JPH0461473B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a high-frequency heating device for high-frequency heating of an object to be heated, such as food, using radio waves.

Prior Art The frequency bands that are 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. This band is not subject to regulations under the Radio Law as long as safety is guaranteed. However, high-frequency oscillators generally have high-frequency components, and in the case of a magnetron that oscillates at a fundamental frequency (hereinafter referred to as _f0 ) of 240MHz, it is 4900MHz, 7350MHz,
It has relatively large power components at 9800MHz, 12250MHz, etc. (Hereinafter, this component will be expressed as 2f ₀ , 3f ₀ , 4f ₀ , 5
(denoted as f ₀ ) These harmonic components are subject to strict regulations under the Radio Law, but meeting these regulations with a radio wave seal mechanism for the heating chamber opening/closing door of high-frequency heating equipment is difficult due to the complexity or large size of the mechanism. When considering the practicality of the device, it is difficult to improve the conventional radio wave seal mechanism. For this reason, various efforts have been made to attenuate the high frequency components of the high frequency waves themselves that enter the heating chamber.

As shown in FIG. 5a, a conventional high-frequency heating device of this kind has a heating chamber formed by protruding conductor rods 2a to 2c of different lengths into a waveguide 1 to form a band pass filter. 3, the incidence of noise frequencies including harmonics other than f ₀ is blocked.
(For example, Japanese Utility Model Publication No. 51-14514) Also, as shown in _FIG . By arranging the conductor plates at intervals of approximately λg/2, a three-dimensional resonant circuit is formed by the interval between each conductor plate, and transmission of frequencies other than f ₀ is blocked. (Japanese Patent Publication No. 59-16714) Problems to be Solved by the Invention However, in the configuration in which the conductor rod protrudes into the waveguide as described above, the frequency that can be blocked is determined by the protrusion length, and the frequency band is very narrow. In order to widen this band, it is possible to increase the number of conductor rods, but this is difficult to do for each harmonic.

In addition, in a configuration that forms a three-dimensional resonant circuit that resonates at f ₀ , harmonic components are reflected to the magnetron side, and even if only f ₀ is ideally transmitted into the heating chamber, the harmonic components disappear inside the magnetron. There's nothing to do. Therefore, there is a risk that the magnetron will malfunction due to the reflected harmonics.

The present invention solves such conventional problems, and aims to attenuate and annihilate each harmonic component other than the fundamental wave with a simple configuration to more completely prevent radio wave leakage from harmonics of the device. .

Means for Solving the Problems In order to solve the above problems, the high-frequency heating device of the present invention includes a high-frequency oscillator, a heating chamber for accommodating an object to be heated, and a radio wave generated by the high-frequency oscillator to the heating chamber. a transmitting waveguide, at least two types of radio wave absorbing materials provided in parallel to the waveguide H plane in the waveguide and having desired different attenuation characteristics for each harmonic of the high frequency oscillator; It includes a conductor plate that covers the radio wave absorbing material and has an opening that shields the fundamental wave of the oscillator and allows harmonic waves to pass through.

Effects According to the present invention, with the above-described configuration, by appropriately selecting the aperture diameter, the conductive plate acts as a blocking plate that blocks the fundamental wave of the high frequency oscillator, and only harmonic components are absorbed by the radio wave absorbing material. . In addition, by appropriately arranging radio wave absorbing materials with different absorption characteristics for frequencies in combination with the conductor plate openings,
Good absorption of harmonic components is achieved over a wide frequency band.

Embodiments Hereinafter, embodiments of the present invention will be described based on the accompanying drawings.

FIG. 1 is a block diagram of a high-frequency heating device showing one embodiment of the present invention, and FIG. 2 is a view taken in the direction of arrow A in FIG.

In FIGS. 1 and 2, 5 is a high frequency oscillator;
Reference numeral 6 designates a heating chamber that accommodates the object to be heated, 7 a heating chamber door, and 8 a waveguide that transmits radio waves generated by a high-frequency oscillator to the heating chamber. On the waveguide H surface 9, radio wave absorbing materials 10 and 11 having different absorption characteristics depending on the frequency are distributed and arranged, and a conductor plate 12 is attached to cover these radio wave absorbing materials. This conductor plate has a predetermined area other than the plate surface corresponding to 1/4 to 1/3 of the H-plane width centered at the center of the waveguide in the tube axis direction (indicated by l in Figure 2). Aperture 1 having an aperture diameter
3 are arranged.

In the above configuration, the radio wave absorbing material 10 has a maximum radio wave absorption amount of 5 to 7 GHz, and that of the radio wave absorbing material 11 is
Use a material that absorbs radio waves of 10 to 12 GHz. In addition, round holes with a diameter of 4 mm are arranged in a houndstooth pattern with an open area ratio of approximately 40%.

This hole blocks the fundamental wave (2450MHz) transmitted within the waveguide and allows each harmonic to leak.
Each leaked harmonic is absorbed or attenuated by each radio wave absorbing material, and the harmonic is not reflected back to the high frequency oscillator. Further, harmonic components attenuated by each absorbing material are transmitted to the heating chamber side. As a result, it is possible to provide a high-frequency heating device in which the amount of harmonic components leaking to the outside of the device is further reduced without changing the characteristics of the radio wave seal mechanism provided on the access door. Furthermore, since there is no opening in the center of the conductor plate, the radio wave absorbing material will not be burned out by the fundamental wave.

Next, another embodiment of the present invention will be described with reference to FIGS. 3 and 4. In FIG. 3, the difference from the above embodiment is that radio wave absorbers 10 and 11 have different absorption characteristics.
The structure is stacked as shown in the figure.

With this configuration, even when the waveguide is short, the waveguide can be provided without reducing the radio wave absorption characteristics.

FIG. 4 shows a configuration in which the diameters of the holes provided in the conductor plate 12 are different, and the diameter of the hole 14 near the center in the tube axis direction (indicated by l in the figure) is different from that in the other portions. The diameter of the aperture 15 is smaller than that of the aperture 15 on the surface, and a radio wave absorbing material that can obtain the maximum amount of radio wave absorption at a higher frequency is placed where the small aperture diameter exists. In other words, two types of radio wave absorbers are arranged in the sand beach on the H surface of the waveguide.

According to this configuration, since the opening diameter is small near the center of the tube axis, it is possible to avoid burning out the radio wave absorbing material due to the fundamental wave, and harmonics leaking from this small opening can be effectively absorbed into the radio wave. Absorbed by absorbent material.

That is, even with this configuration, a waveguide filter can be provided that has a short structural length in the tube axis direction and has good harmonic absorption characteristics.

Effects of the Invention As described above, the high frequency heating device of the present invention provides the following effects.

(1) Since a radio wave absorber that absorbs or attenuates high frequencies is provided, there are no harmonics reflected to the high frequency oscillator side, which has the effect of eliminating abnormal operation of the harmonic oscillator.

(2) By using two or more types of radio wave absorbing materials, the radio wave absorption band can be widened.

(3) Providing a radio wave absorbing material inside a waveguide that prevents the radio wave absorbing material from burning out due to the fundamental wave by carefully arranging holes on the conductor plate that allow harmonics to leak or by carefully adjusting the diameter of the holes. A practical configuration can be provided.

(4) Prevention of harmonic radio wave leakage is more completely achieved.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a high-frequency heating device showing one embodiment of the present invention, FIG. 2 is a view taken in the direction of arrow A in FIG. 1, and FIG. 3 is a diagram of a high-frequency heating device showing another embodiment of the present invention. FIG. 4 is a block diagram of main parts showing still another embodiment of the present invention, and FIG. 5 is a block diagram of a conventional high-frequency heating device. 5... High frequency oscillator, 6... Heating chamber, 8... Waveguide, 9... Waveguide H surface, 10, 11... Radio wave absorbing material, 12... Conductor plate, 13... Opening.

Claims (1)

[Scope of Claims] 1. A high-frequency oscillator, a heating chamber that accommodates an object to be heated, a waveguide that transmits radio waves generated by the high-frequency oscillator to the heating chamber, and a waveguide H within the waveguide.
at least two types of radio wave absorbing materials provided parallel to the surface and having desired different attenuation characteristics for each harmonic of the high frequency oscillator, and an opening that shields the fundamental wave of the high frequency oscillator and allows the harmonic to pass through. and a conductor plate covering the radio wave absorbing material. 2. The high-frequency heating device according to claim 1, wherein at least two types of radio wave absorbing materials are stacked. 3. The high-frequency heating device according to claim 1, wherein at least two types of radio wave absorbing materials are arranged in a distributed manner on the H surface of the waveguide.