JP5894864B2 - High frequency heating device - Google Patents

Description

  The present invention relates to a high-frequency heating apparatus that uses a rotating antenna to radiate microwave energy into a heating chamber to heat food and the like.

  A high-frequency heating device described in Patent Document 1 includes a mounting shelf made of a dielectric material fixed to the bottom surface of a heating chamber, and a horn-shaped rotating antenna at an excitation port portion of a waveguide provided at the center of the bottom surface of the heating chamber. The microwave energy guided by the waveguide is received by a horn-shaped rotary antenna, the microwave is radiated from the tip of the horn into the heating chamber, and the food placed on the mounting shelf is heated at high frequency.

  Further, in Patent Document 2, a planar circuit detector provided in a waveguide portion connected to a horn, having a horn-shaped receiving antenna, having a constant width on the long side surface of the horn portion and a low height at the horn entrance. A wedge-shaped ridge that is raised at the center, receives a microwave signal transmitted through free space by a horn-shaped receiving antenna, and enhances the electric field strength of the received microwave by passing through the ridge. It is intended to be detected at the entrance. The ridge refers to a rectangular parallelepiped protrusion provided along the tube axis on the inner surface side of the center of the long side surface of the waveguide that is a microwave transmission path.

JP 2010-199209 A JP-A-1-132108

  In Patent Document 1, one end of an inner conductor that passes through a coupling hole provided in the center of the bottom surface of the high-frequency supply chamber and faces the vertical direction into the high-frequency supply chamber and is coupled to the rotating antenna protrudes into the waveguide. Thus, the microwave generated by the magnetron and transmitted through the waveguide is coupled to the horn-shaped rotating antenna and radiated from the tip of the horn into the heating chamber.

  In this case, if the microwave transmitted through the waveguide is coupled to a rotating antenna having a similar waveguide shape and transmitted, the reflection can be reduced and the degree of coupling can be increased. As in the prior art, the shape and characteristic impedance are different, and when coupled to a horn-shaped rotating antenna that generates higher-order modes, the reflection between them increases and the degree of coupling decreases. The transmitted microwaves cannot be efficiently coupled to the horn-shaped rotating antenna and supplied.

  Also, if the rotating antenna is formed into a horn shape, microwave power is diffused and radiated in a wide space. Therefore, the effect of increasing the directivity by using the horn shape as described in the prior art is small. Furthermore, in the rotating antenna of Patent Document 1 having a horn-shaped transmission path, the microwave is transmitted as a high-order TE mode wave, and the characteristic impedance is different from the TEM mode, which is a form of microwave transmitted through free space. There is a problem that reflection occurs when radiated to the heating chamber space.

  For this purpose, a means for providing a ridge in the waveguide or horn-shaped portion to convert the TE mode wave into a TEM mode wave and radiating it into free space can be considered, which is similar to Patent Document 2 shown in the conventional example. Although the contents are shown, it is a patent of the receiving antenna, and the height of the ridge is lowered at the horn shape part to suppress the reflected wave, and the electric field strength is increased at the waveguide entrance to increase the electric field strength. The purpose is to capture.

  When this is replaced with a rotating antenna and the effect of the ridge is verified, since the height of the ridge is low at the horn-shaped opening, it is not converted into a TEM mode wave, so the reflection becomes large and microwaves can not be radiated efficiently, Since the electric field does not concentrate when the height of the ridge is low, the electric field strength at the opening of the horn becomes weak and there is no effect of sharpening the directivity. In addition, in the conventional example, the planar circuit detector portion having a high ridge height serves as a microwave feeding portion in the rotating antenna. Therefore, providing a metal tall metal ridge in the vicinity of the feeding portion reflects on that portion. There is a problem that it becomes large and cannot be matched.

  The TE mode has no electric field component in the microwave traveling direction Z (there may be a magnetic field component, and the electric field component is in the X and Y directions on a plane perpendicular to the microwave traveling direction Z). (A)) The appearance of the wave. The TEM mode is a wave having neither an electric field component nor a magnetic field component in the microwave traveling direction Z (the electric field component and the magnetic field component are in the X direction and the Y direction on a plane perpendicular to the microwave traveling direction Z). Appear. The higher-order mode refers to a wave form in which a plurality of electric field components and magnetic field components are generated in the X and Y directions on a plane perpendicular to the microwave traveling direction Z in the transmission line.

The present invention has been made to solve the above problems, and in the high-frequency heating device according to claim 1, a heating chamber including a heating chamber for storing an object to be heated and a dielectric provided on a bottom surface of the heating chamber. An object mounting plate, a high-frequency supply chamber provided at a substantially central portion of the bottom surface of the heating chamber below the heated object mounting plate, a magnetron for generating microwave energy, a waveguide for attaching the magnetron, A coupling hole provided in a central portion of the bottom surface of the high-frequency supply chamber, an inner conductor provided through the coupling hole and facing the high-frequency supply chamber substantially vertically, and substantially horizontal in the high-frequency supply chamber at one end of the inner conductor comprising a rotating antenna conformational a metal linked, a dielectric shaft coupled with said waveguide in said conductor, and a drive unit for rotating the dielectric body axis, to said rotating antenna, the 1 long side, 2nd long side, 1st short side, 2nd short side An enclosed rectangular portion, a third long side that is substantially parallel to the second long side, a first side connecting the third long side and the first short side, the third long side, and the second long side A second side connecting the short sides, and a trapezoidal portion at the second long side, the first long side, the first short side, the second short side, the first side, and the second side. The side is provided with a downward vertical wall portion, the inner conductor is in contact with the lower surface of the rectangular portion of the rotating antenna, and the first long side and the second long side are 1 / 2λ (λ is the microwave The vertical wall height of the rectangular portion is shorter than 1 / 2λ .

  In the rotary antenna of the high-frequency heating device of the present invention, the first long side and the second long side of the rectangular portion are longer than 1 / 2λ (λ is the wavelength of the microwave) and shorter than λ, and the vertical wall of the rectangular portion is Can be coupled to the waveguide portion of the rotating antenna in the same TE mode wave form as the waveguide without generating higher-order mode microwaves by making the height less than 1 / 2λ. Therefore, there is an effect that the reflection is small and the degree of coupling is large, and the microwave energy generated by the magnetron can be efficiently transmitted to the waveguide of the rotating antenna.

1 is a longitudinal sectional view of a main part of a high-frequency heating device according to Embodiment 1. FIG. 1 is a perspective view of a rotary antenna according to Embodiment 1. FIG. FIG. 6 is a perspective view of a rotating antenna according to a second embodiment. The figure which calculated | required the reflection coefficient of the rotating antenna of each Example by analysis. The figure which calculated | required the electric field strength in the radiation path front of the rotating antenna of each Example by analysis. FIG. 6 is a perspective view of a rotating antenna according to a third embodiment. FIG. 6 is a perspective view of a rotating antenna according to a fourth embodiment. FIG. 10 is a perspective view of a rotating antenna according to a fifth embodiment.

  Embodiments of the present invention will be described below with reference to FIGS.

  FIG. 1 is a longitudinal sectional view of a main part of the high-frequency heating device of Example 1, FIGS. 2 and 3 are perspective views of a rotating antenna, and FIGS. 4A and 4B are coupling degrees due to differences in convex portions (ridges) of the rotating antenna. 2 shows an analysis value of a reflection coefficient for evaluating the directivity and an electric field intensity for evaluating directivity.

  As shown in the cross-sectional view of the main part of FIG. 1, the high-frequency heating device of the present embodiment is mounted on a heated object 1 made of a heating chamber 1 that houses an object to be heated 12 and a dielectric provided on the bottom surface of the heating chamber 1. A mounting plate 2, a high-frequency supply chamber 3 provided at a substantially central portion of the bottom surface of the heating chamber 1 below the heated object mounting plate 2, a magnetron 4 that generates microwave energy, and a waveguide to which the magnetron 4 is attached. A tube 5, a coupling hole 6 provided in the center of the bottom surface of the high-frequency supply chamber for radiating microwave energy guided to the waveguide 5 to the high-frequency supply chamber 3, and a high-frequency supply chamber penetrating the coupling hole 6 3, an inner conductor 7 that is provided substantially vertically, and a metal three-dimensional rotating antenna 8 that is connected substantially horizontally to the high-frequency supply chamber 3 at one end of the inner conductor 7. The dielectric shaft 9 connected in the wave tube and the dielectric shaft 9 are rotated through the hole 10. And a drive unit 11 for driving the rotation antenna 8 is rotatable by a drive unit 11. Then, the microwave energy generated in the magnetron 4 is guided to the waveguide 5 and propagated to the rotating antenna 8 by coaxial mode coupling with the inner conductor 7 penetrating the coupling hole 6, and the high-frequency supply chamber 3, the object to be heated Radiated into the heating chamber 1 through the mounting plate 2.

  As shown in FIG. 2 (b), the rotating antenna 8 is formed by integrally forming a rectangular portion 8f serving as the waveguide 13 and a trapezoidal portion 8l serving as the radiation path 14, and the inner conductor 7 includes the rotating antenna. 8 is in contact with the lower surface of the rectangular portion 8f. As a result, the rectangular portion 8f becomes the waveguide 13 that guides the microwave energy transmitted through the inner conductor 7 to the trapezoidal portion 8l, and the trapezoidal portion 8l radiates the microwave energy transmitted through the rectangular portion 8f to the heating chamber 1. The radiation path 14 is

  As shown in FIG. 2A, the rectangular portion 8f is surrounded by a first long side 8a, a second long side 8b, a first short side 8c, and a second short side 8d, and further, the first long side 8a, the first short side 8c, and the second short side 8d are provided with downward vertical walls 8e, and the second long side 8b is open in the vertical direction.

  The trapezoidal portion 8l includes a third long side 8h that is substantially parallel to the second long side 8b and longer than the second long side 8b, a first side 8i that connects the second long side 8b and the third long side 8h, and a second side 8j, the first side 8i and the second side 8j are provided with downward vertical wall portions 8k, and the third long side 8h is open in the vertical direction.

  In the rotating antenna 8 of the present embodiment, the length of the first long side 8a and the second long side 8b is longer than 1 / 2λ (λ is the wavelength of the microwave) and shorter than λ, and the rectangular portion 8f. The height of the vertical wall 8e is shorter than 1 / 2λ.

  In the rotating antenna 8 of the present embodiment described above, the lengths of the first long side 8a and the second long side 8b are longer than 1 / 2λ and shorter than λ, and the vertical wall 8e of the rectangular portion 8f. Is made shorter than ½λ, there is no electric field component in the height direction of the vertical wall 8e, and only one electric field component appears on the first long side 8a and the second long side 8b. It becomes the fundamental mode TE10 of the mode wave, suppresses the generation of higher-order mode microwaves, can be coupled to the waveguide 13 of the rotating antenna 8 in the same TE10 mode wave form as the waveguide 5, and the reflection The degree of coupling can be increased with little.

  The rotating antenna 8 of Example 2 is shown in FIG. Note that the description of the points in common with the first embodiment will be omitted. The difference from the first embodiment is that the lower surface of the rotary antenna 82 of the second embodiment is flat, whereas the lower surface of the rotary antenna 8 of FIG. 3 has a convex portion oriented in the direction perpendicular to the second long side 8b. (Ridge) 15 is provided. As is apparent from FIG. 3, the height and width of the convex portion (ridge) 15 are uniform. Here, the width and height of the convex portion (ridge) 15 are within about 3/1 of the length of the first long side 8a and the second long side 8b of the waveguide 13 of the rotating antenna 8, and the vertical wall 8e. Selected within about 1/2 of the height.

  In the rotating antenna 8 of the present embodiment, a convex portion (ridge) 15 oriented in the direction perpendicular to the second long side 8d is provided on the lower surface of the rectangular portion 8f and the trapezoidal portion 8l. The transmitted TE mode microwave can be converted to a TEM mode wave form, which is a microwave mode transmitted through the heating chamber (free space) through the waveguide 13 and the radiation path 14.

  Specifically, TE mode microwaves transmitted through the waveguide from the magnetron are combined in the same TE mode wave form in a rectangular waveguide, and then guided by the action of the convex portion (ridge) 15. Since it is converted into a TEM mode wave form, which is a microwave mode transmitted through a parallel line or free space through a waveguide or radiation path, it is radiated from the radiation path to the heating chamber space. Generation of reflected waves when radiated into space can be suppressed.

  The rotating antenna 8 of Example 3 is shown in FIG. Note that description of points in common with the second embodiment will be omitted. The difference from the second embodiment is the shape of the convex portion (ridge) 15. In this embodiment, the width of the convex portion (ridge) 15 is uniform, but the height is small on the rectangular portion 8f side, A large wedge shape is formed on the trapezoidal portion 8l side.

  In the rotating antenna 8 of this embodiment, the height dimension of the convex portion (ridge) 15 near the inner conductor 7 provided perpendicularly to the long side surface of the waveguide 13 is shortened and the height dimension toward the radiation path 14 is reached. By making the wedge shape longer, reflection near the inner conductor 7 is suppressed. On the other hand, since the height dimension of the convex portion (ridge) 15 of the lower bottom portion 8-8 of the radiation path 14 is high, the TE mode wave appearance is near the third long side 8h portion of the radiation path 14 in the heating chamber. It is easy to be converted into the same TEM mode wave form that is transmitted through 1, the radiation path and the heating chamber space can be matched, the electric field strength can be increased in addition to the suppression of the reflected wave, and the directivity Also become sharper.

  The rotating antenna 8 of Example 4 is shown in FIG. Note that description of points in common with the second embodiment will be omitted. The difference from the second embodiment is the shape of the convex portion (ridge) 15. In this embodiment, both the height and width of the convex portion (ridge) 15 are small on the rectangular portion 8f side, and on the trapezoidal portion 8l side. It has a large, quadrangular pyramid shape.

  In the rotating antenna 8 of the present embodiment, the height and width of the convex portion (ridge) 15 near the inner conductor 7 are shortened, and the convex portion (ridge) 15 of the convex portion (ridge) 15 from the vicinity of the inner conductor 7 toward the radiation path 14 is shortened. Since the height and width are both rectangular pyramids, the reflection near the inner conductor 7 can be further suppressed than in the third embodiment, and the electric field strength at the bottom of the radiation path can be increased and directed. It has the effect of improving sharpness.

  A rotating antenna 8 of Example 5 is shown in FIG. Note that description of points in common with the second embodiment will be omitted. The difference from the second embodiment is that the shape of the convex portion (ridge) 15 and the notch 16 and the flange 17 are provided.

  In the rotating antenna 8 of the present embodiment, the notch 16 is provided in the trapezoidal portion 8 l of the radiation path 14, so that reflection is suppressed and consistency and directivity are improved. In addition, the rotating antenna 8 is placed directly above the rotating antenna 8. The heated object 12 can also be heated efficiently without unevenness.

  In addition, the vertical wall 8e and the vertical wall portion 8k of the waveguide 13 and the radiation path 14 are provided with flanges 17 at right angles to the vertical wall 8e and the vertical wall portion 8k, and the high-frequency supply port 3 facing the vertical wall 8e and the vertical wall portion 8k. It is possible to increase the directivity by preventing the occurrence of sparks between the bottom surfaces and suppressing the leakage power from the side surface perpendicular to the transmission direction of the microwave power.

  Further, the convex portion 15 is formed in a rounded conical shape and integrally formed by drawing, and an electric field that tends to be generated at a corner portion of a rectangular parallelepiped shape, a wedge shape, or a quadrangular pyramid shape convex portion (ridge) 15. Abnormal heating and sparks due to concentration can be suppressed.

[Reference example]
The characteristics of the rotating antenna 8 of each embodiment will be described using FIG. 4 in comparison with a conventional trapezoidal rotating antenna. FIG. 4A is a diagram obtained by analyzing the reflection coefficient of the rotating antenna of each example, where the vertical axis represents the reflection coefficient and the horizontal axis represents the frequency f (MHz). FIG. 4B is a diagram obtained by analysis with the electric field strength in front of the radiation path of the rotating antenna of each example as a magnetron output of 800 watts, and the vertical axis represents the electric field strength E (V / m).

  As shown in FIG. 4A, when the reflection coefficient of the rotating antenna 8 of the conventional example and Examples 1 to 4 is compared, (Example 4) <(Example 3) <(Example 2) <(Example 1) < (Conventional example). In addition, Example 5 becomes a characteristic in the middle of Example 4 and Example 3.

  In general, the degree of coupling is evaluated from the value of the reflection coefficient, and the degree of coupling increases as the reflection coefficient decreases. Therefore, the effect that the degree of coupling of the rotating antenna 8 of the first embodiment combining the rectangular waveguide 13 and the trapezoidal radiation path 14 is larger than that of the conventional rotating antenna composed of the trapezoidal radiation path, The difference in the degree of coupling due to the difference in the shape of the convex portion (ridge) 15 in the embodiment can be seen.

  Moreover, as shown in FIG. 4B, when the electric field strength in the front of the radiation path of the rotating antenna 8 of Examples 1 to 4 is compared with that of the conventional example, (Conventional Example) <(Example 1) <(Example 2) < (Example 3) <(Example 4) In addition, Example 5 becomes a characteristic in the middle of Example 4 and Example 3.

  In general, the directivity is evaluated from the value of the electric field intensity in the antenna radiation direction, and the directivity becomes sharper as the electric field intensity increases. Therefore, the directivity of the rotating antenna according to the first embodiment, which is a combination of the rectangular waveguide 13 and the trapezoidal radiation path, is sharper than that of the conventional rotating antenna composed of the trapezoidal radiation path, and the respective convexities. The difference in directivity due to the difference in the portion (ridge) 15 can be seen.

  In addition, by providing the convex part (ridge) 15, the electric field strength in the radial direction is increased, and the generation of reflected waves can be suppressed for the following reason. That is, the characteristic impedance differs in free space that propagates in a TEM mode wave form and in a waveguide that propagates in a TE mode wave form. The characteristic impedance of a wave in free space is determined by the dielectric constant ε and permeability μ of free space (which can be regarded as in a vacuum) regardless of the frequency of the propagated wave, and is 377Ω. The characteristic impedance in the case of a waveguide is transmitted. It can be determined by the wave frequency and the long dimension of the waveguide.

  For example, when a microwave having a long side length of 85 mm and a frequency of 2450 MHz is transmitted, it becomes 537Ω. Therefore, when microwaves are radiated from the waveguide to the free space of the heating chamber, the above characteristic impedance is also different depending on the mode of the microwaves. A mismatch occurs at the waveguide exit, which is the boundary surface, and reflection occurs. Therefore, if the convex portion (ridge) 15 is provided in the waveguide and converted into the TEM mode and the characteristic impedance is brought close to the characteristic impedance in the free space, the waveguide and the free space are matched, and the waveguide exit is obtained. Is suppressed, and the electric field strength can be increased. Thus, by providing the convex portion (ridge) 15 on the rectangular waveguide 13 or the trapezoidal radiation path 14 similar to the waveguide, the TE mode wave is converted into the TEM mode wave form, and the characteristics This is because the impedance decreases and approaches the characteristic impedance of free space.

  The width and height of the convex portion (ridge) 15 are within about 3/1 of the length of the long side (first long side and second long side) of the waveguide 13 of the rotating antenna 8, and the rectangular portion 8f. The vertical wall 8e is selected within about 1/2 of the height of the vertical wall 8e because the electric field concentration is weakened when the width of the convex portion (ridge) 15 is increased, and the effect of conversion from the TE mode wave to the TEM mode wave is obtained. This is because the effect of mode conversion and characteristic impedance conversion due to the provision of the convex portion (ridge) 15 cannot be obtained. Further, when the height dimension of the convex portion (ridge) 15 becomes longer than about ½ of the height of the vertical wall 8e, reflection increases in the waveguide 13 and the radiation path 14, and the microwave is difficult to propagate through the rotating antenna. This is because a spark occurs between the bottom surfaces of the high-frequency supply chamber 3 facing the surface of the convex portion (ridge) 15.

DESCRIPTION OF SYMBOLS 1 Heating chamber 2 To-be-heated object mounting plate 3 High frequency supply chamber 4 Magnetron 5 Waveguide 6 Coupling hole 7 Inner conductor 8 Rotating antenna 8a 1st long side 8b 2nd long side 8c 1st short side 8d 2nd short side 8e Vertical wall 8f Rectangular part 8h Third long side 8i First side 8j Second side 8k Vertical wall part 8l Trapezoid part 9 Dielectric shaft 10 Hole 11 Drive part 12 Heated object 13 Waveguide

Claims (3)

A heating chamber that accommodates an object to be heated, a heated object mounting plate made of a dielectric material provided on the bottom surface of the heating chamber, and provided at a substantially central portion of the bottom surface of the heating chamber below the heated object mounting plate. A high frequency supply chamber, a magnetron for generating microwave energy, a waveguide to which the magnetron is attached, a coupling hole provided at the center of the bottom surface of the high frequency supply chamber, and passing through the coupling hole into the high frequency supply chamber. An inner conductor facing substantially vertically, a metal three-dimensional rotating antenna connected substantially horizontally in the high-frequency supply chamber at one end of the inner conductor, and a dielectric connected in the waveguide of the inner conductor comprising a shaft, a driving unit for rotating the dielectric body axis, a,
The rotating antenna is
A rectangular portion surrounded by the first long side, the second long side, the first short side, and the second short side;
A third long side that is substantially parallel to the second long side, a first side connecting the third long side and the first short side, and a second side connecting the third long side and the second short side. And a trapezoidal portion on the second long side,
The first long side, the first short side, the second short side, the first side, and the second side include a downward vertical wall portion,
The inner conductor is in contact with the lower surface of the rectangular portion of the rotating antenna ;
The first long side and the second long side are longer than 1 / 2λ (λ is the wavelength of the microwave) and shorter than λ,
The high- frequency heating apparatus according to claim 1, wherein the height of the vertical wall of the rectangular portion is shorter than ½λ . In the high frequency heating apparatus according to claim 1,
The rectangular portion is a waveguide that guides microwave energy transmitted through the inner conductor to a trapezoidal portion including the second long side, the third long side, the first side, and the second side,
The high frequency heating apparatus , wherein the trapezoidal portion is a radiation path that radiates microwave energy transmitted through the rectangular portion to the heating chamber . In the high frequency heating device according to claim 1 or 2 ,
A high-frequency heating apparatus , wherein convex portions (ridges) oriented in a direction perpendicular to the second long side are provided on the lower surfaces of the rectangular portion and the trapezoidal portion .