Chiral metasurface based on bidirectional equiaxial stretching for controlling circular dichroism frequency band switching

Abstract

The application discloses a kind of chiral metasurface based on bidirectional isometric stretching regulation and control circular dichroism frequency band switching, including a plurality of periodic arrangement chiral metasurface structure unit, structure unit includes upper layer, middle layer and lower layer, upper layer includes rectangular copper sheet and its polyimide substrate, rectangular copper open ring and its polyimide substrate, middle layer includes resin dielectric layer, lower layer includes rectangular copper sheet and its polyimide substrate.The structure is not under external force and is under bidirectional isometric stretching, rectangular copper sheet and rectangular copper open ring respectively with the circularly polarized light of corresponding resonance frequency produce reaction, form higher circular dichroism (CD).The application can dynamically switch the working frequency band of circular dichroism by mechanical stretching only, without additional electric control element, with potential application value in optical devices, communication systems, sensing equipment and other fields.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electromagnetic functional materials, and particularly relates to a chiral metasurface based on bidirectional isometric stretching for regulating and controlling circular dichroism frequency band switching. BACKGROUND

[0002] Chirality, also known as chiral property, refers to a feature that a mirror image of an object cannot coincide with the object itself through any rotation or translation, and the two non-coinciding configurations are called chiral isomers. Chirality exists universally in nature, from the macroscopic structure of organisms such as the left hand and the right hand of a person to the microscopic structure of molecules and enzymes such as the left-handed and right-handed structures of DNA. When chiral materials interact with electromagnetic waves, unique electromagnetic coupling phenomena occur in their internal structures, and the characteristics include optical activity, optical rotation, circular dichroism (CD), etc. Circular dichroism refers to the difference in transmission effect of left-hand circular polarization (LCP) and right-hand circular polarization (RCP) of different polarization modes. It has good application prospects in the fields of analytical chemistry, industrial pharmacy and biological monitoring. By using various special structural designs, researchers have successfully prepared chiral metamaterials in the microwave, terahertz wave and infrared bands. Compared with natural chiral molecules, artificial chiral materials have more excellent CD. However, the chiral metasurfaces proposed by researchers at present often have low efficiency in application, cannot dynamically adjust the characteristics of the metasurface, or the adjustment method is complex and difficult to put into practical application. Mechanical regulation refers to changing the geometric shape or spatial arrangement of the structural units of the metasurface by applying external mechanical force (such as stretching, compression, bending or twisting), which has the advantages of passive low consumption, rapid response and high compatibility, and is an excellent candidate for realizing dynamic regulation of the response characteristics of electromagnetic metasurfaces. SUMMARY

[0003] The application aims to solve the above problems in the prior art and provide a chiral metasurface based on bidirectional isometric stretching for regulating and controlling circular dichroism frequency band switching, so that the circular dichroism can be switched between different frequency bands by applying and releasing bidirectional isometric stretching.

[0004] To achieve the above functions, the application adopts the following technical solutions:

[0005] The application provides a chiral metasurface based on bidirectional equiaxial stretching for regulating circular dichroism frequency band switching, which is formed by periodic arrangement of square structure units; each square structure unit takes a resin medium layer as a base for placing other device structures;

[0006] Two first rectangular copper sheets are placed on the back of the resin medium layer, and the first rectangular copper sheets are coupled with the resin medium layer through first polyimide substrates.

[0007] Two parallel rectangular gaps are formed on the front of the resin medium layer in a through manner, and the thickness of the resin medium layer between the two rectangular gaps is reduced relative to other regions to form a strip region capable of being bent under force; two second rectangular copper sheets, four rectangular copper open rings and eight half-rectangular copper open rings are placed on the front of the resin medium layer, wherein two rectangular copper open rings are placed side by side on the strip region in the form of opposite opening directions, and the other two rectangular copper open rings are distributed on both sides of the two rectangular gaps in the form of opposite opening directions; the eight half-rectangular copper open rings are divided into four pairs and arranged along the four edges of the front of the resin medium layer; in addition to the two rectangular copper open rings on the strip region, the remaining two rectangular copper open rings and the four pairs of half-rectangular copper open rings also have strip regions clamped by the rectangular gaps below, and after splicing with adjacent square structure units on the chiral metasurface, the same strip region and two complete rectangular copper open rings on the strip region as in the current square structure unit are formed.

[0008] Each second rectangular copper sheet is coupled with the resin medium layer through a second polyimide substrate, and each rectangular copper open ring and each half-rectangular copper open ring are coupled with the resin medium layer through a third polyimide substrate.

[0009] As a preferred, the two rectangular gaps are parallel to a pair of edges of the outer contour of the square structure unit, but the end is kept away from another pair of edges; among the four rectangular copper open rings placed on the front of the resin medium layer, the openings are located on the rectangular long edges, and the rectangular long edge directions of the two rectangular copper open rings placed on the strip region are parallel to the long edge directions of the rectangular gaps, and the rectangular long edge directions of the other two rectangular copper open rings distributed on both sides of the two rectangular gaps are perpendicular to the long edge directions of the rectangular gaps.

[0010] As a preferred, the two first rectangular copper sheets placed on the back of the resin medium layer are located on one side of the strip region, and the long edge direction of the first rectangular copper sheet forms a 45° angle with the long edge direction of the rectangular gap; the two second rectangular copper sheets placed on the front of the resin medium layer are located on the other side of the strip region, and the long edge direction of the second rectangular copper sheet is perpendicular to the long edge direction of the first rectangular copper sheet.

[0011] Preferably, the square structure unit has a period of 18-22 mm.

[0012] Preferably, the first and second rectangular copper pieces have a length of 7-7.5 mm, a width of 0.5-1 mm, and a thickness of 0.01-0.05 mm.

[0013] Preferably, the first and second polyimide substrates are square substrates with a side length of 5.5-6 mm and a thickness of 0.1-0.3 mm.

[0014] Preferably, the rectangular copper open ring has a length of 4-5 mm, a width of 2.5-3 mm, a ring body width of 0.4-0.6 mm, an opening distance of 0.1-0.5 mm, and a thickness of 0.01-0.05 mm.

[0015] Preferably, the third polyimide substrate under the rectangular copper open ring is a rectangular substrate with a length of 5.5-6 mm, a width of 2.5-3 mm, and a thickness of 0.1-0.3 mm.

[0016] Preferably, the resin medium layer has different thicknesses in different position areas, with a strip area between the two rectangular voids having a thickness of 0.5-1 mm and the remaining non-strip areas having a thickness of 2-2.5 mm.

[0017] Preferably, the rectangular voids have a length of 14-15 mm and a width of 0.4-0.6 mm, and the strip area has a length of 14-15 mm and a width of 3-3.5 mm, with the distance between the two rectangular copper open rings placed on the strip area being 1-1.5 mm.

[0018] Compared with the prior art, the present application has the following beneficial effects:

[0019] The present application proposes a new chiral metasurface structure, which has rectangular copper pieces and rectangular copper open rings. In the state where the structure is not deformed and in the state where the structure is deformed by 20% bidirectional equiaxial stretching, the structure respectively reacts with circularly polarized light of different frequency bands to form high circular dichroism. The present application realizes the switching of circular dichroism between different frequency bands by applying and releasing bidirectional equiaxial stretching, and by changing the overall size of the structure or the length of the rectangular copper pieces and the opening distance of the rectangular copper open rings, the wave peak of the circular dichroism will shift, which can be flexibly adjusted as needed. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a three-dimensional structure schematic diagram of a chiral metasurface based on bidirectional equiaxial stretching for regulating circular dichroism frequency band switching according to an embodiment of the present application;

[0021] Figure 2are two different angle side views of a chiral metasurface structure unit of an embodiment of the present invention;

[0022] Figure 3 is an exploded view of a chiral metasurface structure unit of an embodiment of the present invention;

[0023] Figure 4 is a top view of a first rectangular copper piece, a second rectangular copper piece and their polyimide substrate;

[0024] Figure 5 is a top view of a rectangular copper split ring and its polyimide substrate;

[0025] Figure 6 is a top view of a resin dielectric layer with rectangular voids;

[0026] Figure 7 are top view and side view of a chiral metasurface structure unit of an embodiment of the present invention under 20% biaxial isotropic stretching state;

[0027] Figure 8 are the transmission response and circular dichroism of a chiral metasurface of an embodiment of the present invention to circularly polarized light of two working frequency bands in the undeformed state, where (a) represents the case of 6-9 GHz, (b) represents the case of 12.5-15.5 GHz;

[0028] Figure 9 are the transmission response and circular dichroism of a chiral metasurface of an embodiment of the present invention to circularly polarized light of two working frequency bands under 20% biaxial isotropic stretching state, where (a) represents the case of 6-9 GHz, (b) represents the case of 12.5-15.5 GHz.

[0029] Figure 10 are the wave peak size chart of circular dichroism of a chiral metasurface of an embodiment of the present invention in the undeformed state when the length of the rectangular copper piece and the opening distance of the rectangular copper split ring are changed, where (a) represents the case of 6-9 GHz, (b) represents the case of 12.5-15.5 GHz.

[0030] Figure 11 are the wave peak size chart of circular dichroism of a chiral metasurface of an embodiment of the present invention under 20% biaxial isotropic stretching state when the length of the rectangular copper piece and the opening distance of the rectangular copper split ring are changed, where (a) represents the case of 6-9 GHz, (b) represents the case of 12.5-15.5 GHz.

[0031] The reference signs in the figure are as follows: square structure unit A, edge structure unit B, first rectangular copper sheet 1, first polyimide substrate 2, resin medium layer 3, second rectangular copper sheet 4, second polyimide substrate 5, rectangular copper open ring 6, third polyimide substrate 7, half-rectangular copper open ring 8, rectangular gap 9. DETAILED DESCRIPTION

[0032] In order to make the above objectives, characteristics and advantages of the present application more apparent, specific embodiments of the present application will be described in detail below with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. It will be apparent, however, to one skilled in the art that the present application can be practiced without using these specific details. In other instances, well-known methods have not been described in detail in order to avoid obscuring the present application. Under the purview of the present application, the technical features in each embodiment of the present application can be combined accordingly without conflict.

[0033] In the description of the present application, it should be understood that when an element is considered to be "connected" to another element, it can be directly connected to the other element or indirectly connected to the other element with an intermediate element. In contrast, when an element is referred to as being "directly" connected to another element, there is no intermediate element.

[0034] In the description of the present application, it should be understood that the terms "first" and "second" are only used for distinguishing purposes and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined with "first" and "second" can explicitly or implicitly include at least one of the features.

[0035] As shown in Figure 1 In a preferred embodiment of the present application, a chiral metasurface based on bidirectional equiaxial stretching for regulating circular dichroism frequency band switching is provided, which realizes the switching of circular dichroism between two frequency bands through the application and release of bidirectional equiaxial stretching.

[0036] For ease of description, the present application defines two perpendicular directions on the plane of the chiral metasurface as x and y directions, and the thickness direction as the y direction, and the corresponding coordinate axis directions are as shown in Figure 2

[0037] ​The chiral metasurface is formed by periodically arranging square structure units A in x and y directions, and the arrangement mode is preferably a rectangular array in the form of N x M, and N and M are integers which can be adjusted according to the actual device size. Each square structure unit A includes an upper layer, a middle layer and a lower layer, the upper layer includes a rectangular copper sheet and its polyimide substrate, a rectangular copper open ring and its polyimide substrate, the middle layer includes a resin medium layer, and the lower layer includes a rectangular copper sheet and its polyimide substrate. The resin medium layer 3 in the middle layer serves as a base for placing other device structures, and the first rectangular copper sheet 1, the first polyimide substrate 2, the second rectangular copper sheet 4, the second polyimide substrate 5, the rectangular copper open ring 6, the third polyimide substrate 7, the half-rectangular copper open ring 8 and the rectangular gap 9 are all placed on the resin medium layer 3, as shown in the exploded view of Figure 3 The specific placement positions of each component on the resin medium layer 3 and the respective structure forms are described in detail below.

[0038] As shown in Figure 2 , two first rectangular copper sheets 1 are placed on the back of the resin medium layer 3, and the first rectangular copper sheets 1 are not placed directly on the back of the resin medium layer 3, but a layer of first polyimide substrate 2 is first laid on the back of the resin medium layer 3, and then the first rectangular copper sheets 1 are placed on the first polyimide substrate 2, so that the first rectangular copper sheets 1 are coupled with the resin medium layer 3 through the first polyimide substrate 2.

[0039] Continuing to refer to Figure 2 , two parallel rectangular gaps 9 are provided on the front of the resin medium layer 3, and the rectangular gaps 9 need to penetrate the thickness direction of the resin medium layer 3. The thickness of the resin medium layer 3 between the two rectangular gaps 9 is reduced relative to other areas, thereby forming a strip area that can be bent under force. Two second rectangular copper sheets 4, four rectangular copper open rings 6 and eight half-rectangular copper open rings 8 are placed on the front of the resin medium layer 3, wherein two rectangular copper open rings 6 are placed side by side on the above-mentioned strip area with opposite opening directions, and the rectangular long side directions of the openings of the two rectangular copper open rings 6 are parallel to the long side directions of the above-mentioned rectangular gaps 9. The other two rectangular copper open rings 6 are distributed on both sides of the two rectangular gaps 9 with opposite opening directions, and the rectangular long side directions of the openings are perpendicular to the long side directions of the above-mentioned rectangular gaps 9. The eight half-rectangular copper open rings 8 are divided into four pairs, and each two half-rectangular copper open rings 8 form a pair. The four pairs of half-rectangular copper open rings 8 are arranged along the four edges of the front of the resin medium layer 3, and one pair of half-rectangular copper open rings 8 is arranged on each edge.

[0040] In addition to the two rectangular copper open rings 6 on the strip area, the remaining two rectangular copper open rings 6 and the four pairs of half-rectangular copper open rings 8 below also have strip areas clamped by rectangular gaps 9. That is, the resin medium layer 3 below all the rectangular copper open rings 6 and the half-rectangular copper open rings 8 is thinned relative to other position areas.

[0041] Since the square structure units A on the chiral metasurface are periodically and continuously spliced, as shown in FIG. 1, each square structure unit A will form the same above-mentioned strip area and the two complete rectangular copper open rings 6 on the strip area through splicing with adjacent square structure units A on the chiral metasurface. Figure 1 Figure 1 Taking the two square structure units A outlined in FIG. 1 as an example, the two half-rectangular copper open rings 8 on the bottom edge of the upper square structure unit A are spliced with the two half-rectangular copper open rings 8 on the top edge of the lower square structure unit A to form two complete rectangular copper open rings 6. The two rectangular copper open rings 6 formed by splicing have the same structural size parameters as the two rectangular copper open rings 6 on each square structure unit A on the strip area. However, it should be noted that among all the periodically arranged square structure units A, the edge structure units B along the entire perimeter of the chiral metasurface can have certain particularity. Considering the support difficulty of the edge position, the half-rectangular copper open rings 8 can not be arranged on the side edges along the outer boundary of these edge structure units. Taking the edge structure unit B in the lower right corner of FIG. 1 as an example, two of its side edges are along the outer boundary of the metasurface, and the half-rectangular copper open rings 8 can not be arranged on these two edges, and the remaining unit structures are the same as the square structure unit A. Figure 1

[0042] ​​In addition, it should be noted that each second rectangular copper sheet 4 is coupled with the resin dielectric layer 3 through the second polyimide substrate 5, and each rectangular copper open ring 6 and each half-rectangular copper open ring 8 is coupled with the resin dielectric layer 3 through the third polyimide substrate 7. Similarly, the third polyimide substrate 7 under each rectangular copper open ring 6 is a complete rectangle, while the third polyimide substrate 7 under each half-rectangular copper open ring 8 is only half of the rectangle, but the third polyimide substrate 7 under the rectangular copper open ring 6 formed by the splicing of two half-rectangular copper open rings 8 after the splicing of adjacent square structure units A will also have the same size parameters as the third polyimide substrate 7 under the rectangular copper open ring 6.

[0043] In addition, referring to Figure 2 As shown in the above square structure unit A, two rectangular voids 9 are parallel to one pair of opposite sides of the outer contour of the square structure unit A, but the ends are kept away from the other pair of opposite sides; among the four rectangular copper open rings 6 placed on the front surface of the resin dielectric layer 3, the openings are all located on the long sides of the rectangles, and the long sides of the two rectangular copper open rings 6 placed on the strip area are both parallel to the long sides of the rectangular voids 9, and the long sides of the other two rectangular copper open rings 6 distributed on both sides of the two rectangular voids 9 are both perpendicular to the long sides of the rectangular voids 9.

[0044] In addition, the specific selection and size parameters of each structure of the above device can be optimized according to the actual performance requirements, and the final device performance should meet the use requirements. In the embodiments of the present application, the size symbols defined in Figure 4 , Figure 5 and Figure 6 are combined to optimize the structure parameters of the chiral metasurface as follows:

[0045] As a preferred embodiment of the present application, the two first rectangular copper sheets 1 placed on the back surface of the resin dielectric layer 3 are both located on the same side of the strip area, and the long sides of the first rectangular copper sheets 1 form a 45° angle with the long sides of the rectangular voids 9, i.e. the deflection angle α relative to the positive half-axis of the y-axis is 45°; the two second rectangular copper sheets 4 placed on the front surface of the resin dielectric layer 3 are both located on the other side of the strip area, and the long sides of the second rectangular copper sheets 4 also form a 45° angle with the long sides of the rectangular voids 9, but the long sides of the second rectangular copper sheets 4 are perpendicular to the long sides of the first rectangular copper sheets 1.

[0046] As a preferred embodiment of the present application, the planar outer contour of the square structure unit A is a square, and the period P of the structure unit is 18-22 mm in the undeformed state.

[0047] As a preferred embodiment of the present application, the length L2 of the first rectangular copper sheet 1 and the second rectangular copper sheet 4 is 7-7.5 mm, the width L3 is 0.5-1 mm, and the thickness h2 is 0.01-0.05 mm.

[0048] As a preferred embodiment of the present application, the first polyimide substrate 2 and the second polyimide substrate 5 are both square substrates, the side length L1 is 5.5-6 mm, and the thickness h1 is 0.1-0.3 mm.

[0049] As a preferred embodiment of the present application, the rectangular copper open ring 6 has a length L6 of 4-5 mm, a width L5 of 2.5-3 mm, a ring body width w of 0.4-0.6 mm, an opening spacing d2 of 0.1-0.5 mm, and a thickness h4 of 0.01-0.05 mm.

[0050] As a preferred embodiment of the present application, the third polyimide substrate 7 below the rectangular copper open ring 6 is a rectangular substrate, the length L4 is 5.5-6 mm, the width L5 is 2.5-3 mm, and the thickness h3 is 0.1-0.3 mm.

[0051] As a preferred embodiment of the present application, the resin medium layer 3 can be regarded as a resin block with a side length P and a thickness h5, through-holes are cut in the center, right angles, and edge midpoints in the horizontal or vertical direction, and the thickness is reduced in the strip area. The resin medium layer 3 has different thicknesses in different position areas, the thickness h6 of the strip area between the two rectangular gaps 9 (also including the half-strip area below the half-rectangular copper open ring 8) is 0.5-1 mm, and the thickness h5 of the remaining non-strip area is 2-2.5 mm. The resin medium layer 3 can realize the required structure through 3D printing.

[0052] As a preferred embodiment of the present application, the length L7 of the rectangular gap 9 is 14-15 mm, and the width L8 is 0.4-0.6 mm; the length L7 of the strip area is 14-15 mm, and the width L9 is 3-3.5 mm; the spacing d1 between the two rectangular copper open rings 6 placed on the strip area is 1-1.5 mm.

[0053] As a preferred embodiment of the present application, the materials used for the first polyimide substrate 2, the second polyimide substrate 5, and the third polyimide substrate 7 are all polyimide, and the relative dielectric constant is 2.35; the material of the resin medium layer 3 is acrylic resin, and the relative dielectric constant is 2.59; the materials of the first rectangular copper sheet 1, the second rectangular copper sheet 4, the rectangular copper open ring 6, and the half-rectangular copper open ring 8 are all copper, and the electrical conductivity is 5.8×10 7 S / m.

[0054] As a preferred embodiment of the present application, the number N×M of square structural units A of the chiral super surface is 5×5.

[0055] The chiral metasurface based on bidirectional equiaxial stretching to regulate the circular dichroism frequency band switching of the present application will deform as shown in the figure based on the strip area when subjected to 20% bidirectional equiaxial stretching. The period of the square structure unit A after deformation is recorded as P'. When the device is not subjected to external force and subjected to bidirectional equiaxial stretching, the rectangular copper sheet and the rectangular copper open ring respectively react with circularly polarized light of corresponding resonance frequency to form high circular dichroism (CD). The device can dynamically switch the working frequency band of circular dichroism by mechanical stretching only, without additional electric control elements, and has potential application value in the fields of optical devices, communication systems, sensing equipment and other fields. Figure 7 The chiral metasurface based on bidirectional equiaxial stretching to regulate the circular dichroism frequency band switching of the present application will deform as shown in the figure based on the strip area when subjected to 20% bidirectional equiaxial stretching. The period of the square structure unit A after deformation is recorded as P'. When the device is not subjected to external force and subjected to bidirectional equiaxial stretching, the rectangular copper sheet and the rectangular copper open ring respectively react with circularly polarized light of corresponding resonance frequency to form high circular dichroism (CD). The device can dynamically switch the working frequency band of circular dichroism by mechanical stretching only, without additional electric control elements, and has potential application value in the fields of optical devices, communication systems, sensing equipment and other fields.

[0056] In order to make the purpose, technical scheme and advantages of the present application more clear, the present application will be further described in detail below with examples.

[0057] Embodiment

[0058] The chiral metasurface based on bidirectional equiaxial stretching to regulate the circular dichroism frequency band switching of the present application will deform as shown in the figure based on the strip area when subjected to 20% bidirectional equiaxial stretching. The period of the square structure unit A after deformation is recorded as P'. When the device is not subjected to external force and subjected to bidirectional equiaxial stretching, the rectangular copper sheet and the rectangular copper open ring respectively react with circularly polarized light of corresponding resonance frequency to form high circular dichroism (CD). The device can dynamically switch the working frequency band of circular dichroism by mechanical stretching only, without additional electric control elements, and has potential application value in the fields of optical devices, communication systems, sensing equipment and other fields. Figures 1 to 7 The specific parameters of each structure are as follows:

[0059] The two first rectangular copper sheets 1 placed on the back of the resin medium layer 3 are located on the same side of the strip area, and the long edge direction of the first rectangular copper sheet 1 forms a 45° angle with the long edge direction of the rectangular gap 9, that is, the deflection angle α relative to the positive half axis of the y axis is 45°; the two second rectangular copper sheets 4 placed on the front of the resin medium layer 3 are located on the other side of the strip area, and the long edge direction of the second rectangular copper sheet 4 also forms a 45° angle with the long edge direction of the rectangular gap 9, but the long edge direction of the second rectangular copper sheet 4 is perpendicular to the long edge direction of the first rectangular copper sheet 1.

[0060] The out-of-plane profile of the square structural unit A is a square, and the period P of the structural unit in the undeformed state is the side length of the square, which is 20 mm. The length L2 of the first rectangular copper sheet 1 and the second rectangular copper sheet 4 is 7 mm, the width L3 is 1 mm, and the thickness h2 is 0.01 mm. The first polyimide substrate 2 and the second polyimide substrate 5 are both square substrates, the side length L1 is 6 mm, and the thickness h1 is 0.1 mm. The length L6 of the rectangular copper open ring 6 is 5 mm, the width L5 is 3 mm, the ring body width w is uniform and w is 0.4 mm, the opening spacing d2 is 0.1 mm, and the thickness h4 is 0.01 mm. The third polyimide substrate 7 below the rectangular copper open ring 6 is a rectangular substrate, the length L4 is 6 mm, the width L5 is 3 mm, and the thickness h3 is 0.1 mm. The resin dielectric layer 3 has different thicknesses in different position areas, the thickness h6 of the strip area between the two rectangular voids 9 and the half strip area below all the half-rectangular copper open rings 8 is 0.5 mm, the thickness h5 of the remaining non-strip area is 2 mm, and the square out-of-plane profile of the resin dielectric layer 3 has a side length of 20 mm. The length L7 of the rectangular void 9 is 14 mm, and the width L8 is 0.5 mm; the length L7 of the strip area is 14 mm, and the width L9 is 3 mm; the spacing d1 between the two rectangular copper open rings 6 placed on the strip area is 1 mm. The materials used for the first polyimide substrate 2, the second polyimide substrate 5 and the third polyimide substrate 7 are all polyimide, and the relative dielectric constant is 2.35; the material of the resin dielectric layer 3 is acrylic resin, and the relative dielectric constant is 2.59; the materials of the first rectangular copper sheet 1, the second rectangular copper sheet 4, the rectangular copper open ring 6 and the half-rectangular copper open ring 8 are all copper, and the electrical conductivity is 5.8×10 7 S / m. The number of periodically arranged square structural units A in the chiral metasurface is N×M=5×5.

[0061] Based on the chiral metasurface designed according to the above structural parameters, the simulation performance test was carried out, and the results are as follows:

[0062] Regarding the calculation of circular dichroism, the formula CD=|t RR | t 2 | t LL | t 2 can be obtained, where t RR and t LL are the transmittances of right-handed and left-handed circularly polarized light, respectively. The transmittance simulation results of this embodiment are calculated by CSTMicrowaveStudio2022 software, in which the unit cell periodic boundary condition is used in the x and y directions, and the open (add space) boundary condition is used in the z direction.

[0063] The transmission response and circular dichroism under circularly polarized light incidence of this embodiment in the undeformed state are as follows: Figure 8As shown, the circular dichroism is close to 0 in the 6-9 GHz range, exhibits obvious circular dichroism in the 12.5-15.5 GHz range, and can reach a maximum of 0.52 at 14.71 GHz.

[0064] When subjected to 20% biaxial equiaxial tension in this embodiment, the deformed structural unit is as follows: Figure 7 As shown, the bidirectional equiaxial stretching is calculated as (P'-P) / P. In this embodiment, the transmission response and circular dichroism under circularly polarized light incidence are as follows: Figure 9 As shown, in contrast to the undeformed state, it exhibits obvious circular dichroism in the 6-9 GHz range, reaching a maximum of 0.71 at 7.70 GHz. The circular dichroism weakens significantly in the 12.5-15.5 GHz range, reaching a maximum of only 0.19 at 14.03 GHz.

[0065] In addition, the structural parameters of the chiral metasurface in this embodiment can be adjusted accordingly, and different parameters will affect the circular dichroism of the final device. The following will further explore the different structural parameters.

[0066] In this embodiment, the length L2 of the first rectangular copper sheet 1 and the second rectangular copper sheet 4, and the opening spacing d2 of the rectangular copper open ring 6 were further adjusted, while keeping other parameters unchanged. The results show that by applying and releasing bidirectional equiaxial stretching, circular dichroism can be generated and eliminated in two frequency bands: without deformation, the circular dichroism reaches a maximum of 0.55 at 14.54 GHz, and under 20% bidirectional equiaxial stretching, the circular dichroism reaches a maximum of 0.72 at 7.73 GHz. Specifically, Figure 10 The paper presents the circular dichroism peak sizes of chiral metasurfaces with different structural parameters in their undeformed state at two different operating frequency bands. (a) represents the 6-9 GHz operating frequency band, and (b) represents the 12.5-15.5 GHz operating frequency band. Additionally, Figure 11 This paper presents the circular dichroism peak sizes of chiral metasurfaces with different structural parameters under 20% biaxial isometric stretching at two different operating frequency bands, where (a) represents the 6-9 GHz case and (b) represents the 12.5-15.5 GHz case. Figure 10 and Figure 11It can be seen that when the chiral metasurface structure does not produce deformation, the rectangular copper pieces on the front and back surfaces react to the incident circularly polarized light in the working frequency band 12.5-15.5 GHz, so that the transmittance of right-handed circularly polarized light is much greater than that of left-handed circularly polarized light, forming a large transmission difference between left and right circularly polarized light, i.e. larger circular dichroism, which can be as high as 0.55; when the structure is subjected to 20% biaxial isotropic stretching, the rectangular copper pieces on the front and back surfaces rotate, the transmission difference between left and right circularly polarized light in the working frequency band 12.5-15.5 GHz is greatly reduced, and the circular dichroism is almost disappeared; the upper rectangular copper open ring also rotates, reacts to the incident circularly polarized light in the working frequency band 6-9 GHz, so that the transmittance of right-handed circularly polarized light is much greater than that of left-handed circularly polarized light, and a significant circular dichroism is generated, which can be as high as 0.72. Therefore, the chiral metasurface structure can produce circular dichroism in different frequency bands by applying or releasing biaxial isotropic stretching, and realize the function of circular dichroism frequency band switching, and by changing L2 and d2, the circular dichroism peaks in the working frequency band 6-9 GHz and the working frequency band 12.5-15.5 GHz can be shifted.

[0067] The above-described embodiments are only some of the preferred implementation schemes of the present application, but are not intended to limit the present application. Those skilled in the art can make various changes and modifications without departing from the spirit and scope of the present application. Therefore, any technical solutions obtained by equivalent replacement or equivalent transformation shall fall within the protection scope of the present application.

Claims

1. A chiral metasurface based on bidirectional equiaxial stretching to regulate the circular dichroism frequency band switching, characterized in that, The chiral metasurface is formed by periodic arrangement of square structure units; each square structure unit takes a resin medium layer (3) as a base for placing other device structures; The back of the resin medium layer (3) is provided with two first rectangular copper sheets (1), and the first rectangular copper sheets (1) and the resin medium layer (3) are coupled through a first polyimide substrate (2); The front of the resin medium layer (3) is provided with two parallel rectangular gaps (9) in a through manner, and the thickness of the resin medium layer (3) between the two rectangular gaps (9) is reduced relative to other regions to form a strip region capable of being bent under force; the front of the resin medium layer (3) is provided with two second rectangular copper sheets (4), four rectangular copper open rings (6) and eight half-rectangular copper open rings (8), wherein two rectangular copper open rings (6) are placed side by side on the strip region in opposite opening directions, and the other two rectangular copper open rings (6) are distributed on both sides of the two rectangular gaps (9) in opposite opening directions; The eight half-rectangular copper open rings (8) are divided into four pairs and arranged along the four edges of the front of the resin medium layer (3); in addition to the two rectangular copper open rings (6) on the strip region, the remaining two rectangular copper open rings (6) and the four pairs of half-rectangular copper open rings (8) also have strip regions clamped by the rectangular gaps (9) below, and after splicing with adjacent square structure units on the chiral metasurface, the same strip region and two complete rectangular copper open rings (6) on the strip region as in the current square structure unit are formed; Each second rectangular copper sheet (4) and the resin medium layer (3) are coupled through a second polyimide substrate (5), and each rectangular copper open ring (6) and each half-rectangular copper open ring (8) and the resin medium layer (3) are coupled through a third polyimide substrate (7).

2. The chiral metasurface based on bidirectional equiaxial stretching to regulate circular dichroism frequency band switching according to claim 1, wherein, The two rectangular gaps (9) are parallel to a pair of edges of the square structure unit, but the ends are kept away from the other pair of edges; among the four rectangular copper open rings (6) placed on the front of the resin medium layer (3), the openings are all located on the long edges of the rectangles, and the long edge directions of the two rectangular copper open rings (6) placed on the strip region are parallel to the long edge directions of the rectangular gaps (9), and the long edge directions of the other two rectangular copper open rings (6) distributed on both sides of the two rectangular gaps (9) are perpendicular to the long edge directions of the rectangular gaps (9).

3. The chiral metasurface based on bidirectional equiaxial stretching to regulate circular dichroism frequency band switching according to claim 1, wherein, The two first rectangular copper sheets (1) placed on the back of the resin medium layer (3) are located on one side of the strip region, and the long edge direction of the first rectangular copper sheet (1) forms a 45° angle with the long edge direction of the rectangular gap (9); the two second rectangular copper sheets (4) placed on the front of the resin medium layer (3) are located on the other side of the strip region, and the long edge direction of the second rectangular copper sheet (4) is perpendicular to the long edge direction of the first rectangular copper sheet (1).

4. The chiral metasurface based on bidirectional equiaxial stretching to regulate circular dichroism frequency band switching of claim 1, wherein, The period of the square structure unit, i.e. the side length of the square, is 18-22 mm.

5. The chiral metasurface based on bidirectional equibiaxial stretching to regulate circular dichroism frequency band switching of claim 1, wherein, The length of the first rectangular copper sheet (1) and the second rectangular copper sheet (4) is 7-7.5 mm, the width is 0.5-1 mm, and the thickness is 0.01-0.05 mm.

6. The chiral metasurface based on bidirectional equibiaxial stretching to regulate circular dichroism frequency band switching of claim 1, wherein, The first polyimide substrate (2) and the second polyimide substrate (5) are both square substrates, with a side length of 5.5-6 mm and a thickness of 0.1-0.3 mm.

7. The chiral metasurface based on bidirectional equibiaxial stretching to regulate circular dichroism frequency band switching of claim 1, wherein, The length of the rectangular copper open ring (6) is 4-5 mm, the width is 2.5-3 mm, the ring body width is 0.4-0.6 mm, the opening spacing is 0.1-0.5 mm, and the thickness is 0.01-0.05 mm.

8. The chiral metasurface based on bidirectional equibiaxial stretching to regulate circular dichroism frequency band switching of claim 1, wherein, The third polyimide substrate (7) below the rectangular copper open ring (6) is a rectangular substrate, with a length of 5.5-6 mm, a width of 2.5-3 mm, and a thickness of 0.1-0.3 mm.

9. The chiral metasurface based on bidirectional equibiaxial stretching to regulate circular dichroism frequency band switching of claim 1, wherein, The resin medium layer (3) has different thicknesses at different position areas, with a strip area between two rectangular voids (9) having a thickness of 0.5-1 mm, and the remaining non-strip areas having a thickness of 2-2.5 mm.

10. The chiral metasurface based on bidirectional equibiaxial stretching to regulate circular dichroism frequency band switching of claim 1, wherein, The length of the rectangular void (9) is 14-15 mm, and the width is 0.4-0.6 mm; the length of the strip area is 14-15 mm, and the width is 3-3.5 mm; the spacing between the two rectangular copper open rings (6) placed on the strip area is 1-1.5 mm.

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