JP2736793B2 - High frequency heating equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-frequency heating apparatus for irradiating microwaves to food stored in a heating chamber to heat the food, and more particularly to a power supply for irradiating the heating chamber with microwaves generated by a magnetron. It concerns the device.

2. Description of the Related Art A conventional power supply device using an oscillation source of 915 MHz, which is one of the frequency bands assigned to a high-frequency heating device, is disclosed in
As described in JP-A-63-40035, the feeding antenna protrudes into the heating chamber.

Problems to be Solved by the Invention In this case, the space efficiency for storing the food to be heated is reduced by an amount corresponding to the protrusion of the antenna, and when cleaning the heating chamber, there is an inconvenience that the antenna is obstructed and is difficult to clean. .

Means for Solving the Problems It is an object of the present invention to provide a high-frequency heating device that improves space efficiency and is easy to clean by improving a power supply device of the high-frequency heating device. The above object is achieved by applying an irradiation element of a planar antenna.

The radiating element for a planar antenna uses radiation from the edge of a planar conductor placed parallel to the ground plane (in this case the wall of the heating chamber). Therefore, there is no protrusion, and space efficiency and cleanability can be improved.

Embodiment Hereinafter, the configuration and operation of an embodiment of the present invention will be described with reference to FIGS. In FIG. 1, magnetron 3
Is guided by a coaxial line composed of an outer conductor 8 and an inner conductor 9 and radiated into the heating chamber 2 by a dielectric plate 10 and a metal plate (hereinafter referred to as a radiation plate) 11 to be heated. The food 5 is heated. In addition,
1 is a wall of the heating chamber, 4 is a rotary mounting table for uniformly heating the food 5 to be heated, 6 is a motor mechanism, and 7 is a drive shaft for transmitting the rotation.

FIG. 2 and FIG. 3 are enlarged views of the main part of FIG.
In FIG. 2, the dielectric plate 10 comprises a heating chamber wall 1 and a radiation plate 11.
It is attached in a form sandwiched between. A through hole 23 having a diameter equal to the inner diameter of the outer conductor 8 is formed in the wall surface 1 of the heating chamber, and a through conductor (hereinafter referred to as an inner conductor) 9 penetrates the center of the through hole 23 and also penetrates through the dielectric 10. Fixing screw 12 on radiation plate 11
It is fixed at. The radiation plate 11 is rectangular as shown in FIG. Accordingly, the dielectric plate has a rectangular shape corresponding to this. Since the radiating plate 11 is a conductor, a radiating plate (metal plate) may be formed and attached as shown in the figure, or may be a conductor film previously deposited on the dielectric plate 10. The position of the fixing screw with respect to the radiation plate (metal plate) 11 is 3rd
As shown, it is located at the center of the width W and at a position 1 from the end.

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

FIG. 4 conceptually shows the structure of FIG.
Accordingly, the outer conductor 8 and the wall surface 1 of the heating chamber in FIG. The fixing screw 12 is omitted. The microwave generated by the magnetron 3 is transmitted through a coaxial line composed of the inner conductor 9 and the ground conductor 28. At this time, electric fields indicated by 13 and 13A are generated in the coaxial line. When this electric field further progresses, the electric field is divided into left and right sides in the figure, and becomes electric fields 14 and 14A. At this time, radiation plate (metal plate) 1
If the length of 1 (dimension L in FIG. 3) is about a half wavelength of the used frequency, resonance occurs, and the electric field is radiated to the outside as indicated by 15 and 15A, and then proceeds downward in the figure as in 16 and 17. Go.
The length of L is said to emit when it is about half a wavelength. It is. Where λ ₀ is the wavelength of the operating frequency and ε _r is the dielectric plate
It has a relative dielectric constant of 10. The distance l from the end of the radiation plate (metal plate) 11 is a factor that determines the radiation impedance when the radiation plate (metal plate) 11 is viewed from the coaxial line. The smaller l is, the larger the radiation impedance is. Conversely, it decreases (minimum at l = L / Z). This radiation impedance is desirably equal to the characteristic impedance of the coaxial line. If the dimension L deviates from the dimension shown by the equation (1), no resonance occurs, and therefore, the microwave is not radiated and is 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 be a dimension that does not resonate, radiation is not emitted in the vertical direction in FIG. 3, but is emitted only in the horizontal direction.

As described above, according to the present embodiment, the power supply device for supplying the microwave into the heating chamber 2 can be extremely flattened, so that the space efficiency can be improved and the cleaning property can be improved. It is needless to say that the present embodiment is not limited to the 915 MHz band high frequency heating device, but can be applied to the 2.45 GHz band high frequency heating device.

Further, this embodiment has the following advantages. In Figure 2, the frequency of radiation is the already mentioned be determined by (1), the radiation susceptible frequency range, i.e., the bandwidth BW is represented by ^{_{BW = 128 0 2 · t (}} 2). Here, the unit of BW is MHz, ₀ is the frequency used, the unit is GHz, t is the thickness of the dielectric plate, and the unit is inch. It goes without saying that it is difficult to radiate a frequency that deviates from the band BW and the reflection increases. (1)
As is apparent from the equation, since BW is proportional to the thickness t, tW
BW can be freely determined by changing.

 This has the following advantages.

In general, the magnetron oscillates unnecessary frequencies having relatively large levels above and below the center frequency ₀ . FIG. 5 shows this state. Reference numeral 20 denotes a magnetron oscillation spectrum. For example, in a magnetron in the 2.45 GHz band, ₀ is 2.45 GHz, and unnecessary frequencies above and below Δ = 200 to 300 MHz exist. As is well known, the frequency assigned to the high-frequency heating device in this band is 2.45 ± 0.05 GH
Since it is z, leakage to the outside of ₀ ± Δ is not allowed. Therefore, when designing this kind of high-frequency heating device, various measures were required. However, in the case of the present embodiment, since the above-mentioned BW can be freely changed, the dielectric plate 10 can be changed so as to obtain reflection as shown in FIG. 19, for example.
If the thickness is selected, microwave radiation of ₀ ± Δ can be suppressed. That is, it is possible to easily provide the power supply device itself with a filter effect.

FIG. 6 shows another embodiment of the present invention. The position where the inner conductor 9 is connected to the radiating plate (metal plate) 11 is closer to the corner, and the size of the radiating plate 11 is different from that shown by the equation (1) by ± Δ. The point is second
This is the difference from the figure. In this way, by properly choosing the dimension of Δ, the radiated electric field 21 and the electric field 22 orthogonal thereto are equal in magnitude and at the same time, the phase can be shifted by 90 °, so that a circularly polarized wave is generated. be able to. Due to the generation of circularly polarized waves, uneven heating of the food 5 to be heated can be reduced.

FIG. 7 shows still another embodiment of the present invention. In the above description, the case where a coaxial line is used as described in FIG. 1 has been described. However, the coupling conductor 24 provided in the waveguide is connected to the radiation plate (metal plate) 11 as shown in FIG. By doing so, a similar effect can be obtained.

Although this embodiment is apparently similar to the rotary antenna disclosed in Japanese Patent Publication No. 62-59436, the structure of the radiation plate (metal plate) 11 and the radiation principle are completely different.

FIG. 8 shows still another embodiment of the present invention. Since the magnetron antenna 26 and the radiation plate (metal plate) 11 are directly connected to each other, the cost can be reduced by the amount of covering the coaxial line or the waveguide. 27 and 27A are screws for fixing the magnetron 3 to the wall of the heating chamber.

Effects of the Invention As described above, according to the present invention, the space efficiency of the heating chamber is improved, and not only the cleaning effect is improved, but also a filter effect of removing unnecessary frequency components generated by the magnetron is obtained. Since a circularly polarized wave can be easily generated, it is possible to provide a high-frequency heating device with reduced heating unevenness.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of one embodiment of the present invention, FIGS. 2 and 3 are enlarged views of main parts of FIG. 1, FIG. 4 is an explanatory view of the operation of the present invention, and FIG. FIGS. 6, 7, and 8 are diagrams illustrating another embodiment of the present invention. 9 ... through conductor, 10 ... dielectric plate, 11 ... metal plate (radiation plate).

Claims (4)

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