JP3609536B2 - microwave - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a microwave oven.
[0002]
[Prior art]
An example of a conventional microwave oven is shown in FIG. In the figure, reference numeral 11 denotes a casing. The casing 11 is provided with an oven 12 for storing food to be heated, and an operation panel 13 is formed on the side thereof. A door 14 for taking in and out the food to be heated is provided on the front surface of the oven 12 so that it can be opened and closed. Around the door 14, radio wave leakage from the gap between the door 14 and the oven front plate 15 is prevented. For this purpose, a choke structure 16 comprising a door 14 and a front plate 15 as shown in FIG. 7 is formed. In order for the choke structure 16 to have a desired radio wave sealing performance, the width of the front plate 15 is required to be approximately 37 mm. Therefore, the ratio of the effective volume in the oven 12 to the external dimension volume of the housing 11 (hereinafter referred to as the effective volume ratio) is approximately 37%.
[0003]
[Problems to be solved by the invention]
In the conventional microwave oven, in order to give the choke structure the desired radio wave sealing performance, it is necessary to secure a necessary space for the choke structure, and the width of the front plate is approximately 37 mm. . For this reason, there existed a problem that the effective volume ratio of oven became small.
[0004]
The present invention has been made in view of the above, and is necessary for obtaining desired radio wave sealing performance by preventing excitation of a mode that is difficult to seal with a door choke structure among a plurality of microwave modes in an oven. An object of the present invention is to provide a microwave oven that can reduce the width of the front plate of the oven and increase the effective volume ratio of the oven.
[0005]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the invention according to claim 1 is a microwave oven having a front plate in an oven opening and having a door and a choke structure composed of the front plate. The gist is that each dimension is in the range of (1/2) · (n + a) (0.3 ≦ a <1, n is a natural number) times the free space wavelength of the oscillation microwave. With this configuration, the width of one period of the microwave mode excited in the oven is defined by the size of the oven. The closer the width of one period of the microwave mode is to the free space wavelength λ of the oscillation microwave, the door choke The electric wave sealing performance of the structure deteriorates. By setting the width and height of the oven opening in a range other than the above formula, the excitation of the microwave mode whose width of one period is close to the free space wavelength λ of the oscillation microwave is hindered, and the radio wave seal of the door choke structure Performance is improved. As a result, the width of the oven front plate necessary for obtaining the desired radio wave sealing performance can be reduced, and the effective volume ratio of the oven can be increased.
[0006]
According to a second aspect of the present invention, in the microwave oven according to the first aspect, each of the width dimension and the height dimension is set to (1/2) · (n + 0.5) with respect to the free space wavelength λ of the oscillation microwave. The gist is that it becomes ± 0.2) times. With this configuration, each of the width dimension and the height dimension of the oven opening is within the range defined by the invention according to claim 1 and within the range defined by the above formula. Even when there is a factor that disturbs the microwave mode, such as heated food, it is possible to prevent excitation of the microwave mode having a width of one cycle that is difficult to seal with the door choke structure.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0008]
1 to 4 are diagrams showing a first embodiment of the present invention. FIG. 1 schematically shows an example of a microwave mode in a microwave oven and an oven. In FIGS. 1A and 1B, 1 is a housing, 2 is an oven, 3 is an operation panel, and 5 is an oven front plate.
[0009]
In the microwave oven having such a configuration, a plurality of microwave modes are excited in the oven 2, and from the theory of a rectangular parallelepiped resonator, the microwave mode is a three-dimensional standing wave. There is a standing wave that satisfies
[0010]
[Expression 1]
(1 / λ) ² = (m / 2W) ² + (l / 2T) ² + (p / 2D) ² (1)
W: width of rectangular parallelepiped resonator (oven) (m)
T: Height of rectangular parallelepiped resonator (oven) (m)
D: Depth (m) of rectangular parallelepiped resonator (oven)
λ: free space wavelength of the oscillating microwave m: number of antinodes in the width direction of the standing wave (integer)
l: Number of antinodes in the height direction of standing wave (integer)
p: number of antinodes in the depth direction of standing wave (integer)
From the theory of a rectangular parallelepiped resonator, the width S of one period of the microwave mode in the oven 2 is as follows in the width direction:
S = 2W / n (n is an integer) (2)
It becomes. The same applies to the height direction and the depth direction. FIG. 1C shows the spatial distribution of the electric field of the fifth order mode (n = 5) in the lateral width direction. The spatial distribution of the electric field in the fifth mode takes a knot for each width obtained by dividing the oven width dimension W into five equal parts. From the above, from the theory of a rectangular parallelepiped resonator, the width S of one period of each standing wave in each of the width direction, height direction and depth direction of each mode is determined by the size of the oven 2. In other words, the width S of one period of the microwave mode in the oven 2 can be limited by the size of the oven 2.
[0011]
FIG. 2 shows the width S of one period of all modes that can occur when the dimension of one side of the oven 2 is L. According to the theory of a rectangular parallelepiped resonator, the width S of one period of the mode cannot be shorter than the free space wavelength λ of the oscillation microwave, and the theoretical minimum value of the width S of one period is λ. The maximum order N of the mode when the dimension of one side of the oven 2 is L is N = (integer part of 2L / λ). In the mode of the maximum order N, the width S of one cycle is the minimum value. . From FIG. 2, for example, when the dimension of one side of the oven 2 is 220 mm, a third-order mode or less may be excited on the side, and the width S of one period of the third-order mode is about 147 mm.
[0012]
Now, by computer simulation, the influence of the width S of one period of the microwave mode in the oven 2 on the radio wave sealing performance of the choke structure composed of the door and the front plate 5 is revealed. became. FIG. 3 shows the influence of the width S of one period of the mode on the radio wave sealing performance of the choke structure by this computer simulation experiment. The frequency of the oscillation microwave in the experiment is 2.5 GHz, and the free space wavelength λ is 120 mm. The relative value of the leaked radio wave amount is 1 when λ = 120 mm. From the results of FIG. 3, it can be seen that the longer the width S of one mode period, the better the radio wave sealing performance of the choke structure. Further, as the width S of one period of the mode is shortened to about the free space wavelength λ of the oscillation microwave, the amount of leaked radio waves rapidly increases, and the radio wave sealing performance of the choke structure is deteriorated. The reason for this is that the choke structure itself is a single resonance structure, and has a radio wave sealing performance by utilizing the resonance characteristics of the choke structure. This is because, for a mode that is substantially equal to the free space wavelength λ of the wave, the resonance condition of the choke structure becomes the all-pass resonance point in the radio wave sealing characteristics, and the radio wave sealing performance is deteriorated. Among the modes in the oven 2, the leakage of the microwave mode in which the width S of one period is equal to the free space wavelength λ of the oscillation microwave is the largest.
[0013]
Therefore, in the present embodiment, the choke structure is prevented by exciting the mode in which the width S of one period is substantially equal to the free space wavelength λ of the oscillation microwave, which is the main cause of the deterioration of the radio wave sealing performance of the choke structure. Therefore, the width of the front plate 5 is reduced to increase the effective volume ratio of the oven 2. FIG. 4 shows the radio wave sealing performance of the choke structure for the variable a when the dimension of one side of the oven 2 is expressed as L = (λ / 2) · (n + a) based on the results of FIGS. Is shown. As described above, the width S of one period of the microwave mode is defined by the size of the oven 2. In order to improve the radio wave sealing performance of the choke structure, the one-period width S of the mode is not shortened so as to approach the free space wavelength λ of the oscillation microwave, and the one-period width S of the mode is increased as much as possible. It is important. For this purpose, from FIG. 4, the width dimension W and the height dimension T of the oven opening are set to (1/2) · (n + a) (0 ≦ a <0. 3, n is a natural number). By making the range other than a multiple, the period width S of the microwave mode becomes approximately 128 mm or more, and the amount of leaked radio waves is S = 120 mm (approximately equal to the free space wavelength λ of the oscillation microwave) Compared to the case of, it can be about half. Actually, there are factors in the oven 2 that disturb the microwave mode such as the unevenness of the wall surface, the grill, the food to be heated, etc., so the mode in the oven 2 is affected and the width of the oven opening For each of the ranges where W and height dimension T are (1/2) · (n + a) (0.7 <a <1, where n is a natural number) times the free space wavelength λ of the oscillation microwave, Since one or more modes of the appropriate order may be excited, the selection range includes the width dimension W and the height dimension T of the oven opening with respect to the free space wavelength λ of the oscillation microwave ( 1/2) · (n + 0.5 ± 0.2) times is preferable.
[0014]
From the above, by limiting the size of the oven 2 to the above suitable range, it is possible to improve the radio wave sealing performance of the choke structure by preventing the generation of a mode that is difficult to seal with the choke structure. The width of the front plate 5 necessary for obtaining the radio wave sealing performance can be reduced to 30 mm or less, which is smaller than the conventional one, and the effective volume ratio of the oven 2 can be increased. As a specific example, when the outer dimensions of the microwave oven are W = 470 mm, T = 380 mm, D = 290 mm (51.8 liter), and the conventional front plate width is 37 mm, the oven size is W = At 310 mm, T = 187 mm, D = 310 mm (17.8 liters), the effective volume ratio is approximately 35%. On the other hand, in the present embodiment, by setting the front plate width to 28 mm, the oven size becomes W = 328 mm, T = 205 mm, D = 310 mm (20.8 liter), and the effective volume ratio is about 40%. To improve.
[0015]
FIG. 5 shows a second embodiment of the present invention. In the present embodiment, in order to further improve the radio wave sealing performance of the choke structure, as shown in FIGS. 5A and 5B, in addition to the configuration of the first embodiment, the front plate 5 And a protruding piece 7 made of an independent metal piece protruding forward from the surface of the front plate 5 over the entire circumference. The protruding length of the protruding piece 7 is preferably about 5 mm to 13 mm. As shown in FIG. 5C, a conductor piece 8 that is electrically connected to the front plate 5, corresponding to the protruding piece 7, is also installed on the side of the operation panel 3.
[0016]
【The invention's effect】
As described above, according to the first aspect of the present invention, each of the horizontal width dimension and the height dimension of the oven opening is set to (1/2) · (n + a) (with respect to the free space wavelength λ of the oscillation microwave. 0.3 ≦ a <1, where n is a natural number) times the range , so that the microwave mode excitation with the width of one cycle that is difficult to seal with the door choke structure in the oven is hindered, and the radio wave sealing performance of the door choke structure Can be improved. As a result, the width of the oven front plate necessary for obtaining the desired radio wave sealing performance can be reduced, and the effective volume ratio of the oven can be increased.
[0017]
According to the second aspect of the invention, each of the width dimension and the height dimension is (1/2) · (n + 0.5 ± 0.2) times the free space wavelength λ of the oscillation microwave. Even if there is a factor that disturbs the microwave mode such as food to be heated in the oven, the door choke can prevent the excitation of the microwave mode with a width of one cycle that is difficult to seal with the door choke structure. The radio wave sealing performance of the structure can be improved reliably. As a result, similar to the above, the width of the oven front plate necessary for obtaining the desired radio wave sealing performance can be reduced, and the effective volume ratio of the oven can be increased.
[Brief description of the drawings]
FIG. 1 is a diagram showing an example of a configuration of a microwave oven according to a first embodiment of the present invention and a microwave mode in an oven.
FIG. 2 is a diagram showing the relationship between the dimension of one side of the oven and the width of one period of the excited microwave mode in the first embodiment.
FIG. 3 is a diagram showing the relationship between the width of one period of the microwave mode and the amount of leaked radio waves from the choke structure in the first embodiment.
FIG. 4 is a diagram showing the relationship between the dimension of one side of the oven and the amount of leaked radio waves from the choke structure in the first embodiment.
FIG. 5 is a configuration diagram of a second embodiment of the present invention.
FIG. 6 is an external view of a conventional microwave oven when the door is opened.
7 is a cross-sectional view of the door choke structure in the conventional microwave oven, taken along the line AA ′ of FIG.
[Explanation of symbols]
2 Oven 5 Oven front plate

Claims (2)

In a microwave oven having a front plate at the oven opening and provided with a door and a choke structure composed of the front plate , the horizontal width and height of the oven opening are set to the free space wavelength of the oscillation microwave ( 1/2) · (n + a) (0.3 ≦ a <1, n is a natural number) times the range. The width and height of each of the horizontal width and the height are (1/2) · (n + 0.5 ± 0.2) times the free space wavelength λ of the oscillation microwave. microwave.

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