Microwave reactor
Patent Information
- Application Number
- JP2025541225
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Filing Date
- 2025-07-09
- Publication Date
- 2025-09-25
Abstract
Description
microwave reactor
[0001] The present disclosure relates to microwave reactors.
[0002] In conventional microwave reactors, microwaves are supplied to the reactor interior through a waveguide. Because the waveguide's opening area is small, few microwaves are reflected back into the waveguide. The current flowing through the conductor in the tube wall heats the waveguide, resulting in losses. However, for smaller reactors, microwaves of only a few kW are sufficient, and the heat and losses generated in the waveguide are tolerable. On the other hand, large-scale plants require high-power microwaves, ranging from hundreds of kW to tens of MW, making the heat and losses generated in the waveguide unnecessarily negligible. For example, passing 1 MW of power at 2.45 GHz through the WRI-26 waveguide generates 3.7 kW of heat per meter, resulting in a microwave loss of 0.016 dB, or 3.7 kW. Because the cross-sectional dimensions of the waveguide must be less than half the wavelength to prevent the generation of higher-order modes, the WRI-26 waveguide is a narrow tube with a cross-section of 8.4 cm x 4.2 cm. Therefore, the wall current generated when a 1 MW microwave propagates through the tube flows concentratedly in an extremely small area of at most 8 cm or less, resulting in the generation of a large amount of heat and loss.
[0003] In addition, chemical reactors are generally installed inside explosion-proof walls to prevent explosions, and the oscillator is installed outside the walls. As a result, the actual length of the waveguide is 2 to 5 meters or more. If the waveguide is 5 meters long, the heat generation and loss will be as high as 18.5 kW, which is a problem from the standpoint of both energy efficiency and heat dissipation design.
[0004] Conventionally, microwaves have been generated using oscillators that use magnetrons. However, magnetrons have poor frequency purity and phase stability, making it difficult to combine microwaves from multiple magnetrons. Furthermore, the microwaves that can be generated by a single magnetron are limited to 10 kW or less at 2.45 GHz, for example, making it difficult to generate high-power microwaves exceeding 10 kW. Furthermore, with magnetrons, the efficiency drops to 60% or less at high powers such as 10 kW, making it impossible to generate high-power, highly efficient microwaves. In response to this, a device has been proposed in which an antenna is installed inside a reactor without using a waveguide (see, for example, Patent Document 1).
[0005] Japanese Patent Application Publication No. 2017-103454
[0006] However, microwaves reflected by the inner wall of the reactor may return directly to the antenna, destroying equipment such as the amplifier that supplies the microwaves to the antenna. Therefore, an isolator to prevent reflected waves is installed between the amplifier output and the antenna. However, when irradiating high-power microwaves of several hundred watts or more, the isolator becomes large and difficult to install, resulting in high costs. For example, when irradiating high-power microwaves of more than 10 kW at 2.45 GHz, the reflected waves can damage equipment.
[0007] The present disclosure has been made to solve the above-mentioned problems, and its purpose is to provide a microwave reactor that can suppress damage to equipment due to reflected waves even when high-power microwaves are irradiated.
[0008] The microwave reactor according to the present disclosure comprises a reactor for storing reactants and a microwave generator for generating a microwave beam, wherein an opening is provided in the reactor, the microwave generator focuses the microwave beam at a center of the opening and causes the microwave beam to enter the interior of the reactor, the inner wall of the reactor reflects the microwave beam, the dimension of the opening is longer than half the wavelength of the microwave beam, and the area of the opening is 1 / 10 or less of the area of a portion of the inner wall of the reactor that is not covered by the reactants.
[0009] In the present disclosure, in a configuration in which a microwave beam is incident on the inside of a reactor without using a waveguide, the area of the opening of the reactor is set to 1 / 10 or less of the area of the part of the inner wall of the reactor that is not covered by the reactant, thereby making it possible to suppress damage to the equipment due to reflected waves even when irradiating high-power microwaves.
[0010] FIG. 1 is a cross-sectional view showing a microwave reactor according to embodiment 1. FIG. 2 is a cross-sectional view showing a microwave reactor according to embodiment 2. FIG. 3 is a diagram showing a calculation result of spatially combining microwaves from a square array antenna. FIG. 4 is a diagram showing a calculation result of spatially combining microwaves from a square array antenna. FIG. 5 is a diagram showing a circular array antenna. FIG. 6 is a diagram showing a calculation result of spatially combining microwaves from a circular array antenna. FIG. 7 is a diagram showing a calculation result of spatially combining microwaves from a circular array antenna. FIG. 8 is a circuit diagram of an oscillator of a microwave reactor according to embodiment 3. FIG. 9 is a circuit diagram of an oscillator according to a comparative example. FIG. 10 is a cross-sectional view showing a microwave reactor according to embodiment 4. FIG. 11 is a cross-sectional view showing a microwave reactor according to embodiment 5. FIG. 12 is a cross-sectional view showing a microwave reactor according to embodiment 6.
[0011] A microwave reactor according to an embodiment will be described with reference to the drawings. The same or corresponding components are designated by the same reference numerals, and repeated description may be omitted.
[0012] Embodiment 1. Figure 1 is a cross-sectional view showing a microwave reactor according to embodiment 1. Reactor 1 contains reactant 2. The inner wall of the lower part of reactor 1 is covered with reactant 2. An opening 3 is provided in the upper part of reactor 1 that is not covered with reactant 2. A microwave generator 4 generates a microwave beam 5, which is an electromagnetic microwave wave. The microwave has a frequency of 0.9 GHz to 30 GHz and a wavelength of 33 cm to 1 cm.
[0013] The microwave generator 4 is, for example, a horn antenna, and emits a microwave beam 5 into the interior of the reactor 1 through the opening 3. The microwaves incident on the interior of the reactor 1 are absorbed by the reactants 2, and the microwaves cause reactions such as chemical reactions, sintering, and drying of the reactants 2.
[0014] Conventionally, microwaves are injected into a reactor via a waveguide, and the diameter of the waveguide is set to half the wavelength or less because the generation of higher modes increases loss. In contrast, in this embodiment, the microwave generator 4 directly injects the microwave beam 5 into the reactor 1 without using a waveguide, so the size of the opening 3 can be made larger than half the wavelength of the microwave beam 5.
[0015] However, if the size of the opening 3 is larger than half the wavelength, higher modes will occur in addition to the TE01 mode, which is the fundamental mode used in waveguides, hindering propagation efficiency. Therefore, the microwave generator 4 concentrates the microwave beam 5 at the center of the opening 3 and makes the microwave beam incident on the inside of the reactor 1. Therefore, since the end of the opening 3 is hardly irradiated with microwaves, no current flows at the edge of the opening 3, and it is possible to suppress heat generation in the power supply part and microwave loss, which are problems when a waveguide is used.
[0016] Since the reactor 1 is made of a metal such as stainless steel, the upper inner wall of the reactor 1 that is not covered with the reactants 2 reflects the microwave beam 5. The microwave beam 5 is multiple-reflected inside the reactor 1, and is repeatedly absorbed and reflected by the reactants 2. Therefore, the microwave beam 5 can be irradiated onto the reactants 2 in the reactor 1 relatively uniformly.
[0017] The microwave beam 5 is almost totally reflected by the inner wall of the reactor 1, resulting in a resonant electromagnetic field distribution inside the reactor 1 due to multiple reflections. If a small opening 3 is opened in the reactor 1 under this condition, a state similar to so-called blackbody radiation occurs. The amount of reflected microwaves emitted from the opening 3 to the outside is very small, proportional to the ratio of the area of the upper inner wall of the reactor 1 not covered by the reactants 2 to the area of the opening 3. If the reflected waves are too large, the amount of microwaves reaching the reactants 2 decreases, reducing the efficiency of the reactor. Furthermore, the reflected waves may damage the microwave generator 4. Therefore, the amount of reflected waves must be kept to a very small amount, less than one-tenth of the amount of microwaves inside the reactor 1. The smaller the area of the opening 3, the greater the amount of reflected waves. Therefore, in this embodiment, the area of the opening 3 in the reactor 1 is set to be less than one-tenth of the area of the portion of the inner wall of the reactor 1 not covered by the reactants 2. This makes it possible to prevent damage to equipment caused by reflected waves even when microwaves of high power, from 100 kW to several tens of MW, exceeding 10 kW, are irradiated.
[0018] Embodiment 2. Figure 2 is a cross-sectional view showing a microwave reactor according to embodiment 2. In this embodiment, the microwave generator 4 has a chamber 6, a plurality of antennas 7, and a plurality of oscillators 8. The chamber 6 is connected to the opening 3 of the reactor 1 and surrounds a space for forming the microwave beam 5. The chamber 6 is made of a conductor such as metal so as to prevent microwaves due to unnecessary side lobes generated by the microwave beam from leaking to the outside.
[0019] The multiple antennas 7 are provided on the wall surfaces of the chamber 6 and spatially combine the microwave beams 5 inside the chamber 6. The multiple oscillators 8 supply phase-controlled microwave electrical signals to the multiple antennas 7, respectively. Each oscillator 8 has an oscillation source and a semiconductor amplifier such as GaN. By matching the phases of the microwaves emitted from the multiple antennas 7, the intensity of the radio waves radiating to the outside is reduced and the microwave beams 5 are concentrated at the center of the opening 3.
[0020] Generally, magnetrons have unstable phases and wide frequency bandwidths, so when microwaves fed from two or more magnetrons are combined, the combined power and efficiency drop significantly due to combined losses.
[0021] In contrast, unlike a magnetron, the microwave generator 4 can emit phase-controlled microwaves from the antennas 7. Therefore, microwaves with both phase and frequency bandwidth controlled can be radiated from each antenna 7, allowing spatial synthesis. This makes it possible to obtain a microwave beam 5 with high output power with little loss. For example, if a 300 W oscillator supplies microwaves to an array antenna having 100 antennas (10 x 10), a 30 kW microwave beam 5 can be obtained. Since microwave efficiency is determined by the efficiency of each antenna 7, an oscillator using a GaN amplifier can achieve a high efficiency of around 70%, making it possible to achieve high efficiency while obtaining a large output of 10 kW or more.
[0022] The spacing between the antennas 7 is approximately half the wavelength, so at 2.45 GHz, it is approximately 6 cm. Therefore, the size of the array antenna is approximately 60 cm x 60 cm, which is a size that is easily feasible. In this method, the microwave power can be increased by spatially combining the number of array antennas, so microwaves of 30 kW or more can easily be achieved. For example, if an output of 1 MW is required at 2.45 GHz, 3,333 300 W oscillators can be spatially combined. If the antennas 7 are arranged in a square, there will be approximately 58 x 58 antennas, and when lined up at λ / 2 intervals, each side will be approximately 3.4 m, which is easily feasible in a large furnace.
[0023] Figures 3 and 4 show the calculation results of spatially combining microwaves from a rectangular array antenna. The rectangular array antenna is composed of 21 x 21 antennas 7 arranged in a square. The size of the rectangular array antenna is approximately 61 cm x 61 cm. Figure 3 shows the amplitude of the microwaves in dB on a plane 8 λ away from the antenna. Figure 4 shows the cumulative power ratio accumulated according to the distance d from the center in units of 10%. The horizontal axis shows the distance from the center in units of wavelength λ. The power cumulative ratio indicates the proportion of microwave power radiated within a circle of radius d from the center. Therefore, Figure 4 shows that, for example, 57% of microwaves pass through an opening with a radius of 10 λ.
[0024] Figure 5 shows a circular array antenna. Multiple antennas 7 are arranged in a circular area at intervals of approximately half a wavelength. The number of antennas is 363, which is almost the same as the number of antennas in the rectangular array described above. The circular array can concentrate microwaves more efficiently at the center of the aperture 3 than the rectangular array.
[0025] Figures 6 and 7 show the calculation results of spatially combining microwaves from a circular array antenna. The diameter of the circular array is approximately 64 cm, equivalent to that of a rectangular array. Figure 6 shows the microwave amplitude in dB on a plane 4.5λ away from the antenna. Figure 7 shows the cumulative power ratio, accumulated in 10% increments, as a function of the distance d from the center. As shown in Figure 6, the sidelobe amplitude of the circular array is reduced compared to the rectangular array in Figure 3. As shown in Figure 7, the proportion of microwaves passing through aperture 3 with a radius of 10λ increases to 86%. This demonstrates that a circular array is superior to a rectangular array in radiating more power to aperture 3. Note that this calculation does not account for the component reflected by the sidewall of chamber 6 and reaching aperture 3, so in reality, a larger proportion of microwaves may be able to pass through aperture 3.
[0026] Embodiment 3. Figure 8 is a circuit diagram of an oscillator of a microwave reactor according to embodiment 3. The oscillator 8 has an oscillation source 9, an amplifier 10 including at least one stage of a transistor, and a reflected wave monitor circuit 12 connected between a final stage transistor 11 of the amplifier 10 and an antenna 7. The oscillation source 9 generates a microwave electrical signal. The amplifier 10 amplifies the microwave electrical signal from the oscillation source 9. The final stage transistor 11 of the amplifier 10 is a GaN transistor. The electrical signal amplified by the GaN transistor is supplied to the antenna 7. The antenna 7 radiates microwaves.
[0027] A drain voltage control circuit 13 controls the drain voltage of the final stage transistor 11. A gate voltage control circuit 14 controls the gate voltage of the final stage transistor 11. A reflected wave monitor circuit 12 monitors the intensity of the reflected wave returning from the antenna 7. The reflected wave monitor circuit 12 is configured, for example, by a circuit in which a detection diode is connected to a directional coupler.
[0028] When the intensity of the reflected wave exceeds a threshold, the reflected wave monitor circuit 12 controls the drain voltage control circuit 13 to quickly reduce the drain voltage of the final stage transistor 11 to 0 V or a low voltage, or controls the gate voltage control circuit 14 to reduce the operating current of the final stage transistor 11. The threshold value of the intensity of the reflected wave for performing such control is, for example, ½ to several times the intensity of the output signal of the oscillator 8.
[0029] Next, the effects of this embodiment will be explained in comparison with a comparative example. Fig. 9 is a circuit diagram of an oscillator according to the comparative example. In the comparative example, an isolator 15 is connected between an LDMOS transistor 16, which is the final stage transistor of an amplifier 10, and an antenna 7.
[0030] As in the first embodiment, the area of the opening 3 of the reactor 1 is set to 1 / 10 or less of the area of the portion of the inner wall of the reactor 1 that is not covered by the reactant 2, thereby suppressing reflected waves from the reactor 1. However, a large reflected wave may enter the antenna 7 due to an unexpected sudden event, such as when the reactor 1 is not filled with the reactant 2. Such an excessively large signal may damage the final stage transistor 11 of the oscillator 8. To prevent this, the comparative example includes an isolator 15. However, the isolator 15 is a magnetic circuit, and as the output increases to 300 W, it becomes larger and more expensive. The isolator 15 also contains a resistor that converts reflected waves into heat. However, the resistor must also be large to handle high power. Furthermore, the resistor may burn out if the reflected power is high. Therefore, recovery requires replacing the isolator 15, which is time-consuming and costly.
[0031] In contrast, in this embodiment, a reflected wave monitor circuit 12 is provided between the final stage transistor 11 of the amplifier 10 and the antenna 7. When a large reflected wave arrives, the reflected wave monitor circuit 12 controls the drain voltage or operating current of the final stage transistor 11 to decrease. This prevents the amplifier 10 connected to the antenna 7 from being destroyed even when a large reflected wave occurs. Furthermore, because only the drain voltage or operating current of the final stage transistor 11 is changed, recovery can be achieved by simply restoring both voltages to their original state. Therefore, recovery can be achieved in a short time without replacing any parts.
[0032] In this embodiment, a reflected wave monitor circuit 12 is provided for each antenna 7. However, one reflected wave monitor circuit 12 may be provided for multiple antennas 7, and control may be performed to lower the drain voltage or operating current of all final stage transistors 11 of multiple oscillators 8 when a reflected wave arrives from the antenna 7. For example, in the case of a 10 x 10 array antenna, a reflected wave monitor circuit 12 may be provided for one oscillator 8 in a block of 10 or 25 antennas 7, and all final stage transistors 11 in the same block may be controlled collectively to lower the drain voltage or operating current. By controlling multiple antennas collectively, the number of control devices can be reduced, thereby reducing costs.
[0033] A microwave reactor is not a free space but a closed space, and the direction of the microwave beam is fixed. Therefore, unlike array antennas such as those used in general radars, there is no possibility of external reflections hitting only one specific unit, but the reflected waves hit the entire reactor. Therefore, even a protection circuit for each block like this is effective.
[0034] In this embodiment, the final stage transistor 11 of the amplifier 10 is a GaN transistor. GaN transistors are more efficient than conventional LDMOS transistors, and can therefore improve the energy efficiency of microwave reactors. Furthermore, GaN transistors have a higher breakdown voltage than LDMOS transistors, making them less susceptible to damage even when high voltages are applied, and therefore have greater resistance to reflected waves.
[0035] Fourth Embodiment Fig. 10 is a cross-sectional view showing a microwave reactor according to a fourth embodiment. A plurality of openings 3 are provided in the reactor 1. A plurality of microwave generators 4 focus microwave beams 5 at the centers of the plurality of openings 3, respectively, and cause the microwave beams 5 to enter the interior of the reactor 1. Note that while the figure shows two openings 3 and two microwave generators 4, the number is not limited to this and may be three or more.
[0036] The dimension of each opening 3 is longer than half the wavelength of the microwave beam 5, and the area of each opening 3 is 1 / 10 or less of the area of the part of the inner wall of the reactor 1 that is not covered with the reactant 2. The multiple openings 3 are arranged so that the microwaves incident from each opening 3 do not directly enter other openings 3 without being reflected by the inner wall of the reactor 1.
[0037] When the reactor 1 is large or the microwave power is very high, multiple microwaves are supplied into the reactor 1 through multiple openings 3 as described above. However, because the reactor 1 is large, multiple reflections within the reactor cause the electromagnetic field distribution to become non-uniform. As a result, the microwaves irradiated onto the reactants 2 are not uniform, and the reaction does not proceed uniformly, resulting in a decrease in yield or a deterioration in reaction efficiency.
[0038] Microwaves incident on the reactor 1, which is a closed space, through each opening 3 are multiple-reflected, generating standing electromagnetic waves with peaks and valleys. The peaks and valleys of the standing waves can be changed by changing the phase of the microwaves. Furthermore, while it was difficult to control the phase of microwaves with conventional magnetrons, the oscillator 8 uses semiconductors such as GaN, so the phase of the microwaves can be precisely controlled.
[0039] Therefore, the oscillators 8 of the multiple microwave generators 4 each control the phase of the microwaves incident from the multiple openings 3 so that the microwave distribution (electromagnetic field distribution) inside the reactor 1 becomes uniform. This allows the reactants 2 in the reactor to be uniformly irradiated with the microwaves, thereby making the reaction of the reactants 2 uniform. An optimal phase control may be determined by a simulation in advance, or the phase may be changed to set conditions that provide good yield.
[0040] 11 is a cross-sectional view showing a microwave reactor according to a fifth embodiment. The reactor 1 is surrounded by an explosion-proof wall 17 to contain gas generated from the reactor 1. Since the oscillator 8 is provided outside the explosion-proof wall 17, the oscillator 8 does not need to be explosion-proof and can be manufactured inexpensively.
[0041] There is a possibility that the reactant 2 in the reactor 1 may scatter or gasify, damaging the antenna 7 of the microwave generator 4. Therefore, a shielding plate 18 is provided at the opening 3 of the reactor 1. The shielding plate 18 prevents the material inside the reactor 1 from escaping from the opening 3 to the outside of the reactor 1. Therefore, the material generated inside the reactor 1 does not adhere to the antenna 7 of the microwave generator 4, preventing deterioration of the antenna 7. The microwave beam 5 can pass through the shielding plate 18.
[0042] The shielding plate 18 is a quartz plate having a thickness of half the wavelength of the microwave beam 5. The microwaves passing through the shielding plate 18 are reflected by the upper and lower surfaces of the shielding plate 18, but the reflected waves from the upper and lower surfaces of the shielding plate 18 cancel each other out. Therefore, it is possible to suppress a decrease in the amount of microwave power supply due to unnecessary reflections.
[0043] The shielding plate 18 is not limited to a quartz plate, but may be a dielectric plate such as glass or resin that is permeable to microwaves, or may be a dielectric plate made of a fibrous material. Also, the shielding plate 18 is not limited to a single dielectric plate, but may be a plurality of dielectric plates.
[0044] Sixth Embodiment. Figure 12 is a cross-sectional view of a microwave reactor according to a sixth embodiment. Since the shielding plate 18 in the fifth embodiment is a quartz plate, microwaves passing through it generate heat due to the tan δ of the quartz. When the heat generation due to dielectric loss at 2.45 GHz is calculated with quartz tan δ = 0.00025, it is 78 W at 100 kW, resulting in a temperature rise of approximately 200°C. Therefore, while it can be used up to approximately 100 kW, at high powers of 1 MW or more, the heat generation is 780 W or more, resulting in a temperature rise of 2000°C or more, potentially causing damage. Since this heat generation is caused by the dielectric loss of the quartz plate, the dielectric loss can be reduced by making the quartz plate sufficiently thinner than half the wavelength. However, there is a risk of damage to the quartz thin film due to the pressure difference between the inside and outside of the reactor.
[0045] Therefore, in this embodiment, the shielding plate 18 has two dielectric thin films 19, 20 and a honeycomb material 21 sandwiched between the two dielectric thin films 19, 20 and having a thickness of ¼ wavelength of the microwave beam 5. The dielectric thin films 19, 20 are quartz thin films with a thickness that is sufficiently thinner than half the wavelength. Therefore, unnecessary heat generation can be suppressed.
[0046] The honeycomb material 21 is a dielectric material with a relative permittivity close to 1 that has little effect on microwaves, such as glass fiber reinforced plastic. By arranging the two dielectric thin films 19, 20 at a distance of 1 / 4 wavelength, reflected waves can be canceled out. This prevents a decrease in the microwave power supply due to unnecessary reflections. Furthermore, by sandwiching the honeycomb material 21 between the two dielectric thin films 19, 20, the strength of the quartz thin film can be supported against the pressure from the reactor 1.
[0047] The dielectric thin films 19 and 20 are not limited to quartz thin films, but may be any dielectric thin film that is microwave-transmittable, such as glass or resin, or may be a dielectric thin film made of a fibrous material. Furthermore, the dielectric thin films 19 and 20 do not have to consist of two thin films, but may consist of multiple thin films.
[0048] REFERENCE SIGNS LIST 1 reactor, 2 reactant, 3 aperture, 4 microwave generator, 5 microwave beam, 6 chamber, 7 antenna, 8 oscillator, 10 amplifier, 11 final stage transistor, 12 reflected wave monitor circuit, 18 shielding plate, 19, 20 dielectric thin film, 21 honeycomb material
Claims
1. a reactor containing reactants; a microwave generator that generates a microwave beam; an opening is provided in the reactor; the microwave generator focuses the microwave beam at a center of the opening and directs the microwave beam into the reactor; the inner walls of the reactor reflect the microwave beam; the size of the aperture is greater than half the wavelength of the microwave beam; 10. A microwave reactor, wherein the area of the opening is 1 / 10 or less of the area of the portion of the inner wall of the reactor that is not covered with the reactant.
2. 2. The microwave reactor of claim 1, wherein the microwave generator directly injects the microwave beam into the reactor without using a waveguide.
3. The microwave generator comprises: a chamber connected to the opening, made of a conductor, and surrounding a space for forming the microwave beam; a plurality of antennas provided on a wall surface of the chamber for spatially combining the microwave beams inside the chamber; 3. The microwave reactor according to claim 1, further comprising a plurality of oscillators for supplying phase-controlled microwave electrical signals to said plurality of antennas, respectively.
4. 4. The microwave reactor of claim 3, wherein the plurality of antennas are circular array antennas.
5. the oscillator has an amplifier including at least one stage of transistor for amplifying the microwave electrical signal, and a reflected wave monitor circuit connected between the final stage transistor of the amplifier and the antenna, 4. The microwave reactor according to claim 3, wherein the reflected wave monitor circuit monitors the intensity of the reflected wave returning from the antenna, and when the intensity of the reflected wave exceeds a threshold, controls so as to reduce the drain voltage or the operating current of the final stage transistor.
6. 6. The microwave reactor according to claim 5, wherein the reflected wave monitor circuit controls the drain voltages or operating currents of all of the final stage transistors of the plurality of oscillators to be reduced when the intensity of the reflected wave exceeds a threshold value.
7. 6. The microwave reactor of claim 5, wherein the final stage transistor is a GaN transistor.
8. a plurality of the openings are provided in the reactor; the plurality of openings are arranged so that the microwave beam incident from each opening does not directly enter another opening without being reflected by an inner wall of the reactor; 4. The microwave reactor according to claim 3, wherein the plurality of oscillators respectively control the phases of the microwave beams incident from the plurality of apertures so that microwave distribution inside the reactor becomes uniform.
9. 3. The microwave reactor according to claim 1, further comprising a shielding plate provided at the opening of the reactor to prevent substances inside the reactor from escaping to the outside of the reactor through the opening.
10. 10. The microwave reactor according to claim 9, wherein the shielding plate is a dielectric plate having a thickness of half the wavelength of the microwave beam.
11. 10. The microwave reactor according to claim 9, wherein the shielding plate comprises two dielectric thin films and a honeycomb material sandwiched between the two dielectric thin films and having a thickness of ¼ wavelength of the microwave beam.