JPS628916B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high-frequency heating device, and particularly aims to effectively suppress leakage of radio waves from around the opening of a heating chamber.

The leakage radio waves in this type of equipment are usually 2450MHz
and an n-th harmonic (n is a positive integer) of the fundamental wave, which is unique to a high-frequency oscillator such as a magnetron that oscillates the fundamental wave.

The chiyoke groove designed to suppress the fundamental wave of the leakage radio waves exhibits good characteristics with respect to the fundamental wave, but does not exhibit favorable characteristics with respect to the harmonics. Therefore, it is conceivable to suppress radio wave leakage by providing separate chiyoke grooves for radio waves of various wavelengths included in the leaked radio waves, but in reality, forming many chiyoke grooves like this would result in a complicated and large structure. Therefore, in the past, harmonics with relatively low energy were suppressed using radio wave absorbing materials such as ferrite rubber.

However, in a structure in which the chiyoke groove suppresses fundamental waves and the radio wave absorbing material suppresses harmonics, for example, if the chiyoke groove is placed around the door, the area around the door will become considerably thicker, resulting in a larger shape. However, the radio wave absorbing material such as the ferrite rubber had a disadvantage in that the radio wave suppressing effect was several steps inferior to that of the chiyoke groove.

Therefore, it has been proposed to suppress the leakage radio waves using a dielectric resonator, which is well known in the field of microwave communication technology. A radio wave suppression structure including a dielectric resonator effectively suppresses leakage radio waves, and has the advantage that the structure can be made smaller. However, as shown in Figure 1, there is a relationship between the radio wave path width G and the resonant frequency f in the path in the dielectric resonator, such that as the path width G becomes smaller, the resonant frequency f changes rapidly. There is. Therefore, the path width G ₁ for the fundamental wave in the leakage radio wave is easy to adjust, but the path width G ₂ for the second harmonic f ₂ , for example, requires fine adjustment.

The present invention has been made in view of the above points, and uses a dielectric resonator for the fundamental wave in the leaked radio waves and a chiyoke groove for the harmonics, making the structure smaller than conventional ones and suppressing the radio waves. The aim is to provide a highly effective radio wave suppression structure. The present invention will be described in detail below based on one example.

2 and 3 show main parts of an embodiment of the present invention, 1 is a high-frequency heating device main body, 2 is a heating chamber disposed within the main body 1 and has an opening 3, and 4 is a heating chamber having an opening 3. A front plate 5 of the main body disposed around 4 is a door that is pivotally supported on one side (not shown) of the front plate 4 and opens and closes the opening 3 rotatably in the direction of the arrow in FIG. When the door 5 is closed, the front plate 4 4
It consists of a frame-shaped metal door frame 6 along the sides and a punching plate 7 that is fixed to the inner edge of the door frame 6 and allows the inside of the heating chamber 2 to be seen through.

The door frame 6 has a frame-shaped flat part 6a whose surface faces parallel to the front plate 4 when the door is closed and which runs along the four sides of the front plate 4, and the outer edge of the flat part 6a is perpendicular to the front plate 4 side ( The bent portion 6b is formed by bending the inner edge of the flat portion 6a in the Y direction in FIG. 2, and the inclined portion 6c has a stepped portion 6d in the middle thereof. Further, a circumferential groove 8 is formed around the door frame 64 from the upper flat part 6a, the bent part 6b, and the inclined part 6c. 9 is the inner edge of the inclined part 6
A frame-shaped metal chiyoke wall fixed to the surface of the stepped portion 6d around c4 and extending from the stepped portion 6d in the radio wave leakage direction (Z direction in FIG. 2) so that its surface faces parallel to the front plate 4. , 10 are fixed between the ends of the bent portion 6b and the inclined portion 6c, and their surfaces closely face the front plate 4 when the door is closed, and the 4 of the circumferential groove 8
It is a frame-shaped low dielectric cover that covers the sides. Note that the cover 10 is not shown in FIG.

11 is a TE mode dielectric resonator with a relative dielectric constant of 90, which is made mainly of barium titanate, for example;
The dielectric resonators 11 are arranged at regular intervals along the four sides of the wall 9.

FIG. 4 shows a resonance state in the TE018 mode of the TE mode dielectric resonator 11a having a height of 2A, a length of 2B, and a width of C, where 12 is an electric line of force and 13 is a magnetic line of force. As is clear from the figure, the electric lines of force 12 form a closed loop inside the dielectric resonator 11a,
Therefore, according to the image theory, even if the conductor plate 14a is inserted horizontally at a position at half the height as shown in FIG. 4, there is no change in the electric lines of force 12 and magnetic lines of force 13.

If the radio wave travels in the direction of the arrow in the figure and has a magnetic field in a direction that coincides with the direction of the magnetic lines of force of the resonator 11a, the radio wave will be resonantly coupled to the dielectric resonator 11a, and its progress Energy decays.

In the present invention, the wall 9 corresponds to the conductor plate 14a, and the dielectric resonator 11 is metallized on one side, and the metallized surface is fixed to the surface of the wall 9 by brazing.

Therefore, the dielectric resonator 11 in this embodiment
If the leakage radio wave (progressing in the Z direction in FIG. 2) has a magnetic field in the side direction of the circumferential groove, it will be resonantly coupled to the leakage radio wave, and the traveling energy of the leakage radio wave will be greatly attenuated. Furthermore, since the frequency of the radio waves to be resonated by the dielectric resonator 11 is 2450 MHz, its resonance dimension is in the direction of the side of the wall 9, that is, X in FIG.
The length a in the direction is 6.0 mm, and the length b in the Y direction in the same figure is
7.5 mm, and the length C in the Z direction in the figure is 11.5 mm.

Further, when a radio wave having a wavelength λ passes through a parallel plate made of metal, the radio wave mode is established as a parallel plate mode when it travels through λ/4 or more within the parallel plate. When the parallel plate mode radio waves travel in the direction of the arrow in FIG. 4, the direction of the magnetic field coincides with the direction of the lines of magnetic force in the dielectric resonator 11a.

In this embodiment, the front plate 4 and the wall 9 correspond to the above-mentioned parallel flat plates, and the radio waves resonated in the dielectric resonator 11 of this embodiment have a frequency of 2450 MHz.
Since it is the fundamental wave of
A dielectric resonator is placed at a position 3 cm away from the radio wave leakage direction (Z direction in Fig. 2).

Therefore, in this embodiment, leakage radio waves (progressing in the Z direction in FIG. 2) having various standing wave modes are generated due to starvation fans (not shown), objects to be heated, etc. in the heating chamber 2.
becomes a parallel plate mode in the path consisting of the front plate 4 and the wall 9, and the direction of the magnetic field coincides with the direction of the magnetic lines of force of the dielectric resonator 11, so the radio waves are resonantly coupled to the dielectric resonator 11. As a result, its traveling energy is greatly attenuated.

Furthermore, as is clear from FIG. 1 above, the resonant frequency of the dielectric resonator also changes depending on the spacing between the parallel plates arranged therein. Therefore, in this embodiment as well, the distance G between the front plate 4 and the wall 9 when the door is closed was determined to be 11.5 mm so that the dielectric resonator 11 resonates at 2450 MHz. Furthermore, in this embodiment, the spacing between the dielectric resonators 11 is set to 30 mm, for example.

On the other hand, in FIGS. 2 and 3, the groove formed by the door frame 6 and the wall 9 and extending in the side direction of the door frame 6 is a wall groove 15.
is to suppress harmonics in the leaked radio waves.

The harmonics in the high-frequency heating device are determined by the magnetron used. The basic oscillation frequency of the magnetron used in this example is 2450MHz, and the harmonic with the largest energy among the harmonics is the second harmonic with a frequency of 4900MHz. It is. Therefore, the length of the harmonic chiyoke groove 15, that is, from the opening center of the chiyoke groove 15 consisting of the outer edge of the chiyoke wall 9 and the bent part 6b in FIG. The length l to the vicinity is given by l=λ/4n (λ...wavelength of fundamental wave, n...order of harmonic wave), and in this example, λ≒12.2cm, n=2
Therefore, l≒1.5cm.

Theoretically, the chiyoke is based on the wavelength of the radio waves to be resonated.
It is only necessary to have a length of 1/4 of the length, but in reality, in a chi-yoke designed based on this theory, resonance characteristics may be affected when the frequency of radio waves changes slightly, such as in high-frequency heating equipment. extremely low. Therefore, as is clear from FIG. 3, the current chiyokes are designed with a deformed cross section rather than a rectangular shape, thereby giving some width to the resonant frequency band.

Here, as an important element to widen the resonant frequency band, the thickness of the cheese yoke, that is, the length of the cheese yoke in the Y direction in Fig. 2, is also increased. It has been confirmed through experiments that it is the most effective.

Therefore, the chiyoke in this example is 4900MHz.
Its thickness (length in the Y direction in Figure 2) was approximately 15 mm in order to cause the front and rear radio waves to resonate.

In order to suppress leakage radio waves from around the heating chamber opening 3 in the high-frequency heating device having the above structure, the dielectric resonator 11 transmits the fundamental wave (2450MHz) to the chiyoke groove 1.
5 to effectively generate the second harmonic (4900MHz). Furthermore, although the length in the radio wave leakage direction (Z direction in Fig. 2) of the radio wave suppression structure of this embodiment is slightly longer than that of the conventional structure consisting of a chiyoke groove and a radio wave absorbing material, its thickness In other words, the length in the Y direction in FIG. 2 is smaller than that of the conventional one. To explain in concrete numerical terms, when a radio wave suppression structure is arranged around a door, the thickness around the conventional door is approximately 33 mm, but in this embodiment, the thickness of the low dielectric cover 10 and the dielectric resonator 11 are approximately 33 mm. , Chiyoke wall 9, Chiyoke groove 15
The thickness around the door including the door frame 6 is approximately 27 mm, which is approximately 3/4 of the conventional thickness. In this embodiment, the case of second-order harmonics has been explained, but it is clear that if the harmonics become third-order, fourth-order, etc., the thickness of the chiyoke groove becomes thinner, and the suppressing structure can also be made smaller.

FIG. 5 shows another embodiment of the present invention, and the difference from the embodiment shown in FIGS. A fixed surface 9a is provided, two perpendicular surfaces of the dielectric resonator 11b are metalized, and the metalized surface is brazed to the yoke wall 9 and the fixed surface 9a. In this figure, the same parts as in FIGS. 2 and 3 are given the same reference numerals.

As in the embodiment shown in FIG. 5, the structure in which the two orthogonal surfaces of the dielectric resonator 11b are metalized is also based on image theory. Specifically, in FIG. 4, the first conductor plate 14 is placed horizontally at a position half the height of the dielectric resonator 11a.
Even if the second conductive plate 14b is inserted perpendicularly to the half-length position, the lines of magnetic force 1
3 and electric lines of force 12. In the embodiment shown in FIG. corresponds to

Therefore, if the configuration is as shown in FIG. 5 above, FIG.
A dielectric resonator 11b half the size of the dielectric resonator 11 shown in FIG. 3 can provide the same radio wave suppression effect as the embodiment shown in FIGS. 2 and 3.

As is clear from the above explanation, the radio wave suppression structure of the high frequency heating device according to the present invention has a sufficient suppression effect not only on the fundamental wave in leaked radio waves but also on harmonics, and is smaller than the conventional structure. becomes. In the above embodiment, the radio wave suppression structure is placed on the door side, but the same effect can be obtained even if the structure is placed on the main body side.

[Brief explanation of the drawing]

Fig. 1 is a radio wave path width vs. resonance frequency characteristic curve of a dielectric resonator, Fig. 2 is an enlarged perspective view of the main part of this embodiment, Fig. 3 is an enlarged sectional view of the main part of Fig. 2, and Fig. 4 is a TE
FIG. 5 is a perspective view showing a resonance state of a mode dielectric resonator, and FIG. 5 is an enlarged sectional view of a main part of another embodiment of the present invention. 1... High frequency heating device, 11... TE mode dielectric resonator, 15... Chiyoke groove.

Claims (1)

[Claims] 1. A high frequency device characterized in that a plurality of TE mode dielectric resonators having a resonance dimension relationship with the leaked radio waves and a harmonic chiyoke groove that resonates with the harmonics of the radio waves are arranged in the radio wave leakage path around the opening of the heating chamber. heating device.