A valley directional antenna based on gyromagnetic photonic crystal

Abstract

The application belongs to the field of antennas, and particularly relates to a valley directional antenna based on a gyromagnetic photonic crystal. The application adopts three dielectric columns and a gyromagnetic YIG column to construct a hexagonal unit cell, and provides a magnetic field through upper and lower magnet layers, so that the unit cell is divided into two arrays with angles theta being opposite numbers, and then the two arrays are adaptively closely arranged into an overall array antenna; an excitation source is arranged at the center of the functional layer. The valley directional antenna can be adjusted through parameters such as a magnetic field, an antenna structure and a frequency, so that the directivity of the antenna is regulated, and the antenna has multiple degrees of freedom adjustment characteristics. In the case that the antenna device has defects, the antenna can continue to work, and has high robustness. The antenna can be used for directional detection and anti-interference. There is no reflected signal, and due to the existence of topological protection, the wave in the waveguide can only be transmitted in one direction. Polarization and mode can be flexibly selected, so that polarization signals can be separated. The antenna has wide application, and can be used for directional detection, anti-interference, near-field detection and far-field detection.

Description

Technical Field

[0001] The present 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 limitations in transmission speed, capacity, and loss. Gyromagnetic photonic crystals are a key material in this field. Gyromagnetic photonic crystals primarily utilize gyromagnetic ferrites, which exhibit nonreciprocal properties. Under an applied magnetic field, the off-diagonal quantities of their magnetic permeability tensor have opposite signs, resulting in a unidirectional transmission of electromagnetic waves. By forming arrays of nonreciprocal photonic crystals, edge states can be formed at their edges that are unidirectional and immune to defects.

[0003] Typically, in topological photonics, to produce the Valley Hall effect, that is, to separate the valley state and form a topologically protected valley polarization state, it is often necessary to break the spatial inversion symmetry in the photonic crystal structure. For example, by introducing different refractive indices or changing the geometry in the lattice, an energy gap can appear in the energy band structure originally at the K point and 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 made different, breaking the spatial inversion symmetry can form the Valley Hall effect. When a magnetic field is applied to the antenna to break the time reversal symmetry, the corresponding valley polarization will also be generated.

[0004] The design methods of traditional directional antennas revolve around aspects such as antenna structure, beamforming, gain optimization, and feeding systems. For example, reflector antennas and horn antennas usually rely on specific shapes, materials, and structures to obtain directivity and gain. Once defects appear 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 easily generated, and traditional directional antennas require 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 have higher robustness and immunity to defects and environmental disturbances in design, and can 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, due to 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.; multiple degrees of freedom of control, for example, magnetic field, shape, frequency, etc. can all be used to control directionality.

[0006] In order to achieve the above purpose, the specific technical solutions of the present invention are 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 magnetic layers are metal plates embedded with magnetic pillars. They are arranged one-to-one above and below the functional layer, with the thickness center of each magnetic pillar aligned with the center of a unit cell gyromagnetic YIG pillar. Each gyromagnetic YIG pillar corresponds to two magnet pillars, one above and one below. The magnetic poles of the magnet pillars embedded in the same magnetic layer are aligned. The magnet pillars are fixed in the metal plates and do not contact the gyromagnetic YIG pillars, thus providing a magnetic field through the upper and lower magnetic layers with a magnitude of 0.35T < B < 0.5T. The metal plates serve as perfect electrical conductors above and below the functional layers, forming a waveguide cavity.

[0009] The functional layer is composed of periodically arranged unit cells; the planar shape of the unit cell is a regular hexagon, and a gyromagnetic YIG column and three dielectric columns that do not touch each other are provided therein. The interlayer structure of the unit 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 unit cell's lattice constant, a, is greater than 0, and the antenna's operating frequency changes as a changes. A diagonal of the unit cell's regular hexagon serves as the longitudinal Y-axis, and the midline of the opposite side perpendicular to it serves as the transverse X-axis. The three dielectric pillars are initially positioned at the extreme left, upper right, and lower right, respectively, forming an equilateral triangle. The center of the triangle serves as the coordinate origin, also the center of the gyromagnetic YIG pillar. θ is the angle of counterclockwise rotation of the three dielectric pillars around the center. The gyromagnetic YIG pillar and the three dielectric pillars are all cylindrical. The radius r of the gyromagnetic YIG pillar satisfies 0 < r < 0.5a, and the radius r' of the dielectric pillar satisfies 0 < r' < r. The center-to-center distance d between the gyromagnetic YIG pillar and the dielectric pillar satisfies r + r' < d < 0.5a - 0.5r'.

[0011] Unit cell arrangement period: Within the rated area, the units are adaptively arranged in the X and Y directions using the sides of a regular hexagon as the basis to form an array. The number of units in both the X and Y directions must be greater than 5. The array is divided into two parts, the upper and lower parts, with equal numbers of units. The angles θ of the dielectric column rotation are opposite (i.e., the rotation directions of the upper and lower parts are opposite), satisfying 10°≤θ≤30°. The number of units along the X and Y axes of each part is the same. The upper and lower parts are then adaptively joined with a 120° zigzag boundary. The 120° zigzag boundary forms a wave propagation channel for directional emission. The excitation source is placed at the center of the entire functional layer array. The upper and lower boundaries of the entire array are 120° zigzag perfect 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 lightweight 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 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 overall 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 control the directionality of the antenna, and has multi-degree-of-freedom adjustment characteristics. It can continue to work even when the antenna device has defects and has high robustness. There is no reflected signal. Due to the existence of topological protection, the waves in the waveguide can only be transmitted in one direction. With 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. It has a wide range of applications and can be used for directional detection, anti-interference, near-field and far-field detection, etc. It effectively solves the problems 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 layer of the valley directional antenna. Figure (a) is a schematic diagram of the primitive cell, and Figure (b) is a schematic diagram of the functional layer of the 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 the 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 functional layer size affects the directivity. Figures (a) and (b) are schematic diagrams of reducing the longitudinal size n and lateral size m of the functional layer, respectively. Figures (c) and (d) are the electric field norm distributions 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 with reference to the accompanying drawings and embodiments.

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

[0024] In this example, the original cell ( Figure 1 (a) The lattice constant a = 15 mm, the radius of the gyromagnetic YIG column is r = 0.14 Å, the radius of the dielectric column is r' = 0.8 Å, the distance between the YIG and dielectric columns is d = 0.35 Å, and the three dielectric columns are initially positioned at the left, upper right, and lower right sides, forming an equilateral triangle. θ is the angle of counterclockwise rotation of the three dielectric columns around the center. The relative dielectric constants of the YIG and dielectric columns are ε1 = 14.3 and ε2 = 4.4, respectively. The relative permeability of the YIG is:

[0025]

[0026] where μ r =1+(ω0+iαω)ω m / ((ω0+iαω) 2 -ω 2 ), k=ωω m / ((ω0+iαω) 2 -ω 2 ),ω m =γM s ,ω0=γH0,γ=1.76×10 11 s -1T -1 ,α=0.0088.μ r represents the diagonal components of the relative permeability tensor, k represents the off-diagonal components 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, M s is the saturation magnetization.

[0027] The valley directional antenna based on gyromagnetic photonic crystal designed in this embodiment has the following top view of the arrangement of the functional layer unit cells: Figure 1 As shown in Figure (b), the array is divided into two parts, with the upper part having θ = 30° and the lower part having θ = -30°. Each part is a 25*8 array. The two parts are then joined 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, while the left and right boundaries are zigzag open boundaries. This is used for directional transmission.

[0028] Figure 2 The interlayer structure diagram of the valley directional antenna in 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 to the Figure 3 (b) The location of the orange five-pointed star, where energy is supplied via the coaxial line of a vector network analyzer (model ZNB20). A 120° zigzag boundary refers to the 120° bend formed by the regular hexagonal boundary when cells are arranged sequentially along a straight line in a single direction along the X 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 1mm-high copper plates and a 3mm-thick acrylic plate in the middle to fix the magnets. 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 fixing the columns is 0.5mm. The magnets are 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 intermediate functional layer, and uses an acrylic plate layer structure with a lightweight intermediate sandwich design for the upper and lower magnetic 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)(b) are two different functional layers, respectively, where (a) is the upper part of which is theta = -30 degrees, and the lower part is theta = 30 degrees, which is called A-type functional layer, and (b) is the upper part of which is theta = 30 degrees, and the lower part is theta = -30 degrees, which is called B-type functional layer.(c)(d) are the field distribution diagrams corresponding to the AB-type functional layer, and the orange pentagram is the position of the linear source.When the frequency is 9.9GHz to 10.5GHz, and the magnetic field B = 0.4T, it can be seen that after the linear source excites energy, the energy propagates along the edge state 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) are the far-field distribution of the right-handed circular polarization at 9.8GHz and the corresponding frequency spectrum from 9.5GHz to 10.5GHz; (c)(d) are the far-field distribution of the left-handed circular polarization at 9.8GHz and the corresponding frequency spectrum from 9.5GHz to 10.5GHzAccording to the equivalent wavelength of B = 0.4T, f = 10GHz, which is 30mm, in order to calculate the far-field, a semicircle with a radius of 1000mm, which is much larger than 10 times the equivalent wavelength, is selected, which is placed on the exit surface, and 181 points are placed every 1°, so as to detect the energy corresponding to different positions. Finally, the normalized directional diagram is drawn, as shown in (a), for the right-handed source, the exit wave has a small angle at 9.8GHz, and the maximum peak corresponds to 135°. (b) shows that as the frequency changes, the exit wave has a small angle range in the corresponding frequency band, and the bandwidth is 1GHz. (c)(d) are the far-field distribution of the left-handed source, and the maximum peak corresponds to 42°, and the bandwidth is 1GHz.

[0034] Since the valley Hall effect based on the spin-magnetic photonic crystal is adopted in the application, the following beneficial effects are obtained:

[0035] 1. The freedom of regulation is high, for example, the magnetic field, shape, frequency, etc. can be regulated to control the directivity;

[0036] Figure 5 In order to control the magnetic field of the upper and lower regions, (a) is the same direction magnetic field 0.4T in the upper and lower regions, and (b) is the opposite magnetic field 0.4T in the upper and lower regions, which can realize the regulation of double waves to single wave; Figure 3 In order to change the shape of the functional layer, different exit directions are realized; Figure 4 (b) can realize the regulation of the directional antenna exit wave by changing the frequency.

[0037] 2. Flexible selection of polarization and mode, the left-handed and right-handed circularly polarized signals can correspond to two valley states K and K' respectively, so as to realize the separation of the polarized 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 and 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, the electric field mode distribution diagram is drawn. It can be seen that when n=4, the electric field mode distribution is greatly attenuated in the direction of about 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. Wide range of applications, anti-interference and near-field and far-field detection, etc.

[0042] Due to the selectivity of the valley, only electromagnetic waves in the direction corresponding to the valley can be incident from free space into the functional layer and become edge states, thereby being detected by the receiving probe. However, since the emission sources at other locations do not satisfy the momentum matching relationship, their energy is strongly reflected at the interface between free space and the functional layer, making it impossible to detect the energy at the receiving probe. Therefore, this high directionality can be used to determine the position of the target, which is particularly advantageous in long-distance detection. The anti-interference feature 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] For near-field and far-field detection, we selected a frequency of 10 GHz, corresponding to a wavelength of 30 mm. We simulated distances greater than 10 times the wavelength for the far field and less than one wavelength for the near field. When the source was positioned at a 15° angle (counterclockwise from horizontal), the receiving probe received energy for both near-field and far-field detection. However, when the object was not positioned at this angle, the receiving probe received no 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 has been 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 by: 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 magnetic layers are both metal plates embedded with magnetic columns. They are arranged one-to-one on the upper and lower magnetic layers of the functional layer, with the center of each magnetic column in the thickness direction aligning with the center of a unit cell gyromagnetic YIG column. One gyromagnetic YIG column corresponds to two magnetic columns, one on the upper and one on the lower. The magnetic poles of the magnetic columns embedded in the same magnetic layer have the same direction. The magnetic 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 magnetic layers. The magnetic field magnitude is 0.35T < B < 0.5T. The metal plates are perfect electrical conductor layers on the upper and lower functional layers, used to form a waveguide cavity. The functional layer is composed of a periodic arrangement of unit cells. The unit cell has a regular hexagonal planar shape, and is provided with a gyromagnetic YIG column and three dielectric columns that do not touch each other. The interlayer structure of the unit cell is that a regular hexagonal metal layer is provided above and below the gyromagnetic YIG column and the three dielectric columns, and is adaptively aligned to form a gap structure in which the upper and lower metal layers sandwich the gyromagnetic YIG column and the three dielectric columns. The lattice constant of the unit cell is a>0, and the antenna operating frequency changes as a changes. A diagonal line of the regular hexagon of the unit cell is used as the longitudinal Y-axis, and the midline of the opposite side perpendicular to the diagonal line is used as the transverse X-axis. The initial positions of the three dielectric columns are respectively at the positive left, upper right, and lower right, and the three dielectric columns form an equilateral triangle. The center point of the equilateral triangle is the coordinate origin, which 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 distance d between the center of the circle of the gyromagnetic YIG column and the dielectric column satisfies r+r'<d<0.5a-0.5r'. Unit cell arrangement period: Within the rated area, the units are adaptively arranged in the X and Y directions using the sides of a regular hexagon as the basis to form an array. The number of units in both the X and Y directions must be greater than 5. The array is divided into two parts, the upper and lower parts, with an equal number of units. The angle θ of the dielectric column rotation is opposite, 10°≤θ≤30°. The number of units along the X and Y axes in each part of the array is the same. The upper and lower parts of the array are then adaptively joined with a 120° zigzag boundary. The 120° zigzag boundary between the upper and lower parts forms a wave propagation channel for directional emission. The excitation source is placed at the center of the entire functional layer array. The upper and lower boundaries of the entire array are 120° zigzag perfect electrical 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 a light material in the middle.

3. The valley-directional antenna based on gyromagnetic photonic crystal according to claim 2, characterized in that: The intermediate light material layer is an acrylic board.

4. The valley-directional antenna based on gyromagnetic photonic crystal according to claim 1, characterized in that: The upper metal layer of the 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 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 according to claim 1, characterized in that: The parameters a, B, r', r, d and θ are adjusted using simulation software to form valley polarization to adjust the directivity of the antenna.

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