JP2543085B2 - High frequency heating equipment - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to improving a radio wave distribution of a high frequency heating device using a rotating radio wave radiator.

2. Description of the Related Art Conventionally, various methods have been proposed and carried out in an attempt to make a radio wave distribution in a heating chamber uniform by rotating a radio wave radiator.
It was found that the method that has a stable effect even in a shaped heating chamber is to rotate a radio wave radiator with a strong directivity of radio wave radiation, such as a waveguide, at the bottom of the heating chamber. ing. Various rotary antennas and the like in which a rod-shaped antenna is bent into an L-shape are proposed and actually implemented, but the biggest problem in these cases is that directivity of radio wave radiation can be provided. It was very difficult, so even if the antenna was rotated, its rotation effect was small and a good radio wave distribution could not be obtained.

Problems to be Solved by the Invention On the other hand, in the case of a waveguide as shown in FIGS. 5 and 6, since the radiation directivity is very strong, the rotation effect is very good, but the directivity is Because it is strong, another problem occurs.

That is, since the directivity is strong and the electric field at the radiation port 17 of the waveguide 9 is very strong, the shape of the waveguide is as shown in FIG. 5 in order to prevent it from directly hitting food. In addition, it is necessary to provide the radiation direction as far as possible from the center of rotation and near the end of the heating chamber 2. However, when this is done, there is a problem that the electric wave distribution at the end of the heating chamber is improved, but the heating near the center is weakened.

The present invention solves the above-mentioned conventional drawbacks, and an object of the present invention is to provide a radio wave feeding structure having a good radio wave heating distribution in which heating unevenness in the central portion is solved.

Means for Solving Problems The present invention is configured to supply radio waves from below the heating chamber,
The substantially sector-shaped antenna for magnetic field coupling is rotated, and the sector-shaped circular arc portion is opposed to the rotating shaft portion from the first radiation port,
Of the second parallel plate line having a slightly larger impedance than the low impedance part that forms the waveguide section at a position closer to the rotation axis than the distance between the radiation axis and the rotation axis. is there.

Operation The high-frequency heating device of the present invention rotates a magnetic-field-coupling substantially fan-shaped antenna, provides two radiation ports having different impedances in a direction opposite to the rotation axis, and sets the radiation port near the rotation axis to have a low impedance. By making the impedance a little higher than the part, facilitating the leakage of radio waves and relaxing the directivity of the antenna, forming the second parallel flat plate line near the rotation axis, and radiating the electric field in the vertical direction from the food bottom surface. This has the effect of strengthening the heating near the center of the food and making the entire radio wave distribution uniform.

Examples Hereinafter, a high frequency heating apparatus according to an example of the present invention will be described with reference to the drawings.

FIG. 1 is an external view of a high-frequency heating apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line AA ′ in FIG. 1, and FIG. 3 is an external perspective view showing the rotating radio wave radiator. FIG. 4 is a sectional view showing the rotating radio wave radiator.

In FIG. 1, reference numeral 1 designates a main body having a heating chamber 2 therein,
Reference numeral 3 is a door that allows the front opening of the heating chamber to rotate.
In FIG. 2, reference numeral 4 denotes a high-frequency oscillator, and the radio wave oscillated by the high-frequency oscillator is transmitted by the waveguide 5, and the rotary radio wave radiator 6 causes the rotary chamber 6 to rotate through the coupling hole 18 provided at the center of the bottom of the heating chamber. Is emitted to. The rotating radio wave radiator 6 is composed of a coaxial portion 7 and a radiation portion 8 as shown in the external perspective view of FIG. 3 and the sectional view of FIG. 4, and the radio wave propagates between the radiation portion 8 and the heating chamber 2. . The radiating part 8 is an arc-shaped part 17 and a low impedance part in which the length of the line is about a quarter of the high frequency electromagnetic wave wavelength.
It consists of 9a, 9b and 10. The coaxial portion 7 is the drive shaft 1 of the motor 11.
Connected to two. Reference numeral 13 is a rail made of a low-loss dielectric material, and the low impedance portions 9a and 9b of the rotating radio wave radiator 6 slide on the rails to rotate, so that the distance between the bottom wall of the heating chamber and the rotary radio wave radiator 6 is increased. Is kept constant. Reference numeral 14 designates a heating chamber and a radio wave supplying section 15 and a heating section in which the rotating radio wave radiator 6 is located.
It is a food placing table for partitioning into 16 and placing food on it. It is made of heat-resistant dielectric material.

The characteristic impedance of the conventional heating chamber was about 300Ω, and the low impedance part was about 20Ω. At this time, if the length of the line of the low impedance part is ¼ wavelength, the impedance of the end face on the center side of the low impedance part is about 1Ω, and the impedance of the arc-shaped part 17 is about 80Ω, so the reflection coefficient is about It was 0.98, and about 98% of the radio wave was reflected and propagated in the direction of the arc-shaped portion 17. Since the characteristic impedance is determined by the distances h ₁ , h ₂ and h ₃ between the radio wave radiator 6 and the heating chamber wall 2, the characteristic impedance of the portion 10 relatively close to the center of the low impedance portion is changed to another low impedance. By setting the value different from that of the parts 9a and 9b, the reflection coefficient of the radio wave can be changed and the amount of leaked radio wave can be adjusted.

For example, the distance between the low impedance part 10 and the heating chamber wall 2
By making h ₂ larger by 2 mm than the conventional height h ₁ , the characteristic impedance becomes about 30Ω and the reflection coefficient becomes
With 0.93, it is possible to increase the leaked radio waves by 5% compared to the conventional 98%.

Therefore, the arcuate portion 17 which is the main radio wave emission port rotates, and the electric field direction near the emission port is vertical and excites in the heating chamber. The whole food is heated by the radio wave from the arc-shaped part 17 which is the radiation port, and the low impedance part which is the second radiation port
A vertical electric field of 10 heats the food near the center of the bottom. Since the electric field direction of the radio wave radiated from the arc-shaped portion 17 is vertical, a vertical electric field is generated in the heating chamber 2, and the uniformity is stable for so-called flat foods having many horizontal components.
Moreover, since the central portion of the food bottom is heated by the leaked radio waves from the relatively low impedance portion, it is possible to prevent the central portion of the food bottom from being extremely heated by the strong electric wave such as when simply opening the opening.

Effects of the Invention As described above, according to the present invention, the following effects can be obtained.

(1) The intensity of radio waves to the center of the bottom of the food is moderately suppressed, the heating state of the center of the bottom with respect to the heating state of the whole food is moderate, and the local heating of the bottom of the food is prevented.
It is possible to provide a high-frequency heating device having excellent heating distribution performance.

(2) Since the heating chamber is excited by an electric field in the vertical direction, a flat food product can have stable uniformity even if the shape changes.

(3) The degree of heating of the bottom of the food can be easily adjusted by the length and height of the line of the second radiation port.

[Brief description of drawings]

FIG. 1 is an external view of a high-frequency heating apparatus according to an embodiment of the present invention, FIG. 2 is a sectional view taken along line AA ′ in FIG. 1, and FIG. 3 is an external perspective view showing the rotating radio wave radiator. 4 is a sectional view showing the rotating radio wave radiator, FIG. 5 is a sectional view of a product showing a conventional example, and FIG. 6 is an external perspective view showing the shape of the rotating radio wave radiator. 2 ... Heating chamber, 6 ... Rotating radio wave radiator, 9a, 9b, 10 ... Low impedance part.

Claims (4)

(57) [Claims] 1. A high frequency oscillator for oscillating high frequency electromagnetic waves in a main body, a heating chamber for heating an object to be heated, and a waveguide for guiding the high frequency electromagnetic waves of the high frequency oscillator to the heating chamber.
A first antenna penetrating a coupling hole between the waveguide and the heating chamber; and a second antenna fixed to the heating chamber side tip of the first antenna substantially perpendicular to the first antenna. One of the second antennas has a substantially fan shape and forms a first radiation port of a parallel plate line.
High-frequency heating device configured to form a second radiating port of a parallel plate line in the direction opposite to the antenna. 2. The low impedance portion of the second antenna is formed by bending the second antenna, the first radiation port and the second radiation port.
Except for the radiation port, the distance between the second antenna and the wall of the heating chamber is half or less, and the length of the line of the low impedance portion is about ¼ of the wavelength of the high frequency electromagnetic wave. The high frequency heating apparatus according to claim 1. 3. The second radiation port has a line length of about 1/4 of the wavelength of the high-frequency electromagnetic wave, and a distance from the heating chamber wall to a value slightly larger than that of the low impedance portion to increase the characteristic impedance. The high frequency heating apparatus according to claim 1, which is configured. 4. The high frequency heating apparatus according to claim 1, wherein the distance between the second radiation port and the first antenna is smaller than the distance between the first radiation port and the first antenna. apparatus.