Gyromagnetic photonic crystal-based valley directional antenna

Abstract

The invention belongs to the field of antennas, and particularly relates to a valley directional antenna based on gyromagnetic photonic crystals. Three dielectric cylinders and a gyromagnetic YIG column are adopted to construct regular hexagonal primitive cells, an upper magnet layer and a lower magnet layer are assisted to provide a magnetic field, the primitive cells are divided into an upper array and a lower array, the angles theta of the upper array and the lower array are opposite, and then the upper array and the lower array are adaptively and tightly arranged to form the whole array antenna. The excitation source is placed in the center of the functional layer. The valley directional antenna provided by the invention can be adjusted through parameters such as a magnetic field, an antenna structure, frequency and the like, so that directional regulation and control of the antenna are realized, and the valley directional antenna has a multi-degree-of-freedom adjustment characteristic; the antenna device can continue to work under the condition that the antenna device has defects, and the robustness is high; the method can be used for directional detection and interference resistance; no reflection signal exists, and due to the existence of topology protection, waves in the waveguide can only be transmitted in a one-way mode; polarization and modes are flexibly selected, so that polarization signals are separated; the method is wide in application and can be used for directional detection, anti-interference, near-far field detection and the like.

Description

Technical Field

[0001] The invention belongs to the field of antennas and relates to a directional antenna, in particular to a valley directional antenna based on gyromagnetic photonic crystals. Background Art

[0002] With the rapid development of the information age, topological photonics has become an emerging research direction due to the limitations of transmission speed, capacity and loss. A very important material in topological photonics is gyromagnetic photonic crystal. The main material used in gyromagnetic photonic crystal is gyromagnetic ferrite material, which has the property of non-reciprocal, that is, under an external magnetic field, the non-diagonal quantities of its magnetic permeability tensor have opposite signs, resulting in the property that electromagnetic waves can only pass in one direction. By forming an array of non-reciprocal photonic crystals, edge states that are unidirectional and immune to defects can be formed at their edges.

[0003] Typically, in topological photonics, the Valley Hall effect, that is, the separation of valley states and the formation of topologically protected valley polarization states, often requires breaking the spatial inversion symmetry in the photonic crystal structure. For example, by introducing different refractive indices in the lattice or changing the geometry, an energy gap may appear in the energy band structure originally at the K point and the K' point, thereby forming valley polarization. By regulating the refractive index of two different sub-lattices (usually by regulating the dielectric constant and magnetic permeability), the refractive index of the sub-lattices is different, and the Valley Hall effect can be formed by breaking the spatial inversion symmetry. When a magnetic field is applied to the antenna to break the time reversal symmetry, the corresponding valley polarization will also occur.

[0004] The design methods of traditional directional antennas revolve around antenna structure, beamforming, gain optimization, feeding system and other aspects. For example, reflector antennas and horn antennas usually rely on specific shapes, materials and structures to obtain directivity and gain. Once defects occur in the antenna itself (material and / or structure), it will not work properly, that is, the anti-defect capability is poor; at the same time, reflected signals are easy to generate, and traditional directional antennas need to perform impedance matching to prevent the generation of reflected signals. Valley directional antennas are a new type of antenna designed using the principles of topological photonics, relying on the topological properties of materials (such as topological edge states or surface states) to achieve directional radiation. Compared with traditional directional antennas, valley directional antennas are designed to be more robust and immune to defects and environmental disturbances, and can also achieve new beam control and directional radiation characteristics. Summary of the invention

[0005] In order to solve the problems existing in the above-mentioned traditional directional antennas, the present invention provides a valley directional antenna based on gyromagnetic photonic crystals. Due to its topological protection property under specific conditions, it has some advantages over traditional antennas: strong robustness and can work even when the device has defects; no reflected signal, because of the existence of topological protection, the waves in the waveguide can only be transmitted in one direction; flexible selection of polarization and mode, left-handed and right-handed circularly polarized signals can correspond to the two valley states of K and K' respectively, thereby realizing the separation of polarization signals; wide application, anti-interference and near-field and far-field detection, etc.; many degrees of freedom in regulation, for example, magnetic field, shape, frequency, etc. can all be used to regulate directionality.

[0006] In order to achieve the above object, the specific technical solution of the present invention is as follows:

[0007] A valley directional antenna based on gyromagnetic photonic crystal has a three-layer stacked structure, which includes an upper magnetic layer, a functional layer and a lower magnetic layer from top to bottom.

[0008] The upper and lower magnet layers are both metal plates embedded with magnet columns, and are arranged one by one on the upper and lower magnet layers of the functional layer in a way that the center of a magnet column in the thickness direction coincides with the center of a unit cell gyromagnetic YIG column. One gyromagnetic YIG column corresponds to two magnet columns in the upper and lower parts. The magnetic poles of the magnet columns embedded in the same magnet layer have the same direction. The magnet columns are fixed in the metal plates and do not contact the gyromagnetic YIG columns, thereby providing a magnetic field through the upper and lower magnet layers, and the magnetic field size is 0.35T<B<0.5T. The metal plates are perfect electrical conductor layers on the upper and lower parts of the functional layer, used to form a waveguide cavity.

[0009] The functional layer is composed of periodically arranged primitive cells; the planar shape of the primitive cell is a regular hexagon, in which a gyromagnetic YIG column and three dielectric columns that do not touch each other are arranged, and the interlayer structure of the primitive cell is that a regular hexagonal metal layer is adaptively aligned above and below the gyromagnetic YIG column and the three dielectric columns, forming a gap structure in which the upper and lower metal layers clamp the gyromagnetic YIG column and the three dielectric columns.

[0010] The lattice constant of the primitive cell is a>0, and the antenna operating frequency changes with the change of a; a diagonal line of the regular hexagon of the primitive cell is taken as the longitudinal Y axis, and the midline of the opposite side perpendicular to the diagonal line is taken as the transverse X axis: the initial positions of the three dielectric columns are respectively the positive left, the upper right, and the lower right, and the three dielectric columns form an equilateral triangle, the center point of the equilateral triangle is the origin of the coordinates, and is also the center point of the gyromagnetic YIG column; θ is the angle of the three dielectric columns rotating counterclockwise around the center. The gyromagnetic YIG column and the three dielectric columns are all cylinders, the radius r of the gyromagnetic YIG column satisfies 0<r<0.5a, the radius r' of the dielectric column satisfies 0<r'<r, and the center distance between the gyromagnetic YIG column and the dielectric column is d, which satisfies r+r'<d<0.5a-0.5r'.

[0011] Arrangement period of primitive cells: In the rated area, primitive cells are adaptively spliced ​​and arranged into arrays in the X-axis and Y-axis directions based on the sides of the regular hexagon. The number of primitive cells in the X-axis and Y-axis directions is required to be greater than 5. The array after primitive cell arrangement is divided into upper and lower parts. The number of primitive cells in the upper and lower parts is equal, and the angle θ of the rotation of the dielectric column is opposite (that is, the rotation direction of the upper and lower parts is opposite), satisfying 10°≤θ≤30°, and the number of primitive cells in each part of the array along the X-axis is the same as the number of primitive cells along the Y-axis. Then the upper and lower parts of the array are adaptively spliced ​​with a 120° sawtooth boundary. The 120° sawtooth boundary of the upper and lower parts forms a channel for wave propagation for directional emission. The excitation source is placed at the center of the entire array of the functional layer. The upper and lower boundaries of the entire array are 120° sawtooth perfect electric conductors or open boundaries, and the left and right boundaries of the entire array are zigzag open boundaries.

[0012] Furthermore, the upper and lower magnet layers are sandwich structures with a light material in the middle.

[0013] Furthermore, the upper metal layer of the intermediate functional layer and the metal layer of the upper magnetic layer are integrally formed as a common metal layer, or the lower metal layer of the intermediate functional layer and the metal layer of the lower magnetic layer are integrally formed as a common metal layer.

[0014] Furthermore, simulation software is used to adjust the parameters a, B, r', r, d and θ to form valley polarization to adjust the directivity of the antenna.

[0015] In summary, the present invention uses three dielectric columns and one gyromagnetic YIG column to construct a regular hexagonal primitive cell, and uses the upper and lower magnetic layers to provide a magnetic field. After the primitive cell is divided into two arrays with opposite angles θ, they are adaptively and tightly arranged into an integral array antenna; the excitation source is placed at the center of the functional layer, and its upper and lower boundaries are 120° sawtooth perfect electrical conductors or open boundaries, and the left and right boundaries are zigzag open boundaries. The valley directional antenna of the present invention can be adjusted by parameters such as magnetic field, antenna structure, and frequency to adjust the directionality of the antenna, and has multi-degree-of-freedom adjustment characteristics; it can continue to work when the antenna device has defects, and has high robustness; there is no reflected signal, and due to the existence of topological protection, the waves in the waveguide can only be transmitted in one direction; the polarization and mode are flexibly selected, and the left-handed and right-handed circularly polarized signals can correspond to the two valley states of K and K', respectively, thereby realizing the separation of polarization signals; it is widely used and can be used for directional detection, anti-interference, near-field and far-field detection, etc. It effectively solves the problem of relatively low adjustment degree and insufficient robustness of existing directional antennas. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1Figure 1 is a diagram of the functional layers of a valley directional antenna. Figure (a) is a schematic diagram of a primitive cell, and Figure (b) is a schematic diagram of the functional layers of an antenna array.

[0017] Figure 2 Schematic diagram of the interlayer cross section of the valley directional antenna;

[0018] Figure 3 Radiation from valley directional antennas;

[0019] Figure 4 Far field diagram of valley directional antenna embodiment;

[0020] Figure 5 Valley directional antenna embodiment magnetic field controlled radiation;

[0021] Figure 6 In the valley directional antenna embodiment, the effect of the functional layer size on the directivity is shown in Figures (a) and (b) respectively showing the schematic diagrams of reducing the longitudinal size n and the lateral size m of the functional layer, and Figures (c) and (d) showing the electric field norm distribution corresponding to the continuous reduction in the size of the functional layer. DETAILED DESCRIPTION

[0022] The technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0023] A valley directional antenna based on gyromagnetic photonic crystal, such as Figure 1 As shown, the antenna array constructed by primitive cells into two upper and lower arrays finally forms a valley directional antenna.

[0024] In this example, the original cell ( Figure 1 a) Lattice constant a = 15 mm, radius of gyromagnetic YIG column r = 0.14a, radius of dielectric column r' = 0.8r, distance between YIG and dielectric column d = 0.35a, initial positions of three dielectric columns are positive left, upper right and lower right, three dielectric columns form an equilateral triangle. θ is the angle of three dielectric columns rotating counterclockwise around the center; relative dielectric constants of YIG and dielectric column are ε1 = 14.3, ε2 = 4.4, relative magnetic permeability of YIG is:

[0025]

[0026] where μ r =1+(ω0+iαω)ω m / ((ω0+iαω) 2 -ω 2 ), κ=ωω m / ((ω0+iαω) 2 -ω 2 ),ω m =γM s ,ω o =γH o , γ=1.76×1011 s -1 T -1 , α=0.0088. r represents the diagonal component of the relative permeability tensor, κ represents the off-diagonal component of the relative permeability tensor, ω m represents the saturated Larmor precession frequency, ω0 represents the Larmor precession frequency, H0 is the external magnetic field, γ is the gyro magnetic ratio, α is the damping coefficient, ω is the operating frequency, and M s is the saturation magnetization.

[0027] The valley directional antenna based on gyromagnetic photonic crystal designed in this embodiment has a top view of the arrangement of the functional layer primitive cells as shown in the following figure. Figure 1 As shown in the figure (b), the array is divided into two parts, the upper part has θ = 30°, the lower part has θ = -30°, and each part is a 25*8 array. Then the two parts are spliced ​​together with a 120° zigzag boundary to form a 25*16 array. The boundary between the upper and lower parts forms a channel for wave propagation, and the left and right boundaries are zigzag open boundaries. It is used for directional transmission.

[0028] Figure 2 The interlayer structure diagram of the valley directional antenna of this embodiment is divided into three layers, the upper and lower magnetic layers and the middle functional layer. Figure 2 After the structure is built, the boards are bonded and fixed with copper tape; the excitation source is welded on Figure 3 (b) The position of the orange five-pointed star, energy is supplied through the coaxial line of the vector network analyzer (model ZNB20). ; The 120° zigzag boundary refers to the 120° bending line boundary formed by the boundary of the regular hexagon when the primitive cells are arranged in sequence on a straight line in a single direction of the X-axis or Y-axis.

[0029] The upper and lower magnet layers are used to apply a magnetic field B = 0.4T to the gyromagnetic YIG columns in the functional layer. The magnet layer consists of two upper and lower copper plates with a height of 1mm and an acrylic plate with a thickness of 3mm in the middle for fixing the magnet. The upper and lower copper plates are used to prevent the magnets from jumping out during installation. The height of the gyromagnetic YIG columns and dielectric columns in the functional layer is 7mm, and the height of the copper plate for fixing the columns is 0.5mm. The magnet is neodymium iron boron, with a height of 3mm and a radius of 4mm.

[0030] Among them, this embodiment uses a common metal layer for the upper metal layer of the middle functional layer, and uses an acrylic plate layer structure with a lightweight intermediate sandwich design for the upper and lower magnet layers. Without affecting the overall antenna performance: on the one hand, it improves the convenience of the assembly process, and on the other hand, it improves the overall lightweight of the antenna.

[0031] The working principle of the valley directional antenna of the present invention is as follows:

[0032] Figure 3 (a) and (b) are two different functional layers, where (a) has an upper part with θ = -30° and a lower part with θ = 30°, which is called a type A functional layer, and (b) has an upper part with θ = 30° and a lower part with θ = -30°, which is called a type B functional layer. (c) and (d) correspond to the field distribution of type AB functional layers, respectively, and the orange five-pointed star is the position of the line source. When the frequency is 9.9 GHz to 10.5 GHz and the magnetic field is B = 0.4 T, it can be seen that after the line source excites energy, the energy propagates along the boundary in the form of edge states to the boundary of the functional layer, and is emitted into the free space in a highly directional direction.

[0033] Figure 4 The far-field distribution of the valley directional antenna is based on the B-type functional layer: (a) (b) is the far-field distribution of 9.8 GHz corresponding to the right-handed circle and the far-field distribution of the corresponding spectrum from 9.5 GHz to 10.5 GHz; (c) (d) is the far-field distribution of 9.8 GHz corresponding to the left-handed circle and the far-field distribution of the corresponding spectrum from 9.5 GHz to 10.5 GHz. According to the solution of B = 0.4T, f = 10 GHz, the equivalent wavelength is 30 mm. In order to calculate the far field, we select a semicircle with a radius of 1000 mm, which is much larger than 10 times the equivalent wavelength. We place this semicircle on the exit surface and place 181 points at intervals of 1° to detect the energy corresponding to different positions. Finally, the normalized directional diagram is drawn. As shown in Figure (a), for a right-handed source, the exit wave at 9.8 GHz has a small angle exit, and the maximum peak corresponds to 135°. Figure (b) shows that as the frequency changes, in the corresponding frequency band, the exit wave has a small angle range with a bandwidth of 1 GHz. Figures (c) and (d) show the far-field conditions corresponding to a left-handed source, where the maximum peak corresponds to 42° and the bandwidth is 1 GHz.

[0034] Since the present invention adopts the valley Hall effect based on gyromagnetic photonic crystal, the following beneficial effects are obtained:

[0035] 1. There are many degrees of freedom for regulation, such as magnetic field, shape, frequency, etc., which can regulate the directionality;

[0036] Figure 5 To control the magnetic field in the upper and lower regions, (a) shows the upper and lower regions with the same magnetic field of 0.4 T, and (b) shows the upper and lower regions with opposite magnetic fields of 0.4 T, which can achieve the regulation from double waves to single wave. Figure 3 To change the shape of the functional layer, different emission directions are achieved; Figure 4 (b) The directional antenna outgoing wave can be regulated to change the frequency.

[0037] 2. Flexible selection of polarization and mode. Left-handed and right-handed circularly polarized signals can correspond to the two valley states of K and K', respectively, thus achieving separation of polarization signals;

[0038] Figure 4 By controlling the polarization of the source, unidirectional wave emission and direction control of the emitted wave can be achieved.

[0039] 3. Strong robustness, can work even when the device has defects;

[0040] When the number of lateral primitive cells remains unchanged and the number of longitudinal primitive cells is 4, 8, 12, and 16 respectively, the schematic diagram of the functional layer is as follows: Figure 6 (a) As shown in the figure, the corresponding far-field electric field mode distribution is based on the solution of the equivalent wavelength of 30mm at B=0.4T, f=10GHz. In order to calculate the far field, we select a semicircle with a radius of 1000mm, which is much larger than 10 times the equivalent wavelength. We place this semicircle on the exit surface and place 181 points at intervals of 1° to detect the energy corresponding to different positions. Finally, draw the electric field mode distribution diagram, and you can see that when n=4, the electric field mode distribution is greatly attenuated in the direction around 135°. When n=16, 12, and 8, the electric field mode distribution has a good directionality. Therefore, it has a certain robustness to the longitudinal reduction of the functional layer; similarly, Figure 6 (c) When the number of lateral unit cells is reduced and the number of longitudinal unit cells remains unchanged, the corresponding electric field norm distribution remains almost unchanged. Therefore, it is also robust to the reduction of the number of lateral unit cells in the functional layer.

[0041] 4. Widely used, anti-interference and near and far field detection, etc.

[0042] Due to the selectivity of the valley, only one electromagnetic wave corresponding to the valley direction can be incident from the free space into the functional layer and become an edge state, so that it can be detected by the receiving probe. However, since the emission sources at other positions do not satisfy the momentum matching relationship, their energy is strongly reflected at the interface between the free space and the functional layer, so that the energy cannot be detected at the receiving probe. Therefore, the high directivity can be used to determine the position of the target, especially in long-distance detection. The anti-interference characteristics can play a role in many aspects. In complex environments, it can shield communication signal interference from other directions and maintain communication stability. At the same time, it can also protect the device from being disturbed and damaged by interference signals.

[0043] In order to perform near-field and far-field detection, we selected a frequency of 10 GHz, which corresponds to a wavelength of 30 mm, and selected a far-field distance greater than 10 times the wavelength and a near-field distance less than one time the wavelength for simulation. When the source is placed at a direction of 15° (counterclockwise from the horizontal direction), the receiving probe can receive energy regardless of near-field or far-field detection, but when the object being detected is placed in a direction other than 15°, the receiving probe cannot receive any energy.

[0044] 5. No reflected signal. Due to the existence of topological protection, the waves in the waveguide can only be transmitted in one direction.

[0045] It can be seen from the above embodiments that the valley directional antenna based on gyromagnetic photonic crystal provided by the present invention is proven to be feasible, and has the characteristics of multi-degree-of-freedom adjustment, high robustness, polarization-controlled radiation, wide application, no reflected waves, overcoming impedance matching, and achieving highly directional emission at small angles.

Claims

1. A valley directional antenna based on gyromagnetic photonic crystal, characterized in that: It is a three-layer laminated structure, which includes an upper magnetic layer, a functional layer and a lower magnetic layer from top to bottom; The upper and lower magnet layers are both metal plates embedded with magnet columns, and are arranged one by one on the upper and lower magnet layers of the functional layer in a manner that the center of a magnet column in the thickness direction coincides with the center of a unit cell gyromagnetic YIG column, and one gyromagnetic YIG column corresponds to a total of two magnet columns on the upper and lower sides; the magnet columns embedded in the same magnet layer have the same magnetic pole direction, and the magnet columns are fixed in the metal plates and do not contact the gyromagnetic YIG columns, thereby providing a magnetic field through the upper and lower magnet layers, and the magnetic field size is 0.35T<B<0.5T; the metal plates are perfect electrical conductor layers on the upper and lower sides of the functional layer, and are used to form a waveguide cavity; The functional layer is composed of periodically arranged primitive cells; the plane shape of the primitive cell is a regular hexagon, in which a gyromagnetic YIG column and three dielectric columns that do not touch each other are arranged, and the interlayer structure of the primitive cell is that a regular hexagonal metal layer is arranged above and below the gyromagnetic YIG column and the three dielectric columns in an adaptive alignment, forming a gap structure in which the upper and lower metal layers clamp the gyromagnetic YIG column and the three dielectric columns; The lattice constant of the primitive cell is a>0, and the antenna operating frequency changes with the change of a; a diagonal line of the regular hexagon of the primitive cell is taken as the longitudinal Y axis, and the midline of the opposite side perpendicular to the diagonal line is taken as the transverse X axis: the initial positions of the three dielectric columns are respectively the positive left, the upper right and the lower right, and the three dielectric columns form an equilateral triangle, the center point of the equilateral triangle is the origin of the coordinates, and is also the center point of the gyromagnetic YIG column; θ is the angle of the three dielectric columns rotating counterclockwise around the center; the gyromagnetic YIG column and the three dielectric columns are all cylinders, the radius r of the gyromagnetic YIG column satisfies 0<r<0.5a, the radius r' of the dielectric column satisfies 0<r'<r, the center distance between the gyromagnetic YIG column and the dielectric column is d, and satisfies r+r'<d<0.5a-0.5r'; Arrangement period of primitive cells: in the rated area, primitive cells are adaptively spliced ​​and arranged into an array in sequence in the X-axis and Y-axis directions based on the sides of the regular hexagon, and the number of primitive cells in the X-axis and Y-axis directions is required to be greater than 5; the array after the primitive cells are arranged is divided into upper and lower parts, the number of primitive cells in the upper and lower parts is equal, and the angle θ of the rotation of the dielectric column is an opposite number, 10°≤θ≤30°, the number of primitive cells in each part of the array along the X-axis is the same as the number of primitive cells along the Y-axis, and then the upper and lower parts of the array are adaptively contacted and spliced ​​with a 120° zigzag boundary, and the 120° zigzag boundary where the upper and lower parts are spliced ​​forms a channel for wave propagation for directional emission; the excitation source is placed at the center of the entire array of the functional layer, the upper and lower boundaries of the entire array are 120° zigzag perfect electric conductors or open boundaries, and the left and right boundaries of the entire array are zigzag open boundaries.

2. The valley directional antenna based on gyromagnetic photonic crystal according to claim 1, characterized in that: The upper and lower magnet layers are sandwich structures with light materials in the middle.

3. The valley directional antenna based on gyromagnetic photonic crystal as claimed in claim 2, characterized in that: The intermediate light material interlayer is an acrylic plate.

4. The valley directional antenna based on gyromagnetic photonic crystal as claimed in claim 1, characterized in that: The upper metal layer of the intermediate functional layer and the metal layer of the upper magnetic layer are integrally formed as a common metal layer, or the lower metal layer of the intermediate functional layer and the metal layer of the lower magnetic layer are integrally formed as a common metal layer.

5. The valley directional antenna based on gyromagnetic photonic crystal as claimed in claim 1, characterized in that: The simulation software is used to adjust the parameters a, B, r', r, d and θ to form valley polarization to adjust the directivity of the antenna.

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