CN116315709B - Dynamic adjustable double-frequency-band polarization conversion flexible super-surface - Google Patents
Dynamic adjustable double-frequency-band polarization conversion flexible super-surface Download PDFInfo
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- 230000010287 polarization Effects 0.000 title claims abstract description 128
- 238000006243 chemical reaction Methods 0.000 title claims abstract description 106
- 229910021542 Vanadium(IV) oxide Inorganic materials 0.000 claims abstract description 54
- GRUMUEUJTSXQOI-UHFFFAOYSA-N vanadium dioxide Chemical compound O=[V]=O GRUMUEUJTSXQOI-UHFFFAOYSA-N 0.000 claims abstract description 54
- 238000005388 cross polarization Methods 0.000 claims abstract description 39
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical group [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims abstract description 22
- 229910052751 metal Inorganic materials 0.000 claims abstract description 21
- 239000002184 metal Substances 0.000 claims abstract description 21
- 239000004642 Polyimide Substances 0.000 claims abstract description 11
- 229920001721 polyimide Polymers 0.000 claims abstract description 11
- 229920000915 polyvinyl chloride Polymers 0.000 claims abstract description 9
- 239000004800 polyvinyl chloride Substances 0.000 claims abstract description 9
- 230000033228 biological regulation Effects 0.000 claims abstract description 8
- 238000000034 method Methods 0.000 claims description 45
- 230000005684 electric field Effects 0.000 claims description 18
- 238000005070 sampling Methods 0.000 claims description 3
- 239000000758 substrate Substances 0.000 claims description 3
- 230000001419 dependent effect Effects 0.000 claims description 2
- 230000008859 change Effects 0.000 abstract description 5
- 229910052802 copper Inorganic materials 0.000 description 11
- 239000010949 copper Substances 0.000 description 11
- 239000010408 film Substances 0.000 description 11
- 230000001276 controlling effect Effects 0.000 description 6
- 239000003989 dielectric material Substances 0.000 description 5
- 230000000737 periodic effect Effects 0.000 description 4
- 230000001105 regulatory effect Effects 0.000 description 4
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- 239000000463 material Substances 0.000 description 3
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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
- H01Q15/24—Polarising devices; Polarisation filters
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
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Abstract
A dynamic adjustable dual-band polarization conversion flexible super-surface belongs to the technical field of electromagnetic metamaterials. The invention aims at the problems that the prior polarization conversion super-surface uses a rigid medium, the working frequency range is limited to a single frequency band, the prior super-surface cannot independently control the cross polarization reflection coefficient and the homopolar reflection coefficient to be maintained in a certain numerical range through phase change, the polarization conversion efficiency is difficult to control in a wide frequency band to be always maintained at a higher level, dynamic regulation and control are difficult to realize, and the like. The super surface unit is composed of a structural top layer, a polyimide medium layer, a polyvinyl chloride medium layer and a bottom layer metal plate, which are formed by combining double symmetrical quarter-opening copper rings with saw teeth and vanadium dioxide rectangular films from the top layer to the bottom layer. The dynamic regulation and control of the polarization conversion efficiency and the relative bandwidth in the double broadband are realized by changing the conductivity of vanadium dioxide, so that the flexibility and the universality are increased for the design of the deformed super-surface device in the microwave field.
Description
Technical Field
The invention belongs to the technical field of electromagnetic metamaterials, and particularly relates to a dynamic adjustable dual-band polarization conversion flexible super-surface.
Background
At present, different polarization conversions are realized by controlling the polarization states of electromagnetic waves, so that the proposal of the polarization converter brings wide application prospect for controlling various polarization states. However, the conventional polarization converter has the defects of complex manufacturing process, large volume, low efficiency and the like, and the super-surface proposal provides a new direction for the defects.
Super-surface is a two-dimensional ultrathin planar structure of a metamaterial, has electromagnetic effect which is not available in the nature, and is widely applied to the design of reflective polarization converters at present. Wherein, the polarization conversion capability of the super surface is measured mainly by the polarization conversion efficiency. Compared with the traditional metamaterial, the super surface can realize the advantages of small volume, wide bandwidth and low loss.
In recent years, the polarization conversion performance of the polarization converter can be greatly improved by optimizing various parameters in the structure of the polarization converter, but most of small polarization converters have single structures, and once the device is manufactured, the functions cannot be changed, so that the application of the polarization converter is greatly limited. In addition, the existing super surface does not independently control the cross polarization reflection coefficient and the homopolar reflection coefficient to be maintained in a certain numerical range through phase change, so that the incident electromagnetic wave is regulated and controlled, and the polarization conversion efficiency is difficult to control to be always maintained at a higher level in a wide frequency band. In the microwave field, there is a lack of polarization conversion super-surface capable of achieving both high polarization conversion efficiency and active regulation of electromagnetic waves in the same structure, and linear polarization conversion super-surface is limited to a single frequency band, and the dielectric material used is limited to a rigid medium which is not flexible. The realization of functions with high polarization conversion efficiency, dual-band characteristics, polarization conversion performance and dynamic adjustment of relative bandwidth by using flexible materials in the same structural unit is still a hotspot and difficulty of the current super-surface research.
Disclosure of Invention
Aiming at the problems that a rigid medium substrate material is difficult to bend and conformal, linear polarization conversion is limited to a single frequency band, cross polarization reflection coefficient and homopolar polarization reflection coefficient cannot be independently controlled, and the requirements of realizing independent regulation and control of polarization conversion efficiency in two working frequency bands and simultaneously realizing dynamic adjustment of polarization conversion efficiency and relative bandwidth in the microwave field are overcome, the invention provides a dynamic adjustable double-frequency-band polarization conversion flexible super-surface.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
A dynamic adjustable double-frequency band polarization conversion flexible super-surface structurally comprises four layers, namely a structural top layer, a polyimide medium layer, a polyvinyl chloride medium layer and a bottom metal plate, wherein the structural top layer is formed by combining a double-symmetrical quarter-opening copper ring with saw teeth and a vanadium dioxide rectangular film from a top layer to a bottom layer. The unit structures are periodically arranged in an o-xyz coordinate system along the x and y directions to form a super-surface microstructure, and o is the origin of coordinates.
According to the design method of the double-frequency-band flexible super-surface, the number of the vanadium dioxide rectangular films is 4, and the vanadium dioxide rectangular films and the metal patterns on the top layer are attached to the second polyimide flexible medium substrate together.
According to the design method of the double-frequency band flexible super surface, the polyimide and polyvinyl chloride medium middle layer and the bottom layer metal plate have the same size but different thicknesses.
According to the design method of the double-frequency-band flexible super-surface, the two sawtooth copper rings of the top layer pattern of the structural unit are arranged in a mirror symmetry mode and are symmetrical about a diagonal line.
According to the design method of the double-frequency-band flexible super-surface, the resonance states of the 4 vanadium dioxide rectangular films can be changed from an insulating state to a metal state in a reversible manner by changing the conductivity, and the conductivity can be changed along with the external temperature; as the applied temperature increases to 68 ℃, the vanadium dioxide will change from a high resistance insulating state to a low resistance metallic state.
The dielectric constant of the vanadium dioxide film in the microwave bandThe method can be expressed as follows:
wherein χ represents the volume fraction of vanadium dioxide in the metallic state, d represents the insulating state, k represents the metallic state, VO 2 represents vanadium dioxide, Represents the dielectric constant of vanadium dioxide, epsilon d represents the relative dielectric constant of the insulating state of vanadium dioxide, epsilon k represents the relative dielectric constant of the metallic state of vanadium dioxide. The dielectric mixing behavior is not frequency dependent at microwave frequencies and it is not significantly affected by ε d and ε k, the dielectric constant/>, of vanadium dioxide in the present inventionIs of constant value,/>
According to the design method of the double-frequency band flexible super-surface, the polarization conversion efficiency value psi of the super-surface unit meets the following conditions:
Ψ≤|Ψ0±ω|
The ψ 0 is the expected value of polarization conversion efficiency, and ω is the relative error result of polarization conversion efficiency.
According to the design method of the double-frequency band flexible super-surface, the polarization conversion efficiency psi of the super-surface unit is obtained by the following steps,
Wherein R xy represents the cross polarization reflection coefficient formed by converting the electromagnetic wave into the x-axis polarization reflection after polarization incidence along the y-axis direction of the coordinate, R yy represents the homopolar reflection coefficient formed by converting the electromagnetic wave into the y-axis polarization reflection after polarization incidence along the y-axis direction, and the two obtaining methods can be expressed as follows,
Where i denotes an incident wave, r denotes a reflected wave,Representing the electric field component of the reflected electric field along the coordinate axis x,Representing the electric field component of the incident electric field along the y-axis,/>Representing the electric field component of the reflected electric field along the y-axis. And rotating the coordinate axes x and y by 45 degrees anticlockwise to obtain the u axis and the v axis respectively. /(I)And m represents any frequency point of the cross polarization reflection coefficient in the working bandwidth, and n represents any frequency point of the homopolar reflection coefficient in the working bandwidth. /(I)And/>Respectively representing the reflection phases in the u and v axis directions at an arbitrary frequency point m. /(I)And/>The reflection phases in the u and v axis directions at an arbitrary frequency point n are respectively represented. α 1 denotes a desired value of the cross-polarization reflection coefficient, α 2 denotes a desired value of the homopolar reflection coefficient, β 1 denotes a relative error of the cross-polarization reflection coefficient, and β 2 denotes a relative error of the homopolar reflection coefficient.
The polarization conversion efficiency ψ of the subsurface unit is expressed as:
According to the design method of the dual-band flexible super-surface, the cross polarization reflection coefficient R xy and the homopolar reflection coefficient R yy of the super-surface unit are respectively converted into cross polarization reflection coefficient control functions And homopolar reflectance control function/>
Further, the polarization conversion efficiency ψ of the subsurface unit may be controlled by a polarization conversion efficiency control functionThe representation is:
and then obtaining a control model F (ψ) of polarization conversion efficiency of the super-surface unit:
Wherein J is the number of random frequency sampling points of the polarization conversion super surface in the working bandwidth, q 1 and q 2 respectively represent the starting values of the working frequencies of cross polarization reflection and homopolar reflection, and g 1 and g 2 respectively represent the final values of the working frequencies of cross polarization reflection and homopolar reflection.
The beneficial effects of the invention are that
(1) The dynamic adjustable double-frequency-band polarization conversion flexible super-surface provided by the invention can realize the conversion from an insulating state to a metal state by only controlling the conductivity of vanadium dioxide under the condition of ensuring the fixation of a structural unit, and can realize the functions of dynamically regulating and controlling the polarization conversion efficiency and the relative bandwidth in the phase change process.
(2) The dynamic adjustable double-frequency band polarization conversion flexible super-surface provided by the invention can independently respond to the cross polarization reflection coefficient and the homopolar reflection coefficient through the control function. Based on the relation between the phase and the reflection coefficient, the independent control of the cross polarization and the homopolar reflection coefficient is realized, so that the capability of regulating and controlling the incident electromagnetic wave of the super-surface unit structure is further improved.
(3) The invention provides a dynamic adjustable double-frequency-band polarization conversion flexible super-surface, which realizes quantization of super-surface polarization conversion efficiency according to given cross polarization and homopolar reflection coefficients. Based on the relation of reflection coefficient to polarization conversion efficiency, the maximization of orthogonal polarization rotation efficiency in two working frequency bands is achieved through a polarization conversion control function and a model.
(4) The dynamic adjustable double-frequency-band polarization conversion flexible super-surface provided by the invention can achieve the advantage that common rigid medium is difficult to realize bending and conformal by using the flexible intermediate medium layer, has a simple super-surface structure, is easy to realize functions, and provides a foundation for designing a device needing to consider the deformed super-surface.
Drawings
FIG. 1 is a schematic diagram of a top layer pattern of a designed dynamically tunable dual-band polarization conversion flexible supersurface unit structure;
FIG. 2 is a side view of a designed dynamically tunable dual band polarization conversion flexible supersurface unit structure;
FIG. 3 is a schematic view of a bottom copper plate of a designed dynamically tunable dual-band polarization conversion flexible subsurface unit structure;
FIG. 4 is a (3X 3) array diagram of a periodic arrangement of designed dynamically tunable dual band polarization conversion flexible subsurface unit structures;
FIG. 5 is a graph of homopolar and cross polarization reflection coefficients of a designed dynamically tunable dual-band polarization conversion flexible subsurface under y-polarization normal incidence conditions using the method of the present invention, in the vanadium dioxide insulating state;
FIG. 6 is a graph of homopolar and cross polarization reflection coefficients of a designed dynamically tunable dual-band polarization conversion flexible subsurface under y-polarization normal incidence conditions using the method of the present invention, in the vanadium dioxide metallic state;
FIG. 7 is a graph showing the phase difference of the designed dynamically tunable dual-band polarization conversion flexible subsurface in the u, v directions of an incident electromagnetic wave in the vanadium dioxide insulating state;
FIG. 8 is a graph showing the phase difference of the designed dynamically tunable dual-band polarization conversion flexible subsurface in the u, v directions of an incident electromagnetic wave in the vanadium dioxide metallic state;
FIG. 9 is a graph of polarization conversion efficiency in the as-insulated vanadium dioxide state obtained by the method of the present invention;
FIG. 10 is a graph of polarization conversion efficiency in the metallic state of vanadium dioxide obtained by the method of the present invention;
FIG. 11 is a graph of polarization conversion efficiency obtained by the method of the present invention for vanadium dioxide conductivities σ1＝10.62S/m,σ2＝2×105S/m,σ3＝102S/m,σ4＝103S/m, and σ 5＝104 S/m, respectively.
Detailed Description
In order to make the main objects, technical solutions and advantages of the present invention more clear, the following describes the implementation method of the present invention in more detail and fully according to the drawings in the embodiments of the present invention. It should be understood that the detailed description and specific examples, while indicating the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
Referring to fig. 1 to 4, the present invention provides a dynamically adjustable dual-band polarization conversion flexible super-surface, and the unit structure includes four layers from top to bottom: the top layer is a pattern layer formed by combining a double-symmetrical quarter-opening copper ring with saw teeth and a vanadium dioxide rectangular film, the first layer of intermediate medium is polyimide, the second layer of intermediate medium is polyvinyl chloride, and the bottom is a square metal copper plate. Periodically arranged in the directions of the x axis and the y axis to form a super-surface microstructure.
The top layer pattern of the structural unit is symmetrical about a diagonal line, a frequency domain solver in CST electromagnetic simulation software is adopted to carry out simulation analysis on the model, the unit structure is set to be a periodic boundary condition along the directions of an x axis and a y axis, and the unit structure is set to be an open boundary condition along the direction of a z axis. The incident electromagnetic wave is in the negative z-axis direction.
Considering the polarization conversion rate and the relative bandwidth comprehensively, the radius ranges of the open copper rings with saw teeth in the embodiment are R 1＝4.30mm、R2 =3.50 mm, the thickness is t 1 =0.035 mm, the width range of the circular rings is w 1 =0.19 mm, the open angle is optimal gamma=110°, the distance range of the two open rings is w 2 =0.44 mm, the saw teeth are composed of two cuboid copper blocks with a multiplied by b, the distance between the two saw teeth is c, and the optimal polarization conversion rate and the relative bandwidth are considered, a is 0.20mm, b is 0.20mm, and c is 0.30mm. The two sawtooth copper rings are arranged in mirror symmetry and are symmetrical about a diagonal line;
The four vanadium dioxide rectangular films in this embodiment can be selected to have a width of L 1 =0.50mm, a length of L 2 =2.50mm, and a thickness of t 2 =0.035 mm, taking into account the optimal polarization conversion rate and the relative bandwidth.
The second intermediate medium is polyimide with the length of p 1 =10 mm, the relative dielectric constant of epsilon 1 =3.1, the loss tangent angle of tan delta 1 =0.05 and the thickness of h 1, and the optimal value of the thickness h 1 is 0.08mm in consideration of the optimal polarization conversion rate and the relative bandwidth.
The third layer of intermediate medium is polyvinyl chloride with the length of p 2 =10 mm, the relative dielectric constant of epsilon 2 =3, the loss tangent angle of tan delta 2 =0.042 and the thickness of h 2. The optimal value of the thickness h 2 is 3.05mm in consideration of the optimal polarization conversion rate and the relative bandwidth.
The fourth layer of square metal plate is copper with the length of p 3 = 10mm and the thickness of t 3 = 0.035mm and the conductivity of 5.80 x 10 7 S/m;
referring to fig. 1, the four vanadium dioxide rectangular films are inlaid in the sawtooth opening copper ring and are attached to the second dielectric layer together with the sawtooth opening copper ring;
Further, when the temperature is lower than the phase transition temperature of the vanadium dioxide by 68 ℃, the vanadium dioxide is in an insulating state, and when the temperature is higher than 68 ℃, the vanadium dioxide is in a metal state;
The conductivity of vanadium dioxide is set to be sigma 1 =10.62S/m when in an insulating state, and the conductivity is set to be sigma 2＝2×105 S/m when in a metal state;
According to the design method of the double-frequency band flexible super-surface, the polarization conversion efficiency value psi of the super-surface unit meets the following conditions:
Ψ≤|Ψ0±ω|
The ψ 0 is the expected value of polarization conversion efficiency, and ω is the relative error result of polarization conversion efficiency.
According to the design method of the dual-band flexible super-surface, the method for obtaining the polarization conversion efficiency psi of the super-surface unit comprises the following steps of,
Wherein R xy represents a cross polarization reflection coefficient formed by converting an electromagnetic wave into an x-axis polarization reflection after polarization incidence in a y-axis direction, R yy represents a homopolar polarization reflection coefficient formed by converting an electromagnetic wave into a y-axis polarization reflection after polarization incidence in a y-axis direction, and the two obtaining methods can be expressed as follows:
where i denotes an incident wave, r denotes a reflected wave, Representing the electric field component of the reflected electric field along the coordinate axis x,Representing the electric field component of the incident electric field along the y-axis,/>Representing the electric field component of the reflected electric field along the y-axis. And rotating the coordinate axes x and y by 45 degrees anticlockwise to obtain the u axis and the v axis respectively. /(I)And m represents any frequency point of the cross polarization reflection coefficient in the working bandwidth, and n represents any frequency point of the homopolar reflection coefficient in the working bandwidth. /(I)And/>Respectively representing the reflection phases in the u and v axis directions at an arbitrary frequency point m. /(I)And/>The reflection phases in the u and v axis directions at an arbitrary frequency point n are respectively represented. α 1 denotes a desired value of the cross-polarization reflection coefficient, α 2 denotes a desired value of the homopolar reflection coefficient, β 1 denotes a relative error of the cross-polarization reflection coefficient, and β 2 denotes a relative error of the homopolar reflection coefficient.
The polarization conversion efficiency ψ of the subsurface unit is expressed as:
According to the design method of the dual-band flexible super-surface, the cross polarization reflection coefficient R xy and the homopolar reflection coefficient R yy of the super-surface unit are respectively converted into cross polarization reflection coefficient control functions And homopolar reflectance control function/>
Further, the polarization conversion efficiency ψ of the super surface unit is less than or equal to |ψ 0 + - ω| can be controlled by a polarization conversion efficiency control functionThe representation is:
and then obtaining a control model F (ψ) of polarization conversion efficiency of the super-surface unit:
Wherein J is the number of random frequency sampling points of the polarization conversion super surface in the working bandwidth, q 1 and q 2 respectively represent the starting values of the working frequencies of cross polarization reflection and homopolar reflection, and g 1 and g 2 respectively represent the final values of the working frequencies of cross polarization reflection and homopolar reflection.
Specific examples: 1) Designing a super-surface unit:
2) The design top layer is a double symmetrical ring-shaped vanadium dioxide film pattern structure with a quarter opening with saw teeth and a rectangle shape: the two band saw tooth split rings are copper sheets with conductivity of 5.80 multiplied by 10 7 S/m, a central angle gamma=110 degrees, an outer circular radius R 1 =4.30 mm, an inner circular radius R 2 =3.50 mm, a circular width w 1 =0.19 mm, a distance between the two circular rings is w 2 =0.44 mm, a width of saw teeth is a=0.20 mm, a length b=0.20 mm, a distance between the two saw teeth is c=0.30 mm, a width L 1 =0.50 mm, a length L 2 =2.50 mm of the four rectangular vanadium dioxide thin films are respectively, the conductivity is sigma 1 =10.62S/m in an insulating state, the conductivity is sigma 2＝2×105 S/m in a metal state, and the thickness of the saw tooth split copper rings is t 1＝t2 =0.035 mm as shown in fig. 1;
3) Designing a second flexible intermediate medium layer: creating a polyimide dielectric material, wherein the relative dielectric constant is epsilon 1 =3.10, the loss tangent angle is tan delta 1 =0.05, the side length p 1 =10 mm and the thickness h 1 =0.08 mm, and the polyimide dielectric material is shown in fig. 2;
4) Designing a third flexible intermediate medium layer: creating a polyvinyl chloride dielectric material, wherein the relative dielectric constant is epsilon 2 =3, the loss tangent angle is tan delta 2 =0.042, the side length p 2 =10 mm and the thickness h 2 =3.05 mm, and the polyvinyl chloride dielectric material is shown in fig. 2;
5) Designing a fourth layer of square metal bottom plate: the material is a copper plate with the conductivity of 5.80 multiplied by 10 7 S/m, the side length of the copper plate is the same as the side length of the medium of the second layer and the third layer, the copper plate is p 3 =10 mm, and the thickness t 3 =0.035 mm, as shown in figure 3;
6) The simulation frequency of the embodiment of the invention is set to be 6-21GHz;
7) The periodic boundary conditions of the cell structure of the embodiment of the invention are set as periodic boundary conditions along the directions of the x axis and the y axis, and are set as open boundary conditions along the direction of the z axis, and incident electromagnetic waves are in the negative direction along the z axis;
8) Simulation results of the cross polarization reflection coefficient R xy and the co-polarization reflection coefficient R yy of the insulating state and the metal state are respectively obtained by setting different conductivities of vanadium dioxide, as shown in fig. 5 and 6.
The expected value α 1 of the cross polarization reflection coefficient is set to 0.92, the expected value α 2 of the homopolar reflection coefficient is set to 0.17, the relative error β 1 of the cross polarization reflection coefficient is set to 0.10, and the relative error β 2 of the homopolar reflection coefficient is set to 0.09. As can be seen from FIG. 5, the cross polarization reflection coefficients obtained by the method of the invention in the insulating state within the two working bandwidths of 8.16-13.19GHz and 14.73-18.77GHz can reach 0.98 and 0.99 respectively, and the relative error of the cross polarization reflection coefficients is kept within 0.07; the homopolar reflection coefficient can reach 0.13 and 0.09 in two working frequency bands respectively, and the relative error of the homopolar reflection coefficient is kept within 0.08.
As can be seen from FIG. 6, the cross polarization reflection coefficient obtained by the method of the invention can reach 0.95 and 0.98 respectively in the two working bandwidths of 6.74-13.83GHz (7.85-10.59 GHz > 80%) and 15.95-18.21GHz, and the relative error of the cross polarization reflection coefficient is kept within 0.06; the homopolar reflection coefficient can reach 0.26 and 0.13 in two working frequency bands respectively, and the relative error of the homopolar reflection coefficient is kept within 0.09.
9) FIG. 7 is a graph showing phase difference curves of incident electromagnetic waves along the u-axis and v-axis when the polarization conversion super surface is in an insulating state, wherein the phase differences are close to +180+/-37 DEG and-180+/-37 DEG in the ranges of 8.16-13.19GHz and 14.73-18.77GHz, and the phase differences are completely equal to +/-180 DEG at four resonance points of 8.97, 11.93, 16.13 and 17.28GHz respectively, so that polarization conversion can be completely realized; the phase difference of 0 degrees at 14.04GHz indicates that the super surface of the embodiment of the invention has double-band characteristics when vanadium dioxide is in an insulating state;
10 FIG. 8 is a graph showing the phase difference curves of the polarization conversion super-surface in a metal state, wherein the phase difference is equal to-180 DEG at three resonance points of 7.20, 12.48 and 17.33GHz, and the phase difference is 0 DEG at 15.42GHz, which shows that the embodiment of the invention can maintain the dual-band characteristic when vanadium dioxide is in the metal state;
11 Calculation by the method of the present invention, the polarization conversion efficiency curves are shown in fig. 9 and 10:
The expected polarization conversion efficiency value ψ 0 was set to 95%, and the polarization conversion efficiency relative error result ω was set to 0.05. As can be seen from FIG. 9, the polarization conversion efficiency obtained by the method of the invention is higher than 90% in two working bandwidths of 8.16-13.19GHz and 14.73-18.77GHz, the average values are 97.71% and 98.21%, the polarization conversion efficiency error value is kept within 0.032, and the relative bandwidths capable of realizing perfect linear polarization conversion are 47.12% and 24.12% respectively; as can be seen from FIG. 10, the polarization conversion efficiency obtained by the method of the present invention is 91.29% and 97.72% in two working bandwidths of 6.74-13.83GHz (7.85-10.59 GHz > 80%) and 15.95-18.21GHz, respectively, and the polarization conversion efficiency error value is kept within 0.037, so that it is proved that the method of the present invention can achieve a better polarization conversion effect.
12 The dynamic regulation and control of the polarization conversion super-surface performance are realized by changing the conductivity of vanadium dioxide.
As shown in fig. 11, when the conductivity of vanadium dioxide is σ1＝10.62S/m,σ2＝2×105S/m,σ3＝102S/m,σ4＝103S/m, and σ 5＝104 S/m, respectively, the relative bandwidth of the first operating band gradually increases as the conductivity increases, and the polarization conversion efficiency value decreases and then increases; the relative bandwidth and polarization conversion efficiency values of the second operating band are both progressively reduced. The method of the invention achieves the effect of actively regulating and controlling the relative bandwidth and polarization conversion performance through the phase change process of vanadium dioxide, and can obtain wide double-band and high-efficiency polarization conversion in both states. Furthermore, when the four vanadium dioxide thin films are replaced with copper films, the relative bandwidths and polarization conversion efficiency values of the two frequency bands are almost equal to those when the vanadium dioxide conductivity is σ 2＝2×105 S/m. This shows that vanadium dioxide behaves like copper in the metallic state. However, the dynamic regulation function cannot be generated only by the copper film, and the polarization conversion efficiency value and the dynamic regulation performance of the relative bandwidth can be obtained by adopting the method.
The foregoing is only illustrative of specific embodiments of the invention. It will be understood by those skilled in the art that various modifications may be made to the exemplary embodiments, or other arrangements and substitutions may be made to part of the features of the embodiments without departing from the spirit and principles of the various embodiments of the invention, without affecting the spirit of the invention.
Claims (9)
1. A dynamic adjustable double-frequency band polarization conversion flexible super-surface design method is characterized in that,
Designing a super-surface unit structure, wherein the structure comprises four layers, namely a structural top layer, a polyimide medium layer, a polyvinyl chloride medium layer and a bottom layer metal plate, wherein the structural top layer is formed by combining double symmetrical quarter-opening copper rings with saw teeth, and vanadium dioxide rectangular films from top layer to bottom layer; the unit structures are periodically arranged in the o-xyz coordinate axis along the x and y directions to form a super-surface microstructure, wherein o is the origin of coordinates; wherein, the two symmetrical quarter open copper rings are mirror symmetry with each other, the whole is symmetrical about diagonal line, and the conductivity is 5.80 multiplied by 10 7 S/m; the number of the vanadium dioxide rectangular films is 4, the dielectric constant epsilon vo2 is calculated by a formula in a microwave section, the conductivity is 10.62S/m in an insulating state, and the conductivity is 2X 10 5 S/m in a metal state; the dynamic regulation and control of polarization conversion efficiency and relative bandwidth are controlled by vanadium dioxide conductivity, and the maximization of orthogonal polarization rotation efficiency in two working frequency bands is achieved through a polarization conversion control function and a model based on the relation of reflection coefficient to polarization conversion efficiency.
2. The dynamically adjustable dual-band polarization conversion flexible super-surface design method according to claim 1, wherein the method comprises the following steps:
The number of the vanadium dioxide rectangular films is 4, and the vanadium dioxide rectangular films and the metal patterns on the top layer are jointly attached to the second polyimide flexible medium substrate.
3. The dynamically adjustable dual-band polarization conversion flexible super-surface design method according to claim 2, wherein the method comprises the following steps:
the polyimide dielectric layer, the polyvinyl chloride dielectric layer and the bottom metal plate have the same size but different thicknesses.
4. A dynamically tunable dual-band polarization conversion flexible subsurface design method according to claim 3, wherein:
The resonance states of the 4 vanadium dioxide rectangular films can be changed from an insulating state to a metal state by changing the conductivity, the conductivity can be changed along with the external temperature, and the vanadium dioxide can be changed from a high-resistance insulating state to a low-resistance metal state along with the increase of the external temperature to 68 ℃.
5. The dynamically adjustable dual-band polarization conversion flexible super-surface design method according to claim 4, wherein the method comprises the following steps: dielectric constant of the vanadium dioxide rectangular film in microwave bandThe expression is as follows:
wherein χ represents the volume fraction of vanadium dioxide in the metallic state, d represents the insulating state, k represents the metallic state, VO 2 represents vanadium dioxide, Represents the dielectric constant of vanadium dioxide, ε d represents the relative dielectric constant of the insulating state of vanadium dioxide, ε k represents the relative dielectric constant of the metallic state of vanadium dioxide, the dielectric mixing behavior is not frequency dependent at microwave frequencies, and it is not significantly affected by ε d and ε k, the dielectric constant of vanadium dioxide/>Is of constant value,/>
6. The dynamically adjustable dual-band polarization conversion flexible super-surface design method according to claim 5, wherein the method comprises the following steps:
the polarization conversion efficiency value ψ of the above-mentioned super surface unit satisfies:
Ψ≤|Ψ0±ω|
The ψ 0 is the expected value of polarization conversion efficiency, and ω is the relative error result of polarization conversion efficiency.
7. The dynamically adjustable dual-band polarization conversion flexible subsurface design method as recited in claim 6, wherein,
The method for obtaining the polarization conversion efficiency psi of the super-surface unit comprises the following steps:
Wherein R xy represents a cross polarization reflection coefficient formed by converting an electromagnetic wave into an x-axis direction polarized reflection after polarization incidence in a y-axis direction of a coordinate, R yy represents a homopolar reflection coefficient formed by converting an electromagnetic wave into a y-axis direction polarized reflection after polarization incidence in a y-axis direction, and the two obtaining methods are shown below,
Where i denotes an incident wave, r denotes a reflected wave,Representing the electric field component of the reflected electric field along the x-direction of the coordinate axis,/>Representing the electric field component of the incident electric field along the y-axis,/>Representing the electric field component of the reflected electric field along the y-direction of the coordinate axis; rotating coordinate axes x and y anticlockwise by 45 degrees to obtain u and v axes respectively; /(I)As phase, m represents any frequency point of the cross polarization reflection coefficient in the working bandwidth, and n represents any frequency point of the homopolar reflection coefficient in the working bandwidth; /(I)And/>Respectively representing reflection phases in u and v axis directions at an arbitrary frequency point m; /(I)And/>Respectively representing reflection phases in u and v axis directions at an arbitrary frequency point n; alpha 1 represents a desired value of the cross polarization reflection coefficient, alpha 2 represents a desired value of the homopolar reflection coefficient, beta 1 represents a relative error of the cross polarization reflection coefficient, and beta 2 represents a relative error of the homopolar reflection coefficient;
The polarization conversion efficiency ψ of the subsurface unit is expressed as:
8. The dynamically adjustable dual-band polarization conversion flexible subsurface design method as recited in claim 7, wherein,
The cross polarization reflection coefficient R xy and the homopolar reflection coefficient R yy of the super surface unit are respectively converted into cross polarization reflection coefficient control functionsAnd homopolar reflectance control function/>
9. The method for designing a dynamically tunable dual-band polarization conversion flexible subsurface according to claim 8, wherein the value of the subsurface unit polarization conversion efficiency ψ is less than or equal to |ψ 0 ±ω| is controlled by a polarization conversion efficiency control functionThe representation is:
And then obtaining a control model F (ψ) of polarization conversion efficiency of the super-surface unit:
Wherein J is the number of random frequency sampling points of the polarization conversion super surface in the working bandwidth, q 1 and q 2 respectively represent the starting values of the working frequencies of cross polarization reflection and homopolar reflection, and g 1 and g 2 respectively represent the final values of the working frequencies of cross polarization reflection and homopolar reflection.
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