A flexible transparent broadband polarization rotator based on metamaterials

Abstract

The application discloses a flexible transparent broadband polarization rotator based on a metamaterial, which is composed of a patterned flexible transparent metal mesh, a flexible transparent PDMS medium substrate and a flexible transparent metal mesh as a reflecting backplane from top to bottom. The polarization rotator can convert horizontal polarization electromagnetic waves in a 9.15-18.25 GHz frequency band into vertical polarization electromagnetic waves, and convert the vertical polarization electromagnetic waves into horizontal polarization electromagnetic waves, and the conversion efficiency is as high as 90%. The FSS structure is novel, the U-shaped structure is adopted as the metamaterial structure, and in addition to the bandwidth of polarization rotation, the biggest advantage of the polarization rotator is that the structure is simple and only the most common three-layer structure can be used to realize the polarization rotation, and the novel conductive material and dielectric material are used, and excellent optical transparency and mechanical flexibility are provided.

Description

Technical Field

[0001] This invention belongs to the field of microwave device technology, specifically relating to a flexible transparent broadband polarization rotator based on metamaterials. Background Technology

[0002] Over the past few decades, metasurfaces, referring to two-dimensional (2D) versions of metamaterials, are artificial periodic structures with a thickness much smaller than the wavelength. Due to the diversity of their unit cell structures and sizes, and many unique properties such as negative refraction and negative permeability, they have experienced a tremendous surge of interest in various scientific and engineering disciplines—properties unattainable in nature. Compared to traditional bulk metamaterials, metasurfaces possess many attractive characteristics, such as ease of fabrication, low profile, and low loss, sparking a wealth of new research in fields like electromagnetic stealth, holographic imaging, and information processing. By designing and arranging individual subwavelength atoms in an ideal manner, metasurfaces provide unprecedented degrees of freedom for engineered optical-matter interactions at the subwavelength scale, enabling complete control over the phase, amplitude, frequency, polarization, and propagation direction of electromagnetic waves. In particular, polarization polarization, an inherent property of electromagnetic waves, plays a crucial role in many fields such as display optics, quantum computing, and chemical sensing. Due to the invariance and independence of polarization in the time and frequency domains, polarization modulation techniques are compatible with other modulation techniques in wireless communication and radar systems. Because the electromagnetic response of natural materials is extremely weak, they usually require high thickness or an external magnetic field to achieve phase accumulation, but the bandwidth is limited and the volume is huge.

[0003] In contrast, metasurfaces exhibit unparalleled capabilities in flexibly controlling polarization in a planar and integrated manner, providing a new platform for general polarization transformations, polarization gratings, holography, and imaging. Domestic and international scholars have also made significant progress in designing polarization rotators using metasurfaces. Most polarization converters suffer from narrow bandwidth; to extend bandwidth, stacking complex multilayer structures has been implemented (Z. Wei, Y. Cao, Y. Fan, X. Yu, and H. Li, “Broadband polarization transformation via enhanced asymmetric transmission through arrays of twisted complementary split-ring resonators,” Appl. Phys. Lett., vol. 99, no. 22, 2011, Art. no. 22 1907.). Another issue to consider is maintaining a high polarization conversion rate. The biggest limitation of traditional polarization converters is the lack of mechanical flexibility and optical transparency. ITO currently dominates the market due to its high light transmittance and low resistance. However, ITO also has certain drawbacks (S. Lai, Y. Wu, and W. Gu, “Design of a Transparent Metamaterial CrossPolarization Converter With Large Incident Angle Range,” IEEE Photonics Journal, vol. 13, no. 4, pp. 1-5, 2021.). In and Sn are rare and expensive metals; In is toxic and environmentally unfriendly; Under high temperature conditions, the thermochemical properties of ITO are unstable, making the device prone to chemical reactions. To address all these issues, we propose using transparent metal mesh to achieve a polarization converter with a simple structure, high polarization conversion rate, wide bandwidth, and good mechanical flexibility and optical transparency. Summary of the Invention

[0004] Technical Problem: To address the problems existing in current broadband polarization rotators, this invention provides a simple, flexible, transparent broadband polarization rotator based on metamaterials. Through the combined action of a patterned FSS (Fluorescent Spindle System) and a reflective backplate, it achieves the conversion of incident horizontally polarized electromagnetic waves into internally vertically polarized electromagnetic waves, or vice versa, within the frequency range of 9.15 GHz to 18.25 GHz, with a conversion efficiency as high as 90%. The use of a metal micromesh and PDMS material achieves both optical transparency and mechanical flexibility in the polarization rotator.

[0005] Technical solution: To achieve the above-mentioned objectives, the present invention provides a flexible transparent broadband polarization rotator based on metamaterials, comprising:

[0006] Reflective base plate: made of transparent metal wire mesh;

[0007] Dielectric substrate: made of transparent PDMS and disposed on the upper surface of the reflective substrate;

[0008] Metal patch: Made of transparent metal mesh, it is placed on the upper surface of the dielectric substrate.

[0009] The flexible transparent broadband polarization converter is a periodic structure with one periodic unit measuring 10mm × 10mm and the entire device having a thickness of 2.7mm.

[0010] The metal patch consists of two nested U-shaped structures, each U-shaped structure having three sides of equal length and the same width.

[0011] The U-shaped structure has a single-side length L = 4.4 mm, a width W = 0.8 mm, and a vertical distance M = 1.3 mm from the center of the U-shaped structure to the side of the U-shaped structure.

[0012] The dielectric substrate is made of PDMS flexible transparent material with a relative permittivity of 2.7 and a loss tangent of 0.015.

[0013] The transparent metal mesh material is a flexible and transparent conductive material with a sheet resistance of 0.12 ohms / square, which can be approximated as an ideal conductor.

[0014] The PDMS flexible transparent material is a cube-shaped periodic structure with a thickness of 2.7 mm, a structural unit period P = 10 mm, and a structural period of 10 mm × 10 mm.

[0015] The polarization rotator is fabricated by placing a metal mesh on a transparent PDMS dielectric substrate, and then cutting out the desired patterned U-shaped structure by setting the output power of the laser cutting machine drill bit.

[0016] Invention Principle: A flexible, transparent, broadband polarization rotator based on metamaterials comprises nested U-shaped metal patches, PDMS dielectric, and a backplate made of metal mesh, arranged sequentially from top to bottom. When a horizontally polarized electromagnetic wave is incident on the device, it first contacts a patterned frequency-selective surface. The metal frequency-selective surface generates strong electromagnetic resonance under the incidence of electromagnetic waves of a specific frequency, resulting in reflection. Simultaneously, due to the structure of the metal frequency-selective surface, the phase of the incident horizontally polarized electromagnetic wave is rotated by 180°. Therefore, the reflected signal contains not only horizontally polarized electromagnetic waves but also vertically polarized ones, with a larger proportion of vertically polarized electromagnetic waves. This achieves a high polarization conversion rate for the polarization rotator. Because of its centrosymmetric structure, this polarization converter is suitable for both horizontally and vertically polarized incident electromagnetic waves.

[0017] Beneficial Effects: Compared with existing technologies, this invention provides a metamaterial flexible transparent broadband polarization rotator that, through the combined action of a patterned FSS structure and a metal backplate, can convert incident vertically polarized electromagnetic waves into horizontally polarized electromagnetic waves within the range of 9.15 GHz to 18.25 GHz, and can also convert incident horizontally polarized electromagnetic waves into vertically polarized electromagnetic waves, with a polarization conversion rate exceeding 90%. Furthermore, it replaces the previous transparent material ITO with a novel flexible transparent material, using a self-synthesized flexible transparent material PDMS, significantly reducing costs. The use of laser cutting technology improves processing time, facilitating large-scale production. This invention can be used in radio frequency circuits, polarization control, polarization separation, polarization rotation devices or systems. Its excellent mechanical flexibility and good optical transparency broaden the application of polarization converters, possessing very broad application prospects and value. Attached Figure Description

[0018] Figure 1 This is a 3D view of a broadband flexible transparent polarization rotator based on metamaterials;

[0019] Figure 2 This is a top view of a broadband flexible transparent polarization rotator based on metamaterials;

[0020] Figure 3 This is a side view of a broadband flexible transparent polarization rotator based on metamaterials;

[0021] Figure 4 It is a 2*2 array diagram of the periodic arrangement of units of a broadband flexible transparent polarization rotator based on metamaterials;

[0022] Figure 5 This is a graph showing the reflection coefficient of the electric field along the x-axis of a broadband flexible transparent polarization rotator based on metamaterials when electromagnetic waves are incident perpendicularly.

[0023] Figure 6 This is a graph showing the co-polarization reflectivity, cross-polarization conversion rate, and polarization conversion rate of the electric field along the x-axis of a broadband flexible transparent polarization rotator based on metamaterials when electromagnetic waves are incident perpendicularly.

[0024] Figure 7 These are reflection amplitude curves along the U-axis and V-axis of a flexible broadband transparent polarization rotator based on metamaterials.

[0025] Figure 8 These are phase curves of a flexible broadband transparent polarization rotator based on metamaterials along the U-axis and V-axis, respectively.

[0026] Figure 9 This is a phase difference diagram of a flexible broadband transparent polarization rotator based on metamaterials in the UV coordinate system.

[0027] The diagram shows: 1. Metal patch; 2. Dielectric substrate; 3. Reflective base plate. Detailed Implementation

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

[0029] Reference Figure 1 , Figure 2 This invention provides a flexible broadband polarization rotator based on metamaterials. The design and principle of the metamaterial broadband polarization rotator are described. The polarization rotator is composed of periodically arranged unit structures, including two nested U-shaped structures, each with the same length and width. Its three-dimensional structure is as follows: Figure 1 As shown, through the combined effect of a patterned frequency-selective surface and a metal mesh backplate, and by reasonable parameter design and optimization, this structure can achieve the conversion of horizontally polarized electromagnetic waves to vertically polarized electromagnetic waves, and vice versa, within the range of 9.15 GHz to 18.15 GHz, with a polarization conversion rate of over 90%. The use of a novel metal mesh instead of traditional ITO material significantly reduces production costs, and the adoption of a self-synthesized PDMS flexible transparent material greatly improves the structure's mechanical flexibility and optical transparency.

[0030] The nested U-shaped structure is composed of two U-shaped structures. The length of one side of each U-shaped structure is L = 4.4 mm, the width is W = 0.8 mm, and the vertical distance from the center of the U-shaped structure to the side of the U-shaped structure is M = 1.3 mm.

[0031] The intermediate dielectric substrate is made of a self-synthesized flexible transparent dielectric material PDMS, with a relative permittivity of 2.72 and a loss tangent of 0.015. The side length of the dielectric substrate is P = 10 mm and the thickness is H = 2.7 mm.

[0032] The thickness of the bottom metal mesh reflective plate is 0.1mm, and the thickness of the top layer of nested U-shaped structures made of metal mesh is also 0.1mm, with a sheet resistance of 0.12 ohms / square.

[0033] The polarization rotator of this reflective metamaterial achieves broadband polarization rotation when a horizontal electromagnetic wave is incident perpendicularly (electric field along the X-axis). This is caused by the combined action of nested U-shaped structures, a metal backplate, and a dielectric layer in the middle layer. This allows the vertically polarized electromagnetic wave to be converted into a horizontally polarized electromagnetic wave. Due to the central rotational symmetry of this structure, it can also convert vertically polarized electromagnetic waves into horizontally polarized waves, achieving a polarization conversion rate of over 90% in the (9.15-18.25) GHz frequency range.

[0034] To achieve greater application value, this polarization rotator uses a flexible and transparent metal micromesh to create a metallized pattern and a metal backplate. It also uses a self-synthesized method to process a flexible and transparent PDMS dielectric substrate with a relative permittivity and loss tangent of 1 / 2.

[0035] The aforementioned flexible, transparent, broadband polarization rotator based on metamaterials is composed of several basic units arranged periodically. A three-dimensional diagram of this polarization converter is shown below. Figure 1 As shown. The top view of the unit is as follows. Figure 2 As shown. Side view as... Figure 3 As shown, where H is the thickness of the dielectric substrate, H1 is the thickness of the metal micromesh, H2 is the thickness of the bottom metal micromesh, and P is the length of the dielectric substrate. The periodically arranged (2*2) array diagram of this polarization converter is shown below. Figure 4 As shown.

[0036] Figure 5 This is the reflection amplitude curve of the polarization rotator when the electromagnetic wave is incident horizontally and vertically (electric field along the X-axis), where r yx R represents the cross-polarization reflection coefficient. xx Represents the same polarization coefficient, from which it can be seen that r yx Within the operating frequency band, specifically 9.15 GHz to 18.25 GHz, the amplitude is relatively high, exceeding 0.9, while r xx The amplitude is small, below 0.1. Figure 6 This is a graph showing the reflection polarization conversion rate of the polarization converter when the electromagnetic wave is incident horizontally and perpendicularly (electric field along the X-axis), where PCR is the reflection polarization conversion rate, and its formula is: When PCR > 0.9, it can be considered that a complete cross-polarization transition has occurred. Figure 7 These are the reflection amplitude curves of the polarization converter along the U-axis and V-axis of the incident electromagnetic wave, respectively, where ruu This represents the amplitude curve of the incident and emitted waves along the U-axis, r vv The reflection amplitude curves, which are incident and emitted along the V-axis, are shown in Figure 7. The difference between the amplitudes of the two curves is small, and they are basically higher than 0.8. This indicates that the reflection amplitude along the u-axis and v-axis is roughly the same as the polarization amplitude along the V-axis. Figure 8 The diagram shows the phase curves of the polarization converter along the U-axis and V-axis of the incident electromagnetic wave. Figure 9 This is a graph showing the phase difference between the polarization converter and the incident electromagnetic wave along the U-axis and V-axis, combined with... Figure 8 , Figure 9 As can be seen, the phase difference of the described polarization converter is approximately 180° within the range of 9.15 GHz to 18.25 GHz, which once again fully demonstrates that the polarization converter has a strong polarization conversion capability in this wide frequency band.

Claims

1. A flexible, transparent, broadband polarization rotator based on metamaterials, characterized in that, The rotator includes: a reflective base plate (3): made of transparent metal mesh; a dielectric substrate (2): made of transparent PDMS and disposed on the upper surface of the reflective base plate (3); and a metal patch (1): made of transparent metal mesh and disposed on the upper surface of the dielectric substrate (2). The flexible transparent broadband polarization converter is a periodic structure, with one periodic unit measuring 10mm × 10mm and the entire device having a thickness of 2.7mm. The metal patch (1) consists of two nested U-shaped structures, each U-shaped structure having three sides of equal length and the same width. The dielectric substrate (2) is made of PDMS flexible transparent material with a relative permittivity of 2.7 and a loss tangent of 0.

015.

2. The flexible transparent broadband polarization rotator based on metamaterials according to claim 1, characterized in that... The U-shaped structure has a single-side length L=4.4mm, a width W=0.8mm, and a vertical distance M=1.3mm from the center of the U-shaped structure to the side of the U-shaped structure.

3. The flexible transparent broadband polarization rotator based on metamaterials according to claim 1, characterized in that: The transparent metal mesh is a flexible, transparent conductive material with a sheet resistance of 0.12 ohms / square.

4. The flexible transparent broadband polarization rotator based on metamaterials according to claim 1, characterized in that: The PDMS flexible transparent material is a cube-shaped periodic structure with a thickness of 2.7 mm, a structural unit period P=10 mm, and a structural period of 10 mm × 10 mm.

5. The flexible transparent broadband polarization rotator based on metamaterials according to claim 1, characterized in that... The polarization rotator is fabricated by placing a metal mesh on a transparent PDMS dielectric substrate (2) and cutting out a patterned U-shaped structure using a laser cutter.

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