A reconfigurable metasurface for flexible manipulation of non-diffracting surface waves

Abstract

The present invention discloses a reconfigurable metasurface for flexibly manipulating non-diffraction surface waves. The metasurface is composed of a passive gradient refractive index unit array and an electrically adjustable gradient refractive index unit array. Unlike existing non-diffraction surface wave generators with fixed structures and functions, the electrically adjustable gradient refractive index unit in the present invention integrates electrically adjustable elements. Through a clever control circuit design, a voltage control module can be used to change the refractive index distribution of the electrically adjustable gradient refractive index unit array in real time, achieving the transition from cylindrical wavefront surface waves to non-diffraction surface waves, and enabling dynamic control of the propagation direction and non-diffraction distance of the non-diffraction surface waves. This invention is expected to be applied to fields such as surface wave energy transmission, short-range communications, and wireless charging.

Description

Technical Field

[0001] The present invention belongs to the technical field of novel artificial metasurface arrays, and in particular relates to a reconfigurable metasurface for flexibly manipulating non-diffraction surface waves. Background Art

[0002] Electromagnetic surface waves (SWRs) are electromagnetic wave propagation modes that exist at the interface between two dissimilar materials. Known in optics as surface plasmons, they are a significant contributor to electromagnetic interference, compatibility, and coupling effects at microwave frequencies. Because they are easily excited by spatial waves, SWRs are also a promising solution for electromagnetic energy and information transmission. Researchers have previously proposed a range of devices to manipulate SWRs, including SWR waveguides, beam shifters, self-focusing metasurfaces, SWR pulse routing, comb-like baseless transmission lines, and hyperbolic metasurfaces. These outstanding research efforts hold the promise of enabling widespread applications of SWRs.

[0003] Like other types of waves in nature, electromagnetic waves naturally diverge during propagation. Researchers hope to counteract this effect, thereby achieving diffraction-free transmission. A typical example of a non-diffraction beam is the Bessel beam, proposed by Durnin et al. in 1987. While an ideal Bessel beam requires infinite energy, this is physically impossible to achieve. However, quasi-Bessel beams, which exhibit non-diffraction properties, have been widely demonstrated. Within the non-diffraction propagation region of a quasi-Bessel beam, the energy of the electromagnetic wave is highly concentrated, making it highly valuable for practical applications. A quasi-Bessel beam is an interference pattern generated by the superposition of countless coherent plane waves. It can be generated using axicon structures, dielectric lenses, and radial slot arrays. In recent years, a large number of non-diffraction beam generators have been realized using technologies such as phase-modulation metasurfaces, gradient-index metasurfaces, holographic metasurfaces, and planar leaky radial waveguides. For electromagnetic surface waves, researchers have achieved non-diffraction surface waves by combining a half-Maxwell fisheye lens with a gradient-index lens. However, the non-diffracting beams in these studies are mostly oriented parallel to the normal of the generator aperture, with only a few devices generating oblique non-diffracting beams. Furthermore, the vast majority of existing devices have fixed performance, making the generated non-diffracting beams difficult to control in real time. Currently, there are no reports of flexible controllable non-diffracting surface wave generators. Summary of the Invention

[0004] The purpose of the present invention is to achieve real-time and dynamic control of the propagation direction and non-diffraction distance of non-diffraction surface waves, and to provide a reconfigurable metasurface for flexible manipulation of non-diffraction surface waves.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a reconfigurable metasurface for flexibly manipulating non-diffraction surface waves, comprising: 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;

[0006] The passive gradient refractive index unit array is used to transform the cylindrical wavefront of the transverse magnetic surface wave excited by the surface wave source into a plane wavefront;

[0007] The electrically adjustable unit array is used to transform the plane wavefront of the transverse magnetic surface wave into a non-diffracting beam, and to change the refractive index distribution in real time under the action of the DC voltage output by the DC voltage module, thereby dynamically switching the direction and non-diffracting distance of the non-diffracting surface wave beam;

[0008] The first passive gradient refractive index impedance matching unit array is used to suppress reflection between the passive gradient refractive index unit array and the unit-free portion of the dielectric plate;

[0009] The second passive gradient refractive index impedance matching unit array is used to suppress reflection between the passive gradient refractive index unit array and the first constant refractive index impedance matching unit array;

[0010] The first constant refractive index impedance matching unit array is used to suppress reflection between the electrically adjustable unit array and the second passive gradient refractive index impedance matching unit array;

[0011] The second constant refractive index impedance matching unit array is used to suppress reflection between the electrically adjustable unit array and the unit-free portion of the dielectric plate.

[0012] The reconfigurable metasurface adopts a printed circuit board structure, including a first metal layer, a first dielectric layer, a second metal layer, a second dielectric layer, and a third metal layer arranged in sequence along a vertical direction;

[0013] 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 and above the second metal layer, and a DC feed line is provided on the third metal layer.

[0014] The electrically tunable unit array includes M rows×N columns of electrically tunable sub-wavelength units;

[0015] The passive gradient refractive index unit array includes P rows×N columns of passive sub-wavelength units;

[0016] 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 each include Q rows×N columns of passive sub-wavelength units;

[0017] And M, N, P, and Q are positive integers greater than or equal to 2.

[0018] The electrically tunable subwavelength unit includes a metal inner ring, a metal middle ring, a metal outer ring, a metal patch, a second metal blind hole and a varactor diode;

[0019] The metal inner ring, the metal middle ring, and the metal outer ring are arranged on a first metal layer, and the metal inner ring is connected to the second metal layer through a second metal blind hole, the second metal layer is connected to one pole of the DC voltage module through a wire, one pole of the varactor diode is connected to the metal inner ring, the other pole of the varactor diode is connected to the metal middle ring, the metal middle ring is connected to the metal outer ring through a metal patch, and the metal outer ring is connected to the metal outer ring of the electrically tunable subwavelength unit adjacent to the propagation direction of the surface wave through a resistor;

[0020] The metal outer ring at the farthest end of the electrically adjustable unit array along the propagation direction of the surface wave is connected to the feed patch through a resistor, the feed patch is connected to the DC feed line through a feed metal through-hole, and the DC feed line is connected to the other pole of the DC voltage module through a wire.

[0021] The passive subwavelength unit includes a square patch, a square ring and a first metal blind hole. 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 to the metal layer connected to the cathode of the varactor diode in the electrically tunable subwavelength unit through the first metal blind hole.

[0022] The side lengths of the square patches in the same column 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, while the side lengths of the square patches in different columns are distributed in a gradient decreasing distribution 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 greater than the side lengths 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.

[0023] The second metal layer is fully covered with metal, and a circular aperture is provided on the second metal layer. The circular aperture is the same as the center of the feed metal through-hole, and the diameter of the circular aperture is larger than the diameter of the feed metal through-hole. The feed patch passes through the circular aperture via the feed metal through-hole and is connected to the DC feed line.

[0024] There are four varactor diodes, and the four varactor diodes are arranged in an array along the edge of the metal inner ring.

[0025] There are four second metal blind holes, and the four first metal blind holes are respectively arranged at the four corners of the metal inner ring.

[0026] Beneficial effects:

[0027] 1. Compared with existing non-diffraction surface wave generators, the present invention utilizes a voltage control module to change the refractive index distribution of an electrically tunable gradient refractive index unit array in real time, thereby dynamically adjusting the propagation direction and non-diffraction distance of the non-diffraction surface wave, thereby meeting various non-diffraction surface wave application requirements;

[0028] 2. The present invention loads a passive gradient refractive index unit array into the reconfigurable metasurface, which enables the rapid conversion of surface wave cylindrical waves into plane wavefronts, thereby significantly reducing the feed-array distance, effectively reducing the system volume, array scale, and array design difficulty;

[0029] 3. The present invention realizes independent control of N rows of electrically tunable subwavelength units by integrating electrically tunable elements, and achieves real-time manipulation of non-diffracting beams with relatively low control difficulty;

[0030] 4. The present invention can be prepared using mature PCB processing technology and component surface mounting technology, and has the advantages of low processing difficulty and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A three-dimensional schematic diagram of the structure of a reconfigurable metasurface for flexibly manipulating non-diffracting surface waves according to the present invention;

[0032] Figure 2 Schematic diagram of the bottom feeder of the reconfigurable metasurface in the present invention;

[0033] Figure 3 This is a schematic diagram of the reconfigurable metasurface in an embodiment of the present invention;

[0034] Figure 4 Layout diagram of a passive gradient refractive index unit array and a passive gradient refractive index impedance matching unit array in an embodiment of the present invention;

[0035] Figure 5 Schematic diagram of the three-dimensional structure of the passive sub-wavelength unit in an embodiment of the present invention.

[0036] Figure 6 is a characteristic curve showing how the equivalent refractive index of the passive subwavelength unit varies with the side length of the square metal sheet inside the unit in an embodiment of the present invention;

[0037] Figure 7Layout diagram of the electrically tunable unit array and the constant refractive index impedance matching unit array in an embodiment of the present invention;

[0038] Figure 8 Schematic diagram of the three-dimensional structure of the electrically tunable subwavelength unit in an embodiment of the present invention;

[0039] Figure 9 Schematic diagram of the top view of the electrically tunable subwavelength unit in an embodiment of the present invention;

[0040] Figure 10 is a characteristic curve showing the change of the equivalent refractive index of the electrically tunable subwavelength unit with the capacitance of the varactor diode in an embodiment of the present invention;

[0041] Figure 11 is the equivalent refractive index distribution of the passive gradient refractive index unit array and the passive gradient refractive index impedance matching unit array in the embodiment of the present invention;

[0042] Figure 12 The voltage distribution diagram of each column of the electrically adjustable unit array that realizes four different non-diffraction beams of "normal short-range non-diffraction", "normal long-range non-diffraction", "right-deflected non-diffraction", and "left-deflected non-diffraction" in an embodiment of the present invention;

[0043] Figure 13 This is a diagram showing the electric field amplitude distribution of the plane wave surface wave after the cylindrical wave front surface wave excited by the waveguide passes through the passive gradient refractive index unit array and the passive gradient refractive index impedance matching unit array, obtained by simulation in an embodiment of the present invention;

[0044] Figure 14 The electric field amplitude distribution diagrams of three real-time switchable non-diffraction beams at 9 GHz obtained by simulation in an embodiment of the present invention;

[0045] Figure 15 A physical image of a reconfigurable metasurface for flexibly manipulating non-diffracting surface waves according to an embodiment of the present invention;

[0046] Figure 16 A diagram of a test environment for a reconfigurable metasurface for flexibly manipulating non-diffraction surface waves in an embodiment of the present invention;

[0047] Figure 17 Graph showing the variation of the phase shift of surface wave propagation with voltage when all cells in the electrically adjustable cell array are controlled by the same reverse bias DC voltage in an embodiment of the present invention;

[0048] Figure 18 These are four real-time switchable non-diffraction beam electric field amplitude distribution diagrams obtained by testing in an embodiment of the present invention.

[0049] In the figure: 1. First passive gradient refractive index impedance matching unit array, 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. DC feed 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. DC 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. Resistor. DETAILED DESCRIPTION

[0050] The present invention will be further explained below with reference to the accompanying drawings.

[0051] The present invention is a reconfigurable metasurface for flexibly manipulating non-diffraction surface waves, and its overall structure is as follows: Figure 1-2 As shown. 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. In the reconfigurable metasurface, 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 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 includes 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 unit array is located on and above the second metal layer 12; the second metal layer 12 is a fully covered metal, and 16 DC feed 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 both F4B, and their relative dielectric constant ε r =2.65, the loss tangent is 0.0015, and the thicknesses are 1.5 mm and 1 mm, respectively. The first passive gradient refractive index impedance matching unit array 1, the passive gradient refractive index unit array 2, the first constant refractive index impedance matching unit array 4, the second passive gradient refractive index impedance matching unit array 3, and the second constant refractive index impedance matching unit array 7 are all composed of passive subwavelength units 5. The electrically tunable array 9 uses electrically tunable subwavelength units 6 loaded with multiple varactor diodes 66.

[0052] In this embodiment, the reconfigurable metasurface is composed of 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, a second constant refractive index impedance matching unit array 7, a DC voltage module 15, and a dielectric plate 16. The first passive gradient refractive index impedance matching unit array 1 is used to suppress reflections between the passive gradient refractive index unit array 2 and the unitless dielectric plate. The passive gradient refractive index unit array 2 is used to transform the cylindrical wavefront of the transverse magnetic surface wave excited by the surface wave source into a plane wavefront. The second passive gradient refractive index impedance matching unit array 3 is used to suppress reflections 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 to suppress reflections 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 unit array 7 is used to suppress reflections between the electrically adjustable unit array 9 and the unitless dielectric plate. The electrically adjustable unit array 9 is used to transform the plane wavefront of the transverse magnetic surface wave into a flexibly controllable non-diffraction beam.

[0053] The reconfigurable metasurface for flexible manipulation of non-diffracting surface waves (NDSWs) of the present invention controls transverse magnetic surface waves through a two-step wavefront shaping process. First, the cylindrical wavefront of a NDSW excited by a surface wave source is converted into a planar wavefront after passing through a passive gradient refractive index array. Then, the electrically tunable array is loaded thereafter to reshape the planar wavefront into a NDSW with adjustable propagation direction and distance. Because the refractive index distribution of the electrically tunable array 9 can be adjusted in real time by a voltage control module, and the NDSW formed after passing through the metasurface has a relatively concentrated energy, the metasurface has promising applications in surface wave energy transmission, short-range communications, and wireless charging.

[0054] In the present invention, the passive gradient refractive index unit array 2 is composed of passive subwavelength units 5 with different equivalent refractive indices arranged in a regular pattern. When the transverse magnetic surface wave emitted from the excitation source passes through different parts of the array, the electromagnetic wave will experience different spatial delays, thereby generating a phase difference, thereby changing the field distribution of the transverse magnetic surface wave. The specific principle is as follows: Figure 3 As shown. Assuming that the center of the lens aperture is the maximum value of the refractive index n(0), the refractive index distribution of the passive gradient refractive index unit array along the x-axis satisfies the formula:

[0055]

[0056] Where F is the distance between the feed source and the first passive gradient refractive index impedance matching unit array 1, and L1 is the total thickness 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 7. For a single unit, its equivalent refractive index satisfies n=φc / pω, where φ is the phase difference of the transverse magnetic surface wave passing through the metasurface unit, p is the unit period, ω is the angular frequency, and c is the speed of light. Taking into account the reflection caused by impedance mismatch during the propagation of electromagnetic waves, impedance matching is required between interfaces. Therefore, it is necessary to add an additional first passive gradient refractive index impedance matching unit array 1 and a second passive gradient refractive index impedance matching unit array 3 composed of passive subwavelength units 5, which are respectively located before and after the passive gradient refractive index unit array 2. The specific layout is as follows: Figure 4 As shown, the passive gradient refractive index unit array 2 has 3 rows × 16 columns of passive sub-wavelength units 5 along the y-axis direction, and the first passive gradient refractive index impedance matching unit array 1 and the second passive gradient refractive index impedance matching unit array 3 include 2 rows × 16 columns of passive sub-wavelength units 5. Their unit structures are symmetrical about the y-axis.

[0057] In this embodiment, the passive subwavelength units 5 on the same column along the y-axis direction in 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 indices of the passive subwavelength units 5 in different columns along the x-axis direction are gradiently distributed.

[0058] The passive subwavelength unit 5 is disposed on the first metal layer 10; the first metal layer 10 includes a centrally located square patch 51 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 to the second metal layer 12 via a first metal blind hole 53. The equivalent refractive index of the passive subwavelength unit 5 for transverse magnetic surface waves varies with the side length l of the square patch 51. The value range of l is: greater than the diameter D1 of the first metal blind hole 53 and less than the side length L of the square ring 52 on the upper layer of the superlens unit. m The width of the slit between the square patch and the square ring is s, as Figure 5 As shown. The equivalent refractive index of the passive subwavelength unit 5 changes with l, and the simulation results are as follows Figure 6 As shown in the figure, it can be seen that when the side length l changes between 1mm and 3.5mm, the unit refractive index changes from 1.18 to 2.88. The specific structural parameters are: s = 0.2mm, p = 5mm, L m =4.8mm, D1=0.5mm. Figure 11 The refractive index distributions of the first passive gradient refractive index impedance matching unit array 1 and the passive gradient refractive index unit array 2 along the x-axis are given. Figure 13The simulated electric field distribution of a waveguide-excited transverse magnetic surface wave after it passes sequentially through the first passive gradient-index impedance matching unit array 1, the second passive gradient-index impedance matching unit array 3 is shown. It can be seen that a distinct plane wavefront has formed after the arrays, meeting the requirements of the present invention for the electromagnetic wavefront state.

[0059] In the present invention, the electrically tunable element array 9 is disposed after the second passive gradient refractive index impedance matching element array 3. During operation, the electrically tunable element array 9 converts transverse magnetic surface waves with a plane wavefront into non-diffracting surface waves. Because the non-diffracting beam can be transformed into the interference result of countless plane waves with the same inclination angle with the central axis, the refractive index distribution of the electrically tunable element array along the x-axis must satisfy the following requirements:

[0060]

[0061] Where t4 is the thickness of the electrically adjustable unit array. Considering the reflection caused by impedance mismatch during electromagnetic wave propagation,

[0062] Impedance matching is required between the interfaces, necessitating the addition of two impedance matching layers. To reduce design complexity, the impedance matching layer consists of two rows of identical passive subwavelength elements 5, referred to here as the first constant refractive index impedance matching element array 4 and the second constant refractive index impedance matching element array 7. Simulation optimization determined that the inner square patch side length, l, is 2.4 mm.

[0063] In this embodiment, the electrically tunable subwavelength units 6 in the same column along the y-axis in the electrically tunable unit array 9 have the same refractive index for transverse magnetic surface waves, and the refractive indices of the electrically tunable subwavelength units 6 in different columns along the x-axis are distributed in a gradient.

[0064] The metal outer ring 63 of the farthest unit in each column of the electrically adjustable unit array 9 in the y direction is connected to the feed patch 41 through a 2.5kΩ resistor 67; the feed patch 41 is connected to one of the 16 DC feed lines 8 on the third metal layer 14 through a feed metal via 42. The electrically adjustable unit array 9 has a total of 7 rows of electrically adjustable subwavelength units 6 along the y-axis direction. The structures of the three different functional arrays are arranged as follows: Figure 7 Each row of the adjustable array is composed of sixteen electrically adjustable sub-wavelength units 6 with completely identical structures. The unit structure is shown in the figure below. Figure 8-9 shown.

[0065] The structure of electrically tunable subwavelength unit 6 is shown in Figure 8-9The first metal layer 10 comprises three concentric square metal rings. Several varactor diodes 66 are positioned between the inner metal ring 61 and the middle metal ring 62. The cathode of each varactor diode 66 is connected to the inner metal ring 61, and the anode of each varactor diode 66 is connected to the middle metal ring 62. Metal patches 64 connect the middle metal ring 62 to the outer metal ring 63. The second metal layer 12 is fully covered with metal. Several second metal blind vias 65 are provided in the inner metal ring 61 of the first metal layer, connecting the inner metal ring 61 to the second metal layer 12. The outer metal rings 63 of adjacent units along the y-direction are connected via 2.5kΩ resistors 67. When the electrically tunable subwavelength units 6 are arrayed, the second metal layer connecting all electrically tunable subwavelength units 6 is connected as a whole. The outer metal rings 63 of each column of units along the y-direction are connected via 2.5kΩ resistors 67. The equivalent refractive index of the electrically tunable subwavelength unit 6 to the transverse magnetic surface wave changes with the capacitance value of the varactor diode 66 as follows: Figure 10 The model of the varactor diode 66 is MACOM MA46H120. The diameter of the second metal blind hole 65 is 0.3 mm.

[0066] In this embodiment, the metal inner ring 61, the metal middle ring 62, and the metal outer ring 63 have the same center. Four varactor diodes 66 are located around the metal middle ring 62, and the metal inner ring 61 is connected to the metal middle ring 62 via the four varactor diodes 66. Four second metal blind vias 65 are defined in the metal inner ring 61, and are located at the four corners of the metal inner ring 61.

[0067] The metal outer ring 63 of the farthest unit in each column of the electrically adjustable unit array 9 in the y direction is connected to the feed patch 41 via a 2.5kΩ resistor 67; the feed patch 41 is connected to one of the 16 DC feed lines 8 via a feed metal through-hole 42. The second metal layer has several circular apertures with a diameter larger than the aperture of the feed metal through-hole 42, so that the feed metal through-hole 42 does not contact the second metal layer. The 16 DC feed lines 8 are connected to the 16 negative output terminals of the DC voltage module 15. The metal inner ring 61 is connected to the second metal layer via a second metal blind hole 65, and the second metal layer is connected to the common positive electrode of the DC voltage module 15. As a result, the varactor diodes on the electrically adjustable subwavelength units 6 in different columns are reverse biased. Because the 2.5kΩ resistance is relatively large and the reverse-biased varactor diode's DC current is negligible, the metal outer rings of the same column of electrically tunable subwavelength elements in the y-direction are approximately at the same potential. All varactors in that column are controlled by approximately the same DC voltage, and the capacitance of the varactor changes with changes in the DC voltage. The 16 columns of electrically tunable subwavelength elements 6 correspond to 16 DC voltage signals, supplied by a DC voltage module 15 via 16 DC feeders 8. By adjusting these 16 DC voltages, the refractive index profile of the electrically tunable element array 9 can be designed. When the refractive index satisfies a certain gradient distribution, the metasurface of the present invention generates a non-diffracting surface wave beam. Furthermore, by real-time changes to the refractive index profile of the electrically tunable element array 9, the direction and non-diffracting distance of the non-diffracting surface wave beam can be dynamically switched. The structural parameters of each module in this embodiment are: w1 = 1.6 mm, w2 = 0.4 mm, w3 = 0.2 mm, w4 = 4.6 mm, and w5 = 0.2 mm.

[0068] Figure 14 The electric field amplitude distributions of three real-time switchable non-diffraction beams at 9 GHz, obtained from simulations of an embodiment of the present invention, are presented. The result of 69.5 mm of normal non-diffraction propagation is referred to as "normal short-range non-diffraction"; the result of 114.3 mm of normal non-diffraction propagation is referred to as "normal long-range non-diffraction"; and the result of 82 mm of non-diffraction propagation with a 25.6° rightward deflection is referred to as "right-deflected non-diffraction." The "left-deflected non-diffraction" beam and the "right-deflected non-diffraction" beam are mirror images and are therefore not shown here.

[0069] In this embodiment, a reconfigurable metasurface sample for flexible manipulation of non-diffraction surface waves was fabricated. Photos of the sample and the test environment are shown in the figure. Figure 15-16 The metasurface was fixed to an acrylic plate using several nylon nuts and bolts for testing. To facilitate testing, a standard waveguide WR90 was selected as the surface wave feed.

[0070] First, the phase shift of the surface wave propagation is tested under the same reverse bias DC voltage control for all units in the electrically adjustable unit array 9. Figure 17As shown in the figure, within the test frequency range, the total phase of the array can be varied by adjusting the voltage over a range of at least 300°. In the non-diffraction beam test, each column of the electrically tunable array of the metasurface sample of the present invention is controlled by the same voltage, and the columns are controlled in parallel by voltage modules. Therefore, the equivalent refractive index of each row of cells can be independently and flexibly adjusted by adjusting the control voltage, seeking to generate non-diffraction beams and precise beam steering. Figure 12 The voltage distribution of each column of the electrically adjustable unit array 9 is given to achieve four different non-diffraction beams of "normal short distance non-diffraction", "normal long distance non-diffraction", "right-deflected non-diffraction" and "left-deflected non-diffraction". The electric field distribution diagram obtained after the test is shown as follows: Figure 18 The four switchable diffraction-free beams achieved in the test are "normal close-range diffraction-free", "normal long-range diffraction-free", "right-deflection diffraction-free", and "left-deflection diffraction-free". Their corresponding diffraction-free distances are 71mm, 115mm, 80mm, and 76mm, respectively. The deflection angle of "right-deflection diffraction-free" is 26°, and the deflection angle of "left-deflection diffraction-free" is 28°.

[0071] In summary, the present invention proposes a reconfigurable metasurface for flexible manipulation of non-diffraction surface waves. It consists of a passive gradient refractive index array with a fixed unit structure, an impedance matching array, and an electrically adjustable array with integrated varactor diodes. It has a highly compact structure and has good working performance in achieving the generation and real-time, dynamic adjustment of non-diffraction surface waves. The near-field test results show that the metasurface sample has achieved a 69.5mm short-range non-diffraction surface wave, a 114.3mm long-range non-diffraction surface wave, a 28° left-biased non-diffraction surface wave, and a 26° right-biased non-diffraction surface wave, totaling four non-diffraction beams in the front, back, left, and right directions. The test results are consistent with the simulation, showing good beam control performance. It can be seen that the present invention can generate a non-diffraction beam with a dynamically adjustable tilt angle and focusing area, and has the advantages of low profile and easy processing. It is expected to be applied to fields such as wireless charging and short-range communication.

[0072] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A reconfigurable metasurface for flexible manipulation of non-diffraction surface waves, characterized in that: The invention comprises: 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 a surface wave; The passive gradient refractive index unit array (2) is used to transform the cylindrical wavefront of the transverse magnetic surface wave excited by the surface wave source into a plane wavefront; The electrically adjustable unit array (9) is used to transform the plane wavefront of the transverse magnetic surface wave into a non-diffracting beam, and to change the refractive index distribution in real time under the action of the DC voltage output by the DC voltage module (15), thereby dynamically switching the direction and non-diffracting distance of the non-diffracting surface wave beam; The first passive gradient refractive index impedance matching unit array (1) is used to suppress reflection between the passive gradient refractive index unit array (2) and the unit-free portion of the dielectric plate (16); The second passive gradient refractive index impedance matching unit array (3) is used to suppress 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 to suppress 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 unit array (7) is used to suppress reflection between the electrically adjustable unit array (9) and the unit-free portion of the dielectric plate (16); The reconfigurable metasurface adopts a printed circuit board structure, comprising 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) arranged in sequence 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 and above the second metal layer (12), and a DC feed line (8) is provided on the third metal layer (14); The electrically tunable unit array (9) comprises M rows×N columns of electrically tunable sub-wavelength units (6); The passive gradient refractive index unit array (2) comprises P rows×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) each include Q rows×N columns of passive sub-wavelength units (5); And M, N, P, Q are positive integers greater than or equal to 2; The electrically tunable subwavelength unit (6) comprises a metal inner ring (61), a metal middle ring (62), a metal outer ring (63), a metal patch (64), a second 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), and the metal inner ring (61) is connected to the second metal layer (12) through a second metal blind hole (65), the second metal layer (12) is connected to one pole of the DC voltage module (15) through a wire, one pole of the varactor (66) is connected to the metal inner ring (61), the other pole of the varactor (66) is connected to the metal middle ring (62), the metal middle ring (62) is connected to the metal outer ring (63) through a metal patch (64), and the metal outer ring (63) is connected to the metal outer ring (63) of the electrically tunable subwavelength unit adjacent to the propagation direction of the surface wave through a resistor (67); The metal outer ring (63) at the farthest end of the electrically adjustable unit array (9) along the propagation direction of the surface wave is connected to the feed patch (41) via a resistor (67), the feed patch (41) is connected to the DC feed line (8) via a feed metal through hole (42), and the DC feed line (8) is connected to the other pole of the DC voltage module (15) via a conductor; Four variable capacitance diodes (66) are respectively located around the metal ring 62; There are four second metal blind holes (65), and the four second metal blind holes (65) are respectively arranged at the four corners of the metal inner ring (61).

2. The reconfigurable metasurface for flexible manipulation of non-diffracting surface waves according to claim 1, wherein: The passive subwavelength unit (5) comprises a square patch (51), a square ring (52) and a first metal blind hole (53), wherein the square patch (51) and the square ring (52) are arranged on a 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 to the metal layer connected to the negative electrode of the varactor diode (66) in the electrically tunable subwavelength unit (6) through the first metal blind hole (53).

3. The reconfigurable metasurface for flexible manipulation of non-diffracting surface waves according to claim 2, characterized in that: The side lengths of the square patches (51) in the same column 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) are the same, while the side lengths of the square patches (51) in different columns are distributed in a gradient decreasing manner from the middle column to the two side columns, and the side lengths of the square patches (51) in the passive gradient refractive index unit array (2) in the same column are greater than the side lengths of the square patches (51) in the first passive gradient refractive index impedance matching unit array (1) and the second passive gradient refractive index impedance matching unit array (3).

4. The reconfigurable metasurface for flexible manipulation of non-diffracting surface waves according to claim 1, wherein: The second metal layer (12) is fully covered with metal, and a circular aperture is provided on the second metal layer (12), the circular aperture having the same center as the feed metal through hole (42), the diameter of the circular aperture being larger than the diameter of the feed metal through hole (42), and the feed patch (41) passing through the circular aperture via the feed metal through hole (42) to be connected to the DC feed line (8).

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