A low-cost, stretchable, angle-insensitive, flexible frequency selective surface

Abstract

The present invention discloses a low-cost, stretchable, angle-insensitive, flexible frequency selective surface, belonging to the technical field of flexible electronic devices. The frequency selective surface is an array composed of N×N structural units, each structural unit comprising, from top to bottom, a patterned copper cloth layer (1) and an elastic fabric dielectric layer (2); the structural unit is divided into an outer ring and an inner ring, the lengths of which along the electric field direction and the magnetic field direction of the electromagnetic wave are P and L, respectively; the pattern structure of the patterned copper cloth layer (1) is a serpentine meander line, which is a structure composed of multiple semicircular rings connected, with an outer ring radius of r and a line width of w. By using the elastic fabric dielectric layer and the serpentine meander line-shaped copper cloth layer, the present invention makes the frequency selective surface flexible and stretchable, and can be widely used in wireless communications, and has broad application prospects in antenna covers of equipment such as radar, electronic navigation and electronic countermeasures.

Description

Technical Field

[0001] The present invention belongs to the technical field of flexible electronic devices and relates to a low-cost, stretchable, angle-insensitive, flexible frequency selective surface. Background Art

[0002] Frequency Selective Surfaces (FSS) are single-layer or multi-layer planar structures formed by a large number of identical structural units arranged in a two-dimensional periodic pattern. They exhibit frequency-selective properties for electromagnetic waves with different operating frequencies, polarization states, and incident angles. According to the implementation method of the periodic units, they can be roughly divided into patch-type and slot-type types. When the resonant unit is in a resonant state, for a patch-type FSS, the electromagnetic waves at that frequency will be totally reflected, exhibiting a band-stop characteristic; for a slot-type FSS, the electromagnetic waves at that frequency will be totally transmitted, exhibiting a bandpass characteristic. This frequency-selective property of frequency selective surfaces enables them to perform as electromagnetic wave filters in open spaces, and they are widely used in radar antenna covers, wireless security shielding, multi-frequency antenna systems, and other fields.

[0003] With the rapid development of frequency selective surface technology, some increasingly complex application scenarios have put forward new requirements for it. For example, the conformality of curved surface structures, including the conformality of developable surfaces and the conformality of non-developable surfaces, has also put forward new requirements for the flexibility of frequency selective surfaces. Among them, for the curved surface shapes that can be developed in a plane, the current research work mainly focuses on realizing the application of frequency selective surfaces in conformal environments through material selection and structural design. For example, Muhammad Farhan Shafique et al. (M. Nauman, R. Saleem, MF Shafique. A Miniaturized Flexible Frequency Selective Surface for X-Band Applications [J]. IEEE Transactions on Electromagnetic Compatibility, 2016, 58 (2): 419-428) used flexible Rogers 5880 as the base material to construct a flexible frequency selective surface, which was applied to the surface of a cylinder and maintained good band-stop shielding properties. Yuan Lin et al. (S. Chen, T. Pan, Z. Yan, L. Dai, Y. Peng, M. Gao, Y. Lin. Flexible Serpentine-like Frequency Selective Surface for Conformal Applications With Stable Frequency Response [J]. IEEE Antennas and Wireless Propagation, 2019, 18(7): 1477-1481) used a planar ultra-thin polyimide substrate to fabricate a flexible band-stop frequency selective surface. Due to the thinness and excellent toughness of the substrate, it can perfectly conform to the developable surface and maintain good shielding properties. However, this type of research is limited to some two-dimensional developable surfaces and is difficult to meet the flexibility requirements of some non-developable surfaces. Summary of the Invention

[0004] Technical problem: In order to overcome the shortcomings of the prior art, the present invention provides a low-cost stretchable angle-insensitive flexible frequency selective surface to solve the technical problems mentioned in the background technology: by designing the complete copper cloth into a serpentine meandering line pattern, the intrinsically non-stretchable copper cloth is turned into a stretchable structure, and combined with an elastic fabric medium substrate, it can be attached to a non-expandable surface, meeting the demand for flexibility of the non-expandable surface.

[0005] Technical solution: In order to solve the above technical problems, the present invention provides a low-cost, stretchable, angle-insensitive, flexible frequency selective surface as follows:

[0006] The frequency selective surface is an array of N×N structural units, each of which is composed of a patterned copper cloth layer and an elastic fabric dielectric layer from top to bottom.

[0007] The structural unit is divided into two parts, an outer ring and an inner ring, and its lengths along the electric field direction and the magnetic field direction of the electromagnetic wave are P and L respectively;

[0008] The pattern structure of the patterned copper cloth layer is a serpentine meandering line, which is a structure composed of a plurality of semicircular rings connected together, with an outer ring radius of r and a line width of w.

[0009] The structural unit is divided into an outer ring and an inner ring, wherein both the outer ring and the inner ring are composed of serpentine lines; each side of the outer ring is a continuous serpentine line, and the inner ring is composed of two horizontal and two longitudinal serpentine lines intersecting in a tic-tac-toe shape.

[0010] The elastic fabric medium layer is square in shape, plays a supporting role in the structure, and has good stretchability.

[0011] The specific parameters of the frequency selective surface are P=16 mm, L=8 mm, r=1.35 mm, w=0.7 mm, and the thickness of the dielectric layer along the direction of the electromagnetic wave magnetic field is h=0.42 mm.

[0012] The number of structural units N is ≥ 25.

[0013] The mechanism of the present invention is as follows: the serpentine meandering line pattern has good flexibility from a mechanical analysis perspective. After the complete rectangular copper cloth is patterned with a serpentine meandering line, not only can the bendability be improved through the sparse feature, but it also has stretchability. At the same time, due to the symmetry of the serpentine meandering line pattern itself and its long equivalent electrical length, the appearance of high-frequency grating lobes is suppressed, making the frequency selective surface angle-insensitive when electromagnetic waves are incident at large angles.

[0014] Beneficial effects: The low-cost, stretchable, angle-insensitive, flexible frequency selective surface provided by the present invention has the following beneficial effects compared to the prior art:

[0015] 1. The frequency selective surface designed in the present invention has a stretchable feature through the selection of dielectric layer materials and the design of the copper cloth layer pattern structure. The stretchability is 22%, and during the stretching process, the filtering function of the frequency selective surface remains unchanged within an acceptable range.

[0016] 2. The frequency selective surface designed by the present invention designs the copper cloth layer into a serpentine meandering line structure, which solves the problem of unstable bandpass filtering function of the frequency selective surface when electromagnetic waves are incident at large angles.

[0017] 3. The present invention has a simple structure, a convenient preparation process, and the dielectric plate and copper cloth layer used are low-cost. It is easy to apply on a large scale and has great application potential in the engineering field. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 is a cross-sectional view of a frequency selective surface structural unit of the present invention;

[0019] Figure 2 The pattern structure of the copper cloth layer of the frequency selective surface of the present invention;

[0020] Figure 3 is the transmission coefficient S obtained by simulating the absorbing surface of the present invention 21 The result graph;

[0021] Figure 4 is the transmission coefficient S obtained from the experimental test of the wave-absorbing surface of the present invention 11 and S 21 Result graph.

[0022] The figure includes: a patterned copper cloth layer 1 and an elastic fabric dielectric layer 2. DETAILED DESCRIPTION

[0023] The structure and performance of the present invention will be further described below with reference to the accompanying drawings.

[0024] A low-cost, stretchable, angle-insensitive, flexible frequency selective surface of the present invention comprises N×N structural units, each of which comprises a copper cloth layer and a dielectric layer from top to bottom.

[0025] The structural unit is divided into two parts, an outer ring and an inner ring, and its width along the electric field and magnetic field directions of the electromagnetic wave are P and L respectively;

[0026] The pattern structure of the copper cloth layer is a serpentine meandering line, which is a semicircular ring structure, with an outer ring radius of r and a line width of w.

[0027] Furthermore, the structural unit is divided into two parts: an outer ring and an inner ring, and both the outer ring and the inner ring are composed of serpentine meandering lines.

[0028] Furthermore, the medium layer is elastic fabric.

[0029] Furthermore, the preferred parameters of the frequency selective surface are P=16 mm, L=8 mm, r=1.35 mm, w=0.7 mm, and the thickness of the dielectric layer along the direction of the electromagnetic wave magnetic field is h=0.42 mm.

[0030] Furthermore, the number N of the structural units is ≥25.

[0031] like Figure 1As shown, a low-cost, stretchable, angle-insensitive, flexible frequency selective surface is a ring-shaped frequency selective surface, which includes N×N structural units. Each structure is composed of a patterned copper cloth layer 1 and an elastic fabric dielectric layer 2 from top to bottom.

[0032] The structural unit is divided into two parts, an outer ring and an inner ring, and its width along the electric field and magnetic field directions of the electromagnetic wave are P and L respectively;

[0033] The pattern structure of the copper cloth layer is a serpentine line, and the specific pattern is as follows: Figure 2 As shown, the meander line is a semicircular ring structure, the outer ring radius is r, and the line width is w;

[0034] The dielectric layer is a square elastic fabric with a thickness of h along the direction of the electromagnetic wave magnetic field. It plays a supporting role in the structure and has good stretchability.

[0035] Example 1

[0036] A low-cost, stretchable, angle-insensitive, flexible frequency selective surface comprises 25×25 structural units, each of which consists of a copper cloth layer and a dielectric layer from top to bottom.

[0037] The copper cloth layer is made of a high-conductivity fabric material with a square resistance of 0.00538Ω / sq, a thickness of 0.1mm, and adhesive on one side.

[0038] The dielectric layer is made of elastic fabric, and its relative dielectric constant ε is obtained by testing at 10 GHz. r =2.9, and the dielectric loss tangent is tanδ=0.02.

[0039] The specific size parameters are: P = 16 mm, L = 8 mm, r = 1.35 mm, w = 0.7 mm, and the thickness of the dielectric layer along the direction of the electromagnetic wave magnetic field h = 0.42 mm.

[0040] CST electromagnetic simulation is performed on this implementation, and the S 21 Parameters such as Figure 3 As shown in the figure, as the incident angle of the electromagnetic wave increases, at the frequency of 7.2GHz, the transmission coefficient S 21 The value of remains unchanged and is always close to 0dB, which means that the angle-insensitive characteristic of the frequency selective surface is achieved.

[0041] The present invention was tested by physical processing and the frequency selective surface structure was prepared. The bandpass filtering characteristics of the present invention were tested. Figure 4 The transmission coefficient S of the frequency selective surface before and after stretching 22% is shown in Figure 2. 21 It remains almost unchanged in the frequency band of 5.5GHz-8GHz, which means that the tensile stability characteristics of the frequency selective surface are achieved.

[0042] Anything not described in detail in the present invention is well known to those skilled in the art.

[0043] The embodiments of the present invention are described above with reference to the accompanying drawings, but the present invention is not limited to the specific embodiments described above, which are merely illustrative and not restrictive. A person skilled in the art, guided by the present invention, may devise various embodiments without departing from the spirit of the present invention and the scope of protection of the claims, all of which fall within the scope of protection of the present invention.

Claims

1. A low-cost, stretchable, angle-insensitive, flexible frequency selective surface, characterized in that: The frequency selective surface is an array composed of N×N structural units, and each structural unit comprises a patterned copper cloth layer (1) and an elastic fabric dielectric layer (2) from top to bottom. The patterned copper cloth layer (1) is divided into two parts, an outer ring and an inner ring. The width of the outer ring along the electric field direction and the magnetic field direction of the electromagnetic wave is P, and the width of the inner ring along the electric field direction and the magnetic field direction of the electromagnetic wave is L. The outer ring and the inner ring are both composed of serpentine winding lines. The outer ring and the inner ring are respectively formed by two horizontal and two longitudinal serpentine winding lines intersecting in a tic-tac-toe shape. The serpentine winding line is a structure composed of a plurality of semicircular rings connected together, wherein the radius of the semicircular rings constituting the outer ring structure is r and the line width is w.

2. The low-cost, stretchable, angle-insensitive, flexible frequency selective surface according to claim 1, characterized in that: The elastic fabric medium layer (2) is square, plays a supporting role in the structure, and has good stretchability.

3. The low-cost, stretchable, angle-insensitive, flexible frequency selective surface according to claim 1, characterized in that: The specific parameters of the frequency selective surface are P=16mm, L=8mm, r=1.35mm, w=0.7mm, and the thickness of the dielectric layer along the direction of the electromagnetic wave magnetic field is h=0.42mm.

4. The low-cost, stretchable, angle-insensitive, flexible frequency selective surface according to claim 1, characterized in that: The number of structural units N≥25.

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