Radio frequency calculation method and system based on time coding metasurface

Abstract

The invention discloses a radio frequency calculation method and system based on a time coding metasurface. The metasurface is composed of a metal patch layer, an F4B dielectric layer and a metal backboard layer. By applying a specific periodic control signal, the metasurface can modulate electromagnetic information of an incident wave. A baseband signal of the incident electromagnetic wave represents a time function needing to be operated, and a control signal of the metasurface corresponds to a coding sequence needing to be operated. After the electromagnetic wave interacts with the metasurface, a reflection echo carries information of an operation result, and Fourier transform and convolution operation can be directly carried out in a radio frequency domain. According to the method, conversion of radio frequency signals is omitted, and calculation is directly completed in a radio frequency domain, so that calculation time delay and energy consumption can be effectively reduced; meanwhile, due to the fact that a traditional radio frequency link is omitted, the radio frequency calculator constructed through the metasurface has low hardware complexity and cost and a simple structure on the premise that the calculation precision is guaranteed, and the method is suitable for the application fields of communication, radar, sensing and the like.

Description

Technical Field

[0001] The present invention relates to a radio frequency calculator based on a time coding metasurface, which can realize Fourier transform and convolution operations in a radio frequency domain, and belongs to the technical field of novel artificial electromagnetic metasurfaces. Background Art

[0002] The field of information science has long been dominated by digital computing, which uses digital means to analyze and process multivariate information. However, traditional digital computing requires frequent analog-to-digital and digital-to-analog conversions, resulting in large operating energy loss and low information retention. This approach not only has strict requirements on energy consumption, but also has problems such as information distortion and computing delays. With the rapid growth of information, the existing computing model urgently needs to be changed.

[0003] As an emerging computing model, RF computing uses RF signals as information carriers and computing objects, and directly completes information processing in the RF domain, thereby avoiding frequent conversions between RF-analog-digital domains. This method can not only effectively reduce computing latency, but also reduce computing energy consumption, and has broad application prospects. However, due to the imperfect theoretical foundation and methodological guidance, RF computing currently lacks suitable hardware support and equipment design methods. Summary of the invention

[0004] Technical issues:

[0005] The problem to be solved by the present invention is to use a time-coded metasurface to directly process the information carried by the radio frequency signal without frequency conversion. The specific implementation method is: when the radio frequency signal to be calculated is incident on the time-coded metasurface, a control signal corresponding to the required operation is applied to the metasurface, and the reflected echo of the metasurface will carry the operation result information. By designing the transformation form of the control signal, the radio frequency information can be processed in two different ways: Fourier transform and convolution operation.

[0006] Technical solution:

[0007] To solve the above technical problems, the present invention proposes a time-coding metasurface that can perform radio frequency computing. The core structure of the invention is a time-coding metasurface, which is a two-dimensional ultra-thin artificial surface formed by M×L sub-wavelength-scale units arranged in a specific way; each unit is integrated with an active controllable device (varicap diode); by connecting to an FPGA, the bias voltage of the active device is controlled, and the reflection phase of the electromagnetic wave is controlled while ensuring a strong reflection amplitude.

[0008] Each unit is made of double-sided copper-clad F4B dielectric substrate (dielectric constant 2.65, loss tangent 0.001), and each unit integrates 4 varactors (SMV-2019) and 4 chip capacitors (0.1pF).

[0009] The control module of the metasurface consists of a field programmable gate array (FPGA) and a digital-to-analog converter (DAC), which can generate any periodic voltage signal that varies with time in the range of 0V to 14V.

[0010] Among them, when the control voltage is switched between any values ​​in the range of 0V to 14V, the metasurface can achieve continuous variable reflection phase in the 4.0GHz to 4.3GHz frequency band while maintaining a high reflection amplitude, and its adjustable range exceeds 360°.

[0011] Among them, the metasurface can complete the information processing of the incident signal in the radio frequency domain by applying the control voltage waveform of the corresponding operation, and directly obtain the result of the corresponding operation.

[0012] The present invention also provides a radio frequency calculation method based on a time-coded metasurface, comprising the following steps:

[0013] The mapping relationship between the echo signal R of the time-coded metasurface and the reflection coefficient code Γ is expressed as the following matrix form:

[0014]

[0015] Among them, I=[I[n]] N×1 is the incident signal matrix, R K×1 , Γ K×N are the echo signal matrix and the reflection coefficient coding matrix respectively, n=0,…,N-1, represents the index of the matrix in the time dimension, N and K represent the length of the input vector and the output vector respectively;

[0016] Design the reflection coefficient encoding matrix Γ according to the RF calculation requirements K×N , so that the echo signal carries the information of the operation result;

[0017] By demodulating the echo signal of the time-coded metasurface, the waveform information containing the required calculation results is obtained.

[0018] Preferably, the radio frequency calculation is Fourier transform, and the reflection coefficient encoding matrix is ​​designed as:

[0019]

[0020] The reflected echo from the metasurface will carry information about the Fourier transform of the incident wave.

[0021] Preferably, the radio frequency calculation is a convolution operation, and the reflection coefficient encoding matrix is ​​designed to be Γ K×N =[Γ0,…,Γ k ,…,Γ (N-M+1) ]T , where Γ k =[[0] 1×k ,H 1×M ,[0] 1×(K-k-1) ], where H 1×M is the impulse response matrix.

[0022] The present invention also provides a radio frequency computing system based on a time-coded metasurface, comprising a time-coded metasurface, a vector signal transceiver, a waveform generator, and a radio frequency calculator; the vector signal transceiver is used to generate an input signal to be calculated, and receive an echo signal to demodulate the calculation result; the waveform generator is used to generate a periodic voltage control signal to achieve periodic switching of the metasurface reflection phase; the radio frequency calculator is used to execute the above method to perform radio frequency calculations.

[0023] Beneficial effects:

[0024] 1. Reduce computing delay and energy consumption: Compared with traditional digital computing, the present invention eliminates the frequent conversion between RF-analog-digital domains and directly uses RF signals as information carriers and computing objects. Information processing is completed directly in the RF space, which can effectively reduce computing delay and reduce computing energy consumption.

[0025] 2. Providing high-precision RF computing tools: The present invention regulates RF signals through time-coded metasurfaces, and can implement Fourier transform and convolution operations in the RF domain. This method provides a high-precision and effective new tool for RF computing, filling the gap in the existing technology that lacks suitable hardware support.

[0026] 3. Low hardware complexity, simple structure and low cost: The RF calculator based on the time-coding metasurface involved in the present invention directly completes the processing of electromagnetic waves on the metasurface, eliminating the complex RF links in traditional electronic systems, and has the advantages of low cost, simple structure and low hardware complexity. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a working principle diagram of the radio frequency calculator based on the time-coded metasurface in the present invention;

[0028] Figure 2 An exploded diagram of the unit structure of the time-coding metasurface of the present invention;

[0029] Figure 3 The transformation relationship between the reflection amplitude and phase of the metasurface unit and the bias voltage at 4.1 GHz, 4.2 GHz and 4.3 GHz when the control voltage of the metasurface in the present invention changes from 0 to 14 V;

[0030] Figure 4 A scene graph is implemented for the radio frequency calculation in the present invention;

[0031] Figure 5 It is the Fourier transform result based on RF calculation in the present invention. ac) RF calculation spectrum display of three incident waveforms: single sine wave, mixed sine wave and frequency modulated continuous wave. df) Time domain waveform (real part and phase) of RF calculation result reconstructed by IFFT;

[0032] Figure 6 The convolution operation results based on radio frequency calculation in the present invention (theoretical and measured comparison results). The target positions added by the simulator are a: 1Km, b: 3Km, c: 10Km, d: 14Km. DETAILED DESCRIPTION

[0033] The present invention provides a radio frequency calculator based on a time-coded metasurface, which is used to implement Fourier transform and convolution, two basic operations that are crucial in signal processing. Figure 1 In this embodiment, a 16×8 full phase modulation reflective metasurface sample is designed, and the unit structure is as follows: Figure 2 As shown in the figure. Each unit integrates 4 varactor diodes and 4 chip capacitors. By adjusting the voltage across the varactor diodes on the metasurface unit, the metasurface can achieve continuous adjustment of the reflection coefficient in the range of 0° to 360°. Figure 3 Figure AB shows the relationship between the reflection amplitude and reflection phase of the metasurface and the change of control voltage when the operating frequencies are 4.1 GHz, 4.2 GHz and 4.3 GHz respectively. The results show that the metasurface can maintain a high reflection amplitude within the above operating frequency band, and the adjustable range of the reflection phase exceeds 360°.

[0034] In order to prove that the time-coding metasurface in the present invention can realize radio frequency computing, a Figure 4 The RF computing system shown in FIG. The system uses a vector signal transceiver to generate the input signal to be calculated and incident it on the metasurface in the normal direction. A waveform generator is used to generate a periodic voltage control signal, which can be converted into a continuous control voltage waveform to achieve periodic switching of the metasurface reflection phase. Figure 3 The voltage-phase relationship curve of the metasurface at 4.2 GHz operating frequency shown in b can obtain the required control voltage encoding. By demodulating the reflected echo signal of the metasurface, the waveform information containing the required calculation results can be obtained.

[0035] The working principle of the radio frequency calculator of the present invention is as follows: Assume that the reflection coefficient of the time coding metasurface is Γ(t), when the carrier frequency is f c When the incident signal of the baseband signal I(t) is irradiated, the reflected echo signal R(t) can be expressed as:

[0036] R(t)=I(t)×Γ(t) (1)

[0037] Obviously, the reflected signal is the product of the incident signal and the reflection coefficient. The core idea of ​​the time-coded metasurface is to achieve the control of electromagnetic waves by discretely encoding the electromagnetic characteristics of the metasurface unit. For the convenience of analysis, the above expression is converted from continuous signal form to discrete vector form. Assume that the discrete sample sequence of the incident signal is I = [I[n]] N×1 , the reflection coefficient sequence Γ at the kth moment k =[Γ k [n]] N×1 , where n = 0, ..., N-1, the reflected signal is expressed as:

[0038] R k =Γ k ·I (2)

[0039] In actual electronic information systems, different types of system responses will present various processing methods for input signals. The output of any linear system can be regarded as the result of the interaction between the system input f(t) and the system response h(t,m), expressed as:

[0040]

[0041] exist Figure 1 In the RF calculator based on the time-coded metasurface shown, different types of system responses can be constructed by flexibly controlling the metasurface using FPGA to achieve the desired target output g(m). In this architecture, the input signal f(t) is replaced by the incident wave signal I(t), and the system function h(t,m) corresponds to the time-varying reflection coefficient Γ(t) of the time-coded metasurface. The output expression in discrete summation form corresponding to the linear system is given:

[0042]

[0043] Coding method Γ of time-coded metasurface k The design of [n] will directly affect the system response of the constructed linear system. In order to intuitively construct the mapping relationship between the system response and the encoding atom, it can be converted into a matrix form:

[0044]

[0045] At this time, the output of the system is expressed as:

[0046] R K×1 =[Γ0 T I, Γ1 T I,…,Γ K-1T ·I] (6)

[0047] In the constructed RF computing system, it is only necessary to design a reflection coefficient code Γ that meets the requirements. i (i=0,…,K-1) to meet the system response required by the RF computing system, then the construction scheme of the RF computing system based on the time-coded metasurface is feasible. In order to enhance the rigor of the theoretical derivation, test cases of RF computing based on the time-coded metasurface are provided for Fourier transform and convolution operations respectively.

[0048] Example 1: Experimental verification of Fourier transform using time-coded metasurface.

[0049] Figure 5 Figure ac shows the RF calculation results of three incident waveforms: a single sine wave, a mixed sine wave, and a frequency modulated continuous wave. In order to verify the accuracy of the RF calculation, this embodiment also provides a theoretical incident signal spectrum calculated by a numerical method. The comparison results show that the RF calculation results are highly consistent with the numerical calculation results, and can accurately reflect the spectral characteristics of the incident signal. Figure 5 DF shows the reconstruction of the time domain waveform after the inverse Fourier transform of the spectrum obtained by RF calculation. The results show that the original waveform information has been restored relatively completely, indicating the correctness of the RF calculation results and verifying the effectiveness of the time-coded metasurface in RF Fourier transform. Therefore, Example 1 proves that the time-coded metasurface can realize the Fourier transform of RF signals.

[0050] Example 2: Experimental verification of convolution operation using time-coded hypersurface.

[0051] In order to verify the feasibility of using time-coded metasurfaces to implement convolution operations, this embodiment uses matched filtering of linear frequency modulation signals as an example to conduct experiments. Matched filtering is widely used in signal detection and recognition, improving anti-interference performance, and signal parameter estimation in multiple fields such as communication, radar, and perception. The experimental settings are as follows: a radar simulator is connected between the signal transmission module and the transmitting antenna to simulate a real radar ranging environment. After the RF signal passes through the simulator, the retransmitted signal carries complex white noise, distance delay, and Doppler frequency. The transmission signal parameters under the simulated environment are: signal bandwidth 1MHz, pulse repetition period (PRT) 100μs, corresponding to a maximum unambiguous distance of 15 kilometers, and a distance resolution of 50 meters. In the distance measurement interval of 0-15 kilometers, with a step size of 1 kilometer, the results of the RF calculation and its deviation from the theoretical position are recorded, and the specific data are shown in Table 1. The peak position of each group of tests falls within the allowable range of resolution, verifying the application effect of the time-coded metasurface in matched filtering. Figure 6The comparison between the RF calculation waveform and the theoretical numerical calculation results is shown when the target distance is 1 km, 3 km, 10 km and 14 km respectively. The results show that the RF calculation waveform presents a Sinc function shape, which is highly consistent with the numerical calculation results. This shows that in a complex, multi-interference, and multi-noise environment, the time-coded metasurface can still achieve accurate RF calculation. This example proves the effectiveness and accuracy of the convolution operation of the time-coded metasurface, and provides a theoretical and experimental basis for its application in actual signal processing.

[0052] In summary, the present invention realizes Fourier transform and convolution operations in signal processing by designing a simple periodic control voltage signal and using a time-coded metasurface. The RF calculator has low cost, simple structure, and is easy to integrate. It has broad application prospects and important research value and is suitable for multiple fields such as communication, radar, and perception.

[0053] The basic principle, main features and advantages of the present invention have been shown and described in detail in the foregoing. It should be understood by those skilled in the art that the present invention is not limited to these embodiments, and the descriptions in the embodiments and the specification are only used to explain the principles of the present invention. Various modifications and improvements can be made to the present invention without departing from the spirit and scope of the present invention, and these modifications and improvements are within the scope of protection of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A radio frequency calculation method based on a time-coded metasurface, characterized in that: The steps include: The mapping relationship between the echo signal R of the time-coded metasurface and the reflection coefficient code Γ is expressed as the following matrix form: Among them, I=[I[n]] N×1 is the incident signal matrix, R K×1 , Γ K×N are the echo signal matrix and the reflection coefficient coding matrix respectively, n=0,…,N-1, represents the index of the matrix in the time dimension, N and K represent the length of the input vector and the output vector respectively; Design the reflection coefficient encoding matrix Γ according to the RF calculation requirements K×N , so that the echo signal carries the information of the operation result; By demodulating the echo signal of the time-coded metasurface, the waveform information containing the required calculation results is obtained.

2. The radio frequency calculation method based on time-coded metasurface according to claim 1, characterized in that: The time-coding metasurface is a reflective structure composed of M×L basic units, in which the units in the same column share the same control signal, which can realize dynamic regulation of the radio frequency signal; the structure of the basic unit from top to bottom is a metal patch, a dielectric substrate and a metal floor; the metal patch is integrated with a varactor diode, and by adjusting the bias voltage at both ends, the reflection phase of the metasurface can be regulated in the range of 0 to 360°.

3. The radio frequency calculation method based on time-coded metasurface according to claim 2, characterized in that: The radio frequency calculation is Fourier transform, so the reflection coefficient encoding matrix is ​​designed as: The reflected echo from the metasurface will carry information about the Fourier transform of the incident wave.

4. The radio frequency calculation method based on time-coded metasurface according to claim 2, characterized in that: The RF calculation is a convolution operation, so the reflection coefficient encoding matrix is ​​designed to be Γ K×N =[Γ0,…,Γ k ,…,Γ (N-M+1) ] T , where Γ k =[[0] 1×k ,H 1×M ,[0] 1×(K-k-1) ], where H 1×M is the impulse response matrix.

5. A radio frequency computing system based on a time-coded metasurface, characterized in that: It includes a time coding metasurface, a vector signal transceiver, a waveform generator, and a radio frequency calculator; the vector signal transceiver is used to generate an input signal to be calculated, and receive an echo signal to demodulate the calculation result; The waveform generator is used to generate a periodic voltage control signal to achieve periodic switching of the metasurface reflection phase; the radio frequency calculator is used to execute any method described in claims 1-4 to perform radio frequency calculations.

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