JPS61121287A - High frequency heater - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Industrial Field of Application The Kihatsu EJ4 relates to a high-frequency heating device for high-frequency heating of objects to be heated, such as food, using radio waves.

Conventional Technology The frequency bands specifically approved for use in high-frequency heating devices are limited to certain specific bands, such as the 2450 MHz band or the 915 MHz band, although this varies somewhat depending on the country. In this band, if safety is guaranteed, it will not be subject to Regulation 1b11 of the Radio Law. However, high-volume oscillators generally emit harmonic components, and in the case of a magnetron that oscillates at a fundamental frequency (hereinafter referred to as fO) of 2450MH2, 49oOMH2, 7350MH2, 9800MH2
It has a relatively large power component such as ゜12250MH2. (Hereinafter, this component will be expressed as 210.310.4/o, 5
Since these harmonic components are subject to strict regulations under the Radio Law, it becomes difficult to seal the heating chamber opening/closing door of a high-frequency heating device. For this reason, various efforts have been made to attenuate the harmonic components of the high frequency itself that enters the heating chamber.

As shown in FIG. 5a, a conventional high-frequency heating device of this kind has a band pass filter configured by protruding bodies 2a to 2c of different lengths inside a waveguide 1. Noise frequencies including harmonics other than IO are prevented from entering the heating chamber 3. (For example, Jikoko Sho 51-145
(No. 14 Publication) Furthermore, as shown in figure b', the conductor plates 4a to 4C having widths in the axial direction of the waveguide are spaced at intervals of yλ9/2 when the wavelength in the waveguide of fO is λ1. Due to the arrangement, a three-dimensional resonant circuit is formed by the spacing between each conductive plate and the transmission of frequencies other than fo is blocked. (For example, Japanese Patent Publication No. 59-16714) Problems to be Solved by the Invention However, in the configuration in which the four-piece beam protrudes into the waveguide as described above, the frequency that can be blocked is determined by the length of the protrusion, and the frequency band is is very narrow. In order to widen this band, it is possible to increase the number of conductor rings, but this is difficult to implement for each harmonic.

In addition, in a configuration that forms a three-dimensional resonant circuit that resonates with f, the harmonic components are reflected to the magnetron side, and even if only fO is ideally transmitted to the heating chamber, the harmonic components disappear inside the magnetron. Never. Therefore, there is a risk that the magnetron will malfunction due to the reflected harmonics.

The present invention solves such conventional problems, and uses a simple configuration to attenuate and eliminate each harmonic component other than the fundamental wave, thereby preventing radio wave leakage due to the harmonics of the device. A space (sub-waveguide) for blocking fO is provided in a part of the waveguide interposed in the chamber, and a radio wave absorber is provided in this space (sub-waveguide).

Function: The high-frequency heating device of the present invention allows radio waves to
By providing a radio wave absorber in a waveguide that has a cutoff wavelength for the propagation mode of By using
(The frequency at which the absorber obtains the maximum amount of radio wave absorption is called the resonant frequency.) It is capable of converting harmonic components into thermal energy and attenuating them.

EXAMPLE Hereinafter, a high frequency heating device according to an example of the present invention will be explained with reference to the drawings.

In Figure 1, 5 is a magnetron and the oscillated high 8
Wave electromagnetic waves (hereinafter referred to as microwaves) propagate within the main wave tube from the magnetron antenna 7 inserted into the main 4-wave tube 6 in a propagation mode (TE 10 mode in this case),
The light enters the heating chamber 9 through the opening 8 provided at the terminal end.

Reference numeral 10 denotes a door provided at the front of the heating chamber 9, which is opened and closed when food is brought in and taken out. Now, when considering the propagation state of microwaves in the main wave tube, the tube wavelength (2g) is first expressed by the formula λ λ: free space wavelength'' = ζ stone - 7 Ac: I, q Yuga. In the TE10 mode, the cutoff wavelength (λC) is the wide side (a
) is twice as much. Therefore, the free space wavelength of fO (λ
0) and the wide side (a) of the main wave tube is 2・a≧λ0
In the case λg becomes a real number and the microwave propagates in the main wave tube without attenuation, λf becomes an imaginary number and rapidly attenuates and no longer propagates when 2·a<λ0.

Therefore, the sub-waveguide 11 has a C dimension of 2·C<λ0, and a radio wave absorber 12 is provided inside it. This will be explained in more detail with reference to FIG. 2, which is a cross-sectional view of the product shown in FIG. The microwave excited in the main wave tube 7 by the magnetron antenna 6 propagates in the tube axis (X-X') direction because the three dimensions are set in the relationship 2a) λ0 described above. X
The microwaves propagating in the X' direction are reflected by the waveguide short-circuit plane (Y-Y' plane) and synthesized in the X' force direction. The antenna (color and distance (d) to the short-circuit surface are parameters when performing impedance matching between the magnetron and the waveguide.Currently, the training waveguide 11 and the radio wave absorber 12 are provided on the short-circuit surface. The cutoff wavelength of the waveguide 11 is λ0(f.

= 2450 MH2 (approximately 12.2 cm ), it is demonstrated that there is almost no change in the state of impedance from the magnetron to the main waveguide 7 with respect to fO compared to when the short-circuit surface is a plane.

Therefore, the radio wave absorber 12 absorbs the extremely large amount of energy 10 and does not generate heat or burn out.

Furthermore, for harmonic components other than f, the propagation mode in the main waveguide is different (for example, 2/o and TE20°3
10, TE30, etc.) Therefore, microwaves freely propagate in the training waveguide, and are replaced by thermal energy and attenuated by the radio wave absorber 12. In order to make it easier for harmonic components to propagate to the sub-waveguide and be attenuated by the absorber, the length of the sub-waveguide should be increased.)
The impedance of the sub-waveguide with respect to harmonics can be matched with that of the magnetron by changing the thickness (1) of the radio wave absorber and its position.

Next, an embodiment of the pond according to the present invention will be explained using FIG. In FIG. 3, the difference from the above embodiment lies in the structure in which a plurality of sub waveguides and radio wave absorbers are provided. According to this structure, among the harmonic components, an even multiple of fO (2fO14
fO) whose propagation modes are TE20. TE40
Therefore, two or four waves stand on the wide side (,) of the main waveguide.Therefore, the sub waveguide 11a at the center of the tube axis always also has a wave node g (weak electric field point), and the radio wave absorber 12aK Although it is difficult to absorb and has little damping effect, the second
, third training waveguide 11b, llc and radio wave absorber 12b
Since the point 112c is located near the wave abdomen (point of strong electric field), the attenuation effect can be increased.

Furthermore, radio wave absorbers with different characteristics are provided in each sub waveguide. Alternatively, the attenuation effect can be increased by separately providing a plurality of types of radio wave absorbers in one training waveguide.

Next, another embodiment of the present invention will be described using FIG. 4. The difference in FIG. 4 from the previous embodiment is that the training waveguide 11 and the radio wave absorber 12 are mounted on the upper surface of the main waveguide and are cylindrical in shape. The fundamental mode of the circular waveguide is TE11, and the cutoff wavelength (λC)
and the circular diameter (g) (3,41・9VC! If you set the dimensions, it becomes a sub-waveguide/.

will no longer propagate.

According to this configuration, since it is cylindrical, a waveguide can be easily created using an aperture or the like. Furthermore, radio wave absorbers with different characteristics can be easily arranged radially, and a wide range of harmonic components can be absorbed and attenuated with a simple configuration.

The same effect can be obtained even if the sub-waveguide is provided on the lower surface, side surface, or load short-circuit surface of the main waveguide.

Note that the radio wave absorber absorbs harmonic components and generates heat, so if composite ferrite or the like is used, silicone rubber, unsaturated plastic IJ 1 Stell, etc. with high heat and humidity resistance may be used as the base material. Furthermore, if the training waveguide and the radio wave absorber are cooled with a cooling means (for example, forced air cooling) that prevents the magnetron from generating heat, the heat generation of the radio wave absorber can be further suppressed. According to the high frequency heating device, the following effects can be obtained.

1) Since a radio wave absorber is provided in the waveguide, harmonic components over a wide range of unnecessary frequencies are converted into natural energy and disappear, so there is no reflection to the magnetron, and stable performance can be obtained.

2) Since the training waveguide has a cutoff wavelength for the fundamental wave, there is no insertion loss or change in impedance in the fundamental wave, and it can be easily applied to existing waveguides.

3) Since there is no burnout and it is possible to appropriately select the radio wave absorber to be used, it is possible to attenuate any harmonic component.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a high-frequency heating device according to a first embodiment of the present invention. Figure 2 shows the high-frequency heating device according to the first embodiment of the invention.
The figure is an enlarged cross-sectional view of the main part of the high-frequency heating device in the second embodiment of the present invention, FIG. 4 is a perspective view of the main part of the high-frequency heating device in the third embodiment of the invention, and FIGS. FIG. 5(b) is a cross-sectional view of a conventional high-frequency heating device. 5... Magnetron, 7... Main wave tube, 9... Heating chamber, 1 word, lla, llb,
Seal 1 c -- Sub-waveguide, 12.12a, f2b, 12
cm radio wave absorber. Name of agent: Patent attorney Toshio Nakao and 1 other person
3 Figure 7...15 Toonl Silkworm Figure 4 Figure 5

Claims (5)

[Claims] (1) A heating chamber that stores an object to be heated and a first waveguide that couples a microwave oscillator, the first waveguide wall having a cutoff frequency higher than the oscillation fundamental frequency of the microwave oscillator. A high-frequency heating device comprising: a second waveguide having a second waveguide, and a radio wave absorber filled in the second waveguide. (2) Two or more second waveguides on the wall of the first waveguide,
Alternatively, the high-frequency heating device according to claim 1 is configured to be installed on two or more different wall surfaces. (3) The high-frequency heating device according to claim 1, wherein the second waveguide is formed integrally with the wall surface of the first waveguide so as to protrude from the wall surface of the first waveguide. (4) The high-frequency heating device according to claim 1, wherein the radio wave absorber is made of a composite ferrite material having a heat resistance temperature of 200° C. or more and having a base material such as silicone rubber or unsaturated polyester. (5) The high-frequency heating device according to claim 1, which is configured to forcibly cool the second waveguide and the radio wave absorber.