CN114665242B

CN114665242B - Device and method for improving electromagnetic field uniformity in microwave cavity by using adjustable artificial magnetic conductor

Info

Publication number: CN114665242B
Application number: CN202210356893.8A
Authority: CN
Inventors: 唐志祥; 夏懿嘉; 请求不公布姓名; 刘弋; 曾益轩
Original assignee: Hunan University
Current assignee: Foshan Esamber Electronic Technology Co ltd
Priority date: 2022-04-06
Filing date: 2022-04-06
Publication date: 2023-03-24
Anticipated expiration: 2042-04-06
Also published as: CN114665242A

Abstract

The invention discloses a device and a method for improving electromagnetic field uniformity in a microwave cavity by using an adjustable artificial magnetic conductor, wherein the device comprises the microwave cavity and the adjustable artificial magnetic conductor, wherein the adjustable artificial magnetic conductor is arranged in the microwave cavity and can work in an in-phase total reflection state or a reverse phase total reflection state by adjustment; the in-phase total reflection state means that the phase difference between a reflected wave and an incident wave of the adjustable artificial magnetic conductor is 0, and the reverse phase total reflection state means that the phase difference between the reflected wave and the incident wave of the adjustable artificial magnetic conductor is pi. The alternation of the node and the antinode in the cavity is realized by continuously changing two working states of the adjustable artificial magnetic conductor, thereby achieving the purpose of improving the uniformity of the electromagnetic field in the cavity.

Description

Device and method for improving electromagnetic field uniformity in microwave cavity by using adjustable artificial magnetic conductor

Technical Field

The invention relates to the technical field of microwaves, in particular to a method for improving electromagnetic field uniformity in a microwave cavity by using an adjustable artificial magnetic conductor.

Background

Microwave treatment such as microwave sterilization, microwave disinfestation, microwave heating, microwave drying and the like has the advantages of high efficiency, rapidness, energy conservation, integral treatment and the like, and is widely applied to the fields of industry, agriculture, medical treatment, food processing and the like.

In order to prevent electromagnetic pollution and electromagnetic interference caused by microwave leakage, microwave processing is usually performed in a metal cavity. Due to the fact that electromagnetic power density of an electromagnetic field resonance mode in the microwave cavity is not distributed uniformly in space, some materials are processed (such as overheated) and some materials are not processed (such as unheated), and therefore popularization and application of microwave processing in more fields are greatly limited. How to effectively improve the uniformity of microwave treatment has become an important issue for the application and popularization of microwave energy.

There are two main ways to improve the uniformity of microwave treatment from the perspective of the microwave chamber. One is to arrange a rotary loading tray in the microwave cavity. The method is one of the simplest and most effective methods for improving the uniformity of microwave treatment at present, but the scheme often leads to over-treatment or under-treatment of the central position of the turntable because the rotating shaft is fixed. Although the combined rotary tray can enrich the space motion trail of the processed material and improve the problem of over-processing or under-processing of the center of the rotary disc, the structure is too complex. Moreover, such rotary loading trays, especially modular rotary trays, are not very convenient for in-cavity cleaning. The other is a flat plate type microwave cavity. The moving parts (namely the electromagnetic stirrer) of the cavity are isolated by the ceramic plate, and no moving part exists in the cavity, so that the problems of inconvenience in cleaning in the cavity and the like caused by rotating the tray are solved. In the flat plate cavity, the heated material is placed in the cavity, and the heating uniformity of the flat plate cavity is mainly dependent on the stirring capability of the electromagnetic stirrer to the modes in the cavity and the complementarity of the spatial distribution of the electromagnetic field of each mode. However, most of the flat-plate microwave cavities in the market are not as uniform as the rotating tray type microwave cavities, and the uniformity of the flat-plate microwave cavities has a great promotion space.

In addition, microwave treatment uniformity may also be improved from the perspective of the microwave source. The spatial power distribution of different frequency electromagnetic wave modes in the same cavity is different, and the microwave cavity is excited by reasonably utilizing a broadband microwave source or a plurality of microwave sources with different working frequencies, so that the microwave treatment uniformity can be effectively improved. However, the use of a broadband microwave source (which is inherently expensive) or a plurality of microwave sources of different frequencies will undoubtedly add significantly to the cost of the microwave treatment apparatus.

An artificial electromagnetic material, also called an electromagnetic metamaterial, is a micro-structure electromagnetic material artificially designed for a specific working wavelength, and can realize electromagnetic characteristics such as negative refraction, in-phase total reflection (total reflection at a magnetic conductor interface) of a microwave band and even an optical band, which are not possessed by many natural materials in the band. Electromagnetic metamaterials have been widely used in antenna design due to their unique electromagnetic properties to reduce back lobe radiation and improve antenna gain.

The non-uniformity of the microwave treatment of the conventional microwave treatment device is mainly caused by the non-uniform spatial distribution of the electromagnetic power density caused by the standing wave electromagnetic field in the microwave cavity. Therefore, the method capable of effectively improving the uniformity of the microwave cavity electromagnetic field has important values for improving the uniformity of microwave treatment, improving the quality of a household microwave oven and further expanding the application of microwave treatment (such as microwave sterilization, microwave disinsection and the like) in other uniformity sensitive fields.

Disclosure of Invention

Aiming at the problem of poor uniformity of the existing microwave treatment, the invention provides a method for improving the uniformity of an electromagnetic field in a microwave cavity by using an adjustable artificial magnetic conductor, so that the microwave treatment uniformity of a microwave treatment device is improved, and the application of microwave treatment (such as microwave sterilization, microwave disinsection and the like) in other uniformity-sensitive fields is further expanded.

In order to realize the technical effects, the technical proposal of the invention is that,

a device for improving the uniformity of an electromagnetic field in a microwave cavity by utilizing an adjustable artificial magnetic conductor comprises a microwave cavity and the adjustable artificial magnetic conductor, wherein the adjustable artificial magnetic conductor is arranged in the microwave cavity and can work in an in-phase total reflection state or a reverse phase total reflection state through adjustment; the in-phase total reflection state refers to that the phase difference between a reflected wave and an incident wave of the adjustable artificial magnetic conductor is 0, and the reverse phase total reflection state refers to that the phase difference between the reflected wave and the incident wave of the adjustable artificial magnetic conductor is pi.

The device for improving the uniformity of the electromagnetic field in the microwave cavity by using the adjustable artificial magnetic conductor is characterized in that the adjustable artificial magnetic conductor is arranged on one or a pair of parallel inner walls of the microwave cavity.

The device for improving the uniformity of an electromagnetic field in a microwave cavity by using the adjustable artificial magnetic conductor comprises a platy body array on the upper layer, an insulating plate on the middle layer and a metal plate on the lower layer, wherein the upper layer and the lower layer are exchanged by turning over the adjustable artificial magnetic conductor, so that the working state of the artificial magnetic conductor is changed.

The device for improving the uniformity of the electromagnetic field in the microwave cavity by using the adjustable artificial magnetic conductor is characterized in that the sheet-shaped body array is an array formed by a plurality of metal sheets distributed at equal intervals.

The device for improving the uniformity of an electromagnetic field in a microwave cavity by using the adjustable artificial magnetic conductor comprises a platy body array on the upper layer, an insulating plate on the middle layer and a metal plate on the lower layer, wherein every two platy bodies in the platy body array are arranged in pairs, each pair of platy bodies are connected with each other through a PIN diode, and the working state of the artificial magnetic conductor is changed by controlling the state of the PIN diode.

The device for improving the uniformity of the electromagnetic field in the microwave cavity by using the adjustable artificial magnetic conductor is characterized in that the sheet-shaped body array is an array formed by a plurality of metal sheets which are distributed at equal intervals.

When the PIN diode is in positive bias, the connected pair of flaky bodies are in a conducting state, so that the adjustable artificial magnetic conductor works in a reverse-phase total reflection state; when the PIN diode is zero-biased or reversely biased, the connected pair of platy bodies are in a disconnected state, so that the adjustable artificial magnetic conductor works in an in-phase total reflection state.

The device for improving the uniformity of the electromagnetic field in the microwave cavity by using the adjustable artificial magnetic conductor is characterized in that the mode index of the microwave cavity in the normal direction of the reflecting surface of the adjustable artificial magnetic conductor is not 0.

A method for improving the electromagnetic field uniformity in a microwave cavity by using an adjustable artificial magnetic conductor, which is characterized in that the method adopts the device as above and comprises the following steps:

when an electromagnetic field exists in the microwave cavity, the working state of the adjustable artificial magnetic conductor is continuously changed, so that the adjustable artificial magnetic conductor is repeatedly changed between an in-phase total reflection state and a reverse total reflection state, and the electromagnetic field in the cavity moves between a node and an anti-node of the standing wave in the direction, so that the continuous change of the electromagnetic field in the cavity is realized, and the uniformity is further kept.

The microwave cavity has the technical effects that the adjustable artificial magnetic conductor which can be manually controlled and can change between the in-phase total reflection state and the reverse phase total reflection state is arranged in the microwave cavity, so that an electromagnetic field in the cavity moves between a node and an antinode of standing waves in the direction, and the continuous change of the electromagnetic field in the cavity is realized so as to keep uniform.

Drawings

Fig. 1 is a schematic three-dimensional structure of an adjustable artificial magnetic conductor 1 according to embodiment 1 of the present invention;

fig. 2 is a schematic three-dimensional structure diagram of a microwave resonant cavity 2 containing an adjustable artificial magnetic conductor 1 in example 1 of the present invention;

fig. 3 is a distribution of intracavity field intensity of the microwave resonant cavity 2 including the adjustable artificial magnetic conductor 1 in working state 1 according to embodiment 1 of the present invention;

fig. 4 is a distribution of intracavity field intensity of the microwave resonant cavity 2 including the adjustable artificial magnetic conductor 1 in the working state 2 according to embodiment 1 of the present invention;

fig. 5 shows the distribution of the cavity field intensity of the microwave resonant cavity 2 when the working state of the adjustable artificial magnetic conductor 1 is continuously changed in embodiment 1 of the present invention.

Fig. 6 is a schematic three-dimensional structure of an adjustable artificial magnetic conductor 6 according to embodiment 2 of the present invention;

fig. 7 is a schematic three-dimensional structure of a microwave cavity 8 including an adjustable artificial magnetic conductor 6 according to example 2 of the present invention;

fig. 8 is the intracavity field intensity distribution of the microwave resonant cavity 8 containing the adjustable artificial magnetic conductor 6 in the working state 1 according to the embodiment 2 of the present invention;

fig. 9 is the intracavity field intensity distribution of the microwave cavity 8 containing the adjustable artificial magnetic conductor 6 in the working state 2 according to the embodiment 2 of the present invention;

fig. 10 is a graph showing the distribution of the cavity field intensity of the microwave resonant cavity 8 when the operating state of the adjustable artificial magnetic conductor 6 is continuously changed in embodiment 2 of the present invention.

Detailed Description

In order to more clearly illustrate the embodiment of the present invention, the technical solutions in the embodiment of the present invention will be clearly and completely described below with reference to the drawings in the embodiment of the present invention. It should be apparent that the described embodiments are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without the need for inventive effort, all fall within the scope of protection of the present invention.

The invention discloses a method for improving electromagnetic field uniformity in a microwave cavity by using an adjustable artificial magnetic conductor, which comprises the following steps:

step 1, designing an adjustable artificial magnetic conductor according to the working frequency of a microwave resonant cavity. The adjustable artificial magnetic conductor has two working states: one is in-phase total reflection state, i.e. the phase difference between the reflected wave and the incident wave is pi, and the interface is the antinode of the synthesized wave. One is in an inverse total reflection state, namely the phase difference between the reflected wave and the incident wave is 0, and the interface is a wave node of the synthesized wave.

And 2, taking the adjustable artificial magnetic conductor as one or a pair of circular bottom surfaces of a cylindrical resonant cavity or a coaxial resonant cavity or one or a pair of reflecting surfaces of a rectangular resonant cavity. And the geometric dimension of the microwave cavity is designed to ensure that the mode index of the working mode of the microwave cavity in the normal direction of the reflecting surface is not 0, namely the electromagnetic field is not uniformly distributed in space.

And 3, changing the working state of the adjustable artificial magnetic conductor, namely changing in-phase total reflection into reverse phase total reflection or changing reverse phase total reflection into in-phase total reflection, so that a node (an antinode) of the standing wave of the electromagnetic field in the cavity in the direction moves to an antinode (an antinode), and further changing the working state of the adjustable artificial magnetic conductor continuously so that the node and the antinode of the electromagnetic field in the cavity in the direction are alternately changed, and the uniformity of the electromagnetic field in the cavity in the direction is improved.

The present invention will be further described with reference to the following examples.

Example 1

The working frequency of the rectangular microwave cavity is set to be 2.45GHz, and the steps of improving the electromagnetic field uniformity in the rectangular microwave cavity shown in the figure 2 by utilizing the adjustable artificial magnetic conductor are as follows:

step 1, designing an adjustable artificial magnetic conductor 1 according to the working frequency of a microwave resonant cavity of 2.45GHz as shown in figure 1. The adjustable artificial magnetic conductor is of a three-layer structure, the upper layer is a square array of square copper sheets with the side length of b =19mm, the center distance between two adjacent square copper sheets is a =20mm, and the thickness of each copper sheet is 0.1mm. The middle layer is a glass fiber insulating board with the thickness of 3.5mm. The bottom layer is a copper plate with the thickness of 0.1mm. The square copper sheet array surface is an in-phase total reflection surface of the adjustable artificial magnetic conductor, the bottom layer copper sheet surface is an opposite-phase total reflection surface opposite to the adjustable artificial magnetic conductor, and the reflection surface of the adjustable artificial magnetic conductor is changed through overturning, so that the working state of the adjustable artificial magnetic conductor is changed;

step 2, taking the artificial magnetic conductor 1 designed in the step 1 as a reflecting surface of the rectangular resonant cavity 2, as shown in fig. 2, where a surface where the waveguide feed-in port 3 (wp =80mm, wq = 40mm) is located is an adjustable artificial magnetic conductor in-phase total reflection surface, and a corresponding surface is an anti-phase total reflection surface of the adjustable artificial magnetic conductor. The transverse dimensions of the rectangular resonant cavity are designed to be p =300mm and q =180mm. When the longitudinal length l =346mm, the electromagnetic wave emitted by the microwave source 4 is fed into the microwave cavity 1 via the waveguide feed opening 3, which is rectangular, and the field intensity distribution of the cavity 1 in the plane 5 is shown in fig. 3. Obviously, 6 wave nodes and 6 anti-node points are clearly visible on the plane, the wave nodes are on the total reflection surface in the reverse direction of the adjustable artificial magnetic conductor, the anti-node points are on the total reflection surface in the same direction, and the working state is 1.

And 3, changing the working state of the adjustable artificial magnetic conductor by overturning, namely changing in-phase total reflection into anti-phase total reflection or changing anti-phase total reflection into in-phase total reflection, which is a working state 2. The field strength distribution of the cavity at plane 5 under the same excitation is shown in fig. 4. Similarly, 6 wave nodes and 6 anti-node points are clearly visible on the plane, and the anti-total reflection surface of the adjustable artificial magnetic conductor is provided with the wave nodes and the homodromous total reflection surface is provided with the anti-node points. In contrast to fig. 3, it can be seen that the antinode and antinode points in fig. 3 are located exactly at the antinode and antinode points in fig. 4. By continuously changing the working state of the adjustable artificial magnetic conductor, the node and the antinode of the electromagnetic field in the cavity in the direction are alternately changed, and finally the time-averaged field intensity distribution of the plane 5 is obtained as shown in fig. 5. The uniformity of fig. 5 is significantly improved compared to fig. 3 and 4.

Example 2

The working frequency of the rectangular microwave cavity is set to be 2.45GHz, and the steps of improving the uniformity of the electromagnetic field in the rectangular microwave cavity 8 by using the adjustable artificial magnetic conductor 6 are as follows:

step 1, designing an adjustable artificial magnetic conductor 6 according to the working frequency of the microwave resonant cavity of 2.45GHz as shown in figure 6. The adjustable artificial magnetic conductor is of a three-layer structure, the upper layer is a square array of square copper sheets with the side length of b =18.5mm, the center distance between two adjacent square copper sheets is a =20mm, and the thickness of each copper sheet is 0.1mm. The middle layer is a glass fiber insulating board with the thickness of 3.6mm. The bottom layer is a copper plate with the thickness of 0.1mm. In the square copper sheet array, two adjacent copper sheets are connected by a PIN diode 7, as shown in FIG. 6. When the PIN diode is forward biased, the two copper sheets connected with the diode are in a conducting state, and the adjustable artificial magnetic conductor works in a reverse phase total reflection state; when the PIN diode is in zero bias or reverse bias, the two copper sheets connected with the diode are in a disconnected state, and the adjustable artificial magnetic conductor works in an in-phase total reflection state at the moment.

Step 2, the adjustable artificial magnetic conductor 6 designed in step 1 is used as two reflecting surfaces of a rectangular resonant cavity 8 as shown in fig. 7, and microwaves are injected into the rectangular microwave cavity from a microwave feed port 9. The transverse dimensions of the rectangular resonant cavity are wp =80mm and wq =40mm, and the cavity length l =300mm. When the PIN diode is forward biased, the field strength distribution within the cavity is as shown in fig. 8. Obviously, the adjustable artificial magnetic conductor works in an inverted total reflection state, and a wave node is on the reflecting surface of the adjustable artificial magnetic conductor, which is a working state 1.

And 3, stopping the forward bias or reverse bias PIN diode of the PIN diode, and changing the reverse total reflection of the adjustable artificial magnetic conductor from the forward bias into the in-phase total reflection at the moment, wherein the working state is a working state 2. Under the same excitation, the field intensity distribution in the resonant cavity is as shown in fig. 9, at this time, the adjustable artificial magnetic conductor works in an in-phase total reflection state, and an anti-node point is on the reflecting surface of the adjustable artificial magnetic conductor. As can be seen by comparing fig. 8, the positions of the nodes and anti-nodes in fig. 8 are exactly the anti-nodes and anti-nodes in fig. 9. By continuously changing the bias voltage (forward bias and reverse bias) of the PIN diode, the adjustable artificial magnetic conductor is continuously switched between two working states of reverse phase total reflection and in-phase total reflection, so that the node and the antinode of the electromagnetic field in the cavity in the direction are alternately changed, and finally the time-averaged field intensity distribution in the cavity is obtained as shown in fig. 10. The uniformity of fig. 10 is significantly improved compared to fig. 8 and 9.

The invention provides a method for improving the uniformity of an electromagnetic field in a microwave cavity by using an adjustable artificial magnetic conductor, which realizes the alternation of a wave node and an antinode in the cavity by continuously changing two working states of the adjustable artificial magnetic conductor, thereby achieving the purpose of improving the uniformity of the electromagnetic field in the cavity.

It is understood that various changes and modifications may be made by those skilled in the art without departing from the spirit and scope of the invention, and it is intended to cover in the appended claims all such changes and modifications.

Claims

1. The device for improving the uniformity of the electromagnetic field in the microwave cavity by using the adjustable artificial magnetic conductor is characterized by comprising a microwave cavity and the adjustable artificial magnetic conductor, wherein the adjustable artificial magnetic conductor is arranged in the microwave cavity and can work in an in-phase total reflection state or a reverse total reflection state by adjustment; the in-phase total reflection state means that the phase difference between a reflected wave and an incident wave of the adjustable artificial magnetic conductor is 0, and the reverse phase total reflection state means that the phase difference between the reflected wave and the incident wave of the adjustable artificial magnetic conductor is pi;

the adjustable artificial magnetic conductor is arranged on one or a pair of parallel inner walls of the microwave cavity;

and the mode index of the microwave cavity in the normal direction of the reflecting surface of the adjustable artificial magnetic conductor is not 0.

2. The apparatus as claimed in claim 1, wherein the adjustable artificial magnetic conductor comprises an upper array of platelets, a middle insulating plate and a lower metal plate, and the upper and lower layers are reversed by turning the adjustable artificial magnetic conductor, so as to change the operating state of the artificial magnetic conductor.

3. An apparatus as claimed in claim 2, wherein the array of platelets is an array of a plurality of equally spaced metal sheets.

4. An apparatus as claimed in claim 1, wherein the adjustable artificial magnetic conductor comprises an upper array of platelets, a middle insulating plate and a lower metal plate, and the platelets in the array are paired with each other, and each pair of platelets is connected to each other through a PIN diode, and the operating state of the artificial magnetic conductor is changed by controlling the state of the PIN diode.

5. An apparatus as claimed in claim 4, wherein the array of platelets is an array of a plurality of equally spaced metal sheets.

6. The apparatus as claimed in claim 4, wherein when the PIN diode is forward biased, the pair of connected sheets is in a conducting state, so that the tunable artificial magnetic conductor operates in a reverse total reflection state; when the PIN diode is zero-biased or reversely biased, the connected pair of platy bodies are in a disconnected state, so that the adjustable artificial magnetic conductor works in an in-phase total reflection state.

7. A method for improving electromagnetic field uniformity in a microwave cavity using an adjustable artificial magnetic conductor, wherein the apparatus of any one of claims 1-6 is used, comprising the steps of:

when an electromagnetic field exists in the microwave cavity, the working state of the adjustable artificial magnetic conductor is continuously changed, so that the adjustable artificial magnetic conductor is repeatedly changed between an in-phase total reflection state and a reverse total reflection state, and the electromagnetic field in the cavity moves between a node and an anti-node of a standing wave in the directions of a reflected wave and an incident wave, so that the continuous change of the electromagnetic field in the cavity is realized, and the uniformity is further kept.