JPS5832758B2 - microwave oven - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an antenna mechanism that radiates microwaves into a heating chamber in a microwave oven that heats food by irradiating it with microwaves.

The radiation of microwaves into the heating chamber in a microwave oven is
Conventional methods include those that radiate directly from a magnetron antenna, and those that radiate from a magnetron into a heating chamber via a waveguide.

These irradiation methods have the problem of uniform heating of food. These are important issues related to the basic performance of microwave ovens, such as the problem of matching the load on the magnetron.

FIG. 1 and FIG. 2 are an example of the irradiation method previously proposed by the inventor of the present application.

Microwave power generated by the magnetron 1 is transmitted to approximately the center of the heating chamber ceiling surface 4 by a strip line 3 electrically connected to a magnetron antenna 2, and is radiated from the antenna 5 into the heating chamber.

S) The IJ tube line 3 is formed by bending a metal plate, and is arranged at a constant distance from the heating chamber wall surface 6 and the heating chamber ceiling surface 4.

Note that the strip line 3 is not limited to a metal plate, and any conductor may have a round, square, or elliptical cross section.

7 is a support part that keeps the strip line 3 at a constant interval as described above, and is λ/4 (λ is the wavelength of the electromagnetic wave oscillated by the magnetron).
Since the short stub is formed, the strip line 3 is electrically unaffected by the stub, and serves to mechanically hold the strip line 3.

The antenna 5 is made by bending the tip of the strip line 3 almost vertically, and the height of the tip 1 from the heating chamber ceiling surface 4 is approximately λ.
/4.

Note that 8 indicates a stirring blade, 9 indicates a food to be heated, and 10 indicates a microwave oven door.

With this configuration, most of the microwave power generated by the magnetron 1 can be irradiated from the center of the heating chamber ceiling surface 4, and by changing the arrangement of the strip line 3, radiation from any position can be avoided. It is possible.

However, the antenna 5 is equivalently a λ/4 monoball antenna 5 having an oscillation source 11 at its root, as shown in FIG.
' Therefore, the radiation directivity becomes stronger as the angle indicated by θ becomes larger, and in the direction of θ=O, the radiation amount becomes extremely small.

The line indicated by 12 in the figure conceptually represents this relationship.

Moreover, it is point symmetric and uniform around the antenna axis.

That is, the radiation in the direction along the heating chamber ceiling surface 4 is large, and the radiation in the direction perpendicular to this is small.

This means that most of the power radiated from the antenna 5 is not directly irradiated onto the loaded food to be heated 9, but is irradiated once or repeatedly by being reflected off the heating chamber wall.

Therefore, the result is that the microwave power is contrasted from the peripheral heating chamber walls toward the center.

According to actual experiments, relatively flat heated foods (e.g.
This tendency was noticeable in the case of pizza pie, shumai, etc.), and uneven heating was observed between the part near the heating chamber wall (surroundings) and the central part, where the temperature rise in the former was large and the temperature rise in the latter was small.

The object of the present invention is to eliminate the drawbacks of the prior art described above, increase the component that radiates microwave power directly toward the food to be heated, and provide a microwave oven with less uneven heating even for a relatively flat load. It is about providing.

It has already been mentioned that the above-mentioned drawback lies in the radiation directivity of the antenna.

Therefore, it is sufficient to form an antenna that has a large directivity of radiation in the direction of the food to be heated.

When microwave power is transmitted using a strip line, the microwave power is transmitted along the walls of the heating chamber (not to mention the side walls, but also the ceiling and the bottom surface), so the power is concentrated near the wall surface.

Therefore, no matter where the radiation is emitted from the heating chamber wall,
An antenna with a large radiation component in the direction perpendicular to the wall surface of the heating chamber at that location is an advantageous antenna for reducing heating unevenness.

Hereinafter, the present invention will be explained in detail based on Examples.

FIG. 4 is a diagram showing an embodiment of the present invention.

The tip of the strip line 3 is bent vertically and turned back at a height t2 from the heating chamber ceiling surface 4.

Furthermore, two semiconductors 13 are arranged at opposing positions and spaced apart from each other by a certain distance d, and are fixed to the heating chamber ceiling surface 4 with set screws 14.

In the figure, the length of tl is approximately λ/2 and t'/'i is approximately λ/4.
, most of the microwave power transmitted from the direction indicated by the arrow 15 by the strip line 3 is radiated in a direction perpendicular to the heating chamber ceiling surface 4.

The state of this radiation will be explained below.

In Figure 4, the length tl of the tip of the antenna is approximately λ/2.
Therefore, a half-wavelength dipole antenna is formed, and at the same time, the height t2 is λ/4, so it becomes equivalently as shown in FIG.

In other words, it can be considered that the half-wavelength dipole antenna 1γ excited by the equivalent excitation source 16 is placed parallel to the conductor plane 18 and separated by λ/4.

In such a case, as is well known, it can be considered that the mirror image excitation source 16' and dipole antenna 17' are placed symmetrically with respect to the conductor plane 18, separated by λ/2.

Moreover, since both are parallel to the conductor plane 18, the phases of the excitation sources are opposite to each other.

Therefore, the radiation directivity exhibited by this antenna is a combination of the directivity of the dipole antenna 17 and 1T.

FIG. 6 is a diagram showing the result of synthesis, and is a side view of FIG. 5.

The directivity of the dipole antenna 1T alone as seen in the same figure is so-called omnidirectional, which radiates with a constant intensity in all directions, but when combined with the mirror image of the dipole antenna 17', it is shown by the arrow 19. The radiation in the female direction is in phase and sums up, resulting in strong radiation.

On the other hand, radiation in the perpendicular direction (direction along the conductor plane 18) is weakened because it has an opposite phase and is summed.

After all, the intensity of radiation is conceptually expressed as shown by the line 20, with maximum radiation in the direction perpendicular to the conductor plane 18.

Therefore, even in the case of a flat-shaped food to be heated, the electric power directly irradiated to the central portion is large, so that heating unevenness is improved compared to the conventional method.

Further, the present invention has the advantage that matching can be easily achieved as described below.

In FIG. 4, the portion of the strip line 3 that rises perpendicularly to the heating chamber ceiling surface 4 and the similarly perpendicular portion of the semiconductor 13 form a pair of parallel flat plate lines; The length t2 is specifically λ/4 as mentioned above.

Now, suppose that the characteristic impedance of strip line 3 is Z
1 The characteristic impedance of the above parallel plate is the radiation impedance of the ZP1 dipole antenna (the shape of the heating chamber,
(including the food to be heated and the stirring blade) is ZX, it can be considered by replacing it with an equivalent circuit as shown in FIG.

When Zo = Z If = Zo−ZX, matching can be achieved.

Also, as is well known, the characteristic impedance of a parallel plate is determined by the width of the plate and the distance between the two plates.

Therefore, ZP can be changed by adjusting the distance d in FIG. 4 and the conductor width of the parallel portion, so matching can be easily achieved.

Further, according to the present invention, applications as shown in FIG. 8 are possible.

A dielectric shaft 21 with low loss is arranged along the central axis of the dipole antenna formed by the strip line 3 and the semiconductor 13, and one end is attached to the heating chamber ceiling surface 4 via a bearing 22. It has a structure that allows free rotation around the center.

Furthermore, since the stirring blade 23 is fixed to the other end of the dielectric shaft 21, the stirring blade can freely rotate according to the movement of the wind inside the heating chamber.

In this way, it is easy to place the antenna and the stirring blade in a symmetrical positional relationship (in this case, point symmetry) close to the antenna, which is the microwave radiation source, so that the microwave power can be This enables sufficient stirring with good symmetry, making it possible to provide a high-performance microwave oven with less uneven heating.

FIG. 9 is a diagram showing another embodiment of the present invention.

The figure just forms a folded antenna.

Therefore, although it is essentially the same as the embodiment shown in FIG.
Since it can be integrally molded as an extension of the strip line, the number of parts can be reduced.

Also, as shown in Fig. 10, by making a through hole 24 in the center of the folded antenna and passing the dielectric shaft through it,
As in the case of the embodiment shown in FIG. 8, it is possible to easily provide a high-performance microwave oven with less uneven heating.

Furthermore, FIG. 11 is a diagram showing another embodiment of the present invention.

It has a structure in which the tip of the strip line 3 is bent to form a loop 25 and then fixed to the heating chamber ceiling surface 4 with a set screw 14.

Similar to the explanation with reference to FIG. 5, microwave power is promptly radiated due to the mirror image relationship.

This is because, as shown in FIG. 12, a loop antenna is formed which has a special oscillation source 16 and is symmetrical with respect to a conductor plane 18.

Therefore, although the radiation directivity includes radiation in a direction along the conductor plane 18, it also radiates strongly in a direction perpendicular to the conductor plane 18, so that heating unevenness can be reduced for the reason already mentioned.

Moreover, although FIG. 11 shows an example of a semicircular shape, it is natural that the same effect can be obtained even in the case of a rectangular shape.

FIG. 13 is a diagram showing an example in which a stirring blade is added to the above-mentioned rectangular loop antenna. By providing a through hole 24 in the center of the rectangular loop, the same effect as in FIGS. 8 and 10 can be obtained. It is possible to provide a high-performance microwave oven with less uneven heating.

The above explanation has all been about the case where microwave power is radiated from the ceiling of the heating chamber, but it goes without saying that microwave ovens that radiate from other walls, such as the floor of the heating chamber, have exactly the same advantages. It is about.

As explained above, according to the present invention, even in a microwave oven using a strip line, an antenna with a large radiation component that directs microwave power in the direction of the heated food can be obtained with a relatively simple structure, and Since the wings can be attached to the center of the antenna, a high-performance microwave oven with less uneven heating can be provided.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a conventional microwave oven, Fig. 2 is an enlarged view of the main part of Fig. 1, Fig. 3 is an explanatory diagram of the radiation directivity of a conventional antenna, and Fig. 4 is an embodiment of the present invention. Perspective view showing an example, fifth
Figure 6 is an explanatory diagram of the radiation directivity of the antenna in Figure 4, Figure 7 is an equivalent circuit diagram showing how to match the antenna in Figure 4, Figures 8, 9, 10, and 11. 13 are diagrams showing other embodiments of the present invention, and FIG. 12 is an explanatory diagram showing the radiation directivity of the embodiment of FIG. 11. 1... Magnetron, 3... Strip line, 4...
... heating chamber wall surface, 13 ... semiconductor, 21 ... dielectric shaft 23 ... stirring blade.

Claims (1)

[Claims] 1. In a microwave oven that heats food by irradiating it with microwaves, a conductor is placed at an appropriate distance from the wall of the heating chamber, and a strip line is formed between the wall of the heating chamber and the conductor. (a) a part perpendicular to the heating chamber wall surface located at the end of the IJ tube line by extending the conductor of the line;
A portion bent so that at least a portion thereof is parallel to the wall surface is provided behind this vertical left portion, and an antenna having strong directivity in the direction perpendicular to the wall surface of the heating chamber located at the end is formed. A microwave oven characterized by: 2. In a microwave oven that heats food by irradiating it with microwaves, a conductor is placed at an appropriate distance from the heating chamber wall, and the heating chamber wall and the conductor form a strip line to generate microwave power. At the end of the strip line, an antenna having strong directivity in the direction perpendicular to the wall surface of the heating chamber located at the end is provided, and furthermore, a rotating antenna having a stirring blade approximately in the center of the antenna is provided. A microwave oven characterized by a shaft arrangement.