Asynchronous Spatiotemporal Encoded Metasurface

Abstract

The present invention discloses an asynchronous spatio-temporal coding metasurface. Specifically, by applying control signals with different time periods to different units on the metasurface, a dynamic spatial electromagnetic wavefront can be generated. The beneficial effects of the present invention are as follows: By applying control signals with different time periods to different spatial units, the present invention can effectively control spatial electromagnetic waves, opening up a new dimension for manipulating electromagnetic waves in the field of artificial electromagnetic metamaterials. The present invention can generate and effectively control a dynamic electromagnetic wavefront, and therefore, it can achieve automatic spatial scanning of electromagnetic waves. In addition, when it is used as a radar target, under static conditions, its radar cross section is time-varying, which is a characteristic not possessed by traditional materials. Under the illumination of monochromatic electromagnetic waves, the present invention can arbitrarily generate multiple frequencies. Compared with traditional multi-frequency generation systems (such as frequency control arrays), the hardware structure of the present invention is simple and does not require related devices such as local oscillators.

Description

Technical Field

[0001] The present invention relates to an asynchronous spatio-temporal coding metasurface, belonging to the technical field of novel artificial electromagnetic metamaterials. Background Art

[0002] The existing spatio-temporal coding metasurface technology can simultaneously design the reflection phase coding of unit cells in space and time, so that the coding metasurface can obtain the ability to control the electromagnetic wave front and spectrum simultaneously. However, all existing coding metasurfaces are designed and implemented under a synchronous framework, that is, a dynamic scattered electromagnetic wave front cannot be obtained. Summary of the Invention

[0003] Technical Problem:

[0004] The technical problem to be solved by the present invention is to provide a coding metasurface that can generate and control a dynamic electromagnetic wave front. The specific implementation method is to apply modulation signals with different time periods to the metasurface units so that the reflection frequencies of different units are no longer the same. Further, due to the different reflection frequencies of different units, the phase gradient on the asynchronous spatio-temporal coding metasurface will change dynamically, that is, a dynamic electromagnetic wave front that all previous coding metasurfaces do not have is generated. Functionally, the asynchronous spatio-temporal coding metasurface with the ability to generate and control a dynamic electromagnetic wave front can realize the automatic scanning of spatial electromagnetic waves, and under static conditions, it has the characteristic of time-varying radar cross section (RCS). Therefore, the present invention has potential application value in the fields of communication, stealth, and radar.

[0005] Technical Solution:

[0006] To solve the above technical problem, the present invention proposes an asynchronous spatio-temporal coding metasurface, including: M sub-wavelength artificial electromagnetic units arranged in a periodic manner; each sub-wavelength artificial electromagnetic unit includes an active control element; by applying different voltages across the active control element, the reflection phase of the sub-wavelength artificial electromagnetic unit for spatial electromagnetic waves can be changed, realizing a reflection phase coverage range greater than 360°.

[0007] Preferably, the voltage applied to the active control element is periodically time-varying. After obtaining the correspondence between the applied voltage and the reflection phase of the sub-wavelength artificial electromagnetic unit, by designing the corresponding applied voltage waveform, it can be ensured that the reflection phase of the unit linearly changes from 0 to 360° within a certain modulation time period, and the purpose is to shift the reflection frequency of the sub-wavelength artificial electromagnetic unit from the incident wave carrier frequency to the first harmonic.

[0008] Preferably, the voltages of the sub-wavelength artificial electromagnetic units in the same column are modulated by the same control signal, and the control signals between columns are independent of each other, that is, a control circuit needs to be set for each column.

[0009] Preferably, the control signal of the voltage is generated by a control circuit, which is composed of a Field Programmable Gate Array (FPGA), a Digital-to-Analog Conversion Module (DAC), and an Amplifier Circuit Module (Amplifier). Using the above three modules, a time-varying voltage waveform with any period can be output to ensure that the reflection phase of the unit varies linearly from 0° to 360° within any time period.

[0010] Preferably, under the condition of keeping the control waveforms of all sub-wavelength artificial electromagnetic units on the coding metasurface unchanged, by applying different time modulation periods to different sub-wavelength artificial electromagnetic units, a certain reflection frequency difference is generated between the units. The reflection frequency difference causes the phase gradient between the units to change with time, that is, a dynamic electromagnetic wavefront is generated. In addition, for different application scenarios, by performing spatial coding on the modulation period, various dynamic behaviors of the electromagnetic wavefront can be designed and realized.

[0011] Preferably, the active control element includes two PIN diodes and two varactor diodes. By adjusting the voltage applied across the two varactor diodes, the resonant structure of the sub-wavelength artificial electromagnetic unit can be equivalently changed, thereby changing its reflection phase of the spatial electromagnetic wave.

[0012] Advantageous Effects:

[0013] 1. Compared with the traditional coding metasurface, the present invention can effectively control the spatial electromagnetic wave by applying control signals with different time periods to different spatial units,

[0014] opening up a new dimension for manipulating electromagnetic waves in the field of artificial electromagnetic metamaterials.

[0015] 2. The present invention can generate and effectively control the dynamic electromagnetic wavefront. Therefore, it can realize the automatic spatial scanning of electromagnetic waves. This characteristic of the asynchronous spatio-temporal coding metasurface can eliminate the entire process of coding design for the traditional coding metasurface to achieve spatial scanning.

[0016] 3. Since the present invention can generate and effectively control the dynamic electromagnetic wavefront, when it is used as a radar target, under static conditions, its radar cross-section area changes with time, which is a characteristic not possessed by traditional materials.

[0017] 4. Under the irradiation of monochromatic electromagnetic waves, the present invention can arbitrarily generate multiple frequencies. Compared with the traditional multi-frequency generation system (such as a frequency control array), the hardware structure of the present invention is simple and does not require related devices such as local oscillators. Description of the Drawings

[0018] Figure 1 This is the asynchronous spatio-temporal coding metasurface of the present invention.

[0019] Figure 2In the present invention, it is the sub-wavelength artificial electromagnetic unit of the asynchronous spatio-temporal coding metasurface.

[0020] Figure 3 In the present invention, it is the curve of the reflectivity of the unit varying with voltage. Among them, (a) is the curve of the reflection amplitude varying with voltage; (b) is the curve of the reflection phase varying with voltage.

[0021] Figure 4 Under the condition that the modulation frequency difference between adjacent arrays is 100 kHz, the law of the spatial scattering pattern varying with time.

[0022] Figure 5 Under the condition that the modulation frequency difference between adjacent arrays is 200 kHz, the law of the spatial scattering pattern varying with time.

[0023] Figure 6 Under the condition that the modulation time period has different spatial distributions, the variation characteristics of the RCS of the asynchronous spatio-temporal coding metasurface with time. Among them, (a) is the time modulation period corresponding to different columns in the coding metasurface; (b) is the characteristic curve of the RCS of the asynchronous spatio-temporal coding metasurface varying with time under different time modulation period distributions. Detailed implementation manners

[0024] As Figure 1 shown, an asynchronous spatio-temporal coding metasurface is composed of M sub-wavelength artificial electromagnetic units arranged in a period. The metasurface used in this embodiment has 8×16 units. Each unit contains two pin diodes and two varactor diodes, as Figure 2 shown. By adjusting the voltage applied across the two varactor diodes from 0 V to 21 V, it can be ensured that at the frequency point of 4.25 GHz, while the reflection amplitude fluctuates less than 3 dB, the reflection phase coverage range of the unit is greater than 360°, as Figure 3 shown.

[0025] The voltage control signal of the present invention can be described by a control waveform and a waveform period. Specifically, the voltage control waveform of the present invention is to make the reflection phase of the unit linearly change from 0° to 360° within a certain time period. Its purpose is to ensure that the reflection frequency of the unit is completely shifted from the incident wave carrier frequency to the first harmonic. At this time, by setting different modulation periods for different units, there will be a frequency difference in the reflection frequencies between the units. Further, the electromagnetic wave reflection frequency difference between the units will cause the spatial phase gradient of the coding metasurface to vary with time, thereby generating a dynamic spatial scattering electromagnetic wave front.

[0026] In the present invention, by performing spatial coding on the time modulation period on the coding metasurface, the behavior of the dynamic electromagnetic wave front can be effectively controlled.

[0027] On the asynchronous spatio-temporal coding metasurface, the units in the same column are modulated by the same control signal, and the modulation signals between columns are independent of each other. The control signal is generated by the FPGA, output by the DAC module, amplified by the Amplifier, and finally loaded onto the coding metasurface in the form of a corresponding voltage (the corresponding voltage that can generate the target reflection phase).

[0028] Embodiment 1:

[0029] In the present invention, the automatic spatial scanning of electromagnetic waves can be realized by using the asynchronous spatio-temporal coding metasurface. Specifically, adopting the modulation waveform described above, keeping the modulation time of each column of units in the coding metasurface unchanged, and keeping the modulation frequency difference between adjacent columns unchanged (i.e., the modulation frequency increases linearly on the array plane). At this time, the coding metasurface will maintain a dynamic phase gradient, that is, generate a dynamic spatial scattering pattern, as Figure 4 shown. Further, the speed of the automatic spatial scanning of electromagnetic waves can be adjusted by adjusting the modulation frequency difference between adjacent columns. As Figure 5 shown, when the modulation frequencies of adjacent columns are increased to twice, the time to complete the same automatic spatial scanning is reduced to half. On the other hand, at the initial moment, the spatial direction of the scattering pattern of the asynchronous coding metasurface can be arbitrarily set by changing the initial transient phase gradient of the metasurface.

[0030] Embodiment 2:

[0031] In the present invention, the asynchronous spatio-temporal coding metasurface is regarded as a radar target, and its radar cross section (RCS) can be observed to be dynamic. Adopting the modulation waveform described above and applying different time modulation periods to each column on the coding metasurface at the same time, the coding metasurface can obtain a time-varying RCS. Further, by designing the spatial distribution of the modulation period on the coding metasurface (i.e., the spatial coding of the time modulation period), the curve characteristics of its time-varying RCS can be effectively controlled. For example, under the condition of keeping the control signal waveform of the entire coding metasurface unchanged, aiming at reducing the RCS of the asynchronous spatio-temporal coding metasurface within a period of time, the present invention respectively performs random spatial coding, genetic algorithm (GA) spatial coding, and particle swarm optimization algorithm (PSO) spatial coding on the modulation period. The curves of the RCS of the asynchronous spatio-temporal coding metasurface changing with time are as Figure 6 (b) shown. It can be seen from the figure that the RCS of the coding metasurface can change with time for all three spatial codings, and after 30 μs, the RCS can be reduced to more than 10 dB. In particular, for the genetic algorithm (GA) spatial coding and the particle swarm optimization algorithm (PSO) spatial coding, the RCS can be reduced to more than 20 dB.

Claims

1. An asynchronous spatio-temporal coding metasurface, characterized in that, it comprises M sub-wavelength artificial electromagnetic units arranged in a periodic manner; each sub-wavelength artificial electromagnetic unit contains an active control element; by applying different voltages across the active control element, the reflection phase of the sub-wavelength artificial electromagnetic unit for spatial electromagnetic waves can be changed, achieving a reflection phase coverage range greater than 360°; the voltage applied to the active control element is periodically time-varying. After obtaining the correspondence between the applied voltage and the reflection phase of the sub-wavelength artificial electromagnetic unit, by designing the corresponding voltage waveform, it can be ensured that the reflection phase of the unit linearly changes from 0 to 360° within a certain modulation time period, with the aim of shifting the reflection frequency of the sub-wavelength artificial electromagnetic unit from the incident wave carrier frequency to the first harmonic; the voltages of the sub-wavelength artificial electromagnetic units in the same column are modulated by the same control signal, and the control signals between different columns are independent of each other; under the condition of keeping the control waveforms of all sub-wavelength artificial electromagnetic units on the coding metasurface unchanged, by applying different time modulation periods to different sub-wavelength artificial electromagnetic units, a certain reflection frequency difference is generated between the units; the reflection frequency difference causes the phase gradient between the units to change with time, that is, a dynamic electromagnetic wavefront is generated; for different application scenarios, by spatially coding the modulation period, various dynamic behaviors of the electromagnetic wavefront can be designed and realized.

2. The asynchronous spatio-temporal coding metasurface according to claim 1, characterized in that, the control signal of the voltage is generated by a control circuit, and the control circuit is composed of a field programmable gate array FPGA, a digital-to-analog conversion module DAC and an amplifier circuit module Amplifier; the control circuit can output a time-varying voltage waveform with any period to ensure that the reflection phase of the unit linearly changes from 0° to 360° within any time period.

3. The asynchronous spatio-temporal coding metasurface according to claim 1, characterized in that, the active control element includes two pin diodes and two varactor diodes; by adjusting the voltage applied across the two varactor diodes, the resonant structure of the sub-wavelength artificial electromagnetic unit can be equivalently changed, thereby changing its reflection phase for spatial electromagnetic waves.

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