A reconfigurable metasurface that achieves polarization conversion between absorption, transmission, and reflection

Abstract

This invention proposes a reconfigurable metasurface that achieves polarization conversion between absorption, transmission, and reflection. The metasurface unit comprises four dielectric plates, each printed with a polygonal phase-change material and a polygonal phase-change material ring; alternating first phase-change material strips and metal strips; multiple polarization-conversion metal units arranged periodically; and second phase-change material strips spatially intersecting the first and metal strips. When electromagnetic waves are irradiated from above, the first phase-change material is in a metallic state and the second phase-change material is in a dielectric or metallic state, resulting in the metasurface exhibiting broadband absorption characteristics. When electromagnetic waves are irradiated from below, if both phase-change materials are in a metallic state, the metasurface achieves linear-to-circular polarization conversion in the reflection state. If the first phase-change material is in a dielectric state and the second phase-change material is in a metallic state, the metasurface achieves linear-to-circular polarization conversion in the transmission state. This design effectively overcomes the limited applicability of existing technologies, broadens their application scenarios, and enhances the absorption bandwidth.

Description

Technical Field

[0001] The present invention belongs to the technical field of terahertz multifunctional devices and relates to a reconfigurable metasurface, specifically a reconfigurable metasurface that realizes polarization conversion of absorption, transmission and reflection, which can be used in fields such as terahertz absorption and communication. Background Art

[0002] With the increasing demand for multifunctional metasurfaces in current communication systems and electromagnetic research, the key research focus has been on how to achieve integrated absorption, transmission, and reflection polarization conversion through multipath modulation. By embedding phase-change materials within the metasurface to control its diverse functions, such metasurfaces must not only achieve multifunctional integration but also possess a highly tunable design to address complex and diverse application scenarios.

[0003] Existing reconfigurable multifunctional metasurfaces primarily achieve functional regulation by employing phase-change materials, but the switching or adjustment of multifunctionality still has limitations. For example, the application publication number CN112838373A, entitled “A Switchable Broadband Multifunctional Metamaterial Absorber / Polarization Converter,” proposes a multifunctional metasurface capable of polarization conversion between absorption and reflection. By using metal as a base plate and graphene and photosensitive silicon as resonant layers, the graphene and photosensitive silicon are adjusted to achieve regulation of the conversion of absorption and reflected waves from the same polarization to circularly polarized and linearly polarized waves. However, in this invention, a non-phase-change material is used as the base plate, and the phase-change material is solely used as a resonant pattern to achieve absorption or polarization conversion functions. This design can only achieve functional design in the two dimensions of reflection and absorption, and cannot further design transmission functions.

[0004] Another example is the patent application with publication number CN117810702A, entitled "A multifunctional terahertz metasurface integrating absorption, transmission and reflection and its preparation method", which uses materials with adjustable properties to achieve absorption, transmission and reflection reconstruction. It discloses an MFM structure that uses Ge2Sb2Te5, vanadium dioxide and graphene to dynamically switch between full transmission, full absorption and full reflection through thermal and electrical control. However, the invention can only realize the transmission function of electromagnetic waves in the case of transmission and reflection, and cannot achieve polarization conversion, and its relative absorption bandwidth is also narrow.

[0005] In summary, although existing technologies can achieve different multifunctional characteristics, their scope of application is relatively narrow. For example, they can only achieve the functions of wave absorption and reflected wave polarization conversion, or realize the transmission and reflection electromagnetic wave propagation and wave absorption functions. They do not realize the coordinated design of terahertz electromagnetic wave transmission and reflection polarization conversion and wave absorption, and it is difficult to meet the requirements of terahertz wave absorption and multi-polarized wave communication. Summary of the Invention

[0006] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and propose a reconfigurable metasurface that can realize polarization conversion of absorption, transmission and reflection, so as to solve the technical problem of the narrow application range caused by insufficient functions in the prior art and to broaden the absorption bandwidth.

[0007] To achieve the above objectives, the technical solution adopted by the present invention includes N×N periodically arranged metasurface units, where N≥2; the metasurface unit includes a first dielectric plate 1, a second dielectric plate 2, a third dielectric plate 3, and a fourth dielectric plate 4 stacked in sequence from top to bottom; the upper and lower surfaces of the first dielectric plate 1 are respectively printed with polygonal phase change material 5, and the polygonal phase change material printed on the lower surface is also nested with a polygonal phase change material ring 6; the lower surfaces of the second dielectric plate 2, the third dielectric plate 3, and the fourth dielectric plate 4 are respectively printed with alternating first phase change material strips 7 and metal strips 8, a plurality of periodically arranged polarization conversion metal units 9, and second phase change material strips 10 that spatially intersect with the first phase change material strips 7 and metal strips 8;

[0008] When electromagnetic waves are irradiated from top to bottom, and the first phase change material is in a metallic state and the second phase change material is in a dielectric state or a metallic state, the metasurface unit realizes broadband wave absorption characteristics; when electromagnetic waves are irradiated from bottom to top, and the first and second phase change materials are both in a metallic state, the metasurface unit realizes linear polarization conversion of the reflection state and alternating circular polarization conversion characteristics; by adjusting the first phase change material to a dielectric state and the second phase change material to a metallic state, the metasurface unit realizes linear polarization conversion characteristics of the transmission state.

[0009] In the above-mentioned reconfigurable metasurface, the first dielectric plate 1 , the polygonal phase change materials 5 printed on its upper and lower surfaces, and the polygonal phase change material ring 6 printed on its lower surface, all have their centers located on the central normal of the first dielectric plate 1 .

[0010] In the above-mentioned reconfigurable metasurface, the width of the first phase change material strip 7 is equal to the width of the metal strip 8 .

[0011] In the above-mentioned reconfigurable metasurface, the width of the second phase-change material strip 10 is equal to the width of the first phase-change material strip 7 .

[0012] In the above-mentioned reconfigurable metasurface, the second phase-change material strip 10 vertically crosses the phase-change material strip 7 and the metal strip 8 .

[0013] The reconfigurable metasurface, the first dielectric plate 1, the second dielectric plate 2, the third dielectric plate 3 and the fourth dielectric plate 4, are all square in shape.

[0014] In the above-mentioned reconfigurable metasurface, the polarization conversion metal structure 9 is composed of two bow-shaped polarization conversion structures that are mirror-symmetrical and arranged opposite to each other, and the symmetry axis is parallel to a diagonal line of the third dielectric plate 3.

[0015] The above-mentioned reconfigurable metasurface, polarization conversion metal unit, consists of an equal-arm L-shaped microstrip and a non-equal-arm L-shaped microstrip spliced ​​with the free ends of its two arms, and the long arms of the two non-equal-arm L-shaped microstrips are perpendicular to the two arms of the equal-arm L-shaped microstrip.

[0016] In the above-mentioned reconfigurable metasurface, the polygonal phase change material 5, the polygonal phase change material ring 6, the first phase change material strip 7 and the second phase change material strip 10 are all made of vanadium dioxide, photosensitive silicon or Ge2Sb2Te5 phase change material.

[0017] In the above-mentioned reconfigurable metasurface, the metallic state or dielectric state of the polygonal phase change material 5, the polygonal phase change material ring 6 and the first phase change material strip 7 is achieved by adjusting the temperature; the metallic state or dielectric state of the second phase change material strip 10 is achieved by adjusting the electric pulse.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The four dielectric plates in the metasurface unit of the present invention are printed with polygonal phase-change material and polygonal phase-change material rings, alternating first phase-change material strips and metal strips, multiple periodically arranged polarization-converting metal units, and second phase-change material strips spatially intersecting the first phase-change material strips and metal strips. When electromagnetic waves are irradiated from top to bottom, with the first phase-change material in a metallic state and the second phase-change material in a dielectric or metallic state, the metasurface unit achieves broadband wave absorption characteristics. When electromagnetic waves are irradiated from bottom to top, with both the first and second phase-change materials in a metallic state, the metasurface unit achieves linear polarization conversion in the reflection state and alternating circular polarization conversion characteristics. Adjusting the first phase-change material to a dielectric state and the second phase-change material to a metallic state allows the metasurface unit to achieve linear polarization conversion in the transmission state. This creates a reconfigurable metasurface capable of polarization conversion in absorption, transmission, and reflection, avoiding the drawback of existing technologies that suffer from limited functionality and effectively broadening its scope of application.

[0020] 2. The present invention utilizes the mutual resonance of the phase change material polygon and the phase change material polygon ring printed on the lower surface of the first dielectric plate, as well as the mutual resonance of the phase change material polygons printed on the upper and lower surfaces of the first dielectric plate. The close resonance points allow electromagnetic waves to be quickly consumed, thereby broadening the absorption bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0022] Figure 2It is a structural schematic diagram of the lower surface of the first dielectric substrate of the present invention.

[0023] Figure 3 It is a structural schematic diagram of the lower surface of the third dielectric substrate of the present invention.

[0024] Figure 4 It is a structural schematic diagram of the polarization conversion metal structure of the present invention.

[0025] Figure 5 It is the reflection state line-to-linear polarization conversion curve diagram and the line-to-circular polarization conversion curve diagram of the present invention.

[0026] Figure 6 It is a transmission state line-to-linear polarization conversion curve diagram of the present invention.

[0027] Figure 7 It is a broadband absorption curve diagram of the present invention. DETAILED DESCRIPTION

[0028] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Reference Figure 1 The present invention comprises a first dielectric substrate 1, a second dielectric substrate 2, a third dielectric substrate 3, and a fourth dielectric substrate 4, arranged in a top-down order parallel to the xoy plane of the three-dimensional coordinate system. Each of the four dielectric substrates has a side length of 84 μm. The first and second dielectric substrates 1 and 2 are constructed of a polycycloolefin copolymer with a relative dielectric constant of 2.35 + i0.01 and thicknesses of 7 μm and 10 μm, respectively, which minimizes the effect on electromagnetic wave propagation. The third dielectric substrate 3 is 6 μm thick, and the fourth dielectric substrate 4 is 5 μm thick.

[0030] Reference Figure 2 The upper surface of the first dielectric substrate 1 is printed with a vanadium dioxide pentagon with a side length of 15 μm, and the lower surface of the first dielectric substrate 1 is printed with a vanadium dioxide pentagon with a side length of 29 μm and a vanadium dioxide pentagon ring 6 with a side length of 49 μm. The resonance of the two vanadium dioxide pentagons printed on the upper and lower surfaces of the first dielectric plate and the resonance of the vanadium dioxide pentagon and pentagon ring printed on the lower surface of the first dielectric plate are used to generate a wave absorbing function and broaden the wave absorbing bandwidth;

[0031] The lower surface of the second dielectric substrate 2 is printed with 13 alternating vanadium dioxide strips 7 and gold strips 8, each 6 μm wide. When the temperature of the vanadium dioxide strips is above 68°C, the vanadium dioxide strips become metallic, and electromagnetic waves cannot penetrate the square patch composed of vanadium dioxide strips 7 and gold strips 8.

[0032] Reference Figure 3, the lower surface of the third dielectric plate 3 is printed with 3×3 periodically arranged polarization conversion metal units 9; the period p is 28 μm;

[0033] Reference Figure 4 The polarization conversion metal unit 9 consists of two mirror-symmetrical, oppositely arranged bow-shaped polarization conversion structures. These structures consist of an equal-arm L-shaped microstrip 91 and a non-equal-arm L-shaped microstrip 92 spliced ​​to the free ends of its two arms. The long arms of the two non-equal-arm L-shaped microstrips are perpendicular to the two arms of the equal-arm L-shaped microstrip. The equal-arm L-shaped microstrip 91 has a side length of 10 μm, while the non-equal-arm L-shaped microstrip 92 has a long side of 6 μm and a short side of 3 μm.

[0034] Seven Ge2Sb2Te5 strips 10 with a width of 6 μm are printed on the lower surface of the fourth dielectric plate 4. The interval between two Ge2Sb2Te5 strips 10 is 6 μm. Electric pulses are applied to the upper and lower levels of the Ge2Sb2Te5 strips 10, and the Ge2Sb2Te5 strips are in a metallic state at this time; since Ge2Sb2Te5 can achieve reversible reconstruction between crystalline and amorphous states at extremely high temperatures (greater than 150°C) or laser pulses and electric pulses, when the temperature of the vanadium dioxide strips is higher than 68°C but less than 150°C, the vanadium dioxide strips appear to be in a metallic state and the Ge2Sb2Te5 strips are in a dielectric state. At this time, electromagnetic waves from bottom to top cannot penetrate the square patch composed of strips 7 and strips 8, and the polarization conversion metal unit 9 can realize the alternating reflection state linear polarization conversion and circular polarization conversion functions. When the temperature of the vanadium dioxide strip is lower than 68°C, the vanadium dioxide strip is in an insulating state. At this time, the polygonal phase change material 5 and the polygonal phase change material ring 6 are both in an insulating state. The polarization conversion metal unit works together with the mutually perpendicular metal strips 8 and Ge2Sb2Te5 strips 10 to realize the polarization conversion function in the transmission state.

[0035] The working principle of the present invention is: using two phase change materials, vanadium dioxide and Ge2Sb2Te5, to jointly regulate the wave absorption, transmission and reflection functions. The metallic state or insulating state of the vanadium dioxide strip mainly affects the wave transmission and absorption properties, while the metallic state or insulating state of the Ge2Sb2Te5 strip mainly affects the wave transmission and reflection properties.

[0036] The absorption rate A(ω) mainly depends on the reflectivity R(ω) and the transmittance T(ω). The interaction between the polygonal phase change material and the polygonal phase change material ring printed on the lower surface of the first dielectric plate, as well as the polygonal phase change material printed on the upper and lower surfaces of the first dielectric plate, can cause electromagnetic waves to resonate in the dielectric substrate layer and be rapidly lost. When R(ω) and T(ω) approach 0, A(ω) approaches 1. The calculation formula of A(ω) is as follows:

[0037] A(ω)=1-R(ω)-T(ω)

[0038] ω represents the frequency. At this time, A(ω), R(ω), and T(ω) respectively represent the absorptivity, reflectivity, and transmittance at the frequency ω.

[0039] To quantify the degree of conversion from linear polarization to circular polarization, we need to use the ellipticity χ. The value range of χ is -1 to 1. When χ is closer to 1, the right-hand circularly polarized wave is more perfect. When χ is closer to -1, the left-hand circularly polarized wave is more perfect.

[0040] Its expression is:

[0041]

[0042] χ is a further derivation of the Stokes parameter. The Stokes parameter is defined as S = [I QU V] T , I represents the total electromagnetic wave intensity, Q represents the polarization component in the x-direction, U represents the polarization component in the 45° angle formed by the xoy plane and the x-axis, and V represents the component of the right-hand circularly polarized wave:

[0043] I=|E x (ω)| 2 +|E y (ω)| 2

[0044] Q=|E x (ω)| 2 -|E y (ω)| 2

[0045]

[0046] Where ω represents the frequency, |E x (ω)|,|E y (ω)| represents the amplitude of the electric field component at frequency ω in the x and y directions, They represent the phases of x-polarized and y-polarized electromagnetic waves at a frequency of ω.

[0047] The following is a description of the technical effects of the present invention in conjunction with simulation experiments:

[0048] 1. Simulation conditions and content:

[0049] The simulation software used was CST, using the Floquet model to simulate infinite arrays and various metasurface functions. When the temperature of the vanadium dioxide strips was set above 68°C, the vanadium dioxide strips were metallic, and when the temperature was set below 68°C, the vanadium dioxide strips were insulating. When an electric pulse was applied to the Ge2Sb2Te5 strips, the Ge2Sb2Te5 strips were metallic, and when no electric pulse was applied, the Ge2Sb2Te5 strips were insulating. The electromagnetic properties of the vanadium dioxide strips, gold strips, and Ge2Sb2Te5 strips in the terahertz band were all given by the Drude model. Electromagnetic waves were incident on the metasurface units perpendicularly along the -z / z direction.

[0050] Simulation 1: When the vanadium dioxide strip is in a metallic state and Ge2Sb2Te5 is in an insulating state, the different reflection polarization characteristics of the present invention are simulated. The results are as follows: Figure 5 (a) and Figure 5 (b) shown.

[0051] Simulation 2, when the vanadium dioxide strip is in an insulating state and the Ge2Sb2Te5 strip is in a metallic state, the transmission function of the present invention is simulated, and the obtained line-to-line polarization conversion curve is as follows: Figure 6 As shown;

[0052] Simulation 3, when the vanadium dioxide strip is in a metallic state and the Ge2Sb2Te5 strip is in a metallic state, the broadband absorption function of the present invention is simulated, and the broadband absorption curve obtained is as follows: Figure 7 As shown;

[0053] 2. Analysis of simulation results:

[0054] Reference Figure 5 ,in, Figure 5 When the linearly polarized wave in (a) is incident vertically on the metasurface structure along the z direction, a cross-polarized reflected wave will be generated. Figure 5 (b) shows the metasurface's highly efficient linear-to-circular polarization conversion of incident waves in the frequency range of 1.5-8 THz, with an absolute value of ellipticity greater than 0.95. Analyzing the electric field distribution at the resonant peak of the curve at 5.73 THz, the resonance originates from the bend of the bow-shaped polarization conversion structure. Analyzing the electric field distribution at the resonant peaks of the curve at 3 THz and 7 THz, the resonance originates from the polarization conversion metal unit.

[0055] Reference Figure 6 When the linearly polarized wave is incident vertically on the metasurface structure along the -z direction, the transmittance is greater than 90%, and the line-to-line polarization conversion rate is greater than 95% in the range of 3.3THz-5THz. The electric field distribution at the resonance peak of the analysis curve at 4THz shows that the resonance comes from the bow-shaped polarization conversion structure and the two perpendicular straight lines.

[0056] Reference Figure 7When the linearly polarized wave is incident vertically on the metasurface structure along the -z direction, the absorption rate is greater than 90% in the range of 1.75THz-11.75THz, and the relative bandwidth is 148%. The electric field distribution at the resonance peaks of 2THz, 6.75THz, and 10THz of the analysis curve shows that the resonances come from the mutual resonance of the two vanadium dioxide pentagons printed on the upper and lower surfaces of the first dielectric plate, and the broadband absorption generated by the resonance of the vanadium dioxide pentagon and pentagonal ring printed on the lower surface of the first dielectric plate.

[0057] In summary, the present invention uses two phase change materials to control the switching of broadband absorption mode, transmission polarization conversion mode, and reflection polarization conversion mode, so that electromagnetic waves incident from different directions can realize the reconfigurable function of absorption, transmission and reflection polarization conversion based on two different phase change materials.

[0058] The above description is only a preferred embodiment of the present invention and does not limit the present invention. For ordinary technicians in this field, several modifications and improvements can be made without departing from the innovative concept of the present invention, but these changes all fall within the scope of protection of the present invention.

Claims

1. A reconfigurable metasurface for achieving polarization conversion between absorption, transmission, and reflection, comprising N×N periodically arranged metasurface units, where N ≥ 2; characterized in that: The metasurface unit comprises a first dielectric plate (1), a second dielectric plate (2), a third dielectric plate (3) and a fourth dielectric plate (4) stacked in sequence from top to bottom; the upper and lower surfaces of the first dielectric plate (1) are respectively printed with polygonal phase change materials (5), and the polygonal phase change material ring (6) is nested on the polygonal phase change material (5) printed on the lower surface; the lower surfaces of the second dielectric plate (2), the third dielectric plate (3) and the fourth dielectric plate (4) are respectively printed with alternately arranged first phase change material strips (7) and metal strips (8), a plurality of periodically arranged polarization conversion metal units (9) and a second phase change material strip (10) spatially intersecting the first phase change material strip (7) and the metal strip (8); When electromagnetic waves are irradiated from top to bottom, and the first phase change material is in a metallic state and the second phase change material is in a dielectric state or a metallic state, the metasurface unit realizes broadband wave absorption characteristics; when electromagnetic waves are irradiated from bottom to top, and the first and second phase change materials are both in a metallic state, the metasurface unit realizes linear polarization conversion of the reflection state and alternating circular polarization conversion characteristics; by adjusting the first phase change material to a dielectric state and the second phase change material to a metallic state, the metasurface unit realizes linear polarization conversion characteristics of the transmission state.

2. The reconfigurable metasurface according to claim 1, wherein: The first dielectric plate (1) has polygonal phase change materials (5) printed on its upper and lower surfaces and a polygonal phase change material ring (6) printed on its lower surface, the centers of which are both located on the central normal line of the first dielectric plate (1).

3. The reconfigurable metasurface according to claim 1, wherein: The width of the first phase change material strip (7) is equal to the width of the metal strip (8).

4. The reconfigurable metasurface according to claim 3, wherein: The width of the second phase-change material strip (10) is equal to the width of the first phase-change material strip (7).

5. The reconfigurable metasurface according to claim 1, wherein: The second phase-change material strip (10) vertically crosses the phase-change material strip (7) and the metal strip (8).

6. The reconfigurable metasurface according to claim 1, wherein: The first dielectric plate (1), the second dielectric plate (2), the third dielectric plate (3) and the fourth dielectric plate (4) all have square plate surfaces.

7. The reconfigurable metasurface according to claim 6, wherein: The polarization conversion metal unit (9) is composed of two bow-shaped polarization conversion structures that are mirror-symmetrical and arranged oppositely, and the symmetry axis is parallel to a diagonal line of the third dielectric plate (3).

8. The reconfigurable metasurface according to claim 7, wherein: The polarization conversion metal unit is composed of an equal-arm L-shaped microstrip and a non-equal-arm L-shaped microstrip spliced ​​with the free ends of its two arms, and the long arms of the two non-equal-arm L-shaped microstrips are perpendicular to the two arms of the equal-arm L-shaped microstrip.

9. The reconfigurable metasurface according to claim 1, wherein: The polygonal phase change material (5), polygonal phase change material ring (6), first phase change material strip (7) and second phase change material strip (10) are all made of vanadium dioxide, Ge2Sb2Te5 or photosensitive silicon phase change material.

10. The reconfigurable metasurface according to claim 9, wherein: The polygonal phase change material (5), the polygonal phase change material ring (6) and the first phase change material strip (7) are realized in a metallic state or a dielectric state by adjusting the temperature; and the second phase change material strip (10) is realized in a metallic state or a dielectric state by adjusting the electric pulse.

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