple sub-steps or multiple stages. These sub-steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these sub-steps or stages is not necessarily sequential, but can be executed in turn or alternately with other steps or at least some of the sub-steps or stages of other steps.

[0044] Example 2 Based on the time-frequency feature generation method for RFID tags in Embodiment 1, this embodiment discloses a time-frequency feature generation device for RFID tags, such as... Figure 7 As shown, the time-frequency feature generation device for RFID tags includes: a time interval pulse function construction module 401, a metasurface time modulation function determination module 402, an echo signal model construction module 403, a time-domain echo signal calculation module 404, a frequency feature generation module 405, and a time-frequency feature generation module 406, wherein: The time interval pulse function construction module 401 is used to construct an equivalent time interval pulse function based on a variable period sequence.

[0045] The metasurface time modulation function determination module 402 is used to determine the metasurface time modulation function based on the time interval pulse function.

[0046] The echo signal model construction module 403 is used to construct an echo signal model modulated by the metasurface based on the metasurface time modulation function.

[0047] The time-domain echo signal calculation module 404 is used to expand the echo signal of the metasurface array unit based on the echo signal model to obtain the time-domain echo signal.

[0048] The frequency feature generation module 405 is used to perform frequency domain transformation on the time-domain echo signal to obtain the frequency features of the echo signal.

[0049] The time-frequency feature generation module 406 is used to perform a short-time Fourier transform on the time-domain echo signal to obtain the time-frequency features of the echo signal.

[0050] In this embodiment, the specific working process and working principle of the time interval pulse function construction module 401, the metasurface time modulation function determination module 402, the echo signal model construction module 403, the time-domain echo signal calculation module 404, the frequency feature generation module 405, and the time-frequency feature generation module 406 are the same as those in Embodiment 1, and therefore will not be described again in this embodiment. Each unit module can be implemented entirely or partially through software, hardware, or a combination thereof. Each unit module can be embedded in or independent of the processor in a computer device in hardware form, or it can be stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each of the above unit modules.

[0051] Example 3 like Figure 8 The diagram illustrates a terminal device disclosed in this embodiment, comprising a transmitter, a receiver, a memory, and a processor. The transmitter transmits instructions and data, the receiver receives instructions and data, the memory stores computer-executed instructions, and the processor executes the computer-executed instructions stored in the memory to implement the method described in Embodiment 1 above.

[0052] It is important to note that the aforementioned memory can be either standalone or integrated with the processor. When the memory is set up independently, the terminal device also includes a bus for connecting the memory and the processor.

[0053] Example 4 This embodiment discloses a computer-readable storage medium storing computer-executable instructions. When a processor executes the computer-executable instructions, it implements the method in Embodiment 1 above.

[0054] Those skilled in the art will understand that all or part of the processes in the methods of the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium. When executed, the computer program can include the processes of the embodiments of the above methods. Any references to memory, storage, databases, or other media used in the embodiments provided in this application can include non-volatile and / or volatile memory. Non-volatile memory may include read-only memory (ROM), programmable ROM (PROM), electrically programmable ROM (EPROM), electrically erasable programmable ROM (EEPROM), or flash memory. Volatile memory may include random access memory (RAM) or external cache memory. By way of illustration and not limitation, RAM is available in a variety of forms, such as static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), dual data rate SDRAM (DDRSDRAM), enhanced SDRAM (ESDRAM), synchronous link DRAM (SLDRAM), RAMbus direct RAM (RDRAM), direct memory bus dynamic RAM (DRDRAM), and memory bus dynamic RAM (RDRAM), etc.

[0055] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0056] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the appended claims.

Claims

1. A method for generating time-frequency features of a radio frequency identification (RFID) tag, characterized in that, The method includes: Based on the variable periodic sequence, an equivalent time interval pulse function is constructed; according to the time interval pulse function, the metasurface time modulation function is determined. Based on the metasurface time modulation function, an echo signal model modulated by the metasurface is constructed; Based on the echo signal model, the echo signal of the metasurface array unit is expanded to obtain the time-domain echo signal; The time-domain echo signal is subjected to frequency domain transformation to obtain the frequency characteristics of the echo signal; the time-domain echo signal is subjected to short-time Fourier transform to obtain the time-frequency characteristics of the echo signal.

2. The method for generating time-frequency features of an RFID tag according to claim 1, characterized in that, The expression for the time interval pulse function is: ； In the formula, Represents a time interval pulse function; Indicates the first The end time of each time interval; Indicates the first The total time of each time interval.

3. The method for generating time-frequency features of an RFID tag according to claim 1, characterized in that, The expression for the metasurface time modulation function is: ； In the formula, This indicates time modulation of the metasurface; This represents the reflectivity amplitude and reflection phase within a time interval; Represents a time interval pulse function; This represents the length of the time-modulated sequence within a variable period; Indicates the first A time interval; This indicates the modulation period of the coded sequence.

4. The method for generating time-frequency features of an RFID tag according to claim 1, characterized in that, The metasurface-modulated echo signal model is expressed as follows: ； In the formula, This represents the echo signal modulated by the metasurface; This indicates metasurface time modulation after echo delay; This represents the received signal after the echo delay; This indicates the echo delay of the hypersurface; This indicates the effect of Doppler frequency shift on the phase; This indicates Doppler frequency shift.

5. The method for generating time-frequency features of an RFID tag according to any one of claims 1 to 4, characterized in that, Based on the aforementioned echo signal model, the echo signal of the metasurface array unit is expanded to obtain the time-domain echo signal. The process expression is as follows: ； In the formula, Represents the time-domain echo signal; This represents the echo signal modulated by the metasurface; Indicates the conjugate of the transmitted signal; The control signal representing the unit cell; Indicates time; Indicates echo delay; Indicates phase change; Indicates spatial phase; Indicates the number of rows in the cell array; Indicates the number of column cells in the cell array; Represents the rows of a cell array; Represents the columns of a cell array.

6. The method for generating time-frequency features of an RFID tag according to claim 5, characterized in that, The frequency characteristics of the echo signal are obtained by performing a frequency domain transformation on the time-domain echo signal. The process expression is as follows: ； In the formula, This represents the time-frequency characteristics of the echo signal; Indicates the first OK The spectrum of the unit time modulation of the column; Represents a constant; Indicates phase change; Indicates spatial phase.

7. The method for generating time-frequency features of an RFID tag according to claim 5, characterized in that, Perform a short-time Fourier transform on the time-domain echo signal to obtain the time-frequency characteristics of the echo signal. The process expression is as follows: ； In the formula, This indicates the frequency characteristics of the echo signal; Indicates the first OK The spectrum of the unit time modulation of the column; Represents a constant; Indicates frequency; This represents the time window in time-frequency transformation; Indicates the correction frequency; Indicates phase change; Indicates spatial phase.

8. A time-frequency feature generation device for radio frequency identification tags, characterized in that, The device includes: The time interval pulse function construction module is used to construct equivalent time interval pulse functions based on variable period sequences. The metasurface time modulation function determination module is used to determine the metasurface time modulation function based on the time interval pulse function; The echo signal model construction module is used to construct an echo signal model modulated by the metasurface based on the metasurface time modulation function. The time-domain echo signal calculation module is used to expand the echo signal of the metasurface array unit based on the echo signal model to obtain the time-domain echo signal. The frequency feature generation module is used to perform frequency domain transformation on the time-domain echo signal to obtain the frequency features of the echo signal. The time-frequency feature generation module is used to perform a short-time Fourier transform on the time-domain echo signal to obtain the time-frequency features of the echo signal.

9. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, The memory stores a computer program, and when the processor executes the computer program, it implements the steps of the time-frequency feature generation method for the radio frequency identification tag according to any one of claims 1 to 7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, It stores a computer program, which, when executed by a processor, implements the steps of the time-frequency feature generation method for the radio frequency identification tag according to any one of claims 1 to 7.

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