Reconfigurable metasurface for realizing absorption, transmission and reflection polarization conversion

Abstract

The invention provides a reconfigurable metasurface capable of realizing absorption, transmission and reflection polarization conversion. The metasurface unit comprises four dielectric plates which are printed with polygonal phase change materials, polygonal phase change material rings, first phase change material strips, metal strips, a plurality of polarization conversion metal units and second phase change material strips, wherein the first phase change material strips and the metal strips are alternately arranged, the polarization conversion metal units are periodically arranged, and the second phase change material strips are spatially crossed with the first phase change material strips and the metal strips. When electromagnetic waves irradiate from the top, the first phase change material is in a metal state, the second phase change material is in a medium state or a metal state, and the metasurface shows the broadband wave-absorbing characteristic. When electromagnetic waves irradiate from the bottom and the two are both in a metal state, the metasurface realizes the linear polarization and circular polarization conversion characteristic of a reflection state. And if the first phase change material is in a medium state and the second phase change material is in a metal state, the metasurface realizes the linear polarization conversion characteristic of a transmission state. According to the design, the defect that the application range is narrow in the prior art is effectively overcome, the application scene is widened, and the wave absorbing bandwidth is enhanced.

Description

Technical Field

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

[0002] With the increasing demand for multifunctional metasurfaces in current communication systems and electromagnetic research, how to achieve a metasurface that integrates absorption, transmission, and reflection polarization conversion functions through multi-path regulation has become the core of current research. By embedding phase change materials in the metasurface to regulate the different functions of the metasurface, such metasurfaces must not only achieve multifunctional integration, but also have a highly adjustable design to cope with complex and changing application scenarios.

[0003] Existing reconfigurable multifunctional metasurfaces mainly use phase change materials to achieve functional regulation, but the switching or adjustment of multifunctionality is still limited. For example, in the application publication number CN112838373A entitled "A Switchable Broadband Multifunctional Metamaterial Absorber / Polarization Converter", a multifunctional metasurface with absorption and reflection polarization conversion is proposed. By using metal as the base plate, graphene and photosensitive silicon as the resonant layer, the graphene and photosensitive silicon are adjusted to achieve the regulation of the conversion of absorption and reflected waves from the same polarization to circular polarization and linear polarization. However, in this invention, non-phase change materials are used as the base plate, and phase change materials are used alone as resonant patterns to achieve absorption or polarization conversion functions. This design can only achieve functional design in two dimensions: 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 the existing technologies can achieve different multifunctional characteristics, they have a narrow scope of application. For example, they can only achieve the functions of wave absorption and reflection wave polarization conversion, or realize the transmission and reflection electromagnetic wave propagation and wave absorption functions, and do not realize the coordinated design of terahertz electromagnetic wave transmission and reflection polarization conversion and wave absorption, making it 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 to propose a reconfigurable metasurface that can realize polarization conversion of absorption, transmission and reflection, so as to solve the technical problem of narrow application scope caused by insufficient functions in the prior art and to broaden the absorption bandwidth.

[0007] To achieve the above-mentioned purpose, the technical solution adopted by the present invention includes N×N periodically arranged metasurface units, 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 materials 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 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;

[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, have their centers located on the central normal line 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] In the above-mentioned 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 oppositely, 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, 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 respectively 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 respectively printed with polygonal phase change materials and polygonal phase change material rings, alternating first phase change material strips and metal strips, multiple polarization conversion metal units arranged periodically, and second phase change material strips intersecting the first phase change material strips and metal strips. 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 and alternating circular polarization conversion characteristics in the reflection state; when the first phase change material is adjusted to a dielectric state and the second phase change material is adjusted to a metallic state, the metasurface unit realizes linear polarization conversion characteristics in the transmission state. A reconfigurable metasurface with absorption, transmission and reflection polarization conversion is formed, which avoids the defect of insufficient functions of the prior art and effectively broadens the scope of application.

[0020] 2. The present invention uses 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, and the mutual resonance of the phase change material polygon printed on the upper and lower surfaces of the first dielectric plate. The close resonance points consume electromagnetic waves quickly, 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 schematic structural 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 is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0029] Reference Figure 1 The present invention includes a first dielectric substrate 1, a second dielectric substrate 2, a third dielectric substrate 3, and a fourth dielectric substrate 4 which are parallel to the xoy plane of the three-dimensional coordinate system and arranged in sequence from top to bottom. The side lengths of the four dielectric substrates are all 84 μm; the first dielectric substrate 1 and the second dielectric substrate 2 are made of polycyclic olefin copolymers, with a relative dielectric constant of 2.35+i0.01, and thicknesses of 7 μm and 10 μm respectively, which have little effect on the propagation of electromagnetic waves; the thickness of the third dielectric substrate 3 is 6 μm, and the thickness of the fourth dielectric substrate 4 is 5 μm.

[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, 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 the 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, with a width of 6 μm. When the temperature of the vanadium dioxide strips is higher than 68°C, the vanadium dioxide strips appear in a metallic state, and electromagnetic waves cannot penetrate the square patch composed of the vanadium dioxide strips 7 and the gold strips 8;

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

[0033] Reference Figure 4 The polarization conversion metal unit 9 is composed of two bow-shaped polarization conversion structures that are mirror-symmetrical and arranged oppositely. The bow-shaped polarization conversion structure is composed of an equal-arm L-shaped microstrip 91 and a non-equal-arm L-shaped microstrip 92 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. The side length of the equal-arm L-shaped microstrip 91 is 10μm, and the long side of the non-equal-arm L-shaped microstrip 92 is 6μm and the short side is 3μm.

[0034] The lower surface of the fourth dielectric plate 4 is printed with 7 Ge2Sb2Te5 strips 10 with a width of 6μm, and the interval between two Ge2Sb2Te5 strips 10 is 6μm. 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; because 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 strip is higher than 68°C but less than 150°C, the vanadium dioxide strip appears in a metallic state, and the Ge2Sb2Te5 strip is 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, wherein the metallic state or insulating state of the vanadium dioxide strip mainly affects the wave transmission and absorption properties, and the metallic state or insulating state of the Ge2Sb2Te5 strip mainly affects the wave transmission and reflection properties.

[0036] The wave 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 and the polygonal phase change material printed on the upper and lower surfaces of the first dielectric plate can make the electromagnetic wave resonate in the dielectric substrate layer and be quickly lost, so that 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 frequency. At this time, A(ω), R(ω), and T(ω) respectively represent the absorbance, 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 respectively 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 combination with simulation experiments:

[0048] 1. Simulation conditions and contents:

[0049] The simulation software used is CST, and the Floquet mode is used to simulate infinite arrays and various functions of the metasurface. When the temperature of the vanadium dioxide strip is set to be higher than 68°C, the vanadium dioxide strip is in a metallic state, and when the temperature of the vanadium dioxide strip is set to be lower than 68°C, the vanadium dioxide strip is in an insulating state. When an electric pulse is applied to the Ge2Sb2Te5 strip, the Ge2Sb2Te5 strip is in a metallic state, and when no electric pulse is applied, it is in an insulating state. The electromagnetic properties of the vanadium dioxide strip, gold strip, and Ge2Sb2Te5 strip in the terahertz frequency band are all given by the Drude model, and the electromagnetic wave is irradiated vertically onto the metasurface unit 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, and the results are as follows: Figure 5 (a) and Figure 5 (b) as 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 efficient linear-circular polarization conversion of the incident wave by the metasurface in the frequency range of 1.5-8THz with an absolute value of ellipticity greater than 0.95. The electric field distribution at the resonance peak of the curve at 5.73THz is analyzed, and the resonance comes from the bending of the bow-shaped polarization conversion structure; the electric field distribution at the resonance peak of the curve at 3THz and 7THz is analyzed, and the resonance comes from the polarization conversion metal unit.

[0055] Reference Figure 6 The transmittance of the linearly polarized wave is greater than 90% after being incident vertically on the metasurface structure along the -z direction. 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 two vertical straight lines.

[0056] Reference Figure 7When the linear 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 of the resonance peaks of the curve at 2THz, 6.75THz, and 10THz is analyzed. 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 jointly generated by the resonance of the vanadium dioxide pentagon and the pentagon 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 are incident from different directions to achieve reconfigurable functions 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 constitute a limitation to the present invention. A person skilled in the art may make several modifications and improvements without departing from the innovative concept of the present invention, but these changes shall all fall within the scope of protection of the present invention.

Claims

1. A reconfigurable metasurface for realizing polarization conversion of absorption, transmission and reflection, comprising N×N periodically arranged metasurface units, 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 also 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 second phase change material strips (10) spatially intersecting the first phase change material strips (7) and the metal strips (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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: 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, characterized in that: The first dielectric plate (1), the second dielectric plate (2), the third dielectric plate (3) and the fourth dielectric plate (4) all have a square plate surface shape.

7. The reconfigurable metasurface according to claim 6, characterized in that: The polarization conversion metal unit (9) is composed of two arc-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, characterized in that: 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, characterized in that: 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, Ge2Sb2Te5 or photosensitive silicon phase change material.

10. The reconfigurable metasurface according to claim 9, characterized in that: The metal 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; and the metal state or dielectric state of the second phase change material strip (10) is achieved by adjusting the electric pulse.

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