CA1162615A - Microwave energy heating device with two waveguides coupled side-by-side - Google Patents
Microwave energy heating device with two waveguides coupled side-by-sideInfo
- Publication number
- CA1162615A CA1162615A CA000367623A CA367623A CA1162615A CA 1162615 A CA1162615 A CA 1162615A CA 000367623 A CA000367623 A CA 000367623A CA 367623 A CA367623 A CA 367623A CA 1162615 A CA1162615 A CA 1162615A
- Authority
- CA
- Canada
- Prior art keywords
- waveguide
- microwave energy
- coupling
- waveguides
- energy
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
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Classifications
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
- H05B6/72—Radiators or antennas
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- H05B6/00—Heating by electric, magnetic or electromagnetic fields
- H05B6/64—Heating using microwaves
- H05B6/78—Arrangements for continuous movement of material
Abstract
ABSTRACT OF THE DISCLOSURE
A method and apparatus for heating objects by microwave energy, comprising the supply of micro-wave energy from a generator to a first waveguide. A
second waveguide is provided which is separated from the first waveguide except for at least one coupling distance between the waveguides such that the micro-wave energy is passed from one waveguide to the other.
A uniform field distribution and heating is obtained.
In addition leakage of the microwave energy is avoided.
A method and apparatus for heating objects by microwave energy, comprising the supply of micro-wave energy from a generator to a first waveguide. A
second waveguide is provided which is separated from the first waveguide except for at least one coupling distance between the waveguides such that the micro-wave energy is passed from one waveguide to the other.
A uniform field distribution and heating is obtained.
In addition leakage of the microwave energy is avoided.
Description
.S
Method and device for heating by microwave energy This invention relates to a method and a device for heating by means of microwave energy. When objects, for example goods, are heated according to methods and by devices using microwave energy, a problem, which arises generally at the heating of cont-inuously passing objects, is that microwave energy radiates out of the heating space when this is open in one or several dir-ections.
It has not been possible, for e~ample, to continuously feed objects into and out of a heating device and simultaneously to prevent microwave energy from radiating out of the heating dev-ice through the discharge and/or feed-in opening thereof.
A further great problem has been to be able to feed-in suffic-ient effect into a space, in which objects are to be heated, and into which the objects continuously have to be fed and, resp-ectively, to be discharged therefrom..
With ~nown devices, moreover, interferences of the field dist-ribution are obtained either at the place of applicator connect-ion or at the feed-in place of load into the waveguide, result-ing in that the intended heating pattern is not achieved.
The present invention solves these problems and in addition prov-ides great possibilities for improving and simplifying in many ways the heating of objects by microwave energy.
The present invention, thus, relates to a method of heating objects by microwave energy, comprising the supply of microwave energy from a generator to a first waveguide.
The invention is characterized in that an additional, a second waveguide is provided which is separated from the first waveguide except for at least one coupling distance between the waveguid-es, which coupling distance is a distance, during and by means of which a coupling of microwave energy distributed in the wave propagation direction of the waveguides is caused to take place so, that microwave energy passes from one waveguide to the other one, in that the second waveguide is dimensioned so as by action of load in the form of said object to conduct micro-wave energy at the same propagation velocity as the first wave-guide, and that said object to be heat~d only is fed into and out of the second waveguide, and microwave energy is fed only into the first waveguide.
The invention also relates to a device having substantially the characterizing features defined in the attached claim 8.
The invention is described in the following, with reference to the accompanying drawings, in which Fig. 1 shows two waveguides, Fig. 2 is a diagram on the coupling of energy between two waveguides where the propagation directions of the energy and the waves are the same, Fig. 3 is a diagram corresponding to that shown in Fig. 2, Fig. 4 shows schematically a device according to one embod-iment of the invention, Fig. 5 is a diagram corresponding to the ones shown in Figs. 2 and 3, Fig. 6 is a cross-section of two waveguides where a so-called ridge waveguide is used as feed waveguide, Fig. 7 shows a further embodiment of a feed waveguide.
~s mentioned above in the introductory portion, the invention relates to a method and a device for microwave heatin~~ where microwave energy is transferred - coupled - between one or more waveguides, thereby eliminating many problems and short-comings.
A device fo~ carrying out said method comp~ises in principle in its simplest design a feed waveguide 1, a load wave~uide
Method and device for heating by microwave energy This invention relates to a method and a device for heating by means of microwave energy. When objects, for example goods, are heated according to methods and by devices using microwave energy, a problem, which arises generally at the heating of cont-inuously passing objects, is that microwave energy radiates out of the heating space when this is open in one or several dir-ections.
It has not been possible, for e~ample, to continuously feed objects into and out of a heating device and simultaneously to prevent microwave energy from radiating out of the heating dev-ice through the discharge and/or feed-in opening thereof.
A further great problem has been to be able to feed-in suffic-ient effect into a space, in which objects are to be heated, and into which the objects continuously have to be fed and, resp-ectively, to be discharged therefrom..
With ~nown devices, moreover, interferences of the field dist-ribution are obtained either at the place of applicator connect-ion or at the feed-in place of load into the waveguide, result-ing in that the intended heating pattern is not achieved.
The present invention solves these problems and in addition prov-ides great possibilities for improving and simplifying in many ways the heating of objects by microwave energy.
The present invention, thus, relates to a method of heating objects by microwave energy, comprising the supply of microwave energy from a generator to a first waveguide.
The invention is characterized in that an additional, a second waveguide is provided which is separated from the first waveguide except for at least one coupling distance between the waveguid-es, which coupling distance is a distance, during and by means of which a coupling of microwave energy distributed in the wave propagation direction of the waveguides is caused to take place so, that microwave energy passes from one waveguide to the other one, in that the second waveguide is dimensioned so as by action of load in the form of said object to conduct micro-wave energy at the same propagation velocity as the first wave-guide, and that said object to be heat~d only is fed into and out of the second waveguide, and microwave energy is fed only into the first waveguide.
The invention also relates to a device having substantially the characterizing features defined in the attached claim 8.
The invention is described in the following, with reference to the accompanying drawings, in which Fig. 1 shows two waveguides, Fig. 2 is a diagram on the coupling of energy between two waveguides where the propagation directions of the energy and the waves are the same, Fig. 3 is a diagram corresponding to that shown in Fig. 2, Fig. 4 shows schematically a device according to one embod-iment of the invention, Fig. 5 is a diagram corresponding to the ones shown in Figs. 2 and 3, Fig. 6 is a cross-section of two waveguides where a so-called ridge waveguide is used as feed waveguide, Fig. 7 shows a further embodiment of a feed waveguide.
~s mentioned above in the introductory portion, the invention relates to a method and a device for microwave heatin~~ where microwave energy is transferred - coupled - between one or more waveguides, thereby eliminating many problems and short-comings.
A device fo~ carrying out said method comp~ises in principle in its simplest design a feed waveguide 1, a load wave~uide
2, a coupling distance 3 and a microwave generator 4.
In Fig. 1 a feed waveguide 1 is shown~ which may have oblong size and rectangular cross-section, and which at one end is connected to a microwave generator (not shown in Fig. 1), for example a magnetron, klystron or transistor-oscillator. The said waveguide is intended only for the feed of microwave energy. A load waveguide 2 has substantially the same dimensions as the feed wavegulde and extends in parallel therewith in such a way, that the two waveguides 1,2 at least along a certain distance have a partition wall 5 in common. In this wall 5 a coupling distance 3 for transferring - coupling - of micro-wave energy from one waveguide to the other one is located. The coupling distance may consist of a slit 6, which with respect to microwave energy transport connects the two waveguides 1,2.
The coupling distance may also consist of aerial elements such as holes, which several per wave length are positioned along the length of the coupling distance.
The load waveguide 2 consists of a microwave applicator, the dimensions of which substantially are determined by the desired heat distribution in the products 19 to be heated. The products are fed into and out of the load waveguide 2 as indicated by arrows in Fig. 4.
According to the present invention, the load waveguide 2 is dimensioned so that the wave propagation constant, or the wave length, therein is the same as in the feed waveguide 1 when the load waveguide contains load to be heated.
When such is the case, microwave energy is coupled over from the feed waveguide 1 to the load waveguide 2 along the length of the coupling distance 3, when the load waveguide contains load. The microwave energy then can be coupled back to the feed ~6'~.5 waveguide 1 via an additional coupling distance 3 whereby, thus, both ends of the load waveguide, i.e. its feed-in end 7 and feed-out end 8, are free from microwave energy.
The basic theory for coupled modes is previously known and described a.o. in the publications J.R. Pierce, "Coupling of Modes of Propagation", J.Appl. Phys., 25, 179-183 ~Febr. 1954), . .
W.H. Lovisell, "Coupled Mode and Parametric Electronics", John Wiley ~ Sons, Inc. USA 1960, D.A. Watkins, "Topics in Electromagnetic Theory", John Wiley & Sons, Inc. USA 19~8, S.E. Miller, "Coupled Wave Theory and Waveguide Applications"
Bell Systems Tech. J., 33, 661-720 (May 1954). It is known in principle from this theory that energy ~s transferred between two waveguides, which are coupledalong a distance, and in which it propagates modes with equal or almost equal wave propagat-ion constant. The coupling takes place between modes propagat-ing in the same direction.
The coupling between waves with the same wave propagation const-ant, but with propagation in opposite direction is extremely small. It is possible to oppress waves in opposite direction very strongly by a suitable choice of the length of the coupl-ing distance.
In Fig. 2 is shown how the effect, which is marked by P along the y-axis, oscillates sinusoidally between two coupled wave-guides, which are marked by Vl,V2, along the length of a coupl-ing distance markeb by L. In order to coupler over all effect between the waveguides V1,V2, as shown in Fig. 2, the wave progagation constants in the two waveguides must be equal. When they are slightly different, only a part of the effect is trans-ferred, viz.
l~ (1 + ~ )2 of the effect. In said formula ~1 and, respectively, ~2 are the wave propagation constants in the respective waveguide, and k is the coupling factor for the field per length unit.
This implies that the coupling to other modes with different wave propagation constants can be oppressed.
The length,along which a certain relation exists between the effect in the waveguides, is determined by the size of the coupling factor. When the coupling distance has the length 1, it applies that all energy was transferred from one waveguide to the other one when k ~ /2.
When losses occur in the waveguide V2, the effect P is affected so, see Fig. 3, that the distribution between the waveguides along the coupling distance is not sinusoidal as in Fig. 2.
At the example in Fig. 3 k - 1.8/m, and the attenuation factor = 1.8/m. When the effect in the waveguide V1 is zero, it applies that the coupling length 1 is 1 = 1//2 ~ k2 ~
It can be observed that the maximum effect in the waveguide V2 in Fig. 3 is substantially lower (29%) than the maximum effect in the waveguide V1.
According to a preferred embodiment of the device according to the present invention, a feed waveguide 1 and a load waveguide 2 are provided where products are fed-in into one end 7 of the load waveguide and fed-out at its other end 8. Microwave energy is fed-in at the end 9 of the feed waveguide 1, which end is located at the feed in end 7 of the load waveguide. It fur_ ther is preferred to provide at the other end 10 of the feed waveguide 1 a reflection-free water load 11 for extinguishing energy possibly remaining in the feed waveguide, see Fig. 4.
1,S
The feed waveguide 1 is coupled to the load waveguide 2 along a coupling distance 3. The dimensions of the load waveguide 2, as mentioned above, are chosen so that the wave~uide, with intended load in the form of products, has the same or subst-antially the same wave propagation constant as the feed wave-guide 1.
Without load in the load waveguide 2, the wave propagation constant of the load waveguide differs from that of the feed waveguide, and the effect, therefore, is not coupled over from the feed waveguide 1 to the load waveguide 2, but is converted to heat in the water load 11. The generator 4 thereby operates against an adjusted load, irrespective of whether load is coupled to the load waveguide or not. No microwave energy, thus, leaks out of the equipment.
When products 19 are being fed into the load waveguide 2, the wave propagation constant is changed so as to be the same in the two waveguides 1,2. Thereby the energy is coupled over to the load waveguide 2,and the products are heated. The effect coupled-over is transported only in the wave propagation direct-ion, so that the feed-in of products does not give rise to any problems with respect to microwave leak, because there is no microwave energy at the feed-in end 7 of the load waveguide 2.
The length of the coupling distance 3 can be chosen so that at the point where the coupling ends, all effect is in the feed waveguide. Thereby all of the remaining Microwave effect is transferred to the water load 11. In this way the feed-out end 8 of the load waveguide is free from microwave energy. The in-vention, thus, permits free passage of products to be heated without risk of microwave leakage.
The coupling distance 3, further, can be divided into two or more sections so that, for example, the first section trans-..S
fers the effect from the feed waveguide 1 to the load waveguide2, and the next section returns the effect to the feed wave-guide 1.
At high attenuation in the load, it may be sufficient to trans-fer the effect to the load waveguide where it is entirely con-verted to heat in the products, before the products arrive at the feed-out end 8.
The maximum microwave effect in the load waveguide 2 is restr-icted either in that the electric field intensity must not become so high that an electric disruption is obtained, or in that the products do not withstand too rapid heating.
In a waveguide, which is fed directly by a generator or via a connection in a point, the heat development as well as the microwave effect fall exponentially in the direction of the effect transport.
The invention offers in this connection great advantages,.in that the heat development can be distributed very uniformly in the wave propagation direction.
By arranging a low coupling, the effect in the load waveguide can be held considerably lower than in the feed waveguide.
Fig. 5, which is a diagram of the same type as shown in Figs.
2 and 3, includes theoretical curves (dashed) and a m-asured curve (fully drawn~ concerning the coupling between two wave-guides Vl,V2. The attenuation factor ~ is measured to be 3.9/m.
and the coupling factor k to be 1.8/m. The coupling distance
In Fig. 1 a feed waveguide 1 is shown~ which may have oblong size and rectangular cross-section, and which at one end is connected to a microwave generator (not shown in Fig. 1), for example a magnetron, klystron or transistor-oscillator. The said waveguide is intended only for the feed of microwave energy. A load waveguide 2 has substantially the same dimensions as the feed wavegulde and extends in parallel therewith in such a way, that the two waveguides 1,2 at least along a certain distance have a partition wall 5 in common. In this wall 5 a coupling distance 3 for transferring - coupling - of micro-wave energy from one waveguide to the other one is located. The coupling distance may consist of a slit 6, which with respect to microwave energy transport connects the two waveguides 1,2.
The coupling distance may also consist of aerial elements such as holes, which several per wave length are positioned along the length of the coupling distance.
The load waveguide 2 consists of a microwave applicator, the dimensions of which substantially are determined by the desired heat distribution in the products 19 to be heated. The products are fed into and out of the load waveguide 2 as indicated by arrows in Fig. 4.
According to the present invention, the load waveguide 2 is dimensioned so that the wave propagation constant, or the wave length, therein is the same as in the feed waveguide 1 when the load waveguide contains load to be heated.
When such is the case, microwave energy is coupled over from the feed waveguide 1 to the load waveguide 2 along the length of the coupling distance 3, when the load waveguide contains load. The microwave energy then can be coupled back to the feed ~6'~.5 waveguide 1 via an additional coupling distance 3 whereby, thus, both ends of the load waveguide, i.e. its feed-in end 7 and feed-out end 8, are free from microwave energy.
The basic theory for coupled modes is previously known and described a.o. in the publications J.R. Pierce, "Coupling of Modes of Propagation", J.Appl. Phys., 25, 179-183 ~Febr. 1954), . .
W.H. Lovisell, "Coupled Mode and Parametric Electronics", John Wiley ~ Sons, Inc. USA 1960, D.A. Watkins, "Topics in Electromagnetic Theory", John Wiley & Sons, Inc. USA 19~8, S.E. Miller, "Coupled Wave Theory and Waveguide Applications"
Bell Systems Tech. J., 33, 661-720 (May 1954). It is known in principle from this theory that energy ~s transferred between two waveguides, which are coupledalong a distance, and in which it propagates modes with equal or almost equal wave propagat-ion constant. The coupling takes place between modes propagat-ing in the same direction.
The coupling between waves with the same wave propagation const-ant, but with propagation in opposite direction is extremely small. It is possible to oppress waves in opposite direction very strongly by a suitable choice of the length of the coupl-ing distance.
In Fig. 2 is shown how the effect, which is marked by P along the y-axis, oscillates sinusoidally between two coupled wave-guides, which are marked by Vl,V2, along the length of a coupl-ing distance markeb by L. In order to coupler over all effect between the waveguides V1,V2, as shown in Fig. 2, the wave progagation constants in the two waveguides must be equal. When they are slightly different, only a part of the effect is trans-ferred, viz.
l~ (1 + ~ )2 of the effect. In said formula ~1 and, respectively, ~2 are the wave propagation constants in the respective waveguide, and k is the coupling factor for the field per length unit.
This implies that the coupling to other modes with different wave propagation constants can be oppressed.
The length,along which a certain relation exists between the effect in the waveguides, is determined by the size of the coupling factor. When the coupling distance has the length 1, it applies that all energy was transferred from one waveguide to the other one when k ~ /2.
When losses occur in the waveguide V2, the effect P is affected so, see Fig. 3, that the distribution between the waveguides along the coupling distance is not sinusoidal as in Fig. 2.
At the example in Fig. 3 k - 1.8/m, and the attenuation factor = 1.8/m. When the effect in the waveguide V1 is zero, it applies that the coupling length 1 is 1 = 1//2 ~ k2 ~
It can be observed that the maximum effect in the waveguide V2 in Fig. 3 is substantially lower (29%) than the maximum effect in the waveguide V1.
According to a preferred embodiment of the device according to the present invention, a feed waveguide 1 and a load waveguide 2 are provided where products are fed-in into one end 7 of the load waveguide and fed-out at its other end 8. Microwave energy is fed-in at the end 9 of the feed waveguide 1, which end is located at the feed in end 7 of the load waveguide. It fur_ ther is preferred to provide at the other end 10 of the feed waveguide 1 a reflection-free water load 11 for extinguishing energy possibly remaining in the feed waveguide, see Fig. 4.
1,S
The feed waveguide 1 is coupled to the load waveguide 2 along a coupling distance 3. The dimensions of the load waveguide 2, as mentioned above, are chosen so that the wave~uide, with intended load in the form of products, has the same or subst-antially the same wave propagation constant as the feed wave-guide 1.
Without load in the load waveguide 2, the wave propagation constant of the load waveguide differs from that of the feed waveguide, and the effect, therefore, is not coupled over from the feed waveguide 1 to the load waveguide 2, but is converted to heat in the water load 11. The generator 4 thereby operates against an adjusted load, irrespective of whether load is coupled to the load waveguide or not. No microwave energy, thus, leaks out of the equipment.
When products 19 are being fed into the load waveguide 2, the wave propagation constant is changed so as to be the same in the two waveguides 1,2. Thereby the energy is coupled over to the load waveguide 2,and the products are heated. The effect coupled-over is transported only in the wave propagation direct-ion, so that the feed-in of products does not give rise to any problems with respect to microwave leak, because there is no microwave energy at the feed-in end 7 of the load waveguide 2.
The length of the coupling distance 3 can be chosen so that at the point where the coupling ends, all effect is in the feed waveguide. Thereby all of the remaining Microwave effect is transferred to the water load 11. In this way the feed-out end 8 of the load waveguide is free from microwave energy. The in-vention, thus, permits free passage of products to be heated without risk of microwave leakage.
The coupling distance 3, further, can be divided into two or more sections so that, for example, the first section trans-..S
fers the effect from the feed waveguide 1 to the load waveguide2, and the next section returns the effect to the feed wave-guide 1.
At high attenuation in the load, it may be sufficient to trans-fer the effect to the load waveguide where it is entirely con-verted to heat in the products, before the products arrive at the feed-out end 8.
The maximum microwave effect in the load waveguide 2 is restr-icted either in that the electric field intensity must not become so high that an electric disruption is obtained, or in that the products do not withstand too rapid heating.
In a waveguide, which is fed directly by a generator or via a connection in a point, the heat development as well as the microwave effect fall exponentially in the direction of the effect transport.
The invention offers in this connection great advantages,.in that the heat development can be distributed very uniformly in the wave propagation direction.
By arranging a low coupling, the effect in the load waveguide can be held considerably lower than in the feed waveguide.
Fig. 5, which is a diagram of the same type as shown in Figs.
2 and 3, includes theoretical curves (dashed) and a m-asured curve (fully drawn~ concerning the coupling between two wave-guides Vl,V2. The attenuation factor ~ is measured to be 3.9/m.
and the coupling factor k to be 1.8/m. The coupling distance
3 was a continuous slit. By decreasing the coupling, the max-imum effect in the load waveguide 2 for a predetermined effect fed-into the feed waveguide 1 decreases.
~ , >t;~ ~i It is also possible to maintain the energy density in the load waveguide 2 on the highest level by varying the coupling factor per length unit. The heating velocity can thereby be controlled by the time so that a desired heating process, for example a drying profile, is obtained.
When applying the invention, the microwave energy is caused to be transferred during a comparatively long distance, which im-plies that interferences of the field pattern in the applicator, i.e. load waveguide, are insignificant. A conventional dis-crete connection of effect to a load waveguide by, for example, a coil, an aerial or opening, as a matter of fact, brings about a strong local interference of the fiead configuration and thereby an interference of the heat distribution.
According to a further, preferred embodiment of the invention, the feed waveguide 1 or load waveguide 2 is designed so that its wave propagation constant slowly is changed along its length.
Hereby the load dependency is decreased, i.e. the effect of that variations in the load change the wave propagation constant and therewith the strength of the coupling. This can be brought about by a continuous change of its dimensions or by inserting a low-loss dielectric material, the position of which in the waveguide and the dielectricity constant of which influence the wave propagation velocity of the waveguide.
When a dielectric material is inserted in the waveguide, the position of the material preferably is displaceable from out-side so that the waveguide easily can be trimmed when the waveguide is in operation.
Fig. 6 is a cross-section of an embodiment of a flexible feed waveguide 1 according to the invention. It consists of a so-called ridge waveguide 12, for example according to SE-PS
366 456, where the effect is concentrated to a zone between a ridge 13 and the slit 14 of the coupling distance 3. A di-electric material lS is provided between the ridge 13 and slit 14. By reducing the distance between the ridge 13 and slit 14, the effect concentration increases, and the coupling to the load waveguide 2 gains in strength.
The wave propagation constant can be caused to assume differ-ent values by filling a greater or smaller portion of the ridge waveguide 12 with a low-loss di~lectric material. The dielectric constant together with the geometric dimensions determine the wave propagation constant of the ridge waveguide.
In order to obtain high values of the wave propagation const-ant, the feed waveguide 1 is designed with a periodic struct-ure where periodically arranged diaphragms extend from two opposed inner walls 17,18 of the feed waveguide 1, as shown in Fig. 7.
Besides the aforementioned advantages can be stated that, due to the operation of the generator against a reflection-free load, the service life of the generator is much longer than it usually is the case. This applies especially to magnetrons, which predominantly are used as microwave generators for heat-ing purposes.
It can further be stated that for materials with low losses a high effeciency degree on a short distance and a good toler-ance against variations in the load are obtained.
The wavelength is long and thereby yields a small variation of the heating in longitudinal direction.
The invention is not restricted to the embodiments described above. Several load waveguides, for example, can be fed by one feed waveguide, in which case the load waveguides 2 are placed in parallel on two respective sides of the feed waveguide 1.
Furthermore, several feed waveguides can in corresponding manner feed effect to one load waveguide.
According to another embodiment, several feed waveguides can couple energy to one load waveguide, where the connection takes place in the same position to different modes in the load waveguide, or the feed waveguides subsequently one after the other couple energy to the same mode in the load waveguide.
The feed-in opening 7 of the load waveguide 2 also can be dim-ensioned so that it has a so-called cut-off frequency, which is lower than the generator frequency, and a feed-out opening 8 with a cut-off frequency, which is hLgher than the generat-or frequency.
The invention, thus, must not be regarded restricted to the embodiments described above, but can be varied within the scope of the attached claims.
~ , >t;~ ~i It is also possible to maintain the energy density in the load waveguide 2 on the highest level by varying the coupling factor per length unit. The heating velocity can thereby be controlled by the time so that a desired heating process, for example a drying profile, is obtained.
When applying the invention, the microwave energy is caused to be transferred during a comparatively long distance, which im-plies that interferences of the field pattern in the applicator, i.e. load waveguide, are insignificant. A conventional dis-crete connection of effect to a load waveguide by, for example, a coil, an aerial or opening, as a matter of fact, brings about a strong local interference of the fiead configuration and thereby an interference of the heat distribution.
According to a further, preferred embodiment of the invention, the feed waveguide 1 or load waveguide 2 is designed so that its wave propagation constant slowly is changed along its length.
Hereby the load dependency is decreased, i.e. the effect of that variations in the load change the wave propagation constant and therewith the strength of the coupling. This can be brought about by a continuous change of its dimensions or by inserting a low-loss dielectric material, the position of which in the waveguide and the dielectricity constant of which influence the wave propagation velocity of the waveguide.
When a dielectric material is inserted in the waveguide, the position of the material preferably is displaceable from out-side so that the waveguide easily can be trimmed when the waveguide is in operation.
Fig. 6 is a cross-section of an embodiment of a flexible feed waveguide 1 according to the invention. It consists of a so-called ridge waveguide 12, for example according to SE-PS
366 456, where the effect is concentrated to a zone between a ridge 13 and the slit 14 of the coupling distance 3. A di-electric material lS is provided between the ridge 13 and slit 14. By reducing the distance between the ridge 13 and slit 14, the effect concentration increases, and the coupling to the load waveguide 2 gains in strength.
The wave propagation constant can be caused to assume differ-ent values by filling a greater or smaller portion of the ridge waveguide 12 with a low-loss di~lectric material. The dielectric constant together with the geometric dimensions determine the wave propagation constant of the ridge waveguide.
In order to obtain high values of the wave propagation const-ant, the feed waveguide 1 is designed with a periodic struct-ure where periodically arranged diaphragms extend from two opposed inner walls 17,18 of the feed waveguide 1, as shown in Fig. 7.
Besides the aforementioned advantages can be stated that, due to the operation of the generator against a reflection-free load, the service life of the generator is much longer than it usually is the case. This applies especially to magnetrons, which predominantly are used as microwave generators for heat-ing purposes.
It can further be stated that for materials with low losses a high effeciency degree on a short distance and a good toler-ance against variations in the load are obtained.
The wavelength is long and thereby yields a small variation of the heating in longitudinal direction.
The invention is not restricted to the embodiments described above. Several load waveguides, for example, can be fed by one feed waveguide, in which case the load waveguides 2 are placed in parallel on two respective sides of the feed waveguide 1.
Furthermore, several feed waveguides can in corresponding manner feed effect to one load waveguide.
According to another embodiment, several feed waveguides can couple energy to one load waveguide, where the connection takes place in the same position to different modes in the load waveguide, or the feed waveguides subsequently one after the other couple energy to the same mode in the load waveguide.
The feed-in opening 7 of the load waveguide 2 also can be dim-ensioned so that it has a so-called cut-off frequency, which is lower than the generator frequency, and a feed-out opening 8 with a cut-off frequency, which is hLgher than the generat-or frequency.
The invention, thus, must not be regarded restricted to the embodiments described above, but can be varied within the scope of the attached claims.
Claims (15)
1. A method of heating objects by means of microwave energy, comprising the supply of microwave energy from a generator to a first waveguide, char-acterized in that an additional, a second waveguide is located separated from the first waveguide except for at least one coupling distance between the wave-guides, which coupling distance consists of a distance, during and by means of which a coupling of microwave energy distributed in the wave propagation direction of the waveguides is caused to take place so that microwave energy passes from one waveguide to the other waveguide, in that the second waveguide is dimensioned so as by action of load in the form of said objects to conduct microwave energy with the same wave propagation constant as said first waveguide, and that said objects to be heated only are fed into and out of said second waveguide, and that microwave energy only is fed into the first waveguide.
2. A method as defined in claim 1, char-acterized in that microwave energy is caused to pass from the first waveguide to the second waveguide and back again to the first waveguide once or several times by applying as many of said coupling distances between the waveguides as there are intended passages of energy between the waveguides.
3. A method as defined in claim 1 or 2, characterized in that the wave propagation constant in the first waveguide is caused to continuously be changed along its length, in that the dimensions of the waveguide are changed.
4. A method as defined in claim 1 or 2, characterized in that the wave propagation velocity in the first waveguide is caused to be changed along the length thereof by inserting a dielectric material, preferably a ceramic material, in the waveguide.
5. A method as defined in claim 1 or 2, characterized in that close to the terminating end of the waveguides, at the latest, all remaining micro-wave energy is coupled over to the first waveguide, whereafter this energy is caused to be converted to heat in a load, for example water load, located at the end of the first waveguide.
6. A method as defined in claim 1, char-acterized in that two or more microwave generators are caused to introduce energy each in a waveguide, and the microwave energy in all such waveguides is caused to be coupled over to a waveguide provided for the heating of objects.
7. A method as defined in claim 1, char-acterized in that a microwave generator is caused to introduce energy into a waveguide, and the micro-wave energy in this waveguide is caused to be coupled over to two or more waveguides provided for the heating of objects.
8. A device for heating objects by means of microwave energy, comprising a generator for the supply of microwave energy to a first waveguide, character-ized in that it comprises an additional, a second wave-guide, which is located at the first waveguide so that the two waveguides at least along a certain distance have a partition wall in common, in which partition wall a coupling distance is located, which consists of a distance comprising a slit, a row of holes or corres-ponding means through said wall, by means of which distance a coupling of microwave energy distributed in the wave propagation direction of the waveguides takes place from one waveguide to the other one, and that the second waveguide is dimensioned so as by action of intended load in the form of objects to be heated in the waveguide to conduct microwave energy with the same wave propagation constant as the first wave-guide.
9. A device as defined in claim 8, char-acterized in that it comprises several coupling dis-tances for coupling-over microwave energy from the first waveguide to the second waveguide and thereafter back to the first waveguide once or several times, the number of said coupling distances being equal to the number of said transfers.
10. A device as defined in claim 8 or 9, characterized in that the cross-sectional dimensions of the first waveguide continuously are changed along at least a section of its length, whereby the wave propagation for energy transported in the waveguide is changed.
11. A device as defined in claim 8 or 9, characterized in that a dielectric material is inser-ted in the first waveguide at least along a section of its length, whereby the wave propagation velocity for energy transported in the waveguide is changed.
12. A device as defined in claim 8 or 9, characterized in that it comprises two coupling dis-tances or one coupling distance of corresponding length for transferring microwave energy fed into the first waveguide to the second waveguide and back to the first waveguide, and that the first waveguide terminates in a reflection-free load, for example a water load.
13. A device as defined in claim 8, char-acterized in that the first waveguide is connected by coupling distances to two or more of second waveguides.
14. A device as defined in claim 8, char-acterized in that two or more of first waveguides are connected by coupling distances to one second wave-guide.
15. A device as defined in claim 8, char-acterized in that the first waveguide is a so-called ridge waveguide.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE8000059-9 | 1980-01-03 | ||
| SE8000059A SE441640B (en) | 1980-01-03 | 1980-01-03 | PROCEDURE AND DEVICE FOR HEATING BY MICROVAGS ENERGY |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1162615A true CA1162615A (en) | 1984-02-21 |
Family
ID=20339882
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000367623A Expired CA1162615A (en) | 1980-01-03 | 1980-12-29 | Microwave energy heating device with two waveguides coupled side-by-side |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4476363A (en) |
| CA (1) | CA1162615A (en) |
| DE (1) | DE3049298A1 (en) |
| FR (1) | FR2473245A1 (en) |
| GB (1) | GB2067059B (en) |
| IT (1) | IT1146250B (en) |
| SE (1) | SE441640B (en) |
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| FR2543778A1 (en) * | 1983-04-01 | 1984-10-05 | Soulier Joel | DEVICE FOR COUPLING AN ELECTROMAGNETIC WAVE ON AN ABSORBENT MATERIAL |
| US4617440A (en) * | 1985-11-07 | 1986-10-14 | Gics Paul W | Microwave heating device |
| US4714810A (en) * | 1986-07-28 | 1987-12-22 | Arizona Board Of Regents | Means and methods for heating semiconductor ribbons and wafers with microwvaes |
| WO1991003140A1 (en) * | 1989-08-18 | 1991-03-07 | James Hardie & Coy Pty. Limited | Microwave applicator |
| US4999469A (en) * | 1990-04-02 | 1991-03-12 | Raytheon Company | Apparatus for microwave heating test coupons |
| US4992762A (en) * | 1990-04-16 | 1991-02-12 | Cascade Microtech, Inc. | Ridge-trough waveguide |
| DE69206736T2 (en) * | 1991-09-27 | 1996-05-30 | Apv Uk Plc | Microwave heating devices |
| FR2722638B1 (en) * | 1994-07-13 | 1996-10-04 | Marzat Claude | MICROWAVE APPLICATOR DEVICE, PARTICULARLY FOR COOKING PRODUCTS ON A METAL SUPPORT |
| GB9511748D0 (en) * | 1995-06-09 | 1995-08-02 | Cobalt Systems Limited | Oven |
| EP0875128A1 (en) * | 1996-01-19 | 1998-11-04 | Belin-Lu Biscuits France | Microwave application device, particularly for baking products on a metal carrier |
| JP3717403B2 (en) | 1998-02-19 | 2005-11-16 | フラマトム アンプ ゲゼルシャフト ミット ベシュレンクテル ハフツング | Microwave sintering method and apparatus for nuclear fuel |
| US6246037B1 (en) * | 1999-08-11 | 2001-06-12 | Industrial Microwave Systems, Inc. | Method and apparatus for electromagnetic exposure of planar or other materials |
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| SE521313C2 (en) * | 2000-09-15 | 2003-10-21 | Whirlpool Co | Microwave and procedure for such |
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| FI122167B (en) * | 2003-08-20 | 2011-09-30 | Metso Paper Inc | Arrangements in connection with the press section and the dryer section in a sheet forming machine |
| KR100960496B1 (en) * | 2003-10-31 | 2010-06-01 | 엘지디스플레이 주식회사 | Rubbing method of liquid crystal display device |
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| SE366456B (en) * | 1972-05-29 | 1974-04-22 | Stiftelsen Inst Mikrovags | |
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| FR2315986A1 (en) * | 1975-07-04 | 1977-01-28 | Olivier Jean | RESONANT PROCESS AND REACTOR FOR TREATING MATERIAL WITH ELECTROMAGNETIC WAVES |
-
1980
- 1980-01-03 SE SE8000059A patent/SE441640B/en not_active IP Right Cessation
- 1980-12-22 GB GB8041033A patent/GB2067059B/en not_active Expired
- 1980-12-26 FR FR8027594A patent/FR2473245A1/en active Granted
- 1980-12-29 CA CA000367623A patent/CA1162615A/en not_active Expired
- 1980-12-29 DE DE19803049298 patent/DE3049298A1/en active Granted
- 1980-12-31 IT IT50492/80A patent/IT1146250B/en active
-
1983
- 1983-09-02 US US06/528,791 patent/US4476363A/en not_active Expired - Fee Related
Also Published As
| Publication number | Publication date |
|---|---|
| GB2067059B (en) | 1983-10-26 |
| GB2067059A (en) | 1981-07-15 |
| IT8050492A0 (en) | 1980-12-31 |
| IT1146250B (en) | 1986-11-12 |
| FR2473245B1 (en) | 1984-01-06 |
| SE8000059L (en) | 1981-07-04 |
| DE3049298A1 (en) | 1981-09-17 |
| FR2473245A1 (en) | 1981-07-10 |
| SE441640B (en) | 1985-10-21 |
| US4476363A (en) | 1984-10-09 |
| DE3049298C2 (en) | 1989-08-03 |
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