Microwave heating device

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 the object with microwaves. [Background technology]

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

[0003] [Patent Document 1] JP 2006-173069 A Summary of the Invention [Problem to be solved by the invention]

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

[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 reach the other focal line of the elliptical cylinder in the same phase as one another." However, although such a result can be obtained only when linear antennas of the same shape are installed on both focal lines, the heated object is not linear and has a certain volume, so that the 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 positions of all ellipses, and there is no description that there is a fixed relational expression between the shape of the ellipse and the wavelength of the microwave.

[0005] In consideration of the above problems, an object of the present invention is to provide a microwave heating device that efficiently heats an object to be heated by irradiating the object with microwaves. [Means for solving the problem]

[0006] The microwave heating device of the present invention is a microwave heating device that irradiates microwaves to heat an object to be heated, and is characterized in that it comprises a conductive main body with a hollow portion in the shape of an elliptical cylinder, a 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 that matches the microwaves, located within the hollow portion. In addition, 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 is B, and the distance that the microwaves reflected from the wall surface of the cavity travel to reach the storage section is C, the elliptical shape of the cavity satisfies the following formula.

number

[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 efficiency of microwave absorption by the heated object in the storage section. In addition, the present invention is a heating device that confines microwaves in a hollow space and efficiently absorbs them into the object to be heated, so there is no radiation (leakage) of microwaves into space and no need for the large-scale shielding devices that have traditionally been required for microwave heating devices. 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 efficiency of microwave absorption for the heated object inside the storage section. In addition, the heating process can be made more efficient by moving multiple objects to be heated inside the storage unit and heating them one by one. [Brief description of the drawings]

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

[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 to 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, upper and lower parts of the cavity 11 are surrounded by a conductor to shield microwaves from leaking out of the cavity 11. In Fig. 1(b), the upper part 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 emitting microwaves, and is disposed on one focal line F of the elliptical cylinder. The radiation antenna 20 passes through the upper part of the cavity 11 and is connected to a microwave oscillator (not shown). The storage unit 30 is a member for storing the objects 100 therein, and is disposed on the other focal line F' of the elliptical cylinder. The storage unit 30 is made of a material that allows microwaves to pass therethrough, such as glass, PTFE resin, and silicone rubber. The portion protruding from the main body 10 is covered with a metal material 31. If the storage unit 30 is structured to penetrate the upper and lower parts of the cavity 11, the objects 100 can be heated while being moved in sequence from the top to the bottom of the storage unit 30, or from the bottom to the top, 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 orthogonal coordinate system, whose major and minor axes intersect at an origin O, 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 the cavity 11 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 microwave (hereinafter referred to as the "direct wave") radiated from the radiation antenna 20 and directly reaching the storage unit 30. B is the distance traveled by the microwave radiated from the radiation antenna 20 to the wall surface of the cavity 11. C is the distance traveled by the microwave reflected on the wall surface of the cavity 11 to the storage unit 30. In other words, B+C corresponds to the distance traveled by the microwave (hereinafter referred to as the "reflected wave") radiated from the radiation antenna 20 and reflected on the wall surface of the cavity 11 to the storage unit 30. In order to align the phases of the direct wave and the reflected wave of wavelength λ in the storage unit 30, it is necessary to satisfy the following formula 2.

number

[0012] However, it is possible that the direct wave and the reflected wave may not have the same phase in the storage section 30 due to the influence of the shapes and materials of the radiating antenna 20 and the storage section 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, and is a tuner for matching the impedance with a load. In the present invention, it is installed inside the cavity 11. Specifically, if the direct wave and the 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 the reflected wave at the heated object 100 within the cavity 11 to be in phase. EXAMPLES

[0013] The heating effect when the microwave heating device of the present invention is used will be described below. [Bactericidal effect] Three Pacific oysters (from Nanao Bay, Noto) were obtained for cooking and stored for 10 days to increase the bacterial count. Next, each oyster was cut in half lengthwise, the midgut gland portion was excised, one of the two pieces was used for the original bacterial count measurement 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, the midgut gland portion was excised, one of the pieces was used for the original bacterial count measurement 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 oyster was diluted 10 times by adding PBS solution to the bag, and this was hand-crushed 30 times. Next, it was crushed in a stomacher for 30 seconds and 5.5 mL was extracted. This process 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, was found to have a sterilization effect of 99.981% compared to sample 1, which was not heat-treated. Similarly, sample 4, which was heat-treated using a microwave heater, was found to have a sterilization effect of 99.992% compared to sample 3, which was not heat-treated, and sample 6, which was heat-treated using a microwave heater, was found to have a sterilization effect of 99.985% 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), 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 the sample when it is 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 showing the temperature change when oysters are heated in the microwave heating device of the present invention and in a microwave oven at an output of 50 W. Figure 5(b) is a graph showing the temperature change when oysters are heated in a microwave oven at an output of 500 W. The following facts were discovered from this experiment. The microwave heating device of the present invention can heat with high efficiency, with a heating efficiency of about 50% relative to the input power. To produce the same amount of heat as a microwave heating device, the input power required is roughly 10 times that of a microwave oven. -When the input power is the same as that of a microwave heating device, the microwave oven barely heats anything.

[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 were obtained as in the experimental results. This demonstrated 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. Since there is no radiation (leakage) of microwaves into space and no need for the large-scale shielding device that was previously required for microwave heating devices, the present invention has industrial applicability. [Explanation of symbols]

[0019] F One focus F' the 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 to 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 section is disposed on the other focal line and stores the object to be heated therein; A microwave heating device comprising a stub tuner for matching the microwaves disposed within the cavity.

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

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

Images