JP2021072221A - Microwave heating device - Google Patents

Abstract

To provide a microwave heating system in which power efficiency can be increased and device dimensions can be reduced by eliminating the need for a matching unit between a microwave generator and a microwave heating device.SOLUTION: The present disclosure relates to a microwave heating device 3 including a cavity resonator 31 for microwave heating, a housing container 32 of a microwave heating target, an exciter 33 of the cavity resonator 31, and a feeder 34 of the exciter 33. The microwave heating device 3 is characterized in that the exciter 33 is fixed at the inside away from the side wall of the cavity resonator 31 and the tilt angle of the exciter 33 with respect to the magnetic field direction of the cavity resonator 31 is adjusted such that the input impedance of the microwave heating device 3 is matched with the output impedance of a microwave generator 1.SELECTED DRAWING: Figure 5

Description

The present disclosure relates to a microwave heating technique using a cavity resonator.

Microwave heating technology using a cavity resonator is applied to applications such as using a microwave-heated catalyst to react ethanol to generate hydrogen, supply hydrogen to a fuel cell, and obtain output power larger than the input power. (See, for example, Patent Document 1 and the like).

The configuration of the conventional microwave heating system is shown in FIG. The conventional microwave heating system M is composed of a microwave generator 1, a matching device 2, and a microwave heating device 3. The configuration of the conventional microwave heating device is shown in FIG. The conventional microwave heating device 3 is composed of a cavity resonator 31 for microwave heating, a storage container 32 for microwave heating, an exciter 33 of the cavity resonator 31, and a feeder line 34 of the exciter 33.

The cavity resonator 31 is a TM010 mode cavity resonator. The containment vessel 32 is arranged on the central axis of the cavity resonator 31 and allows the reactant to flow in and the product material to flow out. Therefore, the electric field strength of the cavity resonator 31 is maximized at the arrangement position of the accommodating container 32, and the reaction efficiency in the accommodating vessel 32 is maximum with respect to the power supplied by the microwave generator 1. Then, the electromagnetic field intensity distribution in the resonator mode becomes a simple distribution that changes monotonously (see FIG. 3).

Japanese Unexamined Patent Publication No. 2019-087410

In the prior art, the exciter 33 is located on the side wall of the cavity resonator 31. Here, in the plane perpendicular to the central axis of the cavity resonator 31, the direction perpendicular to the direction connecting the accommodating container 32 and the exciter 33 is defined as the X-axis direction, and the direction connecting the accommodating container 32 and the exciter 33 is defined as the X-axis direction. The direction parallel to is the Y-axis direction. Then, the direction parallel to the central axis of the cavity resonator 31 is defined as the Z-axis direction.

The impedance matching characteristics of the conventional microwave heating device are shown in FIG. Here, the electric field strength E of the cavity resonator 31 decreases as it approaches the side wall of the cavity resonator 31, and increases as it approaches the central axis of the cavity resonator 31. On the other hand, the magnetic field strength H of the cavity resonator 31 increases as it approaches the side wall of the cavity resonator 31, and decreases as it approaches the central axis of the cavity resonator 31. The TM010 mode of the cavity resonator 31 is disturbed at a position within about 1 mm from the exciter 33, but is not disturbed at a position about 1 mm or more away from the exciter 33.

_{Therefore, it is difficult for the spatial impedance Z 0} = E / H = √ (μ / ε) of the exciter 33 arranged on the side wall of the cavity resonator 31 to be equal to the output impedance of the microwave generator 1 of 50 Ω. That is, it is difficult for the input impedance of the microwave heating device 3 to match the output impedance of 50Ω of the microwave generator 1. Therefore, a matching device 2 is required between the microwave generator 1 and the microwave heating device 3. Then, the microwave heating system M cannot increase the power efficiency and cannot reduce the device size.

Therefore, in order to solve the above problems, the present disclosure improves the power efficiency in the microwave heating system by eliminating the need for a matching device between the microwave generator and the microwave heating device. The purpose is to reduce the device dimensions.

To solve the above problems, the exciter is fixed inside away from the side wall of the cavity resonator. Then, the inclination angle of the exciter with respect to the magnetic field direction of the cavity resonator is adjusted to an appropriate angle. Therefore, the effective spatial impedance of the exciter can be equal to the output impedance of the microwave generator. That is, the input impedance of the microwave heating device can be matched with the output impedance of the microwave generator.

Specifically, the present disclosure comprises a cavity heating device for microwave heating, a storage container for microwave heating, an exciter for the cavity resonator, and a feeding line for the exciter. In the device, the exciter is fixed inside the cavity resonator away from the side wall of the cavity resonator so that the input impedance of the microwave heater matches the output impedance of the microwave generator. It is a microwave heating device characterized in that the inclination angle of the exciter with respect to the magnetic field direction is adjusted.

According to this configuration, the microwave heating system by adjusting the tilt of the exciter inside the cavity resonator, while eliminating the need for a matcher between the microwave generator and the microwave heating device. In, the power efficiency can be increased and the device size can be reduced.

Further, in the present disclosure, the tilt angle of the exciter with respect to the magnetic field direction of the cavity resonator is adjusted according to the temperature change of the dielectric positive contact of the microwave heating target, so that the dielectric positive contact of the microwave heating target is adjusted. The microwave heating device is characterized in that the input impedance of the microwave heating device is adjusted to match the output impedance of the microwave generator regardless of the temperature change of the above.

The electromagnetic field intensity distribution in the resonator mode changes according to the temperature change of the dielectric loss tangent of the microwave heating target, and the input impedance of the microwave heating device does not match the output impedance of the microwave generator. According to this configuration, the spatial impedance of the exciter is effectively adjusted by adjusting the inclination angle of the exciter with respect to the magnetic field direction of the cavity resonator, regardless of the temperature change of the dielectric positive contact of the microwave heating target. , The input impedance of the microwave heating device can be matched with the output impedance of the microwave generator.

Further, the present disclosure is a microwave heating device, wherein the cavity resonator is a TM010 mode cavity resonator, and the storage container is arranged on the central axis of the TM010 mode cavity resonator. ..

According to this configuration, the electric field strength of the cavity resonator can be maximized at the arrangement position of the accommodating vessel, and the reaction efficiency in the accommodating vessel can be maximized with respect to the power supplied by the microwave generator. Then, the electromagnetic field intensity distribution in the resonator mode can be a simple distribution that changes monotonically.

As described above, in the present disclosure, by eliminating the need for a matching device between the microwave generator and the microwave heating device, the power efficiency is increased and the device size is reduced in the microwave heating system. Can be done.

It is a figure which shows the structure of the microwave heating system of the prior art. It is a figure which shows the structure of the microwave heating apparatus of the prior art. It is a figure which shows the impedance matching characteristic of the conventional microwave heating apparatus. It is a figure which shows the structure of the microwave heating system of this disclosure. It is a figure which shows the structure of the microwave heating apparatus of this disclosure. It is a figure which shows the impedance matching characteristic of the microwave heating apparatus of this disclosure. It is a figure which shows the reflection characteristic and the Smith chart of the microwave heating apparatus of this disclosure. It is a figure which shows the temperature change of the dielectric loss tangent of the object of microwave heating of this disclosure. It is a figure which shows the adjustment mechanism of the inclination angle of the exciter of the microwave heating apparatus of this disclosure. It is a figure which shows the adjustment principle of the inclination angle of the exciter of the microwave heating apparatus of this disclosure. It is a figure which shows the adjustment method of the inclination angle of the exciter of the microwave heating apparatus of this disclosure.

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

(Impedance matching of the microwave heating device of the present disclosure)
The configuration of the microwave heating system of the present disclosure is shown in FIG. The microwave heating system M of the present disclosure includes a microwave generator 1 and a microwave heating device 3, but does not require a matching device 2. The configuration of the microwave heating device of the present disclosure is shown in FIG. The microwave heating device 3 of the present disclosure includes a cavity resonator 31 for microwave heating, a container 32 for microwave heating, an exciter 33 of the cavity resonator 31, and a feeder line 34 of the exciter 33.

The cavity resonator 31 is a TM010 mode cavity resonator. The containment vessel 32 is arranged on the central axis of the cavity resonator 31 and allows the reactant to flow in and the product material to flow out. Therefore, the electric field strength of the cavity resonator 31 is maximized at the arrangement position of the accommodating container 32, and the reaction efficiency in the accommodating vessel 32 is maximum with respect to the power supplied by the microwave generator 1. Then, the electromagnetic field intensity distribution in the resonator mode becomes a simple distribution that changes monotonously (see FIG. 6).

In the present disclosure, the exciter 33 is fixed inside the cavity resonator 31 away from the side wall. Then, the inclination angle of the exciter 33 with respect to the magnetic field direction of the cavity resonator 31 is adjusted to an appropriate angle. Here, in the plane perpendicular to the central axis of the cavity resonator 31, the direction perpendicular to the direction connecting the accommodating container 32 and the exciter 33 is defined as the X-axis direction, and the direction connecting the accommodating container 32 and the exciter 33 is defined as the X-axis direction. The direction parallel to is the Y-axis direction. Then, the direction parallel to the central axis of the cavity resonator 31 is defined as the Z-axis direction. The exciter 33 is an exciter loop or the like, and has a radius and / or a number of turns that satisfies the impedance matching characteristic (see FIG. 6) of the microwave heating device 3. The feeder line 34 is a semi-rigid cable or the like, and has a balun (balanced-unbalanced converter) at its tip.

The impedance matching characteristics of the microwave heating device of the present disclosure are shown in FIG. Here, the electric field strength E of the cavity resonator 31 decreases as it approaches the side wall of the cavity resonator 31, and increases as it approaches the central axis of the cavity resonator 31. On the other hand, the magnetic field strength H of the cavity resonator 31 increases as it approaches the side wall of the cavity resonator 31, and decreases as it approaches the central axis of the cavity resonator 31. The TM010 mode of the cavity resonator 31 is disturbed at a position within about 1 mm from the exciter 33, but is not disturbed at a position about 1 mm or more away from the exciter 33.

_{Therefore, the spatial impedance Z 0} = E / H = √ (μ / ε) in the exciter 33 fixed inside the cavity resonator 31 away from the side wall is the spatial impedance E in the vicinity of the side wall of the cavity resonator 31. _It is larger than min / H _{max and smaller than the spatial impedance E max} / H _min near the central axis of the cavity resonator 31, and can be made substantially equal to the output impedance of the microwave generator 1 of 50 Ω. Then, the effective space impedance Z ₀ at changeable exciter 33 the inclination angle _', by appropriately adjusting the inclination angle of the exciter 33, be equal by the output impedance 50Ω of the microwave generator 1 Is possible.

That is, the input impedance of the microwave heating device 3 can be matched with the output impedance of 50Ω of the microwave generator 1. Therefore, the matching device 2 is not required between the microwave generator 1 and the microwave heating device 3. Then, the microwave heating system M can increase the power efficiency and reduce the device size.

The reflection characteristics and Smith chart of the microwave heating device of the present disclosure are shown in FIG. In the reflection characteristics shown in the upper part of FIG. 7, when the excitation frequency is the desired frequency of 2.45 GHz, VSWR is approximately equal to 1, and the impedance matching characteristics of the microwave heating device 3 (see FIG. 6) are satisfied. To. In the Smith chart shown in the lower part of FIG. 7, when the excitation frequency is the desired frequency 2.45 GHz, the point P0 on the Smith chart is near the center of the Smith chart, and the impedance matching characteristic of the microwave heating device 3 (FIG. 7). 6) is satisfied.

(Coping method for temperature change of microwave heating target of the present disclosure)
The temperature change of the dielectric loss tangent of the object to be heated by the microwave of the present disclosure is shown in FIG. The upper part of FIG. 8 shows the electric field strength in the vicinity of the central axis of the cavity resonator 31. (1) When the dielectric loss tangent tan δ to be heated by the microwave changes from 0.01 to 0.001, the peak frequency does not change from the desired frequency of 2.45 GHz, the peak intensity becomes high, and the peak width becomes narrow. .. (2) When the dielectric loss tangent tan δ to be heated by the microwave changes from 0.01 to 0.05, the peak frequency does not change from the desired frequency of 2.45 GHz, the peak intensity becomes low, and the peak width becomes wide. ..

The lower part of FIG. 8 shows a Smith chart. (1) When the dielectric tangent tan δ of the object to be heated by the microwave changes from 0.01 to 0.001, the point on the Smith chart when the excitation frequency is the desired frequency of 2.45 GHz is near the center of the Smith chart. The locus on the Smith chart changes from the point P1 of the Smith chart to the point P2 of the capacitive region of the Smith chart, and when the excitation frequency is swept in the vicinity of the desired frequency of 2.45 GHz, the locus on the Smith chart has a radius to the capacitive region of the Smith chart. Is spreading. (2) When the dielectric tangent tan δ of the object to be heated by the microwave changes from 0.01 to 0.05, the point on the Smith chart when the excitation frequency is the desired frequency of 2.45 GHz is near the center of the Smith chart. The locus on the Smith chart changes from the point P1 of the Smith chart to the point P3 of the inductive region of the Smith chart, and when the excitation frequency is swept near the desired frequency of 2.45 GHz, the locus on the Smith chart has a radius to the inductive region of the Smith chart. Is narrowing.

In this way, the electromagnetic field intensity distribution in the resonator mode changes according to the temperature change of the dielectric positive contact tan δ to be heated by the microwave, and the input impedance of the microwave heating device 3 becomes the output impedance of 50Ω of the microwave generator 1. It becomes inconsistent. However, the resonance frequency of the cavity resonator 31 maintains a state corresponding to the desired frequency of 2.45 GHz.

FIG. 9 shows a mechanism for adjusting the tilt angle of the exciter of the microwave heating device of the present disclosure as a method of coping with the temperature change of the dielectric loss tangent tan δ of the microwave heating target of the present disclosure. By adjusting the tilt angle θ of the exciter 33 with respect to the magnetic field direction of the cavity resonator 31 (the angular coordinate direction of the cavity resonator 31), the spatial impedance of the exciter 33 can be effectively adjusted, and the microwave heating target can be used. The input impedance of the microwave heating device 3 can be matched with the output impedance of 50Ω of the microwave generator 1 regardless of the temperature change of the dielectric positive contact tan δ.

The principle of adjusting the tilt angle of the exciter of the microwave heating device of the present disclosure is shown in FIG. In FIG. 10, the dielectric loss tangent tan δ of the microwave heating target is 0.01 before the temperature change of the microwave heating target, and the relative permittivity ε _r of the microwave heating target is before the temperature change of the microwave heating target. It is 3.0, and the inclination angle θ of the exciter 33 is changed from 0 °.

The upper part of FIG. 10 shows the reflectance coefficient. When the inclination angle θ of the exciter 33 changes from 0 ° to 40 ° via 20 °, the dip frequency hardly changes from the desired frequency of 2.45 GHz, the dip intensity becomes low, and the dip width becomes wide.

The lower part of FIG. 10 shows a Smith chart. When the tilt angle θ of the exciter 33 changes from 0 ° to 40 ° via 20 °, the points on the Smith chart when the excitation frequency is the desired frequency of 2.45 GHz are the points near the center of the Smith chart. The locus on the Smith chart when it changes from P4 through the point P5 in the somewhat inductive region of the Smith chart to the point P6 in the further inductive region of the Smith chart and the excitation frequency is swept near the desired frequency of 2.45 GHz. Narrows the radius to the inductive region of the Smith chart.

In this way, the magnetic flux passing through the exciter 33 (excitation loop, etc.) changes according to the change in the inclination angle θ of the exciter 33, and the input impedance of the microwave heating device 3 becomes the output impedance of the microwave generator 1. It will not match with 50Ω. However, the resonance frequency of the cavity resonator 31 is substantially maintained in a state of matching the desired frequency of 2.45 GHz.

Utilizing this, by adjusting the inclination angle θ of the exciter 33, the magnetic flux passing through the exciter 33 is adjusted, the spatial impedance in the exciter 33 is effectively adjusted, and the microwave heating target is used. The input impedance of the microwave heating device 3 is matched with the output impedance of 50Ω of the microwave generator 1 regardless of the temperature change of the dielectric loss tangent tan δ.

FIG. 11 shows a method of adjusting the tilt angle of the exciter of the microwave heating device of the present disclosure. Before the temperature change of the dielectric loss tangent tan δ of the microwave heating target shown in the upper part of FIG. 11, the inclination angle θ of the exciter 33 is θ ₀ (the reason why it is not 0 ° will be described later), and the excitation frequency is the desired frequency 2. The point on the Smith chart at 45 GHz is at point P7 near the center of the Smith chart, and the locus on the Smith chart when the excitation frequency is swept near the desired frequency 2.45 GHz is the capacitance of the Smith chart. It touches the line that separates the sexual region and the inducible region.

After the temperature change in which the dielectric positive contact tan δ of the microwave heating target shown in the middle left of FIG. 11 becomes small _{, if the inclination angle θ of the exciter 33 remains θ 0} , the excitation frequency is the desired frequency 2.45 GHz. The point on the Smith chart at one time is at point P8 in the capacitive region of the Smith chart, and the locus on the Smith chart when the excitation frequency is swept near the desired frequency of 2.45 GHz is the capacitive of the Smith chart. The radius is extended to the area.

Even after the temperature change in which the dielectric positive contact tan δ of the microwave heating target shown in the lower left column of FIG. 11 becomes small, if the inclination angle θ of the exciter 33 _{increases to θ 1} , the excitation frequency is the desired frequency 2.45 GHz. The point on the Smith chart at that time is at the point P9 near the center of the Smith chart, and the locus on the Smith chart when the excitation frequency is swept near the desired frequency of 2.45 GHz is the capacitive region of the Smith chart. It touches the line that separates the inductive region.

After the temperature change in which the dielectric positive contact tan δ of the microwave heating target shown in the middle right of FIG. 11 becomes large _{, if the inclination angle θ of the exciter 33 remains θ 0} , the excitation frequency is the desired frequency 2.45 GHz. The point on the Smith chart at one time is at point P10 in the inductive region of the Smith chart, and the locus on the Smith chart when the excitation frequency is swept near the desired frequency of 2.45 GHz is the inducibility of the Smith chart. The radius is narrowed to the area.

Even after the temperature change in which the dielectric positive contact tan δ of the microwave heating target shown in the lower right part of FIG. 11 becomes large, if the inclination angle θ of the exciter 33 becomes _{small to θ 2} , the excitation frequency is the desired frequency 2.45 GHz. The point on the Smith chart at that time is at the point P11 near the center of the Smith chart, and the locus on the Smith chart when the excitation frequency is swept near the desired frequency of 2.45 GHz is the capacitive region of the Smith chart. It touches the line that separates the inductive region.

Here, in order to optimize the inclination angle θ of the exciter 33, (1) a directional coupler between the microwave generator 1 and the microwave heating device 3 is used to minimize the reflected power. As described above, the tilt angle θ of the exciter 33 may be feedback-controlled, and (2) the tilt angle θ of the exciter 33 is maximized by using the pickup loop inside the cavity resonator 31. (3) The tilt angle θ of the exciter 33 may be feed forward controlled by using the thermography of the side wall of the cavity resonator 31.

The reason why the inclination angle θ of the exciter 33 is set to θ ₀ (≠ 0 °) before the temperature change of the dielectric loss tangent tan δ of the microwave heating target is that the excitation is performed after the temperature change of the dielectric loss tangent tan δ of the microwave heating target. This is because the inclination angle θ of the vessel 33 is set to θ ₂ (<θ ₀ ) to widen the radius of the locus on the Smith chart when the excitation frequency is swept in the vicinity of the desired frequency of 2.45 GHz. Further, in order to widen the radius of the locus on the Smith chart when the excitation frequency is swept in the vicinity of the desired frequency of 2.45 GHz, it is desirable to increase the radius in the exciter 33 (excitation loop or the like), and / Or, it is desirable to increase the number of turns.

(Supplement to the microwave heating system of the present disclosure)
The temperature change range of the dielectric loss tangent tan δ of the microwave heating target varies depending on the type of the microwave heating target. Therefore, it is desirable to design a variable range of the tilt angle θ of the exciter 33 according to the type of microwave heating target.

Impedance matching may be achieved with high accuracy by increasing the microwave output only at the optimum reaction temperature of the microwave heating target. On the other hand, it is not necessary to reduce the microwave output and realize impedance matching with high accuracy until the optimum reaction temperature of the microwave heating target is raised. Then, the inclination angle θ of the exciter 33 may be fixed to the optimum value at the optimum reaction temperature of the microwave heating target.

In the present embodiment, after exciting the TM010 mode as the resonator mode, the cavity resonator 31 is excited in the magnetic field direction so that the input impedance of the microwave heating device 3 matches the output impedance of the microwave generator 1 of 50Ω. The tilt angle of the vessel 33 is adjusted. As a modification, the magnetic field direction of the cavity resonator 31 is such that the input impedance of the microwave heating device 3 matches the output impedance of the microwave generator 1 of 50Ω after exciting another higher-order mode as the resonator mode. The inclination angle of the exciter 33 with respect to the above may be adjusted.

The microwave heating device of the present disclosure uses a catalyst heated by microwave to react ethanol to generate hydrogen, supply hydrogen to a fuel cell, and obtain output power larger than input power. It can be applied to various applications using microwave heating.

M: Microwave heating system 1: Microwave generator 2: Matching device 3: Microwave heating device 31: Cavity resonator 32: Containment vessel 33: Exciter 34: Feed line

Claims (3)

A microwave heating device including a cavity resonator for microwave heating, a container for microwave heating, an exciter for the cavity resonator, and a feeder line for the exciter.
The exciter is fixed inside away from the side wall of the cavity resonator, and the excitation with respect to the magnetic field direction of the cavity resonator so that the input impedance of the microwave heater matches the output impedance of the microwave generator. A microwave heating device characterized in that the tilt angle of the vessel is adjusted. By adjusting the inclination angle of the exciter with respect to the magnetic field direction of the cavity resonator according to the temperature change of the dielectric tangent of the microwave heating target, the temperature change of the dielectric tangent of the microwave heating target does not matter. The microwave heating device according to claim 1, wherein the input impedance of the microwave heating device is adjusted to match the output impedance of the microwave generator. The cavity resonator is a TM010 mode cavity resonator.
The microwave heating device according to claim 1 or 2, wherein the storage container is arranged on the central axis of the TM010 mode cavity resonator.

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