Microwave band loss type metasurface lens for observing chiral singular point

Abstract

The invention discloses a microwave band loss type metasurface lens for observing chiral singular points, and relates to the field of metasurfaces. The invention aims to solve the problem that a plasmon surface is difficult to form in a microwave band, so that loss is introduced. The microwave band loss type metasurface lens for observing the chiral singular point comprises a plurality of double-resonance-ring units arranged in a rectangular array, and each double-resonance-ring unit comprises a dielectric plate, a split-ring resonator and a line structure; the split resonant ring comprises three coaxially nested rectangular rings and a rectangular sheet located at the center of the innermost rectangular ring, and an opening is formed in one side of the outermost rectangular ring; the line structure is in an I shape; the split resonant ring and the line structure are both fixed on the dielectric plate, and a gap is reserved between the split resonant ring and the line structure. According to the invention, under the condition that a plasmon surface is not formed, through coupling resonance modes in two orthogonal directions and introducing loss, observation of an X-band singular point is realized.

Description

Technical Field

[0001] The invention belongs to the field of super surfaces. Background Art

[0002] Singular points are a unique phenomenon in non-Hermitian systems, which not only show singular properties in mathematics, but also manifest as mode degeneration, phase mutation and other characteristics in physical models. These characteristics make singular points have wide application potential and value in many fields, such as the realization of one-way non-reflection, the exploration of singular rings and complex Dirac points, the innovation of wireless energy transmission technology, and the application of high-order singular points in the field of ultra-sensitive sensing.

[0003] At present, there are many ways to observe singular points, among which optical resonant cavities, optical on-chip systems, and artificial electromagnetic metasurfaces are three typical methods. In optical resonant cavities, researchers have achieved precise observation of singular points by designing specific cavity structures and utilizing the interference and resonance effects of light. On-chip systems have achieved effective manipulation of singular points by integrating micro-nano photonic devices and based on the transmission and coupling mechanisms of optical waveguides. In the field of metasurfaces, researchers have introduced losses by designing plasmon surfaces between metal and dielectric layers, as well as coupling effects between structures, thereby achieving effective control of electromagnetic waves and observation of singular points. For example, a non-Hermitian metasurface in a certain optical band successfully observed singular points through orthogonal coupling of an L-shaped structure and a straight wire structure.

[0004] Most current methods for observing singular points focus on the optical band or the terahertz band. This is because the electromagnetic wave frequencies in these bands are relatively high, making it easier to realize the plasmon effect between metals and dielectrics, thereby introducing losses and manipulating electromagnetic waves. In the microwave band, this singular property has great application potential in the design of devices and systems such as high-Q resonant circuits, microwave sensors, and asymmetric transmission control. However, since the frequency of electromagnetic waves in the microwave band is much lower than the resonant frequency of free electrons, metals become almost ideal conductors, and the electric field is only weakly restricted in the medium, making it difficult for surface plasmons to propagate in it. Therefore, the gain and loss balance design method in the optical band cannot be directly applied in the microwave band, which limits the exploration and application of the excellent electromagnetic properties and phenomena of singular points in the microwave band. Summary of the invention

[0005] The present invention aims to solve the problem that it is difficult to form a plasmon surface in the microwave band, which in turn introduces losses. A microwave band lossy metasurface lens for observing chiral singular points is provided.

[0006] A microwave band lossy metasurface lens for observing chiral singular points, comprising a plurality of double resonant ring units arranged in a rectangular array, each of which comprises: a dielectric plate, an open resonant ring and a line structure;

[0007] The open resonant ring includes three coaxially nested rectangular rings and a rectangular sheet located at the center of the innermost rectangular ring, and an opening is provided on one side of the outermost rectangular ring;

[0008] The line structure is in the shape of "I";

[0009] The open resonant ring and the line structure are both fixed on the dielectric plate, and a gap is left between the two.

[0010] Furthermore, the dielectric plate is made of polytetrafluoroethylene, the open resonant ring and the line structure are made of copper, and the upper surface of the open resonant ring is plated with metal nickel.

[0011] Furthermore, the thickness of the dielectric plate is 1.524 mm and the side length is 12 mm;

[0012] The thickness of the copper material is 0.018mm, and the thickness of the nickel material is 0.006mm.

[0013] Furthermore, the side lengths of the outermost rectangular ring are 4.2 mm and 2.7 mm respectively, the opening is located at the short side of the outermost rectangular ring, and the length of the opening is 0.34 mm;

[0014] The side lengths of the middle layer rectangular rings are 3 mm and 1.5 mm respectively;

[0015] The side lengths of the innermost rectangular ring are 2.4 mm and 0.9 mm;

[0016] The side lengths of the rectangular pieces are 1.8 mm and 0.3 mm respectively.

[0017] Furthermore, the lengths of the main body and two side edges of the wire structure are both 3.7 mm, and the widths of the two side edges are 0.65 mm.

[0018] Furthermore, the microwave band lossy metasurface lens includes 25*25 double resonant ring units arranged in a rectangular array.

[0019] The present invention proposes a microwave band loss-type metasurface lens for observing chiral singular points. The metasurface uses metals with different ohmic loss characteristics to construct a double resonant ring structure in the microwave band (taking the X-band as an example), and can achieve the observation of X-band singular points by coupling the resonant modes in two orthogonal directions and introducing losses without forming a plasmon surface. The applicability of coupled mode theory in the microwave band is proved, and new ideas and methods are provided for the research and application of singular points in the microwave band. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the front view of the double resonant ring unit;

[0021] Figure 2 is a side view of a dual resonant ring unit;

[0022] Figure 3 It is a transmission curve diagram of the open resonant ring and I-shaped cutting line structure in the double resonant ring unit;

[0023] Figure 4 It is the transmission coefficient curve of circular polarization light when s=1.9mm;

[0024] Figure 5 Schematic diagram of the amplitude coefficient of circularly polarized light conversion with frequency and distance, where (a) represents the amplitude conversion coefficient of left-hand circularly polarized light incident to right-hand circularly polarized light output, and (b) represents the amplitude conversion coefficient of right-hand circularly polarized light incident to left-hand circularly polarized light output;

[0025] Figure 6 The phase color scale diagram of circularly polarized light conversion with frequency and distance, where (a) represents the phase of left-handed circularly polarized light incident on right-handed circularly polarized light outgoing, and (b) represents the phase of right-handed circularly polarized light incident on left-handed circularly polarized light outgoing;

[0026] Figure 7 is a diagram of the amplitude coefficient of circularly polarized light conversion in parameter space, where (a) represents the amplitude conversion coefficient of left-hand circularly polarized light incident to right-hand circularly polarized light output, and (b) represents the amplitude conversion coefficient of right-hand circularly polarized light incident to left-hand circularly polarized light output;

[0027] Figure 8 is the phase diagram of circularly polarized light conversion in parameter space, where (a) represents the phase of left-handed circularly polarized light incident on right-handed circularly polarized light outgoing, and (b) represents the phase of right-handed circularly polarized light incident on left-handed circularly polarized light outgoing;

[0028] Fig. 9 are the intrinsic amplitude and phase curves, where (a), (c) and (e) represent the intrinsic amplitudes when s is 0.5 mm, 1.9 mm and 4 mm, respectively, and (b), (d) and (f) represent the intrinsic phases when s is 0.5 mm, 1.9 mm and 4 mm, respectively;

[0029] Fig.10 This is the polarization ellipticity angle curve of the intrinsic polarization state when s=1.9mm. DETAILED DESCRIPTION

[0030] The following will be combined with the accompanying drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0031] Traditional non-Hermitian metasurfaces usually observe singularities in the optical or terahertz bands by introducing losses on the metal dielectric plasmon surface. In contrast, this embodiment is based on the coupled mode theory in the microwave band, and introduces losses by taking advantage of the low ohmic loss and excellent conductivity of copper and the significant ferromagnetic properties of nickel. A non-Hermitian metasurface with a resonant ring-I-shaped cutting line structure is designed to couple the resonances in two orthogonal directions and introduce losses, thereby realizing the observation of singularities.

[0032] In order to accurately control the resonance in two orthogonal directions, this embodiment defines a parameter space composed of two parameters, g and d, which represent the opening size of the nickel resonant ring and the arm length of the I-shaped cutting line copper resonant structure, respectively. By adjusting these two parameters, the resonances in two orthogonal directions can be effectively coupled. The coupling strength is changed by adjusting the distance s between the two resonant structures, controlling the radiation frequency, and optimizing the metasurface structure. After adjustment, a series of unique phenomena caused by singularities can be observed, such as asymmetric transmission of circularly polarized light and topological protection of 2π phase accumulation at singularities. These phenomena enrich the understanding of non-Hermitian physics and provide new ideas for the study and application of singularities in the microwave band.

[0033] A microwave-band lossy metasurface lens for observing chiral singular points described in this embodiment includes: 25*25 double resonant ring units arranged in a rectangular array.

[0034] like Figure 1 and Figure 2 As shown, each dual resonant ring unit includes: a polytetrafluoroethylene dielectric plate, an open resonant ring with nickel plated on the copper surface, and a copper I-shaped cutting line structure.

[0035] Two closed rings and a rectangular sheet made of nickel are coaxially nested inside the open resonant ring. The influence of the closed ring and the rectangular sheet on the resonant frequency can be ignored, but they can effectively increase the resonant loss of the resonant ring. The period of the resonant ring unit c = 12mm, the thickness of the polytetrafluoroethylene dielectric plate h = 1.524mm, the copper thickness h1 = 0.018mm, and the nickel plating thickness of the resonant ring h2 = 0.006mm. The geometric parameters of the nickel resonant ring are L1 = 4.2mm, L2 = 2.7mm, w1 = 0.5mm, g = 0.34mm, L4 = 3mm, L5 = 1.5mm, L6 = 2.4mm, L7 = 0.9mm, L8 = 1.8mm, L9 = 0.3mm, and the gaps between the resonant rings are all 0.1mm. The geometric parameters of the copper I-shaped structure are L3 = 3.7mm, w2 = 0.65mm, and d = 3.7mm. The distance between the two resonant rings is marked as s as an adjustable parameter. These parameters are optimized to ensure the desired coupling strength and loss characteristics within the microwave frequency band.

[0036] This implementation method utilizes the differences in ohmic loss and ferromagnetic properties between copper and nickel metals in the microwave frequency band, introduces loss through nickel-plated open resonant rings and copper I-shaped cutting line structures, and equivalently fits a non-Hermitian system. This design enables the metasurface to effectively control electromagnetic waves without relying on the surface plasmon effect, and observe the singularity phenomenon unique to non-Hermitian systems.

[0037] Based on the above non-Hermitian metasurface model, singular point characteristics such as eigenvalue degeneracy parameters, chiral amplitude and phase response were observed at specific frequencies in the X-band (10GHz). These characteristics are manifested as degeneracy of eigenvalue amplitude and eigenphase near the singular point, asymmetric transmission of circularly polarized light, and topological protection of 2π phase at the singular point. These observations verify the effectiveness and accuracy of the designed non-Hermitian metasurface model in the microwave band.

[0038] In this embodiment, the split resonant ring and the I-shaped cutting line structure both resonate in a frequency range close to 10 GHz, and the resonance amplitude is shown in the following figure. Figure 3 As shown. Nickel metal has significant ferromagnetic properties. Under TE wave incidence conditions, it exhibits resonance characteristics near 10 GHz, and the transmittance is about 0.65 at this time. In contrast, copper metal does not have ferromagnetic properties and has small ohmic losses. When TM waves are incident, it also resonates near 10 GHz, but the transmittance is almost 0 at this time, which means that electromagnetic waves can hardly penetrate. The open resonant ring and the I-shaped structure can respond to electromagnetic wave irradiation in their respective orthogonal directions, respectively, to achieve independent resonance effects.

[0039] Figure 4The transmission coefficient of circularly polarized light is shown when the distance between the two resonant rings is set to 1.9 mm. Based on the characteristic equation theory of planar non-Hermitian matrices, the eigenvalues ​​will degenerate at the singular point. When the incident light is pure left-hand circularly polarized light (LCP), the output light also remains pure LCP, which means that the conversion channel from left circularly polarized light to right circularly polarized light (RCP) is completely suppressed. That is, at a frequency of 10 GHz, the transmission coefficient T from LCP to RCP is +- is 0, while the opposite conversion path T -+ This result leads to asymmetry in the transmission of circularly polarized light, and the singular point is successfully observed.

[0040] Figure 5 It was demonstrated that when the distance between the scanning resonant cavity elements changed from 0 mm to 5 mm, a bias zero point was observed in the asymmetric transmission characteristics of circularly polarized light in the three-dimensional space composed of frequency and distance.

[0041] Figure 6 The color scale diagram of the circularly polarized light transmission phase in the three-dimensional space composed of frequency and distance is shown when the distance between the scanning resonant cavity elements changes from 0 mm to 5 mm. A circle around the non-Hermitian metasurface singular point has the robust feature of 2π phase accumulation. That is, no matter which closed path is chosen to circle the singular point, the 2π phase accumulation effect can be achieved.

[0042] Figure 7 The variation of the transmission coefficient of circularly polarized light at 10 GHz by scanning the parameter space R (composed of L1 and d) is presented. The results show that the cross-polarized light exhibits asymmetric transmission in the parameter space, and the transmission of circularly polarized light has a bias zero point.

[0043] Figure 8 The variation of the phase of circularly polarized light transmission in the parameter space R (composed of L1 and d) at a frequency of 10 GHz is demonstrated, showing topological protection of the 2π phase around the singular point.

[0044] Fig. 9 The physical nature of the singular point is revealed, that is, two or more eigenvalues ​​and their corresponding eigenstates are simultaneously degenerate, and the corresponding eigenstates are also merged into a quantum state. As the distance s changes, the non-Hermitian system changes from an unbroken state to a broken state, and the eigenamplitude and eigenphase degenerate into a point at s = 1.8 mm and 10 GHz, further proving the existence of the singular point.

[0045] Fig.10The polarization ellipticity angle of the eigenpolarization state, that is, the exchange phenomenon of the eigenpolarization state, is shown when s = 1.9 mm. At the singular point, the eigenstate is approximately a circular polarization state. As the distance changes, the path around the singular point will exchange the two eigenstates, from linear polarization to elliptical polarization, then degenerate to circular polarization, then transform to elliptical polarization and finally return to linear polarization.

[0046] In summary, based on coupled mode theory and the characteristic equation of a planar non-Hermitian matrix, the present invention proposes a new type of non-Hermitian metasurface. The unique ohmic loss of copper and nickel metals and the ferromagnetic properties of nickel metal are used to introduce a loss mechanism, so as to realize the design of a non-Hermitian metasurface in the X-band to observe singular points. The present invention breaks the conventional method of traditional non-Hermitian metasurfaces that rely on metal-medium to form a plasmon surface to introduce losses in the optical band or terahertz band, and proves the feasibility of designing a non-Hermitian metasurface in the microwave band to observe singular points.

[0047] Although the present invention is described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the present invention. It should therefore be understood that many modifications may be made to the exemplary embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that the various dependent claims and features described herein may be combined in a manner different from that described in the original claims. It should also be understood that the features described in conjunction with a single embodiment may be used in other described embodiments.

Claims

1. A microwave band lossy metasurface lens for observing chiral singular points, characterized in that: It includes a plurality of double resonant ring units arranged in a rectangular array, each of which includes: a dielectric plate, an open resonant ring and a line structure; The open resonant ring includes three coaxially nested rectangular rings and a rectangular sheet located at the center of the innermost rectangular ring, and an opening is provided on one side of the outermost rectangular ring; The line structure is in the shape of "I"; The open resonant ring and the line structure are both fixed on the dielectric plate, and a gap is left between the two.

2. The microwave band lossy metasurface lens for observing chiral singular points according to claim 1, characterized in that: The dielectric plate is made of polytetrafluoroethylene, the open resonant ring and the line structure are both made of copper, and the upper surface of the open resonant ring is plated with metal nickel.

3. The microwave band lossy metasurface lens for observing chiral singular points according to claim 2, characterized in that: The dielectric plate has a thickness of 1.524 mm and a side length of 12 mm; The thickness of the copper material is 0.018mm, and the thickness of the nickel material is 0.006mm.

4. The microwave band lossy metasurface lens for observing chiral singular points according to claim 3, characterized in that: The side lengths of the outermost rectangular ring are 4.2 mm and 2.7 mm respectively, the opening is located at the short side of the outermost rectangular ring, and the length of the opening is 0.34 mm; The side lengths of the middle layer rectangular rings are 3 mm and 1.5 mm; The side lengths of the innermost rectangular ring are 2.4 mm and 0.9 mm; The side lengths of the rectangular pieces are 1.8 mm and 0.3 mm respectively.

5. The microwave band lossy metasurface lens for observing chiral singular points according to claim 3, characterized in that: The length of the main body and two sides of the wire structure is 3.7 mm, and the width of the two sides is 0.65 mm.

6. A microwave band lossy metasurface lens for observing chiral singular points according to claim 1, 2, 3, 4 or 5, characterized in that: The microwave-band lossy metasurface lens includes 25*25 double-resonance ring units arranged in a rectangular array.

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