Electric field uniformity analysis method

Abstract

The invention relates to the technical field of microwaves, and particularly discloses an electric field uniformity analysis method which comprises the following steps: firstly, establishing a geometric model of a microwave resonant cavity in a COMSOL, then inputting electromagnetic performance parameters of a cavity wall and a material in the cavity, and then feeding an electromagnetic field into the microwave resonant cavity, electromagnetic field distribution follows a Maxwell equation set; in the microwave resonant cavity, performing electric field analysis by taking a symmetry plane in the height direction as a reference, then selecting an upper plane position and a lower plane position of the symmetry plane, continuing to perform analysis, and extracting electric fields on X and Z coordinate direction paths on the planes; according to the extracted electric field data, the electric field extreme value difference and the variable coefficient in the cavity plane in the coordinate path direction are analyzed, and according to the analysis result, the uniformity of the electric field intensity in the plane is qualitatively evaluated. By analyzing the uniformity of the electric field, the temperature uniformity of material heating in the microwave cavity structure mode is determined.

Description

Technical Field

[0001] The invention relates to the field of microwave technology, and in particular to a method for analyzing the electric field uniformity of a microwave resonance cavity under the condition of introducing a mode stirrer. Background Art

[0002] It is well known that the resonant mode of the electromagnetic field in the microwave resonant cavity will lead to the uneven distribution of electromagnetic power density in space, which is one of the main challenges facing the current microwave heating technology. The uniformity of the electric field distribution directly affects the heating effect of the composite material. The more uniform the electric field, the more uniform the heating process of the composite material. However, the uneven distribution of the electric field often leads to local overheating and ablation of the composite material during the heating process, and some areas may not be fully cured, which greatly limits the promotion and application of microwave heating technology in the field of composite materials. Therefore, how to effectively improve the uniformity of microwave heating and propose a scientific and reasonable judgment method has become a key issue that needs to be solved in the field of microwave energy application.

[0003] In response to the above problems, there have been many related studies in this field. For example, the invention patent application with application number 202311529571.X discloses a power distribution method for improving the uniformity of the electromagnetic field in the resonant cavity. This method analyzes the field distribution under multiple resonant modes through electromagnetic simulation and MATLAB to determine the optimal power distribution method. However, this method relies too much on complex simulation and calculation, which may lead to longer computing time and the demand for high-performance computing resources. For example, the invention patent with authorization announcement number CN114665242B discloses a device for improving the uniformity of the electromagnetic field in a microwave cavity using an adjustable artificial magnetic conductor, and discloses an adjustable artificial magnetic conductor for improving the uniformity of the electromagnetic field in the microwave cavity. By adjusting the total reflection state of the magnetic conductor, the distribution of the electromagnetic field in the cavity can be optimized. The method for improving the uniformity of the electromagnetic field is to observe the changes in the distribution of nodes and amplitudes in the electromagnetic field. However, the adjustment process of the adjustable artificial magnetic conductor is complicated, requiring high-precision control, and it is impossible to quantitatively describe the improvement effect of the electric field strength, which increases the difficulty of operation. For another example, the invention patent with the authorization announcement number CN107104262B discloses a method and a resonant cavity structure for improving the uniformity of the electromagnetic field distribution of a microwave resonant cavity, and specifically discloses that a plurality of strong electromagnetic field regions and weak electromagnetic field regions are set in the microwave resonant cavity, and these regions are separated by a perforated isolation boundary. The electromagnetic field in the weak electromagnetic field region is introduced after multiple reflections from the boundary of the strong electromagnetic field region, thereby effectively heating the object in the weak electromagnetic field region. However, the resonant cavity structure in this method is complex, which may cause electromagnetic field leakage and uneven heat distribution, affecting the heating efficiency and uniformity of the target object. Summary of the invention

[0004] The purpose of the present invention is to provide an electric field uniformity analysis method to solve the problems raised in the background technology. Based on Maxwell's equations, the present invention uses COMSOL multi-physics field software to calculate the electromagnetic field distribution inside the cavity, and qualitatively evaluates the uniformity of the electromagnetic field inside the cavity by analyzing the two indicators of the electric field extreme value difference and the coefficient of variation along the coordinate path in the cavity plane.

[0005] To achieve the above object, the present invention provides an electric field uniformity analysis method, which is applicable to a microwave resonant cavity under the condition of introducing a mode stirrer, and the method comprises the following steps:

[0006] S1. Establish an electromagnetic field model: First, establish the geometric model of the microwave resonant cavity in COMSOL, then input the electromagnetic performance parameters of the cavity wall and the internal materials of the cavity, and then feed the electromagnetic field into the microwave resonant cavity. The electromagnetic field distribution follows Maxwell's equations, and the partial differential equation is as follows (1):

[0007]

[0008] In formula (1), is the Hamiltonian operator, is the magnetic field strength, is the electric displacement vector, is the current density, is the electric field strength, Magnetic induction intensity, is the space charge density, t is the time and is the spatial position;

[0009] Step S2, extracting finite element result data: in the microwave resonant cavity, the electric field analysis is performed based on the symmetry plane in the cavity height direction, and then a plane position above and below the symmetry plane is selected to continue the analysis; the electric field data on the X and Z coordinate direction paths are extracted on these planes;

[0010] Step S3, processing the uniformity data of the electric field strength: analyzing the electric field extreme value difference and the coefficient of variation along the coordinate path in the cavity plane according to the electric field data extracted in step S2, and qualitatively evaluating the uniformity of the electric field strength in the plane according to the analysis results; wherein the coefficient of variation is calculated as follows:

[0011]

[0012] In formula (2), Cov is the coefficient of variation, N is the total number of statistical electric field strengths, |E i | is the absolute value of the statistical electric field strength, i is the electric field strength number, is the average value of the electric field strength.

[0013] Furthermore, the electromagnetic loss of the cavity wall is ignored during the analysis, and the boundary condition of the electromagnetic field in the resonant cavity can be expressed as:

[0014]

[0015] In formula (3), is the normal unit vector of the corresponding surface, is the surface current density, is the surface charge density.

[0016] Furthermore, 4-8 microwave slot antennas are arranged inside the microwave resonance cavity, and the input power of each microwave slot antenna is 500-3000W.

[0017] Furthermore, in step S2, a plane is selected above and below the symmetry plane and at a position of 1 / 6 to 1 / 5 of the cavity height to extract the electric field strength, and the two planes are symmetrically arranged with respect to the symmetry plane.

[0018] Furthermore, in step S3, the calculation formula for the extreme value difference of the electric field intensity in the plane or in the path direction is:

[0019] R=E max -E min (4)

[0020] Among them, R is the extreme value difference of the electric field intensity in the direction of the coordinate path in the plane, and E max is the maximum value of the electric field intensity on the coordinate path in the plane, E min is the minimum value of the electric field intensity on the coordinate path in the plane.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] The electric field uniformity analysis method of the present invention can accurately predict the electric field distribution of a perturbation resonant cavity through finite element simulation and theoretical calculation, thereby optimizing the design and reducing problems in experiments; it can identify potential design defects or performance problems in advance through simulation, reduce the number of tests and modifications of physical prototypes, and thus save development time and cost; it can explore different design parameters and configurations in the design stage, find the best design solution, and improve the overall performance of the resonant cavity; it can verify the accuracy of theoretical calculations through simulation, and ensure the effectiveness of theoretical models in practical applications; it allows detailed analysis under complex geometries and material properties, and is suitable for design problems that are difficult to handle with traditional calculation methods.

[0023] In addition to the above-described purposes, features and advantages, the present invention has other purposes, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings are used to provide a further understanding of the embodiments of the present invention and constitute a part of the specification. Together with the following specific implementations, they are used to explain the embodiments of the present invention, but do not constitute a limitation on the embodiments of the present invention. In the accompanying drawings:

[0025] Figure 1 It is a schematic diagram of a finite element model of an electromagnetic field of a microwave resonant cavity in an electric field uniformity analysis method of the present invention;

[0026] Figure 2 The figure shows the change of electric field intensity in the microwave resonant cavity with distance when no mode stirrer is introduced; (a) is the change of electric field intensity in the X direction, and (b) is the change of electric field intensity in the Z direction;

[0027] Figure 3 1 is the electric field distribution on the working plane position path in the stirrer mode of the present invention; (a) is the change of electric field intensity in the X direction, and (b) is the change of electric field intensity in the Z direction;

[0028] Figure 4 It is a schematic diagram of the optical fiber position distribution in the present invention;

[0029] Figure 5 Schematic diagram of the curve of the change of the temperature of the composite material heated by microwave over time in the present invention; (a) is the change under the condition of the mode stirrer speed of 0 r / min, (b) is the change under the condition of the mode stirrer speed of 5.6 r / min;

[0030] Among them, 1-temperature measuring optical fiber; 2-the 4th layer of unidirectional laminate; 3-the 5th layer of unidirectional laminate. DETAILED DESCRIPTION

[0031] The present invention will be described in detail below in conjunction with the various embodiments shown in the accompanying drawings, but it should be noted that these embodiments are not limitations of the present invention, and any equivalent transformations or substitutions in functions, methods, or structures made by ordinary technicians in the field based on these embodiments are all within the scope of protection of the present invention.

[0032] See also Figure 1 , an embodiment of the present invention provides an electric field uniformity analysis method for a microwave resonant cavity under the condition of introducing a mode stirrer, mainly for the case of introducing a mode stirrer in the microwave resonant cavity, to evaluate the electric field uniformity inside the resonant cavity containing the mode stirrer. By analyzing the electric field uniformity, the temperature uniformity of the material heated in the microwave cavity structure mode can be determined. Therefore, reasonable and accurate electromagnetic field uniformity analysis is crucial to the molding quality of the material. The method specifically includes the following steps:

[0033] S1. Establish an electromagnetic field model: First, establish the geometric model of the microwave resonant cavity in COMSOL, then input the electromagnetic performance parameters of the cavity wall and the internal materials of the cavity, and then feed the electromagnetic field into the microwave resonant cavity. The electromagnetic field distribution follows Maxwell's equations, and the partial differential equation is as follows (1):

[0034]

[0035] In formula (1), is the Hamiltonian operator, is the magnetic field strength, is the electric displacement vector, is the current density, is the electric field strength, Magnetic induction intensity, is the space charge density, t is the time and is the spatial position;

[0036] Usually, the microwave resonant cavity is made of metal materials. In order to reduce the calculation time of the finite element model and provide relatively accurate simulation results, the electromagnetic loss of the cavity wall is ignored in the analysis process of the present invention. The boundary condition of the electromagnetic field in the resonant cavity can be expressed as:

[0037]

[0038] In formula (3), is the normal unit vector of the corresponding surface, is the surface current density, is the surface charge density.

[0039] In an embodiment of the present invention, four microwave slit antennas are arranged inside the microwave resonant cavity, and the input power of each microwave slit antenna is 500W. The interior of the microwave slit antenna is an air domain, and the mode stirrer is located in the rotating domain. As needed, the rotation speed of the mode stirrer can be set, the mesh type selects a dynamic mesh, and the analysis type adopts frequency domain-transient simulation. When the minimum mass of the unit is 0.001-0.002, the mesh of the model will be re-divided. During the implementation process, the total time is set to T=60 / n according to different rotation speeds, where n is the rotation speed of the mode stirrer (in RPM) and T is in seconds.

[0040] Step S2, extract finite element result data: The selection of the electric field analysis plane in the microwave resonant cavity is based on the symmetry plane y=0mm in the cavity height direction, and a plane position is selected above and below the symmetry plane. Specifically, the selection height of the two plane positions is 1 / 6 of the cavity height, that is, the plane y=200mm above the symmetry plane and the plane y=-200mm below the symmetry plane. Select the electric field distribution of two planes (y=200mm and y=-200mm) and the material working plane (y=-510mm). Extract the electric field on the path in the X and Z coordinate directions on these planes to accurately describe the change of the electric field strength along the path. The cross section and path direction are as follows: Figure 1 shown.

[0041] Step S3, data processing of uniformity of electric field strength: To evaluate the uniformity of the electric field strength in the plane, the present invention adopts the coefficient of variation (Cov) indicator. This method is practical and feasible in actual engineering design and manufacturing. The smaller the coefficient of variation, the more uniform the electric field distribution. The coefficient of variation is calculated based on the electric field data extracted in step S2, and the uniformity of the electric field strength in the plane is evaluated based on the calculation results; the calculation method of the coefficient of variation is:

[0042]

[0043] In formula (2), Cov is the coefficient of variation, N is the total number of statistical electric field strengths, |E i | is the absolute value of the statistical electric field strength, i is the electric field strength number, is the average value of the electric field strength. The smaller the extreme value difference of the electric field strength in the plane or path direction, the smaller the distribution change of the electric field strength. At the same time, according to the fact that the microwave power absorbed by the material is proportional to the square of the electric field strength, the more uniform the microwave absorption at different positions of the material during the heating process, the calculation formula for the extreme value difference of the electric field strength is:

[0044] R=E max -E min (4)

[0045] Among them, R is the extreme value difference of the electric field intensity in the direction of the coordinate path in the plane, and E max is the maximum value of the electric field intensity on the coordinate path in the plane, E min is the minimum value of the electric field intensity on the coordinate path in the plane.

[0046] Example

[0047] First, the geometric model of the microwave resonant cavity was established in the COMSOL software, and the electromagnetic performance parameters of the 304 stainless steel wall, the slit antenna and the air in the cavity were input. The input power of a single slit antenna is 500W, and the rotation speeds of the mode stirrer are 0r / min and 5.6r / min respectively. By comparing the uniformity of the electric field intensity in different coordinate directions of each plane under the condition of introducing the mode stirrer, the electromagnetic shielding condition was set on the stirrer surface, and the cavity boundary condition shown in equation (2) was set in COMSOL. When the rotation speed of the mode stirrer is 0r / min, the electric field at the positions of y=200mm, y=-200mm and y=-510mm (working plane) changes along the coordinate direction as shown in Figure 2 shown. Figure 2 It is shown in the figure that at different Y-section positions, the change of electric field strength along the X direction is relatively drastic. At the position of y=-510mm, the extreme value difference of the electric field strength is the largest, reaching 150003.749V / m. At y=200mm, the minimum extreme value difference of the electric field strength is also 112386.775V / m, which indicates that the temperature uniformity inside the material in the resonant cavity structure is poor. Compared with the X direction, the extreme value difference of the electric field strength in the Z direction is slightly relaxed. Specifically, at y=-200mm, the minimum extreme value difference of the electric field strength is 79788.857V / m, and at y=-510mm, the maximum extreme value difference is 91718.054V / m, indicating that under this electric field distribution condition, the change of electric field strength is still relatively drastic. From another perspective, according to the cavity electric field uniformity evaluation standard (Formula (3)), the coefficients of variation in the X and Z directions at the y = -200 mm position are 0.384 and 0.377, respectively, both of which are relatively low, indicating that the cavity electric field strength uniformity at this position is the best. In contrast, the coefficient of variation in the Z direction at the y = 200 mm position increases slightly, and the coefficients of variation in the X and Z directions are 0.383 and 0.400, respectively, indicating that the cavity electric field uniformity at this position decreases slightly. Furthermore, when at the working plane position, the coefficients of variation in the X and Z directions increase significantly, and the coefficients of variation in the X and Z directions are 0.584 and 0.645, respectively. This indicates that the electric field uniformity at the working table position is significantly lower than that at other positions, and the microwave heating effect of the composite laminate in the working plane is not good, so the design must be further optimized to improve the uniformity of the electric field.

[0048] When the speed of the mode agitator is 5.6r / min (taking the material heating plane as a representative), Figure 3As shown in the figure, in the y = -510mm working plane, the change of electric field intensity along the X or Z direction path shows that after the introduction of the mode stirrer, the change of electric field intensity on the X path is significantly reduced, and the maximum extreme value difference is only 6158.47V / m, which is 95.89% lower than that when the mode stirrer is not introduced. Similarly, the change of electric field intensity in the Z direction also shows a similar trend, and the maximum extreme value difference is reduced by 91.99%. However, in the range of X = 400-500mm and Z = 1100-1200mm, the change of the electric field intensity amplitude is relatively large, so when conducting microwave heating experiments, experiments should be avoided as much as possible in this range.

[0049] From another perspective, according to formula (3), the coefficients of variation in the X and Z directions at the position y = -510 mm are 0.44504 ​​and 0.51885, respectively, which are 23.8% and 19.53% higher than the case without the mode stirrer. In summary, it can be seen from the above two perspectives that the electromagnetic field is greatly improved after the mode stirrer is introduced.

[0050] In order to verify the accuracy of the analysis process of the present invention, a microwave heating experiment of a composite material was carried out. The composite material grade was T700 / TRE231, the ply angle was [0 / 90 / 0 / 90]s, and 1# to 5# temperature measuring optical fibers 1 were embedded in the composite material to characterize the heating temperature at different positions. The position distribution diagram of the temperature measuring optical fibers is shown in FIG. Figure 4 As shown, the five temperature measuring optical fibers 1 are all arranged between the fourth unidirectional laminate 2 (90°) and the fifth unidirectional laminate 3 (90°). The experimental process is to increase the temperature from room temperature to 130°C at a heating rate of 2°C / min and keep the temperature for 50 minutes. Figure 5 The microwave heating test results are as follows: Figure 5 (a) It can be seen that only the temperature of the 2# temperature measuring optical fiber completely coincides with the target temperature, and the temperatures of the other temperature measuring points deviate from the preset process, and the degree of deviation gradually increases as the process proceeds. This is mainly due to the existence of cold spots and hot spots with large electric field differences in the microwave field. At the end of the process, the maximum deviation between each temperature measuring point and the target temperature reaches 53.23°C, indicating that the electric field distribution in the microwave resonant cavity is extremely uneven, which fully verifies the correctness of the finite element result analysis of the present invention.

[0051] Figure 5 (b) shows the temperature changes of five locations (temperature measurement points) inside the composite material with the target temperature when the speed of the mode stirrer is 5.6 r / min. Figure 5Compared with (a), the difference between the temperature of each temperature measurement point and the target temperature is significantly improved, and the temperature change in the heating stage is basically linear, which shows that the heating rate is effectively controlled. The maximum temperature difference at the end of the process is 4.68 ° C, which shows that the introduction of the mode stirrer in the present invention can increase the number of modes in the cavity, thereby reducing the difference between the electric field strength of the cold spot and the hot spot in the electric field, and the results are consistent with the results of the finite element model.

[0052] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for analyzing electric field uniformity, characterized in that: Suitable for introducing a microwave resonant cavity under the condition of a mode stirrer, the method comprises the following steps: S1. Establish an electromagnetic field model: First, establish the geometric model of the microwave resonant cavity in COMSOL, then input the electromagnetic performance parameters of the cavity wall and the internal materials of the cavity, and then feed the electromagnetic field into the microwave resonant cavity. The electromagnetic field distribution follows Maxwell's equations, and the partial differential equation is as follows (1): In formula (1), is the Hamiltonian operator, is the magnetic field strength, is the electric displacement vector, is the current density, is the electric field strength, Magnetic induction intensity, is the space charge density, t is the time and is the spatial position; Step S2, extracting finite element result data: in the microwave resonant cavity, the electric field analysis is performed based on the symmetry plane in the cavity height direction, and then a plane position above and below the symmetry plane is selected to continue the analysis; the electric field data on the X and Z coordinate direction paths are extracted on these planes; Step S3, processing the uniformity data of the electric field strength: analyzing the electric field extreme value difference and the coefficient of variation along the coordinate path in the cavity plane according to the electric field data extracted in step S2, and evaluating the uniformity of the electric field strength in the plane according to the calculation and analysis results; wherein the coefficient of variation is calculated as follows: In formula (2), Cov is the coefficient of variation, N is the total number of statistical electric field strengths, |E i | is the absolute value of the statistical electric field strength, i is the electric field strength number, is the average value of the electric field strength.

2. The method according to claim 1, characterized in that The electromagnetic loss of the cavity wall is ignored during the analysis, and the boundary condition of the electromagnetic field in the microwave resonant cavity is expressed as: In formula (3), is the normal unit vector of the corresponding surface, is the surface current density, is the surface charge density.

3. The method according to claim 1, characterized in that 4-8 microwave slot antennas are arranged inside the microwave resonance cavity, and the input power of each microwave slot antenna is 500-3000W.

4. The method according to claim 3, characterized in that In the step S2, a plane is selected above and below the symmetry plane and at a position of 1 / 6 to 1 / 5 of the cavity height to extract the electric field strength.

5. The method according to claim 1, characterized in that In step S3, the calculation formula of the extreme value difference of the electric field intensity in the plane or in the path direction is: R=E max -AND min (4) Among them, R is the extreme value difference of the electric field intensity in the direction of the coordinate path in the plane, and E max is the maximum value of the electric field intensity on the coordinate path in the plane, E min is the minimum value of the electric field intensity on the coordinate path in the plane.

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