CN114678695A - Asynchronous space-time coded hyper-surface - Google Patents
Asynchronous space-time coded hyper-surface Download PDFInfo
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- CN114678695A CN114678695A CN202210253056.2A CN202210253056A CN114678695A CN 114678695 A CN114678695 A CN 114678695A CN 202210253056 A CN202210253056 A CN 202210253056A CN 114678695 A CN114678695 A CN 114678695A
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
- H01Q15/0006—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices
- H01Q15/0086—Devices acting selectively as reflecting surface, as diffracting or as refracting device, e.g. frequency filtering or angular spatial filtering devices said selective devices having materials with a synthesized negative refractive index, e.g. metamaterials or left-handed materials
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01Q—ANTENNAS, i.e. RADIO AERIALS
- H01Q15/00—Devices for reflection, refraction, diffraction or polarisation of waves radiated from an antenna, e.g. quasi-optical devices
Abstract
The invention discloses an asynchronous space-time coding super surface. In particular, by applying control signals having different time periods to different elements on the super surface, a dynamic spatial electromagnetic wave front can be generated. The invention has the beneficial effects that: according to the invention, the control signals with different time periods are applied to different space units, so that the space electromagnetic waves can be effectively controlled, and a new dimension capable of controlling the electromagnetic waves is developed for the field of artificial electromagnetic metamaterials. The invention can generate and effectively control the dynamic wavefront of the electromagnetic wave, thereby realizing the automatic space scanning of the electromagnetic wave. In addition, when the material is used as a radar target, the radar scattering cross section is time-varying under a static condition, which is not possessed by the traditional material. Under the irradiation of monochromatic electromagnetic waves, the invention can generate a plurality of frequencies at will. Compared with the traditional multi-frequency generation system (such as a frequency control array), the multi-frequency generation system has a simple hardware structure and does not need related devices such as a local vibration source and the like.
Description
Technical Field
The invention relates to an asynchronous space-time coding super surface, and belongs to the technical field of novel artificial electromagnetic metamaterials.
Background
The existing space-time coding super surface technology can design unit reflection phase coding in space and time at the same time, so that the coded super surface obtains the regulation and control capability of electromagnetic wave front and frequency spectrum at the same time. However, the existing coded super-surface is designed and realized under a synchronous frame, namely, a dynamic scattered electromagnetic wave front cannot be obtained.
Disclosure of Invention
The technical problem is as follows:
the technical problem to be solved by the invention is to provide a coded super surface capable of generating and controlling the wave front of a dynamic electromagnetic wave. This is accomplished by applying modulation signals having different time periods to the super-surface elements so that the reflection frequencies of the different elements are no longer uniform. Furthermore, due to the difference of reflection frequencies of different units, the phase gradient on the asynchronous space-time coding super surface can be dynamically changed, namely, dynamic electromagnetic wave fronts which are not possessed by all the previous coding super surfaces are generated. Functionally, the asynchronous space-time coding super-surface with the capability of generating and controlling the wavefront of the dynamic electromagnetic wave can realize the automatic scanning of the space electromagnetic wave, and has the characteristic of time-varying radar scattering cross-sectional area (RCS) under the static condition. Therefore, the method has potential application value in the fields of communication, stealth and radar.
The technical scheme is as follows:
to solve the above technical problem, the present invention provides an asynchronous space-time coding super surface, comprising: m sub-wavelength artificial electromagnetic units which are arranged periodically; each sub-wavelength artificial electromagnetic unit comprises an active control element; by applying different voltages to two ends of the active control element, the reflection phase of the sub-wavelength artificial electromagnetic unit to the space electromagnetic wave can be changed, and the coverage range of the reflection phase larger than 360 degrees is realized.
Preferably, the voltage loaded to the active control element is periodically time-varying, and after the corresponding relationship between the loaded voltage and the reflection phase of the sub-wavelength artificial electromagnetic unit is obtained, the reflection phase of the unit can be ensured to be linearly changed from 0 to 360 degrees within a certain modulation time period by designing a corresponding loaded voltage waveform, so that the reflection frequency of the sub-wavelength artificial electromagnetic unit is shifted to a first-order harmonic from an incident wave carrier frequency.
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 the columns are independent, that is, each column needs to be provided with a control circuit.
Preferably, the control signal of the voltage is generated by a control circuit, and the control circuit consists of a field programmable gate array FPGA, a digital-to-analog conversion module DAC and an amplification circuit module Amplifier; the three modules can be used for outputting time-varying voltage waveforms with any period so as to ensure that the cell reflection phase realizes linear change of 0-360 degrees in any time period.
Preferably, under the condition of keeping the control waveforms of all the sub-wavelength artificial electromagnetic units on the coded super-surface unchanged, different time modulation periods are applied to different sub-wavelength artificial electromagnetic units, so that a certain reflection frequency difference is generated among the units; the reflection frequency difference can cause the phase gradient among the units to change along with time, namely, dynamic electromagnetic wave front is generated; in addition, for different application scenes, by carrying out spatial coding on the modulation period, the dynamic behavior of various electromagnetic wave wavefronts can be designed and realized.
Preferably, the active control element comprises two pin diodes and two varactors; by adjusting the voltages loaded at the two ends of the two variable capacitance diodes, the resonance structure of the sub-wavelength artificial electromagnetic unit can be equivalently changed, and the reflection phase of the sub-wavelength artificial electromagnetic unit on the space electromagnetic wave is further changed.
Has the advantages that:
1. compared with the traditional coded super surface, the invention applies control signals with different time periods to different space units,
the electromagnetic wave in the space can be effectively controlled, and a new dimension capable of controlling the electromagnetic wave is developed for the field of artificial electromagnetic metamaterials.
2. The invention can generate and effectively control the dynamic wavefront of the electromagnetic wave, thereby realizing the automatic space scanning of the electromagnetic wave. The characteristic of the asynchronous space-time coding super surface can save the whole process of making coding design for realizing space scanning by the traditional coding super surface.
3. The invention can generate and effectively control the dynamic electromagnetic wave front, when the dynamic electromagnetic wave front is used as a radar target, the radar scattering cross section is changed along with time under the static condition, and the characteristic is not possessed by the traditional material.
4. Under the irradiation of monochromatic electromagnetic waves, the invention can generate a plurality of frequencies at will. Compared with the traditional multi-frequency generation system (such as a frequency control array), the multi-frequency generation system has a simple hardware structure and does not need related devices such as a local vibration source and the like.
Drawings
FIG. 1 is a block diagram of an asynchronous space-time coded hyper-surface of the present invention.
FIG. 2 is a diagram of a sub-wavelength artificial electromagnetic unit of an asynchronous space-time coding super surface in the invention.
FIG. 3 is a graph showing the reflectance of a cell according to the present invention. Wherein, (a) is a curve of the reflection amplitude changing with the voltage; and (b) is a curve of the reflection phase along with the voltage change.
FIG. 4 shows the time-varying law of the spatial scattering pattern under the condition that the modulation frequency difference of adjacent arrays is 100 kHz.
FIG. 5 shows the time-varying law of the spatial scattering pattern under the condition that the modulation frequency difference of adjacent arrays is 200 kHz.
FIG. 6 is a graph of the time-varying characteristics of an asynchronous space-time coded hyper-surface RCS with different spatial distributions of modulation time periods. Wherein, (a) is the time modulation period corresponding to different columns in the coded super surface; (b) the characteristic curve of the RCS of the asynchronous space-time coding super surface along with the change of time under the condition of different time modulation period distribution.
Detailed Description
As shown in FIG. 1, an asynchronous space-time coded super surface is composed of M sub-wavelength artificial electromagnetic units arranged periodically. The super surface used in this example has 8 × 16 cells. Each cell contains two pin diodes and two varactors as shown in fig. 2. By adjusting the voltage loaded at the two ends of the two varactors from 0V to 21V, it can be ensured that the unit reflection phase coverage is larger than 360 ° while the reflection amplitude fluctuation is smaller than 3dB at the frequency point of 4.25GHz, as shown in fig. 3.
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 invention is to make the unit reflection phase change from 0 degree to 360 degrees linearly in a certain time period, so as to ensure that the unit reflection frequency is completely shifted to a first-order harmonic from the incident wave carrier frequency. In this case, different modulation periods are set for different cells, and the reflection frequency between the cells has a frequency difference. Furthermore, the electromagnetic wave reflection frequency difference between units can lead the spatial phase gradient of the coding super surface to change along with time, thereby generating dynamic spatial scattering electromagnetic wave front.
In the invention, the behavior of the dynamic electromagnetic wave wavefront can be effectively controlled by carrying out spatial coding on the time modulation period on the coded super surface.
On an asynchronous space-time coded super-surface, the elements in the same column are modulated by the same control signal, and the modulation signals between the columns are independent. The control signal is generated by the FPGA, is output by the DAC module, is amplified by the Amplifier and is loaded on the coded super surface in the form of corresponding voltage (corresponding voltage capable of generating a target reflection phase).
Example 1:
in the invention, the asynchronous space-time coding super surface can be utilized to realize automatic space scanning of electromagnetic waves. Specifically, with the modulation waveform described above, the modulation time of each column of cells in the encoded super surface is kept constant, and the modulation frequency difference between two adjacent columns is kept constant (i.e., the modulation frequency increases linearly over the wavefront). At this point, the encoded super-surface maintains a dynamic phase gradient, i.e., a dynamic spatial scattering pattern is generated, as shown in FIG. 4. Further, the speed of the electromagnetic wave space automatic scanning can be adjusted by adjusting the modulation frequency difference between two adjacent columns. As shown in fig. 5, when the modulation frequency of two adjacent columns is doubled, the time for completing the same spatial auto-scan is reduced to half. On the other hand, at the initial instant, the spatial orientation of the scattering pattern of the asynchronously encoded super-surface can be arbitrarily set by changing the super-surface initial transient phase gradient.
Example 2:
in the invention, the asynchronous space-time coding super surface is regarded as a radar target, and the radar scattering cross section (RCS) of the radar target is observed to be dynamic. The time-varying RCS of the encoded super-surface is achieved by applying the modulation waveform described above to each column of the encoded super-surface simultaneously with a different time modulation period. Further, by designing the spatial distribution of the modulation period on the coded super-surface (i.e., spatial coding of the time modulation period), the curve characteristics of the time-varying RCS can be effectively controlled. For example, under the condition of keeping the waveform of the control signal of the whole coded super-surface unchanged, the method aims to reduce the RCS of the asynchronous space-time coded super-surface in a period of time, random space coding, Genetic Algorithm (GA) space coding and Particle Swarm Optimization (PSO) space coding are respectively adopted for a modulation period, and the obtained curve of the RCS of the asynchronous space-time coded super-surface along with the change of time is shown in figure 6 (b). As can be seen from the figure, all three spatial codes can make the RCS of the coded super-surface change along with time, and can reduce the RCS to more than 10dB after 30 mus, especially the Genetic Algorithm (GA) spatial code and the Particle Swarm Optimization (PSO) spatial code can reduce the RCS to more than 20 dB.
Claims (6)
1. An asynchronous space-time coded super-surface is characterized by comprising M sub-wavelength artificial electromagnetic units which are periodically arranged; each sub-wavelength artificial electromagnetic unit comprises an active control element; by applying different voltages to two ends of the active control element, the reflection phase of the sub-wavelength artificial electromagnetic unit to the space electromagnetic wave can be changed, and the coverage range of the reflection phase larger than 360 degrees is realized.
2. The asynchronous space-time coded metasurface of claim 1, wherein a voltage applied to the active control element is periodically time-varying, and after a corresponding relationship between the applied voltage and a reflection phase of the subwavelength artificial electromagnetic unit is obtained, a linear change of the reflection phase of the unit from 0 to 360 ° within a certain modulation time period is ensured by designing a corresponding applied voltage waveform, so that a reflection frequency of the subwavelength artificial electromagnetic unit is shifted from an incident wave carrier frequency to a first-order harmonic.
3. The asynchronous space-time coded metasurface of claim 1 wherein voltages of sub-wavelength artificial electromagnetic units in a same column are modulated by a same control signal, the control signals between each column being independent of each other.
4. The asynchronous space-time coded hyper-surface of claim 3, wherein control signals of the voltages are generated by a control circuit, the control circuit is composed of a Field Programmable Gate Array (FPGA), a digital-to-analog conversion module (DAC) and an amplification circuit module (Amplifier); the three modules can be used for outputting a time-varying voltage waveform with any period so as to ensure that the cell reflection phase realizes linear change from 0 degrees to 360 degrees in any time period.
5. The asynchronous space-time coded metasurface of claim 1, wherein a certain reflection frequency difference is generated between units by applying different time modulation periods to different subwavelength artificial electromagnetic units under the condition that control waveforms of all subwavelength artificial electromagnetic units on the coded metasurface are kept unchanged; the reflection frequency difference can cause the phase gradient among the units to change along with time, namely, dynamic electromagnetic wave front is generated; in addition, for different application scenes, by carrying out spatial coding on the modulation period, the dynamic behavior of various electromagnetic wave wavefronts can be designed and realized.
6. The asynchronous space-time coded hyper-surface of claim 1, wherein the active control element comprises two pin diodes and two varactors; by adjusting the voltages loaded at the two ends of the two variable capacitance diodes, the resonance structure of the sub-wavelength artificial electromagnetic unit can be equivalently changed, and the reflection phase of the sub-wavelength artificial electromagnetic unit on the space electromagnetic wave is further changed.
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