Transmission range extending method for terahertz vortex electromagnetic waves

Abstract

The invention discloses a transmission range extending method of terahertz vortex electromagnetic waves, and belongs to the technical field of terahertz electromagnetism. The method comprises the following steps: firstly, constructing a numerical green function data set; then verifying the validity and accuracy of the numerical green function data set; and finally, optimizing mode combination and amplitude-phase distribution of the vortex electromagnetic waves based on the numerical Green function data set to realize transmission range extension of the vortex electromagnetic waves. The method is realized based on a numerical green function and a genetic algorithm, mode combination and amplitude-phase regulation and control are carried out on vortex electromagnetic waves, the transmission efficiency in an obstacle environment is improved, and transmission range extension of the vortex electromagnetic waves under the condition that an obstacle exists in a transmission path is realized.

Description

Technical Field

[0001] The invention belongs to the field of terahertz electromagnetic technology, and specifically relates to a method for extending the transmission range of terahertz vortex electromagnetic waves based on numerical Green's function and genetic algorithm. Background Art

[0002] In recent years, with the rapid development of 6G communications and the Internet of Things, spectrum resources have become increasingly scarce, but people's demand for higher communication rates and larger channel capacities continues to grow. Orbital Angular Momentum (OAM) and terahertz have attracted much attention as the two key technologies to break through the communication bottleneck, and related research is also in full swing.

[0003] Electromagnetic waves can carry both energy and momentum when radiating, where momentum includes linear momentum and angular momentum. Angular momentum is composed of spin angular momentum and orbital angular momentum. When the beam is twisted, the equiphase surface of the electromagnetic wave is spirally distributed, and the OAM mode of the beam is no longer zero. This type of electromagnetic wave is called a vortex electromagnetic wave. In theory, vortex electromagnetic waves have infinite modes at any frequency, and vortex electromagnetic waves of different modes are orthogonal to each other and do not interfere with each other. This feature also makes vortex electromagnetic waves a new multiplexing technology that can greatly improve spectrum efficiency. At the same time, the terahertz band provides rich spectrum resources, with a frequency range from 0.1THz to 10THz. The organic combination of the two can provide new possibilities for wireless communications. However, most of the current research on OAM is based on line-of-sight transmission in free space. However, in actual transmission scenarios, the transmission of OAM beams will be affected by various obstacles, which greatly reduces the energy transmission efficiency. Using a combination of vortex electromagnetic waves of different modes to construct structural electromagnetic waves for transmission is expected to improve this problem and achieve extended transmission range of vortex electromagnetic waves. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for extending the transmission range of terahertz vortex electromagnetic waves. The method is based on numerical Green's function and genetic algorithm, and realizes the transmission range extension when there are obstacles in the transmission path through mode multiplexing of vortex electromagnetic waves.

[0005] The technical solution adopted by the present invention is as follows:

[0006] A method for extending the transmission range of a terahertz vortex electromagnetic wave comprises the following steps:

[0007] S1. Construct numerical Green's function dataset;

[0008] The present invention adopts the following method to construct the numerical Green's function data set:

[0009] S11. Model a scatterer in the simulation software; set the radiation source to a point source and set the frequency and sampling surface of the point source;

[0010] S12. Meshing is performed at the location of the point source, and electric dipoles of different polarizations (xyz) are placed at the point source to simulate the field distribution of the electric dipoles of each polarization on the sampling surface;

[0011] S13. Changing the position of the point source, simulating multiple times to obtain the field distribution data of electric dipoles with different polarizations at different positions;

[0012] S14. Arrange the field distribution data obtained in step S13 to obtain a numerical Green's function data set.

[0013] S2. Verify the validity and accuracy of the numerical Green’s function dataset;

[0014] S21. Construct a dipole unit and its array, and obtain the simulated calculation field distribution of the dipole unit and its array through simulation software;

[0015] S22. Calculate the field distribution of the dipole unit and its array using the numerical Green's function data set to obtain the numerically calculated field distribution;

[0016] S23. Compare the simulated calculated field distribution and the numerical calculated field distribution. If the error is less than the threshold, it indicates the validity and accuracy of the numerical Green's function data set obtained in step S1, and proceed to step S3.

[0017] S3. Optimize the mode combination and amplitude-phase distribution of the vortex electromagnetic wave to achieve the transmission range extension of the vortex electromagnetic wave;

[0018] S31. Solve the field distribution of different modes of vortex electromagnetic waves of the antenna array to be optimized based on the numerical Green's function data set;

[0019] S32. Determine the position and size of the antenna array to be optimized, select a point on the receiving surface as the target receiving position; interpolate the field distribution obtained in step S31 to obtain the field strength value of the target receiving position;

[0020] S33. The amplitude and phase of vortex electromagnetic waves of different modes are controlled to obtain the mode combination and amplitude and phase distribution corresponding to the maximum field strength at the target receiving position, thereby realizing the transmission range extension of vortex electromagnetic waves.

[0021] Further, in step S33, the mode combination and amplitude-phase distribution of the vortex electromagnetic wave are optimized based on a genetic algorithm, including the following steps:

[0022] It is known that the complex amplitude of the field of N-mode vortex electromagnetic waves at the target receiving position is Among them A nxrepresents the amplitude of the x-component of the electric field of the n-th mode vortex electromagnetic wave at the target receiving position, Indicates the corresponding phase; the corresponding A ny , A nz , Represent the amplitude and phase of the y and z components respectively; expressed in matrix as:

[0023]

[0024] Among them, the column vector A x , A y , A z They represent the x, y, and z components of the complex amplitude of the vortex electromagnetic waves of different modes, and j is an imaginary unit;

[0025] The excitation matrix of vortex electromagnetic waves of different modes is written as a column vector I:

[0026]

[0027] Among them, I n represents the excitation amplitude of the nth mode vortex electromagnetic wave, represents the initial phase of the excitation of the n-th mode vortex electromagnetic wave; the total field at the receiving position is expressed as:

[0028] E=(xA x +yA y +zA x )I

[0029] Among them, x, y, z represent the direction vectors in the x, y, and z directions respectively;

[0030] The power at the receiving location is expressed as the square of the modulus of the total field, so |E| 2 As the objective function, the excitation matrix I is the decision variable, the constraint condition is a nonlinear equality constraint, and the sum of the squares of the moduli of the excitation matrix elements is set to a constant 1, which means that the input power is constant;

[0031] I1 2 +I2 2 +I2 2 +L+I N 2 =1

[0032] Will I n and Use x respectively n and x n+N To represent, the number of decision variables is 2N, and the optimization problem is described as:

[0033]

[0034] 0<xi <1,i=1,2,L,N

[0035] 0<x i <2π,i=N+1,N+2,L,2N

[0036] For each mode, the lower and upper bounds of the excitation amplitude are set to 0 and 1, respectively, and the lower and upper bounds of the initial phase are set to 0 and 2π, respectively.

[0037] The genetic algorithm is used to solve the optimization problem and obtain the mode combination and amplitude-phase distribution of the vortex electromagnetic wave corresponding to the maximum field intensity at the target receiving position, thereby realizing the transmission range extension of the vortex electromagnetic wave.

[0038] Furthermore, the antenna array to be optimized is a uniform circular array (UCA), and the array unit is a half-wave array.

[0039] Further, in step S22, the field distribution of the dipole unit and its array is calculated using the numerical Green's function data set as follows:

[0040] The half-wave array is divided into multiple current elements, and the amplitude and phase distribution of each current element is obtained according to the current distribution of the half-wave array. The corresponding amplitude and phase distribution is assigned to the numerical Green's function obtained in step S1 to obtain the field distribution of the current element; the total field obtained by superimposing the field vectors generated by all current elements is the numerically calculated field distribution.

[0041] The field distribution generated by the half-wave array or UCA is calculated using the numerical Green's function data set, and then compared with the field distribution simulated by FEKO to verify the feasibility and accuracy of the numerical Green's function.

[0042] Further, in step S23, the threshold is set to 20%.

[0043] The beneficial effects of the present invention are as follows:

[0044] The present invention provides a method for extending the transmission range of terahertz vortex electromagnetic waves based on numerical Green's function and genetic algorithm. In the terahertz frequency band, by combining modes and regulating the amplitude and phase of vortex electromagnetic waves, the transmission efficiency of vortex electromagnetic waves in obstacle environments is improved, and the transmission range of vortex electromagnetic waves is extended. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solution of the present invention, the accompanying drawings required for use in the present invention are briefly introduced below.

[0046] Figure 1 It is a flow chart for realizing the present invention;

[0047] Figure 2Schematic diagram of electric field sampling when an ideal conductor ball blocks the object;

[0048] Figure 3 Flowchart for the construction of numerical Green's function dataset;

[0049] Figure 4 A comparison chart of the results based on FEKO simulation and numerical Green's function calculation;

[0050] Figure 5 It is a schematic diagram of an 8-element uniform circular dipole antenna array;

[0051] Figure 6 Schematic diagram of vortex electromagnetic wave transmission when the obstacle is an ideal conductor sphere;

[0052] Figure 7 After genetic algorithm optimization: (a) receiving surface field distribution diagram of the target receiving position (-4λ, 4λ, 6λ); (b) OAM mode amplitude and initial phase;

[0053] Figure 8 This is a comparison diagram of the normalized field intensity of structural waves composed of different mode vortex electromagnetic waves and mode multiplexing when the target receiving position is (-4λ, 4λ, 6λ). DETAILED DESCRIPTION

[0054] In order to make the above-mentioned objects and features of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0055] The present invention provides a terahertz vortex electromagnetic wave transmission range extension method based on numerical Green's function and genetic algorithm.

[0056] Reference Figure 1 The present embodiment provides a method for extending the transmission range of terahertz vortex electromagnetic waves based on numerical Green's function and genetic algorithm, comprising the following steps:

[0057] S1. Construct numerical Green's function dataset;

[0058] The Green's function in the electromagnetic field can be interpreted as the field distribution of a point source of unit intensity in space under certain boundary conditions. However, for some random environments, such as some irregular or inhomogeneous scatterers in the environment, it is difficult to obtain an analytical solution to the Green's function. Usually, numerical methods such as the moment method, finite element method or finite difference time domain method can be used to obtain the numerical Green's function.

[0059] S11. Reference Figure 2 , the scatterer is set to an ideal conductor sphere with a radius of 2λ; the radiation source is set to a point source, the frequency of the point source is 0.11THz, and the sampling surface size is set to 8λ×8λ;

[0060] S12. Reference Figure 3 , using FEKO to simulate; meshing is performed at the location of the point source, and electric dipoles of different polarizations (xyz) are placed at the point source to simulate the field distribution of electric dipoles of various polarizations on the sampling surface;

[0061] S13. Change the position of the point source and simulate multiple times to obtain the field distribution data of electric dipoles with different polarizations at different positions; to speed up the solution process, the solution method of FEKO simulation is set to multi-layer fast multipole.

[0062] S14. Arrange the field distribution data obtained in step S13 to obtain a numerical Green's function data set.

[0063] S2. Verify the validity and accuracy of the numerical Green’s function dataset;

[0064] S21. Reference Figure 4 , construct a dipole unit and a uniform ring antenna array constructed by 8 dipole units, and obtain the simulation calculation field distribution of the dipole unit and its array through simulation software;

[0065] S22. Calculate the field distribution of the unit and array in step S21 using the numerical Green's function data set to obtain a numerically calculated field distribution;

[0066] S23. Reference Figure 5 , the simulation calculation field distribution and the numerical calculation field distribution are compared, and the maximum error is 8.6%, which verifies that the numerical Green's function data set obtained in step S1 is effective and accurate.

[0067] S3. Optimize the mode combination and amplitude-phase distribution of the vortex electromagnetic wave to achieve the transmission range extension of the vortex electromagnetic wave;

[0068] S31. Solve the field distribution of different modes of vortex electromagnetic waves of 8-unit dipole UCA based on numerical Green's function data set;

[0069] For a vortex electromagnetic wave of mode l, the phase of the mth dipole of the UCA is in M is the number of UCA units. The field distribution of 7 modes of vortex electromagnetic waves with modes l=0, ±1, ±2, and ±3 are obtained based on the numerical Green's function data set obtained in step S1.

[0070] S32. Determine that the 8-unit uniform annular dipole array antenna is located on the xy plane of z = -4λ and the array radius is λ; select (-4λ, 4λ, 6λ) as the target receiving position, and the field strength values ​​of different modes of vortex electromagnetic waves at this point are obtained by interpolation of the field distribution obtained in step S31;

[0071] S33. Reference Figure 6 , the amplitude and phase of vortex electromagnetic waves of different modes are controlled to obtain the mode combination and amplitude and phase distribution corresponding to the maximum field strength at the target receiving position, thereby realizing the vortex transmission range extension of electromagnetic waves.

[0072] Specifically, a genetic algorithm is used here to optimize the amplitude and phase distribution of vortex electromagnetic waves of different mode combinations. First, the problem to be solved is transformed into an optimization problem. It is known that the complex amplitude of the field of N modes of vortex electromagnetic waves at the target receiving position is (According to the 7 vortex wave modes solved in step S31, N is taken as 7), where A nx represents the amplitude of the x-component of the electric field of the n-th mode vortex electromagnetic wave at the target receiving position, is its phase, and the corresponding A ny , A nz , Represent the amplitude and phase of the y and z components respectively. It can be expressed as a matrix:

[0073]

[0074] Among them, the column vector A x , A y , A z They represent the x, y, and z components of the complex amplitude of the vortex electromagnetic waves of different modes, and j is an imaginary unit;

[0075] The excitation matrix of vortex electromagnetic waves of different modes can be written as a column vector I:

[0076]

[0077] Among them I n represents the excitation amplitude of the nth mode vortex electromagnetic wave, represents the initial phase of the excitation of the n-th mode vortex electromagnetic wave. Then, the total field at the receiving position can be expressed as:

[0078] E=(xA x +yA y +zA x )I

[0079] Among them, x, y, z represent the direction vectors in the x, y, and z directions respectively;

[0080] The power at the receiving point is expressed as the square of the modulus of the total field, so |E| 2 As the objective function, the excitation matrix I is the decision variable, the constraint condition is a nonlinear equality constraint, and the sum of the squares of the moduli of the excitation matrix elements is set to a constant 1, which means that the input power is constant;

[0081] I12 +I2 2 +I2 2 +L+I N 2 =1

[0082] Will I n and Use x respectively n and x n+N To represent, the number of decision variables is 2N, and the optimization problem is described as:

[0083]

[0084] 0<x i <1,i=1,2,L,N

[0085] 0<x i <2π,i=N+1,N+2,L,2N

[0086] The lower and upper bounds of the excitation amplitude of each mode are set to 0 and 1, respectively, and the lower and upper bounds of the initial phase are set to 0 and 2π, respectively, and then the optimization problem is solved by a genetic algorithm.

[0087] Reference Figure 7 When the target receiving position is selected as (-4λ, 4λ, 6λ), the genetic algorithm is used to optimize the appropriate vortex electromagnetic wave mode combination and initial phase distribution, and the field distribution at the target receiving position shows obvious convergence.

[0088] Reference Figure 8 The field intensity generated by the vortex electromagnetic wave based on the optimized specific mode combination and amplitude-phase distribution is 92.3% higher than that of the single-mode vortex electromagnetic wave, which significantly improves the energy transmission efficiency and realizes the transmission range extension of the vortex electromagnetic wave.

[0089] The advantages of the present invention are: based on the numerical Green's function data set constructed under different obstacle environments, the transmission effect of vortex electromagnetic waves of different modes under different obstacle environments is simulated efficiently and quickly, and the amplitude and phase distribution of vortex electromagnetic waves of different modes are optimized by genetic algorithms, which significantly improves the transmission efficiency of vortex electromagnetic waves and realizes the transmission range extension of vortex electromagnetic waves. At the same time, the invention is not only applicable to the terahertz frequency band, but also to other frequency bands.

Claims

1. A method for extending the transmission range of terahertz vortex electromagnetic waves, characterized in that: The following steps are involved: S1. Construct numerical Green's function dataset; S2. Verify the validity and accuracy of the numerical Green's function data set obtained in step S1; S21. Construct a dipole unit and its array, and obtain the simulated calculation field distribution of the dipole unit and its array through simulation software; S22. Calculate the field distribution of the dipole unit and its array using the numerical Green's function data set to obtain the numerically calculated field distribution; S23. Compare the simulated calculated field distribution with the numerical calculated field distribution. If the error is less than the threshold, proceed to step S3; S3. Optimize the mode combination and amplitude-phase distribution of the vortex electromagnetic wave to achieve the transmission range extension of the vortex electromagnetic wave; S31. Solve the field distribution of different modes of vortex electromagnetic waves of the antenna array to be optimized based on the numerical Green's function data set; S32. Determine the position and size of the antenna array to be optimized, select a point on the receiving surface as the target receiving position; interpolate the field distribution obtained in step S31 to obtain the field strength value of the target receiving position; S33. The amplitude and phase of vortex electromagnetic waves of different modes are controlled to obtain the mode combination and amplitude and phase distribution corresponding to the maximum field strength at the target receiving position, thereby realizing the transmission range extension of vortex electromagnetic waves.

2. A terahertz vortex electromagnetic wave transmission range extension method as claimed in claim 1, characterized in that: In step S33, the mode combination and amplitude-phase distribution of the vortex electromagnetic wave are optimized based on the genetic algorithm, including the following steps: It is known that the complex amplitude of the field of N modes of vortex electromagnetic waves at the target receiving position is Among them A nx represents the amplitude of the x-component of the electric field of the n-th mode vortex electromagnetic wave at the target receiving position, Indicates the corresponding phase; the corresponding A ny , A nz , Represent the amplitude and phase of the y and z components respectively; expressed in matrix as: Among them, the column vector A x , A y , A z They represent the x, y, and z components of the complex amplitude of the vortex electromagnetic waves of different modes, and j is an imaginary unit; The excitation matrix of vortex electromagnetic waves of different modes is written as a column vector I: Among them, I n represents the excitation amplitude of the nth mode vortex electromagnetic wave, represents the initial phase of the excitation of the n-th mode vortex electromagnetic wave; the total field at the target receiving position is expressed as: E=(xA x +yA y +zA x )YES Among them, x, y, z represent the direction vectors in the x, y, and z directions respectively; |E 2 As the objective function, the excitation matrix I is the decision variable, and the constraint condition is a nonlinear equality constraint. The sum of the squares of the moduli of the excitation matrix elements is set to a constant 1, which means that the input power is constant: I1 2 +I2 2 +I2 2 +L+I N 2 =1 Will I n and Use x respectively n and x n+N To represent, the number of decision variables is 2N, and the optimization problem is described as: 0<x i <1,i=1,2,L,N 0<x i <2π,i=N+1,N+2,L,2N The lower and upper bounds of the excitation amplitude for each mode are set to 0 and 1, respectively, and the lower and upper bounds of the initial phase are set to 0 and 2π, respectively; The genetic algorithm is used to solve the optimization problem and obtain the mode combination and amplitude-phase distribution of the vortex electromagnetic wave corresponding to the maximum field intensity at the target receiving position, thereby realizing the transmission range extension of the vortex electromagnetic wave.

3. A terahertz vortex electromagnetic wave transmission range extension method as claimed in claim 2, characterized in that: The antenna array to be optimized is a uniform annular array, and the array unit is a half-wave array.

4. A method for extending the transmission range of terahertz vortex electromagnetic waves as claimed in claim 3, characterized in that: In step S22, the field distribution of the dipole unit and its array is calculated using the numerical Green's function data set as follows: The half-wave array is divided into multiple current elements, and the amplitude and phase distribution of each current element is obtained according to the current distribution of the half-wave array. The corresponding amplitude and phase distribution is assigned to the numerical Green's function obtained in step S1 to obtain the field distribution of the current element; the total field obtained by superimposing the field vectors generated by all current elements is the numerically calculated field distribution.

5. A method for extending the transmission range of terahertz vortex electromagnetic waves as claimed in claim 4, characterized in that: In step S23, the threshold is set to 20%.

6. A method for extending the transmission range of a terahertz vortex electromagnetic wave according to any one of claims 1 to 5, characterized in that: In step S1, a numerical Green's function data set is constructed in the following manner: S11. Model a scatterer in the simulation software; set the radiation source to a point source and set the frequency and sampling surface of the point source; S12. Meshing is performed at the location of the point source, and electric dipoles of different polarizations are placed at the point source to simulate and obtain the field distribution of the electric dipoles of each polarization on the sampling surface; S13. Changing the position of the point source, simulating multiple times to obtain the field distribution data of electric dipoles with different polarizations at different positions; S14. Arrange the field distribution data obtained in step S13 to obtain a numerical Green's function data set.

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