JPH02155194A - Microwave oven - Google Patents

Abstract

PURPOSE:To efficiently use space of a microwave oven and easily clean it by utilizing radiation of radiating elements for a flat antenna from an edge of a flat conductor placed parallel to an earth plane. CONSTITUTION:A dielectric plate 10 is fixed as sandwiched between a wall face 1 of a heating chamber and a radiation plate 11 made of almost a metal plate in which length L of one leg thereof is about a half wave length of the used frequency. Drilled on the wall face 1 of the heating chamber is a throughhole 23 whose diameter is equal to an inner diameter of an outer conductor 8. A pierce conductor (an inner conductor) 9 is made to pierce in the center of the throughhole 23 and also is made to pierce in the dielectric plate 10. Then, the pierce conductor 9 is fixed to the radiation plate 11 by a fixing screw 12 to electrically connected thereto. Microwave produced by a magnetron 3 is introduced by a coaxial line composed of the outer and the inner conductors 8 and 9 and radiated into a heating chamber 2 by the dielectric plate 10 and the radiation plate 11 to heat food 5 to be heated. Since, there is no protrusion, space of a microwave oven is efficiently used and the microwave oven is easily cleaned.

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a high-frequency heating device that heats food stored in a heating chamber by irradiating microwaves, and particularly relates to a power supply device that irradiates microwaves generated by a magnetron into the heating chamber. It is related to the device.

Conventional technology A conventional power supply device using an oscillation source of 915MIIz, which is one of the frequency bands assigned to high-frequency heating devices,
As described in Japanese Patent Publication No. 63-40035, the feeding antenna was shaped to protrude into the heating chamber.

Problems to be Solved by the Invention In this case, there was an inconvenience in that the space efficiency for storing the heated food decreased due to the protruding antenna, and it was difficult to clean the inside of the heating chamber because the antenna got in the way. .

Means for Solving the Problems An object of the present invention is to provide a high-frequency heating device that improves space efficiency and is easy to clean by improving the power supply device of the high-frequency heating device.

The above object is achieved by applying a radiating element of a planar antenna.

The radiating element for a working planar antenna utilizes radiation from the edge of a planar conductor placed parallel to the earth plane (in this case the heating chamber wall). Therefore, there are no protruding parts, which improves space efficiency and cleaning efficiency.

EXAMPLE Below, the structure and operation of an example of the present invention are shown in FIGS. 1 to 5.
This will be explained using figures. In FIG. 1, microwaves generated by a magnetron 3 are guided by a coaxial line composed of an outer conductor 8 and an inner conductor 9, and are guided into a heating chamber 2 by a dielectric plate 10 and a metal plate (hereinafter referred to as a radiation plate) 11. The structure is such that the food to be heated 5 is heated by the radiation. In addition, 1 is a heating chamber wall surface, 4 is a rotating mounting table for evenly heating the food to be heated 5, 6 is a motor mechanism, and 7
is the axle that transmits the rotation.

2 and 3 are enlarged views of the main parts of FIG. 1. In FIG. 2, a dielectric plate 10 is connected to a heating chamber wall surface 1 and a radiation plate 1.
It is attached in a way that it is sandwiched between 1. Heating chamber wall 1
A through hole 23 with a diameter equal to the inner diameter of the outer conductor 8 is bored in the through hole 23 , and a through hole 23 (hereinafter referred to as the inner conductor) passes through the center of the through hole 23 , and at the same time passes through the dielectric 10 to form the radiation plate 11 . It is fixed with a fixing screw 12. The radiation plate 11 is rectangular as shown in FIG. Therefore, the dielectric plate is also relatively large and rectangular. Since the radiation plate 11 is a conductor, the radiation plate (metal plate) may be formed and attached as shown in the figure, or it may be a conductive film deposited on the dielectric plate 10 in advance. The position of the fixing screw relative to the radiation plate (metal plate) 11 is at the center of the width W, as shown in FIG.

It is placed at position Q from the end.

The reason why microwaves are quickly radiated into the heating chamber 2 with such a structure will be explained with reference to FIG. 4.

FIG. 4 conceptually shows the structure of FIG. 2. Therefore, the outer conductor 8 and the heating chamber wall surface 1 in FIG. 2 are shown as a ground conductor 23 in one piece.

Further, the fixing screw 12 is omitted. The microwave generated by the magnetron 3 is transmitted through a coaxial line consisting of an inner conductor 9 and a ground conductor 28, but at that time, there is a
An electric field of 3.13A is generated.

As this electric field progresses further, it splits into the left and right sides of the figure.

The electric field becomes 14.14A. At this time, radiation plate (metal plate) 1
If the length of 1 (dimension L in Figure 3) is approximately half the wavelength of the frequency used, it will resonate and the electric field will be radiated to the outside as shown at 15.15A, and will eventually move downward in the figure as shown at 16.17. I'll go. I mentioned that radiation occurs when the length of L is about half a wavelength, but in detail, λ.

Press L 0.49 ■7 (1). However, λ. is the wavelength of the frequency used, and εr is the relative dielectric constant of the dielectric plate 10. In addition, the radiation plate (metal plate) 11
The distance from the end of @Q is from the coaxial line to the radiation plate (metal plate) 1
This is a factor that determines the radiation impedance when looking at the 1 side. The smaller Q is, the larger the radiation impedance is, and as Q increases, it becomes smaller (minimum at Q=L/Z). It is desirable that this radiation impedance be equal to the characteristic impedance of the coaxial line.

If the dimensions deviate from the dimensions shown in equation (1), resonance will not occur, and therefore the microwave will not be radiated, but will be reflected at the end of the radiation plate 11 and returned to the coaxial line side. . Therefore, by selecting the dimension W in FIG. 3 to a dimension that does not resonate, the radiation will not be radiated in the vertical direction in the figure, but will be radiated only in the horizontal direction.

In this way, according to this embodiment, the microwave heating chamber 2
Since the power feeding device inside can be made extremely flat, space efficiency can be increased, and at the same time, cleaning efficiency can also be improved. Note that this example uses 915MIIz
It is not limited to belt high frequency heating equipment, but is 2.45GH
Needless to say, the present invention can also be applied to a Z-band high-frequency heating device.

Furthermore, this embodiment has the following advantages.

In FIG. 2, it has already been mentioned that the radiating frequency is determined by equation (1), but the frequency range where it is easy to radiate, that is, the bandwidth BW is expressed as BW=128f0'·9 (2). However, the unit of BW is MH2, fo is the operating frequency in G11z, and f- is the thickness of the dielectric plate in inches. Needless to say, it becomes difficult to radiate frequencies outside this band BW, and reflection increases.

As is clear from equation (1), the BW is proportional to the thickness, so the BW can be freely determined by changing the light.

This provides advantages as described below.

Generally, a magnetron oscillates unnecessary frequencies with relatively high levels at frequencies above and below the center frequency f. Figure 5 shows the situation. 20 is the oscillation spectrum of the magnetron. For example, in a 2.45GHz band magnetron, f is 2.45Gllz, and Δf is above and below it.
There are unnecessary frequencies from =zoo to 300MHz. As is well known, the frequency assigned to high frequency heating devices in this band is 2.45±0.05Gl-1z. Leakage of ±Δf to the outside is not allowed. therefore,
When designing this type of high-frequency heating device, various measures were required. However, in the case of this embodiment, since the BW mentioned above can be changed freely, for example, as shown in FIG.
If the thickness of the dielectric plate 10 is selected so as to obtain the reflection shown in the figure, it is possible to suppress the microwave radiation of the holes ±Δf. In other words, it is possible to easily provide a filter effect to the power supply device itself.

FIG. 6 shows another embodiment of the invention. Radiation plate (metal plate)
The second point is that the position where the inner conductor 9 is connected to 11 is closer to the corner, and the dimensions of the radiation plate 11 are different from those shown by equation (1) by ±Δ.
This is the difference from the figure. In this way, by judiciously choosing the dimension of Δ, the radiated electric field 21 and the orthogonal t field 22 are of equal magnitude and at the same time have a phase of 90'.
Since it can be shifted, circularly polarized waves can be generated. By generating circularly polarized waves, uneven heating of the heated food 5 can be reduced.

FIG. 7 shows yet another embodiment of the present invention. The explanation so far has been given for the case where a coaxial m-path is used as described in FIG. 1, but as shown in FIG. 7, the coupling conductor 24 provided in the waveguide is A similar effect can be obtained by connecting to.

At first glance, this embodiment is similar to the rotating antenna disclosed in Japanese Patent Publication No. 62-59436, but the radiation plate (metal plate)
The structure and radiation principle of No. 11 are completely different.

FIG. 8 shows yet another embodiment of the present invention. The magnetron antenna 26 and the radiation plate (gold YAFi) 11 are directly connected, and the cost can be reduced by eliminating the coaxial line and waveguide. Note that 27.27A is a screw for fixing the magnetron 3 to the wall surface of the heating chamber.

Effects of the Invention As described above, the present invention not only improves the space efficiency of the heating chamber and makes it easier to clean, but also provides a filter effect that removes unnecessary frequency components generated by the magnetron. Since circularly polarized waves can be easily generated, it is possible to provide a high-frequency heating device with reduced heating unevenness.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of one embodiment of the present invention, and FIG. Fig. 3 is an enlarged view of the main part of Fig. 1, Fig. 4 is an explanatory diagram of the operation of the present invention, Fig. 5 is an explanatory diagram of the filter effect of the present invention, and Figs. 6, 7, and 8 are diagrams of the present invention. It is a figure showing other examples of. 9... Penetrating conductor, 10... Dielectric plate, 11
...Metal plate (radiation plate).

Claims (1)

[Claims] 1. A dielectric plate having approximately the same shape as the metal plate is sandwiched between a substantially square metal plate whose sides are approximately half the wavelength of the operating frequency and the heating chamber wall surface, and the heating chamber wall surface is A high-frequency heating device characterized in that one end of a penetrating conductor and the metal plate are electrically connected. 2. The high-frequency heating device according to claim 1, wherein the through conductor is an inner conductor of a coaxial line for guiding microwaves generated by a magnetron to the heating chamber. 3. The high frequency heating device according to claim 1, wherein the through conductor is disposed within a waveguide for guiding microwaves generated by a magnetron to the heating chamber. 4. The high-frequency heating device according to claim 1, wherein the through conductor is an antenna of the magnetron.