JPS6224920B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to improving the uniform heating characteristics and high frequency output characteristics of a high frequency heating device constituting a coaxial waveguide using electric field coupling.

Conventionally, in high-frequency heating equipment, a high-frequency oscillator made of a magnetron is generally installed on the top of the heating chamber, and its antenna section is exposed directly into the heating chamber, but the size of the high-frequency oscillator, especially the high-frequency The disadvantage was that the dimensions were high.

In order to lower the height of this vessel, it is possible to introduce radio waves from the top of the heating chamber using a waveguide, but this has the drawback of making the design difficult in terms of uniform distribution and output. Ta. Therefore, as shown in FIG. 1, the high-frequency waves emitted from the magnetron 1 are guided through a waveguide 2, and are guided into the heating chamber 5 through a power supply opening 4 by a conductor 3 that constitutes a coaxial line fixed to the upper part of the waveguide. A coaxial power feeding method using so-called magnetic field coupling is considered, but in this case, the waveguide 2 and the conductor 3
A considerable amount of heat was generated at the point of contact with the wire, and the loss due to the heat generated here was close to 20 to 30 W, making efficient high-frequency electrical transmission quite difficult.

The present invention eliminates the above-mentioned drawbacks of the conventional technology with a simple configuration.
This will be explained with reference to the figures. Note that the same numbers are used for the same parts as in the conventional configuration described above, and the explanation thereof will be omitted. First, the internal conductor 6 constituting the coaxial line is supported by a support plate 7 made of resin, and the support plate 7 has a hook part 8 provided on one side connected to a hole provided in the top surface of the heating chamber 5. The other end is held by a clip 9 made of resin such as polypropylene and attached to the top of the heating chamber.

In the above configuration, in order to efficiently send the radio waves from the magnetron 1 to the heating chamber 5, as shown in _{FIG .}
~30 mm is suitable), it is sufficient to adjust the lengths of l _F and l ₂ . According to experiments, it becomes extremely difficult to achieve matching when the length of l ₂ exceeds approximately λ ₀ /4 with respect to the free space wavelength λ ₀ in the air of the radio wave used. Further, the length of l ₃ influences the radio frequency radiation characteristics, and even if the length is approximately λ ₀ /4 or more, the length of the metal conductor is only long, and the uniform heating characteristics will not be improved. Naturally, the length of l ₃ also affects the high frequency output, but if this is approximately λ ₀ /4 or less, matching can be easily achieved without any problem.

Fig. 3 is a Smith chart showing the load characteristics of the magnetron, 10 shows the movement of the operating point when the length of the metal conductor 6 protruding into the heating chamber 5 is changed, and 10a is l ₃ = 40 mm, 10b is l ₃ = 30 (≒λ ₀ /
4), 10c has l ₃ = 25mm, 10d has l ₃ = 22mm,
10e has l ₃ =18 mm. 11 shows the movement of the operating point when the length of the metal conductor 6 protruding into the waveguide 2 is changed, 11a is l ₂ = 40 mm, 11b is l ₂
= 30 (≒λ ₀ /4), 11c is l ₂ = 25mm, 11d
is l ₂ =22 mm, and 11e is l ₂ =18 mm. Note 10
The width of 11 and 11 occurs when the length of 1 _F shown in FIG. 2b is changed.

As is clear from the above, l ₂ and l ₃ are approximately λ
It is clear that matching cannot be achieved well when the ratio is _0/4 or more. According to experiments, l ₂ = 22-27mm, l ₃ =
Good results with good consistency have been obtained for dimensions of 18 to 25 mm. It was also found that by changing the dimensions of the internal conductor 6, the degree of heat generation of the conductor itself changes, and that there are dimensions that do not generate much heat, but even in that case, the length of l ₂ and the length of l ₃ are λ ₀ / It could not be found in cases of 4 or higher. Furthermore, for unnecessary radiation, l ₂ and l ₃ are approximately λ
At _{λ 0} /4 or more, it increases and it is very difficult to satisfy the standard, but at λ ₀ /2 or less, a dimension that satisfies the standard was found.

As described above, the high frequency output is efficiently extracted into the heating chamber, and the uniform heating characteristics are further improved.
The dimensions of _the conductor 6 _that minimize the heat generation _of I couldn't find the time.

At this time, the distance _l4 between the conductor 6 and the waveguide 2 needs to be at least 4 mm due to the problem of sparks.

As mentioned above, the lengths of l ₂ and l ₃ of the conductor 6 should be λ ₀ /4 or less, but if the lengths of l ₂ and l ₃ are not λ ₀ /8 or more, the matching will be extremely poor. It is true that it becomes difficult, but the lengths of l ₂ and l ₃ are λ
Even if it is less than _0/8 , matching can be achieved, although it is not so easy, by making the tip of the conductor 6 into a large spherical shape or into a T-shape.

Further, in the power supply opening 4, a strong electric field is generated from the end 4a toward the conductor 6. Furthermore, if a metal or dielectric material (resin, etc.) is disposed at or near the tip 12 of the conductor 6, a very strong electric field may be generated, causing sparks or melting of the resin. Therefore, the feed opening 4 and the tip 12 of the conductor 6
By arranging the support part 13 at a position a predetermined distance away from the support part 13, the problem described above can be solved by preventing the support part 13 from melting due to sparks.

As is clear from the above description, the present invention provides a conductor constituting a coaxial waveguide by electric field coupling between the waveguide and the heating chamber, and furthermore, the protrusion dimension of the conductor into the waveguide. l ₂ and protrusion dimensions into the heating chamber
By setting l ₃ to λ ₀ /4 or less, we can obtain an extremely good high-frequency heating device that can efficiently transmit radio waves into the heating chamber, minimize the heat generated by the conductor, and sufficiently suppress unnecessary radiation. I can do things. In addition, since the support part is configured to be spaced apart from the power supply opening and the tip of the conductor, a strong electric field can cause
There is no need to worry about the support part melting and deforming.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the configuration of a conventional coaxial power feeding system, and FIG.
FIG. 2b is a sectional view taken along line A-A in FIG. 2a,
FIG. 3 is a Smith Chart showing the load characteristics of the magnetron. 1... High frequency oscillator (magnetron), 2...
Waveguide, 4... Power supply opening, 5... Heating chamber, 6...
. . . conductor, 12 . . . tip end of the conductor, 13 . . . support portion.

Claims (1)

[Claims] 1. A high-frequency oscillator, a waveguide that sends radio waves generated from the high-frequency oscillator into a heating chamber, and a rod-shaped conductor that configures coaxial power feeding by electric field coupling provided at a power feeding opening between the waveguide and the heating chamber. The conductor is supported by a resin support plate, and the support part of the support plate is arranged at a predetermined distance from the power supply opening and the tip of the conductor, and the entire length of the conductor is A high-frequency heating device in which the diameter is λ ₀ /4 or more, the protrusion dimension into the waveguide is λ ₀ /4 or less, and the protrusion dimension into the heating chamber is λ ₀ /4 or less.