JP2009181900A - Microwave heating device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a microwave heating device capable of uniformly heating and drying by uniformly distributing an electric field of a waveguide type microwave heating oven of the microwave heating device when heating and drying a paper and a film having a wide width or simultaneously heating and drying numerous thread-like objects. <P>SOLUTION: In the microwave heating device using a waveguide at a microwave frequency with a range of 300 MHz to 30 GHz, the microwave heating device is provided with a microwave oscillator 1, an isolator 2, a phase shifter 3, the waveguide type microwave heating oven 4, and a dummy load 5. A phase is changed by continuously shifting the phase shifter 3 in order to move a position of an electric field, and the electric field in the waveguide is set up to be uniform. Calorific value P in an object to be heated becomes uniform by making the electric field uniform, and uniform heating can be attained. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a microwave heating apparatus for heating and drying an object to be heated made of a dielectric using microwaves, and more particularly to a microwave heating apparatus using a waveguide.

A sheet-like object to be heated such as paper or film, or a filamentous object to be heated such as a resin or a water purifier filter has a large surface area with respect to its volume, and thus is heated with a microwave of 300 MHz to 30 GHz. In the case of microwave ovens, industrial tunnel type microwave heating devices, and industrial batch type microwave heating devices, the amount of heat released is large relative to the heat generation rate, so the temperature of the object to be heated does not rise to a predetermined temperature. . When heating an object having such a shape with microwaves, it is known to efficiently heat the object by concentrating the electric field in a bending waveguide furnace.
Toyoaki Omori Konobu Technox 14 Electromagnetic waves and food: 43-44, 1993

However, the conventional method has the following problems.

When drying a wide paper or film, or drying a large number of filamentous materials at the same time, when microwave heating is performed in a folded waveguide heating furnace, even if there is unevenness in the electric field, the dried area absorbs microwaves. However, it has not been put to practical use in applications other than drying because unevenness in electric field becomes unevenness in heating.

In the bent waveguide furnace, a TE ₁₀ mode, which is a fundamental mode of a waveguide, is usually used. In this waveguide, when looking at the power distribution of the microwave, if there is no reflection, a power standing wave does not occur, so the distribution is uniform with respect to the traveling direction of the waveguide. If the in-tube wavelength of the waveguide is λg, the electric field advances while repeating strength at intervals of λg / 4.
Industrial Research Institute Industrial Research Committee Microwave Application Technology: 216, 2004

On the other hand, heating by microwaves, the calorific value per unit volume of the heated object P, and the angular velocity omega, the dielectric constant epsilon ^', the dielectric loss ^epsilon'', the dielectric loss tangent tan [delta, when the electric field intensity and E,
P = ωε ^′ tanδE ²
= ^Ωε'' E ²
Can be expressed as

In applications other than drying, heating is performed using microwaves in proportion to the dielectric loss and dielectric loss tangent of the object to be heated. When the electric field is strong and weak at intervals of λg / 4, the amount of heat generated by the object to be heated is proportional to E ² , and the strength of the electric field becomes uneven heating, making it difficult to put it to practical use.

  The present invention relates to a microwave heating apparatus using a waveguide in a microwave frequency band with a frequency in the range of 300 MHz to 30 GHz. In the microwave heating apparatus, an isolator, a phase shifter, a waveguide-type microwave heating furnace, and a dummy. The microwave heating apparatus is composed of a load and is characterized in that the phaser is continuously varied to vary the phase and move the position of the electric field to make the electric field in the waveguide uniform. By making the electric field uniform, the heating value P of the object to be heated also becomes uniform, so that uniform heating can be achieved.

The phase shifter used in the present invention has a microwave ferrite and a matching element inside the waveguide, has a magnetic field circuit that forms a DC magnetic field outside the waveguide, and adjusts the magnetic field circuit. Thus, the microwave phase shifter is characterized by changing the phase of λg / 4 or more by varying the strength of the magnetic force applied to the microwave ferrite.

As a method of adjusting the magnetic field circuit, a method of controlling the magnetic force using an electromagnet or a method of controlling the magnetic force by moving the permanent magnet away from or close to the microwave ferrite using a permanent magnet is used. .

  The microwave ferrite inside the waveguide has the same in-tube wavelength as λg unless it receives a DC magnetic field from the outside. When a magnetic force is applied from the outside, circularly polarized waves are generated around the microwave ferrite, and the microwave is bent to the tube wall at the end face of the waveguide to have an in-tube wavelength longer than λg. The angle bent to the wall varies depending on the material of the microwave ferrite and the strength of the magnetic force, but when the wavelength is increased by about λg / 4, an external magnetic force of about 500 to 600 Gauss is required.

The time for changing the in-tube wavelength of the phase shifter is preferably ½ or less of the time for the article to be heated to pass through the waveguide heating furnace, and the magnetic force is preferably varied. When the magnetic force is varied within a time of ½ or less, the electric field applied to the object to be heated becomes uniform.

When microwave heating is performed in a waveguide furnace using the apparatus and method according to the present invention, microwave heating of an object to be heated, which has been difficult with the conventional method, becomes possible.

  Hereinafter, an embodiment relating to a microwave heating apparatus and method according to the present invention will be described with reference to the drawings. 1 to 12 show an embodiment of the invention related to the present invention.

FIG. 1 is a configuration diagram of a microwave heating apparatus. The microwave oscillator 1 is a 300 MHz to 30 GHz microwave oscillator, and includes an isolator 2, a phase shifter 3, a waveguide microwave heating furnace 4, and a dummy load 5. The microwave generated by the microwave oscillator 1 passes through the isolator 2, the phase shifter 3, and the waveguide-type microwave heating furnace 4, and is terminated at the dummy load 5 without reflection. The position of the phase shifter 3 is the same whether it is placed between the isolator 2 and the waveguide type microwave heating furnace 4 or between the waveguide type microwave heating furnace 4 and the dummy load 5. . In addition, the same effect can be obtained by inserting a short-circuit plate in place of the dummy load 5 in the above configuration.

  FIG. 2 is a diagram in which the object to be heated 10 flows through the waveguide type microwave heating furnace 4. A slit 9 is provided in the center of the waveguide of the maximum electric field intensity (Ex) 6 of the waveguide type microwave heating furnace 4, and the object to be heated 10 has the slit 9 parallel to the maximum electric field intensity (Ex) 6. Move in the flow direction 7 of the object to be heated.

  FIG. 3 is a cross-sectional view of a phaser using a permanent magnet. The inside of the waveguide 11 is composed of a matching element 13 and a microwave ferrite 12 in parallel with the long side of the waveguide and vertically. The outside of the waveguide 11 is constituted by a yoke 15 that connects the permanent magnet 14 and the upper and lower permanent magnets 14 in parallel with the microwave ferrite 12 and above and below. Since the permanent magnet 14 applies a magnetic field perpendicularly to the microwave ferrite 12, the pair of upper and lower permanent magnets 14 includes an N pole and an S pole, respectively. The polarity of the upper and lower permanent magnets 14 has the same effect in the N pole and S pole or in the S pole and N pole. Changing the magnetic force of the permanent magnet 14 changes the phase. By moving the upper and lower permanent magnets 14 and the yoke 15 in the longitudinal direction of the waveguide 11, the magnetic force to the microwave ferrite 12 is maximum when the microwave ferrite 12 is directly above and below the microwave ferrite 12, and the magnet is separated from the microwave ferrite 12. When it is, the magnetic force to the microwave ferrite 12 is minimized, and the magnetic force to the microwave ferrite 12 is increased or decreased to change the phase.

  FIG. 4 is a cross section of a phase shifter using an electromagnet. The outside of the waveguide 11 is composed of an electromagnet 16 that is parallel to and vertically above the microwave ferrite 12. Since the electromagnet 16 applies a magnetic field perpendicularly to the microwave ferrite 12, the upper and lower pairs of electromagnets 16 each have an N pole and an S pole. The polarity of the upper and lower electromagnets 16 has the same effect in the N pole and S pole or in the S pole and N pole. When the current passed through the electromagnet 16 is continuously increased or decreased, the magnetic force of the electromagnet 16 increases or decreases, and the phase of the magnetic force applied to the microwave ferrite 12 is increased or decreased.

  FIG. 5 is a plan sectional view of FIGS. 3 and 4. When a magnetic force is applied in the direction of the external magnetic force 18, the microwave ferrite 12 disposed in the waveguide 11 in the microwave generates a positive circular polarization 18 and a negative circular polarization 19. The microwave traveling direction 17 is influenced by the positive circularly polarized wave 18 and the negative circularly polarized wave 19 and is bent in the microwave traveling direction 22 when receiving an external magnetic force, and when there is no external magnetic force 18 (0 ) In the direction of microwave travel 21 when no external magnetic force is applied. The angle at which the microwave is bent is determined by the material of the microwave ferrite 12 and the strength of the external magnetic force 18. Since the microwaves go straight or bend according to the strength of the external magnetic force 18, the wavelength in the tube can be expanded and contracted behind the phase shifter 3 to change the phase.

FIG. 6 shows the electric field intensity distribution of the waveguide cross section. When a 2.45 GHz microwave is used, the waveguide 11 uses a WRJ-2 waveguide. The waveguide mode is a TE ₁₀ mode, the central portion of the waveguide 11 has a maximum electric field strength of 6 and the electric field strength distribution is an electric field strength distribution 8.

FIG. 7 is a cross-sectional plan view of the waveguide 11 and shows the TE ₁₀ mode electromagnetic field distribution. The electric field (into the paper) 23, the electric field 24 (out of the paper), and the magnetic field 25 are as shown in the figure.

FIG. 8 shows only the electric field intensity distribution 8 in the TE ₁₀ mode electromagnetic field distribution of FIG. The maximum electric field strength 6 is the interval of λg / 4, and the maximum and minimum (0) are repeated in the Z direction.

FIG. 9 shows an electric field intensity distribution 8 in which the electric field intensity distribution 8 of FIG. 8 is replaced with a positive distribution.

FIG. 10 is a diagram showing an electric field strength distribution 26 in which the phase is shifted by λg / 4 to the electric field strength distribution 8 of FIG.
When the electric field strength distribution 26 moved by λg / 4 is superimposed on the electric field strength distribution 8, there are no portions where the electric field strength is weak, and the unevenness of the electric field strength is eliminated and uniformized. When the λg / 4 phase is continuously changed by the phase shifter, the electric field intensity distribution as shown in FIG. 10 is obtained.

FIG. 11 is a diagram in which water is uniformly immersed in the thermal paper 28 and heated in place of the article to be heated 10 of the waveguide heating furnace 4 in FIG. 2 when the phase of the phase shifter 3 is not changed. When heated for a certain time, the heat-sensitive paper containing moisture is heated, and the heat-sensitive reaction portions 27 appear at regular intervals. When the frequency is 2.45 GHz and the WRJ-2 waveguide is used, a portion that does not respond thermally at a pitch of 37 mm appears. This coincides with the location of Ex and 0 in the electric field intensity distribution 8 of FIG.

12 is a diagram in which water is uniformly immersed in the thermal paper 28, and the waveguide heating furnace 4 in FIG. 2 is also heated in place of the object to be heated 10. When the phase of the phase shifter 3 is continuously changed, FIG. FIG. When heated for a certain time, the heat-sensitive paper containing moisture is heated, and the heat-sensitive reaction part 27 appears in a strip shape. This is a result when a frequency of 2.45 GHz and a WRJ-2 waveguide is used. This result coincides with the distribution obtained by synthesizing the electric field intensity distribution 8 in FIG. 10 and the electric field intensity distribution shifted by λg / 4.

In the microwave heating apparatus shown in FIG. 1, instead of the article to be heated 10 of the waveguide type microwave heating furnace 4 shown in FIG. 2, a thermal paper in which water is uniformly immersed in the thermal paper 28 is placed. FIG. 11 shows the result of microwave heating when the phaser 3 is not attached or when the phaser 3 is attached and the phase is not changed.
Since the electric field intensity distribution 8 in the waveguide does not move, electric field unevenness occurs at a fixed position and appears as unevenness like the thermal reaction part 27.

In the microwave heating apparatus shown in FIG. 1, instead of the article to be heated 10 of the waveguide type microwave heating furnace 4 shown in FIG. 2, a thermal paper in which water is uniformly immersed in the thermal paper 28 is placed. FIG. 12 shows the result of microwave heating when the phase shifter 3 is attached and the phase is continuously changed.
When the position of the electric field intensity distribution 8 in the waveguide is moved by λg / 4, the unevenness of the electric field is eliminated and uniformized, and appears as a heat-sensitive reaction part 27 that is uniformed like a belt like the heat-sensitive reaction part 27. .
By continuously moving the phase by λg / 4 or more by the phase shifter 3, it was confirmed that the electric field was made uniform and coincided with the heat-sensitive reaction unit 27 to eliminate the heating unevenness.

This apparatus can be used for a microwave heating apparatus using a waveguide type microwave heating furnace. In particular, the width of the object to be heated 10 is wide in a waveguide type microwave heating furnace, and when heating a thin object, the object to be heated can be used as a means for uniformly heating the object. Similarly, the object to be heated 10 can be used as a means for heating a large number of yarn-like objects at the same time.

It is a lineblock diagram of the microwave heating device concerning the embodiment of the present invention. It is a figure of the waveguide type microwave heating furnace which constitutes the microwave heating device concerning the embodiment of the present invention. It is a block diagram when using the permanent magnet of the phaser which comprises the microwave heating device concerning embodiment of this invention. It is a block diagram when using the electromagnet of the phaser which comprises the microwave heating device concerning embodiment of this invention. It is a conceptual diagram which changes the phase of the phase shifter concerning embodiment of this invention. It is a conceptual diagram of the electric field strength distribution of the waveguide cross section concerning embodiment of this invention. It is a conceptual diagram of the electric field strength distribution of the waveguide plane cross section concerning embodiment of this invention. It is a conceptual diagram of the electric field strength distribution concerning embodiment of this invention. It is a conceptual diagram of the electric field strength distribution concerning embodiment of this invention. It is a conceptual diagram when the phase is moved by λg / 4 in the electric field intensity distribution according to the embodiment of the present invention and when the phase is not moved. It is a figure of the heating result by the thermal paper concerning embodiment of this invention. It is a figure of the heating result by the thermal paper concerning embodiment of this invention.

Explanation of symbols

1 Microwave Oscillator 2 Isolator 3 Phaser 4 Waveguide Microwave Furnace 5 Dummy Load 6 Maximum Electric Field Strength (Ex)
7 Flow direction of object to be heated 8 Electric field intensity distribution 9 Slit 10 Object to be heated 11 Waveguide 12 Microwave ferrite 13 Matching element 14 Permanent magnet 15 Yoke 16 Electromagnet 17 Microwave traveling direction 18 External magnetic force (out of paper)
19 Positive Circular Polarization 20 Negative Circular Polarization 21 Microwave Travel Direction Without External Magnetic Force 22 Microwave Travel Direction with External Magnetic Force 23 Electric Field (Inside of Paper)
24 Electric field (out of paper)
25 Magnetic field 26 λg / 4 electric field intensity distribution moved 27 Thermal reaction part 28 Thermal paper

Claims (7)

In a microwave heating apparatus using a waveguide at a microwave frequency in the range of 300 MHz to 30 GHz, the microwave oscillator, an isolator, a phase shifter, a waveguide-type microwave heating furnace, and a dummy load are configured. A microwave heating apparatus characterized in that a phase shifter is continuously varied and a phase is varied to move the position of an electric field to make the electric field in the waveguide uniform.
In a phase shifter that controls the phase of a microwave, it has a microwave ferrite and a matching element inside the waveguide, a magnetic circuit that forms a DC magnetic field outside the waveguide, and adjusts the magnetic field circuit Therefore, the microwave phase shifter is characterized by changing the in-tube wavelength of λg / 4 or more by changing the strength of the magnetic force to the microwave ferrite.
2. The microwave heating apparatus according to claim 1, wherein the object to be heated is placed horizontally with a uniform electric field.
2. A microwave heating method using the microwave heating apparatus according to claim 1, wherein the object to be heated is placed in a uniform electric field and horizontally.
3. The phase shifter according to claim 2, wherein the magnetic field circuit is composed of an electromagnet, and the in-tube wavelength is changed by λg / 4 or more by controlling the magnetic force of the electromagnet.
3. The phase shifter according to claim 2, wherein the magnetic field circuit is composed of a pair of permanent magnets, and the in-tube wavelength is changed by λg / 4 or more by controlling the magnetic force of the permanent magnets.
2. The microwave microwave heating apparatus according to claim 1, wherein the in-tube wavelength of the microwave phase shifter according to claim 2 is changed in a time that is half or less of a time during which an object to be heated passes through the waveguide. Microwave heating device.

Images