Multi-ring Huygens metasurface phase shift unit in shape of bee head

Abstract

The invention provides a bee-head-shaped multi-ring Huygens metasurface phase shift unit, which has ultra wide band, high transmissivity and more than 360-degree phase regulation capability, and structurally comprises a first metal layer, a dielectric substrate layer and a second metal layer from top to bottom in sequence, the first metal layer is located on the upper surface of the dielectric substrate and comprises an inner-layer arc group, a first circle of small-angle arc, a second circle of large-angle arc and an outer-layer arc group, the inner-layer arc group comprises a small arc, a large arc and a rectangular connecting strip, and the outer-layer arc group comprises a third circle of large-angle arc, two outermost circles of small arcs and two corner-cut rectangular connecting strips; the second metal layer is located on the lower surface of the dielectric substrate and is antisymmetric to the first metal layer in structure; according to the bee-head-shaped multi-ring Huygens metasurface phase shift unit, the problems that a Huygens metasurface unit is narrow in bandwidth and poor in transmission performance are solved, and a phase shift unit foundation is provided for a high-gain lens, an orbital angular momentum surface and a holographic imaging surface.

Description

Technical Field

[0001] The invention relates to a "bee head" shaped multi-ring Huygens metasurface phase shift unit, belonging to the field of artificial electromagnetic materials. Background Art

[0002] Electromagnetic metasurfaces are a new type of two-dimensional metamaterial that has gradually attracted attention due to its low profile, lightweight, low cost and wide application in electromagnetic wave front control. These metasurfaces are widely used in lens antenna design, orbital angular momentum surfaces, optical instruments, electromagnetic stealth materials and 5G communications. In the future, they may also be extended to sensors and imaging systems, especially in high-frequency and optical frequency bands.

[0003] In order to achieve wavefront modulation of any electromagnetic wave, the metasurface must be able to change the phase within a range of 360° and maintain a transmission amplitude close to 1. Traditional wavefront control methods mainly rely on phase accumulation in electromagnetic wave propagation, and usually require a multi-layer structure to achieve 360° phase coverage, which limits the miniaturization of applications related to the microwave frequency band. Currently, most metasurface structures focus on the electric resonance effect, but do not give enough consideration to the magnetic resonance between metals. Therefore, when relying solely on electric resonance to achieve 360° phase coverage, multi-layer dielectrics or thicker air gaps are usually required, which increases the profile height of the overall structure.

[0004] By designing a subwavelength-scale unit structure, the Huygens metasurface can flexibly control the amplitude, phase, and polarization of electromagnetic waves without the need for a complex feeding network, making the design relatively simple. However, existing Huygens metasurfaces usually have a narrow bandwidth, mainly because the resonant frequencies of electric resonance and magnetic resonance are close, resulting in limited bandwidth. In response to this challenge, current research is focusing on the use of new materials (such as graphene and superconducting materials) and optimized design to enhance the bandwidth and phase control capabilities of metasurfaces.

[0005] In general, the working bandwidth of most metasurface units is relatively limited, and the cross-section is generally thick. In order to achieve 360° phase coverage, it is often necessary to introduce a multilayer structure or a thicker air gap, which not only complicates the design of the unit structure and increases the difficulty of processing, but also may affect the stability of its performance. Therefore, it is still of great significance to promote the research on the feasibility and efficiency of metasurfaces in practical applications, especially the performance in non-ideal environments will be a key area for future development. Summary of the invention

[0006] The object of the present invention is to provide a "bee head" shaped multi-ring Huygens metasurface phase shift unit.

[0007] To achieve the above-mentioned purpose of the invention, the technical solution of the present invention is as follows:

[0008] A "bee head" shaped multi-ring Huygens metasurface phase shift unit comprises, from top to bottom, a first metal layer (1), a dielectric substrate layer (2), and a second metal layer (3), wherein the first metal layer (1) is located on the upper surface of the dielectric substrate (2), and the second metal layer (3) is located on the lower surface of the dielectric substrate (2); the first metal layer (1) comprises an inner arc group (101), a first circle of small-angle arcs (102), a second circle of large-angle arcs (103), and an outer arc group (104), wherein the inner arc group (101) comprises a small arc (1013), a large arc (1011), and a rectangular connecting strip (1012), and the outer arc group comprises a third circle of large-angle arcs (1043), two outermost circles of small arcs (1041, 1045), and two corner-cut rectangular connecting strips (1042, 1044); and the second metal layer (3) has a structure that is antisymmetric to that of the first metal layer (1).

[0009] As a preferred embodiment, the upper and lower surfaces of the dielectric substrate layer are rectangular, the long side length is p1=5.5 mm, the short side length is p=4.1 mm, and the dielectric substrate is made of Rogers 4003C with a relative dielectric constant of 3.0.

[0010] As a preferred embodiment, all arcs in the inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group are concentric arcs, and the distance between the centers of the concentric circles and the rectangular center point of the rectangular dielectric substrate is ee=0.7 mm.

[0011] As a preferred embodiment, the opening directions of all arcs in the inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group are the short side directions of the rectangular dielectric substrate on the side farthest from all the arcs.

[0012] As a preferred embodiment, the inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group are axially symmetrical about the long axis of the rectangular dielectric substrate.

[0013] As a preferred embodiment, the inner diameter of the small arc of the inner arc group is r1, the inner diameter of the large arc of the inner arc group is r2, the inner diameter of the first circle of small-angle arc is r3, the inner diameter of the second circle of large-angle arc is r4, the inner diameter of the third circle of large-angle arc of the outer arc group is r5, and the inner diameter of the two outermost circles of small arc of the outer arc group is r6. r, r1, r2, r3, r5, and r6 are used to adjust the resonant frequency of magnetic resonance and electric resonance, and their values ​​satisfy r <r1<r2<r3<r5<r6。

[0014] As a preferred method, the center angle of the small arc in the inner arc group is θ1=116°, the center angle of the large arc in the inner arc group is θ2=124°, the center angle of the first circle of small-angle arcs is θ3=120°, the center angle of the second circle of large-angle arcs and the center angle of the third circle of large-angle arcs in the outer arc group are θ4=116°.

[0015] As a preferred embodiment, the width of all arcs in the inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group is wa=0.1 mm.

[0016] As a preferred embodiment, the distance between the two outermost small arcs of the outer arc group and the long side and the wide side of the rectangular dielectric substrate is q=0.1 mm.

[0017] As a preferred embodiment, the lengths of the long and short sides of the upper and lower surfaces of the dielectric substrate layer satisfy p1>p, p≥2*(r5+wa), and p1≥2*(r5+wa+ee).

[0018] Principle of the present invention:

[0019] The passive Huygens metasurface can theoretically realize a passive and lossless metasurface structure. The scattering field of the induced current and magnetic current caused by the metasurface structure can generate an output field by interacting with the incident wave. Its unit structure consists of an electric resonance part and a magnetic resonance part, which regulate the electric field and magnetic field respectively, thereby realizing the free regulation of electromagnetic waves. The electromagnetic characteristics of the Huygens metasurface can be described by the electric surface admittance Yes and the magnetic surface impedance Zms. According to the derivation, the relationship between the electric admittance and the reflection coefficient and the transmission coefficient on the metasurface is:

[0020]

[0021] The relationship between magnetic impedance, reflection coefficient and transmission coefficient is:

[0022]

[0023] where η 0 is the free space wave impedance, the lower right subscript s represents the surface distribution of this function, the lower right subscript e indicates that this term is related to the surface current of the Huygens surface, and the lower right subscript m indicates that this term is related to the surface magnetic current (or circular current) of the Huygens surface.

[0024] According to the relationship between electrical admittance, magnetic impedance, reflection coefficient and transmission coefficient, under ideal conditions, that is, T = 1, R = 0, we can get Yes = Zms, that is, the electrical admittance and magnetic impedance are equal, the Huygens resonance is excited, and the transmission amplitude is close to full transmission. When the transmission coefficient of the Huygens metasurface is 1, the normalized electrical admittance Yes*η 0 and normalized magnetic impedance Zms / η 0The real part is 0, the imaginary part is equal, and with the change of the normalized electrical admittance Yes and the imaginary part of the normalized magnetic impedance Zms, the phase of the transmitted electromagnetic wave can achieve a phase coverage of 0° to 360°.

[0025] In the present invention, the first metal layer and the second metal layer are two sets of antisymmetric electric dipoles. The first metal layer and the second metal layer are antisymmetricly distributed on both sides of the dielectric substrate, so that the surface current can be adjusted to form a current loop, generate orthogonal magnetic current, and thus produce the Huygens effect.

[0026] The present invention simultaneously adopts a variety of means to broaden the bandwidth of the "bee head" shaped multi-ring Huygens metasurface phase shift unit. First, the "bee head" shaped multi-ring Huygens metasurface phase shift unit described in the present invention is a rectangular periodic structure, rather than a square periodic structure, in order to compress the size of the non-main polarization direction, thereby expanding the bandwidth. Secondly, the first metal layer and the second metal layer are composed of multiple arcs to form a strip coupling structure. Arcs of different lengths produce multi-mode resonance, and a total of 8 mode resonance frequencies are generated, achieving the effect of expanding the bandwidth. Thirdly, the two cut-corner rectangular connecting strips in the outer arc group connect the third circle of large-angle arcs and the two outermost small arcs, extending their electrical length and increasing the current area of ​​the metal structure. The current area of ​​the metal structure is further increased by increasing the width of the two cut-corner rectangular connecting strips, so that the frequency center moves to the low frequency, expanding the low-frequency bandwidth, and the phase coverage range will also increase. Finally, the small arcs in the inner arc group play a role in expanding the high-frequency bandwidth. Through the above means, the "bee head" shaped multi-ring Huygens metasurface phase shift unit described in the present invention has an ultra-wideband performance of 24GHz-42GHz, and at the same time has a phase control capability of more than 360°.

[0027] In the present invention, the central angle of the first circle of small-angle arcs is smaller than the central angle of the second circle of large-angle arcs. The transmission performance can be improved by adjusting the central angle of the first circle of small-angle arcs, so that the "bee head" shaped multi-ring Huygens metasurface phase shift unit described in the present invention has ultra-wideband performance and high projection.

[0028] Compared with the prior art, the present invention has the following significant advantages: 1) the inner diameters of all arcs in the inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group of the phase shift unit can be used to adjust the resonant frequencies of magnetic resonance and electric resonance, and a phase control range of more than 360° can be achieved under the condition that the transmission coefficient is greater than -2dB; 2) the phase shift unit utilizes multiple resonant modes of current to expand the bandwidth and enlarge the phase control range; 3) the lens unit maintains high transmittance characteristics within a larger bandwidth.

[0029] The present invention is described in further detail below in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 Schematic diagram of the three-dimensional split structure of the reference metasurface phase shift unit of the present invention;

[0031] Figure 2 is a perspective top view of a reference metasurface phase shift unit of the present invention;

[0032] Figure 3 Two top views and dimension markings of the reference metasurface phase shift unit of the present invention;

[0033] Figure 4 Two bottom views and dimension markings of the reference metasurface phase shift unit of the present invention;

[0034] Figure 5 A front view and dimension marking of a reference metasurface phase shift unit of the present invention;

[0035] Figure 6 The transmission coefficient (S21) and phase-frequency variation curve of the reference metasurface phase shift unit of the present invention;

[0036] Figure 7 The normalized electrical admittance and magnetic impedance of the reference metasurface phase shift unit of the present invention vary with frequency; DETAILED DESCRIPTION

[0037] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0038] This embodiment provides a "bee head" shaped multi-ring Huygens metasurface phase shift unit, which has ultra-wide bandwidth, high transmittance and greater than 360° phase control capability.

[0039] A "bee head" shaped multi-ring Huygens metasurface phase shift unit comprises, from top to bottom, a first metal layer (1), a dielectric substrate layer (2), and a second metal layer (3), wherein the first metal layer (1) is located on the upper surface of the dielectric substrate (2), and the second metal layer (3) is located on the lower surface of the dielectric substrate (2); the first metal layer (1) comprises an inner arc group (101), a first circle of small-angle arcs (102), a second circle of large-angle arcs (103), and an outer arc group (104), wherein the inner arc group (101) comprises a small arc (1013), a large arc (1011), and a rectangular connecting strip (1012), and the outer arc group comprises a third circle of large-angle arcs (1043), two outermost circles of small arcs (1041, 1045), and two corner-cut rectangular connecting strips (1042, 1044); and the second metal layer (3) has a structure that is antisymmetric to that of the first metal layer (1).

[0040] In this embodiment, the thickness of the first metal layer and the second metal layer is t=0.018 mm, and the thickness of the substrate layer is h=1.3 mm.

[0041] In this embodiment, the upper and lower surfaces of the dielectric substrate layer are rectangular, the long side length is p1=5.5 mm, the short side length is p=4.1 mm, and the plate material of the dielectric substrate is Rogers 4003C, with a relative dielectric constant of 3.0.

[0042] In this embodiment, all arcs in the inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group are concentric arcs, and the distance between the centers of the concentric circles and the rectangular center point of the rectangular dielectric substrate is ee=0.7 mm.

[0043] In this embodiment, the inner diameter of the small arc of the inner arc group is r1=0.7mm, the inner diameter of the large arc of the inner arc group is r2=0.9mm, the inner diameter of the first circle of small-angle arcs is r3=1.6mm, the inner diameter of the second circle of large-angle arcs is r4=1.75mm, the inner diameter of the third circle of large-angle arcs of the outer arc group is r5=1.9mm, and the inner diameter of the two outermost small arcs of the outer arc group is r6=2.2mm.

[0044] In this embodiment, the central angle of the small arc in the inner arc group is θ1=116°, the central angle of the large arc in the inner arc group is θ2=124°, the central angle of the first circle of small-angle arcs is θ3=120°, the central angle of the second circle of large-angle arcs and the central angle of the third circle of large-angle arcs in the outer arc group are θ4=116°.

[0045] In this embodiment, the width of all arcs in the inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group is wa=0.1 mm.

[0046] In this embodiment, the length and width of the rectangular connecting strips of the inner arc group are wa=0.1 mm.

[0047] In this embodiment, the length of the two corner-cut rectangular connecting strips of the outer arc group is wb=0.3 mm, and the width is wm=0.2 mm.

[0048] In this embodiment, the distance between the two outermost small arcs of the outer arc group and the long side and the wide side of the rectangular dielectric substrate is q=0.1 mm.

[0049] Figure 1 Schematic diagram of the three-dimensional split structure of the reference metasurface phase shift unit of the present invention;

[0050] Figure 2 is a perspective top view of a reference metasurface phase shift unit of the present invention;

[0051] Figure 3 , 4 5 are a top view, a bottom view, and a front view of the reference metasurface phase shift unit of the present invention, comprising a first metal layer 1, a dielectric substrate layer 2, and a second metal layer 3;

[0052] Figure 6 The transmission coefficient and phase distribution of the reference metasurface phase shift unit of the present invention are shown in FIG. 1 . The metasurface phase shift unit can satisfy a phase control of more than 360° while still maintaining a good transmission coefficient and a wide transmission bandwidth.

[0053] Figure 7 The normalized electrical admittance and magnetic impedance of the reference metasurface phase shift unit of the present invention are equal near the eight resonance points, forming Huygens resonance. It should be noted that there are two Huygens resonance points in the five circles from left to right.

[0054] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A "bee head" shaped multi-ring Huygens metasurface phase shift unit comprises, from top to bottom, a first metal layer (1), a dielectric substrate layer (2), and a second metal layer (3), wherein the first metal layer (1) is located on the upper surface of the dielectric substrate (2), and the second metal layer (3) is located on the lower surface of the dielectric substrate (2); The first metal layer (1) comprises an inner arc group (101), a first circle of small-angle arcs (102), a second circle of large-angle arcs (103), and an outer arc group (104), wherein the inner arc group (101) comprises a small arc (1013), a large arc (1011), and a rectangular connecting strip (1012), and the outer arc group comprises a third circle of large-angle arcs (1043), two outermost circle small arcs (1041, 1045), and two corner-cut rectangular connecting strips (1042, 1044); The structure of the second metal layer (3) is antisymmetric to that of the first metal layer (1).

2. The "bee head" shaped multi-ring Huygens metasurface phase shift unit according to claim 1, characterized in that: The thickness of the first metal layer and the second metal layer is t, and the thickness of the dielectric substrate layer is h.

3. The "bee head" shaped multi-ring Huygens metasurface phase shift unit according to claim 2, characterized in that: The upper and lower surfaces of the dielectric substrate layer are rectangular, with a long side length of p1 and a short side length of p. The dielectric substrate is made of Rogers 4003C with a relative dielectric constant of 3.

0.

4. The "bee head" shaped multi-ring Huygens metasurface phase shift unit according to claim 3, characterized in that: All arcs in the inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group are concentric arcs, and the distance between the centers of the concentric circles and the rectangular center point of the rectangular dielectric substrate is ee.

5. The "bee head" shaped multi-ring Huygens metasurface phase shift unit according to claim 4, characterized in that: The inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group are axially symmetrical about the long axis of the rectangular dielectric substrate, and the opening directions of all arcs are the short side directions of the rectangular dielectric substrate on the side far from all arcs.

6. The "bee head" shaped multi-ring Huygens metasurface phase shift unit according to claim 5, characterized in that: The inner diameter of the small arc of the inner arc group is r1, the inner diameter of the large arc of the inner arc group is r2, the inner diameter of the first circle of small-angle arc is r3, the inner diameter of the second circle of large-angle arc is r4, the inner diameter of the third circle of large-angle arc of the outer arc group is r5, and the inner diameter of the two outermost small arcs of the outer arc group is r6. The values ​​of r, r1, r2, r3, r5, and r6 satisfy r <r1<r2<r3<r5<r6。 7. The "bee head" shaped multi-ring Huygens metasurface phase shift unit according to claim 6, characterized in that: The center angle of the small arc in the inner arc group is θ1, the center angle of the large arc in the inner arc group is θ2, the center angle of the first circle of small-angle arcs is θ3, the center angle of the second circle of large-angle arcs and the center angle of the third circle of large-angle arcs in the outer arc group are θ4.

8. The "bee head" shaped multi-ring Huygens metasurface phase shift unit according to claim 7, characterized in that: The width of all arcs in the inner arc group, the first circle of small-angle arcs, the second circle of large-angle arcs, and the outer arc group is wa. The length and width of the rectangular connecting strips in the inner arc group are wa. The length and width of the two corner-cut rectangular connecting strips in the outer arc group are wb and wm.

9. The "bee head" shaped multi-ring Huygens metasurface phase shift unit according to claim 8, characterized in that: The distance between the two outermost small arcs of the outer arc group and the long side and the wide side of the rectangular dielectric substrate is q.

10. The "bee head" shaped multi-ring Huygens metasurface phase shift unit according to claim 9, characterized in that: The lengths of the long and short sides of the upper and lower surfaces of the dielectric substrate layer satisfy p1>p, p≥2*(r5+wa), p1≥2*(r5+wa+ee).

Images