Microwave heating structure

Abstract

The invention discloses a microwave heating structure, which relates to the technical field of waveguide heating and comprises a first microwave source, a second microwave source and a gradually-changed straight waveguide component, the first microwave source and the second microwave source are arranged at the two ends of the gradually-changing straight waveguide component respectively, and the gradually-changing straight waveguide component is a gradually-changing sinking straight waveguide component or a gradually-changing upward-protruding straight waveguide component. The invention aims to realize the heating of a large-size and complex-structure workpiece in a closed space through microwave radiation by using a microwave radiation method, and breaks through the limitation of non-uniform heating in a cavity in the traditional microwave heating. The microwave power absorbed by the to-be-heated substance is improved by enhancing the electric field, the heating uniformity is improved through the periodic structure, and compared with a traditional heating cavity, the heating cavity has obvious advantages in heating of low-loss thin materials.

Description

Technical Field

[0001] This invention relates to the field of waveguide heating technology, and more specifically to the field of microwave heating structure technology. Background Technology

[0002] In recent decades, electromagnetic heating technologies, represented by microwave heating, have gradually replaced traditional heating methods and become the mainstream choice in industrial and civilian fields due to their significant advantages of high efficiency, low cost, and environmental friendliness. Traditional heating methods have obvious limitations: heat is mainly conducted to the interior through the material surface. Even if the surface temperature rises significantly, the central area is difficult to heat simultaneously, often requiring a long time to achieve uniform heating, resulting in relatively low efficiency. In contrast, microwave heating uses a unique "inside-out" heating mechanism—it acts directly on the polar molecules inside the material, causing them to vibrate at high frequency to generate heat. It does not rely on a long heat conduction process and can heat materials quickly and uniformly. At the same time, microwave heating has a high degree of "targeting," doing work only on the object being heated, without raising the ambient temperature, reducing energy waste and effectively maintaining the temperature stability of the operating space.

[0003] The heating structure of a surface plasmon polariton (SSPP) waveguide is a sophisticated auxiliary functional unit, its core being the use of the slow-wave effect to control the transmission characteristics of electromagnetic waves. The most commonly used technique is metal-based microheaters. By carefully designing their geometry, materials, and locations, efficient and localized thermal management can be achieved, thereby endowing SSPP light sources with key functions such as wavelength tuning and switching modulation, greatly enhancing their application potential in electromagnetic wave modulation and transmission. However, the trade-off between thermal management and electromagnetic performance remains a core design challenge.

[0004] Patent publication number CN213124695U, entitled "Waveguide Structure for Microwave Heating," discloses the following: A waveguide structure for microwave heating includes a square waveguide tube, a connecting seat at the bottom of the tube, a wave-emitting aperture in the middle of the tube, and an adjustable matching block on the inner side of the tube. This invention improves the efficiency of waveguides in sterilizing and heating rice and dishes. Without a load, the reflectivity is close to 10%, and with a load, it is close to 1.5%, exhibiting low reflection and excellent conduction. It also ensures uniform heating of both sides of the food container and is suitable for microwave heating and sterilization within pressure pipelines.

[0005] The aforementioned patents and existing microwave heating technologies are not perfect, and they still face bottlenecks in the field of low-loss material heating. These materials (such as some plastics, glass, and certain insulating materials) have weak microwave absorption capabilities and extremely low energy loss in conventional waveguide structures, making it difficult for microwave energy to be effectively converted into the material's own heat energy, thus failing to achieve efficient and rapid heating effects.

[0006] Therefore, overcoming the challenge of microwave heating low-loss materials and improving their energy utilization efficiency remains a key challenge to be solved in this field. The microwave power absorbed by a material is not only related to its size and dielectric constant, but also proportional to the square of the electric field amplitude. Therefore, strengthening the electric field is an effective way to improve heating efficiency. One common method is to increase the input power, but this method cannot significantly improve the microwave energy utilization efficiency. Another method is to use a ridge waveguide as the reaction cavity. A ridge waveguide is a waveguide that enhances the electric field in the ridge region and can be used to design ridge waveguides in microwave heating and drying systems to process sheet-like, filamentous, or cylindrical materials. However, ridge waveguides have relatively stringent requirements on the heated material and the waveguide cavity structure. Therefore, designing a microwave heating structure that can improve heating efficiency and uniformity by enhancing the electric field without compressing the waveguide cavity has become a requirement for industrial production. Summary of the Invention

[0007] The purpose of this invention is to solve the aforementioned technical problems by providing a microwave heating structure. This solution enhances the microwave power absorbed by low-loss materials by strengthening the electric field and improves the uniformity of heating through a periodic structure.

[0008] To achieve the above objectives, the present invention specifically adopts the following technical solution: The present invention provides a microwave heating structure, including a first microwave source, a second microwave source, and a tapered straight waveguide component; the first microwave source and the second microwave source are respectively disposed at both ends of the tapered straight waveguide component, and the tapered straight waveguide component is a tapered downward straight waveguide assembly or a tapered upward convex straight waveguide assembly.

[0009] In one embodiment, the system further includes a phase modulation system that fixes the phase of either the first microwave source or the second microwave source; when the phase of the first microwave source is fixed, the phase modulation system causes the phase of the second microwave source to change periodically; when the phase of the second microwave source is fixed, the phase modulation system causes the phase of the first microwave source to change periodically, thereby improving the uniformity of the transverse electric field.

[0010] In one embodiment, the tapered straight waveguide assembly includes a strip-shaped shell, microwave feed ports disposed at both ends of the strip-shaped shell, and a metal array uniformly distributed within the strip-shaped shell. The strip-shaped shell includes a heating cavity in the middle, and left and right sinking transition cavities symmetrically disposed on both sides of the heating cavity. The top positions of the metal arrays located in the left and right sinking transition cavities and the heating cavity are on the same horizontal line, and the bottom positions of the metal arrays located in the left and right sinking transition cavities gradually sink along the microwave transmission direction.

[0011] In one embodiment, a left microwave feed port is provided at the left end of the left submerged transition cavity, and a right microwave feed port is provided at the right end of the right submerged transition cavity. The left microwave feed port is connected to a first microwave source, and the right microwave feed port is connected to a second microwave source.

[0012] In one embodiment, the metal arrays in the left sinking transition cavity, the right sinking transition cavity, and the heating cavity are arranged at equal intervals.

[0013] In one embodiment, the gradient upward convex straight waveguide assembly includes a strip-shaped shell, microwave feed ports disposed at both ends of the strip-shaped shell, and a metal array uniformly distributed within the strip-shaped shell. The strip-shaped shell includes a central heating cavity in the middle and left and right convex transition cavities symmetrically disposed on both sides of the central heating cavity. The bottom positions of the metal arrays located in the left, right, and heating cavities are on the same horizontal line, and the top positions of the metal arrays located in the left and right convex transition cavities are gradually raised along the microwave transmission direction.

[0014] In one embodiment, a left microwave feed port is provided at the left end of the left convex transition cavity, and a right microwave feed port is provided at the right end of the right convex transition cavity. The left microwave feed port is connected to the first microwave source, and the right microwave feed port is connected to the second microwave source.

[0015] In one embodiment, the metal arrays in the left convex transition cavity, the right convex transition cavity, and the heating cavity are arranged at equal intervals.

[0016] The beneficial effects of this invention are as follows: 1. The purpose of this invention is to use microwave radiation to heat large and complex workpieces in a closed space, overcoming the limitation of uneven heating in traditional microwave heating within cavities. This solution increases the microwave power absorbed by the material to be heated by enhancing the electric field and improves the uniformity of heating through a periodic structure; By designing surface waveguide structures (SSPPs), tapered straight waveguides can precisely control the location and extent of the localized field, concentrating heating in a specific area and avoiding overheating of surrounding materials. Due to the high energy confinement capability of SSPPs, electromagnetic waves propagate along the surface with low loss, enabling precise delivery of microwave energy to the heating area and reducing cavity reflections and energy waste.

[0017] 2. The phase modulation system fixes the phase of either the first microwave source or the second microwave source; when the phase of the first microwave source is fixed, the phase modulation system causes the phase of the second microwave source to change periodically; when the phase of the second microwave source is fixed, the phase modulation system causes the phase of the first microwave source to change periodically, in order to improve the uniformity of the transverse electric field.

[0018] 3. The gradient upward convex straight waveguide assembly is easier to process. Microwaves are fed into the left and right ends of the waveguide. The electric field near the metal array is significantly enhanced. The periodic structure makes the electric field distribution inside the material more uniform, and the energy absorption efficiency is 87%.

[0019] 4. The tapered downward straight waveguide assembly exhibits low microwave reflection, readily forming a stable SSPPs surface wave propagation mode. Furthermore, it provides strong confinement of the electromagnetic field, making it less susceptible to the influence of the waveguide's upper wall. Microwaves are fed into the left and right ports of the waveguide, resulting in a significant enhancement of the electric field near the metal array. The periodic structure further homogenizes the electric field distribution within the material, achieving an energy absorption efficiency of 95%. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a schematic diagram of the structure of the convex straight waveguide component of the present invention connected to a microwave source; Figure 2 This is a schematic diagram of the structure of the sunken straight waveguide component of the present invention connected to a microwave source; Figure 3 This is a schematic diagram of a one-dimensional groove subwavelength periodic structure; Figure 4 This is a dispersion relation diagram of an SSPPs waveguide structure; Figure 5 These are electric field distribution diagrams for two SSPPs waveguide structures, where (a) is a sunken transition structure and (b) is a convex transition structure. Figure 6 This is a diagram showing the heating electric field distribution of a submerged transition SSPPs waveguide structure; Figure 7 This is a diagram showing the heating temperature distribution of a submerged transition SSPPs waveguide structure. Figure 8 This is a diagram showing the heating electric field distribution of the convex transition SSPPs waveguide structure; Figure 9 This is a diagram showing the heating temperature distribution of the convex transition SSPPs waveguide structure. Reference numerals: 1. First microwave source; 2. Left microwave feed port; 3. Left convex transition cavity; 4. Heating cavity; 5. Material to be heated; 6. Right convex transition cavity; 7. Right microwave feed port; 8. Second microwave source; 9. Left submerged transition cavity; 10. Right submerged transition cavity. Detailed Implementation

[0022] To make the technical problems, technical solutions, and technical effects of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0024] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, the terms "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0025] In the description of the embodiments of the present invention, it should be noted that the terms "inner", "outer", "upper", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use. 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, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0026] Example 1 like Figure 1 As shown, this embodiment provides a microwave heating structure, including a first microwave source 1, a second microwave source 8, and a gradient straight waveguide component; the first microwave source 1 and the second microwave source 8 are respectively disposed at both ends of the gradient straight waveguide component, and the gradient straight waveguide component is a gradient downward straight waveguide assembly or a gradient upward convex straight waveguide assembly.

[0027] It also includes a phase control system, which fixes the phase of the first microwave source 1 or the second microwave source 8; when the phase of the first microwave source 1 is fixed, the phase control system causes the phase of the second microwave source 8 to change periodically; when the phase of the second microwave source 8 is fixed, the phase control system causes the phase of the first microwave source 1 to change periodically, in order to improve the uniformity of the transverse electric field.

[0028] The gradient upward convex straight waveguide assembly includes a strip-shaped shell, microwave feed inlets located at both ends of the strip-shaped shell, and a metal array evenly distributed within the strip-shaped shell. The strip-shaped shell includes a central heating cavity 4 in the middle and left convex transition cavities 3 and right convex transition cavities 6 symmetrically arranged on both sides of the central heating cavity 4. The bottom positions of the metal arrays located in the left convex transition cavity 3, right convex transition cavity 6, and heating cavity 4 are on the same horizontal line, and the top positions of the metal arrays located in the left convex transition cavity 3 and right convex transition cavity 6 are gradually raised along the microwave transmission direction.

[0029] The left convex transition cavity 3 is provided with a left microwave feed port 2 at its left end, and the right convex transition cavity 6 is provided with a right microwave feed port 7 at its right end. The left microwave feed port 2 is connected to the first microwave source 1, and the right microwave feed port 7 is connected to the second microwave source 8.

[0030] The metal arrays in the left convex transition cavity 3, the right convex transition cavity 6, and the heating cavity 4 are arranged at equal intervals.

[0031] Example 2 like Figure 2 As shown, this embodiment provides a microwave heating structure, including a first microwave source 1, a second microwave source 8, and a gradient straight waveguide component; the first microwave source 1 and the second microwave source 8 are respectively disposed at both ends of the gradient straight waveguide component, and the gradient straight waveguide component is a gradient downward straight waveguide assembly or a gradient upward convex straight waveguide assembly.

[0032] It also includes a phase control system, which fixes the phase of the first microwave source 1 or the second microwave source 8; when the phase of the first microwave source 1 is fixed, the phase control system causes the phase of the second microwave source 8 to change periodically; when the phase of the second microwave source 8 is fixed, the phase control system causes the phase of the first microwave source 1 to change periodically, in order to improve the uniformity of the transverse electric field.

[0033] The gradient-sinking straight waveguide assembly includes a strip-shaped shell, microwave feed entrances at both ends of the strip-shaped shell, and a metal array evenly distributed within the strip-shaped shell. The strip-shaped shell includes a heating cavity 4 in the middle, and left sinking transition cavities 9 and right sinking transition cavities 10 symmetrically arranged on both sides of the heating cavity 4. The top positions of the metal arrays located in the left sinking transition cavity 9, right sinking transition cavity 10, and heating cavity 4 are on the same horizontal line, and the bottom positions of the metal arrays located in the left sinking transition cavity 9 and right sinking transition cavity 10 gradually sink along the microwave transmission direction.

[0034] The left sink transition cavity 9 is provided with a left microwave feed port 2 at its left end, and the right sink transition cavity 10 is provided with a right microwave feed port 7 at its right end. The left microwave feed port 2 is connected to the first microwave source 1, and the right microwave feed port 7 is connected to the second microwave source 8.

[0035] The metal arrays in the left sinking transition cavity 9, the right sinking transition cavity 10, and the heating cavity 4 are arranged at equal intervals.

[0036] The principle analysis of the SSPPs waveguide structure in Embodiments 1 and 2 is as follows: Microwave-heated structures (SSPPs waveguides) possess excellent characteristics such as low loss and super-strong focusing. The following theoretical analysis of the basic properties of SSPPs waveguides is presented using a one-dimensional subwavelength groove periodic structure.

[0037] like Figure 3 As shown, h Indicates the height of the metal unit. a Indicates the thickness of the metal unit. d Let represent the spacing between the metal elements (i.e., the period of the metal array). Then, the dispersion relation of the SSPPs of the one-dimensional subwavelength groove periodic structure can be given by the following equation: (1) (2) (3) in, Representing the periodic structure n Wave number of spatial harmonics; Indicates the attenuation constant; Used to simplify expressions; The free-space wavenumber is given. The dispersion equation reflects the modulation of the equivalent dielectric constant of SSPPs, through... a , d and h Adjusting the dispersive properties of periodic structures.

[0038] The dispersion curves of SSPPs structures at different sizes obtained from simulation calculations are as follows: Figure 4 As shown. Metal height h The effect is most pronounced on dispersion characteristics. a and d It will also affect the dispersion characteristics, but the impact is small. Therefore, we can determine it first. h The value is then fine-tuned. a and d Obtain the desired structure.

[0039] Due to the presence of metallic and radiation losses in the SSPP structure, its propagation constant Usually plural: (4) Real part Determines the phase change of the wave; imaginary part Determines wave attenuation. Effective wavelength of SSPPs: (5) Due to SSPPs > Its wavelength Typically smaller than the wavelength of free space This is known as the slow wave effect.

[0040] Embodiments 1 and 2 disclose two types of SSPPs waveguide structures: convex and recessed. A periodic metal array is added below the lower surface of the feed waveguide (Example 2), and a recessed metal gradient transition structure is provided, such as... Figure 2 As shown. This structure exhibits low microwave reflection, readily forms stable SSPPs surface wave propagation modes, and possesses strong electromagnetic field confinement, making it less susceptible to the influence of the waveguide's upper wall.

[0041] A periodic metal array is added above the lower surface of the feed waveguide, and a convex metal gradient transition structure is provided (Example 1), such as... Figure 1 As shown. This structure is easier to manufacture, but the metal reflects electromagnetic waves significantly, which can easily lead to lower transmission efficiency, and the electric field distribution is easily affected by the upper wall of the waveguide.

[0042] The electric field distribution and S-parameters of the SSPPs waveguide structure when microwaves are fed only from the left port side are as follows: Figure 5 As shown.

[0043] Analysis of the heating effect of SSPPs waveguide structure: The heating effect of the sunken transition structure SSPPs waveguide is as follows: Based on the dispersion relationship calculated above, the height of the metal array was set to 24mm, the width to 7mm, and the period (spacing) to 14mm, and the heating effect was analyzed.

[0044] The waveguide is fed with 100W microwave power at each of its left and right ports, with an initial temperature of 20℃ and a heating time of 30s. The load dielectric constant is 2⁻⁰.²J. The electric field distribution is as follows. Figure 6 As shown, the electric field enhancement effect near the metal array is significant, and the periodic structure makes the electric field distribution inside the material more uniform. The temperature distribution after heating for 30 seconds is shown in the figure. Figure 7 As shown, the energy absorption efficiency is 95%.

[0045] The heating effect of the waveguide on the convex transition structure of SSPPs waveguides is as follows: A 24mm high metal array was placed above the lower surface of the waveguide. The electric field distribution and the temperature distribution after heating were analyzed by selecting a=7mm and d=14mm.

[0046] The waveguide is fed with 100W microwave power at each of its left and right ports, with an initial temperature of 20℃ and a heating time of 30s. The load dielectric constant is 2⁻⁰.²J. The electric field distribution is as follows. Figure 8As shown, the electric field enhancement effect near the metal array is significant, and the periodic structure makes the electric field distribution inside the material more uniform. The temperature distribution after heating for 30 seconds is shown in the figure. Figure 9 As shown, the energy absorption efficiency is 87%.

[0047] Example 3 This embodiment provides an example of the applicability of the microwave heating structure in the field of frozen and refrigerated aquatic food processing, focusing on how the structure can be optimized and operated to meet the common dielectric properties and heating requirements of materials in this field.

[0048] Frozen and refrigerated aquatic products (such as various types of fish, shrimp, shellfish, and their processed products) typically exhibit low dielectric constants and loss factors in the microwave frequency band. This is mainly due to the fact that some of their internal water molecules are in a frozen or bound state, the structural characteristics of myofibril proteins, and the possible ice crystal effect, making them typical "low-loss materials." Traditional microwave heating methods are inefficient for such materials and are prone to quality deterioration due to uneven heating.

[0049] This embodiment uses, as follows: Figure 2 The gradient-sinking straight waveguide assembly shown serves as the core heating structure. This assembly comprises a strip-shaped outer shell and an equally spaced metal array within it. The outer shell contains a left sinking transition cavity 9, a heating cavity 4, and a right sinking transition cavity 10, formed sequentially. The geometric parameters of the metal array (such as height, width, and period) can be optimized based on the typical dielectric properties of the target aquatic product material.

[0050] The first microwave source 1 and the second microwave source 8 feed microwaves into the waveguide from both ends through the left and right microwave feed ports (2, 7), respectively. To address the stringent requirements for lateral uniformity when heating blocky or sheet-like aquatic food materials, this embodiment specifically utilizes the aforementioned phase modulation system. This system can be configured to: fix the phase of the first microwave source 1, and cyclically change the phase of the second microwave source 8 at a preset period (e.g., 0.05 seconds to 0.5 seconds). This dynamic phase modulation strategy aims to actively intervene in the interference field distribution formed within the heating cavity 4, thereby significantly improving the electric field uniformity perpendicular to the microwave transmission direction (i.e., within the material plane). This is crucial for avoiding overheating at the material edges, insufficient heating at the center, or the appearance of localized cold spots.

[0051] During operation, microwave energy propagates within the gradually descending straight waveguide structure. Once its SSPPs mode is excited, the energy is strongly localized in the region near the interface between the metal array and the material, and a significant electric field enhancement effect is generated due to charge oscillation. This dual mechanism of "field localization" and "field enhancement" effectively overcomes the bottleneck of weak microwave energy absorption by low-loss aquatic food raw materials.

[0052] This microwave heating structure achieves longitudinal concentration and enhancement of the electric field through its unique periodic metal array design, while the dual-source phase modulation system further optimizes the uniformity of the transverse field. This combination makes it particularly suitable for solving common challenges in aquatic food processing: rapid and efficient heating of low-dielectric, low-loss materials, and the need for uniform temperature rise in materials with uneven thickness and irregular shapes. The structure's high energy absorption efficiency translates to shorter processing times and lower energy consumption. Its design does not rely on the precise shape of specific materials, but rather adapts to products of different sizes and thicknesses through field distribution modulation, demonstrating its application potential in various processing stages such as thawing frozen fish fillets, preheating refrigerated seafood products, and cooking prepared aquatic products.

[0053] Therefore, this embodiment demonstrates how the microwave heating structure, as a general-purpose heating platform, can specifically meet the key technical requirements of the low-loss aquatic food processing industry for efficient and uniform microwave heating through its core SSPPs waveguide design and phase modulation function.

Claims

1. A microwave heating structure, characterized in that, It includes a first microwave source (1), a second microwave source (8), and a gradient straight waveguide component; the first microwave source (1) and the second microwave source (8) are respectively disposed at both ends of the gradient straight waveguide component, and the gradient straight waveguide component is a gradient sinking straight waveguide assembly or a gradient convex straight waveguide assembly.

2. The microwave heating structure according to claim 1, characterized in that, It also includes a phase control system, which fixes the phase of the first microwave source (1) or the second microwave source (8); when the phase of the first microwave source (1) is fixed, the phase control system causes the phase of the second microwave source (8) to change periodically; when the phase of the second microwave source (8) is fixed, the phase control system causes the phase of the first microwave source (1) to change periodically, in order to improve the uniformity of the transverse electric field.

3. The microwave heating structure according to claim 2, characterized in that, The gradient-sinking straight waveguide assembly includes a strip shell, microwave feed inlets at both ends of the strip shell, and a metal array evenly distributed within the strip shell. The strip shell includes a heating cavity (4) in the middle and left sinking transition cavities (9) and right sinking transition cavities (10) symmetrically arranged on both sides of the heating cavity (4). The top positions of the metal arrays located in the left sinking transition cavity (9), the right sinking transition cavity (10), and the heating cavity (4) are on the same horizontal line, and the bottom positions of the metal arrays located in the left sinking transition cavity (9) and the right sinking transition cavity (10) gradually sink along the microwave transmission direction.

4. The microwave heating structure according to claim 3, characterized in that, The left sink transition cavity (9) is provided with a left microwave feed port (2) at its left end, and the right sink transition cavity (10) is provided with a right microwave feed port (7) at its right end. The left microwave feed port (2) is connected to the first microwave source (1), and the right microwave feed port (7) is connected to the second microwave source (8).

5. A microwave heating structure according to claim 3, characterized in that, The metal arrays in the left sinking transition cavity (9), the right sinking transition cavity (10), and the heating cavity (4) are arranged at equal intervals.

6. A microwave heating structure according to claim 2, characterized in that... The gradient upward convex straight waveguide assembly includes a strip shell, microwave feed inlets at both ends of the strip shell, and a metal array evenly distributed within the strip shell. The strip shell includes a central heating cavity (4) in the middle and a left convex transition cavity (3) and a right convex transition cavity (6) symmetrically arranged on both sides of the central heating cavity (4). The bottom positions of the metal arrays located in the left convex transition cavity (3), the right convex transition cavity (6), and the heating cavity (4) are on the same horizontal line, and the top positions of the metal arrays located in the left convex transition cavity (3) and the right convex transition cavity (6) are gradually raised along the microwave transmission direction.

7. A microwave heating structure according to claim 6, characterized in that, The left convex transition cavity (3) is provided with a left microwave feed port (2) at its left end, and the right convex transition cavity (6) is provided with a right microwave feed port (7) at its right end. The left microwave feed port (2) is connected to the first microwave source (1), and the right microwave feed port (7) is connected to the second microwave source (8).

8. A microwave heating structure according to claim 6, characterized in that, The metal arrays in the left convex transition cavity (3), the right convex transition cavity (6), and the heating cavity (4) are arranged at equal intervals.

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