JPS6331916B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency heating device with an improved radio wave leakage prevention mechanism.

A microwave oven, which is a typical example of a conventional high-frequency heating device, uses a contact method using a conductive gasket and a method using a radio wave absorbing material to prevent radio wave leakage from the gap created between the heating chamber and the door. , a chiyoke method using resonance, etc. have been proposed and put into practical use.

One of the difficulties in configuring this radio wave leakage prevention mechanism
There are countermeasures against harmonics.

Although the above-mentioned contact method has sufficient performance in principle against this harmonic, it requires manufacturing precision to maintain contact precision. Furthermore, this contact method has the disadvantage that performance deteriorates significantly if fragments of the object to be heated adhere to it.

On the other hand, most radio wave absorbing materials exhibit sufficient performance within a predetermined band, and do not exhibit sufficient performance for both the fundamental wave and its harmonics.

In addition, since the Chi-Yoke method that utilizes resonance uses resonance, it necessarily requires structural dimensions that are related to the wavelength of the fundamental wave. The conventional Chi-Yoke system configuration will be described below. FIG. 1 shows a typical conventional radio wave leakage prevention mechanism using a chiyoke method. A is a configuration diagram and b is an equivalent circuit.

The conventional chi-yoke type radio wave leakage prevention mechanism has a chi-yoke cavity that starts from the entrance A of the radio wave passage 3 formed by the heating chamber opening flange 1 and the entrance/exit door 2 at a length B that is 1/4 of the fundamental wavelength of the leaked radio wave. The first disadvantage is that the Z-direction dimension must be at least 1/4 of the fundamental wavelength of the leaked radio wave, making it difficult to make it compact. In addition, the impedance Z _B when looking from the input end B of the Chi-Yoke cavity 5 to the Chi-Yoke cavity 5 side is ideally configured to be infinite for the fundamental wave, and therefore for the second harmonic. becomes zero. Furthermore, if the impedance when looking at the space from the terminal C of this radio wave leakage prevention mechanism is Z _L ,
The equivalent circuit of this radio wave leakage prevention mechanism is shown in figure b, and the impedance Z _A of the radio wave leakage prevention mechanism seen from terminal A-A' is Z _A (Z _L + Z _B ) + Jtanβl/1 + J (Z _L + Z _B )tanβl,
β=2π/λ _gi where λ _gi is given by the leakage radio wave wavelength and l is given by the radio wave path length. However, each impedance is normalized.

Since the oscillation frequency of a magnetron, which is a typical example of a high-frequency heating heat source, fluctuates within 2450±50MHz depending on the load, the radio wave path length l is equivalently given to the leakage radio wave fundamental wavelength λ _gi as l = λ _g1 /4± Δλ ₁ and for the second harmonic, l=λ _g2 /2±Δλ ₂ .

Therefore, for the fundamental wave, Z _B j∞, tanβl∞
Therefore, Z _A is 0, and for the second harmonic, Z _B is 0,
From tanβl0, it becomes Z _A Z _L.

For the fundamental wave, changes in Z _L , that is, fluctuations in the gap at the C end caused by the assembly of the heating chamber flange 1 and the door 2, can be fully absorbed, but for the second harmonic, the The second drawback is that it has little strength.

In view of these circumstances, the present invention introduces a parallel transmission line used for transmitting radio waves into a radio wave leakage prevention mechanism, and connects a T-branch line to a part of the transmission line to create a new and compact mechanism. The main object of the present invention is to provide a radio wave leakage prevention mechanism that includes a mechanism that has sufficient performance against harmonics to be comparable to the fundamental wave.

The present invention will be explained below with reference to the drawings.

FIG. 2 shows the radio wave leakage prevention mechanism of the present invention,
A is a configuration diagram, and b is its equivalent circuit.

The parts in the figure that are compared with FIG. 1 are indicated by the same numbers. A group of 6 transmission lines having a width W and arranged with a gap S between adjacent transmission lines facing the heating chamber opening flange 1 are formed. This transmission line 6 has a branch path 7 at a length l ₁ from the input end A of the radio wave path 3 at B, and its depth is approximately 1/4 of the leakage radio wave wavelength λ _g . The equivalent circuit of such a transmission line is expressed as shown in diagram b, as is well known in microwave engineering.

The big difference here from Figure 1 is that the width of the transmission line is restricted to W, so the radio wave path and branch path can be positioned as a transmission line, so inductive and capacitive parameters can be interposed at the branch point. It becomes possible to express an equivalent circuit. For calculating these parameter values, please refer to "waveguide Handbook" M.
It is explained in detail in IT Radiation Laboratory p.337. The impedance _ZA seen from point A toward the radio wave sealing device is related using each parameter of the equivalent circuit. Let the impedance _{Z A} obtained in this way be Z _A = R _{+ J}
Microwave power P _L leaking out of the main body from point C
The present inventors have experimentally confirmed that the relationship is expressed by the following equation.

P _L ∝R・Z _OV / (Z _OV +R) ² +X ²・P _io Using this relational expression supported by experiment,
As a result of simulation under certain P _io conditions, the smaller l ₁ is, the more microwave power leaks.
The result was that P _L was small. To demonstrate this l ₁ dimension
When we actually measured the attenuation characteristics of the radio wave seal device for 30 mm and 12 mm, we found that the amount of radio wave leakage was 1/2 to 1/3 lower when l ₁ = 12 mm than when l ₁ = 30 mm. It can be inferred from the above relational expression that the leakage amount can be reduced even if the _l1 dimension is small by designing the value of X to be large. The main structural dimensions at the time of actual measurement are as follows.

The gap between the heating chamber opening flange and the radio wave seal device is 1 mm and 4 mm, and the opposing dimension of the branch path is 8 mm.
Depth of branch path l ₂ = 32 mm, when l ₁ = 12 mm, l ₃ = 10 mm,
When l ₁ = 30 mm, l ₃ = 12 mm, transmission line width W = 10 mm,
Gap S=10mm.

Calculatedly, the smaller the _l1 dimension, the better the result, but in order to prevent the θ-direction transmission of radio waves incident at an angle θ to the Z direction of the radio wave sealing device, the _l1 dimension faces the heating chamber opening flange. Considerable dimensions should be provided for this purpose. Therefore, in the real configuration l ₁ =
12 mm is considered to be approximately the minimum dimension of l ₁ .
As a result, the conventionally well-known fact that the dimension from the entrance of the radio wave path to the chiyok cavity in the Chiyoke method used is 1/4 wavelength, but as shown in the present invention, it consists of a T branch formed through a gap S. By using a radio wave leakage prevention mechanism that periodically arranges transmission lines, the length up to the branch point can be reduced.
Since l ₁ can be made sufficiently smaller than 1/4 wavelength, it has been shown that the Z-direction radio wave leakage prevention mechanism can be configured more compactly than the conventional chi-yoke method.

This radio wave leakage prevention mechanism requires that the depth of the branch path be approximately 1/4 of the leakage radio wave wavelength.
The depth dimension of this branch path may be made to be effectively 1/4 wavelength with respect to harmonics.

FIG. 3 is a block diagram of a radio wave leakage prevention means of a high frequency heating device showing an embodiment of the present invention.

The branch paths 8a, 8b, 8c, 8d, and 8e are filled with a dielectric material 9 having a predetermined dielectric constant,
The depth of the branch path filled with this dielectric is configured to be 1/4 the wavelength of the fundamental wave of leakage radio waves, and the depth of the branch path without dielectric is 1/4 of the wavelength of the fundamental wave of the leakage radio wave.
It is configured so that the wavelength is the same.

FIG. 4 is a cross-sectional configuration diagram of a radio wave leakage prevention means showing another embodiment of the present invention.

This branch path 10a, 10 has the same depth.
For b, 10c, 10d, and 10e, the amount of dielectric material of the same material filled into the branch path is changed, and the depth of the branch path is equivalently set to 1/4 wavelength for the fundamental wave and harmonics, respectively. It was formed. In addition, in FIGS. 2 to 4, 12 is the terminal short-circuit surface of the branch path.

In the configuration shown in FIG. 3, the T-branch path length is determined based on the dielectric constant of the dielectric material, whereas
The configuration shown in Figure 4 is equivalent to the fundamental wave and harmonics by using a dielectric material with an appropriate dielectric constant and configuring the filling rate of the dielectric material in the branch path appropriately. It has a 1/4 wavelength and has the advantage of allowing a wide range of dielectric materials to be selected.

Although it is not necessary to completely fill the branch path for the fundamental wave with dielectric material, it is clear that complete filling is the most compact way to make the branch path more compact.

Further, although FIG. 4 shows a case in which the dielectric bodies are individualized, a structure in which a one-piece dielectric body whose thickness is periodically changed may be inserted into the branch path may also be used.

Further, this radio wave leakage prevention means may be arranged on the access door or on the heating chamber side.

As described above, the present invention provides a high-frequency heating device having a novel radio wave leakage prevention means in which transmission lines having a T-shaped cross section and having a branch channel whose terminal end is short-circuited are arranged periodically, in which a dielectric layer is filled into the branch channel. (1) Countermeasures against harmonics can be analytically designed.

(2) Countermeasures against fundamental waves and harmonics can be taken simply by changing the filling factor of the dielectric layer, making design easy and selecting dielectric materials easy.

(3) The radio wave leakage prevention means can be made more compact.

(4) The depth of the branch path is constant and manufacturing control is easy.

It has the following effects.

[Brief explanation of the drawing]

Fig. 1 shows a conventional radio wave leakage prevention mechanism of the Chiyoke type, where a is a block diagram and b is an equivalent circuit diagram. Fig. 2 is a radio wave leakage prevention mechanism of the present invention, where a is a block diagram and b is an equivalent circuit. 3 is a configuration diagram of a radio wave leakage prevention means of a high frequency heating device showing one embodiment of the present invention, and FIG. 4 is a sectional diagram of the radio wave leakage prevention means showing another embodiment of the invention. 1... Heating chamber flange, 2... Access door, 3...
...Radio wave path, 6...Transmission line, 7, 8a, 8b,
8c, 8d, 8e, 10a, 10b, 10c, 1
0d, 10e... Branch path, 9, 11... Dielectric material,
12... Short circuit surface.

Claims (1)

[Claims] 1. A heating chamber for accommodating an object to be heated, an access door for taking the object into and out of the heating chamber, and a radio wave leak prevention means provided in a radio wave passage formed by the heating chamber and the access door. The radio wave leakage prevention means has a periodic array configuration of a transmission line having a T-shaped cross section and having a branch path whose terminal end is short-circuited, and the branch path has a high-frequency heating layer having dielectric layers having mutually different filling rates. Device.