Microwave heating equipment

Abstract

To provide a microwave heating device that efficiently heats a heating target object by irradiating the heating target object with microwaves.SOLUTION: A microwave heating device 1 that irradiates a heating target object 100 with microwaves to heat the target object 100 includes a conductive main body 10 having an elliptical cylindrical cavity portion 11, a microwave radiation antenna 20 arranged on one focal line F of the elliptical cylinder, a storage section 30 that is arranged on the other focal line F' and accommodates the heating target object therein, and a stub tuner 40 for matching microwaves, these components being arranged in the cavity portion. Even if a direct wave and a reflected wave are not in phase in a storage section, the direct wave and the reflection wave can be matched in phase with each other by operating the stub tuner, whereby the absorption efficiency of the microwaves by the heating target object in the storage section can be increased.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a microwave heating device that efficiently heats an object to be heated by irradiating it with microwaves. [Background technology]

[0002] A technology has been disclosed that includes a microwave heating device that has a metal body with an elliptical cavity, a radiation antenna fixed at one focal line of the ellipse, and a mechanism that makes the object to be heated stand still or pass through the other focal line, thereby enabling concentrated irradiation of microwaves in phase with respect to the object to be heated (Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-173069 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the technology of Patent Document 1 has the following problems. Paragraph

[0008] states, "It is generally known that when microwaves or electromagnetic waves radiated from one focal line of an elliptical cylinder are reflected by the wall of the elliptical cylinder, they arrive at the other focal line of the elliptical cylinder in a concentrated manner in phase." However, while such a result can be obtained only when linear antennas of the same shape are installed on both focal lines, the object to be heated is not linear but has a certain volume, and as a result, microwaves cannot be superimposed. Furthermore, there is no description of a means for matching the direct wave and the reflected wave to be in phase when they are not in phase at the other focal line of the elliptical cylinder. Furthermore, it is not possible to superimpose microwaves at the other focal line position of all ellipses, and there is no description that there is a fixed relationship between the shape of the ellipse and the wavelength of the microwave.

[0005] In consideration of the above-mentioned problems, an object of the present invention is to provide a microwave heating device that irradiates microwaves onto an object to be heated and heats it efficiently. [Means for solving the problem]

[0006] The microwave heating device of the present invention is a microwave heating device that irradiates microwaves onto an object to be heated to heat it, and includes a conductive main body having an elliptical cylindrical cavity, the microwave radiation antenna arranged on one focal line of the elliptical cylinder, a storage section arranged on the other focal line and storing the object to be heated inside, and a stub tuner for matching the microwaves arranged inside the cavity. The stub tuner is provided between the radiation antenna and the storage section, and the load impedance is adjusted to the characteristic impedance of the transmission line by operating the stub tuner, thereby matching the direct wave and the reflected wave at the object to be heated in the cavity to be in phase. It is characterized by: Furthermore, when the distance that the microwaves radiated from the radiation antenna travel to directly reach the storage section is defined as A, the distance that the microwaves travel to reach the wall surface of the cavity section is defined as B, and the distance that the microwaves reflected on the wall surface of the cavity section travel to reach the storage section is defined as C, the elliptical shape of the cavity section satisfies the following formula:

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[0007] In the present invention, even if the direct wave and the reflected wave are not in phase in the storage section, the stub tuner can be operated to align the two so that they are in phase, thereby increasing the microwave absorption efficiency for the heated object inside the storage section. Furthermore, the present invention is a heating device that confines microwaves to a hollow space and allows the heated object to efficiently absorb them, so there is no radiation (leakage) of microwaves into space and it does not require the large-scale shielding device that microwave heating devices have traditionally required. Furthermore, by designing the elliptical shape of the cavity to satisfy the above formula, the direct wave and the reflected wave will be in phase in the storage section and will reinforce each other, thereby increasing the microwave absorption efficiency for the heated object inside the storage section. Furthermore, the heating process can be made more efficient by sequentially heating a plurality of objects to be heated while moving them inside the storage section. [Brief explanation of the drawings]

[0008] [Figure 1] Cross-sectional view (a) of the microwave heating device along line AA and plan view (b) [Figure 2] (a) shows a general ellipse in a two-dimensional Cartesian coordinate system, and (b) shows a schematic diagram of a cross section of an elliptical cylinder with a hollow cavity along the horizontal plane. [Figure 3] Graph showing the sterilization effect of microwave irradiation [Figure 4] Table (a) showing the heating conditions using a microwave heating device and (b) evaluation of each sample after heating [Figure 5] Graph (a) shows the temperature change when oysters are heated in a microwave oven and a microwave at 50W output, and graph (b) shows the temperature change when oysters are heated in a microwave oven at 500W output. [Figure 6] Graph showing the results of coupled analysis of electromagnetic fields and heat transfer using simulation software and experimental results DETAILED DESCRIPTION OF THE INVENTION

[0009] An embodiment of a microwave heating device according to the present invention will be described. As shown in FIG. 1, the microwave heating device 1 is a device that irradiates microwaves onto an object to be heated 100 to heat it, and includes a main body 10, a radiation antenna 20, a storage section 30, and a stub tuner 40. The main body 10 is made of a conductor and has an elliptical cylindrical cavity 11. The walls, top, and bottom of the cavity 11 are surrounded by a conductor to shield microwaves from leaking outside the cavity 11. Note that in Figure 1(b), the top of the cavity 11 is not shown so that the inside of the cavity 11 can be seen.

[0010] The radiation antenna 20 is an antenna for radiating microwaves, and is placed on one focal line F of the elliptical cylinder. The radiation antenna 20 passes through the top of the cavity 11 and is connected to a microwave oscillator (not shown). The storage unit 30 is a component for storing the objects 100 therein and is positioned on the other focal line F' of the elliptical cylinder. The storage unit 30 is made of a material that allows microwaves to pass through, such as glass, PTFE resin, or silicone rubber. The portion that protrudes from the main body 10 is covered with a metal material 31. If the storage unit 30 is designed to penetrate the upper and lower parts of the hollow portion 11, multiple objects 100 can be heated while being moved sequentially from above to below or from below to above the storage unit 30, as shown by the arrows in FIG. 1 . The stub tuner 40 is a device that can insert a conductor rod 41 at any height within the cavity 11 in order to match the microwaves within the main body 10. The position of the stub tuner 40 is not limited, but it is preferable to place it between the radiating antenna 20 and the storage section 30.

[0011] Next, a method for matching the wavelength of microwaves will be described. An ellipse 200 in a two-dimensional Cartesian coordinate system, in which the origin O is the intersection of the major and minor axes, can be expressed by Equation 1 in FIG. 2(a). FIG. 2(b) is a schematic diagram showing a cross section of the elliptical cylinder of cavity 11 taken along the horizontal plane, with one focus of the ellipse at F and the other focus at F'. A is the linear distance from F to F', which corresponds to the distance traveled by the microwaves radiated from radiating antenna 20 and directly reaching storage unit 30 (hereinafter referred to as "direct waves"). B is the distance traveled by the microwaves radiated from radiating antenna 20 to the wall surface of cavity 11. C is the distance traveled by the microwaves reflected by the wall surface of cavity 11 to storage unit 30. In other words, B+C corresponds to the distance traveled by the microwaves radiated from radiating antenna 20, reflected by the wall surface of cavity 11, and reaching storage unit 30 (hereinafter referred to as "reflected waves"). In order to align the phases of the direct wave and reflected wave of wavelength λ in storage unit 30, the following equation 2 must be satisfied.

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[0012] However, it is conceivable that the direct wave and the reflected wave may not be in phase in the housing 30 due to the influence of the shapes and materials of the radiating antenna 20 and the housing 30. Therefore, the present invention is characterized in that a stub tuner 40 is further installed in the elliptical cylindrical cavity 11 to match the microwaves. Generally, the stub tuner 40 is installed in a coaxial cable or a waveguide to match the impedance with the load. In the present invention, the stub tuner 40 is installed inside the cavity 11. Specifically, if the direct wave and reflected wave are not in phase within the cavity 11 and the reflection coefficient with the load impedance becomes large, the stub tuner 40 can be operated to match the load impedance to the characteristic impedance of the transmission line, thereby matching the direct wave and reflected wave at the heated object 100 within the cavity 11 to be in phase. [Example]

[0013] The verification of the heating effect when using the microwave heating device of the present invention will be described. [Bactericidal effect] Three Pacific oysters (produced in Nanao Bay, Noto) were obtained for heating and stored for 10 days to increase the bacterial count. Next, each oyster was cut in half lengthwise, and the midgut gland portion was excised. One of the two pieces was used for measuring the original bacterial count and designated as Sample 1, and the other was used for heat sterilization and designated as Sample 2. The other two oysters were similarly cut in half lengthwise, and the midgut gland portion was excised. One piece was used for measuring the original bacterial count and designated as Samples 3 and 5, and the other was used for heat sterilization and designated as Samples 4 and 6. Samples 2, 4, and 6 were placed in the storage compartment of a microwave heating device and subjected to heat treatment. The temperatures of the top, center, and bottom of the samples were measured during heating, and heating was stopped when all three points reached 80°C.

[0014] Next, for sample 1, 9 times the weight of the oysters were diluted with PBS solution in a bag, resulting in a 10-fold dilution. This was then hand-crushed 30 times. The oysters were then crushed in a stomacher for 30 seconds, and 5.5 mL of the extract was extracted. This procedure was repeated for samples 2 to 6. The 10-fold diluted solutions of Samples 1 to 6 were further diluted 10,000-fold by the pour plate method, and this was cultured on an agar medium at 35°C for 48 hours, and the viable cell count was calculated. As shown in the graph in Figure 3, Sample 2, which was heat-treated using a microwave heater, had a 99.981% sterilization effect compared to Sample 1, which was not heat-treated. Similarly, Sample 4, which was heat-treated using a microwave heater, had a 99.992% sterilization effect compared to Sample 3, which was not heat-treated, and Sample 6, which was heat-treated using a microwave heater, had a 99.985% sterilization effect compared to Sample 5, which was not heat-treated.

[0015] [Texture, appearance, flavor] Three raw oysters (from Noto) (samples 1 to 3) were obtained and heated using a microwave heating device under the conditions shown in Figure 4(a). They were then refrigerated for 30 minutes and then tasted. Heating at 70°C for 12 seconds is a sterilization condition that can kill all norovirus present in triple digits. As shown in Figure 4(b), the texture of the cooked oysters was found to be the same as that of raw oysters.

[0016] [Compared to a microwave oven] Figure 5(a) is a graph of the temperature change when oysters are heated at 50 W using the microwave heating device of the present invention and a microwave oven. Figure 5(b) is a graph of the temperature change when oysters are heated at 500 W using a microwave oven. The following facts were discovered through this experiment. The microwave heating device of the present invention can heat with high efficiency, with a heating efficiency of approximately 50% relative to the input power. To generate the same amount of heat as a microwave heating device, the input power of a microwave oven is roughly 10 times higher. - Microwave ovens can barely heat food when using the same input power as microwave heating equipment.

[0017] [Comparison with numerical calculations] Figure 6 shows the results of a coupled analysis of electromagnetic fields and heat transfer using the simulation software COMSOL, along with the experimental results. In the simulation, impedance matching was achieved by adjusting the stub tuner to the optimal position, and the same heating characteristics as the experimental results were obtained. This demonstrates that the mechanism of this device is correct in principle. [Industrial Applicability]

[0018] The present invention is a heating device that confines microwaves in a hollow space and allows the heated object to efficiently absorb them. There is no radiation (leakage) of microwaves into space, and the present invention does not require the large-scale shielding device that microwave heating devices have traditionally required, making it industrially applicable. [Explanation of symbols]

[0019] F One focus F' other focus 1. Microwave heating device 10 Main body 11 Cavity 20 Radiating Antenna 30 Storage area 31 Metal materials 40 Stub Tuner 41 Conductor rod 100 Heated object 200 oval

Claims

1. In a microwave heating device that irradiates microwaves onto an object to be heated, a conductive body having an elliptical cylindrical cavity; The microwave radiation antenna is disposed on one focal line of the elliptical cylinder, and a storage unit is disposed on the other focal line and stores the object to be heated therein. a stub tuner for matching the microwave is provided in the cavity between the radiating antenna and the storage section; A microwave heating device characterized by operating the stub tuner to match the load impedance to the characteristic impedance of the transmission line, thereby matching the direct wave and reflected wave at the heated object within the cavity so that they are in phase.

2. The microwave heating device according to claim 1, characterized in that, when the distance that the microwaves radiated from the radiation antenna travel to directly reach the storage section is A, the distance that the microwaves travel to reach the wall surface of the cavity section is B, and the distance that the microwaves reflected on the wall surface of the cavity section travel to reach the storage section is C, the elliptical shape of the cavity section satisfies the following formula:

3. 3. The microwave heating device according to claim 1, wherein the plurality of objects to be heated are heated sequentially while moving inside the storage section.

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