A stretch-insensitive flexible polarization conversion metasurface and its design method

Abstract

The present invention relates to the field of metamaterials, specifically a stretch-insensitive flexible polarization conversion metasurface and a design method thereof. The present invention arranges the basic units of the asymmetric cross-shaped patch layer in a matrix in the same direction to achieve a polarization conversion effect; and then supplemented with a dielectric layer to reduce the influence of tensile deformation on the overall structure, and the cross-shaped structure of the patch layer can produce a compensation effect, so the current intensity at the resonance point is stronger than that of the traditional polarization conversion structure, achieving deformation insensitivity and at the same time having polarization conversion performance. Under a deformation rate of 20%, the polarization conversion rate PCR of the present invention in the frequency band of 6 to 17 GHz is ≥80%, which can be used in the field of antenna covers with complex curves, and is expected to become an important component of future wearable electromagnetic devices.

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 a key component of radar stealth technology. Electromagnetic metamaterials are man-made composite structures that diffract within the subwavelength range using tiny periodic or quasi-periodic structures, achieving unique electromagnetic properties not found in nature, such as negative magnetic permeability, negative dielectric constant, supertransparency, and superreflectivity. However, most current electromagnetic metamaterials possess only a single function. With the increasing demand for system miniaturization and functional integration, the demand for multifunctional electromagnetic control devices in practical applications is also increasing. Therefore, it is desirable for electromagnetic structures to possess the advantages of flexibility and deformability to enable applications in complex environments.

[0003] The polarization of an electromagnetic wave refers to the temporal variation of the electric field vector at any spatial location during propagation. The electric field vector of an electromagnetic wave propagating along the z-axis at any given coordinate point in space can be classified into three polarization states: linear polarization, circular polarization, and elliptical polarization, based on the phase and amplitude of its electric field components in the x and y directions. The conditions required for different polarization states indicate that, after passing through a certain structure, an electromagnetic wave exhibits different responses in different polarization directions. When the phase and amplitude meet the appropriate conditions, the electromagnetic wave can be arbitrarily controlled between different polarization states. Structures that meet these conditions must exhibit anisotropy. In contrast to anisotropic materials, isotropic materials exhibit the same physical and chemical properties in all directions. Therefore, for artificial electromagnetic structures capable of polarization conversion, their anisotropy primarily manifests itself in the differences in the material's response to electromagnetic waves in different directions.

[0004] Currently, most polarization-converting materials are still planar structures attached to metal surfaces. However, practical applications often involve a variety of curved surfaces, necessitating the design of polarization-converting metasurfaces that meet these requirements. Current research focuses more on the bending properties of polarization-converting materials, with less attention paid to their stretchability. However, in real-world applications, such as wearables, stretching is unavoidable, and in most cases, this affects the device's electromagnetic performance. Therefore, designing metamaterials that are stretch-insensitive is essential.

[0005] The integration of different functions requires in-depth research on the independent and interactive 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 applied value and has important guiding significance for promoting the application and development of electromagnetic metamaterials. Summary of the Invention

[0006] In response to 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-deformation insensitivity 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 is a square with a side length of p on the plane, 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 completely overlap 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. An asymmetric cross is a cross formed by two rectangles of different lengths intersecting at right angles 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 the long and short rectangles overlap with the two diagonals of the square substrate layer, respectively. This makes the asymmetric cross of the patch layer obliquely 45° to the basic unit square to which it belongs, and the planar edges 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 and a width of w = 1mm ± 0.1mm. The 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, which is 4.9 to 5.1 mm, and is disposed between the polarization conversion layer and the bottom layer. The dielectric layer separates the polarization conversion layer and the bottom layer, thereby reducing the impact of deformation on the overall structure and making the structure more stretch-insensitive.

[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 dielectric layer is electromagnetic foam or air.

[0015] Furthermore, when air is selected as the dielectric layer, 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: 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 tensile insensitivity 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 enhance its practicality. Practicality refers to the resistance to negative effects such as breakage or separation due to bending or stretching during use, as well as the comfort of use 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 pattern orientation of the patch layer is consistent 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 built 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: Perform parameter scanning 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 a period of p, and the asymmetric cross-shaped long and short sides of the 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 a polarization-conversion artificial structure, surface currents are generated in the upper metal pattern layer and the underlying 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 occur. If the induced currents generated by the metal pattern and the underlying 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 maintain three resonance points in the overall structure when stretched. For example, when stretched by 5%, the asymmetric cross-shaped patch can produce magnetic resonance or electric resonance at 9.62 GHz, 14.98 GHz, and 18.58 GHz, 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. Ultimately, 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 to protect 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 curves and is expected to become an important component of future wearable electromagnetic devices. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0026] Figure 2 Schematic diagram of the overall three-dimensional structure of the polarization conversion substrate in 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% are shown;

[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% are shown;

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

[0033] Figure 9 A physical picture of a test sample of the embodiment;

[0034] Figure 10 A test environment for an embodiment;

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

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

[0037] Figure 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 with reference to the accompanying drawings and embodiments.

[0039] Example 1

[0040] The basic unit structure of this embodiment consists 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, such as 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 L of the cross-shaped patch is 14mm, the long side width w is 1mm, the short side length a of the metal patch is 5mm, and the short side width b is 1mm; 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. The basic unit is modeled and simulated using the simulation software CSTStudioSuite, and its electromagnetic performance simulation results are shown as follows Figure 3 As shown, PCR Figure 4 As shown, the -10 dB low reflection 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 main function of the polarization conversion layer is to convert the incident TE polarized electromagnetic wave into TM polarized wave. The polarization conversion patch layer structure 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 resultant 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 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, the angle between the electric field of the electromagnetic wave and the x-axis is in the first or third quadrant. At this time, the value of the composite electric field strength is a time-varying function, while the trajectory direction of the composite electric field is fixed. Therefore, the polarization form of the composite wave is linear polarization. When α < 0, it indicates that the composite wave moves in the second or fourth quadrant, and the composite electromagnetic wave is still a linearly polarized wave.

[0054] Materials with low dielectric constants have a weaker response to electric fields, so when deformed, they become less sensitive to electric fields. This is very beneficial for applications that require maintaining polarization stability or reducing deformation interference. Therefore, the substrate of the polarization conversion layer is made of a material with a dielectric constant of 1 to 1.5 (such as electromagnetic foam) to convert incident linearly polarized waves with TE polarization into linearly polarized waves with 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 the thickness change on the tensile deformation.

[0056] The structure was stretched by 10% and the stretching effect was simulated by printing the patch pattern on the stretchable silicone. The specific changes during stretching were that the substrate side length p increased, the thickness t decreased, and the lengths L and a of the rectangular strips in both directions of the asymmetric cross patch increased, while the widths w and b decreased. Therefore, the stretching experiment was simulated using the simulation software CSTStudio Suite. The electromagnetic performance results are shown in the figure below. Figure 5 As shown, PCR Figure 6 As shown, when stretched by 10%, the -10dB low reflection band is 6.78 to 18.71GHz, and the bandwidth with a polarization conversion efficiency higher than 90% is 6.78 to 17.22GHz, 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 printed with an asymmetric cross pattern as a carrier, which is then covered on the intermediate 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 is 1mm, the short side length a of the metal edge is 5mm, and the short side width b is 1mm. The intermediate 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: in this embodiment, the dielectric layer 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 Figure 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: Figure 10 shown.

[0062] Analyze the error between the simulation results and the actual test results, and get the reflectivity when not stretched as follows Figure 11 As shown, the reflectivity after stretching 10% is Figure 12 As shown, the reflectivity of the stretched 20% is as Figure 13 As shown in the figure, 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] As can be seen from the above examples, 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 achieves polarization conversion and enhances deformation insensitivity. It is composed of a periodic arrangement of asymmetric cross-shaped basic units on a plane. The selection of flexible materials and the regulation of the dielectric layer enable the structure to achieve better stretch insensitivity. It is particularly suitable for the field of antenna covers with complex surfaces and wearable electromagnetic devices, used to protect the equipment from deformation.

Claims

1. A stretch-insensitive flexible polarization conversion metasurface, characterized by: The surface layer is composed of a periodic arrangement of asymmetric cross-shaped basic units. The basic unit is a square with a side length of p, p = 11mm ± 0.1mm. In the height direction, from top to bottom, the polarization conversion layer, dielectric layer and bottom layer are arranged in sequence, and they completely overlap in the height direction. The polarization conversion layer is divided into a patch layer and a substrate layer. 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. The asymmetric cross refers to a cross formed by two rectangles of different lengths intersecting at right angles 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 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° to the basic unit square to which it belongs, and the planar edges 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 = 14 mm ± 0.1 mm and a width of w = 1 mm ± 0.1 mm. The short side rectangle of the metal patch has a length of a = 5 mm ± 0.1 mm and a width of b = 1 mm ± 0.1 mm. The dielectric layer has a height of h, which is disposed between the polarization conversion layer and the bottom layer, and 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-converting metasurface according to claim 1, wherein: 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, wherein: The medium layer is electromagnetic foam or air.

4. The stretch-insensitive flexible polarization conversion metasurface according to claim 3, wherein: 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, wherein: 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, wherein: 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.

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. The matrix is ​​arranged in the simulation software to complete the modeling of the metasurface; Step 2: According to the metasurface model of the initial basic unit built in step 1, the parameter optimization range of the simulation software is set as follows: 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 to 5.2 mm; and the corresponding polarization conversion efficiency (PCR), bandwidth performance, and stretching index are set. Step 3: Perform parameter scanning through simulation software to obtain the basic unit parameters with the optimal polarization conversion efficiency PCR and bandwidth.

Images