Double-ridge waveguide cut by low-power microwave thermal cracking method and design method

Abstract

The invention discloses a double-ridge waveguide cut by a low-power microwave thermal cracking method and a design method, and relates to the technical field of microwave cutting. Comprising an electric field heating cavity, two metal ridges symmetrically arranged in a heating area, two stepped impedance converters symmetrically arranged at the two ends of the electric field heating cavity and waveguide ports arranged at the tail ends of the stepped impedance converters. A containing gap used for containing a to-be-cut material exists between the two metal ridges, and an inlet and an outlet of the to-be-cut material corresponding to the containing gap are symmetrically formed in the wall of the heating cavity. According to the invention, the problem of low energy utilization rate in microwave cutting of the low-loss material is solved, so that microwave hot cracking cutting of the low-loss brittle material at a low power level is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of microwave cutting, and more specifically to the technical field of double-ridge waveguide cut by low-power microwave thermal cracking method and design method. Background Art

[0002] Cutting of glass and ceramics has been applied in various industries, including microelectronics, transportation, optoelectronics and medical integrated electronics. Although these materials have desirable properties such as high temperature resistance (ceramics greater than 1000 ° C), corrosion resistance and high mechanical strength (compressive strength of some technical ceramics greater than 1000 MPa), their brittleness and low toughness make cutting difficult. Traditional cutting methods have their own limitations. Mechanical cutting produces burrs and microcracks, which affect edge quality. Water jet cutting can cause tool damage and material corrosion. Although laser cutting is highly accurate, it can cause surface damage, bubbles and unpredictable crack propagation. All of these methods are surface cutting techniques and can cause various surface problems. In contrast, microwave cutting provides a volumetric method that has the potential to more effectively address these challenges. Microwaves have been widely studied in the processing of glass and ceramics. Microwaves heat the material internally, and when the temperature exceeds the thermal crack threshold, thermal stress is generated, which promotes the cutting process. Given the bulk heating advantages and local heating characteristics of microwave technology, people have aroused great interest in its application in cutting materials. However, achieving efficient cutting is challenging due to the low loss of glass and alumina ceramics and the unfocused nature of microwave energy.

[0003] Nevertheless, due to the low loss of glass materials and the microwave energy density, researchers usually choose higher power levels when using microwave processing to process glass. For example, based on the thermally controlled fracture method, the power used when cutting glass plates using an internally heated circular microwave spot is 1kW. Previous studies have shown that a power of 1400W was used to study the microwave-induced crack growth behavior of ceramic materials. For microwave cutting of ceramics, hot crack and trajectory control methods were used, with powers ranging from 500 to 1500W. In these methods, the microwave power used for cutting is high and the energy utilization rate is relatively low. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problem of low energy utilization rate in microwave cutting of low-loss materials. The present invention provides a double-ridge waveguide cut by low-power microwave thermal cracking method and a design method.

[0005] In order to achieve the above-mentioned purpose, the present invention specifically adopts the following technical solutions:

[0006] One aspect of the present invention provides a double-ridge waveguide cut by a low-power microwave thermal cracking method, comprising an electric field heating cavity, two metal ridges symmetrically arranged in a heating region, two step impedance converters symmetrically arranged at both ends of the electric field heating cavity, and a waveguide port arranged at the end of each step impedance converter;

[0007] There is a receiving gap between the two metal ridges for placing the material to be cut, and the inlet and outlet of the material to be cut corresponding to the receiving gap are symmetrically arranged on the wall of the heating cavity.

[0008] Specifically, the 3D simulation model of the double-ridge waveguide is as follows Figure 1 As shown. Microwave power is introduced into the waveguide through the waveguide port and transmitted to the electric field heating cavity through the step impedance converter, which is used to reduce the gap between the metal ridges and enhance the electric field. Then, the material to be cut (thin glass plate and ceramic plate) is placed between the two ridges.

[0009] This double-ridge waveguide design improves energy coupling by 32 times compared to the conventional WR340 waveguide, enabling significant energy loading even for low-loss materials.

[0010] In one embodiment, the electric field heating cavity is a rectangular cavity, and the two metal ridges are symmetrically arranged inside the rectangular cavity along the length direction.

[0011] In one embodiment, the waveguide port is a WR340 waveguide port, and a flange is disposed at the end of the WR340 waveguide port.

[0012] In one embodiment, the WR340 waveguide port includes a first rectangular cavity and a second rectangular cavity, the size of the first rectangular cavity is larger than the size of the second rectangular cavity, the WR340 waveguide port is installed at one end of the first rectangular cavity, the second rectangular cavity is detachably installed at the other end of the first rectangular cavity through a flange, and the end of the second rectangular cavity is connected to one end of the electric field heating cavity.

[0013] In one embodiment, the two inlets and outlets are strip-shaped holes on the side wall of the electric field heating cavity symmetrically arranged along the length direction, and the width of each inlet and outlet is greater than or equal to the accommodation gap.

[0014] In one embodiment, two metal ridges are disposed inside the rectangular cavity in an up-and-down symmetrical manner along the length direction, and the two metal ridges are an upper metal ridge and a lower metal ridge respectively.

[0015] In one embodiment, the upper metal ridge is fixed or detachably installed at the top of the electric field heating cavity, and the lower metal ridge is fixed or detachably installed at the bottom of the electric field heating cavity.

[0016] In one embodiment, the upper metal ridge and the lower metal ridge each include two stepped mounting seats arranged at both ends to cooperate with the corresponding step impedance converter, a horizontal mounting seat connected between the two stepped mounting seats, and a convex strip arranged on each horizontal mounting seat along the length direction.

[0017] In one embodiment, the convex strips of the upper metal ridge are located on the lower surface of the horizontal mounting seat, and the convex strips of the lower metal ridge are mounted on the upper surface of the corresponding horizontal mounting seat.

[0018] In one embodiment, the length of the protruding strip is the same as that of the horizontal mounting seat, and two ends of the protruding strip are aligned with two ends of the horizontal mounting seat.

[0019] Another aspect of the present invention provides a design method for a double-ridge waveguide cut by a low-power microwave thermal cracking method, using the above-mentioned double-ridge waveguide cut by a low-power microwave thermal cracking method, comprising the following steps:

[0020] S1. The influence of double-ridge waveguide size on transmission performance was analyzed through electromagnetic thermal simulation, and the double-ridge waveguide model with the best size was determined;

[0021] S2, performing electromagnetic thermal simulation on the double-ridge waveguide model obtained in step S1 to optimize the double-ridge waveguide model and improve the electric field concentration in the double-ridge waveguide model;

[0022] S3, performing multi-physics field simulation on the double-ridge waveguide model obtained in step S2 to study the influence of dielectric constant, material thickness, short-circuit surface position and movement speed on the heating process;

[0023] S4. Establish an experimental system, and for the double-ridge waveguide model obtained in step S3, cut alumina ceramic and glass plates at powers of 200 W and 300 W respectively.

[0024] In one embodiment, in step S1 to step S2, in order to quantitatively predict the propagation of the electromagnetic field, the application of Maxwell's equations is as follows:

[0025]

[0026] in, represents the magnetic field, represents the magnetic field strength, is the electric displacement vector, and ρ e are the conduction current density and the free charge density, respectively. and ρ e are all assumed to be zero;

[0027] According to the electric field calculated using Maxwell's equations, the absorbed power P of the thin glass sheet is a The calculation formula of energy efficiency η is as follows:

[0028]

[0029] Among them, P i is the input power of the double-ridge waveguide, and Q represents the heat source;

[0030] Heat is generated by electromagnetic power loss, and the temperature change can be calculated using the heat conduction equation:

[0031]

[0032] Where ρ represents density, C ρ is the specific heat capacity, k refers to thermal conductivity, Q(t) represents the power dissipation density and T represents the temperature;

[0033] The motion of the short-circuit surface is modeled using coordinate transformation theory to reduce the computational complexity of dealing with moving boundaries in microwave simulations. The coordinate transformation is defined as follows:

[0034]

[0035] in, and Represent the position vectors in the original coordinate system and the transformed coordinate system respectively;

[0036] Under this transformation, the dielectric constant ε r and magnetic permeability μ r In the new coordinate system it can be described by the following equation:

[0037]

[0038] Where Λ is the transformation matrix, which is defined as:

[0039] Λ=(detJ)·(J -1 ) T ;

[0040] Where J is the Jacob matrix describing the deformation of the coordinate system under transformation. The transformation of electric and magnetic fields between the original coordinate system and the transformed coordinate system can be expressed as:

[0041]

[0042] In one embodiment, in step S1 to step S3, the input parameters and boundary conditions are:

[0043] The relative dielectric constants of alumina ceramic thin plates and glass thin plates at a frequency of 2.45 GHz are used, and the remaining parameters are from the COMSOL material library. In addition, it is assumed that the physical parameters of alumina ceramic thin plates and glass thin plates remain unchanged when the temperature changes;

[0044] In the simulation, except for the WR340 waveguide port, all cavity surfaces of the double-ridge waveguide are specified as perfect electric conductors. The electric field at a perfect electric conductor is perpendicular to the conductor surface and is calculated as follows:

[0045]

[0046] in, is the unit normal vector of the cavity surface, and is the electric field vector;

[0047] Heat transfer boundary conditions are considered to account for the natural convection that occurs between the air and the material in the microwave cavity during microwave heating:

[0048]

[0049] Where h represents the heat transfer coefficient of air, which is usually taken as 10W / (m 2 K), and represents the temperature of the air, T air Indicates the air temperature.

[0050] The beneficial effects of the present invention are as follows:

[0051] 1. This invention is used to perform microwave cutting of low-loss materials at lower power levels. By compressing the electric field, we can significantly enhance the absorption of microwave energy by these materials, thereby achieving effective cutting at lower power. This research is expected to be applied to precision manufacturing fields such as electronics, optical devices and medical implants, where clean and efficient cutting of low-loss materials is critical. By enhancing the electric field strength rather than increasing the input power, our method provides a more energy-efficient method for microwave cutting.

[0052] 2. A new double-ridge waveguide was designed to enhance the microwave energy concentration between the ridges, so that the reflection coefficient (S11) reached -16.003dB and the electric field strength reached 5.51×10 5 V / m.

[0053] 3. Electromagnetic thermal simulation and multiphysics modeling prove that this waveguide design can increase energy coupling by 32 times compared to traditional waveguides and is very effective even for low-loss materials.

[0054] 4. The double-ridge waveguide shows excellent heating efficiency. When the microwave power is 400W, the maximum temperature rise of the material within 60 seconds is 113.85℃, which far exceeds the traditional waveguide design.

[0055] 5. Using the optimized waveguide, alumina ceramic and glass sheets were successfully cut at low power levels (200 W and 300 W, respectively), verifying the practical application of the design.

[0056] 6. The designed double-ridge waveguide can achieve an electric field strength of about 40kV / m at a frequency of 2.45GHz with a microwave power of 250W, which is about 2.5 times that of the WR340 waveguide. Heating the rubber film with a power of 150W in a single-ridge waveguide can achieve an electric field strength of more than 200kV / m, which is 77.9 times that of the WR340 single-mode waveguide. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0058] Figure 1 It is a schematic diagram of the three-dimensional structure of the present invention.

[0059] Figure 2 is a picture of the transmission and reflectance measurement system.

[0060] Figure 3 It is a picture of the microwave heating experimental system.

[0061] Figure 4 is a schematic diagram of the cross section of the device cavity, with the double ridge width represented as w and the distance represented as d.

[0062] Figure 5 It is a schematic diagram of the effect of waveguide size on transmission performance (S11).

[0063] Figure 6 It is a schematic diagram of the effect of waveguide size on the electric field size (V / m).

[0064] Figure 7 is a schematic diagram of the S parameters of the proposed double-ridge waveguide.

[0065] Figure 8 It is a schematic diagram of the WR340 waveguide.

[0066] Fig. 9 Cross-sectional diagram of the electric field distribution in (a) double-ridge waveguide and (b) WR340 waveguide.

[0067] Fig.10 It is a schematic diagram of the changes in the real part of the relative dielectric constant and the imaginary part of the relative dielectric constant.

[0068] Fig.11 It is a schematic diagram of the effect of glass sheet thickness (tan δ = 0.01).

[0069] Fig.12It is a schematic diagram of the effect of glass sheet thickness (tan δ = 0.1).

[0070] Fig.13 It is a schematic diagram of the effect of glass sheet thickness (tan δ = 1).

[0071] Fig.14 It is a schematic diagram showing the change in the position of the electric field amplitude point as the short-circuited surface moves.

[0072] Fig.15 Schematic diagram of the effect of the short-circuit surface position (tan δ = 0.01).

[0073] Fig.16 Schematic diagram of the effect of the short-circuit surface position (tan δ = 0.1).

[0074] Fig.17 Schematic diagram of the effect of the short-circuit surface position (tan δ = 1).

[0075] Fig.18 It is a schematic diagram of simulation results under different short-circuit surface velocities.

[0076] Fig.19 These are ceramic sheet samples and ceramic sheet cutting effect pictures.

[0077] Fig. 20 This is a diagram of heat distribution when cutting ceramic sheets.

[0078] Fig.21 Here are pictures of the cut glass sheets and glass plate samples.

[0079] Figure numerals: 1 - electric field heating cavity, 2 - step impedance converter, 3 - waveguide port, 4 - upper metal ridge, 5 - lower metal ridge, 6 - convex strip. DETAILED DESCRIPTION

[0080] In order to make the technical problems, technical solutions and technical effects of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0081] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0082] It should be noted that similar reference numerals and letters represent similar items in the following drawings, so once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings. In addition, the terms "first", "second", etc. are only used to distinguish the description and cannot be understood as indicating or implying relative importance.

[0083] In the description of the embodiments of the present invention, it should be noted that the terms "inside", "outside", "upper", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is usually placed when used. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0084] Example 1

[0085] like Figure 1 As shown, the present invention provides a double-ridge waveguide cut by a low-power microwave thermal cracking method, comprising an electric field heating cavity 1, two metal ridges symmetrically arranged in a heating area, two step impedance converters symmetrically arranged at both ends of the electric field heating cavity 1, and a waveguide port arranged at the end of each step impedance converter 2;

[0086] There is a receiving gap between the two metal ridges for placing the material to be cut, and the inlet and outlet of the material to be cut corresponding to the receiving gap are symmetrically arranged on the wall of the heating cavity.

[0087] Specifically, the 3D simulation model of the double-ridge waveguide is as follows Figure 1 As shown. Microwave power is introduced into the waveguide through the waveguide port and transmitted to the electric field heating cavity 1 through the step impedance converter 2, which is used to reduce the gap between the metal ridges and enhance the electric field. Then, the material to be cut (thin glass plate and ceramic plate) is placed between the two ridges.

[0088] This double-ridge waveguide design improves energy coupling by 32 times compared to the conventional WR340 waveguide, enabling significant energy loading even for low-loss materials.

[0089] The electric field heating cavity 1 is a rectangular cavity, and two metal ridges are symmetrically arranged inside the rectangular cavity along the length direction.

[0090] The waveguide port is a WR340 waveguide port 3, and a flange is provided at the end of the WR340 waveguide port 3.

[0091] The WR340 waveguide port 3 includes a first rectangular cavity and a second rectangular cavity. The size of the first rectangular cavity is larger than that of the second rectangular cavity. The WR340 waveguide port 3 is installed at one end of the first rectangular cavity. The second rectangular cavity is detachably installed at the other end of the first rectangular cavity through a flange. The end of the second rectangular cavity is connected to one end of the electric field heating cavity 1.

[0092] The two inlets and outlets are strip-shaped holes on the side wall of the electric field heating cavity 1 symmetrically arranged along the length direction, and the width of each inlet and outlet is greater than or equal to the accommodation gap.

[0093] Two metal ridges are arranged inside the rectangular cavity in a vertically symmetrical manner along the length direction, and the two metal ridges are an upper metal ridge 4 and a lower metal ridge 5 respectively.

[0094] The upper metal ridge 4 is fixedly or detachably installed on the top of the electric field heating cavity 1 , and the lower metal ridge 5 is fixedly or detachably installed on the bottom of the electric field heating cavity 1 .

[0095] The upper metal ridge 4 and the lower metal ridge 5 each include two stepped mounting seats arranged at both ends to match the corresponding step impedance converter 2, a horizontal mounting seat connected between the two stepped mounting seats, and a convex strip 6 arranged on each horizontal mounting seat along the length direction.

[0096] The convex strips 6 of the upper metal ridge 4 are located on the lower surface of the horizontal mounting seat, and the convex strips 6 of the lower metal ridge 5 are mounted on the upper surface of the corresponding horizontal mounting seat.

[0097] The length of the convex strip 6 is the same as that of the horizontal mounting seat, and two ends of the convex strip 6 are aligned with two ends of the horizontal mounting seat.

[0098] Example 2

[0099] This embodiment provides a design method for a double-ridge waveguide cut by a low-power microwave thermal cracking method, using the above-mentioned double-ridge waveguide cut by a low-power microwave thermal cracking method, comprising the following steps:

[0100] S1. The influence of double-ridge waveguide size on transmission performance was analyzed through electromagnetic thermal simulation, and the double-ridge waveguide model with the best size was determined;

[0101] S2, performing electromagnetic thermal simulation on the double-ridge waveguide model obtained in step S1 to optimize the double-ridge waveguide model and improve the electric field concentration in the double-ridge waveguide model;

[0102] S3, performing multi-physics field simulation on the double-ridge waveguide model obtained in step S2 to study the influence of dielectric constant, material thickness, short-circuit surface position and movement speed on the heating process;

[0103] S4. Establish an experimental system, and for the double-ridge waveguide model obtained in step S3, cut alumina ceramic and glass plates at powers of 200 W and 300 W respectively.

[0104] Specifically, the focus of this proposal is to design a double-ridge waveguide to solve this problem, aiming to optimize the transmission efficiency and the generation of local strong electric fields. This proposal solves the problem of low energy utilization in microwave cutting of low-loss materials, thereby realizing microwave thermal cutting of low-loss brittle materials at low power levels.

[0105] According to the microwave dissipation principle, it can be proved that the heat dissipation in the high-frequency electromagnetic field is the result of the material absorbing microwaves. The power loss expression per unit volume of the medium is as follows:

[0106]

[0107] Where Q is the power loss per unit volume (W / m 3 ), f represents microwave frequency, ε 0 Refers to the absolute dielectric constant of vacuum, ε r ″ represents the relative dielectric constant of the medium, and is the electric field strength. As can be seen from the formula, increasing the electric field strength is an effective way to achieve effective heating of low-loss materials.

[0108] The control equation of this embodiment is:

[0109] Microwave heating is a ubiquitous physical phenomenon that is classified as the interaction between electromagnetic and thermal fields. In order to make quantitative predictions about the propagation of electromagnetic fields, Maxwell's equations are applied as follows:

[0110]

[0111] in, represents the magnetic field, represents the magnetic field strength, is the electric displacement vector, and ρ e are the conduction current density and the free charge density, respectively. and ρ e are all assumed to be zero;

[0112] According to the electric field calculated using Maxwell's equations, the absorbed power P of the thin glass sheet is a The calculation formula of energy efficiency η is as follows:

[0113]

[0114] Among them, P i is the input power of the double-ridge waveguide, and Q represents the heat source;

[0115] Heat is generated by electromagnetic power loss, and the temperature change can be calculated using the heat conduction equation:

[0116]

[0117] Where ρ represents density, C ρ is the specific heat capacity, k refers to thermal conductivity, Q(t) represents the power dissipation density and T represents the temperature;

[0118] The motion of the short-circuit surface is modeled using coordinate transformation theory to reduce the computational complexity of dealing with moving boundaries in microwave simulations. The coordinate transformation is defined as follows:

[0119]

[0120] in, and Represent the position vectors in the original coordinate system and the transformed coordinate system respectively;

[0121] Under this transformation, the dielectric constant ε r and magnetic permeability μ r In the new coordinate system it can be described by the following equation:

[0122]

[0123] Where Λ is the transformation matrix, which is defined as:

[0124] Λ=(detJ)·(J -1 ) T ;

[0125] Where J is the Jacob matrix describing the deformation of the coordinate system under transformation. The transformation of electric and magnetic fields between the original coordinate system and the transformed coordinate system can be expressed as:

[0126]

[0127] Input parameters and boundary conditions of this example:

[0128] In step S1 to step S3, input parameters and boundary conditions:

[0129] The relative dielectric constants of alumina ceramic thin plates and glass thin plates at a frequency of 2.45 GHz are used, and the remaining parameters are from the COMSOL material library. In addition, it is assumed that the physical parameters of alumina ceramic thin plates and glass thin plates remain unchanged when the temperature changes;

[0130] In the simulation, except for the WR340 waveguide port, all cavity surfaces of the double-ridge waveguide are specified as perfect electric conductors. The electric field at a perfect electric conductor is perpendicular to the conductor surface and is calculated as follows:

[0131]

[0132] in, is the unit normal vector of the cavity surface, and is the electric field vector;

[0133] Heat transfer boundary conditions are considered to account for the natural convection that occurs between the air and the material in the microwave cavity during microwave heating:

[0134]

[0135] Where h represents the heat transfer coefficient of air, which is usually taken as 10W / (m 2 K), and represents the temperature of the air, T air Indicates the air temperature.

[0136] Table 1. Relevant input parameters

[0137]

[0138]

[0139] Dimensional optimization of the double-ridge waveguide of this embodiment

[0140] Through electromagnetic simulations and experimental evaluation, we systematically varied the width and spacing of the double-ridge waveguide to determine the most efficient configuration. The ridge width (w) and ridge spacing (d) varied in the experiment as shown in Figure 4 The key parameter used for optimization is the reflection coefficient S 11 , which represents the power reflected from the waveguide back to the light source. 11 The lower the value, the better the transmission characteristics, that is, the less energy is lost through reflection and the more energy is absorbed by the material. Figure 4 As shown in the figure, the tested ridge widths ranged from 0.2mm to 4.5mm, and the ridge spacings ranged from 1mm to 3mm. The results show that both ridge width and ridge spacing have a significant effect on the reflection coefficient. For example, with a ridge width of 0.2mm and a spacing of 1mm, the reflection coefficient is relatively low at -27.59dB. However, if the spacing is increased to 2mm, the reflection coefficient drops to -11.45dB. Similarly, for a ridge width of 1mm, a spacing of 1.4mm produces an extremely low reflection coefficient of -31.987dB, while increasing the spacing to 2mm produces -16.01dB. Figure 6 The electric field distribution of the cross section at the center of the waveguide is shown. It can be seen that the electric field is concentrated between the two ridges. After evaluating a series of configurations, a ridge width of 1mm and a ridge spacing of 2mm were finally selected as the optimized dimensions. This configuration was chosen because it takes into account both manufacturability and performance. 11The measured result is -16.01dB. The maximum electric field strength of this size can reach 5.51×10 5 V / m.

[0141] Transmission coefficient and reflection coefficient of the double-ridge waveguide of this embodiment

[0142] Transmission performance test setup

[0143] In order to verify the consistency between the simulated performance and the actual performance of the double-ridge waveguide, we used a vector network analyzer (N5230A, Agilent Technologies, USA) to measure the device under no-load condition, such as Figure 2 This setup allows for accurate measurements of transmission and reflection coefficients, especially S 11 and S 21 , which is crucial to understanding the impedance matching and transmission efficiency of the waveguide. 11 It indicates how much microwave power is reflected back to the sound source due to impedance mismatch, S 11 The lower the value, the better the impedance matching and the less energy loss caused by reflection. On the other hand, S 21 Displays the microwave power that successfully passes through the waveguide. The higher the value, the higher the energy transmission efficiency and the smaller the loss. The waveguide is connected to the vector network analyzer via a coaxial cable. The transition from waveguide to coaxial facilitates the connection between the analyzer and the waveguide.

[0144] By using S 11 and S 21 Simulations and experimental measurements were performed to evaluate the transmission performance of the double-ridge waveguide. 11 The value of is lower than -15dB and reaches -16.01dB at 2.45GHz, indicating that the waveguide has good impedance matching and low reflection loss at this frequency. 11 The experimental measurement value of is about -10dB, which is slightly higher than the simulation value, but the overall trend is consistent, which verifies the effectiveness of the simulation model. 21 The simulation and experimental results show that this parameter changes little over the entire frequency range and is very consistent. This indicates that most of the input power can be effectively transmitted through the waveguide with minimal loss. Combining the simulation and experimental results, this double-ridge waveguide can achieve low reflection and high transmission efficiency in the target frequency band.

[0145] Comparison between this embodiment and conventional waveguide

[0146] In order to evaluate the performance of the proposed double-ridge waveguide, the double-ridge waveguide is compared with the conventional WR340 waveguide, as shown in Figure 8As shown, the focus is on the electric field distribution, absorbed microwave power and average temperature rise at 400W input power. The heating time is 60 seconds and the dielectric constant of the heated material is 6.809-0.0735J. The cross-sectional distribution of the electric field intensity shows a significant difference between the two waveguides. Fig. 9 As shown, the maximum electric field strength of the double-ridge waveguide reaches 5.51×10 5 V / m, while the maximum electric field strength of the WR340 waveguide is only 2.29×10 4 This concentrated electric field in the double-ridge design is a key factor in its enhanced performance because it significantly amplifies the absorption of microwave energy inside the material.

[0147] The absorbed microwave power further highlights the superiority of the double-ridge waveguide, as shown in Table 2. The material in the proposed waveguide absorbed 2.63W of microwave energy, while the WR340 waveguide absorbed only 0.08W of microwave energy under the same conditions. The significant increase in absorbed power can be attributed to the enhanced interaction between the energy-focusing electric field and the material, which enables more efficient energy coupling. In terms of temperature rise, the heating efficiency of the double-ridge waveguide is much higher. Over a period of 60 seconds, the average temperature of the material in the double-ridge waveguide rose by 9.13℃, while the temperature rise of the WR340 waveguide was very low. In addition, the maximum temperature reached by the material in the double-ridge waveguide was 113.85℃, while it was only 1.01℃ in the WR340 waveguide, which shows that the heating performance of the double-ridge waveguide is superior and the effect of inducing thermal effects in low-loss materials is significantly better.

[0148] Table 2 Comparison of average temperature change and absorbed microwave energy of the two waveguides.

[0149]

[0150]

[0151] Sensitivity analysis of this example

[0152] Effect of dielectric properties of materials on heating performance

[0153] like Fig.10As shown, in actual microwave cutting, materials with different dielectric constants may be processed. As the real part of the dielectric constant increases, the ability of the material to absorb microwave energy tends to decrease. This trend is obvious in all the loss tangent values ​​tested. For example, when the loss tangent value is 0.01, the absorbed microwave energy drops significantly from 8.2391W to 1.8372W when the real part of the dielectric constant increases from 2 to 9.5. The reason for the decrease in absorbed energy is that the material with a higher real part has a higher degree of polarization in the electric field, which reduces the ability to absorb microwave energy and convert it into heat energy. On the other hand, the loss tangent is directly related to the ability of the material to dissipate energy in the form of heat. The higher the tanδ value, the stronger the energy dissipation ability. In this study, for any given real part of the dielectric constant, the absorbed microwave energy increases as the loss tangent increases. For example, when the real part value is 2, the absorbed microwave energy rises from 8.2391W when tanδ=0.01 to 262.76W when tanδ=1.0. This pattern holds for all values ​​of the real part, indicating that materials with higher loss tangent values ​​absorb microwave energy better.

[0154] Effect of Material Thickness on Heating Performance

[0155] On the effect of material thickness on heating performance, especially the absorbed microwave energy and average temperature rise under different dielectric properties.

[0156] like Fig.11 As shown in the figure, for a low-loss material with tanδ = 0.01, as the thickness increases from 0.5mm to 1.6mm, the absorbed energy gradually increases. However, due to the poor energy dissipation capacity of the material, the temperature rise is still relatively slow. The effect of thickness on the absorbed microwave energy and the average temperature rise is relatively small. In this case, the material's ability to absorb microwave energy is limited by its low loss tangent, which means that electromagnetic waves do not convert a lot of energy into heat when passing through the material. When the real part of the relative dielectric constant is low (such as ε r ′=2,6), the effect of thickness is more obvious, and the material absorbs slightly more energy. However, when the real part increases to 10, the overall energy absorption decreases and the effect of thickness decreases.

[0157] exist Fig.12 In the graph, for the material with tanδ = 0.1, the absorbed microwave energy and the generated temperature rise increase dramatically with increasing thickness. The material is now more efficient in converting microwave energy into heat, which is reflected in the steep curves of energy absorption and temperature rise. When the thickness increases from 0.5mm to 1.6mm, the absorbed energy and temperature increase significantly at all values ​​of the real part of the dielectric constant. When ε r When ε′=2 and ε′=6, this rise is most obvious, and the energy absorbed by the material increases significantly.r When ′=10, this effect is not so obvious, but the overall trend of energy absorption and temperature rise remains unchanged with increasing thickness.

[0158] exist Fig.13 In the figure, the high-loss material with tanδ=1 exhibits different behaviors with increasing thickness. Initially, the absorbed microwave energy and temperature both rise sharply with increasing thickness. However, after exceeding a certain thickness (about 1.2 mm), the average temperature rise begins to decrease, especially for materials with high values ​​of the real part of the relative dielectric constant (ε r This behavior can be attributed to two factors: first, as the material heats up, the heat diffuses from the hotter area (near the waveguide ridge) to the surrounding area. In thicker materials, this heat diffusion dilutes the temperature rise because the heat is distributed over a larger volume. In addition, in thicker and highly lossy materials, the microwave energy is attenuated more in the first few mm, so that deeper layers cannot receive enough energy. Therefore, less heat is generated in these areas, further contributing to the overall temperature rise.

[0159] By comparing these three cases, we can clearly see that the relationship between material thickness and heating performance is strongly affected by the dielectric properties of the material and its loss tangent. For low-loss materials (tanδ=0.01), increasing the thickness can moderately improve the absorbed energy and temperature rise. For medium-loss materials (tanδ=0.1), the effect of increasing the thickness is more obvious, which can significantly improve the energy absorption and heating efficiency. However, for high-loss materials (tanδ=1), the situation is more complicated. Initially, increasing the thickness will promote energy absorption and temperature rise, but beyond a certain level, energy saturation, thermal diffusion and microwave attenuation will cause the average temperature rise to decrease, especially in materials with higher real part values ​​of the dielectric constant. This analysis shows that to optimize microwave heating performance, it is necessary not only to adjust the material thickness, but also to carefully consider the dielectric properties and loss tangent of the material. For high-loss materials, increasing the thickness does not necessarily lead to better heating performance. In some cases, increasing the thickness may even reduce the overall temperature rise.

[0160] Effect of the position of the short-circuit surface on the heating performance

[0161] How the change of the short-circuit position in a double-ridge waveguide affects the electric field distribution, the absorbed microwave energy and the subsequent temperature rise. Fig.14 As shown in the figure, the electric field distribution changes significantly with the change of the short-circuit surface position. When the surface moves from near the waveguide entrance (1mm) to a position farther away from the surface (up to 51mm), the electric field distribution gradually moves, but the maximum electric field intensity remains unchanged. The electric field maximum moves with the movement of the short-circuit surface, so the electric field distribution in the waveguide can be changed by adjusting the position of the short-circuit surface, thereby achieving cutting.

[0162] exist Fig.15 In the figure, for low-loss materials with tanδ=0.01, the absorbed microwave energy and average temperature rise show a clear trend. When the short-circuited surface is located near the waveguide inlet (0mm), the absorbed energy is the highest and the temperature rise is also high. When the surface is far away from the waveguide inlet (about 30-40mm), the absorbed energy is lower and the temperature is also lower, reaching the lowest point. This is because at these locations, the concentration of the electric field distributed on the material is low, reducing the material's ability to effectively absorb energy. However, as the surface moves away, the absorbed energy and temperature begin to rise again because the electric field begins to re-concentrate.

[0163] Fig.16 A similar trend is shown for a medium loss material (tan δ = 0.1), but the absorbed microwave energy and temperature rise are larger than for the low loss material. The energy absorption and temperature rise are at their maximum when the shorting surface is at or near the waveguide entrance. Both parameters decrease as the surface moves away. Again, the parameter values ​​start to increase at locations beyond 40 mm.

[0164] exist Fig.17 In the figure, the position of the short-circuit surface has the greatest impact on high-loss materials (tanδ=1). Initially, when the surface is close to the waveguide entrance (0mm), the absorbed energy and temperature are relatively large. As the surface moves away, these values ​​gradually decrease, reflecting the energy concentration loss caused by the diffusion of the electric field. However, in this high-loss case, when the surface moves more than 40mm, the recovery of energy absorption and temperature rise is more significant. This shows that high-loss materials are more sensitive to changes in the electric field distribution, especially at the two ends of the short-circuit surface.

[0165] Comparison of the three cases shows that the location of the short-circuit surface has a significant effect on the heating properties of the different materials. In all cases, moving the surface close to the waveguide entrance results in the highest absorbed energy and temperature rise due to the concentrated electric field. Moving the surface farther away, the electric field initially becomes more diffuse, reducing the energy and temperature. When the surface continues to move beyond 40mm, both energy absorption and temperature rise recover.

[0166] This analysis highlights the importance of optimizing the shorting surface location for different material types. For high-loss materials, small adjustments in the surface location can result in significant changes in heating performance, so precise control is essential to achieve efficient microwave heating.

[0167] Effect of adjustment speed on short-circuit surface

[0168] The speed of the short-circuit surface plays a key role in regulating the temperature gradient of the glass or ceramic sheet and generating thermal cracks. The experimental setup includes a double-ridge waveguide that can receive 400W of microwave power at one end and a speed-adjustable short-circuit surface at the other end, which we used to simulate different moving speeds (1mm / s, 1.5mm / s and 2mm / s) within 300 seconds.

[0169] The results show that when the moving speed is 1mm / s, the temperature distribution is uneven, with a high local temperature peak. This temperature gradient contributes to the formation and expansion of thermal cracks. In contrast, when the moving speed of the short road surface is increased to 2mm / s, the temperature distribution becomes more uniform and the peak temperature decreases. This reduces the possibility of thermal crack formation.

[0170] These findings have important practical implications, highlighting the importance of controlling the surface speed during microwave cutting to optimize temperature gradient and crack formation. In actual operation, a slower surface speed (e.g., 1 mm / s) is recommended to form a temperature gradient that is favorable for crack propagation. A deeper understanding of the operating parameters of microwave-assisted glass cutting technology is very valuable and may have guiding significance for microwave processing technology of other materials, thereby enhancing the capabilities of practitioners in this field.

[0171] Cutting Experimental Device of This Example

[0172] A complete experimental system for microwave-assisted material cutting. The system is designed to test the ability of a double-ridge waveguide to heat and cut low-loss materials by thermal cracking. A solid-state microwave generator is used to adjust the output power, which can be adjusted from 0W to 1000W. To protect the system, a circulator is installed between the generator and the double-ridge waveguide. The circulator ensures that any reflected microwave energy is directed to the water load, preventing potential damage to the generator. The double-ridge waveguide has a bilaterally symmetrical design and is connected to an adjustable short-circuit surface on the right side. By adjusting the position of the short-circuit surface, the distribution of the standing wave within the waveguide can be controlled, resulting in a non-uniform temperature gradient. This temperature gradient is critical to the cutting process because it facilitates thermal cracking, thereby achieving precise cutting of materials such as glass and ceramics. By carefully controlling the power output of the solid-state generator and the position of the short-circuit surface, the system can generate local thermal stresses that control the fracture of low-loss materials. Compared with traditional methods, this method provides a way to efficiently cut materials at lower microwave powers. Selected material Al 2 O 3 Ceramics and glass are used as specific cutting test objects, and the specific cutting test results are as follows:

[0173] A l 2 O 3 The ceramic cutting test results are as follows:

[0174] Due to the limitations of thermal imaging technology in obtaining the thermal distribution of glass, ceramics were chosen as an alternative material to analyze the thermal distribution during the cutting process of low-loss materials. Graphite powder was applied to the surface of the ceramic as a coating material to improve the microwave absorption capacity of the ceramic, because the loss tangent value of the ceramic is extremely low, as shown in Table 1.

[0175] High-purity, 8000 mesh graphite powder (particle diameter 1.6μm) has strong adhesion to the ceramic surface. The graphite powder is carefully mixed with anhydrous ethanol to make a graphite-anhydrous ethanol solution. The solution is evenly sprayed on the ceramic surface with a spray gun, and a uniform graphite coating is formed after the anhydrous ethanol evaporates quickly. The effectiveness of graphite coating in microwave-assisted ceramic cutting stems from several key factors. The excellent microwave absorption properties of graphite greatly improve the surface absorption capacity of ceramics. The coating can convert microwaves into heat, forming a sharp temperature gradient in the ceramic. This controlled heating along a predetermined path will produce thermal stresses, which can cause precise cracks. The fine graphite particle size (1.6μm) ensures uniform coating and heat distribution.

[0176] The application of surface treatment greatly improves the microwave absorption capacity of the ceramic sheet, enabling it to be effectively heated by 200W microwave radiation. The final cutting result is as follows Fig.19 As shown, the heat distribution is Fig. 20 The results show that under the influence of obvious non-uniform temperature gradient, ceramics can be cracked along a predetermined path, thus realizing microwave thermal cracking cutting.

[0177] The results of the glass cutting experiment are as follows:

[0178] A glass sheet with a thickness of 0.7 mm was used for microwave thermal cracking and cutting experiments. The microwave power in the experiment was set to 300 W, which is lower than the other microwave cutting experiments mentioned in the previous section. The short-circuit surface moving speed was selected as 1 mm / s, referring to other microwave cutting glass examples. The experimental results are shown in Figure 2. Fig.21 As shown in Figure 2, from the perspective of the cutting entrance, there is an obvious offset crack on the right side. However, the overall linearity of the remaining cracks is satisfactory, indicating that the microwave thermal cracking glass plate was successfully cut.

Claims

1. A double-ridge waveguide cut by low-power microwave thermal cracking method, characterized in that: It comprises an electric field heating cavity, two metal ridges symmetrically arranged in the heating area, two step impedance converters symmetrically arranged at two ends of the electric field heating cavity, and a waveguide port arranged at the end of each step impedance converter; There is a receiving gap between the two metal ridges for placing the material to be cut, and the inlet and outlet of the material to be cut corresponding to the receiving gap are symmetrically arranged on the wall of the heating cavity.

2. A double-ridge waveguide cut by low-power microwave thermal cracking method according to claim 1, characterized in that: The electric field heating cavity is a rectangular cavity, and the two metal ridges are symmetrically arranged inside the rectangular cavity along the length direction.

3. A double-ridge waveguide cut by low-power microwave thermal cracking method according to claim 2, characterized in that: The waveguide port is a WR340 waveguide port, and a flange is arranged at the end of the WR340 waveguide port.

4. A double-ridge waveguide cut by low-power microwave thermal cracking method according to claim 3, characterized in that: The WR340 waveguide port includes a first rectangular cavity and a second rectangular cavity, the size of the first rectangular cavity is larger than that of the second rectangular cavity, the WR340 waveguide port is installed at one end of the first rectangular cavity, the second rectangular cavity is detachably installed at the other end of the first rectangular cavity through a flange, and the end of the second rectangular cavity is connected to one end of the electric field heating cavity.

5. A double-ridge waveguide cut by low-power microwave thermal cracking method according to claim 2, characterized in that: The two metal ridges are arranged inside the rectangular cavity in a vertically symmetrical manner along the length direction, and the two metal ridges are respectively an upper metal ridge and a lower metal ridge.

6. A double-ridge waveguide cut by low-power microwave thermal cracking method according to claim 5, characterized in that: The upper metal ridge is fixedly or detachably mounted on the top of the electric field heating cavity, and the lower metal ridge is fixedly or detachably mounted on the bottom of the electric field heating cavity.

7. A double-ridge waveguide cut by low-power microwave thermal cracking method according to claim 5, characterized in that: The upper metal ridge and the lower metal ridge each include two stepped mounting seats arranged at both ends and matched with the corresponding step impedance converter, a horizontal mounting seat connected between the two stepped mounting seats, and a convex strip arranged on each horizontal mounting seat along the length direction.

8. A design method for a double-ridge waveguide cut by a low-power microwave thermal cracking method, using a double-ridge waveguide cut by a low-power microwave thermal cracking method as claimed in any one of claims 1 to 7, characterized in that: The steps include: S1. The influence of double-ridge waveguide size on transmission performance was analyzed through electromagnetic thermal simulation, and the double-ridge waveguide model with the best size was determined; S2, performing electromagnetic thermal simulation on the double-ridge waveguide model obtained in step S1 to optimize the double-ridge waveguide model and improve the electric field concentration in the double-ridge waveguide model; S3, performing multi-physics field simulation on the double-ridge waveguide model obtained in step S2 to study the influence of dielectric constant, material thickness, short-circuit surface position and movement speed on the heating process; S4. Establish an experimental system, and for the double-ridge waveguide model obtained in step S3, cut alumina ceramic and glass plates at powers of 200 W and 300 W respectively.

9. The design method of a double-ridge waveguide cut by low-power microwave thermal cracking method according to claim 8, characterized in that: In step S1 to step S2, in order to quantitatively predict the propagation of the electromagnetic field, the application of Maxwell's equations is as follows: in, represents the magnetic field, represents the magnetic field strength, is the electric displacement vector, and ρ e are the conduction current density and the free charge density, respectively. and ρ e are all assumed to be zero; According to the electric field calculated using Maxwell's equations, the absorbed power P of the thin glass sheet is a The calculation formula of energy efficiency η is as follows: Among them, P i is the input power of the double-ridge waveguide, and Q represents the heat source; Heat is generated by electromagnetic power loss, and the temperature change can be calculated using the heat conduction equation: Where ρ represents density, C ρ is the specific heat capacity, k refers to thermal conductivity, Q(t) represents the power dissipation density and T represents the temperature; The motion of the short-circuit surface is modeled using coordinate transformation theory to reduce the computational complexity of dealing with moving boundaries in microwave simulations. The coordinate transformation is defined as follows: in, and Represent the position vectors in the original coordinate system and the transformed coordinate system respectively; Under this transformation, the dielectric constant ε r and magnetic permeability μ r In the new coordinate system it can be described by the following equation: Where Λ is the transformation matrix, which is defined as: A=(detJ)·(J -1 ) T ; Where J is the Jacob matrix describing the deformation of the coordinate system under transformation. The transformation of electric and magnetic fields between the original coordinate system and the transformed coordinate system can be expressed as:

10. The design method of a double-ridge waveguide cut by low-power microwave thermal cracking method according to claim 9, characterized in that: In step S1 to step S3, input parameters and boundary conditions: The relative dielectric constants of alumina ceramic thin plates and glass thin plates at a frequency of 2.45 GHz are used, and the remaining parameters are from the COMSOL material library. In addition, it is assumed that the physical parameters of alumina ceramic thin plates and glass thin plates remain unchanged when the temperature changes; In the simulation, except for the WR340 waveguide port, all cavity surfaces of the double-ridge waveguide are specified as perfect electric conductors. The electric field at a perfect electric conductor is perpendicular to the conductor surface and is calculated as follows: in, is the unit normal vector of the cavity surface, and is the electric field vector; Heat transfer boundary conditions are considered to account for the natural convection that occurs between the air and the material in the microwave cavity during microwave heating: Where h represents the heat transfer coefficient of air, which is usually taken as 10W / (m 2 K), and represents the temperature of the air, T air Indicates the air temperature.

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