JPH07217835A - Electromagnetic wave heater - Google Patents

Abstract

PURPOSE:To provide an electromagnetic wave heater which can efficiently heat in a wide dielectric constant range with a simple structure. CONSTITUTION:A microwave is guided from a magnetron of a microwave generator 1 to a waveguide 2. The waveguide 2 is disposed vertically, and a microwave output is guided from below to above. A resinous wedge-shaped vessel 3 is placed downward on the way of the waveguide 2, and an object 4 to be heated is introduced into the vessel 3. As the vessel, a conical shape, a square conical shape and a semispherical shape, etc., in a downward protruding shape can be used, in addition to the wedge shape. A cover of an electromagnetic wave shielding structure for passing gas but shielding the electromagnetic wave such as a punching metal 5 in this case is provided at an end of the waveguide. It can efficiently heat substance having wide dielectric constant such as substance containing water, etc.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heating device for heating an object using electromagnetic waves including microwaves. It is particularly suitable for incineration or drying of raw materials and industrial waste such as plastics.

[0002]

2. Description of the Related Art A heating device using microwaves is already widely used in industrial and domestic microwave ovens. When a substance having a large dielectric loss, such as water, is exposed to microwaves, heat is generated in proportion to the magnitude of the dielectric loss, thereby heating the substance. Many heating devices (for example, reference: “Nikkei New Material March 30, 1992)
As shown in FIG. 6, a turntable 8 is placed in the applicator 7, and an object to be heated is placed thereon and rotated. The device is devised so that the microwave can be emitted into the applicator 7 from the ceiling surface or the lateral wall surface to uniformly heat the entire object. However, in this case, since the microwave is irregularly reflected on the metal wall surface in the applicator 7 to irradiate the object, the microwave is not sufficiently absorbed by the object and is largely reflected. At present, only about half of the microwave output contributes to heating, depending on the shape and size of the object.

FIG. 7 shows a device in which the entire applicator 7 is designed like a resonator in order to efficiently heat the device, and is devised so that the maximum microwave output can be introduced into the applicator 7 ( Reference: Japanese Patent Publication No. 56-54548). In this case, the permittivity changes greatly depending on the lid of the object and the temperature change. Therefore, the impedance adjuster 9 shown in FIG. 7 always adjusts the resonance state to the optimum state to follow the change of the dielectric constant of the object.

[0004]

In such a resonance type system, a power monitor is introduced in the middle of a waveguide for feeding a microwave to monitor an incident wave and a reflected wave, and the reflected wave is always minimized. You have to tune the adjusting rod like so. For this reason, it is necessary to add a power monitor and a movable part for adjustment and a feedback system for controlling the movable part, which has a drawback that the system becomes expensive.

An object of the present invention is to provide an electromagnetic wave heating device having a simple structure and capable of efficiently heating in a wide dielectric constant range.

[0006]

An electromagnetic wave heating device of the present invention has an electromagnetic wave generator, a waveguide for guiding electromagnetic waves, and a container for containing an object to be heated, said container being non-magnetic and having a low dielectric loss. , And has a convex shape, and is located in the waveguide, and the container is arranged so that the direction of the convex of the container faces the direction of the electromagnetic wave.

Alternatively, the shape of the container is conical, pyramidal, wedge-shaped, or bowl-shaped.

Alternatively, the waveguide is tapered.

Alternatively, the waveguide or the container is provided with a lid having an opening and shielding electromagnetic waves.

Alternatively, a plurality of convex-shaped containers are installed in the waveguide.

Alternatively, it has an electromagnetic wave generator, a waveguide for guiding the electromagnetic wave, a container for containing an object to be heated, and a lid for the waveguide, and the lid of the waveguide has a long side of the wavelength of the electromagnetic wave for heating. It is characterized in that rod-shaped ferrite is mounted parallel to the long side on the surface of the long side of the rectangular waveguide of one-half or less. Due to this ferrite, only that surface is an open wall.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, the present invention will be described with reference to the drawings. FIG. 1A is a configuration diagram of an electromagnetic wave heating apparatus showing an embodiment of the present invention. Microwaves are guided from the magnetron of the microwave generator 1 to the waveguide 2. The waveguide 2 is arranged vertically, and the microwave output is guided from the bottom to the top. A resinous wedge-shaped container 3 is placed downward in the middle of the waveguide 2,
The object to be heated 4 is placed therein. The lid of the device is attached to the end of the waveguide and has an electromagnetic shield structure with an opening so that gas can escape but microwave does not leak. Here, punching metal 5 with a small hole diameter is used. . FIG. 1 (b) is the same as the other one except that the structure of the cover shielding structure is changed. That is, the lid of the above-mentioned electromagnetic shielding structure is attached to the wedge-shaped container.

A feature of the present invention is that the heating container is made of a low dielectric loss material such as resin or glass and has a wedge shape. When water is put into the wedge-shaped container 3 as the heating object 4 having a large dielectric loss, the shape of the water becomes wedge-shaped. The wedge-shaped loss body substantially absorbs the microwave traveling from the tip end direction of the wedge. This is also clear from the fact that the electromagnetic wave absorber used in an anechoic chamber has a similar shape.

Further, another structural feature is that the wedge-shaped container 3 is placed in the middle of the waveguide 2. Specifically, the waveguide 2 is arranged vertically so that microwaves travel from bottom to top. Furthermore, when the tip of the wedge-shaped container 3 is directed downward, the heating object 4 inside does not spill, and the heating object 4 naturally becomes a wedge shape of the container, and the heating object 4 becomes a wedge shape, and the tip of the microwave-shaped object 3 is heated. The microwaves can be opposed to each other in the traveling direction, and the microwaves can be irradiated in parallel with the tip direction of the wedge. Therefore, electromagnetic waves are efficiently absorbed. Even if the wedge-shaped container is arranged downward in an applicator such as a conventional microwave oven, the components other than the microwave components incident from the direction of the angle of the wedge are not efficiently absorbed by the wedge-shaped container. In order to heat efficiently, a wedge shape must be in the middle of the waveguide 2.

Although the present invention has been described here by using the wedge-shaped container 3 for the sake of clarity, the same efficiency can be obtained in the case of each of the conical, pyramidal, and bowl-shaped containers, although the degree is different. Can be expected. That is, similar to the above, the cone, the pyramid, and the tip of the bowl-shaped container are arranged downward so as to face the microwave in the middle of the waveguide in which the microwave propagates from bottom to top, and the heating target is placed in the container. Efficient heating can be realized by putting and heating an object. As described above, it goes without saying that this is essentially different from the case where a cone, a pyramid, or a bowl-shaped container is placed in an applicator that is irradiated with electromagnetic waves from various directions, such as a conventional microwave oven.

In the description, the case where one wedge-shaped container is used is shown. However, when the waveguide and the container are enlarged, such as when heating with a large capacity, the following may be done. When the waveguide is enlarged, as shown in FIG. 2A, a well-designed tapered waveguide or the like is used to suppress reflection at the joint of the waveguides as much as possible. Then, the large wedge-shaped container 3 is placed at the tip of the taper. Alternatively, as shown in FIG. 2B, a plurality of wedge-shaped or other convex containers of the above-described shape may be arranged in the tapered waveguide.

In order to show the effect of the present invention, the calculation results of the electromagnetic wave absorption amount in the case of a wedge type and a quadrangular pyramid (pyramid type) having a height of 15 cm are shown in FIGS. 3 (a) and 3 (b). ε ′
And ε ″ are the real part and the imaginary part of the dielectric constant. In the figure, the absorption amount of 10 dB reflects 1/10 of the irradiated microwave, that is, the remaining 90% is absorbed. 20
In the case of dB, it is shown that the absorption efficiency is 1/100, that is, 99%. It can be seen that the pyramid type has a larger absorption amount with the same permittivity than the wedge type, and the same absorption amount can warm an object in a wider permittivity range.

The structure of the lid is, as described above, an electromagnetic shielding structure that allows gas to pass but does not allow electromagnetic waves to pass.
I showed an example using punching metal, but in addition to this,
It is also possible to use a cut-off mode waveguide as shown in FIG. The structure of the lid of the present invention is, as shown in FIG. 4 (b), a lid having a rectangular waveguide whose long side is equal to or less than ½ of the wavelength of the electromagnetic wave to be heated. The surface is an open wall in which ferrite, which is a magnetic material, is formed into a rod shape and mounted parallel to the long side. This can significantly reduce the length of the waveguide. It is theoretically derived that when magnetic rods are arranged on the wall including the long side of the waveguide, the wall has a characteristic closer to an open wall as the magnetic permeability increases, and the rectangular waveguide is used. The long side of the cross section of the pipe is a
Letting b be the short side, the damping constant in the case of FIG. 4 (a) is π / a, whereas one side including the long side is an open wall as shown in FIG. 4 (b). The damping constant is {(π / a)
2+ (π / b) 2} ^1/2 , and the damping constant can be increased by the difference. The frequency of the heating device is 2.
If the frequency is 45 GHz, ferrite is suitable as the magnetic material, and the diameter of the ferrite rod is about 1 mm, so that it does not substantially hinder the exhaust.

As the lid of this electromagnetic shielding structure, the lengths of the waveguides in the cutoff mode are compared in FIGS. 4 (a) and 4 (b). In the case of a rectangular waveguide having a long side of 55 mm and a short side of 27.5 mm, the relationship between the length L and the shielding amount is as shown in FIG. In order to obtain a practically sufficient shield amount of 90 dB, the structure shown in FIG. 4 (a) for comparison requires a length of 20 cm, whereas FIG. 4 (b) of the present invention. With the structure shown in Fig. 10, 10 cm or less is sufficient, and
It can be shortened to 2 or less, and the device can be downsized.

[0020]

By using the electromagnetic wave heating device of the present invention, it is possible to efficiently heat an object to be heated having a wide dielectric constant range such as a substance containing water with a simple structure. It is suitable for heating or melting substances whose permittivity is likely to change due to the generation of gas or changes in state during heating. Further, the device can be downsized.

Further, it is suitable for incineration or drying of raw materials and industrial waste such as plastics. It is also suitable for melting a substance having a high melting point. In this case, the container may be made of a non-magnetic, low dielectric loss ceramic.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an electromagnetic wave heating apparatus showing an embodiment of the present invention.

FIG. 2 is a diagram showing another embodiment of the present invention.

FIG. 3A is a diagram showing a relationship between a dielectric constant of a heating target and a radio wave absorption efficiency in the case of a wedge-shaped container (height 10 cm);
(B) is a figure showing the same relationship in the case of a pyramid type container (height 10 cm).

FIG. 4 is a view for explaining a lid for the electromagnetic shield structure of the present invention. (A) is a diagram for comparison, (b)
FIG. 4 is a diagram for explaining the present invention.

FIG. 5 is a diagram for explaining the present invention and is a diagram showing a relationship between a shielding amount and a side length.

FIG. 6 is a diagram showing a structure of a conventional microwave oven.

FIG. 7 is a view showing a structure of a conventional resonance type applicator.

[Explanation of symbols]

 1 Electromagnetic Wave Generator 2 Waveguide 3 Wedge Type Container 4 Heating Object 5 Punching Metal 6 Tapered Waveguide 7 Applicator 8 Turntable 9 Impedance Adjuster

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI technical display area H05B 6/80 Z

Claims (7)

[Claims] 1. An electromagnetic wave generator, a waveguide for inducing an electromagnetic wave, and a container for containing an object to be heated, the container having a non-magnetic, low dielectric loss, and convex shape. An electromagnetic wave heating device, characterized in that it is positioned inside and the convex direction of the container is arranged to face the electromagnetic wave direction. 2. The electromagnetic wave heating device according to claim 1, wherein the container has a conical shape, a pyramidal shape, a wedge shape, or a bowl shape. 3. The electromagnetic wave heating device according to claim 1, wherein the waveguide is tapered. 4. The electromagnetic wave heating device according to claim 1, wherein the waveguide or the container has a lid which has an opening and shields electromagnetic waves. 5. The electromagnetic wave heating device according to claim 1, wherein a plurality of convex-shaped containers are installed in the waveguide. 6. An electromagnetic wave generator, a waveguide for inducing electromagnetic waves, a container for containing an object to be heated, and a lid for the waveguide, the long side of the waveguide having a wavelength of the electromagnetic wave for heating. Two
An electromagnetic wave heating device, characterized in that a rod-shaped magnetic body is mounted parallel to the long side on the surface of the long side of a rectangular waveguide of one-tenth or less. 7. The waveguide has a lid in which a rod-shaped magnetic body is mounted parallel to the long side on the surface of the long side of a rectangular waveguide whose long side is one-half or less of the wavelength of an electromagnetic wave to be heated. The electromagnetic wave heating device according to claim 1, wherein: