CN117691328A - Power distribution method for improving distribution uniformity of electromagnetic field in resonant cavity - Google Patents
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Abstract
The invention discloses a power distribution method for improving the distribution uniformity of an electromagnetic field in a resonant cavity, and belongs to the field of microwave energy transmission. According to the invention, superposition of multiple degenerate resonance modes is adopted, electromagnetic field distribution in a resonance cavity under a single resonance mode is obtained through electromagnetic simulation, and accurate field distribution expressions under different resonance modes are represented by MATLAB; and then, carrying out power distribution on each resonant mode in MATLAB, and calculating the variance of the magnetic field amplitude at the sample point under different power distribution modes, so as to quickly and accurately obtain the power distribution mode when the electromagnetic field distribution in the resonant cavity is most uniform. Under the condition that the total input power is unchanged, the method effectively improves the uniformity of electromagnetic field distribution in the resonant cavity, and reduces the occurrence of resonance zero points, thereby reducing the area with low energy transmission efficiency in the resonant cavity and enabling stable high-efficiency wireless energy transmission to be possible.
Description
Technical Field
The invention belongs to the field of microwave energy transmission, and particularly relates to a power distribution method for improving the distribution uniformity of an electromagnetic field in a resonant cavity.
Background
With the rising of the mobile internet and the internet of things and the continuous innovation of wireless communication technology, the wireless interconnection technology and products deeply influence the production and life modes of people at all levels. In order to solve the problem of the last kilometer of power transmission, researchers have proposed the concept of wireless power transmission. Wireless energy transfer refers to a process of transferring energy wirelessly from a source to a load. Currently, wireless energy transmission technologies mainly include electromagnetic induction type, magnetic resonance type, radiation type and the like. In recent years, there are well established theories about these technologies, and mature commercial applications have been found in some fields. But when the transceiver is too far apart or there is an obstacle in between, the efficiency of the wireless energy transfer system will drop dramatically. In addition, most of these systems can only perform single-to-single wireless power transmission, which greatly restricts the further development of wireless power transmission technology in the civil field. Therefore, in order to solve the above problems, researchers have proposed a cavity resonance type wireless energy transmission technology based on these technologies, which can theoretically realize full-space and multi-target energy transmission and has a wide application prospect.
However, the microwave resonant cavity commonly used at present is mainly a single-mode resonant cavity, such as 'Cavity Resonator Wireless Power Transfer System for Freely Moving Animal Experiments', and adopts TM 110 A resonant mode. The disadvantage of this structure is that the electromagnetic field in the interior space of the cavity is unevenly distributed, there are magnetic field resonance nulls, and the received energy at different locations within the cavity is also significantly different. Currently, researchers mostly increase the efficiency at each point as much as possible through dynamic impedance matching, but this greatly increases the complexity of the system and increases its cost of use. There are also some wireless energy transmission systems "Three-Dimensional Charging via Multimode Resonant Cavity Enabled Wireless Power Transfer" based on multimode resonant cavities, which employ TE 011 And TE (TE) 012 The two resonant modes respectively work under two frequencies, corresponding receiving ends are designed aiming at different resonant modes, and each time the corresponding resonant modes need to be manually selected according to the positions of the receiving ends, so that the design complexity is increased, and the resonant modes cannot be applied in actual life. Therefore, how to improve the field distribution uniformity in the resonant cavity on one hand, and eliminate the resonance zero point as much as possible on the other hand, and reduce the area with low wireless energy transmission efficiency in the resonant cavity is also a current research hot spot.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a power distribution method for improving the distribution uniformity of an electromagnetic field in a resonant cavity by superposition of multiple degenerate resonant modes. The method comprises the steps of firstly obtaining electromagnetic field distribution in a resonant cavity under a single resonant mode through electromagnetic simulation, and accurately representing field distribution expressions under different resonant modes by means of MATLAB; and then, carrying out power distribution on each resonant mode in MATLAB, and calculating the variance of the magnetic field amplitude at the sample point under different power distribution modes, so as to quickly and accurately obtain the power distribution mode when the electromagnetic field distribution in the resonant cavity is most uniform. Under the condition of constant total input power, the uniformity of electromagnetic field distribution in the resonant cavity is improved, and the occurrence of resonance zero points is reduced, so that the area with low energy transmission efficiency in the resonant cavity is reduced, and stable high-efficiency wireless energy transmission is possible.
The technical aim of the invention is realized by the following technical scheme:
the power distribution method for improving the distribution uniformity of the electromagnetic field in the resonant cavity is characterized by comprising the following steps of:
s1, a resonant cavity is established, the working frequency and a corresponding group of degenerate resonant modes are determined, and the total number of the resonant modes is N.
S2, setting a magnetic field amplitude variance functionTo characterize the uniformity of the field distribution within the resonant cavity; wherein H is q Magnetic field amplitude representing the q-th sample point in the resonator,/->Representing the average value of the magnetic field amplitude at all sample points in the resonant cavity, q=k 3 The total number of sample points in the resonant cavity when K sample points are uniformly taken in the X, Y, Z direction is shown.
S3-1, simulating an ith resonant mode of the excitation resonant cavity, and then extracting magnetic field amplitude values at Q sample points to obtain a magnetic field amplitude variance D of the ith resonant mode i ；
According to the general field distribution expression of the ith resonance mode, calculating the magnetic field amplitude variance D 'corresponding to the Q sample points' i 。
S3-2. Adjusting the amplitude H in the field distribution expression of the ith resonant mode i Is set to a value of D i With D' i Identical, thereby determining H in the ith resonant mode i And further determines the field distribution expression for which the ith resonant mode is accurate.
S3-3. Repeating steps S3-1 to S3-2 to determine N accurate field distribution expressions of the resonant modes.
S4, according to a resonance mode superposition principle, the N accurate field distribution expressions of the resonance modes are linearly superposed, then a distribution variance function D of a superposition magnetic field in the resonance cavity under different power distribution is calculated, and P corresponding to the minimum time of D is obtained i Thereby finally determining the power distribution mode; wherein,P i representing the power of the ith resonant mode, P i The value of (2) is 0-1.
Further, in step S3-1, step S3-2, MATLAB is used to calculate the magnetic field amplitude variance D' i In step S4, MATLAB is used to calculate the distribution variance function D of the superimposed magnetic field inside the resonant cavity under different power distributions.
Further, the resonant cavity is a metal closed resonant cavity or a super-surface resonant cavity.
The beneficial effects of the invention are as follows:
the power distribution method for improving the distribution uniformity of the electromagnetic field in the resonant cavity is suitable for resonant cavities with different sizes and super-surface resonant cavities, and has wide application range and strong practicability.
The power distribution method for improving the distribution uniformity of the electromagnetic field in the resonant cavity adopts degenerate resonant modes, namely the resonant frequencies of each resonant mode are the same, so that the receiving end does not need to carry out multi-frequency work, and the design complexity of the system is reduced.
The power distribution method for improving the uniformity of electromagnetic field distribution in the resonant cavity can calculate by means of commercial mathematical software MATLAB, so that the electromagnetic field distribution after superposition of multiple modes can be accurately represented, further, the optimized power distribution modes of different resonant modes can be rapidly and accurately determined, repeated work of frequently leading out a magnetic field is avoided, and time and energy are saved.
The power distribution method for improving the distribution uniformity of the electromagnetic field in the resonant cavity can improve the distribution uniformity of the electromagnetic field in the resonant cavity, so that the energy received by the receiving end at each position in the resonant cavity is as consistent as possible, the movement of the receiving end at each position in the resonant cavity is avoided, the output voltage in the circuit is greatly fluctuated, and the efficient and stable wireless energy transmission can be performed in the resonant cavity.
The power distribution method for improving the distribution uniformity of the electromagnetic field in the resonant cavity can reduce the occurrence of resonance zero points, thereby effectively reducing the area with low energy transmission efficiency in the resonant cavity and avoiding that certain positions in the resonant cavity cannot transmit wireless energy.
Drawings
FIG. 1 is a flow chart of a power distribution method for improving uniformity of electromagnetic field distribution in a resonant cavity;
FIG. 2 is a schematic diagram of a metal resonator in an embodiment;
FIG. 3 is a graph showing the magnetic field amplitude variance at different power distributions in an embodiment;
FIG. 4 is a simulated excited TE of the embodiment 203 A comparison graph of the resonance mode magnetic field distribution (a) and the magnetic field distribution (b) overall at the optimal power distribution ratio;
FIG. 5 is a simulated excited TE of an embodiment 203 A comparison of the front view of the resonant mode magnetic field distribution (a) and the magnetic field distribution (b) at the optimum power split ratio;
FIG. 6 is a simulated excited TE of an embodiment 203 A comparison of side views of resonant mode magnetic field distribution (a) and magnetic field distribution (b) at optimum power split ratio;
FIG. 7 is a simulated excited TE of an embodiment 203 Resonant mode magnetic field distribution (a) and optimizationA comparison of the top view of the magnetic field distribution (b) at the power split ratio;
FIG. 8 is a graph showing the magnetic field distribution on a line segment taken in the X direction at the middle position of the resonant cavity;
fig. 9 is a graph showing the magnetic field distribution on a line segment taken in the Z direction at the middle position of the resonant cavity.
Detailed Description
The technical scheme of the present invention will be further described with reference to the accompanying drawings and examples, and the present invention includes but is not limited to the following examples.
Since the varying electric field can generate a magnetic field, the varying magnetic field can generate an electric field, so the present embodiment only presents the whole flow by optimizing the magnetic field amplitude. The flow chart of the present embodiment is shown in fig. 1, and includes the following steps:
s1, a metal closed resonant cavity shown in fig. 2 is established in ANSYS HFSS, wherein the length is a, the width is b, and the height is d. Wherein a is 1000mm, b is 1000mm, and d is 1000mm.
According to the size of the resonant cavity, the resonant frequencies corresponding to different resonant modes are calculated, and the calculation formula is shown in (1):
wherein epsilon is the dielectric constant in vacuum, mu is the magnetic permeability in vacuum, and each group of m, n and p values represents a resonant mode.
The resonant mode of the resonant cavity can be obtained from the main mode to the higher-order mode resonant frequency according to calculation. Here, in order to promote the uniformity of electromagnetic field distribution inside the resonant cavity as much as possible, on the one hand, and to facilitate the explanation, on the other hand, a set of degenerate resonant modes having more degenerate resonant modes is selected: TE (TE) 023 /TE 032 /TE 203 /TE 302 /TM 230 /TM 320 The resonance frequency was 540.4MHz.
S2, uniformly selecting 11 sample points in the resonant cavity according to the X, Y, Z direction, wherein Q=1331 sample points are selected in total.
S3, in ANSYS HFSS, respectively exciting the degenerate resonant modes, extracting the magnetic field amplitude values at the sample points under different resonant modes, and calculating the magnetic field distribution variance D of different resonant modes i 。
In MATLAB, the magnetic field amplitude variance D 'at these sample points in different resonance modes is calculated from the field distribution expression of each resonance mode' i 。
Wherein the general magnetic field distribution expression for the ith resonant mode at (x, y, z) is:
TE mnp resonance mode:
TM mnp resonance mode:
H zi ＝0 (7)
wherein j is an imaginary symbol, H i Is the magnetic field amplitude of the ith resonant mode, H xi 、H yi 、H zi X, Y, Z-side of sample points at coordinates (x, y, z) for the ith resonant mode, respectivelyComponent of the directed magnetic field, k c The cutoff wave number of the resonant mode, ω is the resonant angular frequency of the resonant mode.
In equations 2-8, once the cavity size and resonant mode are determined, most of the parameters are known quantities. Unknown quantity is only H i Its magnitude is related to the excitation signal strength; by adjusting H i The variance of the magnetic field amplitude of the sample point calculated by MATLAB is the same as the variance of the magnetic field amplitude of the sample point obtained by simulation, thus obtaining H i And thus the results of the simulation can be accurately simulated with MATLAB. In this example, TE is finally obtained 023 /TE 032 /TE 203 /TE 302 /TM 230 /TM 320 H corresponding to resonance mode i Sequentially 5.95, 8.86, 5.66, 8.63, 4052.75 and 4101.76.
S4, according to the principle of superposition of resonance modes, as shown in formula 9-formula 12, by means of MATLAB, accurate field distribution expressions of different resonance modes are linearly superposed to obtain magnetic field amplitudes at all sample points under a superposition field, and magnetic field amplitude variances at all sample points under different power distributions are calculated, so that the corresponding power distribution mode when the superposition field is most uniform is rapidly determined. In this embodiment, TE is finally obtained 023 /TE 032 /TE 203 /TE 302 /TM 230 /TM 320 The optimal power distribution modes of the six resonant modes are 0W, 0.85W, 0W and 0.15W.
Wherein H is x 、H y 、H z The magnetic field components of the superimposed field in the direction X, Y, Z of the sample point at (x, y, z), respectively, and H represents the magnetic field magnitude of the superimposed field at the sample point at (x, y, z).
FIG. 3 shows the variance of the magnetic field amplitude at a sample point in the cavity for different power distribution modes. It can be seen that compared with the magnetic field distribution of a single resonant mode, the power distribution mode finally optimized through MATLAB has the advantages that the uniformity is improved by 45.2%, and the uniformity of the magnetic field distribution in the resonant cavity is remarkably improved.
Fig. 4-7 are diagrams of the magnetic field distribution in the final optimized power splitting mode versus the different viewing angles of the magnetic field distribution in a single resonant mode. It can be seen that the magnetic field distribution of the resonant mode in the power distribution mode optimized by the method reduces the occurrence of resonance zero points, and the overall magnetic field distribution is more uniform, which means that compared with the magnetic field distribution of a single resonant mode in the power distribution mode, the superposition field of the resonant mode in the invention can effectively reduce the area with low energy transmission efficiency in the resonant cavity, and the whole resonant cavity can realize efficient and stable wireless energy transmission.
Fig. 8-9 show the magnetic field distribution on a line segment taken in the X and Z directions at the middle of the resonator, respectively. It can be seen that the magnetic field distribution in a multimode superposition can keep the maximum amplitude unchanged in a single resonance mode, while the minimum value is increased and the resonance zero is eliminated as much as possible.
In summary, the method of the invention can rapidly determine the optimized power distribution modes of different resonance modes in a shorter time, greatly improve the efficiency, avoid the repeated work of frequently leading out the magnetic field and save the time and energy.
It should be noted that this embodiment is only an illustration of the method of the present invention, and that different higher order degenerate resonant modes may be selected to achieve different effects. In addition, the invention can further simplify the flow within the allowable error range, does not need electromagnetic simulation, and only passes through MATLAB, calculating to determine H corresponding to different resonance modes according to the conservation of electromagnetic energy i The ratio relation between the two is still capable of obtaining an optimized result, and the simplified method is a qualitative research method, has the advantages of higher speed, has the defects of ideal effect, poor accuracy and error of about 5 percent.
While the invention has been described in terms of specific embodiments, any feature disclosed in this specification may be replaced by alternative features serving the equivalent or similar purpose, unless expressly stated otherwise; all of the features disclosed, or all of the steps in a method or process, except for mutually exclusive features and/or steps, may be combined in any manner.
Claims (3)
1. The power distribution method for improving the distribution uniformity of the electromagnetic field in the resonant cavity is characterized by comprising the following steps of:
s1, establishing a resonant cavity, and determining the working frequency and a corresponding group of degenerate resonant modes, wherein the total number of the resonant modes is N;
s2, setting a magnetic field amplitude variance functionTo characterize the uniformity of the field distribution within the resonant cavity; wherein H is q Magnetic field amplitude representing the q-th sample point in the resonator,/->Representing the average value of the magnetic field amplitude at all sample points in the resonant cavity, q=k 3 Representing the total number of sample points when K sample points are uniformly taken in the X, Y, Z direction in the resonant cavity;
s3-1, simulating an ith resonant mode of the excitation resonant cavity, and then extracting magnetic field amplitude values at Q sample points to obtain a magnetic field amplitude variance D of the ith resonant mode i ；
According to the general field distribution expression of the ith resonance mode, calculating the magnetic field amplitude variance D 'corresponding to the Q sample points' i ；
S3-2Adjusting the amplitude value H in the field distribution expression of the ith resonant mode i Is set to a value of D i With D' i Identical, thereby determining H in the ith resonant mode i Further determining an i-th accurate field distribution expression for the resonant mode;
s3-3, repeating the steps S3-1 to S3-2, and determining N accurate field distribution expressions of the resonant modes;
s4, according to a resonance mode superposition principle, the N accurate field distribution expressions of the resonance modes are linearly superposed, then a distribution variance function D of a superposition magnetic field in the resonance cavity under different power distribution is calculated, and P corresponding to the minimum time of D is obtained i Thereby finally determining the power distribution mode; wherein,P i representing the power of the ith resonant mode, P i The value of (2) is 0-1.
2. The power distribution method for improving electromagnetic field distribution uniformity in a resonant cavity as claimed in claim 1, wherein in step S3-1, step S3-2, MATLAB is used to calculate the magnetic field amplitude variance D' i In step S4, MATLAB is used to calculate the distribution variance function D of the superimposed magnetic field inside the resonant cavity under different power distributions.
3. A power distribution method for improving uniformity of electromagnetic field distribution in a resonant cavity according to claim 1 or 2, wherein said resonant cavity is a metal closed resonant cavity or a super surface resonant cavity.
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