JPS6243315B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to a high frequency heating device.

A magnetron is currently used as a high frequency supply means in this type of device. In addition, a waveguide is used as a means for transmitting the microwaves emitted from the magnetron to the heating chamber from the viewpoint of matching with the output impedance of the magnetron.

However, when such a waveguide is used, a problem arises in that the device becomes large. Therefore, a method has been proposed in which microwaves emitted from a high frequency supply means are transmitted through a coaxial cable and the microwaves are supplied into the heating chamber by radiation from an antenna. In such a configuration, the coaxial cable is flexible and has a smaller volume than the waveguide, so the device can be made smaller.

However, the antennas that have been proposed in the past with such a configuration have used simple coupling methods such as electric field coupling in which the inner conductor of the coaxial cable is extended into the heating chamber, or magnetic field coupling in which the inner conductor of the coaxial cable is formed into a loop. In such an antenna, matching can be achieved when the impedance inside the heating chamber is constant, but when the impedance changes, a problem arises in that matching cannot be achieved.

The present invention has been made in view of the above points, and will be described below based on the drawings.

FIG. 1 shows an embodiment of the present invention, in which 1 is a heating chamber;
2 is an antenna arranged in the heating chamber; 3 is a coaxial cable connected to the antenna as a microwave transmission means; 4 is a high frequency supply means for supplying microwaves to the antenna 2 via the cable; The means consist of a magnetron or a solid state oscillator.

The antenna 2 has an inner conductor 5 as shown in FIG.
In a coaxial line consisting of an outer conductor 6 and an outer conductor 6, the outer conductor 6
A slit 7 is provided in the outer conductor 6, and one end of each of the metal pieces 8, 8, . . . is electrically connected to the outer peripheral surface of the outer conductor 6. The antenna 2 and the coaxial cable 3 can be connected by electrically connecting the inner conductor 5 of the antenna 2 to the core wire of the coaxial cable 3 and the outer conductor 6 to the outer diameter wire of the coaxial cable 3, respectively. In addition, such an antenna 2 is constructed by simply pulling the coaxial cable 3 into the heating chamber 1, partially removing the outer diameter wire (forming a slit), and then using a metal wire with one end electrically connected to the outer diameter wire that was not removed. You can just attach one piece.

Further, the other end of the antenna 2 is supported by a jig 9 made of an insulating material and attached to the inner wall of the heating chamber 1.

FIG. 3 shows the electromagnetic field at the antenna 2 when microwaves are transmitted in the coaxial cable 3 in TEM mode. In the figure, electric lines of force and magnetic lines of force are shown by solid lines and broken lines, respectively. Further, in the figure, 1a is the top surface of the heating chamber, and 1b is one side wall of the heating chamber located parallel to the antenna 2.

4A and 4B show cross sections taken along the line AA in FIG. 3. As is clear from the figure, the electromagnetic field in this portion is in the well-known TEM mode, similar to that in the coaxial cable 3. In other words, the electric lines of force exist radially from the inner conductor 5 to the outer conductor 6, and the magnetic lines of force exist radially from the inner conductor 5 to the outer conductor 6.
They exist in concentric circles around the center. Energy therefore exists within the outer conductor 6.

FIG. 4B shows a sectional perspective view taken along the line BB in FIG. 3.
When the inner conductor 5 is exposed (slit 7 part)
In this case, the electromagnetic field in such a part is caused by the lines of electric force in the inner conductor 5.
This results in a parallel two-line mode that exists perpendicularly to the top surface 1a and one side wall 1b, respectively. Therefore, the plane where the lines of electric force intersect at right angles (hereinafter referred to as image line 10)
Energy exists within the two wires between the inner conductor 5 and the inner conductor 5.

However, since the impedance of the antenna 2 is discontinuous, a disturbance occurs in the electromagnetic field generated between the inner conductor 5 and the image line 10, and this electromagnetic field is generated in the metal piece 8 attached to the outer conductor 6. Combines with electromagnetic fields. As a result, the electromagnetic field in the metal piece 8 becomes a radiation mode, and microwave energy is oscillated from the antenna 2 into the heating chamber 1. Further, at this time, the directional direction of the radiated microwaves coincides with the extending direction of the metal pieces 8, 8, . . . .

According to the inventor's experiments, it was confirmed that the impedance matching between the heating chamber 1 and the antenna 2 changes depending on the length L of the metal pieces 8, 8, . . . .

For example, the dimensions of the heating chamber 1 are width l ₁ = 375 mm, depth l ₂ = 414 mm, and height l ₃ = 248 mm, and the antenna 2 has the diameter of the inner conductor 5 as shown in FIG.
_The metal _{pieces 8 ,} 8...The length L is 15 mm, 30 mm, 60 mm, and the load (water) in heating chamber 1 is 500 c.c., 1, 2.
We investigated impedance matching as follows. The wavelength of the microwave at this time was approximately 2450MHz.

FIG. 5 is a Smith Chart showing the results of such an experiment, in which the ○ mark indicates when the load is 500 c.c., the △ mark indicates when the load is 1, and the × mark indicates when the load is 2.

As is clear from Fig. 5, the length of the metal piece 8 is L.
= 30mm Even if the load fluctuates, the standing wave ratio V・S=
It was found that matching could be achieved within a range of 4 or less. Matching within such a standing wave ratio V·S=4 is a practical matching, and is a matching comparable to that in the case of power feeding using a conventional waveguide.

Incidentally, the length L of the metal piece 8 = 30 mm corresponds to 1/4 wavelength of the oscillated microwave, and according to the inventor's experiments, the impedance matching is the best when the length is set to 1/4 wavelength of the oscillation wavelength. Good results have been obtained.

Further, the slit width B ₁ and the slit interval B ₂ of the antenna may be determined by impedance matching with the heating chamber 1, and are not limited to the dimensions of the above embodiment, and the microwave radiation from the metal piece 8 can be uniformly determined. To achieve this, the slit width B ₁ and the spacing B ₂ may be varied in one antenna.

Further, in this embodiment, the antenna 2 is arranged close to the corner formed by the top surface 1a and one side wall 1b of the heating chamber 1, but the antenna 2 is not limited to this and the arrangement position is not limited. However, when placed in a corner like this, the effective volume of the heating chamber can be increased.
Furthermore, it is also possible to concentrate the microwave energy approximately at the center of the heating chamber due to the corner reflector effect.

Furthermore, although the extending direction of all the metal pieces 8 in this embodiment is toward the approximate center of the bottom surface of the heating chamber, the antenna 2
Since the microwaves emitted from the metal pieces 8 have directivity in the extending direction of the metal pieces 8, the extending direction of each metal piece 8 is made different to emit microwaves with various directivities. It is also possible to make the electric field distribution uniform.

Further, the inner conductor 5 and outer conductor 6 of the coaxial line are usually fixed relative to each other by a low dielectric material, for example, plastic, but the outer conductor 6 may be rotatably mounted around the inner conductor 5. With this configuration, it is possible to change the extending direction of the metal pieces 8, 8... relative to the heating chamber 1 depending on the type of cooking, so the electric field suitable for the type of cooking can be changed. It is very convenient to make.

As is clear from the above description, the high-frequency heating device of the present invention can achieve good impedance matching even with load fluctuations, and since it is antenna-fed, the device itself can be made smaller.

[Brief explanation of the drawing]

1 to 5 show embodiments of the present invention, FIG. 1 is a perspective perspective view, FIGS. 2 and 3 are enlarged perspective views of main parts, and FIG. 4A is A-A in FIG. 3. 4B is a cross-sectional perspective view taken along the line B--B in FIG. 3, and FIG. 5 is a Smith Chart. DESCRIPTION OF SYMBOLS 1... Heating chamber, 2... Antenna, 4... High frequency supply means, 5... Inner conductor, 6... Outer conductor, 7...
Slit, 8...metal piece.

Claims (1)

[Claims] 1 a heating chamber, an antenna disposed within the heating chamber,
In a high-frequency heating device comprising a high-frequency supply means for supplying microwaves into the heating chamber through the antenna, the antenna consists of a coaxial line, a slit is formed in the outer conductor, and a slit is formed on the outer circumferential surface of the outer conductor. A high-frequency heating device characterized in that one end of a metal piece is electrically connected.