A method for transmission range enhancement of terahertz vortex electromagnetic waves

Abstract

This invention discloses a method for extending the transmission range of terahertz vortex electromagnetic waves, belonging to the field of terahertz electromagnetic technology. The method first constructs a numerical Green's function dataset; then verifies the effectiveness and accuracy of the dataset; finally, it optimizes the mode combination and amplitude-phase distribution of the vortex electromagnetic waves based on the dataset, thereby achieving extended transmission range. This method, based on numerical Green's functions and a genetic algorithm, improves transmission efficiency in obstructed environments by combining modes and controlling the amplitude and phase of the vortex electromagnetic waves, thus achieving extended transmission range even when there are obstacles in the transmission path.

Description

Technical Field

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

[0002] In recent years, with the rapid development of 6G communication and the Internet of Things, spectrum resources have become increasingly scarce, but the demand for higher communication rates and larger channel capacity continues to grow. Orbital angular momentum (OAM) and terahertz are two key technologies for breaking through communication bottlenecks and have attracted much attention, with related research being carried out vigorously.

[0003] Electromagnetic waves can carry both energy and momentum during radiation, with momentum including linear momentum and angular momentum. Angular momentum is composed of spin angular momentum and orbital angular momentum. When a beam is distorted, 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. Theoretically, vortex electromagnetic waves possess an infinite number of modes at any frequency, and different modes of vortex electromagnetic waves are orthogonal to each other and do not interfere with each other. This characteristic makes vortex electromagnetic waves a new multiplexing technology that can greatly improve spectral efficiency. Meanwhile, the terahertz band provides abundant spectral resources, with a frequency range from 0.1 THz to 10 THz. The organic combination of these two can provide new possibilities for wireless communication. However, most current research on OAM is based on line-of-sight transmission in free space. In actual transmission scenarios, the transmission of OAM beams is affected by various obstacles, which greatly reduces the energy transmission efficiency. Using combinations of vortex electromagnetic waves of different modes to construct structured electromagnetic waves for transmission is expected to improve this problem and achieve extended transmission range of vortex electromagnetic waves. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method for extending the transmission range of terahertz vortex electromagnetic waves. This method, based on numerical Green's functions and a genetic algorithm, achieves transmission range extension even when obstacles exist in the transmission path through mode multiplexing of vortex electromagnetic waves.

[0005] The technical solution adopted in this invention is as follows:

[0006] A method for extending the transmission range of terahertz vortex electromagnetic waves includes the following steps:

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

[0008] The numerical Green's function dataset is constructed in this invention as follows:

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

[0010] S12. Mesh out the point source location and place electric dipoles of different polarizations (xyz) at the point source location to simulate the field distribution of electric dipoles of each polarization on the sampling surface.

[0011] S13. Change the position of the point source and perform multiple simulations to obtain the field distribution data of electric dipoles with different polarizations at different positions;

[0012] S14. Based on the field distribution data obtained in step S13, we obtain a numerical Green's function dataset.

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

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

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

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

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

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

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

[0020] S33. Amplitude and phase modulation of vortex electromagnetic waves of different modes are performed 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] Furthermore, 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] Given that the complex amplitude of the field at the target receiving position for N modes of vortex electromagnetic waves is... Where A nxLet x represent the amplitude of the x-component of the electric field of the nth mode vortex electromagnetic wave at the target receiving position. Indicates the corresponding phase; the corresponding A ny A nz , Let x and y represent the amplitude and phase of the y and z components, respectively; represented by a matrix as follows:

[0023]

[0024] Wherein, column vector A x A y A z These represent the x, y, and z components of the complex amplitude of vortex electromagnetic waves in different modes, with j being the imaginary unit;

[0025] The excitation matrices of vortex electromagnetic waves in different modes can be written as a column vector I:

[0026]

[0027] Among them, I n This represents the excitation amplitude of the vortex electromagnetic wave in the nth mode. Let represent the initial phase of the excitation for the nth mode vortex electromagnetic wave; then the total field at the receiving position is expressed as:

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

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

[0030] The power at the receiving position is expressed as the square of the magnitude of the total field; therefore, |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 squares of the moduli of the excitation matrix elements is set to a constant 1, representing that the input power is constant.

[0031] I1 2 +I2 2 +I3 2 +…+I N 2 =1

[0032] Will I n and Using x respectively n and x n+N Let be the number of decision variables, 2N, and the optimization problem be described as follows:

[0033]

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

[0035] 0 < x i <2π, i=N+1,N+2,…,2N

[0036] 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.

[0037] By using a genetic algorithm to solve the optimization problem, the mode combination and amplitude-phase distribution of the vortex electromagnetic wave corresponding to the maximum field strength at the target receiving position are obtained, 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 elements are half-wave arrays.

[0039] Furthermore, in step S22, the method for calculating the field distribution of the dipole unit and its array using the numerical Green's function dataset is as follows:

[0040] The half-wave array is divided into multiple current elements. The amplitude and phase distribution of each current element is obtained based on 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 a half-wave inductor or UCA is calculated using a numerical Green's function dataset, and then compared with the field distribution simulated by FEKO to verify the feasibility and accuracy of the numerical Green's function.

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

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

[0044] This 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 band, by combining modes and modulating amplitude and phase of vortex electromagnetic waves, the transmission efficiency of vortex electromagnetic waves in obstructed environments is improved, thus achieving extended transmission range. Attached Figure Description

[0045] To more clearly illustrate the technical solution of the present invention, the accompanying drawings used in the present invention will be briefly described below.

[0046] Figure 1 This is a flowchart illustrating the implementation of the present invention;

[0047] Figure 2A schematic diagram of electric field sampling when an ideal conducting sphere acts as a barrier.

[0048] Figure 3 A flowchart for constructing a numerical Green's function dataset;

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

[0050] Figure 5 A schematic diagram of an 8-element uniform ring dipole antenna array;

[0051] Figure 6 A schematic diagram of vortex electromagnetic wave transmission when the obstacle is an ideal conducting sphere;

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

[0053] Figure 8 A comparison of the normalized field strength of vortex electromagnetic waves of different modes and structure waves composed of mode multiplexing when the target receiving position is (-4λ, 4λ, 6λ). Detailed Implementation

[0054] To make the above-mentioned objectives and features of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] This invention provides a method for extending the transmission range of terahertz vortex electromagnetic waves based on numerical Green's function and genetic algorithm.

[0056] Reference Figure 1 This embodiment provides a terahertz vortex electromagnetic wave propagation range extension method based on numerical Green's function and genetic algorithm, which includes the following steps:

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

[0058] In electromagnetic fields, the Green's function can be interpreted as the field distribution in space of a point source of unit intensity under certain boundary conditions. However, for some random environments, such as those with irregular or non-uniform scatterers, it is difficult to obtain an analytical solution for the Green's function. In such cases, numerical methods such as the method of moments, the finite element method, or the finite-difference time-domain method can be used to obtain the numerical Green's function.

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

[0060] S12. Reference Figure 3 The simulation was performed using FEKO. A mesh was generated at the point source location, and electric dipoles with different polarizations (xyz) were placed at the point source location. The field distribution of each polarization electric dipole on the sampling surface was obtained through simulation.

[0061] S13. Change the position of the point source and perform multiple simulations to obtain field distribution data of electric dipoles with different polarizations at different positions; to accelerate the solution process, the solution method of FEKO simulation is set to multilayer fast multipole.

[0062] S14. Based on the field distribution data obtained in step S13, we obtain a numerical Green's function dataset.

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

[0064] S21. Reference Figure 4 A dipole element and a uniform ring antenna array composed of 8 such dipole elements are constructed, and the simulated field distribution of the dipole element and its array is obtained through simulation software.

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

[0066] S23. Reference Figure 5 The simulated field distribution and the numerical field distribution were compared, and the maximum error was 8.6%, which verified that the numerical Green's function dataset obtained in step S1 was effective and accurate.

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

[0068] S31. Solve the field distribution of vortex electromagnetic waves in different modes of an 8-element dipole UCA based on a numerical Green's function dataset;

[0069] For a vortex electromagnetic wave of mode l, the phase of the m-th dipole in the UCA is... in M represents the number of UCA elements. Based on the numerical Green's function dataset obtained in step S1, the field distribution of the vortex electromagnetic waves for the seven modes l = 0, ±1, ±2, ±3 is calculated.

[0070] S32. Determine that the 8-element uniform ring 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 value of the vortex electromagnetic wave of different modes at this point is obtained by interpolation of the field distribution obtained in step S31;

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

[0072] Specifically, a genetic algorithm is used here to optimize the amplitude and phase distribution of vortex electromagnetic waves with different mode combinations. First, the problem to be solved is transformed into an optimization problem. Given that the complex amplitude of the field at the target receiving position for N modes of vortex electromagnetic waves is... (Based on the 7 vortex wave modes obtained in step S31, N is set to 7), where A nx Let x represent the amplitude of the x-component of the electric field of the nth mode vortex electromagnetic wave at the target receiving position. It is its phase, the corresponding A ny A nz , Let represent the amplitude and phase of the y and z components, respectively. Represented by matrices:

[0073]

[0074] Wherein, column vector A x A y A z These represent the x, y, and z components of the complex amplitude of vortex electromagnetic waves in different modes, with j being the imaginary unit;

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

[0076]

[0077] Among them I n This represents the excitation amplitude of the vortex electromagnetic wave in the nth mode. Let represent the initial phase of the excitation for the nth 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] Where x, y, and 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; therefore, |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 squares of the moduli of the excitation matrix elements is set to a constant 1, representing that the input power is constant.

[0081] I12 +I2 2 +I3 2 +…+I N 2 =1

[0082] Will I n and Using x respectively n and x n+N Let be the number of decision variables, 2N, and the optimization problem be described as follows:

[0083]

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

[0085] 0 < x i <2π, i=N+1,N+2,…,2N

[0086] 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. 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), a suitable combination of vortex electromagnetic wave modes and initial phase distribution are optimized using a genetic algorithm, and the field distribution at the target receiving position shows obvious convergence.

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

[0089] The advantages of this invention are as follows: Based on a numerical Green's function dataset constructed under different obstacle environments, it efficiently and rapidly simulates the transmission effects of vortex electromagnetic waves of different modes under different obstacle environments. Furthermore, by optimizing the amplitude and phase distribution of vortex electromagnetic waves of different modes through a genetic algorithm, it significantly improves the transmission efficiency of vortex electromagnetic waves and achieves extended transmission range. Moreover, this invention is applicable not only to the terahertz band but also to other frequency bands.

Claims

1. A method for extending the transmission range of terahertz vortex electromagnetic waves, characterized in that, Includes the following steps: S1. Construct a numerical Green's function dataset; S2. Verify the validity and accuracy of the numerical Green's function dataset obtained in step S1; S21. Construct a dipole element and its array, and obtain the simulation calculation field distribution of the dipole element and its array through simulation software; S22. The field distribution of the dipole unit and its array is calculated using the numerical Green's function dataset to obtain the numerically calculated field distribution; S23. Compare the simulated field distribution with the numerical field distribution. If the error is less than the threshold, proceed to step S3. S3. Optimize the mode combination and amplitude-phase distribution of vortex electromagnetic waves to achieve extended transmission range of vortex electromagnetic waves; S31. Solve the field distribution of vortex electromagnetic waves in different modes of the antenna array to be optimized based on the numerical Green's function dataset; S32. Determine the position and array size of the antenna array to be optimized, and select a point on the receiving surface as the target receiving position; obtain the field strength value of the target receiving position by interpolation of the field distribution obtained in step S31; S33. Amplitude and phase modulation of vortex electromagnetic waves of different modes are performed 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. The terahertz vortex electromagnetic wave transmission range extension method as described 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 a genetic algorithm, including the following steps: Given that the complex amplitude of the field at the target receiving position for N modes of vortex electromagnetic waves is... Where A nx Let x represent the amplitude of the x-component of the electric field of the nth mode vortex electromagnetic wave at the target receiving position. Indicates the corresponding phase; the corresponding A ny A nz , Let x and y represent the amplitude and phase of the y and z components, respectively; represented by a matrix as follows: Wherein, column vector A x A y A z These represent the x, y, and z components of the complex amplitude of vortex electromagnetic waves in different modes, with j being the imaginary unit; The excitation matrices of vortex electromagnetic waves in different modes can be written as a column vector I: Among them, I n This represents the excitation amplitude of the vortex electromagnetic wave in the nth mode. Let represent the initial phase of the excitation of the nth mode vortex electromagnetic wave; then the total field at the target receiving position is expressed as: E=(xA x +yA y +zA x )YES Where x, y, and 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, representing a fixed input power. I1 2 +I2 2 +I3 2 +…+I N 2 =1 Will I n and Using x respectively n and x n+N Let be the number of decision variables, 2N, and the optimization problem be described as follows: 0<x i <1,i=1,2,…,N 0<x i <2π,i=N+1,N+2,…,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. By using a genetic algorithm to solve the optimization problem, the mode combination and amplitude-phase distribution of the vortex electromagnetic wave corresponding to the maximum field strength at the target receiving position are obtained, thereby realizing the transmission range extension of the vortex electromagnetic wave.

3. The terahertz vortex electromagnetic wave transmission range extension method as described in claim 2, characterized in that, The antenna array to be optimized is a uniform ring array, and the array elements are half-wave elements.

4. The terahertz vortex electromagnetic wave transmission range extension method as described in claim 3, characterized in that, In step S22, the method for calculating the field distribution of the dipole unit and its array using the numerical Green's function dataset is as follows: The half-wave array is divided into multiple current elements. The amplitude and phase distribution of each current element is obtained based on 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. The terahertz vortex electromagnetic wave transmission range extension method as described in claim 4, characterized in that, In step S23, the threshold is set to 20%.

6. A terahertz vortex electromagnetic wave transmission range extension method as described in any one of claims 1-5, characterized in that, In step S1, the numerical Green's function dataset is constructed as follows: S11. Model the scattering body in the simulation software; set the radiation source as a point source and set the frequency and sampling surface of the point source; S12. Mesh out the point source location and place electric dipoles of different polarizations at the point source location to simulate the field distribution of each polarization electric dipole on the sampling surface; S13. Change the position of the point source and perform multiple simulations to obtain the field distribution data of electric dipoles with different polarizations at different positions; S14. Based on the field distribution data obtained in step S13, we obtain a numerical Green's function dataset.

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