JPH08138859A - Microwave heating device - Google Patents

Abstract

PURPOSE: To provide a microwave heating device by which nonuniformity of heating of food, particularly, nonuniformity of heating in the vertical direction can be restrained. CONSTITUTION: A radiating antenna 4 is composed of an elliptic metallic plate, and a hole 4b into which a magnetron antenna 6 is penetratingly inserted is opened on the slightly upper side than its central part. Since a radius (a long diameter) r1 of the radiating antenna 4 on the more lower side than the hole 4b is set almost equal to a distance L up to the tip from a radiating antenna installing position of the magnetron antenna 6, a degree of coupling with a microwave in a lower part of the radiating antenna 4 is high. Though the radius (the long diameter) r1 of a lower part of the radiating antenna 4 is set longer than a radius (a short diameter) r2 of an upper part, since it is bent to the heating chamber side, space distances in the upper and lower parts are equal to each other. Therefore, electric field strength Eo in the lower part of the radiating antenna 4 is higher than electric field strength E1 in the upper part, so that a lower part of food is sufficiently heated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave heating apparatus such as a microwave oven for introducing microwaves oscillated by a magnetron into a heating chamber from a waveguide to heat food.

[0002]

2. Description of the Related Art FIG. 4 is a schematic sectional view showing a conventional microwave oven disclosed in Japanese Patent Publication No. 4-80520. Food
A side surface of an oven cavity 11 that accommodates and heats 15 is formed to form a subcavity 12, and a magnetron 13 is attached to the subcavity 12. A magnetron output unit 14 is attached from the magnetron 13 to the oven cavity 11. Oven cavity
A metal plate 16 having an opening is installed at the boundary between 11 and the sub-cavity 12.

The microwave oscillated by the magnetron 13 is radiated from the magnetron output section 14, passes through the opening of the metal plate 16 and is introduced into the oven cavity 11,
Heat 15

Here, the length of the magnetron output section 14 is about λ / 4≅30 mm, which is the most efficient output, where λ is the wavelength of the microwave. However, when the side surface of the oven cavity 11 is pressed to form the sub-cavity 12, the protruding length of the sub-cavity 12 is limited to about 20 mm, and the length of the magnetron output unit 14 is also limited to about 20 mm. Magnetron output section with a length of about 20 mm 14
When directly attached, magnetron 13 and oven cavity 11
The degree of coupling with is extremely low. In the conventional microwave oven shown in FIG. 4, this decrease in coupling degree is compensated by the metal plate 16, and the shape of the metal plate 16 and the position of the opening with respect to the magnetron output unit 14 are changed to change the magnetron 13 to the magnetron. The electromagnetic field distribution of microwaves radiated via the output unit 14 can be easily changed. That is, it is possible to obtain an oven impedance that matches the magnetron characteristics.

However, in such a microwave oven,
A metal plate to improve heating unevenness depending on the type of food 15.
It is necessary to change the shape of the 16 openings. Also metal plate 16
Since the opening of the sub-cavity 12 is partially blocked by the metal plate 16, the radiated microwave is reflected by the metal plate 16 and returns to the magnetron 13. In this case magnetron 13
There is a problem that the temperature rises excessively. More food
Since microwaves are irradiated from above 15 to the food 15, the food 15 having a large dielectric constant may not sufficiently penetrate the microwaves to the bottom thereof, and uneven heating may occur.

FIG. 5 is a schematic cross-sectional view showing a microwave oven having a waveguide formed separately from the oven cavity 11 whose protruding length is not limited by the manufacturing method. An opening is provided in the side wall of the heating chamber (cavity) 21, and a mortar-shaped waveguide 17 is attached to the opening. A magnetron 13 is provided on the small diameter side of the waveguide 17, and a magnetron antenna (magnetron output section) 14 is formed so as to project from the magnetron 13 in the tube axis direction of the waveguide 17.
In the middle of the magnetron antenna 14, a radiation antenna 18 is provided as an auxiliary antenna of the magnetron 13.

The microwave oscillated by the magnetron 13 is radiatively diffused by the radiation antenna 18 and introduced into the heating chamber 21 to heat the food 15.

[0008]

However, also in the microwave oven shown in FIG. 5, microwaves are applied to the food 15 from above as in the microwave oven shown in FIG. Heating unevenness often occurs between the bottom and the top.

The present invention has been made in view of such circumstances, and by making the lower part of the radiating antenna longer than the upper part and bending it toward the heating chamber to increase the electric field strength, uneven heating of food, particularly upper and lower parts, is performed. An object of the present invention is to provide a microwave heating device capable of suppressing uneven heating in the direction.

[0010]

According to a first aspect of the present invention, there is provided a microwave heating apparatus, wherein a waveguide and a magnetron are provided on a side wall of a heating chamber, and the microwave oscillated by the magnetron is used for conducting the electromagnetic wave. In a microwave heating device, which is transmitted to a magnetron antenna projecting in the tube axis direction of a wave tube, diffused and radiated by a plate-shaped radiation antenna mounted substantially perpendicular to the magnetron antenna and introduced into a heating chamber, A hole for inserting the magnetron antenna is formed above the center of the antenna, and the lower part of the radiating antenna is bent toward the heating chamber.

In the microwave heating apparatus according to the second invention, in the first invention, the distance from the magnetron antenna to the lower end of the radiation antenna along the radiation antenna is determined based on the wavelength of the microwave. It is characterized by being

In the microwave heating apparatus according to the third invention, in the second invention, the distance from the magnetron antenna to the lower end of the radiation antenna along the radiation antenna is such that the radiation antenna of the magnetron antenna is attached. Is substantially the same as the distance from the open position to the tip, and these distances are longer than the distance from the magnetron antenna to the upper end of the radiation antenna.

[0013]

In the first aspect of the invention, since the lower portion of the radiation antenna, which is below the hole for inserting the magnetron antenna, is longer than the upper portion (upper portion) of the hole, the electric field strength on the lower side is the electric field on the upper side. Higher than strength. Thereby, the bottom side of the food can be heated more strongly than before. Also, since the lower part is bent toward the heating chamber side, even if the lower part is longer than the upper part, a space distance is secured between the tip and the waveguide, that is, the space between the edge of the radiating antenna and the waveguide. It is possible to make the distances above and below approximately the same.

According to the second invention, in addition to the operation of the first invention, the degree of coupling with the microwave in the lower part of the radiation antenna is good, and the microwave can be efficiently radiated.

In the third invention, in addition to the operation of the second invention, the electric field strength below the magnetron antenna can be made higher than the electrolytic strength above.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a schematic vertical sectional view showing a microwave heating apparatus according to the present invention, and FIG. 2 is a horizontal sectional view thereof. Reference numeral 1 in the figure denotes a heating chamber for heating a food 7 placed on a rotating turntable 5. An opening is provided on the side wall of the heating chamber 1, and a mortar-shaped waveguide 2 is attached to the opening. A magnetron 3 is provided on the small diameter side of the waveguide 2, and a magnetron antenna 6 is formed so as to project from the magnetron 3 in the tube axis direction of the waveguide 2. In the middle of the magnetron antenna 6, there is provided a radiation antenna 4 whose lower portion is bent to the heating chamber 1 side longer than its upper portion.

FIG. 3 (a) is an enlarged view of the radiation antenna 4 viewed from the direction A in FIG. 1, and FIG. 3 (b) is an enlarged sectional view showing the waveguide 2 of FIG. The radiation antenna 4 is made of a metal plate having an oval shape, and a hole 4b through which the magnetron antenna 6 is inserted is opened slightly above the central portion thereof. Ribs 4a for mounting the magnetron antenna 6 at predetermined intervals are provided on one surface side (the magnetron 3 side) of the hole 4b. The lower part of the radiation antenna 4 is bent toward the heating chamber 1.

The radiation antenna 4 and the magnetron antenna 6
The degree of coupling with and is determined by the relationship between the distance L from the radiation antenna mounting position of the magnetron antenna 6 to the tip and the distance from the magnetron antenna 6 to the tip of the radiation antenna 4. If these distances are equal, the degree of coupling will be the best. In the present embodiment, if the distance from the magnetron antenna 6 to the lower end of the radiating antenna 4 along the radiating antenna 4 is r ₁ and the distance from the magnetron antenna 6 to the upper end of the radiating antenna 4 is r ₂ , then L≈r ₁ The radiation antenna 4 is designed so that the relationship of L> r ₂ is established. However, the distance L is λ /, where λ is the wavelength of the microwave.
It is set as 4. This allows the magnetron antenna 6
Has a high degree of coupling with the microwave oscillated by the magnetron 3.

Since the distance r ₁ is substantially equal to the distance L, the degree of coupling with the magnetron antenna 6 below the radiation antenna 4 is high. Therefore, the microwave is efficiently radiated. Further, since the lower portion of the radiating antenna 4 is longer than the upper portion, but is bent, a sufficient spatial distance to the waveguide 2 in the lower portion is ensured and can be made equal to the spatial distance in the upper portion. In this case, the electric field strength E ₀ in the lower part of the radiating antenna 4 becomes higher than the electric field strength E ₁ in the upper part as shown in FIG. Therefore, even when the microwave is applied from above the food 7, the lower portion of the food 7 is sufficiently heated, and uneven heating of the food 7 in the vertical direction can be suppressed to the minimum.

Further, as shown in FIG. 2, the microwave in the horizontal plane has a radial electric field distribution (e ₀ around the waveguide 2).
> E ₁ > e ₂ ), but turntable 5 shows food 7
Since the food is heated while rotating, the food 7 is heated even in the horizontal direction.

[0021]

As described above, in the microwave heating apparatus according to the present invention, the distance from the magnetron antenna to the lower end of the radiating antenna is made longer than the distance from the magnetron antenna to the upper end of the radiating antenna, and the lower part of the radiating antenna is By bending to the heating chamber side, the electric field strength on the lower side becomes higher than the electric field strength on the upper side, and the bottom side of the food can be heated more strongly than before. When the distance from the magnetron antenna to the lower end of the radiation antenna is determined based on the microwave wavelength, the coupling degree between the radiation antenna and the microwave is good, and the microwave is efficiently radiated. From the above, the present invention has excellent effects such as suppressing uneven heating of food, especially uneven heating in the vertical direction.

[Brief description of drawings]

FIG. 1 is a schematic vertical sectional view showing a microwave heating device according to the present invention.

FIG. 2 is a schematic cross-sectional view showing a microwave heating device according to the present invention.

FIG. 3 is a schematic diagram showing the shape of a radiation antenna.

FIG. 4 is a schematic cross-sectional view showing a conventional microwave oven.

FIG. 5 is a schematic cross-sectional view showing a conventional microwave oven.

[Explanation of symbols]

 1 heating chamber 2 waveguide 3 magnetron 4 radiating antenna 4b hole 6 magnetron antenna 7 food

Claims (3)

[Claims] 1. A waveguide and a magnetron are provided on a side wall of a heating chamber, and microwaves oscillated by the magnetron are transmitted to a magnetron antenna projecting in a tube axis direction of the waveguide. In the microwave heating device which is diffused and radiated by a plate-shaped radiation antenna mounted substantially perpendicular to the magnetron antenna and introduced into the heating chamber, a hole for inserting the magnetron antenna above the center of the radiation antenna. Is opened, and the lower part of the radiating antenna is bent toward the heating chamber. 2. The microwave heating according to claim 1, wherein the distance from the magnetron antenna to the lower end of the radiation antenna along the radiation antenna is determined based on the wavelength of the microwave. apparatus. 3. The distance from the magnetron antenna to the lower end of the radiating antenna along the radiating antenna is substantially the same as the distance from the position where the radiating antenna is attached to the tip of the magnetron antenna. The microwave heating apparatus according to claim 2, wherein the distance is longer than the distance from the magnetron antenna to the upper end of the radiation antenna.