CN115225120B - Calculation method and device for evaluating electromagnetic super-surface wireless radio frequency power transmission efficiency - Google Patents
Calculation method and device for evaluating electromagnetic super-surface wireless radio frequency power transmission efficiency Download PDFInfo
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Abstract
The invention relates to a calculation method for evaluating the wireless radio frequency power transmission efficiency of an electromagnetic super surface, which at least solves the problem that the radio frequency transmission efficiency of a wireless energy transmission system based on the super surface is difficult to accurately and quickly evaluate. The method provided by the invention mainly evaluates the radio frequency transmission efficiency of the wireless energy transmission system based on the super surface in a numerical calculation mode, greatly improves the evaluation accuracy of the near field compared with the traditional calculation formula, has the characteristics of rapidness and high efficiency compared with the method only by simulation calculation, can be used for simplifying the design and verification process of the wireless energy transmission system based on the super surface, and has important significance for developing the remote and high-power wireless energy transmission technology based on the super surface and the technology of the Internet of things.
Description
Technical Field
The present disclosure relates to wireless energy transmission technologies, and in particular, to a computing method and device for evaluating electromagnetic super-surface wireless radio frequency power transmission efficiency.
Background
Wireless Power Transfer (WPT) technology has been widely used, such as mobile devices, wearable devices, implantable medical devices, and electric vehicles. These applications mostly use stationary wireless charging methods based on inductive or resonant coupling, but both methods are only suitable for charging in the near field range. On the other hand, for long distance energy transmission over distances greater than 1m, only transmission by microwave radiation is possible. In order to solve the problem that the transmission of microwaves in space is accompanied by strong attenuation and loss, the Microwave Power Transfer (MPT) system of the current new type generally adopts a transmitting antenna with beamforming technology. In the far-field area, the high-gain directional beam can increase the propagation distance and the transmission power, and the near-field focused beam can focus electromagnetic waves at a point inside the outer boundary of the near-field area. Therefore, a near-field focused beam can improve near-field transmission efficiency of electromagnetic energy, and is generally adopted in a WPT system in a near-field range.
The Friis formula and Goubau formula are widely used due to their simple calculation form, but large errors are generated in the fresnel region and the induced near field region, so that the analysis method of WPT efficiency is still widely researched. Improved Friis and Goubau formulas were proposed in 2013 and 2018, respectively. In 2021, a calculation method for calculating WPT efficiency between large array antennas was proposed, however, there is no simple and effective numerical calculation method for transmission efficiency in the current advanced ultra-surface based WPT system. At present, a very accurate result can be obtained by modeling the structures of the super surface and the receiving antenna in the WPT system and the surrounding electromagnetic environment by using commercial electromagnetic simulation software such as High Frequency Structure Simulator (HFSS). However, with the development of WPT technology, the transmission power and the transmission distance increase, and the aperture of the antenna also continuously increases. This results in electromagnetic simulations that require a long time and a large amount of computational resources, and sometimes may not be possible to simulate at all. It is therefore highly desirable to provide a numerical calculation method that can accurately calculate the WPT efficiency of a hypersurface.
Disclosure of Invention
In view of the above prior art, the problems to be solved by the present invention are at least: due to the fact that the super-surface aperture is too large, near-field transmission efficiency is difficult to evaluate, transmission efficiency under different conditions cannot be calculated according to different beam shapes, and accurate results can be obtained efficiently and quickly.
In order to solve the technical problems, the technical scheme of the invention is as follows:
in a first aspect, the present invention provides a calculation method for evaluating wireless rf power transmission efficiency of an electromagnetic super-surface, the method comprising the following steps:
obtaining the distance R from the geometric center of the mth super-surface unit to the phase center of the receiving antenna m M =1,2, …, M is the total number of super surface units;
obtaining the radiation electric field E from the m-th super-surface unit to the receiving antenna m ；
Based on said distance R m And E m Calculating the received power P of the receiving antenna according to the following formula H ：
In the formula: η represents the spatial wave impedance;
obtaining feed power P of input feed source F By using
The transmission efficiency of the super surface to the receiving antenna is calculated.
In the technical scheme, the super-surface unit is regarded as an independent radiation unit, and the problem that the near-field transmission efficiency is difficult to evaluate due to the fact that the super-surface caliber is too large in the traditional method is solved through the small caliber and the wide far-field range of a single unit. During calculation, vector superposition is carried out on the radiation electric field of each super-surface unit based on a field superposition principle, so that an expression of the transmission efficiency from the super-surface to the receiving antenna is obtained, and the accuracy of near-field radio frequency efficiency evaluation of the wireless energy transmission system is greatly improved.
In the above technical solution, one obtaining manner of the radiation electric field includes the following steps:
obtaining the radiation power density W from the m-th super-surface unit to the receiving antenna m ；
Obtaining the radiation phase beta of the mth super-surface unit m ；
Calculating the m-th super surface unit to connect according to the following formulaRadiation electric field E of receiving antenna m :
In the above technical solution, the radiation power density W m One of the acquisition modes of (1) comprises the following steps:
obtaining the received power from the m-th super-surface unit to the receiving antenna
The radiation power density W is obtained by the following calculation m ：
Substituting equation (3) into equation (2) yields the following:
in this solution, if the received power from the m-th super-surface unit to the receiving antenna is obtained
Radiation phase beta of mth super-surface unit m And the distance R from the geometric center of the mth super-surface unit to the phase center of the receiving antenna m M =1,2, …, M is the total number of super surface units, and E can be calculated m And thus the transmission efficiency of the super surface to the receiving antenna can be calculated.
In the above technical solution, the received power from the mth super-surface unit to the receiving antenna
The method for obtaining the data comprises the following steps:
establishing a rectangular coordinate system by taking the phase center of the mth super surface unit as an origin;
space unit vector based on rectangular coordinate system
Further obtaining the coordinate vector of the receiving antenna
Based on coordinate vectors
Angle of pitch theta m Azimuth angle
Obtaining the m-th super-surface unit
Actual gain in the direction of joint polarization with the receiving antenna
One acquisition mode is through simulation acquisition, the simulation condition is infinite period boundary, and unit coupling is considered; and acquire the receiving antenna at
Actual gain in the direction in the combined polarization state with the m-th super-surface cell
One acquisition mode is to acquire the data by simulation or darkroom multi-probe measurement;
obtaining the emergent power of the mth super-surface unit
Calculating the received power from the mth super-surface unit to the receiving antenna by using the following formula
In the formula: λ is the operating wavelength.
Substituting equation (5) into equation (4) yields the following:
in the above technical solution, the obtaining of the emergent power of the mth super surface unit
One way of obtaining comprises the following steps:
obtaining the unit size of the mth super surface unit and further obtaining the amplitude response S m (l)；
Obtaining incident power of the mth super-surface unit
Calculating the emergent power of the mth super-surface unit based on the following formula
Substituting equation (7) into equation (6) yields the following:
in the above technical solution, the obtaining of the radiation phase of the mth super-surface unitBit beta m One way of obtaining comprises the following steps:
obtaining the cell size of the mth super-surface cell, and then obtaining the phase response
Obtaining the distance from the m-th super-surface unit to the central phase of the feed antenna
Calculating the radiation phase beta of the mth super-surface unit according to the following formula m ：
In the formula: k represents the free space wavenumber.
Substituting the formula (9) into any of the formulas (2), (4), (6) and (8) can obtain a new calculation of the radiation electric field E from the mth super-surface unit to the receiving antenna m One of the calculation formulas is as follows:
substituting equation (10) into equation (1) yields:
the calculation formula for calculating the wireless energy transfer efficiency is thus available:
in the calculation process using the formula (12), the super-surface unit is regarded as an independent radiation unit, and the problem that the near-field transmission efficiency is difficult to evaluate due to the overlarge super-surface caliber in the traditional method is solved because the caliber of a single unit is small and the far-field range is wide. By extracting the amplitude response and the phase response on the super-surface elements, the shape of the radiation beam is recorded. Therefore, the invention can accurately calculate the transmission efficiency of the radio frequency power no matter what relative position the receiving antenna and the super surface are in and no matter what form the energy transmission wave beam generated by the super surface is. Compared with a method of pure simulation and simulation evaluation, the method based on the numerical calculation has the advantages of high efficiency, high speed, convenience in use, small occupied calculation resource and the like.
In the above technical solution, the m-th super surface unit has ground incident power
One way of obtaining is by the following steps:
simulating and obtaining the surface electric field distribution of the m-th super-surface unit radiated by the feed horn
The incident power on each super-surface unit is calculated according to the following formula
In the formula: where δ is the area of the super surface unit.
In a second aspect, the present invention provides a computing apparatus for evaluating wireless rf power transmission efficiency of an electromagnetic super-surface, the apparatus comprising a computing module;
the computing module is configured to implement the following operations:
calculating incident power of super-surface unit
Extracting the amplitude response S of the units in the super surface according to the unit size distribution on the super surface and the corresponding relation between the super surface unit size and the amplitude-phase response m (l) Phase response
Determining the distance R from the geometric center of the mth super-surface unit to the phase center of the receiving antenna m Distance from the m-th super-surface unit to the central phase of the feed antenna
A rectangular coordinate system is established by taking the center of the super surface as the origin, and the space unit vector based on the rectangular coordinate system
Further obtaining the coordinate vector of the receiving antenna
Based on coordinate vectors
Angle of pitch theta m Azimuth angle
Obtaining the m-th super-surface unit
Actual gain in the direction of joint polarization with the receiving antenna
And acquire the receiving antenna at
Actual gain in the direction in the combined polarization state with the m-th super-surface cell
Obtaining feed power P of input feed source F ；
Substituting the obtained data into the following formula to calculate to obtain the transmission efficiency from the super surface to the receiving antenna
In the formula: k represents the free space wavenumber.
In the technical scheme, according to the relative position relation between the feed source and the super surface, the electric field distribution of the feed source radiated to the super surface is obtained through a simulation means, and the incident power on each super surface unit can be calculated according to Poynting's theorem; the super-surface unit is regarded as an independent radiation unit, and the problem that the near-field transmission efficiency is difficult to evaluate due to the fact that the caliber of a single unit is small and the far-field range is wide is solved, and the accuracy of near-field radio frequency efficiency evaluation of a wireless energy transmission system is greatly improved. By extracting the amplitude response and the phase response on the super-surface elements, the shape of the radiation beam is recorded. Therefore, the invention can accurately calculate the transmission efficiency of the radio frequency power no matter what relative position the receiving antenna and the super surface are in and no matter what form the energy transmission wave beam generated by the super surface is. Compared with a method for evaluating the radio frequency transmission efficiency of a wireless energy transmission system by only adopting commercial simulation software, the method for evaluating the radio frequency transmission efficiency of the wireless energy transmission system by adopting the numerical calculation has the advantages of high efficiency, high speed, convenience in use, small occupied calculation resource and the like.
Drawings
In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed to be used in the description of the embodiments are briefly introduced below, and it is obvious that the drawings in the following description are only some embodiments of the present application, and it is obvious for those skilled in the art to obtain other drawings based on these drawings without inventive labor.
FIG. 1 is a schematic diagram of the principle of the method using the present invention;
FIG. 2 is a schematic flow chart of the present invention;
FIG. 3 is a schematic diagram of an input power distribution of a super-surface unit in an embodiment of the present invention;
FIG. 4 is a schematic diagram of a four-layer square ring transmission unit according to an embodiment of the present invention;
FIG. 5 is a graph illustrating amplitude and phase response of a four-layer square ring transmission unit according to an embodiment of the present invention;
FIG. 6 is a schematic diagram of amplitude distribution of transmission coefficients of super-surface units in an embodiment of the present invention;
FIG. 7 is a schematic diagram of the compensated phase distribution of the super-surface units according to the embodiment of the present invention;
FIG. 8 is a diagram illustrating the far field gain direction of a four-layered square ring transmission unit according to an embodiment of the present invention;
fig. 9 is a schematic structural diagram of a receiving antenna used in the embodiment of the present invention;
FIG. 10 is a diagram illustrating the far field gain direction of a receiving antenna used in an embodiment of the present invention;
FIG. 11 is a schematic diagram of a wireless energy transfer system based on a transmissive super-surface in an embodiment of the present invention;
FIG. 12 is a graph illustrating the variation of the transmission efficiency of the wireless radio frequency power with the vertical distance under various methods according to the embodiment of the present invention;
FIG. 13 (a) is a schematic structural diagram of a reflective super-surface unit in an embodiment of the present invention;
FIG. 13 (b) is a graph illustrating the amplitude and phase response of an embodiment of the present invention as a function of the length of the unit branches;
FIG. 14 is a schematic view of a reflection-subsurface-based wireless energy transfer system as analyzed in an embodiment of the present invention;
fig. 15 is a schematic diagram illustrating a variation curve of the wireless rf power transmission efficiency evaluation with distance according to various methods in the embodiment of the present invention.
Detailed Description
The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and not all of the embodiments.
The invention aims to provide a numerical calculation method for evaluating the wireless radio frequency power transmission efficiency of an electromagnetic super surface, and the feed power of an input feed source is recorded as P F The received power of the receiving antenna is denoted as P H The expression for the transmission efficiency of the surface to the receiving antenna is
The principle of the invention is that the super-surface unit is regarded as an independent radiation unit, the radiation electric field radiated to a receiving antenna by the single super-surface unit is calculated by extracting the amplitude and phase response on the super-surface unit, the stability of a radiation directional diagram of the super-surface unit is based on the field superposition principle, and the required wireless energy transmission efficiency is calculated by Poynting theorem and the vector summation of the electric field. The schematic diagram is shown in fig. 1.
According to the principles of the present invention:
first, the received power from the mth super surface unit to the receiving antenna is written according to the conventional Friis formula as follows:
wherein: lambda is the wavelength of operation and,
the output power of the mth super-surface unit,
is the m-th superReceived power, R, of surface unit to receiving antenna m M =1,2, …, M is the total number of super-surface elements, which is the distance from the geometric center of the M-th super-surface element to the phase center of the receive antenna. Establishing a rectangular coordinate system by taking the phase center of the mth super-surface unit as an origin; space unit vector based on rectangular coordinate system
Further obtaining the coordinate vector of the receiving antenna
θ m Is based on coordinate vectors
The pitch angle of (a) of (b),
is based on coordinate vectors
Is measured.
Is the m-th super surface unit
The actual gain in the direction in the combined polarization state with the receiving antenna,
is a receiving antenna
Actual gain in the direction associated with the m-th super-surface cell polarization state.
Secondly, in the implementation process of the method, the super-surface unit is assumed to be uniformly radiated in all directions, so that the radiation power density W from the mth super-surface unit to the receiving antenna m Expressed as:
in the formula:
the received power of the mth super-surface unit to the receive antenna.
Then, according to Poynting's theorem, the radiation electric field E from the m-th super-surface unit to the receiving antenna can be written m ：
In the formula: η represents the free-space wave impedance; beta is a m Is the radiation phase of the mth super-surface element.
Next, the magnitude response S of the super-surface element is extracted based on the relationship with the element size l and the corresponding relationship between the super-surface element size and the magnitude response m (l) And phase response
Thereby, it is possible to obtain:
(I) Output power
And incident power
The relationship of (1) is:
(II) phase of radiation beta m And amplitude response
The relationship of (1):
in the formula: k represents the free space wavenumber.
Is the distance from the m-th super-surface element to the center phase of the feed antenna.
Finally, based on the data obtained above, a complete expression of the radiated electric field from the mth super-surface element to the receiving antenna is obtained as follows:
according to Poynting's theorem, the power density is obtained by utilizing the square of electric field assignment, the radiation power is obtained by multiplying the power density by the spherical area, the radiation electric field of each super-surface unit is subjected to vector superposition in the process, and the expression of the feed power of the input feed source can be obtained, which is shown as follows:
the calculation formula for calculating the wireless energy transfer efficiency is thus available:
as can be seen from equation (12), the method of the present invention, when implemented, needs to obtain data including:
(1) Total number of units M of the super surface;
(2) Incident power
(3) Extracting the amplitude response S of the units in the super surface according to the unit size distribution on the super surface and the corresponding relation between the unit size and the amplitude-phase response of the super surface m (l) Phase response
(4) Determining the distance R from the geometric center of the mth super-surface unit to the phase center of the receiving antenna m Distance from the m-th super-surface unit to the central phase of the feed antenna
(5) A rectangular coordinate system is established by taking the phase center of the mth super-surface unit as the origin, and a space unit vector based on the rectangular coordinate system
Further obtaining the coordinate vector of the receiving antenna
Based on coordinate vectors
Angle of pitch theta m Azimuth angle
Obtaining the m-th super-surface unit
Actual gain in the direction of joint polarization with the receiving antenna
And acquiring the receiving antenna at
Actual gain in the direction in the combined polarization state with the m-th super-surface cell
In one embodiment, the central working frequency of the wireless energy transmission system based on the transmission super surface is 10GHz, the transmitting end of the wireless energy transmission system is composed of the transmission super surface and a feed source loudspeaker, the beam radiated by the super surface is a focused beam with a focus located at (0.1,0,0.5) m, and the standard loudspeaker with 10GHz is used as the feed source. The super surface is composed of 18 multiplied by 18 super surface units, and the distance between the feed horn and the super surface is 150mm.
In this embodiment, the calculation flow is as shown in fig. 2. The operations of the flow diagrams may be performed out of order. Rather, the operations may be performed in reverse order or simultaneously. In addition, one or more other operations may be added to the flowchart. One or more operations may be removed from the flowchart.
Step 1: the incident power of the super-surface unit is calculated.
According to the relative position relation between the feed source and the super surface, an observation surface with the size of 216mm multiplied by 216mm is drawn through simulation to simulate the super surface, and the electric field distribution radiated onto the super surface by the feed source is extracted
The input power on each super-surface unit is calculated according to Poynting's theorem using the following equation
In the formula: where δ is the area of the super surface unit.
The power distribution in this example is shown in fig. 3, and the super-surface unit structure used for the calculation is shown in fig. 4, and the area thereof is 12mm × 12mm.
And 2, step: and extracting the amplitude response and the phase response of the super-surface unit.
The transmission super-surface unit used in this embodiment is a four-layer square ring transmission super-surface unit shown in fig. 4, the unit operates at 10GHz, the outer ring side length a =9mm, the unit side length d =12mm, the distance H =6mm between each layer, the line width Δ s =0.15mm,the thickness t =1mm of each layer of dielectric, the dielectric constant of the dielectric being 2.2. The phase and amplitude response of the cell as the inner loop becomes longer b is plotted in figure 5. According to the analyzed cell size distribution of the super surface and the corresponding relation between the cell size and the amplitude-phase (amplitude and phase) response of the super surface, the phase response beta is drawn c (l) The profile and the magnitude response | S (l) | profile are shown in fig. 6 and 7, respectively.
And step 3: and extracting three-dimensional far-field gain directional patterns of the super-surface unit and the receiving antenna respectively.
The far-field gain pattern of the super-surface unit in the array is obtained by using infinite periodic boundaries of commercial simulation software, and is shown in fig. 8. The structure of the receiving antenna in the wireless energy transmission system is shown in fig. 9, and a three-position gain directional pattern obtained by simulation or darkroom multi-probe measurement is shown in fig. 10.
And 4, step 4: the relative position between the receiving antenna and the super-surface is determined.
Fig. 11 is a schematic diagram of a wireless energy transmission system based on a transmission super-surface analyzed by the present embodiment. The position of the geometric center of the receiving antenna is expressed by coordinates with the center of the super surface as the origin of coordinates.
And 5: the prepared data is substituted into the proposed transmission efficiency evaluation formula (12).
For the wireless energy transmission system based on the transmission super surface analyzed in the embodiment, the prepared data is substituted into the formula (12), and the wireless radio frequency power transmission efficiency can be calculated.
According to the structural parameters of the components of the system, the wireless energy transmission system based on the transmission super surface is simulated by using high frequency electromagnetic simulation software HFSS, and the simulation model diagram is shown in FIG. 11. In a space rectangular coordinate system, receiving antennas move along tracks (0.1, 0, h) m,0.1m & lth & lt5m, and the positions of the receiving antennas are sequentially substituted into a formula (12) provided by the invention to calculate the wireless radio frequency transmission efficiency.
The results of the traditional Fris formula and the Gaubou formula are used as comparison, the wireless radio frequency power transmission efficiency is obtained through simulation and is used as an accurate result, and the correctness of the method for evaluating the transmission efficiency is verified through comparison.
The conventional Friis and Gaubou equations are shown below:
friis formula:
gaubou formula:
in the two formulas: g t And G r Far field gain patterns, A, of the transmitting and receiving antennas, respectively t And A r The effective apertures of the transmitting antenna and the receiving antenna, respectively, and R is the distance between the receiving antenna and the transmitting antenna.
Fig. 12 is a graph showing the variation curves of the efficiency of the rf power transmission obtained by the efficiency evaluation results obtained by the four methods as the vertical distance h between the receiving antenna and the super-surface is increased. It can be seen from fig. 12 that the result calculated by the method of the present invention is very close to the simulation result, especially in the near field range of h <5m, the calculation result of the method of the present invention is closer to the simulation result than the calculation result of the conventional formula, the accuracy is greatly improved, the method of the present invention not only can accurately record the information of the transmitted beam, but also accurately calculate the position of the focus.
In another embodiment, the center working frequency of the wireless energy transmission system based on the super surface is 2.45GHz, the transmitting end of the wireless energy transmission system is composed of the reflecting super surface and the feed horn, and the beam radiated by the super surface is a directional high-gain beam with the deflection angle of 2 degrees. The reflection super-surface unit selects a cross dipole reflection unit, the structure of which is shown in fig. 13 (a), and the structural parameters of the unit are as follows: the unit aperture size d =55mm, the medium thickness H =3mm, the branch width W =1mm, and the variation curve of the unit reflection phase and amplitude response with the branch length is shown in fig. 13 (b). The reflecting super-surface analyzed consists of 20 multiplied by 20 units, the feed horn is a standard horn of 2.45GHz, and the distance between the feed horn and the super-surface is 0.7m.
The specific implementation steps and required parameters are the same as in the previous embodiment.
According to the structural parameters of the components of the system, the wireless energy transmission system based on the transmission super surface is simulated by using high frequency electromagnetic simulation software HFSS, and the simulation model diagram is shown in FIG. 14. In a rectangular spatial coordinate system, the receiving antenna moves along (0, -rsin2 DEG, rcos2 DEG), 2 ≦ r ≦ 25 m. The positions of the receiving antennas are sequentially substituted into the formula provided by the invention to calculate the wireless radio frequency transmission efficiency. In order to compare and verify the efficiency evaluation accuracy of the invention, the results of the traditional Friis formula and the Gaubou formula are used as comparison, the wireless radio frequency power transmission efficiency is obtained through simulation as an accurate result, and as the vertical distance r between the receiving antenna and the super surface increases, the change curve of the radio frequency power transmission efficiency of the efficiency evaluation result obtained by the four methods is shown in fig. 15.
It can be seen from fig. 15 that the calculated results of the present invention are very close to the simulation results, especially in the near field range of h <10m, not only the variation trend of the simulation results is the same, but also the values are very close. Compared with the calculation result of the traditional formula, the calculation result of the method is closer to the simulation result, and the accuracy is greatly improved.
In conclusion, the calculation principle of the method is based on the electric field superposition principle, the super-surface unit is regarded as an independent radiation unit, the radiation electric field is independently calculated, and then the total transmission power is calculated through vector superposition, so that the accuracy of near-field calculation is improved. . The radiation beam shape of the super-surface is recorded by extracting the phase and amplitude response of each super-surface unit, and the transmission efficiency of any point in the super-surface radiation space can be calculated according to the beam shape no matter what form the energy transmission beam generated by the super-surface is. In the process of calculating the radiation electric field of the unit, a far-field gain directional diagram of the super-surface unit is introduced, the far-field gain directional diagram of the unit in the array is simulated through an infinite period boundary in high-frequency electromagnetic simulation software HFSS under the condition of considering unit coupling, and the calculation is carried out by combining a numerical calculation method.
Through the above description of the embodiments, those skilled in the art will clearly understand that the calculation method of the present disclosure can be implemented by software plus necessary general-purpose hardware, and certainly can also be implemented by special-purpose hardware including special-purpose integrated circuits, special-purpose CPUs, special-purpose memories, special-purpose components and the like. Generally, functions performed by computer programs can be easily implemented by corresponding hardware, and specific hardware structures for implementing the same functions may be various, such as analog circuits, digital circuits, or dedicated circuits. However, more often than not for the purposes of this disclosure, software program implementations are preferred embodiments.
Although the embodiments of the present invention have been described above with reference to the accompanying drawings, the present invention is not limited to the above-described embodiments and application fields, and the above-described embodiments are illustrative, instructive, and not restrictive. Those skilled in the art, having the benefit of this disclosure, may effect numerous modifications thereto without departing from the scope of the invention as defined by the appended claims.
Claims (9)
1. A computational method for evaluating wireless radio frequency power transfer efficiency of an electromagnetic super-surface, the method comprising the steps of:
obtaining the distance R from the geometric center of the mth super-surface unit to the phase center of the receiving antenna m M =1,2, …, M is the total number of super surface units;
obtaining the radiation electric field E from the m-th super-surface unit to the receiving antenna m ；
Based on said distance R m And E m Calculating the received power P of the receiving antenna according to the following formula H ：
In the formula: η represents the spatial wave impedance;
obtaining feed power P of input feed source F By using
Calculating the transmission efficiency from the super surface to the receiving antenna;
wherein a radiation electric field E from the m-th super-surface unit to the receiving antenna is obtained m The method comprises the following steps:
first, the received power from the mth super-surface unit to the receiving antenna is written according to Friis formula as follows:
wherein: lambda is the wavelength of operation and,
the output power of the mth super-surface unit,
for the received power, R, of the m-th super-surface unit to the receiving antenna m M =1,2, …, M being the total number of super-surface elements, being the distance from the geometric center of the mth super-surface element to the phase center of the receive antenna;
establishing a rectangular coordinate system by taking the phase center of the mth super-surface unit as an origin;
space unit vector based on rectangular coordinate system
Further obtain the receiving dayCoordinate vector of line
θ m Is based on coordinate vectors
The pitch angle of (a) of (b),
is based on coordinate vectors
The azimuth of (d);
secondly, suppose that the super-surface element is uniformly radiating omnidirectionally, so that the radiation power density W from the m-th super-surface element to the receiving antenna m Expressed as:
in the formula:
the received power from the mth super-surface unit to the receiving antenna;
then, writing a radiation electric field E from the mth super-surface unit to the receiving antenna according to Poynting's theorem m ：
In the formula: η represents the free-space wave impedance; beta is a beta m Is the radiation phase of the mth super-surface element;
next, the magnitude response S of the super-surface element is extracted based on the relationship with the element size l and the corresponding relationship between the super-surface element size and the magnitude response m (l) And phase response
Thereby obtaining:
(I) Output power
And incident power
The relationship of (1) is:
(II) phase of radiation beta m And amplitude response
The relationship of (1):
in the formula: k represents the wave number in free space,
the distance from the m-th super-surface unit to the central phase of the feed source antenna;
finally, based on the data obtained above, a complete expression of the radiated electric field from the mth super-surface element to the receiving antenna is obtained as follows:
according to Poynting's theorem, the power density is obtained by utilizing the square of electric field assignment, the radiation power is obtained by multiplying the power density by the spherical area, the radiation electric field of each super-surface unit is subjected to vector superposition in the process, and the expression of the feed power of the input feed source is obtained, which is shown as follows:
thereby obtaining a calculation formula for calculating the wireless energy transmission efficiency:
2. the method according to claim 1, characterized in that said radiated electric field is obtained by:
obtaining the radiation power density W from the m-th super-surface unit to the receiving antenna m ；
Obtaining the radiation phase beta of the mth super-surface unit m ；
Calculating the radiation electric field E from the mth super-surface unit to the receiving antenna according to the following formula m :
3. The method of claim 2, wherein the radiated power density W m The method comprises the following steps:
obtaining the received power from the m-th super-surface unit to the receiving antenna
The radiation power density W is obtained by the following calculation m ：
4. The method of claim 3, wherein the received power from the mth super-surface unit to the receive antenna
The method comprises the following steps:
establishing a rectangular coordinate system by taking the phase center of the mth super-surface unit as an origin;
space unit vector based on rectangular coordinate system
Further obtaining the coordinate vector of the receiving antenna
Based on coordinate vectors
Angle of pitch theta m Azimuth angle
Obtaining the m-th super-surface unit
Actual gain in the direction of joint polarization with the receiving antenna
And acquiring the receiving antenna at
Actual gain in the direction in the combined polarization state with the m-th super-surface cell
Obtaining the emergent power of the mth super surface unit
Calculating the received power of the mth super-surface unit to the receiving antenna by using the following formula
In the formula: λ is the operating wavelength.
5. The method of claim 4, wherein:
the emergent power of the m-th super surface unit is obtained
The method comprises the following steps:
obtaining the unit size of the mth super surface unit and further obtaining the amplitude response S m (l)；
Obtaining incident power of the mth super-surface unit
Calculating the emergent power of the mth super-surface unit based on the following formula
6. The method of claim 4, wherein:
the m-th super surface unit is arranged in
Actual gain in the direction of joint polarization with the receiving antenna
Obtaining through simulation;
the receiving antenna is arranged at
Actual gain in the direction in the combined polarization state with the m-th super-surface cell
The measurement is obtained by means of simulation or darkroom multi-probe measurement.
7. The method of claim 5, wherein the incident power of the mth super-surface unit
The method comprises the following steps:
simulated acquisition of feed horn radiationDistribution of surface electric field to the m-th super-surface unit
The incident power on the mth super-surface unit is calculated according to the following formula
In the formula: where δ is the area of the super surface unit.
8. The method according to any one of claims 2-7, wherein said obtaining a radiation phase β of the mth super-surface unit m The method comprises the following steps:
obtaining the cell size of the mth super-surface cell, and then obtaining the phase response
Obtaining the distance from the mth super-surface unit to the phase center of the feed antenna
Calculating the radiation phase beta of the mth super-surface unit according to the following formula m ：
In the formula: k represents the free space wavenumber.
9. A computing device for assessing wireless radio frequency power transfer efficiency of an electromagnetic super-surface, the device comprising a computing module;
the computing module is configured to implement the following operations:
calculating incident power of super-surface unit
Extracting the amplitude response S of the units in the super surface according to the unit size distribution on the super surface and the corresponding relation between the size and the amplitude-phase response of the units on the super surface m (l) Phase response
Determining the distance R from the phase center of the mth super-surface unit to the phase center of the receiving antenna m Distance between the m-th super-surface unit and the phase center of the feed antenna
A rectangular coordinate system is established by taking the phase center of the mth super-surface unit as the origin, and a space unit vector is based on the rectangular coordinate system
Further obtaining the coordinate vector of the receiving antenna
Based on coordinate vectors
Angle of pitch θ of m Azimuth angle
Obtaining the m-th super-surface unit
Direction and receptionActual gain of antenna under joint polarization state
And acquire the receiving antenna at
Actual gain in the direction in the combined polarization state with the m-th super-surface cell
Obtaining feed power P of input feed source F ；
Substituting the obtained data into the following formula to calculate to obtain the transmission efficiency from the super surface to the receiving antenna
In the formula: k represents the free space wavenumber.
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| CN110033073A (en) * | 2019-04-15 | 2019-07-19 | 西安电子科技大学 | Radio frequency energy based on Meta Materials collects RFID tag system |
| CN114336073A (en) * | 2021-12-31 | 2022-04-12 | 北京邮电大学 | Super surface unit and super surface energy collector with same |
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| CN114401031B (en) * | 2022-01-21 | 2024-04-16 | 中国人民解放军国防科技大学 | Intelligent super-surface-based secure communication method in radiation mode |
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| CN110033073A (en) * | 2019-04-15 | 2019-07-19 | 西安电子科技大学 | Radio frequency energy based on Meta Materials collects RFID tag system |
| CN114336073A (en) * | 2021-12-31 | 2022-04-12 | 北京邮电大学 | Super surface unit and super surface energy collector with same |
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