Stretch-insensitive flexible polarization conversion metasurface and design method thereof

Abstract

The invention relates to the field of metamaterials, in particular to a flexible polarization conversion metasurface insensitive to stretching and a design method of the flexible polarization conversion metasurface. According to the invention, the basic units of the asymmetric cross-shaped patch layer are arranged in the same direction in a matrix manner, so that the polarization conversion effect is achieved; the dielectric layer is supplemented to reduce the influence of tensile deformation on the whole structure, and the cross-shaped structure of the patch layer can generate a compensation effect, so that the current intensity of a resonance point is stronger than that of a traditional polarization conversion structure, deformation insensitivity is realized, and the polarization conversion performance is realized. Under the deformation rate of 20%, the polarization conversion rate PCR in the frequency band of 6-17 GHz is larger than or equal to 80%, and the antenna housing can be used in the field of antenna housings with complex curved surfaces and is expected to become an important component of wearable electromagnetic equipment in the future.

Description

Technical Field

[0001] The present invention relates to the field of metamaterials, and in particular to a stretch-insensitive flexible polarization conversion metasurface and a design method thereof. Background Art

[0002] Electromagnetic metamaterial design is one of the important means of radar stealth technology. Electromagnetic metamaterial is a man-made composite structure that diffracts in the subwavelength range with a tiny periodic or quasi-periodic structure to achieve exotic electromagnetic properties that do not exist in nature, such as negative magnetic permeability, negative dielectric constant, super-transparency, super-reflection, etc. However, most electromagnetic metamaterials currently have only a single function. With the continuous requirements for system miniaturization and functional integration, the demand for multifunctional electromagnetic control devices in practical applications is also increasing. For this reason, people hope that electromagnetic structures have the advantages of flexibility and deformability to achieve applications in complex environments.

[0003] The polarization of electromagnetic waves refers to the characteristics of the electric field vector at any position in space changing with time during the propagation process. The electric field vector of an electromagnetic wave at any given coordinate point in space propagating along the z-axis can be divided into three polarization forms: linear polarization, circular polarization, and elliptical polarization, according to the different phases and amplitudes of the electric field components in the x and y directions. According to the conditions that must be met for different polarization states of electromagnetic waves, electromagnetic waves have different responses in different polarization directions after passing through a certain structure. When the phase and amplitude meet the corresponding conditions, it is possible to achieve arbitrary regulation between different polarization forms of electromagnetic waves. Structures that meet such conditions must have anisotropic characteristics. In contrast to anisotropic materials are isotropic materials, whose material properties have the same physical and chemical properties in all directions. Therefore, for artificial electromagnetic structures that can achieve polarization conversion, their anisotropy is mainly manifested in the differences in the response of materials to electromagnetic waves in different directions.

[0004] At present, most polarization conversion materials are still planar structures attached to metal surfaces, but in actual applications, various curved surfaces are often used, and it is necessary to design polarization conversion metasurfaces that meet the needs of curved surface applications. Current research focuses more on the bending properties of polarization conversion materials, and rarely on the tensile properties of polarization conversion materials. However, when applied to real devices, such as wearable devices, stretching is inevitable. In most cases, stretching will affect the electromagnetic properties of the device, so it is necessary to design metamaterials that are insensitive to stretching.

[0005] The integration of different functions requires in-depth research on the independence and interaction mechanisms of each unit, which has important guiding significance for the theoretical research of electromagnetic metamaterials. In summary, the research on flexible polarization conversion metasurfaces has important theoretical and application value, and has important guiding significance for promoting the application and development of electromagnetic metamaterials. Summary of the invention

[0006] In view of the above-mentioned problems or shortcomings, and to solve the problem of stretch-insensitivity of existing electromagnetic polarization conversion structures, the present invention provides a stretch-insensitive flexible polarization conversion metasurface and a design method thereof, which is a reflective polarization conversion metasurface with an asymmetric cross-shaped patch, and achieves stretch-insensitive deformation characteristics while ensuring performance.

[0007] A stretch-insensitive flexible polarization conversion metasurface is composed of a periodic arrangement of asymmetric cross-shaped basic units on the surface in a plane. The basic unit on the plane is a square with a side length of p, p = 11mm±0.1mm; in the height direction, from top to bottom, there are a polarization conversion layer, a dielectric layer and a bottom layer (metal reflective layer), which are completely overlapped in the height direction.

[0008] The polarization conversion layer is divided into a patch layer and a substrate layer. The function of the polarization conversion layer is to regulate the incident electromagnetic wave and convert the TE polarized electromagnetic wave into the TM polarized electromagnetic wave.

[0009] The substrate layer is a square with a side length of p and a thickness of t=1 mm±0.1 mm, and is made of a flexible material with a dielectric constant of 1 to 1.5.

[0010] The patch layer is an asymmetric cross-shaped metal patch. The asymmetric cross refers to a cross formed by two rectangles of different lengths intersecting each other at their midpoints. The asymmetric cross-shaped patch layer is attached to the substrate layer in such a way that the midlines of the length direction of its long and short rectangles overlap with the two diagonals of the square substrate layer respectively, so that the asymmetric cross of the patch layer is obliquely distributed at 45° with the basic unit square to which it belongs, and the edges of the plane figures of the patch layer and the substrate layer to which it belongs do not intersect. The long side rectangle of the metal patch has a length of L = 14mm ± 0.1mm, a width of w = 1mm ± 0.1mm, a short side rectangle of the metal patch has a length of a = 5mm ± 0.1mm, and a width of b = 1mm ± 0.1mm.

[0011] The dielectric layer has a height of h, and is disposed between the polarization conversion layer and the bottom layer, where h = 4.9-5.1 mm. The dielectric layer separates the polarization conversion layer and the bottom layer, thereby reducing the influence of deformation on the overall structure, so that the structure can better achieve stretch insensitivity.

[0012] The bottom layer is a square metal reflective layer with a side length of p.

[0013] Furthermore, the dielectric constants of the substrate of the polarization conversion layer and the intermediate dielectric layer are the same or tend to be the same, so that the overall performance of the metasurface is better.

[0014] Furthermore, the medium layer is electromagnetic foam or air.

[0015] Furthermore, when air is selected as the dielectric layer, the thickness t of the substrate layer of the polarization conversion layer has a great influence on the polarization conversion efficiency (PCR) during tensile deformation. Therefore, in order to reduce the influence of the thickness t on the structure during deformation: the thickness of the substrate layer is reduced, and the reduced thickness is replaced by an air dielectric layer, thereby reducing the influence of the thickness change on the tensile deformation, so as to achieve a better stretch-insensitive effect.

[0016] Furthermore, when air is not selected as the dielectric layer, the substrate is removed, and the patch layer is directly disposed on the dielectric layer to achieve a better stretch-insensitive effect.

[0017] Furthermore, the patch layer uses a flexible conductive coating as the surface pattern layer material, and the substrate uses a flexible material to improve its practicality. Practicality refers to the fact that it is not easy to break or separate due to bending or stretching during use, and the comfort when used as a wearable device.

[0018] The design method of the stretch-insensitive flexible polarization conversion metasurface comprises the following steps:

[0019] Step 1. Set the initial values ​​of the parameters of the polarization conversion layer, dielectric layer and bottom layer in the basic unit: p = 11 mm, t = 1 mm, L = 14 mm, w = 1 mm, a = 5 mm, b = 1 mm, h = 5 mm.

[0020] The patch layer of the basic unit is overlapped with the diagonal of the square substrate in the thickness direction, and the patterns of the patch layer are oriented in the same direction and arranged in a matrix in the simulation software to complete the modeling of the metasurface.

[0021] Step 2. According to the metasurface model of the initial basic unit constructed in step 1, set the parameter optimization range of the simulation software, p = 11mm ± 0.1mm, t = 1mm ± 0.1mm, L = 14mm ± 0.1mm, w = 1mm ± 0.1mm, a = 5mm ± 0.1mm, b = 1mm ± 0.1mm, h = 4.8 ~ 5.2mm; and set the corresponding polarization conversion efficiency PCR, bandwidth performance and stretching indicators.

[0022] Step 3: Scan parameters through simulation software to obtain the basic unit parameters with the optimal polarization conversion efficiency PCR and bandwidth.

[0023] The present invention achieves polarization conversion effect by arranging basic units in a matrix with p as period, and the long and short sides of the asymmetric cross-shaped metal patches are oriented in the same direction, so that the patch layer pattern of the polarization conversion layer forms a periodic arrangement, and the dielectric layer can reduce the influence of tensile deformation on the overall structure. When electromagnetic waves are incident on the surface of the polarization conversion artificial structure, surface currents will be formed in the upper metal pattern layer and the bottom PEC of the structure; if the surface current of the pattern layer in the structure is in opposite directions to the current induced by the PEC, magnetic resonance will be generated; if the induced currents generated by the metal pattern and the bottom PEC are in the same direction, the resonance mode is electric resonance; when in a resonant state, the current on the structure is the largest, and the asymmetric cross-shaped patch can keep the overall structure at three resonance points when stretched; for example, when stretched by 5%, the asymmetric cross-shaped patch can produce magnetic resonance or electric resonance at 9.62GHz, 14.98GHz, and 18.58GHz, and because the cross-shaped structure of the patch can produce a certain compensation effect, the current intensity at the resonance point is stronger than that of the traditional polarization conversion structure. Finally, the entire structure obtains stretch-insensitive characteristics while ensuring performance.

[0024] To sum up, the deformation-insensitive electromagnetic structure of the present invention uses a flexible material as a substrate and a flexible conductive coating as a surface pattern layer (patch layer) material to achieve tensile properties under stress for protecting the device from deformation, and at the same time achieve polarization conversion performance; it is insensitive to deformation, and at a deformation rate of 20%, the polarization conversion rate (PCR) in the frequency band of 6 to 17 GHz is ≥80%. This material can be used in the field of antenna covers with complex curved surfaces, and is expected to become an important component of future wearable electromagnetic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic top view of a polarization conversion layer structure of an embodiment;

[0026] Figure 2 This is a schematic diagram of the overall three-dimensional structure of the polarization conversion substrate of the embodiment;

[0027] Figure 3 The electromagnetic performance simulation results of the embodiment when not stretched;

[0028] Figure 4 is the polarization conversion efficiency of the embodiment when it is not stretched;

[0029] Figure 5 The electromagnetic performance simulation results of the embodiment when stretched by 10%;

[0030] Figure 6 is the polarization conversion efficiency when the embodiment is stretched by 10%;

[0031] Figure 7 The electromagnetic performance simulation results of the embodiment when stretched by 20%;

[0032] Figure 8 is the polarization conversion efficiency when the embodiment is stretched by 20%;

[0033] Fig. 9 A physical picture of a test sample of an embodiment;

[0034] Fig.10 A test environment for an embodiment;

[0035] Fig.11 Comparison between the reflectivity test curve and the simulation curve when the embodiment is not stretched:

[0036] Fig.12 Comparison between the reflectivity test curve and the simulation curve when the embodiment is stretched by 10%;

[0037] Fig.13 Comparison between the reflectivity test curve and the simulation curve when the embodiment is stretched by 20%. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0039] Example 1

[0040] The basic unit structure of this embodiment is composed of a polarization conversion layer, a dielectric layer and a reflective layer. The polarization conversion layer uses a 1mm thick substrate, and the intermediate dielectric layer (air) is 5mm thick. The structure of the polarization conversion layer with a substrate is adopted. Figure 2 As shown. Due to the lower dielectric constant, the effect of thickness change on structural performance during stretching is reduced. The long side of the cross-shaped patch is L = 14mm, the long side width is w = 1mm, the short side length of the metal patch is a = 5mm, and the short side width is b = 1mm; the bottom layer uses a square aluminum foil with a thickness of 0.1mm and a side length of p = 11mm to be pasted on the back of the electromagnetic foam to reflect electromagnetic waves. The basic unit is modeled and simulated using the simulation software CSTStudioSuite, and the simulation results of its electromagnetic performance are shown in Figure 3 As shown, PCR Figure 4 As shown, the -10 dB low reflection frequency band is 7.16 to 19.47 GHz, and the bandwidth for polarization conversion efficiency higher than 90% is 7.66 to 18.9 GHz.

[0041] The working principle of polarization conversion is shown in formulas (1)-(7). The function of the polarization conversion layer is mainly to convert the incident TE polarization electromagnetic wave into TM polarization wave. The structure of the polarization conversion patch layer selected by the present invention is as follows: Figure 1 As shown, an asymmetric cross-shaped metal patch is used to realize the polarization conversion function. The shorter rectangle increases the number of resonance points, thereby producing a certain compensation during stretching, thereby reducing the electromagnetic loss after stretching.

[0042] For an electromagnetic wave propagating along the z-axis, the components of the electric field in the x and y directions can be expressed as E x , E y , the phase is E x ,but:

[0043]

[0044] The electric field of the synthetic electromagnetic wave can be expressed as follows:

[0045]

[0046] Assume that the phase difference between the electric fields in the x and y directions is For simplicity, we take the position z=0 for analysis and assume that the initial phase value is 0. Then formulas (1) and (2) can be expressed as:

[0047]

[0048] Linearly polarized wave: For formulas (4) and (5), if the phase difference or Then the polarization form of the electromagnetic wave is linear polarization.

[0049] when When (n=0, ±1, ±2, ...), the magnitude of the electric field of the synthetic electromagnetic wave can be obtained as:

[0050]

[0051] In this case, the angle between the electric field of the synthetic electromagnetic wave and the x-axis can be expressed as follows:

[0052]

[0053] According to formulas (6) and (7), when α>0, it means that the angle between the electric field of the electromagnetic wave and the x-axis is in the first quadrant or the third quadrant. At this time, the value of the synthetic electric field strength is a time-varying function, while the trajectory direction of the synthetic electric field is fixed. Therefore, the polarization form of the synthetic wave is linear polarization. When α<0, it means that the synthetic wave moves in the second quadrant or the fourth quadrant, and the synthesized electromagnetic wave is still a linearly polarized wave.

[0054] Materials with small dielectric constants have weaker response to electric fields, so when deformation occurs, the insensitivity to electric field response increases, which is very beneficial for applications that need to maintain polarization stability or reduce deformation interference. Therefore, the substrate layer of the polarization conversion layer selects a material with a dielectric constant of 1 to 1.5 (such as electromagnetic foam) to convert the incident linearly polarized wave of TE polarization into a linearly polarized wave of TM polarization, generating polarization conversion at 7.16 to 18.9 GHz.

[0055] The thickness t of the polarization conversion layer substrate layer has a great influence on the polarization conversion efficiency (PCR) during tensile deformation. Therefore, in order to reduce the influence of the thickness t on the structure during deformation: 1. The thickness of the substrate layer is reduced, and the reduced thickness is replaced by an air dielectric layer, thereby reducing the influence of thickness change on tensile deformation.

[0056] The structure was stretched by 10% as a whole. The patch pattern was printed on the stretchable silicone to simulate the stretching effect. It was found that the specific changes during stretching were that the substrate side length p increased, the thickness t decreased, the lengths L and a of the rectangular strips in both directions of the asymmetric cross patch increased, and the widths w and b decreased. Therefore, the simulation software CSTStudio Suite was used to simulate the stretching experiment, and the electromagnetic performance results are shown in the figure. Figure 5 As shown, PCR Figure 6 As shown, when stretched by 10%, the -10dB low reflection band is 6.78 to 18.71 GHz, and the bandwidth with polarization conversion efficiency higher than 90% is 6.78 to 17.22 GHz, which is 92.88% of the bandwidth when not stretched.

[0057] When the structure is stretched by 20%, its electromagnetic performance results are as follows Figure 7 As shown, PCR Figure 8 As shown, the -10 dB low reflection band is 6.31 to 15.05 GHz, and the bandwidth where the polarization conversion efficiency is higher than 90% is 6.31 to 15.05 GHz, which is 77.76% of the bandwidth when not stretched.

[0058] Example 2

[0059] The basic unit in this embodiment: the top polarization conversion layer adopts a substrate-free structure. Due to the limitations of the experimental equipment, the patch layer of this embodiment uses aramid paper to print an asymmetric cross pattern as a carrier, and then covers the middle dielectric layer. The thickness of the aramid paper and the patch layer can be ignored relative to the overall unit structure; the long side L of the cross-shaped patch is 14mm, the long side width w=1mm, the short side length a=5mm of the metal edge, and the short side width b=1mm. The middle dielectric layer uses a 6mm thick electromagnetic foam with a dielectric constant close to that of aramid paper (dielectric constant 1.1). The bottom layer uses a square aluminum foil with a thickness of 0.1mm and a side length of p=11mm pasted on the back of the electromagnetic foam to reflect electromagnetic waves, and finally obtains a polarization conversion electromagnetic structure with stretching insensitivity.

[0060] Since the thickness t of the polarization conversion layer substrate layer has a great influence on the polarization conversion efficiency (PCR) during tensile deformation, in order to reduce the influence of the thickness t on the structure during deformation: the dielectric layer of this embodiment uses electromagnetic foam, and the patch layer is directly covered on the electromagnetic foam, thereby reducing the influence of thickness change on deformation.

[0061] The actual sample of this embodiment is shown in the figure Fig. 9 As shown in the figure, the free space method is used to test the reflection performance of the sample. The test environment is as follows: Fig.10 shown.

[0062] Analyze the error between the simulation results and the actual test results, and get the reflectivity when not stretched as follows Fig.11 As shown, the reflectivity of the stretched 10% is Fig.12 As shown, the reflectivity of the stretched 20% is Fig.13 As shown, the comparison of the simulation test shows that the positions of the resonance frequencies are basically corresponding, and the amplitude difference is not large, which achieves the expected effect and verifies the effectiveness of the structure.

[0063] It can be seen from the above embodiments that the simulation and experimental results of the present invention are consistent with the theoretical analysis, proving that the design of the present invention can effectively achieve insensitivity to polarization conversion after stretching. The overall electromagnetic structure of the present invention is simple and efficient, the top polarization conversion layer realizes polarization conversion, enhances deformation insensitivity, and is composed of asymmetric cross-shaped basic units arranged periodically on the plane, supplemented by the selection of flexible materials and the regulation of the dielectric layer, so that the structure can better achieve stretching insensitivity, especially suitable for complex curved antenna covers and wearable electromagnetic devices, used to protect the device from deformation.

Claims

1. A stretch-insensitive flexible polarization conversion metasurface, characterized in that: The surface layer is composed of a periodic arrangement of asymmetric cross-shaped basic units on the plane, and the basic unit on the plane is a square with a side length of p, p = 11mm ± 0.1mm; in the height direction, from top to bottom, there are polarization conversion layer, dielectric layer and bottom layer, and they are completely overlapped in the height direction; The polarization conversion layer is divided into a patch layer and a substrate layer, and the polarization conversion layer regulates the incident electromagnetic wave and converts the TE polarized electromagnetic wave into the TM polarized electromagnetic wave; The substrate layer is a square with a side length of p and a thickness of t = 1 mm ± 0.1 mm, and is made of a flexible material with a dielectric constant of 1 to 1.5; The patch layer is an asymmetric cross-shaped metal patch, and the asymmetric cross refers to a cross formed by two rectangles of different lengths intersecting each other at their midpoints at right angles; the asymmetric cross-shaped patch layer is attached to the substrate layer in such a way that the midlines of the length directions of the long and short rectangles overlap with the two diagonals of the square substrate layer respectively, so that the asymmetric cross of the patch layer is obliquely distributed at 45° with the basic unit square to which it belongs, and the edges of the plane figures of the patch layer and the substrate layer to which it belongs do not intersect; wherein the long side rectangle of the metal patch has a length of L=14mm±0.1mm, a width of w=1mm±0.1mm, a short side rectangle of the metal patch has a length of a=5mm±0.1mm, and a width of b=1mm±0.1mm; The dielectric layer has a height of h, and is disposed between the polarization conversion layer and the bottom layer, where h=4.9-5.1 mm; the dielectric layer separates the polarization conversion layer and the bottom layer, thereby reducing the influence of deformation on the overall structure; The bottom layer is a square metal reflective layer with a side length of p.

2. The stretch-insensitive flexible polarization conversion metasurface according to claim 1, characterized in that: The dielectric constants of the substrate of the polarization conversion layer and the intermediate dielectric layer are the same or tend to be the same, so that the overall performance of the metasurface is better.

3. The stretch-insensitive flexible polarization conversion metasurface according to claim 1, characterized in that: The medium layer is electromagnetic foam or air.

4. The stretch-insensitive flexible polarization conversion metasurface according to claim 3, characterized in that: When air is selected as the dielectric layer, the thickness of the substrate layer is reduced to reduce the influence of thickness change on tensile deformation.

5. The stretch-insensitive flexible polarization conversion metasurface according to claim 3, characterized in that: When air is not selected as the dielectric layer, the substrate is removed and the patch layer is directly arranged on the dielectric layer to achieve a better stretch-insensitive effect.

6. The stretch-insensitive flexible polarization conversion metasurface according to claim 1, characterized in that: The patch layer uses a flexible conductive coating as the surface pattern layer material, and the substrate uses a flexible material to improve its practicability.

7. The design method of the stretch-insensitive flexible polarization conversion metasurface according to claim 1, characterized in that: The following steps are involved: Step 1, set the initial values ​​of the parameters of the polarization conversion layer, dielectric layer and bottom layer in the basic unit: p = 11 mm, t = 1 mm, L = 14 mm, w = 1 mm, a = 5 mm, b = 1 mm, h = 5 mm; The patch layer of the basic unit is overlapped with the diagonal of the square substrate in the thickness direction, and the pattern orientation of the patch layer is consistent and arranged in a matrix in the simulation software to complete the modeling of the metasurface; Step 2: According to the metasurface model of the initial basic unit constructed in step 1, the parameter optimization range of the simulation software is set, p = 11 mm ± 0.1 mm, t = 1 mm ± 0.1 mm, L = 14 mm ± 0.1 mm, w = 1 mm ± 0.1 mm, a = 5 mm ± 0.1 mm, b = 1 mm ± 0.1 mm, h = 4.8-5.2 mm; and the corresponding polarization conversion efficiency PCR, bandwidth performance and stretching index are set; Step 3: Scan parameters through simulation software to obtain the basic unit parameters with the optimal polarization conversion efficiency PCR and bandwidth.

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