JP2024005084A - microwave heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To ensure that, when heating a heating object using microwaves, the microwave magnetic field or microwave electric field is evenly distributed near the center axis of a cavity resonator, and the object to be heated by microwaves is thereby evenly heated.

SOLUTION: Provided is a microwave heating device M comprising: a cavity resonator 1 that focuses a microwave magnetic field or microwave electric field on the center axis; an accommodation container 2 that accommodates the object to be heated by microwaves on the center axis of the cavity resonator 1; and two excitation loops 3 that are installed at 90-degree interval in the inside and on the side wall of the cavity resonator 1, where the ones adjacent to each other are excited at a 90-degree phase difference, or n excitation loops 3 (n=3 or greater) that are installed at 360/n-degree interval in the inside and on the side wall of the cavity resonator 1, where the ones adjacent to each other are excited at a 360/n-degree phase difference. The microwave heating device M is further characterized in that the microwave magnetic field distribution or the microwave electric field distribution rotates around the center axis of the cavity resonator 1 with the passage of time.

SELECTED DRAWING: Figure 4

COPYRIGHT: (C)2024,JPO&INPIT

Description

The present disclosure relates to a technique for heating a heating target using microwaves.

A technique for heating a heating target using microwaves is disclosed in Patent Document 1 and the like. For example, microwaves are used to heat catalysts to generate hydrogen. In Patent Document 1, a microwave electric field is concentrated on the central axis of the cavity resonator using the fundamental mode (TM01 mode, etc.) of the cavity resonator, and a microwave-heated object (dielectric material, etc.) is accommodated on the central axis. contained in a container. On the other hand, the microwave magnetic field is concentrated on the central axis of the cavity resonator by using a higher-order mode (TM11 mode, etc.) of the cavity resonator, and the microwave-heated object (conductor, etc.) is accommodated on the central axis. It may be stored in a container.

JP2021-072221A

The configuration of a conventional microwave heating device is shown in FIG. The microwave heating device M includes a cavity resonator 1, a container 2, and an excitation loop 3. The cavity resonator 1 concentrates the microwave magnetic field on the central axis using a higher-order mode (TM11 mode, etc.). The housing container 2 houses a microwave-heated object (such as a conductor) on the central axis of the cavity resonator 1 . One excitation loop 3 (which is an example of an exciter and may also be an excitation antenna) is installed inside the cavity resonator 1 and on the side wall.

FIG. 2 shows simulation results of the magnetic field distribution of a conventional microwave heating device. In the left column of FIG. 2, the overall microwave magnetic field distribution of the cavity resonator 1 is shown. The right column of FIG. 2 shows the microwave magnetic field distribution near the central axis of the cavity resonator 1. Then, in the vicinity of the central axis of the cavity resonator 1, the microwave magnetic field is concentrated on the side closer to the excitation loop 3, and the microwave magnetic field is weakened on the side farther from the excitation loop 3. In other words, a hot spot occurs in which a part of the microwave-heated object is extremely heated.

The simulation results of the magnetic field distribution of the conventional microwave heating device are also shown in FIG. In the left column of FIG. 3, the storage container 2 (glass tube) is replaced with air in the simulation. Then, as in the right column of FIG. 2, the microwave magnetic field is concentrated on the side near the excitation loop 3 in the vicinity of the central axis of the cavity resonator 1. In the middle column of FIG. 3, the microwave heating target (carbon catalyst as a conductor) is replaced with air in the simulation. Then, unlike the right column of FIG. 2, the microwave magnetic field is concentrated near the center axis of the cavity resonator 1 on the side far from the excitation loop 3. In the right column of FIG. 3, the container 2 (glass tube) and the microwave heating target (carbon catalyst as a conductor) are replaced with air in the simulation. Then, as in the middle column of FIG. 3, the microwave magnetic field is concentrated near the central axis of the cavity resonator 1 on the side far from the excitation loop 3. In other words, the object of microwave heating (carbon catalyst as a conductor) has a greater influence on the generation of hot spots than the container 2 (glass tube).

1 to 3 show that a hot spot occurs when the cavity resonator 1 concentrates the microwave magnetic field on the central axis. On the other hand, when the cavity resonator 1 concentrates the microwave electric field on the central axis, a hot spot may occur.

Therefore, in order to solve the above problems, the present disclosure provides a method for heating a heating target using microwaves by uniformly distributing a microwave magnetic field or a microwave electric field near the central axis of a cavity resonator. The purpose of wave heating is to uniformly heat the object.

In order to solve the above problem, a plurality of exciters are installed inside and on the side walls of the cavity resonator in order to uniformly heat the object to be heated by microwaves. Then, by applying the principle of a circularly polarized antenna to a microwave heating device, a plurality of exciters are not excited with the same phase but with a predetermined phase difference.

Specifically, the present disclosure provides a cavity resonator that concentrates a microwave magnetic field or a microwave electric field on a central axis, a housing container that accommodates a microwave heating target on the central axis of the cavity resonator, and Two exciters installed at 90 degree intervals inside and on the side walls of the cavity resonator, and adjacent exciters are excited with a phase difference of 90 degrees, or two exciters installed at 360/n degree intervals inside and on the side walls of the cavity resonator. n number of exciters (n is 3 or more), which are installed at The microwave heating device is characterized in that it rotates around the central axis of the cavity resonator.

According to this configuration, the microwave magnetic field or the microwave electric field can be distributed almost uniformly near the central axis of the cavity resonator at each time. If time averaging is taken, the microwave magnetic field or microwave electric field can be distributed more uniformly near the central axis of the cavity resonator. Therefore, the microwave heating target can be heated uniformly.

Further, the present disclosure is a microwave heating device characterized in that the n exciters are an odd number of exciters of three or more.

According to this configuration, since the exciters are not opposed to each other via the central axis of the cavity resonator, coupling between the exciters can be suppressed, and power inflow between the exciters can be prevented.

Further, in the present disclosure, the two exciters or the n exciters are excited at a frequency swept in a predetermined width, and adjacent ones are switched with a phase difference of ±90 degrees or ±360/n degrees. This microwave heating device is characterized in that it is excited with a phase that is swept over a predetermined width, or is excited with a combination of the above operations.

According to this configuration, by sweeping the excitation frequency, the direction in which the microwave magnetic field or microwave electric field is strong can be rotated, and by switching between left rotation and right rotation, the direction in which the microwave magnetic field or microwave electric field is strong can be rotated. By sweeping the excitation phase, the direction in which the microwave magnetic field or microwave electric field is strong can be rotated.

As described above, the present disclosure provides a method for uniformly distributing a microwave magnetic field or a microwave electric field in the vicinity of the central axis of a cavity resonator when heating an object using microwaves. Can be heated.

FIG. 1 is a diagram showing the configuration of a conventional microwave heating device. It is a figure which shows the simulation result of the magnetic field distribution of the microwave heating device of a prior art. It is a figure which shows the simulation result of the magnetic field distribution of the microwave heating device of a prior art. FIG. 1 is a diagram showing the configuration of a microwave heating device according to a first embodiment. It is a figure showing the simulation result of the magnetic field distribution of the microwave heating device of a 1st embodiment. It is a figure showing the simulation result of the magnetic field distribution of the microwave heating device of a 1st embodiment. It is a figure showing the simulation result of the magnetic field distribution of the microwave heating device of a 1st embodiment. It is a figure which shows the simulation result of the magnetic field distribution of the microwave heating device of 2nd Embodiment. It is a figure which shows the simulation result of the magnetic field distribution of the microwave heating device of 2nd Embodiment. It is a figure showing the simulation result of the magnetic field distribution of the microwave heating device of the 1st and 2nd embodiments.

Embodiments of the present disclosure will be described with reference to the accompanying drawings. The embodiments described below are examples of implementation of the present disclosure, and the present disclosure is not limited to the following embodiments.

(Microwave heating device of first embodiment)
FIG. 4 shows the configuration of the microwave heating device of the first embodiment. The microwave heating device M includes a cavity resonator 1, a container 2, and a plurality of excitation loops 3 (three excitation loops 3-1, 3-2, and 3-3 in FIG. 4). The cavity resonator 1 concentrates the microwave magnetic field on the central axis using a higher-order mode (TM11 mode, etc.). The housing container 2 houses a microwave-heated object (such as a conductor) on the central axis of the cavity resonator 1 . A plurality of excitation loops 3 (which is an example of an exciter and may also be an excitation antenna) are installed inside and on the side wall of the cavity resonator 1 at predetermined intervals as shown in FIGS. 5 and 6.

That is, in order to uniformly heat the microwave-heated object, a plurality of excitation loops 3 are installed inside the cavity resonator 1 and on the side walls. Then, by applying the principle of a circularly polarized antenna to the microwave heating device M, the plurality of excitation loops 3 are not excited with the same phase but with a predetermined phase difference.

Here, when a plurality of excitation loops 3 are excited in the same phase, the microwave magnetic field distribution shown in FIG. The magnetic field distribution will be broken. On the other hand, when a plurality of excitation loops 3 are excited with a predetermined phase difference, the microwave magnetic field distribution shown in FIGS. 5 and 6 is realized using the principle of a circularly polarized antenna, and The microwave magnetic field distribution becomes almost uniform.

Simulation results of the magnetic field distribution of the microwave heating device of the first embodiment are shown in FIGS. 5 and 6. In FIG. 5, the overall microwave magnetic field distribution of the cavity resonator 1 is shown. FIG. 6 shows the microwave magnetic field distribution near the central axis of the cavity resonator 1. In the upper left column of FIGS. 5 and 6, one excitation loop 3 is installed inside the cavity resonator 1 and on the side wall. In the middle upper columns of FIGS. 5 and 6, two excitation loops 3-1 and 3-2 are installed inside the cavity resonator 1 and on the side wall at 90 degree intervals, and adjacent ones have a phase difference of 90 degrees. Excited. In the upper right column, lower left column, middle lower column, and lower right column of FIGS. 5 and 6, n excitation loops 3-1, ..., 3-n (n≧3) They are installed on the side wall at intervals of 360/n degrees, and adjacent ones are excited with a phase difference of 360/n degrees.

In the upper left column of FIGS. 5 and 6 (one excitation loop 3), the microwave magnetic field is concentrated on the side near the excitation loop 3 near the center axis of the cavity resonator 1, and the microwave magnetic field is concentrated on the side far from the excitation loop 3. The wave magnetic field weakens. In the upper middle column of FIGS. 5 and 6 (two excitation loops 3-1 and 3-2), the central axis of the cavity resonator 1 is different from the upper left column of FIGS. The microwave magnetic field is distributed almost uniformly in the vicinity. However, the magnetic field distribution near the loops due to the two excitation loops 3-1 and 3-2 is disordered, and the circularly polarized magnetic field distributions due to the two excitation loops 3-1 and 3-2 are not superimposed as they are. The uniformity of the microwave magnetic field distribution near the central axis of the cavity resonator 1 becomes low.

In the upper right column, lower left column, middle lower column, and lower right column of FIGS. 5 and 6 (3, 4, 5, and 6 excitation loops 3-1, ..., 3-n), FIG. 6 (two excitation loops 3-1, 3-2), the microwave magnetic field is distributed almost uniformly near the central axis of the cavity resonator 1. In other words, the magnetic field distribution near the loops due to the 3, 4, 5, and 6 excitation loops 3-1, ..., 3-n is not disturbed, and the 3, 4, 5, and 6 excitation loops are not disturbed. The circularly polarized magnetic field distributions caused by the excitation loops 3-1, . In the lower left column, lower middle column, and lower right column of FIGS. 5 and 6 (4, 5, and 6 excitation loops 3-1, ..., 3-n), the upper right column of FIGS. (Compared to the three excitation loops 3-1, 3-2, and 3-3), the microwave magnetic field distribution near the central axis of the cavity resonator 1 is almost the same.

The simulation results of the magnetic field distribution of the microwave heating device of the first embodiment are also shown in FIG. In FIG. 7, the overall microwave magnetic field distribution of the cavity resonator 1 is shown. 5 and 6 show the microwave magnetic field distribution of the cavity resonator 1 at each time, FIG. 7 shows the time change of the microwave magnetic field distribution of the cavity resonator 1. In FIG. 7, three excitation loops 3-1, 3-2, and 3-3 are installed at 120 degree intervals inside the cavity resonator 1 and on the side walls, and adjacent loops are excited with a phase difference of 120 degrees. However, it is almost the same even when n excitation loops 3-1, . . . , 3-n (n≠3) are installed.

Here, the principle of a circularly polarized antenna is applied to the microwave heating device M. Therefore, the microwave magnetic field distribution rotates around the central axis of the cavity resonator 1 as time changes, so that the order of the left column, middle column, and right column of FIG. 7 is repeated. In other words, as the order of the left column, middle column, and right column of FIG. Rotates around the central axis of the cavity resonator 1.

In this way, as shown in FIGS. 5 and 6, the microwave magnetic field can be distributed almost uniformly near the central axis of the cavity resonator 1 at each time. As shown in FIG. 7, if time averaging is taken, the microwave magnetic field can be distributed more uniformly near the central axis of the cavity resonator 1. Therefore, the microwave heating target can be heated uniformly.

4 to 7 show that when the cavity resonator 1 concentrates the microwave magnetic field on the central axis, the microwave magnetic field is uniformly distributed. On the other hand, when the cavity resonator 1 concentrates the microwave electric field on the central axis, it is possible that the microwave electric field is uniformly distributed.

(Microwave heating device of second embodiment)
In the upper right column, lower left column, middle lower column, and lower right column (three or more excitation loops 3-1, ..., 3-n) of FIGS. The wave magnetic field distribution becomes almost the same. However, the plurality of excitation loops 3 is an odd number of three or more excitation loops 3-1, . . . , rather than an even number of excitation loops 3-1, 3-n of four or more. , 3-n.

In other words, when an even number of excitation loops 3-1, . It is not possible to suppress the coupling between the two, and it is not possible to prevent power inflow between the excitation loops 3. On the other hand, when an odd number of three or more excitation loops 3-1, . Coupling between them can be suppressed, and power inflow between the excitation loops 3 can be prevented.

FIG. 8 shows simulation results of the magnetic field distribution of the microwave heating device of the second embodiment. FIG. 8 shows the microwave magnetic field distribution near the central axis of the cavity resonator 1+the change in the microwave magnetic field distribution due to the change in the excitation frequency of the cavity resonator 1. The three excitation loops 3-1, 3-2, and 3-3 are installed inside the cavity resonator 1 and on the side walls at 120 degree intervals, and adjacent loops are excited with a phase difference of 120 degrees. , n excitation loops 3-1, . . . , 3-n (n≠3) are installed.

Generally, two excitation loops 3-1, 3-2 or n excitation loops 3-1, . . . , 3-n are excited at a frequency that is swept over a predetermined width. In FIG. 8, the excitation frequency is basically 2.45 GHz, but the sweep frequency width is 5 to 10 kHz. Then, by sweeping the excitation frequency, it is possible to rotate the direction in which the microwave magnetic field is strong.

The simulation results of the magnetic field distribution of the microwave heating device of the second embodiment are also shown in FIG. FIG. 9 shows the overall microwave magnetic field distribution of the cavity resonator 1 + the change in the microwave magnetic field distribution due to the change in the excitation phase of the cavity resonator 1. The three excitation loops 3-1, 3-2, and 3-3 are installed inside the cavity resonator 1 and on the side walls at 120 degree intervals, and adjacent loops are excited with a phase difference of 120 degrees. , n excitation loops 3-1, . . . , 3-n (n≠3) are installed.

Generally, two excitation loops 3-1, 3-2 or n excitation loops 3-1, ..., 3-n have a phase difference of ±90 degrees or ±360/ It is excited by switching at n degrees. In FIG. 9, in a certain period, compared to the excitation phase of the excitation loop 3-1, the excitation phase difference of the excitation loop 3-2 is 120 degrees, and the excitation phase difference of the excitation loop 3-3 is 240 degrees. On the other hand, in other periods, compared to the excitation phase of the excitation loop 3-1, the excitation phase difference of the excitation loop 3-2 is 240 degrees, and the excitation phase difference of the excitation loop 3-3 is 120 degrees. Then, by switching between left rotation and right rotation, the direction in which the microwave magnetic field is strong can be switched.

The two excitation loops 3-1, 3-2 or the n excitation loops 3-1, . . . , 3-n may be excited with a phase swept in a predetermined width. Then, by sweeping the excitation phase, it is also possible to rotate the direction in which the microwave magnetic field is strong. Further, the two excitation loops 3-1, 3-2 or the n excitation loops 3-1, . . . , 3-n may be excited by combining the above three types of operations. However, sweeping the excitation frequency is the easiest, sweeping the excitation phase is the most complex, and switching between left and right rotation is somewhere in between.

FIG. 10 shows simulation results of the magnetic field distribution of the microwave heating devices of the first and second embodiments. In FIG. 10, a situation was simulated in which a loop-shaped probe (50Ω termination) was installed in the immediate vicinity and outside of the container 2, rotated 360 degrees around the central axis of the cavity resonator 1, and measured the excitation power. Here, the unit of the excitation amplitude axis is dBA/m, and the unit of the azimuth axis around the central axis of the cavity resonator 1 is deg. (degree).

Then, when one excitation loop 3 is installed inside and on the side wall of the cavity resonator 1, the excitation power of the probe largely depends on the angle around the central axis of the cavity resonator 1, and the maximum value of the excitation power The difference between this value and the minimum value was 21 dB. This result was consistent with the microwave magnetic field distribution shown in the upper left column (one excitation loop 3) of FIGS. 5 and 6.

On the other hand, three excitation loops 3-1, 3-2, and 3-3 are installed inside the cavity resonator 1 and on the side walls at 120 degree intervals, and adjacent loops are excited with a phase difference of 120 degrees. At times, the excitation power of the probe was almost independent of the angle around the central axis of the cavity resonator 1, and the difference between the maximum and minimum values of the excitation power was 4 dB. This result was consistent with the microwave magnetic field distribution shown in the upper right column of FIGS. 5 and 6 (three excitation loops 3-1, 3-2, and 3-3).

Although not shown in FIG. 10, when the three excitation loops 3-1, 3-2, and 3-3 were excited at a frequency swept over a predetermined width, the direction in which the microwave magnetic field was strong rotated.

8 to 10 show that when the cavity resonator 1 concentrates the microwave magnetic field on the central axis, the microwave magnetic field is uniformly distributed. On the other hand, when the cavity resonator 1 concentrates the microwave electric field on the central axis, it is possible that the microwave electric field is uniformly distributed.

The microwave heating device of the present disclosure can uniformly heat the catalyst and the like without hot spots when heating the catalyst and the like using microwaves to generate hydrogen and the like.

M: Microwave heating device 1: Cavity resonator 2: Container container 3, 3-1, 3-2, 3-3, 3-4, 3-5, 3-6: Excitation loop

Claims (3)

a cavity resonator that concentrates a microwave magnetic field or a microwave electric field on a central axis;
a container that accommodates a microwave-heated object on the central axis of the cavity resonator;
Two exciters installed at 90 degree intervals inside and on the side walls of the cavity resonator and excited with a phase difference of 90 degrees between adjacent exciters, or 360/n degrees inside and on the side walls of the cavity resonator. n exciters (n is 3 or more) installed at intervals and excited with a phase difference of 360/n degrees between adjacent ones;
A microwave heating device comprising: a microwave magnetic field distribution or a microwave electric field distribution rotating around the central axis of the cavity resonator as time changes. The microwave heating device according to claim 1, wherein the n exciters are an odd number of exciters of three or more. The two exciters or the n exciters are excited with a frequency that is swept over a predetermined width, and adjacent ones are excited while being switched with a phase difference of ±90 degrees or ±360/n degrees, The microwave heating device according to claim 1 or 2, characterized in that the microwave heating device is excited with a phase swept by , or is excited with a combination of the above operations.

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