JPH08330065A - Microwave thawing/heating device - Google Patents

Abstract

PURPOSE: To uniformly thaw and heat the frozen food in a bowl and simplify and miniaturize a device. CONSTITUTION: Microwaves in the axially symmetrical electric field mode are generated by a magnetron 10, a rectangular wave guide 11, a circular wave guide 12, and a corner section 13, and the center section of an object 16 to be heated is arranged near the center axis of the circular wave guide 12 by a thawing/heating section 15. A cover body 18 having a short-circuit plate 23 at the upper section is provided on the thawing/heating section 15, and conical dielectric substances 21, 20 are arranged nearby above and below the heated object 16. The unbiased electric field distribution strong at the center section is obtained in the axially symmetrical mode, and the heating efficiency at the center section of a bowl is improved. Since the dielectric substances 20, 21 serve as a matching unit, the incidence efficiency of the microwaves is improved, and the microwaves transmitting the heated object 16 can be reflected to be utilized again by the short-circuit plate 23. Microwaves in the circular polarization mode may be generated in the circular wave guide 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a microwave thawing and heating apparatus, and more particularly to the construction of an apparatus for thawing and heating frozen food such as bowls.

[0002]

2. Description of the Related Art Microwave thawing and heating devices such as microwave ovens, commercial microwave ovens, and microwave ovens for large-scale processing are objects to be heated that are placed in the oven by guiding microwaves emitted from a magnetron into the oven. Can be thawed or heated. In such a thawing and heating device, in order to achieve uniform thawing and heating of the object to be heated, a table on which the object to be heated is rotated, a stirrer, a rotating antenna, etc. Waves are supplied.

[0003]

However, recently, it is possible to thaw frozen foods that have been cooked (or semi-cooked) with a certain height and width, such as katsu-don, oyakodon and soboro-don.
Heating is performed, and when these frozen foods are thawed and heated, there is a problem that it is difficult to heat them to a uniform temperature.

FIG. 12 shows the result of thawing and heating a bowl using a conventional apparatus in which a microwave is supplied to a rectangular oven, which is a frozen katsudon (about -20 ° C.). )
1 was heated at a microwave output of 3 kW for 2 minutes, and the temperature was measured at the measurement points shown in FIG. 11. That is, with respect to the katsudon 1 having a radius of about 55 mm and a depth of about 60 mm, the center point A and five points B, C, F, and G shifted from the center point at intervals of 25 mm are used for the surface portion (depth About 10m
m), center part (depth about 30 mm), bottom part (depth about 50)
mm). According to this measurement result, it can be seen that the center point A is lower than the other points, as shown in the graphs of the front surface portion 101, the central portion 102, and the bottom surface portion 103. This is because the above bowls have height (thickness) and width, and various ingredients are placed on the rice, so microwaves cannot be applied well to the center. It is a thing.

Further, in order to eliminate the above-mentioned non-uniform heating state, the following means have been conventionally used. That is, by rotating the turntable on which the object to be heated is placed, the microwaves are uniformly incident on the object to be heated, or the electromagnetic waves in the oven are disturbed by a stirrer (rotating body).
The secondary antenna arranged at the microwave inlet is rotated to radiate the microwave in each direction. However, the addition of various members as described above complicates the configuration and increases the size of the device.

The present invention has been made to solve the above problems, and an object thereof is to achieve uniform thawing and heating even in frozen foods such as bowls, and to realize simplification and miniaturization of the structure. It is an object of the present invention to provide a microwave thawing and heating device capable of performing the above.

[0007]

In order to achieve the above object, a microwave defrosting / heating apparatus according to the invention of claim 1 is a microwave generating apparatus for generating a microwave in an axially symmetric electric field mode or a circular polarization mode. Section, a circular waveguide for guiding the microwave of the above mode to the side of the object to be heated, and a central portion of the object to be heated near the central axis of the circular waveguide (vertical direction, lateral direction, diagonal direction, etc. (A central portion as viewed from the direction), and a thawing heating unit for applying the microwave of the above mode to the object to be heated. Here, the thawing and heating includes not only the operations of thawing and heating after thawing, but also the operations of only thawing and only heating after thawing. A second aspect of the present invention is characterized in that a dielectric is arranged in the vicinity of the object to be heated arranged in the thawing heating section, at a position before or after transmission of microwaves. According to a third aspect of the present invention, the dielectric has a conical shape, and its length in the microwave transmission direction is a value n times λg / {(ε) ^1/2 · 2} (λg: inside the waveguide). Wavelength, ε: relative permittivity of dielectric material, n:
Integer) is set. According to a fourth aspect of the present invention, the dielectric is formed in a flat plate shape, and its length in the microwave transmission direction is 2n + 1 of λg / {(ε) ^1/2 · 4}.
Doubled value (λg: Wavelength in the waveguide, ε: Dielectric constant of dielectric,
(an integer including n: 0). Fifth
The invention described in claim is characterized in that the thawing heating section is provided with a short-circuit plate for reflecting microwaves toward the object to be heated, at a position after the object to be heated has passed through the microwave.

[0008]

According to the structure described in the first claim, the axially symmetric electric field mode or circular polarization mode microwaves formed by the microwave generating section move toward the center position of the circular waveguide,
The electric field strength becomes high. Therefore, by arranging the central portion of the object to be heated near the central axis of the circular waveguide as in the above configuration, for example, the heating efficiency of the central portion of the bowl can be improved. Uniform thawing or heating is performed.

According to the structure of the second aspect, since the flat plate-shaped or conical-shaped dielectric is arranged at the position before or after the transmission of microwaves in the object to be heated, this dielectric is matched. And the microwave efficiently enters the object to be heated. Here, when the dielectric has a conical shape, the incidence efficiency particularly at the central portion is improved.

According to the structure of the third aspect, the efficiency of incidence of microwaves on the object to be heated by the conical dielectric material is surely improved. The incident efficiency of microwaves on the object to be heated by the dielectric will be surely improved.

According to the structure of the fifth aspect, the microwave is reflected by the short-circuit plate arranged at the terminal end of the circular waveguide, and the microwave is given to the object to be heated from two opposite directions. Therefore, there is an advantage that the thawing and heating efficiency of the object to be heated is improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows a microwave thawing and heating apparatus according to the first embodiment, and this first embodiment utilizes an axially symmetric electric field mode. In FIG. 1, the magnetron 10 is connected to a rectangular waveguide 11, and this rectangular waveguide 11 is connected to a circular waveguide 12, and a short-circuit block 13 shown in the figure is provided at this connection. These members constitute a microwave generator, and the short-circuit block 13 is arranged to convert the microwave propagated from the rectangular waveguide 11 into an axially symmetric electric field mode, that is, a TM ₀₁ mode.

FIG. 2 shows the TM ₀₁ mode excited in the circular waveguide 12, and as shown in the figure, in this circular waveguide 12, the lines of electric force F 1 radiate from the central axis. A broadened axisymmetric electric field is formed. Therefore, this TM ₀₁
According to the mode, the closer to the central axis of the circular waveguide 12,
A microwave having a high electric field strength can be obtained. Further, in this mode, since there is no bias of the electric field in the circumferential direction, it is not necessary to provide a mechanism for rotating the turntable unlike the conventional microwave oven.

As shown in FIG. 1, a trumpet-shaped tube 14 that spreads upward is arranged on the upper portion of the circular waveguide 12, and a thawing and heating section ( Oven) 15 is provided. In the thawing / heating section 15, a mounting table 17 for placing the object 16 to be heated is arranged,
A lid 18 is provided on the upper part. In addition, an inverted conical dielectric body 20 is provided on the lower surface of the mounting table 17 while the lid body 18 is provided.
Also, a cone-shaped dielectric 21 is attached to the support 22, and as the dielectrics 20 and 21, for example, a synthetic resin material, alumina, or the like is used. Further, the lid 18
Is the short-circuit plate 23, and this short-circuit plate 23 is approximately (2n + 1) λg / 4 (λg:
The microwaves are arranged at positions separated by a distance D (wavelength in the waveguide). The lid 18 can be opened as shown by a chain line, for example.

The dielectric 20 below the mounting table 17 described above.
Serves as a so-called matching device for efficiently injecting the microwave guided from the circular waveguide 12 into the object 16 to be heated, and the short-circuit plate 23 reflects the microwave transmitted through the object 16 to be heated again. It has a role of making the object 16 to be heated incident. Therefore, in the embodiment, the microwave is applied to the object to be heated 16 from the upper and lower two directions. Then, the lid 18
The dielectric 21 on the side promotes the incidence of the microwave reflected by the short-circuit plate 23 on the object to be heated. The short circuit plate 23 is located at the distance D = (2n + 1) from the object 16 to be heated.
By separating them by about λg / 4, it is possible to improve the incidence of reflected microwaves.

FIG. 3 shows an example in which the dielectrics 20 and 21 are formed in a flat plate shape instead of a conical shape. That is,
In this example, the plate-shaped dielectric 25 is used for the mounting table of the thawing and heating unit 15, and the plate-shaped dielectric 26 is provided below the lid 18. And such dielectrics 20, 2
It is preferable that the heights (thicknesses) of 1, 25 and 26 are obtained by the following calculation formulas. That is, in the cone-shaped dielectrics 20 and 21, when the wavelength in the waveguide is λg and the relative permittivity of the dielectric is ε, the height h (length in the transmission direction) of the cone is λg / { N times (ε) ^1/2 · 2} (n = 1,
2, 3 ...) and the flat plate-shaped dielectric 2
5 and 26, the thickness t (length in the transmission direction) is set to λg
2n + 1 times / ((ε) ^1/2 · 4} (n = 0, 1, 2,
3 ...).

The above calculation formula takes the wavelength of the microwave and the matching condition into consideration. That is, from the viewpoint of microwave transmission efficiency, each of the dielectrics 20, 21, 2,
The thickness of 5, 26 is preferably λg / 4. Further, assuming that the relative permittivity of air is ε 0 and the relative permittivity of the object to be heated (freezing bowl) is ε 1, each dielectric 2 placed between them is
The relative permittivity ε of 0, 21, 25, 26 is ε = (εO · ε
1) It is preferable that the matching condition of ^1/2 be satisfied. If these conditions are applied to the conical dielectrics 20 and 21 or the flat dielectrics 25 and 26, the above formula is obtained.

Such dielectrics 20, 21, 25, 26
According to the above, the incidence efficiency of microwaves on the article to be heated 16 can be reliably improved, and the flat plate-shaped dielectric 25,
In the case of No. 26, the incident efficiency on the entire surface is improved, and with the conical dielectrics 20 and 21, the incident efficiency at the central portion is improved.

The first embodiment has the above-mentioned structure, and the microwave oscillated by the magnetron 10 of FIG. 1 is propagated to the circular waveguide 12 through the rectangular waveguide 11, but at this connection portion. The presence of the short circuit block 13 converts the microwave to the TM ₀₁ mode. Then, the microwave in the axially symmetric electric field mode is transmitted through the dielectric 20 to the object to be heated 1
The microwaves supplied to the heating element 6 and transmitted through the object 16 to be heated are reflected by the short-circuiting plate 23 and are again given to the object 16 to be heated via the dielectric 21. In this way, in the first embodiment, the microwave 16 incident from above and below causes the object 16 to be heated of the bowl to be thawed and heated.

FIG. 5 shows the result of actual temperature measurement performed by the thawing heating apparatus of the first embodiment, and this measurement was carried out at each point in FIG. That is, the same frozen katsudon (initial weight 450 g, initial temperature about -17 ° C.) 27 as in the case of FIG. 11 described above is heated at a microwave output of 1.2 kW for 3 minutes and 48 seconds, and the center point A and 30mm from the center point
The temperatures of the ingredient part, the central part and the bottom part were measured at nine points B to I which were shifted at intervals. And A, B,
C, H, and I (black circles) are connected by solid lines, and A, D, E, F, and G (white circles) are connected by dotted lines. According to the measurement results, the temperature from the part of the ingredient to the bottom part was about 60 ° C. or higher, and a good temperature was obtained in the central part of the bowl as a whole.

That is, in the first embodiment, the TM ₀₁ mode, which is the axially symmetric electric field mode shown in FIG. 2, is used to increase the electric field at the center portion, and the conical dielectric body 20 is used to center the electric field. By efficiently injecting a microwave into the portion, the central portion of the bowl is efficiently thawed and heated. Further, the microwave can be reflected by the short-circuit plate 23 of the lid 18 and the dielectric 21 can be used to achieve efficient thawing and heating of the ingredient. The short-circuit plate 23 and the dielectric 20 are effective when the tool is thick such as a katsudon or when the microwave absorption is poor. For example, in the case of a soboro bowl, the microwave is used. It is not always necessary, as it has good absorption.

FIG. 6 shows the configuration of the apparatus of the second embodiment, which uses the circular polarization mode. In FIG. 6, similar to the first embodiment, the magnetron 30 is connected to the rectangular waveguide 31, and the rectangular waveguide 31 is connected to the circular waveguide 33 via the corner portion 32. A circularly polarized wave generating element 34 is arranged along the axial direction on the wall surface in the circular waveguide 33. The circularly polarized wave generating element 34 has, for example, a length of 2λg and has a step difference as shown in FIG. It has a rectangular parallelepiped shape, and these members form a circularly polarized wave generation unit for microwaves.

Then, on the upper part of the circular waveguide 33,
Similar to the first embodiment, the trumpet tube 14 and the thawing heating unit 1
5, a mounting table 17 on which the object 16 to be heated 16 is placed, and a lid 18 are arranged. Further, an inverted conical dielectric 20 is provided on the lower surface of the placing table 17 and a support 22 for the lid 18 is provided. The dielectric 21 is attached, and the upper surface of the lid 18 serves as a short-circuit plate 23. Of course, the dielectrics 25 and 26 of FIG.
May be used.

8 and 9 are explanatory views of the circularly polarized wave, and FIG. 8 is a view of the circular waveguide 33 of FIG. 6 viewed from the upper side. As shown in FIG. 8, the circularly polarized wave generating element 34 is arranged with respect to the reference line 100 of the circular waveguide 33 (or the traveling direction of microwaves in the rectangular waveguide 31).
It is placed at an angle of 5 degrees. In such a configuration,
The microwave oscillated from the magnetron 30 passes through the rectangular waveguide 31, is redirected at the corner 32 (FIG. 6) at a right angle, and propagates into the circular waveguide 33. TE ₁₁ mode is formed. And
The TE ₁₁ mode microwave propagating through the circular waveguide 33 has a shape in which one side thereof is blocked by the circularly polarized wave generating element 34. As a result, as shown in FIG. 9, electric fields Ex and E
A rotating circular polarization consisting of the z component is formed.

According to such microwave circular polarization, the electric field strength of the central portion of the TE ₁₁ mode microwave, which is the fundamental mode, is high, so that the central portion of the bowl is heated well. Further, as described above, since the microwave rotates, the same effect as that of the turntable in the conventional microwave oven is exhibited, and the microwave is uniformly applied to the object to be heated.

FIG. 10 shows the result of actual temperature measurement performed by the thawing heating device of the second embodiment. As in the case of the first embodiment, this measurement was performed by heating a frozen katsudon (initial weight 450 g, initial temperature of about -17 ° C.) 27 at a microwave output of 1.2 kW for 3 minutes and 48 seconds, and This was carried out for each point. Also in the case of this measurement result, it is understood that the temperature from the ingredient portion to the bottom surface portion is about 60 ° C. or higher, and that the central portion of the bowl also has a good overall temperature.

In the above embodiment, the conical dielectric body 20,
21 or the flat plate-shaped dielectrics 25 and 26 are used, the flat plate-shaped dielectric and the conical dielectric are combined, or the lower side is a flat plate-shaped dielectric and the upper side is a conical-shaped dielectric. It may be a combined shape such as a dielectric, or various other shapes can be adopted. The sizes and shapes of such dielectrics 20, 21, 25, 26 are made to correspond to the size of the thawing and heating unit 15, the type of object to be heated, and the like.
It will be determined in consideration of the efficiency for uniformly heating the whole.

Further, in the above embodiment, the short-circuit plate 23 is arranged on the upper surface of the lid body 18, but it may be arranged at other places such as the lower side of the lid body 18, and when it is arranged on the lower side, the dielectric short circuit 23 is formed. Body 21,
26 may be eliminated. Furthermore, the circular waveguides 12, 3
Although the trumpet-shaped tube 14 is arranged on the upper part of 3, the thaw heating part may be provided on the upper part of the circular waveguides 12 and 33 without using the trumpet-shaped tube 14.

Furthermore, in the above embodiment, the circular waveguide 1
Although the central portion of the object 16 to be heated in the lateral direction is arranged in the vicinity of the central axes of 2 and 33, the circular waveguide is horizontally arranged and the object 16 to be heated is arranged in the longitudinal direction in the vicinity of the central axis. It is possible to adopt a configuration in which the central portion is arranged, a configuration in which the diagonal central portion of the object to be heated 16 is arranged in the vicinity of the central axis of the circular waveguide which is diagonally arranged, or the like.

[0030]

As described above, according to the first aspect of the invention, the microwave of the axially symmetric electric field mode or the circular polarization mode is generated, and the microwave of this mode is applied to the object to be heated. Therefore, it becomes possible to uniformly thaw and heat a bowl or the like having the height and width on which the ingredients are placed, including the central portion thereof. Moreover, since a bowl or the like can be uniformly heated without providing a turntable, a stirrer, a secondary antenna, etc., simplification and downsizing of the device can be achieved.

According to the second aspect of the present invention, since the dielectric is arranged in the vicinity of the object to be heated arranged in the thawing heating section, before or after the microwave is transmitted, the microwave is transmitted. There is an advantage that it can be satisfactorily incident on the object to be heated.

According to the invention described in claim 3 or 4,
The length of the conical dielectric in the microwave transmission direction is λg /
The value of n times {(ε) ^1/2 · 2} or the length of the flat plate dielectric in the microwave transmission direction is λg / {(ε) ^1/2
Since the value is set to 2n + 1 times 4}, the incidence efficiency of microwaves on the object to be heated can be reliably improved.

According to the fifth aspect of the present invention, since the short-circuit plate is provided at the position after the microwave of the object to be heated is transmitted, the microwave can be applied to the object to be heated from two opposite directions, and the object is thawed. There is an advantage that the heating efficiency is improved.

[Brief description of drawings]

FIG. 1 is a sectional view showing a microwave thawing heating apparatus according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an electric field distribution of an axially symmetric electric field mode in the circular waveguide of FIG.

FIG. 3 is a cross-sectional view showing another example of the dielectric material arranged in the thawing and heating section.

FIG. 4 is a diagram showing measurement points in a test of thawing and heating a bowl of Example.

5A and 5B are graphs showing test results using the apparatus of the first embodiment, where FIG. 5A is the temperature of the tool, FIG. 5B is the temperature of the central portion, and FIG. 5C is the temperature of the bottom portion. FIG.

FIG. 6 is a cross-sectional view showing the configuration of the device of the second embodiment.

FIG. 7 is a perspective view showing the configuration of the circularly polarized wave generating element of FIG.

8 is a diagram showing an electric field distribution of a TE ₁₁ mode formed by the circular waveguide of FIG.

FIG. 9 is an explanatory diagram showing circularly polarized waves formed in the second embodiment.

10A and 10B are graphs showing the test results using the apparatus of the second embodiment, where FIG. 10A is the temperature of the tool, FIG. 10B is the temperature of the central portion, and FIG. 10C is the temperature of the bottom portion. FIG.

FIG. 11 is a diagram showing measurement points in a conventional test of thawing and heating a bowl.

FIG. 12 is a graph showing test results using a conventional device.

[Explanation of symbols]

 10, 30 ... Magnetron, 11, 31 ... Rectangular waveguide, 12, 33 ... Circular waveguide, 15 ... Thaw heating part, 16 ... Heated object, 18 ... Lid, 20, 21 ... Conical dielectric, 23 ... Short-circuit plate, 25, 26 ... Flat plate-shaped dielectric material, 32 ... Corner part, 34 ... Circular polarization generating element.

Claims (5)

[Claims] 1. A microwave generator for generating a microwave of an axially symmetric electric field mode or a circularly polarized wave mode, a circular waveguide for guiding the microwave of the mode to the side of an object to be heated, and a circular waveguide of the circular waveguide. Place the center of the heated object near the central axis,
A microwave thawing and heating device comprising: a thawing and heating unit for applying the microwave of the above mode to an object to be heated. 2. The microwave according to claim 1, wherein a dielectric is arranged at a position before or after transmission of microwaves in the vicinity of the object to be heated arranged in the thawing and heating section. Thaw heating device. 3. The dielectric has a conical shape, and its length in the microwave transmitting direction is n of λg / {(ε) ^1/2 · 2}.
Doubled value (λg: Wavelength in the waveguide, ε: Dielectric constant of dielectric,
(n: integer). The microwave thawing heating device according to claim 2, wherein 4. The dielectric is formed in a flat plate shape, and its length in the microwave transmission direction is 2 of λg / {(ε) ^1/2 · 4}.
The microwave defrosting / heating apparatus according to claim 2, wherein the value is set to n + 1 times (λg: wavelength in waveguide, ε: relative permittivity of dielectric material, an integer including n: 0). 5. The first defrosting heating section is provided with a short-circuit plate for reflecting the microwave toward the object to be heated, at a position after the object to be heated has passed through the microwave. The microwave thawing and heating device according to the item.