CN116259981A - Reconfigurable super-surface for flexibly controlling diffraction-free surface wave - Google Patents
Reconfigurable super-surface for flexibly controlling diffraction-free surface wave Download PDFInfo
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- CN116259981A CN116259981A CN202310425068.3A CN202310425068A CN116259981A CN 116259981 A CN116259981 A CN 116259981A CN 202310425068 A CN202310425068 A CN 202310425068A CN 116259981 A CN116259981 A CN 116259981A
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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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- 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
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
- Y02D30/00—Reducing energy consumption in communication networks
- Y02D30/70—Reducing energy consumption in communication networks in wireless communication networks
Abstract
The invention discloses a reconfigurable super-surface for flexibly controlling a diffraction-free surface wave, which consists of a passive gradient refractive index unit array and an electrically adjustable gradient refractive index unit array. Unlike available diffraction-free surface wave generator with fixed structure and function, the electrically adjustable gradient refractive index unit of the present invention has integrated electrically adjustable element, and through smart control circuit design, the voltage control module may be used to alter the refractive index distribution of the electrically adjustable gradient refractive index unit array in real time to form the surface wave from cylindrical surface wave to diffraction-free surface wave and realize the dynamic regulation and control of the propagation direction and diffraction-free distance of diffraction-free surface wave. The invention is expected to be applied to the fields of surface wave energy transmission, short-range communication, wireless charging and the like.
Description
Technical Field
The invention belongs to the technical field of novel artificial super-surface arrays, and particularly relates to a reconfigurable super-surface for flexibly controlling a diffraction-free surface wave.
Background
Electromagnetic surface waves are modes of electromagnetic wave propagation that exist at the interface of two different materials. They are referred to in optics as surface plasmons; at microwave frequencies they are important factors leading to electromagnetic interference, compatibility and coupling effects. Surface waves are also an effective solution for electromagnetic energy and information transmission, since they are easily excited by spatial waves. Heretofore, researchers have proposed a range of devices to manipulate them, including surface wave waveguides, beam shifters, self-focusing surfaces, surface wave pulse routing, comb-like free-radical transmission lines, hyperbolic supersurfaces, and the like. These outstanding studies are expected to realize a wide range of applications of surface waves.
As with other types of waves in nature, electromagnetic waves undergo natural divergence during propagation. Researchers want to counteract this effect by some means, resulting in diffraction-free transmission phenomena. Bessel beams are a typical non-diffracted beam, proposed by Durnin et al in 1987. This is physically impossible to achieve because an ideal bessel beam requires infinite energy, but quasi-bessel beams with non-diffractive properties have been widely demonstrated. In the diffraction-free propagation region of the quasi-Bessel beam, the energy of electromagnetic waves is very concentrated, so that the method has high application value. quasi-Bessel beams are interference patterns created by superposition of innumerable coherent plane waves, which can be created using axicon structures, dielectric lenses, and radial slot arrays. In recent years, a large number of non-diffracting beam generators have been realized based on phase modulation supersurfaces, gradient index supersurfaces, holographic supersurfaces, planar leaky radial waveguides, and the like. For electromagnetic surface waves, researchers have achieved non-diffracted surface waves by combining a half maxwell fish-eye lens with a graded index lens. However, the direction of the undiffracted beam in the above-mentioned studies is mostly parallel to the normal direction of the generator aperture, and only a few devices are involved in the generation of oblique undiffracted beams. Moreover, most of the existing devices have fixed performance, and the generated diffraction-free beam cannot be controlled in real time. At present, no report on flexible control of a non-diffraction surface wave generator is known.
Disclosure of Invention
The invention aims to realize real-time and dynamic regulation and control of the propagation direction and the diffraction-free distance of the diffraction-free surface wave, and provides a reconfigurable super surface for flexibly controlling the diffraction-free surface wave;
in order to achieve the above purpose, the present invention adopts the following technical scheme: the reconfigurable super surface for flexibly controlling the diffraction-free surface wave comprises a first passive gradient refractive index impedance matching unit array, a passive gradient refractive index unit array, a second passive gradient refractive index impedance matching unit array, a first constant refractive index impedance matching unit array, an electrically adjustable unit array and a second constant refractive index impedance matching unit array which are sequentially arranged on a dielectric plate along the propagation direction of the surface wave;
the passive gradient refractive index unit array is used for converting the cylindrical wavefront of the transverse magnetic surface wave excited by the surface wave source into a planar wavefront;
the electrically adjustable unit array is used for converting the plane wavefront of the transverse magnetic surface wave into a diffraction-free wave beam, and changing the refractive index distribution in real time under the action of direct current voltage output by the direct current voltage module so as to dynamically switch the direction and diffraction-free distance of the diffraction-free wave beam;
the first passive gradient index impedance matching unit array is used for inhibiting reflection between the passive gradient index unit array and the non-unit part of the dielectric plate;
the second passive gradient index impedance matching unit array is used for inhibiting reflection between the passive gradient index unit array and the first constant index impedance matching unit array;
the first constant refractive index impedance matching unit array is used for inhibiting reflection between the electrically adjustable unit array and the second passive gradient refractive index impedance matching unit array;
the second constant refractive index impedance matching cell array is for suppressing reflection between the electrically tunable cell array and the cell-free portion of the dielectric plate.
Further, the unit-free dielectric plate comprises a first metal layer, a first dielectric layer, a second metal layer, a second dielectric layer and a third metal layer which are sequentially connected with one another along the vertical direction;
the first passive gradient refractive index impedance matching unit array, the passive gradient refractive index unit array, the second passive gradient refractive index impedance matching unit array, the first constant refractive index impedance matching unit array, the electrically adjustable unit array and the second constant refractive index impedance matching unit array are located on the second metal layer and above, and the third metal layer is provided with a direct current feeder.
Further, the array of electrically tunable elements comprises M rows by N columns of electrically tunable sub-wavelength elements;
the passive gradient refractive index unit array comprises P rows by N columns of passive sub-wavelength units;
the first passive gradient refractive index impedance matching unit array, the second passive gradient refractive index impedance matching unit array, the first constant refractive index impedance matching unit array and the second constant refractive index impedance matching unit array respectively comprise Q rows and N columns of passive subwavelength units;
and M, N, P, Q is a positive integer of 2 or more.
Further, the electrically tunable sub-wavelength unit comprises a metal inner ring, a metal middle ring, a metal outer ring, a metal patch, a first metal blind hole and a varactor diode;
the metal inner ring, the metal middle ring and the metal outer ring are arranged on the first metal layer, the metal inner ring is connected with the second metal layer through a first metal blind hole, the second metal layer is connected with one pole of the direct-current voltage module through a wire, one pole of the varactor is connected with the metal inner ring, the other pole of the varactor is connected with the metal middle ring, the metal middle ring is connected with the metal outer ring through a metal patch, and the metal outer ring is connected with the metal outer ring of the electrically adjustable sub-wavelength unit adjacent along the propagation direction of the surface wave through a resistor;
the metal outer ring at the far end along the propagation direction of the surface wave in the electrically adjustable unit array is connected with a feeding patch through a resistor, the feeding patch is connected with a direct current feeder through a feeding metal through hole, and the direct current feeder is connected with the other pole of the direct current voltage module through a wire.
Further, the passive sub-wavelength unit comprises a square patch, a square ring and a second metal blind hole, wherein the square patch and the square ring are arranged on the first metal layer, the square patch is arranged on the inner side of the square ring, and the center of the square patch is connected with the metal layer connected with the negative electrode of the varactor diode in the electrically adjustable sub-wavelength unit through the second metal blind hole.
Further, the side lengths of the square patches in the same column in each of the passive gradient refractive index unit array, the first passive gradient refractive index impedance matching unit array and the second passive gradient refractive index impedance matching unit array are the same, the side lengths of the square patches in different columns are distributed in a gradient decreasing mode from the middle column to the two side columns, and the side lengths of the square patches in the passive gradient refractive index unit array in the same column are larger than those of the square patches in the first passive gradient refractive index impedance matching unit array and the second passive gradient refractive index impedance matching unit array.
Further, the second metal layer is fully covered by metal, a circular hole is formed in the second metal layer, the center of the circular hole is the same as that of the feeding metal through hole, the diameter of the circular hole is larger than that of the feeding metal through hole, and the feeding patch penetrates through the circular hole through the feeding metal through hole and is connected with the direct current feeder.
Further, the number of the varactors is four, and the four varactors are arrayed along the edge of the metal inner ring.
Further, the number of the first metal blind holes is four, and the four first metal blind holes are respectively arranged on four corners of the metal inner ring.
The beneficial effects are that:
1. compared with the existing non-diffraction surface wave generator, the invention utilizes the voltage control module to change the refractive index distribution of the electrically adjustable gradient refractive index unit array in real time, thereby dynamically adjusting the propagation direction and the non-diffraction distance of the non-diffraction surface wave, and meeting the application requirements of various non-diffraction surface waves;
2. according to the invention, the passive gradient refractive index unit array is loaded in the reconfigurable super surface, so that the surface wave cylindrical wave is rapidly converted into the plane wave front, thus greatly reducing the distance between a feed source and an array, and effectively reducing the system volume, the array scale and the array design and difficulty;
3. according to the invention, through integrating the electrically adjustable elements, the mutually independent control of N rows of electrically adjustable sub-wavelength units is realized, and the real-time control of diffraction-free beams is realized under lower control difficulty;
4. the invention can be prepared by using a mature PCB processing technology and an element surface-mounting technology, and has the advantages of small processing difficulty, low cost and the like.
Drawings
FIG. 1 is a schematic three-dimensional view of a reconfigurable supersurface for flexible manipulation of non-diffracted surface waves in accordance with the invention;
FIG. 2 is a schematic view of a bottom feed line of a reconfigurable subsurface of the present invention;
FIG. 3 is a schematic diagram of a reconfigurable subsurface in accordance with an embodiment of the present invention;
FIG. 4 is a layout of an array of passive gradient index units and an array of passive gradient index impedance matching units in an embodiment of the invention;
fig. 5 is a schematic three-dimensional structure of a passive sub-wavelength unit according to an embodiment of the present invention.
FIG. 6 is a graph showing the equivalent refractive index of a passive sub-wavelength cell according to the side length of a square metal sheet inside the cell;
FIG. 7 is a layout diagram of an array of electrically tunable cells and an array of constant index impedance matching cells in an embodiment of the invention;
FIG. 8 is a schematic diagram of a three-dimensional structure of an electrically tunable sub-wavelength unit according to an embodiment of the present invention;
FIG. 9 is a schematic top view of an electrically tunable sub-wavelength unit according to an embodiment of the present invention;
FIG. 10 is a graph showing the equivalent refractive index of an electrically tunable sub-wavelength unit as a function of capacitance of a varactor according to an embodiment of the present invention;
FIG. 11 is an equivalent refractive index distribution of an array of passive gradient index units and an array of passive gradient index impedance matching units in an embodiment of the invention;
FIG. 12 is a voltage distribution diagram of each column of cells of an electrically tunable cell array implementing four different non-diffracted beams, namely "normal close-range non-diffraction", "normal far-range non-diffraction", "right-bias non-diffraction", "left-bias non-diffraction", in an embodiment of the present invention;
FIG. 13 is a graph showing the electric field amplitude distribution of a plane wave front surface wave after a cylindrical surface wave excited by a waveguide obtained by simulation in the embodiment of the present invention passes through a passive gradient refractive index unit array and a passive gradient refractive index impedance matching unit array;
FIG. 14 is a graph showing the electric field amplitude distribution of three diffraction-free beams switchable in real time at 9GHz obtained by simulation in the example of the present invention;
FIG. 15 is a pictorial representation of a reconfigurable subsurface for flexible manipulation of non-diffracted surface waves, in accordance with an embodiment of the present invention;
FIG. 16 is a diagram of a test environment for flexibly manipulating reconfigurable subsurface of non-diffracted surface waves in an embodiment of the invention;
FIG. 17 is a graph showing the phase shift of surface wave propagation as a function of voltage for all cells in an array of electrically tunable cells under the same reverse bias DC voltage control in an embodiment of the present invention;
fig. 18 is a graph showing the electric field amplitude distribution of four real-time switchable non-diffracted beams obtained by testing in the example of the present invention.
In the figure: 1. the array of first passive gradient refractive index impedance matching units, 2, passive gradient refractive index unit array, 3, second passive gradient refractive index impedance matching unit array, 4, first constant refractive index impedance matching unit array, 5, passive subwavelength unit, 6, electrically tunable subwavelength unit, 7, second constant refractive index impedance matching unit array, 8, direct current feeder line, 9, electrically tunable unit array, 10, first metal layer, 11, first dielectric layer, 12, second metal layer, 13, second dielectric layer, 14, third metal layer, 15, direct current voltage module, 16, dielectric plate, 41, feed patch, 42, feed metal through hole, 51, square patch, 52, square ring, 53, first metal blind hole, 61, metal inner ring, 62, metal middle ring, 63, metal outer ring, 64, metal patch, 65, second metal blind hole, 66, varactor diode, 67, resistance.
Detailed Description
The invention is further explained below with reference to the drawings.
A reconfigurable supersurface for flexible manipulation of non-diffracted surface waves in accordance with the invention has the general structure shown in fig. 1-2. The horizontal transverse direction is the x direction, the propagation direction of the surface wave is the y direction, and the vertical direction is the z direction. The first passive gradient index impedance matching unit array 1, the passive gradient index unit array 2, the second passive gradient index impedance matching unit array 3, the first constant index impedance matching unit array 4, the electrically adjustable unit array 9 and the second constant index impedance matching unit array 7 in the reconfigurable super surface are sequentially arranged on the dielectric plate 16 along the y direction. The dielectric plate 16 is a printed circuit board structure, and the dielectric plate 16 sequentially comprises a first metal layer 10, a first dielectric layer 11, a second metal layer 12, a second dielectric layer 13 and a third metal layer 14 from top to bottom along the z direction; wherein the cell array is located on the second metal layer 12 and above; the second metal layer 12 is a full-coverage metal, and 16 direct current feeder lines 8 are arranged on the third metal layer 14. The materials of the first dielectric layer 11 and the second dielectric layer 13 are F4B, and the relative dielectric constant epsilon r =2.65, loss tangent of 0.0015, thickness of 1.5mm and 1mm, respectively. The first passive gradient index impedance matching unit array 1, the passive gradient index unit array 2, the first constant index impedance matching unit array 4, the second passive gradient index impedance matching unit array 3 and the second constant index impedance matching unit array 7 are all formed by arranging passive sub-wavelength units 5, and the electrically tunable array 9 adopts an electrically tunable sub-wavelength unit 6 loaded with a plurality of varactors 66.
In this embodiment, the reconfigurable super surface is composed of a first passive graded index impedance matching unit array 1, a passive graded index unit array 2, a second passive graded index impedance matching unit array 3, a first constant index impedance matching unit array 4, an electrically tunable unit array 9, a second constant index impedance matching unit array 7, a dc voltage module 15, and a dielectric plate 16. The first passive gradient index impedance matching unit array 1 is used for suppressing reflection between the passive gradient index unit array 2 and the non-unit dielectric plate. The passive gradient index unit array 2 is used for converting a cylindrical wavefront of a transverse magnetic surface wave excited by a surface wave source into a planar wavefront. The second passive graded index impedance matching unit array 3 is used to suppress reflection between the passive graded index unit array 2 and the first constant index impedance matching unit array 4. The first constant refractive index impedance matching unit array 4 is used to suppress reflection between the electrically tunable unit array 9 and the second passive graded refractive index impedance matching unit array 3. The second constant refractive index impedance matching unit array 7 is used to suppress reflection between the electrically tunable unit array 9 and the non-unit dielectric plate. The electrically tunable element array 9 is used for transforming the planar wavefront of the transverse magnetic surface wave into a flexibly steerable non-diffracted beam.
The control of transverse magnetic surface waves for flexibly manipulating reconfigurable supersurfaces of non-diffracting surface waves of the present invention consists of two steps of wave front shaping: firstly, after a transverse magnetic surface wave excited by a surface wave source passes through a passive gradient refractive index array, the front of a cylindrical wave of the surface wave is converted into a plane wave front; then, the electrically tunable array is loaded, and the transverse magnetic surface wave with the plane wave front is remodelled into a non-diffraction surface wave with adjustable propagation direction and distance. Because the refractive index distribution of the electrically adjustable array 9 can be adjusted in real time by the voltage control module, and the energy of the formed diffraction-free beam is concentrated after the transverse magnetic surface wave passes through the super surface, the electrically adjustable array is expected to be applied to the fields of surface wave energy transmission, short-range communication, wireless charging and the like.
The passive gradient refractive index unit array 2 in the invention is composed of passive sub-wavelength units 5 with different effective refractive indexes which are regularly arranged, when the transverse magnetic surface wave emitted from an excitation source passes through different parts of the array, electromagnetic waves can experience different space delays, so that phase differences are generated, and the field distribution of the transverse magnetic surface wave is changed, and the specific principle is shown in figure 3. Assuming that the lens aperture center is the maximum value n (0) of refractive index, the refractive index distribution of the passive gradient refractive index unit array along the x-axis satisfies the formula:
wherein F is the distance between the feed source and the first passive gradient index impedance matching unit array 1, L 1 Is the total thickness of the passive graded index cell array 2, the first passive graded index impedance matching cell array 1, and the second passive graded index impedance matching cell array 7. For a single cell, its equivalent refractive index satisfies n=Φc/pω, where Φ is the phase difference of the transverse magnetic surface wave traveling through the supersurface cell, p is the cell period, ω is the angular frequency, and c is the speed of light. In consideration of reflection caused by impedance mismatch during electromagnetic wave propagation, impedance matching needs to be performed between interfaces, so that an additional first passive gradient index impedance matching unit array 1 and a second passive gradient index impedance matching unit array 3 formed by passive sub-wavelength units 5 need to be added, and the additional first passive gradient index impedance matching unit array and the additional second passive gradient index impedance matching unit array are respectively located before and after the passive gradient index unit array 2, and the specific layout is shown in fig. 4. The passive gradient index unit array 2 has 3 rows×16 columns of passive sub-wavelength units 5 in total along the y-axis direction, and the first passive gradient index impedance matching unit array 1 and the second passive gradient index impedance matching unit array 3 include 2 rows×16 columns of passive sub-wavelength units 5, and their unit structures are symmetrical about the y-axis.
In this embodiment, the passive sub-wavelength units 5 on the same column along the y-axis direction in each of the passive gradient refractive index unit array 2, the first passive gradient refractive index impedance matching unit array 1, and the second passive gradient refractive index impedance matching unit array 3 have the same refractive index for transverse magnetic surface waves, and the refractive indexes of the passive sub-wavelength units 5 on different columns along the x-axis direction are distributed in a gradient manner.
The passive sub-wavelength unit 5 is arranged on the first metal layer 10; the first metal layer 10 comprises a square patch 51 at the center and a square ring 52 surrounding the patch, the second metal layer 12 is fully covered with metal, and the center of the square patch 51 is connected with the second metal layer 12 through a metal blind hole 53. The equivalent refractive index of the passive sub-wavelength unit 5 to the transverse magnetic surface wave changes along with the side length l of the square patch 51, and the value range of l is as follows: larger than diameter D of blind metal hole 53 1 Is smaller than the upper layer of the super lens unitSide length L of square ring 52 m . The slit width between the square patch and the square ring is s, as shown in fig. 5. The equivalent refractive index of the passive sub-wavelength unit 5 varies with the variation of l, and the results of the simulation process are shown in fig. 6, which shows that the unit refractive index varies from 1.18 to 2.88 when the side length l varies between 1mm and 3.5 mm. The specific structural parameters are as follows: s=0.2 mm, p=5 mm, l m ＝4.8mm，D 1 =0.5 mm. Fig. 11 shows refractive index distributions along the x-axis of the first passive graded index impedance matching unit array 1 and the passive graded index unit array 2. Fig. 13 shows the electric field distribution diagram of the waveguide excited transverse magnetic surface wave obtained by simulation after passing through the first passive gradient index impedance matching unit array 1, the passive gradient index unit array 2 and the second passive gradient index impedance matching unit array 3 in sequence, and it can be seen that a significant planar wavefront has been formed after the arrays. The invention meets the requirements of the electromagnetic wave front state.
The electrically tunable element array 9 is arranged behind the second passive graded index impedance matching element array 3 in the present invention. In use, the array of electrically tunable elements 9 converts a transverse magnetic surface wave having a planar wavefront into a non-diffracting surface wave. Since the non-diffracted beam can be converted into the interference result of innumerable plane waves having the same inclination angle with the central axis, the refractive index distribution of the electrically tunable element array along the x-axis needs to satisfy:
wherein t is 4 Is the thickness of the array of electrically tunable cells. In view of reflection due to impedance mismatch during electromagnetic wave propagation, impedance matching needs to be performed between interfaces, and two impedance matching layers need to be added here. In order to reduce design difficulty, the impedance matching layer is composed of two rows of passive sub-wavelength units 5 with the same structure, the two impedance matching layers are called a first constant refractive index impedance matching unit array 4 and a second constant refractive index impedance matching unit array 7, and the side length l=2.4 mm of the square patch at the inner layer is determined through simulation optimization.
In this embodiment, the electrically tunable sub-wavelength units 6 on the same column in the y-axis direction in the electrically tunable unit array 9 have the same refractive index for the transverse magnetic surface wave, and the refractive indexes of the electrically tunable sub-wavelength units 6 on different columns in the x-axis direction are distributed in a gradient manner.
The metal outer ring 63 of each most remote unit in the y direction in the electrically adjustable unit array 4 is connected with the feeding patch 41 through a resistor 67 of 2.5kΩ; the feeding patch 41 is connected to one of the 16 dc feeder lines 8 on the third metal layer 14 through a feeding metal via 42. The electrically tunable element array 4 has 7 rows of electrically tunable sub-wavelength elements 6 along the y-axis direction, and the structural arrangement of the three different functional arrays is shown in fig. 7. Each row of the tunable array is formed by sixteen electrically tunable sub-wavelength units 6 of identical structure, the unit structure diagrams being shown in fig. 8-9.
The structure of the electrically tunable sub-wavelength unit 6 is shown in fig. 8 to 9, the first metal layer 10 comprises three concentric square metal rings, wherein a plurality of varactors 66 are arranged between the metal inner ring 61 and the metal middle ring 62, the cathode of each varactor 66 is connected to the metal inner ring 61, the anode of each varactor 66 is connected to the metal middle ring 62, and the metal middle ring 62 is connected with the metal outer ring 63 through a metal patch 64; the second metal layer 12 is a full-coverage metal; the metal inner ring 61 of the first metal layer is provided with a plurality of first metal blind holes 65 for connecting the metal inner ring 61 with the second metal layer 12. The metal outer rings 63 of adjacent cells in the y-direction are connected by a resistor 67 of 2.5kΩ. When the electrically tunable sub-wavelength units 6 are formed into an array, the second metal layers to which all the electrically tunable sub-wavelength units 6 are connected in one piece, with a resistance 67 of 2.5kΩ between the metal outer rings 63 of each column of units in the y-direction. The equivalent refractive index of the electrically tunable sub-wavelength unit 6 to the transverse magnetic surface wave changes with the capacitance value of the varactor diode 66 as shown in fig. 10. The varactor 66 is of the type MACOM MA46H120. The diameter of the first metal blind hole 65 is 0.3mm.
In this embodiment, the centers of the metal inner ring 61, the metal middle ring 62, and the metal outer ring 63 are the same. Four varactors 66 are located around the metal middle ring 62, respectively, and the metal inner ring 61 is connected to the metal middle ring 62 through the four varactors 66. Four first metal blind holes 65 are formed in the metal inner ring 61, and the four first metal blind holes 65 are located at four corners of the metal inner ring 61 respectively.
The metal outer ring 63 of each most remote unit in the y direction in the electrically adjustable unit array 4 is connected with the feeding patch 41 through a resistor 67 of 2.5kΩ; the feeding patch 41 is connected to one of the 16 dc feeder lines 8 through a feeding metal via 42. The second metal layer has a plurality of circular apertures having a diameter greater than the aperture of the feed metal vias 42 such that the feed metal vias 42 do not contact the second metal layer. The 16 direct current feeder lines 8 are connected with 16 negative electrode output ends of the direct current voltage module 7. The metal inner ring 61 is connected to a second metal layer through a first metal blind hole 65, which is connected to the common positive electrode of the dc voltage module 7. Thereby, the varactors on the electrically tunable sub-wavelength units 6 of different columns are in a reverse biased state. Because the resistance of 2.5kΩ is large and the dc current of the reverse-biased varactors is negligible, the metal outer rings of the same column of electrically tunable sub-wavelength units in the y-direction are approximately equipotential, all varactors on the column are approximately controlled by the same dc voltage, and the capacitance of the varactors changes with the change of the dc voltage. The 16-column electrically adjustable sub-wavelength units 6 correspond to 16 paths of direct-current voltage signals and are provided by the direct-current voltage modules 7 through 16 direct-current feeder lines 8. By adjusting these 16 direct-current voltages, the refractive index distribution of the electrically tunable cell array 4 can be designed. When the refractive index meets a certain gradient distribution, the super-surface of the invention generates non-diffraction surface wave beams. Moreover, by changing the refractive index distribution of the electrically tunable element array 9 in real time, the direction and the non-diffraction distance of the non-diffraction surface wave beam can be dynamically switched. The structural parameters of each module in this embodiment are: w (w) 1 ＝1.6mm，w 2 ＝0.4mm，w 3 ＝0.2mm,w 4 =4.6 mm and w 5 ＝0.2mm。
Fig. 14 shows three diffraction-free beam electric field amplitude distributions at 9GHz, which were simulated in the examples of the present invention, and which were switchable in real time. Wherein, the normal non-diffraction propagates 69.5mm, referred to herein as "normal near non-diffraction"; the result of the normal non-diffracting propagation of 114.3mm is referred to herein as "normal long-range non-diffracting"; the result of deflection 25.6 deg. to the right, without diffraction propagation 82mm, is referred to herein as "right deflection without diffraction". And the "left-hand undiffracted" beam and the "right-hand undiffracted" beam are left-right mirror images and are therefore not shown here.
This example fabricated reconfigurable supersurface samples for flexible manipulation of non-diffracted surface waves, sample photographs and test environment photographs as shown in fig. 15-16. The super surface is fixed on an acrylic plate by a plurality of nylon nuts and bolts for testing. For testing, standard waveguide WR90 is selected as the surface wave feed source.
First, the change of the phase shift of the surface wave propagation with voltage under the same reverse bias dc voltage control of all the cells in the electrically tunable cell array 9 was tested, as shown in fig. 17. It can be seen that the total phase of the array can be varied over at least 300 by adjusting the voltage over the test frequency range. In the diffraction-free beam test, each column unit in the electrically adjustable array of the super-surface sample piece is controlled by the same voltage, and the columns are controlled in parallel by the voltage module, so that the equivalent refractive index of each row of units can be independently and flexibly adjusted by adjusting the control voltage, and the generation of diffraction-free beams and accurate beam control are sought. Fig. 12 shows the voltage distribution of each column of the electrically tunable cell array 9 in order to realize four different diffraction-free beams of "normal close-range diffraction-free", "normal far-range diffraction-free", "right-bias diffraction-free", "left-bias diffraction-free", in this embodiment. The electric field distribution obtained after the test is shown in fig. 18. The four switchable non-diffraction beams realized by the test are respectively "normal close non-diffraction", "normal long-distance non-diffraction", "right deviation non-diffraction" and "left deviation non-diffraction", the non-diffraction distances of the switchable non-diffraction beams are respectively 71mm, 115mm, 80mm and 76mm, the deflection angle of the "right deviation non-diffraction" is 26 degrees, and the deflection angle of the "left deviation non-diffraction" is 28 degrees.
In summary, the invention provides a reconfigurable super surface for flexibly controlling a diffraction-free surface wave, which consists of a passive gradient refractive index array with a fixed unit structure, an impedance matching array and an electrically adjustable array of an integrated varactor, has a highly compact structure, and has better working performance in the aspects of realizing the generation and real-time and dynamic adjustment of the diffraction-free surface wave. Near field test results show that the super-surface sample piece respectively realizes 69.5mm near-distance non-diffraction surface wave, 114.3mm long-distance non-diffraction surface wave, left deviation 28 degree non-diffraction surface wave and right deviation 26 degree non-diffraction surface wave, and total non-diffraction beams in four directions, namely front, back, left and right, and the test results are relatively consistent with simulation, and good beam control performance is shown. It can be seen that the invention can generate the diffraction-free light beam with dynamically adjustable inclination angle and focusing area, has the advantages of low profile, easy processing and the like, and is expected to be applied to the fields of wireless charging, short-range communication and the like.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (9)
1. The reconfigurable super-surface for flexibly controlling the diffraction-free surface wave is characterized by comprising a first passive gradient refractive index impedance matching unit array (1), a passive gradient refractive index unit array (2), a second passive gradient refractive index impedance matching unit array (3), a first constant refractive index impedance matching unit array (4), an electrically adjustable unit array (9) and a second constant refractive index impedance matching unit array (7) which are sequentially arranged on a dielectric plate (16) along the propagation direction of the surface wave;
the passive gradient refractive index unit array (2) is used for converting the cylindrical wavefront of the transverse magnetic surface wave excited by the surface wave source into a planar wavefront;
the electrically adjustable unit array (9) is used for converting the plane wavefront of the transverse magnetic surface wave into a diffraction-free wave beam, and changing the refractive index distribution in real time under the action of direct current voltage output by the direct current voltage module (15), so as to dynamically switch the direction and diffraction-free distance of the diffraction-free wave beam;
the first passive gradient index impedance matching unit array (1) is used for suppressing reflection between the passive gradient index unit array (2) and a unit-free part of the dielectric plate (16);
the second passive gradient refractive index impedance matching unit array (3) is used for inhibiting reflection between the passive gradient refractive index unit array (2) and the first constant refractive index impedance matching unit array (4);
the first constant refractive index impedance matching unit array (4) is used for inhibiting reflection between the electrically adjustable unit array (9) and the second passive gradient refractive index impedance matching unit array (3);
the second constant refractive index impedance matching cell array (7) is for suppressing reflection between the electrically tunable cell array (9) and a cell-free portion of the dielectric plate (16).
2. The reconfigurable super surface for flexibly manipulating a diffraction-free surface wave according to claim 1, wherein the reconfigurable super surface adopts a printed circuit board structure, and comprises a first metal layer (10), a first dielectric layer (11), a second metal layer (12), a second dielectric layer (13) and a third metal layer (14) which are sequentially arranged along a vertical direction;
the first passive gradient refractive index impedance matching unit array (1), the passive gradient refractive index unit array (2), the second passive gradient refractive index impedance matching unit array (3), the first constant refractive index impedance matching unit array (4), the electrically adjustable unit array (9) and the second constant refractive index impedance matching unit array (7) are located on the second metal layer (12) and above, and the third metal layer (14) is provided with a direct current feeder line (8).
3. Reconfigurable supersurface for flexible manipulation of non-diffracted surface waves according to claim 2, characterized in that said array of electrically tunable elements (9) comprises M rows x N columns of electrically tunable sub-wavelength elements (6);
the passive gradient refractive index unit array (2) comprises P rows by N columns of passive sub-wavelength units (5);
the first passive gradient refractive index impedance matching unit array (1), the second passive gradient refractive index impedance matching unit array (3), the first constant refractive index impedance matching unit array (4) and the second constant refractive index impedance matching unit array (7) respectively comprise Q rows and N columns of passive subwavelength units (5);
and M, N, P, Q is a positive integer of 2 or more.
4. A reconfigurable supersurface for flexible manipulation of non-diffracted surface waves according to claim 3, wherein the electrically tunable sub-wavelength unit (6) comprises an inner metal ring (61), an intermediate metal ring (62), an outer metal ring (63), a metal patch (64), a first metal blind hole (65) and a varactor diode (66);
the metal inner ring (61), the metal middle ring (62) and the metal outer ring (63) are arranged on the first metal layer (10), the metal inner ring (61) is connected with the second metal layer (12) through a first metal blind hole (65), the second metal layer (12) is connected with one pole of the direct-current voltage module (15) through a wire, one pole of the varactor (66) is connected with the metal inner ring (61), the other pole of the varactor (66) is connected with the metal middle ring (62), the metal middle ring (62) is connected with the metal outer ring (63) through a metal patch (64), and the metal outer ring (63) is connected with the metal outer ring (63) of an electrically adjustable sub-wavelength unit adjacent along the propagation direction of the surface wave through a resistor (67);
the metal outer ring (63) at the far end in the propagation direction of the surface wave in the electrically adjustable unit array (9) is connected with the feeding patch (41) through a resistor (67), the feeding patch (41) is connected with the direct current feeder (8) through a feeding metal through hole (42), and the direct current feeder (8) is connected with the other pole of the direct current voltage module (15) through a wire.
5. A reconfigurable super surface for flexibly manipulating a diffraction free surface wave according to claim 3, characterized in that the passive sub-wavelength unit (5) comprises a square patch (51), a square ring (52) and a second metal blind hole (53), the square patch (51) and the square ring (52) are arranged on the first metal layer (10), the square patch (51) is arranged inside the square ring (52), and the center of the square patch (51) is connected with the metal layer connected with the negative electrode of the varactor diode (66) in the electrically tunable sub-wavelength unit (6) through the second metal blind hole (53).
6. The reconfigurable super surface for flexibly manipulating a diffraction-free surface wave according to claim 5, wherein the square patches (51) of the same column in each of the passive gradient refractive index unit array (2), the first passive gradient refractive index impedance matching unit array (1) and the second passive gradient refractive index impedance matching unit array (3) have the same side length, the square patches (51) of different columns are each distributed in a gradient decreasing manner from the middle column to the two side columns, and the side length of the square patches (51) of the passive gradient refractive index unit array (2) in the same column is larger than the side lengths of the square patches (51) of the first passive gradient refractive index impedance matching unit array (1) and the second passive gradient refractive index impedance matching unit array (3).
7. The reconfigurable super surface for flexibly manipulating non-diffracted surface waves according to claim 4, wherein the second metal layer (12) is fully covered with metal, and the second metal layer (12) is provided with a circular aperture, the circular aperture is the same as the center of the feeding metal through hole (42), the diameter of the circular aperture is larger than the diameter of the feeding metal through hole (42), and the feeding patch (41) is connected with the direct current feeder (8) through the feeding metal through hole (42) through the circular aperture.
8. The reconfigurable metasurface for flexibly manipulating non-diffracted surface waves of claim 4, wherein the number of varactors (66) is four and four of the varactors (66) are arrayed along a metal inner ring edge.
9. The reconfigurable supersurface for flexibly manipulating non-diffracted surface waves according to claim 4, wherein said first metallic blind holes (65) are four and four said first metallic blind holes (65) are disposed at four corners of the metallic inner ring (61), respectively.
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