JPS6345794A - Radio frequency heater - Google Patents

Abstract

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

Description

[Detailed description of the invention] Industrial applications The present invention relates to an improvement in the door structure of a high-frequency heating device.

Conventional technology Grooves with different characteristic impedances are provided in the depth direction on the periphery of the door of a high-frequency heating device, and by making the characteristic impedance of the grooves discontinuous in the depth direction, the effective depth is reduced to a quarter of the wavelength used. A proposal was made in JP-A-60-25 that even if the value is smaller than 1, the impedance at the entrance of the groove is maximized, and leakage radio waves can be reduced in the same way as the Chimique groove.
It is in Publication No. 190. In this conventional example, the shape is quite complicated, such as providing grooves with different widths in the depth direction of the groove and deforming the shape of the peripheral wall of the groove in the depth direction. Furthermore, it is necessary to consider reflection prevention at discontinuous portions of characteristic impedance.

In addition, as shown in FIG. 7, a cavity resonator 12 for preventing radio wave leakage is bent on the outer periphery of the l-'a 5 to have a cross-section shaped like an opening. A structure having an inlet 25 in which the end cut of the surface 11 and the other wall surface (first wall surface 8) of the cavity resonator 12 are opposed to each other is shown in Japanese Utility Model Application Publication No. 61-795. In this conventional example, there is no description that the peripheral wall of the cavity resonator 12 is divided into a plurality of conductor pieces.Therefore, inside the cavity resonator 12, the traveling direction shown in FIG. Since the generated higher-order mode radio waves enter, the cavity resonator 12 is removed from the resonant state, and the radio wave leakage prevention effect is reduced. Assume that the rising surface 23 and the projecting surface 11 of the cavity resonator 12 shown in FIG. 7 are divided into conductor pieces having a width smaller than 1/2 of the wavelength used in the longitudinal direction (X direction). In this case, the cavity resonator 12 can be regarded as a plurality of parallel resonant elements each having an equivalent capacitance tc and an equivalent inductance L arranged in the longitudinal direction (X direction) of the door 5. In each parallel resonant element, as shown in equation (2) below,
The larger the ratio AM/G between the distance QM between the entrance 25 of the cavity resonator 12 and the center of area 0 of the cavity cross section and the entrance dimension G, the larger the equivalent capacitance C becomes. In the cavity resonator 12 of FIG.
When /G=1.0, the equivalent capacitance C becomes smaller than when Qx/G≧1.5 of the present invention, which will be described later. For that reason, see (3) below.
) According to the equation, the equivalent inductance L must be increased to resonate with the frequency of the leaked radio waves. Therefore, as is clear from equation (1) below, the cavity resonator 1
Because it is necessary to increase the cross section AB of 2.

The cavity resonator 12 of the conventional example is large, and the door is made smaller.
It is not suitable for cost reduction.

In addition, FIG. 7 shows each radical in the drawings of the specification of Utility Model Publication No. 61-795 in the same proportion, and the names and numbers of the constituent elements are the same as those in the present invention. It's Nishide.

Problems to be Solved by the Invention It is necessary to provide a groove with a complicated shape in the depth direction of the groove, and it takes time and effort to prevent reflections at discontinuous parts of the characteristic impedance, and it is not suitable for downsizing the door. It is a point.

Means for solving the problem: A cavity resonator with a square-shaped cross section for preventing leakage radio waves was installed around the door, and a part of the wall of this cavity resonator was formed with a large number of U-shaped conductor pieces. In addition, an inlet is provided in the cavity resonator to introduce leakage radio waves, and the ratio 12M/G between the distance QM between this inlet and the center of area of the cross section of the cavity and the inlet dimension G is set to be 1.5 or more, and a capacitance is provided at the inlet. It is equipped with an adjustment element.

Operation With the above configuration, radio waves that are about to leak through the U-shaped conductor piece are introduced into the cavity resonator with the square-shaped cross section as TEM waves. This cavity resonator forms a parallel resonant element consisting of an equivalent inductance L proportional to the cross-sectional area of the cavity and an equivalent capacitance C based on the disturbed electric field near the entrance of the cavity as a cylindrical coil with approximately one turn. . If the entrance of the cavity is made smaller and a capacitive element is provided, C becomes larger, and L can be made smaller by that amount. That is, the radio wave sealing effect is maximized when each side of the 0-shaped cross section, which can reduce the cross-sectional area of the cavity, is smaller than one-fourth of the wavelength used. .

Embodiment The structure and operation of a high-frequency heating device according to an embodiment of the present invention will be explained with reference to the drawings.

In Figures 1 and 2, 1 is a heating chamber, and 2 is a heating chamber 1.
3 is the outer box. Reference numeral 4 designates a group of small holes provided in the center of the door 5 as wide as possible to allow viewing into the heating chamber 1.

Reference numeral 6 denotes a step surrounding this small hole group 4;
is a translucent door cover 15 fixed to the inner surface of the small hole group 4.
This prevents the end portion of the door from being peeled off during cleaning, etc., and improves the flatness of the sealing surface 7 that makes plane contact with the flange 2 when the door 5 is closed.

Reference numeral 8 denotes a first wall surface bent from the end of the sealing surface 7 at a substantially right angle to the flange 2. Reference numeral 9 denotes a second wall surface extending substantially parallel to the flange 2 from the end of the first wall surface 8. 10 is a large number of U-shaped conductor pieces welded to the second wall surface 9. This U-shaped conductor piece 10 has a mounting surface 19 which is welded to the second wall surface 9, a standing edge surface 23 that faces substantially parallel to the first wall surface 8, and an end cut that is attached to the first wall surface. 8 and an overhanging surface 11 facing each other. Width D of each U-shaped conductor piece 10 in the longitudinal direction around the door 5 (X direction)
is smaller than half of the wavelength used.

The opening-shaped cross section surrounded by the first wall surface 8 and the U-shaped conductor piece 10 forms a cavity resonator 12 having a narrow entrance 25 . A projection piece 14 protruding from the opaque dielectric cover 13 that blocks the entrance 25 of the cavity resonator 12 is attached to a hole 18 provided on the rising surface 23 of the U-shaped conductor piece 10. . A protruding piece 17 protruding from a dielectric door frame 24 for holding a translucent door outer cover 16 covering the front surface of the door 5 is hooked onto the outermost peripheral edge 20 of the second wall surface 9. It has become. Further, a capacitance adjustment element 26 protrudes from the back surface of the dielectric cover 13 toward the inside of the cavity resonator 12.

Next, the effects of the embodiment configured as described above will be explained. The radio wave sealing effect will be qualitatively explained using a simple equivalent circuit as shown in FIG. 4 with respect to incident radio waves directed toward the planar contact portion between the flange 2 surrounding the entrance portion of the heating chamber 1 and the sealing surface 7. 21 is a capacitor corresponding to the planar contact portion between the flange 2 and the sealing surface 7, and acts as a type of bypass capacitor. The planar contact portion is considered to be a parallel plate line, and the capacity of this line is proportional to the gap between the parallel plates, so the capacitance 21 becomes larger as the gap of the planar contact portion is smaller.

The width D (third width) of the U-shaped conductor piece 10 increases the radio wave sealing effect.
(X direction in the figure) is made smaller than half of the wavelength used, so the cavity resonator 12 with a cross section formed by the first wall surface 8 and each U-shaped conductor piece 10 is The traveling direction of the radio waves that have entered the interior is limited to the yz plane in FIG. If there is no overhanging surface 11, the electric field will be distributed as shown in Figure 6, and the length of the parallel plate line will cause parallel resonance at about one-fourth of the free space wavelength λ, and the impedance will be maximum, preventing radio wave leakage. However, in the case of a 2450 MHz high frequency heating device, the Q is 30.61 m, and if it is attempted to be mounted on a door, it will be thick, which is disadvantageous both in terms of design and cost.

When the cavity resonator 12 is formed by providing the projecting surface 11 and having a mouth-shaped cross section and a narrow entrance 25 as in the present invention, an electric field distribution as shown in FIG. 5 is obtained. In this case, most of the electric lines of force are concentrated between the vicinity of the end cut of the overhanging surface 11 and the first wall surface 8. The cavity resonator 12 is represented in FIG. 4 as a parallel resonant element consisting of an equivalent inductance L and an equivalent capacitance C, where the equivalent inductance L is 0.

It works as a one-turn cylindrical coil with approximately the same cross section as the cavity resonator 12, and means the isometric inductance as a constant of the coil, and the value per unit length in the cylinder axis direction (X direction) is It becomes as shown in equation (1).

Further, the equivalent capacitance C is based on the disturbed electric field near the entrance 25 of the cavity resonator 12, and is approximately given by equation (2).

1=. AB... (1) where AB: area μ of the mouth-shaped cross section of the cavity resonator 12. : Permeability e of the medium in the cavity resonator 12: 2.72 ΩM: Distance ε between the entrance 25 of the cavity resonator 12 and the center of area 0 of the cavity cross section. : To the permittivity of the medium in the cavity resonator 12 : A correction term related to the shape of the vicinity of the inlet 25 G : Gap of the inlet 25 (inlet dimension) The resonant frequency f0 of the cavity resonator 12 can be expressed by equation (3). .

(From the η equation, it can be seen that the smaller the gap G of the inlet 25 or the larger lM/G, the larger the equivalent capacitance C becomes.If the resonant frequency f is constant, the larger the equivalent capacitance C is, the more the equivalent inductance L It can be seen from equation (3) that the zero equivalent inductance L can be reduced by reducing the area AB of the mouth-shaped cross section of the cavity resonator 12 from equation (1), that is, the cavity In order to make the resonator 12 smaller, the gap between the inlet 25 is narrowed to increase the equivalent capacitance C, and the cavity area AB is correspondingly reduced to reduce the equivalent inductance L.

Constant resonance frequency f, C heating frequency of high frequency heating device)
Parallel resonance may be caused in the inlet 25 to maximize the impedance at the inlet 25 to prevent radio wave leakage.

In a high-frequency heating device with a heating frequency of 2450 MHz and a high-frequency output of 500 W, the gap between the flange 2 and the sealing surface 7 is 2 m! +, the difference in level between the protruding surface 11 and the sealing surface 7 is 3
m, the width of the U-shaped conductor piece is 15 mm, and the water is 275 m.
I heated the Q and measured the amount of radio wave leakage at a distance of 5afi from around the door 5. As a result, when G=5mm, A
B = 15, 4 x 15, 9 m, fix/
When G = 2.1, the amount of radio wave leakage is less than O,1 mw/d, and if G = 8 mm, in order to suppress the amount of radio wave leakage to the same small amount as above, AB = 20.4 x 18.4 +
a, QM/G=1.75, so the area of the mouth-shaped cross section also increases. Through such experiments, the gap G of the inlet 25 was narrowed to about 4 to 8 LII11, and fiM/G was reduced to 1.
By setting the number to 5 or more, the cavity resonator 12 with a cross-sectional shape
Dimension A and dimension B of are each a quarter of the wavelength λ used.
It has become clear that it can be made considerably smaller than 30.6-.

Furthermore, since the capacitance adjustment element 26 protrudes from the back surface of the dielectric cover 13 toward the inside of the cavity resonator 12,
Since the dielectric is inserted into the inlet 25 where the lines of electric force are concentrated, the equivalent capacitance C increases, and the equivalent inductance L can be reduced accordingly. That is, by providing the capacitance adjustment element 26, the cavity resonator 12 can be further downsized.

Effects of the Invention As described above, according to the present invention, the entrance of a cavity resonator having a square cross section surrounded by a large number of U-shaped conductor pieces and the first wall surface is connected to the projecting surface of the U-shaped conductor piece. The end cut and the first wall face each other to make it narrow, and 2M/G≧1.5.
Since we selected the dimensions as shown below and made the capacitance adjustment element protrude from the back side of the dielectric cover toward the inside of the cavity resonator, we determined that the cross-sectional dimensions A and B of the cavity resonator correspond to the wavelength λ used. It can be made smaller than one quarter, the shape of the resonant cavity is simple, the door can be made smaller and thinner, a compact high frequency heating device can be provided, and the economic ripple effect is also large.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a main part showing only the metal part of a door 5 of a high-frequency heating device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of a main part showing a radio wave seal around the door, and FIG. Figure 4 is a simplified equivalent circuit diagram of the radio wave seal part of the door 5, Figure 5 is an electric field distribution diagram of the radio wave seal part, and Figure 6 is the electric field of the parallel plate line with the same termination short-circuited. A distribution diagram, FIG. 7 is a configuration explanatory diagram showing a conventional radio wave seal structure, and FIG. 8 is a diagram showing the direction of the electric field.

Claims (1)

[Claims] A sealing surface (7) located at the periphery of the door (5) that opens and closes the opening of the heating chamber (1) and in planar contact with the flange (2) of the opening of the heating chamber (1) when the door (5) is closed; Sealing side (7
), a first wall surface (8) substantially perpendicular to the flange (2), a second wall surface (9) substantially perpendicular to the first wall surface (8), and a second wall surface (9) substantially perpendicular to the first wall surface (8); (9), a rising surface (23) substantially perpendicular to the rising surface (23), and a projecting surface (11) substantially perpendicular to the high-frequency heating device, the end surface of which is in contact with the second wall surface (9). Many U-shaped conductor pieces (1
0), and the first wall surface (8) and the U-shaped conductor piece (10)
A cavity resonator (12) having a mouth-shaped cross section and an inlet (25) is formed by and, and the distance (l_M) between the inlet (25) and the center of area (O) of the cavity cross section, and the inlet. The ratio l_M/G with the dimension (G) is 1.5 or more, and the capacitance adjustment element (26 )
A high-frequency heating device characterized by protruding.