CN108987935A - A kind of vortex wave Meta Materials reflective array for polarizing controllable and its design method - Google Patents

Abstract

The invention discloses a kind of vortex wave Meta Materials reflective array for polarizing controllable and its design methods, are made of the anisotropic cellular construction of electromagnetism, and cellular construction includes upper layer structured metal layer, middle layer dielectric layer and lower metal backsheet layer.Upper layer structured metal layer uses orthogonal I-shape construction, adjust the horizontal brachium of I-shape construction, can effective controlled level polarized wave reflected phase, without being had an impact to vertical polarization wave phase, regulate and control the vertical brachium of I-shape construction, the reflected phase that vertically polarized wave can effectively be controlled, will not have an impact horizontal polarized wave.The Meta Materials reflective array can not only effectively generate vortex wave beam, while realize to the polarized regulation of vortex wave beam, can reduce the cost of traditional vortex wave device, promote the development of multifunction vortex wave device.

Description

A Polarization Controllable Vortex Wave Metamaterial Reflectarray and Its Design Method

technical field

The invention belongs to the fields of orbital angular momentum, wireless communication and new artificial electromagnetic materials, and specifically relates to a metamaterial reflection array capable of generating vortex beams and simultaneously regulating the polarization of the vortex beams.

Background technique

With the development of the times, new media and new technologies are emerging one after another. Webcasting, video calls, driverless driving, and the Internet of Things have put forward higher requirements for communication capacity, response speed, and delay. In particular, the limited resource of spectrum is becoming more and more tense under the demand of rapid development. How to improve the utilization of spectrum has once again become an important challenge for communication technology. In recent years, the emergence and development of Orbital Angular Momentum (OAM) technology has made people see a new dawn. In 1992, Allen et al. found that under the condition of paraxial propagation, the phase factor exp(-ilφ) of the beam has the characteristics of a definite orbital angular momentum lh, where l is the topological charge, h is Planck’s constant, and φ is the orientation horn. The OAM multiplexing technology can use the orbital angular momentum mode carried by the carrier as a modulation parameter, and utilize the inherent orthogonality of the orbital angular momentum mode to modulate multiple signals to different orbital angular momentum modes. In this way, people can obtain multiple independent orbital angular momentum channels on the same carrier frequency. Since the orbital angular momentum can theoretically have an infinite dimensional order, theoretically the same carrier frequency can obtain infinite transmission capacity by using the orbital angular momentum electromagnetic vortex multiplexing. In addition to effectively increasing the information capacity of the channel, the orbital angular momentum technology also makes the encoded information more confidential and the transmission process more secure. In the optical band, OAM beams also have novel applications in the fields of manipulating photon spin Hall effect, optical imaging, quantum entanglement, information storage, and biomedicine.

Due to the unique and novel properties of OAM, the application of OAM is more and more extensive, and the generation and control methods of OAM beams have also aroused great interest of researchers. The generation methods of orbital angular momentum mainly include spiral phase plate method, computational holography method, antenna array method and spiral reflector method. The first two methods are derived from optics and are mainly used at higher frequencies, while the latter two methods are used at lower frequencies. The design idea of the spiral phase plate method is that when the beam passes through the surface of the phase plate at different heights, different phase factors are added to the reflected wave, thereby forming an electromagnetic vortex wave. Due to the limitation of the precision of the spiral gradient, it is difficult to obtain high-quality OAM Beam; Computational holography uses a computer to make a phase hologram that can interfere with vortex waves. When the beam shines on the phase hologram, the vortex beam is generated through wave interference. However, the production of holograms is very complicated, which is not conducive to OAM practice. Application; Different antenna units of the antenna array method will produce a 360° gradient phase difference for the same input signal, and these units will be fan-shaped along the axis to form a vortex beam. If these units are arranged in some specific ways, it will also Different modes of orbital angular momentum beams can be obtained. This method introduces a large number of phase shifters and T/R components, resulting in too complicated system structure, high application and maintenance costs, and cannot be widely promoted.

With the emergence of new electromagnetic functional materials, metamaterials have become a research hotspot due to their specific electromagnetic properties. The emergence of metamaterials provides a new opportunity for the generation and regulation of OAM beams. Metamaterials can achieve many electromagnetic properties that cannot be achieved by natural materials by arranging well-designed structural units periodically or aperiodically, such as inverse Cherenkov, inverse Doppler phenomenon, negative refractive index, superluminal speed , super-resolution, etc. Different from traditional materials, the design of metamaterials is often not restricted by the material system, and has extremely high flexibility. Through the selection of matrix materials and the design of structural units, multiple electromagnetic functions can be simultaneously realized in the same structure. Here, we use metamaterial reflectarrays to realize OAM beam generation and control the polarization state of OAM beams. This work can reduce the cost of traditional OAM devices and promote the development of multifunctional OAM devices. This metamaterial will have a very high application prospect in the field of OAM microwave communication.

Contents of the invention

In order to reduce the cost of traditional OAM devices and promote the development of multifunctional OAM devices, a polarization-controllable vortex metamaterial reflectarray and its design method are proposed, which has a very high application prospect in the field of OAM communication.

The invention discloses a polarization-controllable vortex wave metamaterial reflection array, which includes an electromagnetic anisotropy unit, and the electromagnetic anisotropy unit includes a metal structure layer, a dielectric layer and a metal back plate layer sequentially from top to bottom , the metal structure layer is an orthogonal I-shaped structure.

The invention also discloses a method for designing a polarization-controllable vortex wave metamaterial reflection array, which includes the following steps:

Step 1: According to the working frequency of the vortex wave, simulate the structural size of the electromagnetic anisotropy unit that meets the working frequency band;

Step 2: Based on the superposition principle of the antenna far-field pattern, calculate the phase distribution of the generated vortex wave according to the phase distribution characteristics of the incident wave and the topological charge of the vortex beam;

Step 3: According to the polarization direction of the incident electromagnetic wave, the polarization direction of the vortex beam can be controlled by adjusting the phase difference between the horizontally polarized reflected wave and the vertically polarized reflected wave;

Step 4: According to the phase distribution of the horizontal and vertical polarized waves, determine the structural size of the electromagnetic anisotropy unit, and arrange it according to the phase distribution.

The phase of the electromagnetic anisotropy unit in step 1 changes linearly in the working frequency band, and the amplitude of the reflected wave tends to 1.

Adjusting the length of the horizontal arm of the metal structure layer of the anisotropic unit can control the reflection phase of the horizontally polarized wave, and adjusting the length of the vertical arm of the metal structure layer can control the reflection phase of the vertically polarized wave.

Beneficial effects: Compared with the prior art, the metamaterial reflection array of the present invention can not only effectively generate the vortex beam, but also realize the regulation of the polarization of the vortex beam. The metamaterial reflection array can reduce the traditional vortex wave The cost of the device promotes the development of multifunctional vortex wave devices, and the designed metamaterial will have a very high application prospect in the field of orbital angular momentum microwave communication in the future.

Description of drawings

Fig. 1 is a front view of a metal structure on a single unit of an anisotropic metamaterial.

Fig. 2 is a side view of a single unit structure of an anisotropic metamaterial.

Fig. 3 is the reflection phase distribution of the y-polarized unit corresponding to the arm length l _y of the I-shaped structure designed in the present invention.

Fig. 4 is the reflection phase distribution of the x-polarized unit corresponding to the arm length l _y of the I-shaped structure designed in the present invention.

Fig. 5 is a schematic diagram of the upper metal pattern structure of the circularly polarized OAM wave metamaterial reflector array designed in the present invention.

Fig. 6 is a schematic diagram of the upper metal pattern structure of the cross-polarized OAM wave metamaterial reflector array designed in the present invention.

Fig. 7 shows the test results of the near-field amplitude and phase distribution of the circular polarization OAM and cross-polarization OAM metamaterial reflectarrays of the present invention.

Detailed ways

The present invention will be further described below in conjunction with the accompanying drawings and examples.

Example 1

A polarization-controllable vortex wave metamaterial reflectarray composed of electromagnetic anisotropic unit structures. The anisotropic unit structure includes an upper metal pattern layer, a middle dielectric substrate, and a bottom metal backplane. The structure of the upper metal pattern layer is shown in Figure 1. It consists of two orthogonal I-shaped layers. The metal pattern layer is located at Above the dielectric substrate, the underlying metal backplane is located below the dielectric substrate. Both the metal pattern layer and the metal backplane are made of conductive materials such as copper and silver. The dielectric substrate can be FR-4, F4b, PMI, plexiglass, poly Imide, PET, PDMS and other materials. The direct positional relationship of the metal pattern layer, the dielectric substrate, and the metal backplane is shown in Figure 2.

The polarization-controllable vortex wave metamaterial reflectarray uses anisotropic unit structure to independently control and design the phase distribution of horizontally polarized waves (x-polarized waves) and vertically polarized waves (y-polarized waves). . Adjusting the arm length _ly of the horizontal I-shape, the phase distribution of reflected waves with different polarizations is shown in Fig. 3 and Fig. 4. It can be seen from Figure 3 that the phase of the horizontally polarized (y-polarized) reflected wave can be regulated by changing the arm length l _y . The reflected phase of the unit changes linearly in a wide frequency band, and the phase change range should satisfy 360° as much as possible. °, where the phase change is at 270°. Meanwhile, it can be seen from Fig. 4 that the change of the arm length l _y hardly affects the vertically polarized (x-polarized) waves. This shows that changing the arm length _ly can independently adjust the phase of the horizontally polarized wave without affecting the vertically polarized wave (x-polarized wave). Due to the symmetry of the unit structure, the phase of the x-polarized wave can be adjusted by changing the length of the arm length l _x . The electromagnetic anisotropy based on the unit structure means that the phase of the y-polarized ( _{x-polarized) waves can be adjusted separately by controlling the arm length ly (l x )} .

In order to realize the control of the polarization of the orbital angular momentum beam, the phases of the x-polarized wave and y-polarized wave should be designed respectively. According to the superposition principle of the far-field pattern, the corresponding phase compensation information can be calculated. In the case of plane wave incidence, it is assumed that the polarization of the incident wave is along the 45° direction, such as the v direction shown in Figure 1, and is perpendicular to the surface of the metamaterial reflector array, and the incident electromagnetic wave can be decomposed into horizontally polarized waves with the same intensity and phase , Vertically polarized waves. At this time, in order to generate the orbital angular momentum beam, the OAM phase should be compensated for the phase of the x-polarized wave. The OAM phase is helically distributed in a section perpendicular to the propagation direction, so the OAM beam is also called a vortex beam. The positive or negative of the orbital angular momentum topological charge determines the direction of the OAM vortex, and the size of the OAM topological charge determines the speed of the phase change along the circumferential direction. When the horizontally polarized wave and the vertically polarized wave have the same OAM topological charge, the OAM polarization can be regulated by adjusting the initial compensation phase of the horizontally polarized wave and the vertically polarized wave. When the initial phase difference between the x-polarized wave and the y-polarized wave is 0°, 90°, 180°, and 270°, the corresponding OAM reflected wave polarizations are v-polarized, right-handed circularly polarized, and crossed with the incident wave linear polarization and left-handed circular polarization. When a 45° polarized point source is incident on the metamaterial reflectarray, the incident is approximately regarded as a spherical wave, and the phase compensation of the point source should also be considered.

For this reason, when point source incident is considered, the metamaterial reflectarray designed with the working center frequency at 15 GHz, according to the phase compensation method, the phases of horizontally polarized waves and vertically polarized waves are designed respectively, and the phase of the two polarization directions and the working According to the geometric relationship of the glyph arm length, the top view of the corresponding metamaterial reflector array can be obtained, as shown in Fig. 5 and Fig. 6 . In Fig. 5, the initial phase difference between the x-polarized wave and the y-polarized wave of the M1 metamaterial reflector array is 90°. According to the compensation theory, M1 will generate circularly polarized OAM when the V-polarized point source is incident. At the same time, for the M2 reflector array, the initial phase difference between the x-polarized wave and the y-polarized wave is 180°, and M2 will generate cross-line polarized OAM when the V-polarized point source is incident.

According to the geometric design and material composition of the arrays M1, M2, the corresponding reflective arrays M1, M2 are processed. And put the obtained principle sample into the microwave anechoic chamber for near-field test, and finally get the test result as shown in Figure 7. It can be seen from the figure that there is a phase singularity in the middle of the amplitude, and the phase is spirally distributed around the central singularity, indicating that the reflectarray can generate the expected OAM beam. It can be seen from Fig. 7 that the M1 reflection wave polarization is mainly circular polarization, and the M2 reflection wave is cross polarization. Due to the good linearity of the anisotropic element over a wide frequency range, it is shown that polarization-controllable OAM beams can be generated over a wide frequency range.

As shown in Figures 1 and 2, let the period of the unit structure be p, the upper layer is two orthogonal I-shaped metal patterns, the line width of the I-shaped is w, the length of the short arm of the I-shaped is a, the horizontal direction is I-shaped, and the vertical direction is I-shaped. The arm lengths of I-shape are lx, ly respectively. The thickness of the intermediate dielectric substrate is h, and the lower layer is a metal backplane. Both the thickness of the lower metal back plate and the upper metal pattern are t. According to the operating frequency range of the reflectarray, the geometric size of the anisotropic unit structure is optimized. In this embodiment, the research on orbital angular momentum beam generation and polarization control in the 14-16GHz range is mainly aimed at, so the optimized parameters are specifically set as follows: p=6mm, h=2mm, w=0.2mm, a=1.8mm, t = 0.018 mm. The above-mentioned polarization-controllable OAM metamaterial reflectarray can generate OAM beams in the wide frequency range of 14-16GHz, and at the same time realize the regulation and design of the polarization state of the beams.

Claims (4)

1. A polarization-controllable vortex wave metamaterial reflector array, characterized in that: it includes an electromagnetic anisotropy unit, and the electromagnetic anisotropy unit includes a metal structure layer, a dielectric medium layer and a metal structure layer from top to bottom. As for the backplane layer, the metal structure layer is an orthogonal I-shaped structure. 2. A method for designing a polarization-controllable vortex metamaterial reflector array, characterized in that: comprising the following steps: Step 1: According to the working frequency of the vortex wave, simulate the structural size of the electromagnetic anisotropy unit that meets the working frequency band; Step 2: Based on the superposition principle of the antenna far-field pattern, calculate the phase distribution of the generated vortex wave according to the phase distribution characteristics of the incident wave and the topological charge of the vortex beam; Step 3: According to the polarization direction of the incident electromagnetic wave, the polarization direction of the vortex beam can be controlled by adjusting the phase difference between the horizontally polarized reflected wave and the vertically polarized reflected wave; Step 4: According to the phase distribution of the horizontal and vertical polarized waves, determine the structural size of the electromagnetic anisotropic unit, and arrange it according to the phase distribution to obtain the metamaterial reflector array. 3. A method for designing a polarization-controllable vortex metamaterial reflector array according to claim 2, characterized in that: the phase of the electromagnetic anisotropic unit in the step 1 changes linearly in the working frequency band, and the reflection The wave amplitude tends to 1. 4. A method for designing a polarization-controllable vortex metamaterial reflector array according to claim 2, characterized in that: adjusting the length of the horizontal arm of the metal structure layer of the anisotropic unit can control the horizontally polarized wave The reflection phase of the vertically polarized wave can be controlled by adjusting the vertical arm length of the metal structure layer.