CN114928907A

CN114928907A - Microwave equipment with two-dimensional periodic structure

Info

Publication number: CN114928907A
Application number: CN202210621052.5A
Authority: CN
Inventors: 王清源
Original assignee: Chengdu Jihengte Technology Co ltd
Current assignee: Wuxi Carbon Technology Co ltd
Priority date: 2022-06-02
Filing date: 2022-06-02
Publication date: 2022-08-19

Abstract

The invention provides microwave equipment with a two-dimensional periodic structure, which comprises two metal flat plates and at least one feed-in transmission line. Two-dimensional periodic pits are arranged on the inner surfaces of a pair of parallel metal flat plates, a broadband stop band is realized near the working frequency of the microwave equipment, and the feed-in transmission line is well isolated from other parts or other feed-in transmission lines, so that each feed-in transmission line can be independently prepared through a tuner. The microwave equipment with the two-dimensional periodic structure has the characteristic of simple structure, and can be widely used for heating and drying various materials.

Description

Microwave equipment with two-dimensional periodic structure

Technical Field

The invention relates to the field of uniform and efficient microwave heating, in particular to microwave treatment equipment with a two-dimensional periodic structure.

Background

Microwave heating may replace various conventional heating means. Microwave devices utilize microwave energy to heat various materials including, but not limited to, wood, grain, medicinal materials, spices, dairy products, and the like. In the field of microwave chemistry, microwave energy is used to accelerate various chemical reactions. Microwave energy is also used in the production of new materials such as nanomaterials, synthetic diamonds, and the like.

In any cavity, such as a heating cavity, electromagnetic waves will resonate in the form of the various natural modes of the cavity. At a certain operating frequency, a plurality of modes are excited together, and the amplitude of the electric field is maximum at some positions in space and is small at other positions in space. At typical microwave energy application frequencies of 2450MHz, the distance between these electric field concentrations is half the operating wavelength of the microwaves used, around 62 mm, resulting in non-uniformity of the heated object in the corresponding dimension.

Technical personnel in international and domestic fields make continuous efforts to solve the problem of uniformity of microwave heating. Attempts have been made to improve the uniformity of heating by increasing the number of microwave feeds, changing the shape of the feeds, changing the position of the microwave feeds on the external surface of the heating chamber, or changing the polarization direction of the electric field at the microwave feeds, or simultaneously randomly changing the four variables. However, up to now, due to the high complexity of the problem, the microwave boundary lacks clear theoretical guidance for the problem, and the three-dimensional electromagnetic simulation is difficult to complete due to the huge calculation amount. Therefore, the problem of uniformity of heating in microwave ovens, especially large microwave equipment, has not been well solved.

Disclosure of Invention

The invention aims to provide microwave equipment with a two-dimensional periodic structure. Here, a plurality of microwave sources may be provided, and the microwave sources therein are isolated from each other. We can process each microwave source independently, measure its reflection coefficient or make a match by a tuner. In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a microwave device with a two-dimensional periodic structure comprises a cover plate positioned in a Y direction and a bottom plate positioned in a-Y direction, wherein at least one feed-in transmission line is arranged on the bottom plate. A channel is provided between the cover plate and the base plate. The feed transmission line delivers microwave energy to a path between the cover and base. A two-dimensional periodic structure is arranged on the lower surface of the cover plate, or on the upper surface of the base plate, or on both the lower surface of the cover plate and the upper surface of the base plate. X, Y and the Z direction form a rectangular coordinate system.

The two-dimensional periodic structure herein refers to a structure in which periodic units having a certain same shape are arranged at equal periods in any two mutually perpendicular directions on the XZ plane. Such structures are referred to in the optical arts as photonic crystal structures.

Larger scale microwave devices may be constructed by repeating the above structure in one direction along a horizontal plane or in two mutually perpendicular directions. In this case, we will have a large area cover and base and a plurality of microwave sources located on the cover or base. The number of the microwave sources can be several or as many as tens of thousands. The addition of any number of microwave sources, since the input transmission lines are isolated from each other, does not add to the complexity of the problem, but merely results in an equally proportional change in the size and throughput of the device.

Generally, a conveyor belt and an object to be heated positioned above the conveyor belt are also provided in the passage.

In a preferred design, the conveyor belt is tightly attached to the upper surface of the bottom plate.

Further, the periodic unit of the two-dimensional periodic structure is a pit. In this case, periodic units of pits of the same shape are periodically provided on the lower surface of the base plate or/and the upper surface of the base plate by milling, or electrical discharge, or pressing. Or through holes which are arranged in a two-dimensional periodic manner can be arranged on a metal plate with the thickness being the same as the depth of the pits by means of wire cutting, punching or the like, and then the metal plate and another metal plate are overlapped and welded or connected together by screws.

The resulting depression is a blind hole.

At least 2 said pits are present in-X, -Z and Z directions around the centre point of a feed formed at the connection of at least one said feed transmission line with said cover plate or said base plate. This arrangement allows microwaves fed from the feed to achieve a microwave stop band over a wide bandwidth around the operating frequency of the microwave device, which microwaves will reach the channel but do not propagate with said channel in the horizontal plane, but are confined near the feed of the feed transmission line.

In a preferred design, the periodic units of the two-dimensional periodic structure are columns with axes along the Y direction.

The column body is a structure formed by the space occupied by the pits, the column body is not a structure protruding from the surface of the cover plate or the bottom plate, but a space lacking in the inward recess, if a solid column body structure is inserted into the pits, the pits can be filled, and the size of the column body along the Y direction is the depth of the pits. The columnar body may be a column having a diameter reduced due to a process problem or a column having a constant diameter, and the cross-sectional shape thereof may be arbitrary, and is preferably rectangular, circular, polygonal, or the like.

The cross section of the periodic unit of the two-dimensional periodic structure is square, circular or regular polygon, and can be in any other shape.

The cross section can be the cross section of a columnar body or the cross section of the opening of a pit.

In a preferred design, the cross section of the periodic unit of the two-dimensional periodic structure is in a shape of a clover. The so-called "clover-shape" here is composed of a "cross" in the center and a triangular or fan-shaped structure at and connected to each of the four apexes of the "cross". In this shape, a columnar dimple is symmetrical with respect to two mutually perpendicular planes of symmetry passing through the axis of the columnar dimple.

In order to obtain a wider stop band around the operating frequency, the distance between the center points of the pits is more than 20% of the operating wavelength. Meanwhile, the depth of the pits in the Y direction is 15% -35% of the working wavelength. Furthermore, the height of the channel in the Y direction is less than 50% of the operating wavelength.

In a specific design, modeling calculation and optimization are required to be performed on a microwave structure in a channel so as to obtain final structure parameters. By changing the three-dimensional shape and the distance between pit periodic units, a wider band-stop photonic crystal structure comprising the working frequency is required to be obtained. For heated objects of different dielectric constants and different lengths, our design must compromise the bandwidth of the bandstop of the microwave structure and the higher attenuation constant over distance. For fast processing equipment we prefer to use a higher power microwave source. In this case, a microwave structure with a high power capacity is also required. In addition, for ceramic sintering and powder metallurgy applications, it is desirable that the microwave structure have very low surface resistivity to reduce microwave loss of the device itself, and also have the ability to withstand high temperatures. Often we need to add insulation in the channels.

The invention provides microwave equipment with a two-dimensional periodic structure. The microwave device comprises two metal plates. A two-dimensional periodic structure of pits is provided on opposing faces on one or both of the metal plates. Such two metal plates can realize a microwave stop band within a wide bandwidth around the operating frequency of the microwave device. When microwave energy is fed into a channel between two flat plates through a feed transmission line, the microwave reaches the channel and does not propagate in a horizontal plane along with the channel, but is limited near a feed port of the feed transmission line, and can be used for uniformly and efficiently heating or drying a heated object. Thus, good isolation between the feed transmission lines can be achieved, and each microwave source can be matched conveniently through the tuner. The microwave equipment can be used in the field of uniform and efficient microwave heating.

Meanwhile, according to the two-dimensional periodic structure of the pits, the pits are contracted towards the inner direction of the cover plate or the bottom plate, so that no protrusion is arranged on the inner plane of the cavity of the cover plate or the bottom plate, and the microwave energy or the microwave range is biased to the vicinity of the feed opening under the influence of the microwave stop band. Therefore, the transmission belt can be directly arranged on the inner cavity plane of the cover plate or the bottom plate, and the corresponding heated objects can be close to the surface where the feed opening is located at a closer distance. Simultaneously, the distance between the cover plate and the bottom plate can be greatly reduced by the design, so that the thickness of the microwave equipment is greatly reduced.

Drawings

Fig. 1 is a side sectional view of example 1 of the present invention.

Fig. 2 is a bottom view of the cover plate of fig. 1.

Fig. 3 is a top view of the base plate of fig. 1.

Figure 4 a side cross-sectional view of embodiment 2.

Fig. 5 is a bottom view of the cover plate of fig. 4.

Fig. 6 is a top view of the base plate of fig. 4.

Fig. 7 shows a periodic unit of the periodic structure, a clover-shaped pit, in example 3.

Fig. 8 is the energy leakage loss (dB) of example 4.

Figure 9 is a side sectional view of embodiment 5.

The reference numbers in the drawings correspond to the names: 1-cover plate, 2-bottom plate, 3-feed transmission line, 4-pit, 5-channel, 6-heated object.

Some of the terms specified in this specification are as follows:

a cross-section, i.e. a section of a horizontal plane through an object.

Horizontal, i.e. any plane parallel to the XZ plane.

Upward, i.e., Y-direction, i.e., vertically upward from the horizontal.

The lower, i.e. -Y direction, i.e. the direction vertically downwards from the horizontal.

And on the left, the X direction.

The right direction is the-X direction.

The working wavelength is the wavelength in the air corresponding to the working frequency of the microwave source of the microwave equipment.

Feeding a port: the interface of any feed transmission line and any metal flat plate.

Detailed Description

Example 1

As shown in fig. 1, 2 and 3.

A microwave device with a two-dimensional periodic structure comprises a cover plate 1 located in the Y direction and a bottom plate 2 located in the-Y direction, wherein a feed-in transmission line 3 is arranged on the bottom plate 2. Between the cover plate 1 and the base plate 2 a channel 5 is provided. The feed transmission line 3 feeds microwave energy into a channel 5 between the cover 1 and the base 2. A two-dimensional periodic structure is arranged on the lower surface of the cover plate 1. X, Y and the Z direction form a rectangular coordinate system.

A conveyor belt and a heated object 6 positioned above the conveyor belt are also provided in the passage. The conveyor belt is tightly attached to the upper surface of the bottom plate 2.

The periodic unit of the two-dimensional periodic structure is a pit 4. At this time, two-dimensional periodic through holes are formed in a metal plate having the same thickness as the height of the pits 4 by wire cutting, and then the metal plate and another metal plate are overlapped and welded together.

The periodic unit of the two-dimensional periodic structure is a columnar body with the axis along the Y direction.

The cross section of the periodic unit of the two-dimensional periodic structure is square.

The pits are 11 rows and 10 columns in total.

The bottom plate 2 is not provided with the pits 4, the central point of a feed opening formed by surrounding the connection part of at least one feed transmission line 3 and the bottom plate 2 is projected on the cover plate 1, and the cover plate is provided with at least 2 pits 4 in the-X direction, the-Z direction and the Z direction by taking the projection point as the central point. This arrangement allows microwaves fed from the feed to achieve a microwave stop band over a wide bandwidth around the operating frequency of the microwave device, which microwaves will reach the channel but do not propagate with said channel in the horizontal plane, but are confined near the feed of the feed transmission line.

For example, with reference to the figures, there are 4 such pits, or 5 or more, in the-X direction, the-Z direction and the Z direction.

Example 2

As shown in fig. 4, 5, and 6.

The difference from embodiment 1 is only that the same number of dimples of the same size are also provided on the upper surface of the base plate 2. In the vicinity of the feed opening of the feed transmission line 3, the recess 4 on the base plate 2 which conflicts with the feed opening is not provided.

At least 2 said pits 4 are present in the bottom plate 2 in-X-direction, -Z-direction and Z-direction around the centre point of the feed opening formed by the connection of at least one said feed transmission line 3 with said bottom plate 2. This arrangement makes it possible to achieve a microwave stop band in a wide bandwidth around the operating frequency of the microwave device for microwaves fed in from the feed, which will reach the channel but not propagate with said channel in the horizontal plane, but which are confined near the feed of the feed transmission line.

For example, with reference to the figures, there are 4 of said pits, or 5 or more, in the-X direction, the-Z direction and the Z direction.

Example 3

As shown in fig. 7.

Compared with example 1, the difference is only that the shape of the cross section of the periodic unit of the two-dimensional periodic structure is "clover-shaped". The cross-sectional shape of the "clover-shaped" pits is shown in fig. 4.

Example 4

As shown in fig. 1, 2, 3, and 8.

Example 4 specific implementation. On the basis of example 1, dimples were provided only on the cover plate, the dimples were square dimples, the dimple side length was 92.4 mm, the height (dimple depth) was 34.34 mm, the spacing between the sides of adjacent dimples was 3.28 mm, and the channel height was 30 mm.

Fig. 8 is a plot of leakage loss versus frequency for example 4, obtained by this calculation. In the calculations, a standard BJ26 rectangular waveguide (cross-sectional dimension 86.36 mm x 43.18 mm) fed microwave energy into the channel from the lower end of the baseplate. The boundary conditions for the four sides in the computational model were all set to full absorption.

It can be seen from fig. 8 that in the frequency range of 2.3GHz to 2.55GHz, only-13 dB (5%) of the energy fed into the microwaves in the channel passes through the channel to the four sides and is absorbed. The remaining microwave energy is reflected along the feed transmission line. Thus, the present embodiment achieves good isolation between the feed transmission line and the surrounding devices. When the conveyor belt and the heated object are arranged in the channel, the feed transmission line can be well matched, so that the feed microwave is basically absorbed by the heated object.

Example 5

As shown in fig. 9.

Compared with embodiment 1, the difference is only that two feed transmission lines 3 are provided on the substrate.

The foregoing is merely a preferred embodiment of the invention and is not intended to limit the invention in any manner. The main innovation points of the invention are as follows: the band stop containing the working frequency is realized by arranging the two-dimensional periodic pit array on one or two inner surfaces between two flat plates, so that effective isolation among a plurality of feed-in transmission lines is realized. According to the technical spirit of the present invention, any simple modification, equivalent replacement, and improvement made to the above embodiments within the spirit and principle of the present invention are still within the protection scope of the technical solution of the present invention.

Claims

1. A microwave device with a two-dimensional periodic structure comprises a cover plate (1) positioned in a Y direction and a bottom plate (2) positioned in a-Y direction, wherein at least one feed-in transmission line (3) is arranged below the bottom plate (2); a channel (5) is arranged between the cover plate (1) and the bottom plate (2); the feed transmission line (3) transmits microwave energy to a channel (5) between the cover plate (1) and the bottom plate (2); a two-dimensional periodic structure is arranged on the lower surface of the cover plate (1), or on the upper surface of the bottom plate (2), or on the lower surface of the cover plate (1) and the upper surface of the bottom plate (2) simultaneously; characterized in that the periodic unit of the two-dimensional periodic structure is a pit (4); x, Y and the Z direction form a rectangular coordinate system.

2. A microwave device with a two-dimensional periodic structure according to claim 1, characterized in that around the center point of the feed formed at the connection of at least one feed transmission line (3) to the cover plate (1) or the bottom plate (2) there are at least 2 pits (4) in-X direction, -Z direction and Z direction.

3. A microwave device with a two-dimensional periodic structure according to claim 1, wherein the periodic units of the two-dimensional periodic structure are columns with axes along the Y direction.

4. A microwave device with a two-dimensional periodic structure according to claim 1, characterized in that the shape of the cross-section of the periodic cells of the two-dimensional periodic structure is square.

5. A microwave device with a two-dimensional periodic structure according to claim 1, characterized in that the shape of the cross-section of the periodic elements of the two-dimensional periodic structure is circular.

6. A microwave device with a two-dimensional periodic structure according to claim 1, characterized in that the periodic units of the two-dimensional periodic structure are equilateral polygons in cross section.

7. A microwave device with a two-dimensional periodic structure according to claim 1, characterized in that the shape of the cross-section of the periodic units of the two-dimensional periodic structure is clover-shaped.

8. A microwave device with a two-dimensional periodic structure according to any of claims 1 to 7, characterized in that the distance between the centre points of the pits (4) is more than 20% of the operating wavelength.

9. A microwave device with a two-dimensional periodic structure according to any of the claims 1 to 7, characterized in that the depth of the pits (4) in the Y-direction is 15-35% of the operating wavelength.

10. A microwave device with a two-dimensional periodic structure according to any of the claims 1-7, characterized in that the height of the channels (5) in the Y-direction is less than 50% of the operating wavelength.