CA1118844A - Combination microwave oven with a multi-port radiator - Google Patents
Combination microwave oven with a multi-port radiatorInfo
- Publication number
- CA1118844A CA1118844A CA000312734A CA312734A CA1118844A CA 1118844 A CA1118844 A CA 1118844A CA 000312734 A CA000312734 A CA 000312734A CA 312734 A CA312734 A CA 312734A CA 1118844 A CA1118844 A CA 1118844A
- Authority
- CA
- Canada
- Prior art keywords
- radiator
- microwave energy
- plenum
- accordance
- source
- 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
Links
- 239000004020 conductor Substances 0.000 claims abstract description 44
- 238000010438 heat treatment Methods 0.000 claims abstract description 10
- 230000005855 radiation Effects 0.000 claims description 11
- 230000007704 transition Effects 0.000 claims description 9
- 230000008878 coupling Effects 0.000 claims description 7
- 238000010168 coupling process Methods 0.000 claims description 7
- 238000005859 coupling reaction Methods 0.000 claims description 7
- 230000005540 biological transmission Effects 0.000 claims description 6
- 239000002184 metal Substances 0.000 claims description 6
- 230000010287 polarization Effects 0.000 claims description 6
- 238000000034 method Methods 0.000 claims description 5
- 239000011343 solid material Substances 0.000 claims 2
- 238000010411 cooking Methods 0.000 abstract description 3
- 239000011797 cavity material Substances 0.000 description 15
- 239000000463 material Substances 0.000 description 3
- 241000287828 Gallus gallus Species 0.000 description 2
- 239000002196 Pyroceram Substances 0.000 description 2
- 230000009471 action Effects 0.000 description 2
- 238000003466 welding Methods 0.000 description 2
- NLZUEZXRPGMBCV-UHFFFAOYSA-N Butylhydroxytoluene Chemical compound CC1=CC(C(C)(C)C)=C(O)C(C(C)(C)C)=C1 NLZUEZXRPGMBCV-UHFFFAOYSA-N 0.000 description 1
- 229910000639 Spring steel Inorganic materials 0.000 description 1
- 229910000831 Steel Inorganic materials 0.000 description 1
- 239000011358 absorbing material Substances 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 238000001816 cooling Methods 0.000 description 1
- 238000002788 crimping Methods 0.000 description 1
- 208000002925 dental caries Diseases 0.000 description 1
- 210000003298 dental enamel Anatomy 0.000 description 1
- 230000001419 dependent effect Effects 0.000 description 1
- 239000003989 dielectric material Substances 0.000 description 1
- 239000000428 dust Substances 0.000 description 1
- 230000005684 electric field Effects 0.000 description 1
- 239000002320 enamel (paints) Substances 0.000 description 1
- 239000011152 fibreglass Substances 0.000 description 1
- 238000009413 insulation Methods 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 230000007246 mechanism Effects 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 229920000136 polysorbate Polymers 0.000 description 1
- 230000009467 reduction Effects 0.000 description 1
- 230000000284 resting effect Effects 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- KUAZQDVKQLNFPE-UHFFFAOYSA-N thiram Chemical compound CN(C)C(=S)SSC(=S)N(C)C KUAZQDVKQLNFPE-UHFFFAOYSA-N 0.000 description 1
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
- H05B6/725—Rotatable antennas
-
- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F24—HEATING; RANGES; VENTILATING
- F24C—DOMESTIC STOVES OR RANGES ; DETAILS OF DOMESTIC STOVES OR RANGES, OF GENERAL APPLICATION
- F24C15/00—Details
- F24C15/02—Doors specially adapted for stoves or ranges
- F24C15/021—Doors specially adapted for stoves or ranges sealings for doors or transparent panel
-
- 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
- H05B6/647—Aspects related to microwave heating combined with other heating techniques
- H05B6/6482—Aspects related to microwave heating combined with other heating techniques combined with radiant heating, e.g. infrared heating
-
- 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
- H05B6/76—Prevention of microwave leakage, e.g. door sealings
- H05B6/766—Microwave radiation screens for windows
Landscapes
- Physics & Mathematics (AREA)
- Electromagnetism (AREA)
- Engineering & Computer Science (AREA)
- Chemical & Material Sciences (AREA)
- Combustion & Propulsion (AREA)
- Mechanical Engineering (AREA)
- General Engineering & Computer Science (AREA)
- Constitution Of High-Frequency Heating (AREA)
- Electric Ovens (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
A combination electric heat and microwave oven employing a common cavity for cooking food with either microwave energy, electric resistance heating, or both in which the oven is supplied with microwave energy through a rotating multi-port radiator having a plenum fed from a magnetron through a waveguide and a coaxial line whose outer conductor extends into the plenum and whose central conductor supports said radiator.
A combination electric heat and microwave oven employing a common cavity for cooking food with either microwave energy, electric resistance heating, or both in which the oven is supplied with microwave energy through a rotating multi-port radiator having a plenum fed from a magnetron through a waveguide and a coaxial line whose outer conductor extends into the plenum and whose central conductor supports said radiator.
Description
Cross Re~erence to Related ~pplications Canadian application Serial Nu~er 2gl,677, filed November 24, 1977 entitled "Radiating Mode Stirrer Heating System", W. W. Teich, assigned to the same assignee as this application.
Background of the In~ention In the aforemen-tioned copending application, there i9 disclosed a combination microwave oven using a rotating radia-tor for microwave energy with provision for supplying resistance heat by heating elements positioned around -the rotating radiator. ~Iowever, such an oven was made relatively expensive by using a belted dri~e to rotate the radiator and by using an individually machined waveguide to coaxial line transition structure.
In addition, substantial radiation of energy between the rotating radiator and the adjacent wall of the oven reduced the energy radiated directly into the body to be heated.
$~ ' Summary of ~he Invention In accordance Wit}l this invention, there is provided a microwave oven which more efficiently couples microwave energy into a body to be heated with a plurality of simultaneously radiated patterns.
~ ore specifically) this combination discloses that the output of a magnetron may be impedance matched into coaxial line in a manner such that the standing wave ratio on the line may be substantially a multi-port unity. Specifically, this is achieved by forming a waveguide thorugh which the magnetron output is coupled to the coaxial line with an impedance transition of substantially conical shape formed of stamped sheet metal surrounding the central conductor of the coaxial line.
In accordance with this invention, the waveguide to coaxial line transition is spaced in waveguide from the output of said magnetron, and from the ends of said waveguide by distances greater than one half wavelength of the energy in said guide.
In addition, the outer conductor of the coaxial trans-mission line extends through the oven wall and into the plenum of a rotating radiator having a plurali~y of ports radiating ~icrowave energy into the oven in a plurality of simultaneous radiation patterns whose axes are substantially paralle~ to the axis of rotation o said radiator and whose axes are spaced at diferent distances from said axis of rotation.
In accordance with this invention, a iood body is positioned on a rack in the radiation patterns from the rotating radiator so that a substantial portion of the microwave energy is absorbed on passing through the food body first time prior to reflection from walls of the oven. Therefore, high efficiency heating may be achieved with microwave energy even though the 8~4 walls of the oven are made o inexpcnsive material such as enamelled steel.
In accordance with this invention~ the magnetron may be tightly co~pled to the oven through a coupling mechanism such as a waveguide and coaxial transi-tion thereby increasing the efficiency of conversion of input power electrical energy to microwave energy coupled into the body to be heated. More specifi-callyl in the case of light loads or if the oven is energized~ with no food body positioned therein, m~crowave energy radiation into the oven and reflect-ed back to a multi-port rotating radiator from the opposite wall such as the top wall of the oven will arrive at a common junction such as the central conductor of a coaxial line transition with substantially different phases so that relatively low amounts of energy are coupled back into the magnetron and large portions of the energy are reflected back into the oven where the energy is absorbed by the walls of the oven.
In accordance with the invention there is provided in combination:
an enclosure comprising a cavity supporting a body to be heated; a source of microwave energy; means for simultaneously radiating a plurality of different microwave energy patterns having different polarizations from said source into said cavity in directions predominantly parallel to a common axis through a multi-port radiator while rotating said ports about said axis at different dis-tances from said axis; and said radiator comprising a plenum supplied by acoaxial line whose central and outer conductors extend into said plenum.
In accordance with another aspect of the invention there is provided the method of heating a body comprising the steps o: supplying mlcrowave energy to an enclosure containing said body from a source oE microwave energy comprising coupling said source to a rotating radiator having a plurality of radiating elements positioned at different distances from an axis oE said radiator and a coaxial line whose inner conductor supports said radiator and whose outer conductor extends into said enclosure; and rotating said radiator about said axis.
Brief Description of the Drawings Other and further objects and advantages of this invention will be apparent as the description thereof progresses reference being had to the accompanylng drawings wherein:
FIG. 1 illustrates a vertlcal sectional vlew o~ a combination microwave oven embodying the inventlon taken along line 1-1 of FIG. 2;
FIG. 2 illustrates a front view of the oven illustrated in FIG. 1 with the door removed;
FIG. 3 illustrates a fragmentary transverse sect;ional view of the oven of FIG. 1 taken along line 3-3 of FIG. Z; and FIG. 4 illustrates a sectional view of the radiator lllustrated in FIG. 3 ta~en along line 4-4 of FIG. 3 ~l8~3~4 Descri~tion of the Preferred Embodiment Referring now to FIGS. 1 and 2, ~here is shown a microwave cavity 10 closed by a door 12 and supplied with microwave energy from a rotating radiator 14 in the bottom o the oven. Radiator 14 is fed with microwave energy from a magnetron 16 through a ~aveguide 18 and a coaxial line 20 having a central conductor 22 rigidly connected to rota~ing radiator 14 and extending through waveguide 18 to a gear reduction motor 24.
;lotor 24 is attached to the bottom o waveguide 18 and rotates central conductor 22 to rotate radiator 14. Coaxial line 20 has an outer conductor 26 rigidly connected to the upper wall of waveguide 18 and extending through the bottom wall of enclosure 10 into a plenum 28 in radiator 14.
As shown more specifically in ~IGS. 3 and 4, plenum 28 comprises an upper plate 30 connected to central conductor 22 and IIaving a plurality of ports 32 therein spaced at different distances at the axis of conductor 22. !licrowave energy is radiated rom plenum 28 înto the oven enclosure 10 through ports 32 which are covered by ceramic members 34 and, hence, are transparent to microwave energy and prevent dust and cooking particles from entering the plenum 28.
A lower plenum cover 38 of radiator 14, which prevents radiation of microwave energy radially outwardly and directs it through the ports 32, and the lower sur~ace o~ cover 3~ is positioned suficiently above the bottom wall o enclosure 10 or radiator 14 to rotate Ereely. An aperture in cover 38 surrounds the upper end of outer coaxial conductor 26 which thus extends slightly into plenum 28 therel~y substantially preventing micro-wave energy from radiating into enclosure 10 from beneath radiator 14. The length of outer conductor 26 which extends into plenum 28 may be adjusted to improve impedance matching conditions.
As shown in Figure 1) a substantially conical waveguide to co~
axial line transition member 40 is formed of sheet metal and attached to the bottom wall of guide 18 surrounding central conductor 22. Transi~ion 40 ex-tends from the botto~ wall upwardly along conductor 22 for distancesto an effective electrical quarter wavelength at the frequency of magnetron 16 so that it produces a choking action to energy attemyting to escape from wave-guide 18 toward motor 24. Transition 40 is spaced from the ends of the wave-guide by a distance greater than one-half the wave length of the microwave energy in the guide. A bearing 42 of dielectric material is positioned be-tween transition 40 and conductor 22 to insure against arcing in the bearing.
The ends of waveguide 18 are closed by shorting members 44 and 46 respectively which are adjusted to provide a substantially flat standing wave ratio between the output probe 48 of magnetron 16 and central conductor 22.
As shown in Figures 3 and 4, radiator ports 32 are each fed with microwave energy through separate waveguide sections S0 whose axes are at 120 to each other and whose inner ends form a common junction region con taining the central conductor 22. An impedance matching conical member 54 is connected to conductor 22 to increase its radius as it approaches upper plate 30 of plenum 28. Waveguides 50 have side walls fQrming the sides of plenum 28 and are of different lengths with the maximum length difference being on the order of ~/3 or less to that energy radiated into the plenum 28 ~rom central conductor 22 arrives at ports 32 in respectively different phases. Since the width of guides 50 is selected to be between 2/3~ and ~, the primary modo exc.lted in waveguides 50 is the T~l 0 mode; and since the ports 32 are slots extcnding across the guides 50, the radiation patterns radiated from each of the ports wi.ll have di~ferent polarizations.
.~, r Energy reflected back to the ports 32, for example, from the top wall of the microwave cavity 10 will couple into the ports 32 dependent upon the polarization and will propagate toward the common junction at central conductor 22. However~ as a result of the different distances that the waves travel, which distance differences are double the length differences of wa~e-guides 50, the waves will arrive at central conductor 22 in different phases preferably selec~ed so that substantial cancellation of the electrical field vector will ~ccur thereby causing this junction of the waveguides 50 at central conducto,r 22 to reflect such energy back through ports 32 into the cavity.
As a result, a substantial isolation of the magnetron from reflected waves occurs. Furthermore, while this ef~ect is preferably chosen to be 3naximized when the microwave cavity has no food body positioned therein and the geometry of ~he oven is fixed, substantial amounts of cancellation will occur for light loads such as small food bodies which do not absorb substantially all the microwave radiation on the first pass of the microwave energy through the food body. Under these condltions it, therefore, is possible to couple magnet.ron 16 to the oven cavity 10 as tightly as possible thereby allowing magnetron 16 to operate close to its maximum efficiency for converting its electrical energy input to microwave energy output while maintaining low microwave energy field gradien~s and, hence, low wall losses in the waveguide 18. Such a match is achieved primarily by selecting the position of the waveguide and shorting member 44 to be on t.he order of an eigh~h o a guide wavelength ~rom the axis of the output 48 of magnetron 16, so that energy radiated from antenna 48 toward shorting member 46 reflects ~oward antenna 48 in a phase adding ~o direct radiation therefrom for producillg directional radiation from antenna 48 along gu;de 18 ~o central conductor 22. Similarly, waveguide shorting member 46 is positioned to reflect energy radiated from magnetron output 48 past conductor 22 to be out of phase wi~h energy reflected by central conductor 22 toward ~agnetron output 48 and will cancel thereby assis~ing the impedance match between coaxial line 20 and waveguide 18.
As a result, the~standing wave ratio in those regions may be made close to unity, for example, being within 20 percent of unity for the majority of rotational positions of radiator 14. Therefore,~
peak voltage gradients which might occur due to resonance are avoided and high heating efficiency in the oven may be achieved.
In accordance with this invention, oven cavity 10 may be made of relati~ely lossy or energy absorbing material which may ~ absorb, for example, a few percent of microwave energy impinging ~ thereon and reflecting therefrom. Such material may be, forexample, conventional sheet stee.l used in conventional ovens and ~: coated with conventional enamel, all in accordance with well-known practice. In addition, conventional broiler,and heating units 58 and 60 may be positioned adjacent the upper and lower walls of the cavity 10 held by conventional fastners 62 in accordance with well-known practice. ~lowever, in the case of the heating unit 60, it preferably is formed in arcuate shape so that its closest portion is positioned around, and spaced from, the periphery of radiator 14 so as not to interfere with tlle pattern of microwave energy radiated there.~rom.
.~loments 58 and 60 extend through the back wall of cavity 10 and have the outer covering of the calrod unit grounded to the wall of cavity 10 by tabs 66 attached, for example, by welding or crimping to the calrod unit and screwed to the back wall of cavity 10 by screws 68. Tubular elements 64, ~hose 3'~4 lengths are preferably an effective quarter wavelength the microwave fre quency in cavity 10, are attached by welding to oven wall 10 and surround the calrod unit spaced therefrom by an enamel coating on element 64, Thus, microwave energy is prevented from escaping from the oven 1~ through the space between the outer surface of the elements 58 and 60 and the inner surface of tubular elements 64 due to the choking action of tubular mem-bers 64. Electrical connections to power and control terminals may be made to the calrod heater and broiler units in accordance with well-known prac-tice.
A food body 70 may be positioned, for example, on a rack 72 above radiator 14 in a dish 74 preferably transparent to microwave energy and resting on a plate 76 of material which is transparent to ~icrowave energy such as pyroceram. Rack 72 may be, for example, a welded wire rod having apertures substantially greater than ~/2 and adjustably suppo~ted at dif-ferent levels in cavity 10 by means of grooves 78 in the side walls of cav-ity lO or in any other desired manner.
Any desired configuration can be used for the radiator 14. The dimensions of the ports are substantially greater than those producing cut-off of transmission at the frequency of the microwave energy being used.
An example providing good results at 2.45 K~H using waveguides 50 which are 4 inches wide and 1 inch high, fed by a central conductor 22 which is 1/2 inch in diameter and an outer conductor 26 which is 2 inches in diameter, having lengths of 1 lnch, 3 1/4 inches, and 2 inches rom the axis of con-ductor 22 feeding ports 32 having widths o 1/2 inch, 1/4 inch, and 1 inch respectively. The waveguide 18, which may also be 4 inches wide, is shown as 2 inches high and the distances rom shorting member 44 to the center of magnetron output 48J to the axis of conductor 22, and to shorting plate 46 are 3/4 inch, 5 inches, and 10 1/4 inches respectively. ~\dditional explanation of radia~or 14 may be found in the aforementioned Teich application.
~ ir from a blower ~not shown' is blown in a conventional manner through the cooling ~ins of magne~ron 16 and then into oven 10, for example, through waveguide 18 via apertures 80 in shorting plates 46 and 44, ~ransmission line 20 and the space between outer conductor 26 and the aperture in plate 38 where the air circula~es past calrod heater 60 to conduct that air past food body 70 during cooking. The air then exits through a canister 82 at the top of the oven to the center of a surface burner unit 84.
During the oven's self-cleaning cycle with food body 70 removed, the temperature of the oven is raised to 750F -- 1,000F by energizing both calrod units 58 and 60 to vaporize deposits on the wall of oven 10 and to blow the vapor out through canister 82 which may contain a catalyst to complete oxidation of the vapor in lccordance with well-known pr~actice.
Door 12 has a hea~ seal 86, such as a tube of woven fiber-glass over a tubular woven spring steel mesh, positioned between the oven wall surface and the door surface to prevent escape of hot gas from the oven. A slotted choke structure 88 on door 12 prevents microwave energy from leaI~ing out of oven 10 around the periphery of door 12. Choke structure 88 may be of the type described in patent No. 3,767,884 by Osepchuk, et al. ~hermal insulation 90 o~, for example, ~iberglass is provided around oven 10 in a well-known manner surrounded by a metal skin 92.
A light ~4 may illuminate oven 10 through an apertured metal plate 96 cover with pyroceram 98.
This completes the description of the embodiments of the invention disclosed herein. However, many modifications thereof t~ill be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For~ example, any desired number of ports 32 can be used and means ~or rotating radiator 14 other than motor 24 could be used. AccordinglyJ it is intended that this invention be not limited to the specific embodiments disclosed herein except as defined by the appended claims.
:30
Background of the In~ention In the aforemen-tioned copending application, there i9 disclosed a combination microwave oven using a rotating radia-tor for microwave energy with provision for supplying resistance heat by heating elements positioned around -the rotating radiator. ~Iowever, such an oven was made relatively expensive by using a belted dri~e to rotate the radiator and by using an individually machined waveguide to coaxial line transition structure.
In addition, substantial radiation of energy between the rotating radiator and the adjacent wall of the oven reduced the energy radiated directly into the body to be heated.
$~ ' Summary of ~he Invention In accordance Wit}l this invention, there is provided a microwave oven which more efficiently couples microwave energy into a body to be heated with a plurality of simultaneously radiated patterns.
~ ore specifically) this combination discloses that the output of a magnetron may be impedance matched into coaxial line in a manner such that the standing wave ratio on the line may be substantially a multi-port unity. Specifically, this is achieved by forming a waveguide thorugh which the magnetron output is coupled to the coaxial line with an impedance transition of substantially conical shape formed of stamped sheet metal surrounding the central conductor of the coaxial line.
In accordance with this invention, the waveguide to coaxial line transition is spaced in waveguide from the output of said magnetron, and from the ends of said waveguide by distances greater than one half wavelength of the energy in said guide.
In addition, the outer conductor of the coaxial trans-mission line extends through the oven wall and into the plenum of a rotating radiator having a plurali~y of ports radiating ~icrowave energy into the oven in a plurality of simultaneous radiation patterns whose axes are substantially paralle~ to the axis of rotation o said radiator and whose axes are spaced at diferent distances from said axis of rotation.
In accordance with this invention, a iood body is positioned on a rack in the radiation patterns from the rotating radiator so that a substantial portion of the microwave energy is absorbed on passing through the food body first time prior to reflection from walls of the oven. Therefore, high efficiency heating may be achieved with microwave energy even though the 8~4 walls of the oven are made o inexpcnsive material such as enamelled steel.
In accordance with this invention~ the magnetron may be tightly co~pled to the oven through a coupling mechanism such as a waveguide and coaxial transi-tion thereby increasing the efficiency of conversion of input power electrical energy to microwave energy coupled into the body to be heated. More specifi-callyl in the case of light loads or if the oven is energized~ with no food body positioned therein, m~crowave energy radiation into the oven and reflect-ed back to a multi-port rotating radiator from the opposite wall such as the top wall of the oven will arrive at a common junction such as the central conductor of a coaxial line transition with substantially different phases so that relatively low amounts of energy are coupled back into the magnetron and large portions of the energy are reflected back into the oven where the energy is absorbed by the walls of the oven.
In accordance with the invention there is provided in combination:
an enclosure comprising a cavity supporting a body to be heated; a source of microwave energy; means for simultaneously radiating a plurality of different microwave energy patterns having different polarizations from said source into said cavity in directions predominantly parallel to a common axis through a multi-port radiator while rotating said ports about said axis at different dis-tances from said axis; and said radiator comprising a plenum supplied by acoaxial line whose central and outer conductors extend into said plenum.
In accordance with another aspect of the invention there is provided the method of heating a body comprising the steps o: supplying mlcrowave energy to an enclosure containing said body from a source oE microwave energy comprising coupling said source to a rotating radiator having a plurality of radiating elements positioned at different distances from an axis oE said radiator and a coaxial line whose inner conductor supports said radiator and whose outer conductor extends into said enclosure; and rotating said radiator about said axis.
Brief Description of the Drawings Other and further objects and advantages of this invention will be apparent as the description thereof progresses reference being had to the accompanylng drawings wherein:
FIG. 1 illustrates a vertlcal sectional vlew o~ a combination microwave oven embodying the inventlon taken along line 1-1 of FIG. 2;
FIG. 2 illustrates a front view of the oven illustrated in FIG. 1 with the door removed;
FIG. 3 illustrates a fragmentary transverse sect;ional view of the oven of FIG. 1 taken along line 3-3 of FIG. Z; and FIG. 4 illustrates a sectional view of the radiator lllustrated in FIG. 3 ta~en along line 4-4 of FIG. 3 ~l8~3~4 Descri~tion of the Preferred Embodiment Referring now to FIGS. 1 and 2, ~here is shown a microwave cavity 10 closed by a door 12 and supplied with microwave energy from a rotating radiator 14 in the bottom o the oven. Radiator 14 is fed with microwave energy from a magnetron 16 through a ~aveguide 18 and a coaxial line 20 having a central conductor 22 rigidly connected to rota~ing radiator 14 and extending through waveguide 18 to a gear reduction motor 24.
;lotor 24 is attached to the bottom o waveguide 18 and rotates central conductor 22 to rotate radiator 14. Coaxial line 20 has an outer conductor 26 rigidly connected to the upper wall of waveguide 18 and extending through the bottom wall of enclosure 10 into a plenum 28 in radiator 14.
As shown more specifically in ~IGS. 3 and 4, plenum 28 comprises an upper plate 30 connected to central conductor 22 and IIaving a plurality of ports 32 therein spaced at different distances at the axis of conductor 22. !licrowave energy is radiated rom plenum 28 înto the oven enclosure 10 through ports 32 which are covered by ceramic members 34 and, hence, are transparent to microwave energy and prevent dust and cooking particles from entering the plenum 28.
A lower plenum cover 38 of radiator 14, which prevents radiation of microwave energy radially outwardly and directs it through the ports 32, and the lower sur~ace o~ cover 3~ is positioned suficiently above the bottom wall o enclosure 10 or radiator 14 to rotate Ereely. An aperture in cover 38 surrounds the upper end of outer coaxial conductor 26 which thus extends slightly into plenum 28 therel~y substantially preventing micro-wave energy from radiating into enclosure 10 from beneath radiator 14. The length of outer conductor 26 which extends into plenum 28 may be adjusted to improve impedance matching conditions.
As shown in Figure 1) a substantially conical waveguide to co~
axial line transition member 40 is formed of sheet metal and attached to the bottom wall of guide 18 surrounding central conductor 22. Transi~ion 40 ex-tends from the botto~ wall upwardly along conductor 22 for distancesto an effective electrical quarter wavelength at the frequency of magnetron 16 so that it produces a choking action to energy attemyting to escape from wave-guide 18 toward motor 24. Transition 40 is spaced from the ends of the wave-guide by a distance greater than one-half the wave length of the microwave energy in the guide. A bearing 42 of dielectric material is positioned be-tween transition 40 and conductor 22 to insure against arcing in the bearing.
The ends of waveguide 18 are closed by shorting members 44 and 46 respectively which are adjusted to provide a substantially flat standing wave ratio between the output probe 48 of magnetron 16 and central conductor 22.
As shown in Figures 3 and 4, radiator ports 32 are each fed with microwave energy through separate waveguide sections S0 whose axes are at 120 to each other and whose inner ends form a common junction region con taining the central conductor 22. An impedance matching conical member 54 is connected to conductor 22 to increase its radius as it approaches upper plate 30 of plenum 28. Waveguides 50 have side walls fQrming the sides of plenum 28 and are of different lengths with the maximum length difference being on the order of ~/3 or less to that energy radiated into the plenum 28 ~rom central conductor 22 arrives at ports 32 in respectively different phases. Since the width of guides 50 is selected to be between 2/3~ and ~, the primary modo exc.lted in waveguides 50 is the T~l 0 mode; and since the ports 32 are slots extcnding across the guides 50, the radiation patterns radiated from each of the ports wi.ll have di~ferent polarizations.
.~, r Energy reflected back to the ports 32, for example, from the top wall of the microwave cavity 10 will couple into the ports 32 dependent upon the polarization and will propagate toward the common junction at central conductor 22. However~ as a result of the different distances that the waves travel, which distance differences are double the length differences of wa~e-guides 50, the waves will arrive at central conductor 22 in different phases preferably selec~ed so that substantial cancellation of the electrical field vector will ~ccur thereby causing this junction of the waveguides 50 at central conducto,r 22 to reflect such energy back through ports 32 into the cavity.
As a result, a substantial isolation of the magnetron from reflected waves occurs. Furthermore, while this ef~ect is preferably chosen to be 3naximized when the microwave cavity has no food body positioned therein and the geometry of ~he oven is fixed, substantial amounts of cancellation will occur for light loads such as small food bodies which do not absorb substantially all the microwave radiation on the first pass of the microwave energy through the food body. Under these condltions it, therefore, is possible to couple magnet.ron 16 to the oven cavity 10 as tightly as possible thereby allowing magnetron 16 to operate close to its maximum efficiency for converting its electrical energy input to microwave energy output while maintaining low microwave energy field gradien~s and, hence, low wall losses in the waveguide 18. Such a match is achieved primarily by selecting the position of the waveguide and shorting member 44 to be on t.he order of an eigh~h o a guide wavelength ~rom the axis of the output 48 of magnetron 16, so that energy radiated from antenna 48 toward shorting member 46 reflects ~oward antenna 48 in a phase adding ~o direct radiation therefrom for producillg directional radiation from antenna 48 along gu;de 18 ~o central conductor 22. Similarly, waveguide shorting member 46 is positioned to reflect energy radiated from magnetron output 48 past conductor 22 to be out of phase wi~h energy reflected by central conductor 22 toward ~agnetron output 48 and will cancel thereby assis~ing the impedance match between coaxial line 20 and waveguide 18.
As a result, the~standing wave ratio in those regions may be made close to unity, for example, being within 20 percent of unity for the majority of rotational positions of radiator 14. Therefore,~
peak voltage gradients which might occur due to resonance are avoided and high heating efficiency in the oven may be achieved.
In accordance with this invention, oven cavity 10 may be made of relati~ely lossy or energy absorbing material which may ~ absorb, for example, a few percent of microwave energy impinging ~ thereon and reflecting therefrom. Such material may be, forexample, conventional sheet stee.l used in conventional ovens and ~: coated with conventional enamel, all in accordance with well-known practice. In addition, conventional broiler,and heating units 58 and 60 may be positioned adjacent the upper and lower walls of the cavity 10 held by conventional fastners 62 in accordance with well-known practice. ~lowever, in the case of the heating unit 60, it preferably is formed in arcuate shape so that its closest portion is positioned around, and spaced from, the periphery of radiator 14 so as not to interfere with tlle pattern of microwave energy radiated there.~rom.
.~loments 58 and 60 extend through the back wall of cavity 10 and have the outer covering of the calrod unit grounded to the wall of cavity 10 by tabs 66 attached, for example, by welding or crimping to the calrod unit and screwed to the back wall of cavity 10 by screws 68. Tubular elements 64, ~hose 3'~4 lengths are preferably an effective quarter wavelength the microwave fre quency in cavity 10, are attached by welding to oven wall 10 and surround the calrod unit spaced therefrom by an enamel coating on element 64, Thus, microwave energy is prevented from escaping from the oven 1~ through the space between the outer surface of the elements 58 and 60 and the inner surface of tubular elements 64 due to the choking action of tubular mem-bers 64. Electrical connections to power and control terminals may be made to the calrod heater and broiler units in accordance with well-known prac-tice.
A food body 70 may be positioned, for example, on a rack 72 above radiator 14 in a dish 74 preferably transparent to microwave energy and resting on a plate 76 of material which is transparent to ~icrowave energy such as pyroceram. Rack 72 may be, for example, a welded wire rod having apertures substantially greater than ~/2 and adjustably suppo~ted at dif-ferent levels in cavity 10 by means of grooves 78 in the side walls of cav-ity lO or in any other desired manner.
Any desired configuration can be used for the radiator 14. The dimensions of the ports are substantially greater than those producing cut-off of transmission at the frequency of the microwave energy being used.
An example providing good results at 2.45 K~H using waveguides 50 which are 4 inches wide and 1 inch high, fed by a central conductor 22 which is 1/2 inch in diameter and an outer conductor 26 which is 2 inches in diameter, having lengths of 1 lnch, 3 1/4 inches, and 2 inches rom the axis of con-ductor 22 feeding ports 32 having widths o 1/2 inch, 1/4 inch, and 1 inch respectively. The waveguide 18, which may also be 4 inches wide, is shown as 2 inches high and the distances rom shorting member 44 to the center of magnetron output 48J to the axis of conductor 22, and to shorting plate 46 are 3/4 inch, 5 inches, and 10 1/4 inches respectively. ~\dditional explanation of radia~or 14 may be found in the aforementioned Teich application.
~ ir from a blower ~not shown' is blown in a conventional manner through the cooling ~ins of magne~ron 16 and then into oven 10, for example, through waveguide 18 via apertures 80 in shorting plates 46 and 44, ~ransmission line 20 and the space between outer conductor 26 and the aperture in plate 38 where the air circula~es past calrod heater 60 to conduct that air past food body 70 during cooking. The air then exits through a canister 82 at the top of the oven to the center of a surface burner unit 84.
During the oven's self-cleaning cycle with food body 70 removed, the temperature of the oven is raised to 750F -- 1,000F by energizing both calrod units 58 and 60 to vaporize deposits on the wall of oven 10 and to blow the vapor out through canister 82 which may contain a catalyst to complete oxidation of the vapor in lccordance with well-known pr~actice.
Door 12 has a hea~ seal 86, such as a tube of woven fiber-glass over a tubular woven spring steel mesh, positioned between the oven wall surface and the door surface to prevent escape of hot gas from the oven. A slotted choke structure 88 on door 12 prevents microwave energy from leaI~ing out of oven 10 around the periphery of door 12. Choke structure 88 may be of the type described in patent No. 3,767,884 by Osepchuk, et al. ~hermal insulation 90 o~, for example, ~iberglass is provided around oven 10 in a well-known manner surrounded by a metal skin 92.
A light ~4 may illuminate oven 10 through an apertured metal plate 96 cover with pyroceram 98.
This completes the description of the embodiments of the invention disclosed herein. However, many modifications thereof t~ill be apparent to persons skilled in the art without departing from the spirit and scope of this invention. For~ example, any desired number of ports 32 can be used and means ~or rotating radiator 14 other than motor 24 could be used. AccordinglyJ it is intended that this invention be not limited to the specific embodiments disclosed herein except as defined by the appended claims.
:30
Claims (18)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. In combination:
an enclosure comprising a cavity supporting a body to be heated;
a source of microwave energy;
means for simultaneously radiating a plurality of different microwave energy patterns having different polarizations from said source into said cavity in directions predominantly parallel to a common axis through a multi-port radiator while rotating said ports about said axis at different distances from said axis; and said radiator comprising a plenum supplied by a coaxial line whose central and outer conductors extend into said plenum.
an enclosure comprising a cavity supporting a body to be heated;
a source of microwave energy;
means for simultaneously radiating a plurality of different microwave energy patterns having different polarizations from said source into said cavity in directions predominantly parallel to a common axis through a multi-port radiator while rotating said ports about said axis at different distances from said axis; and said radiator comprising a plenum supplied by a coaxial line whose central and outer conductors extend into said plenum.
. 2. The combination in accordance with Claim 1 wherein:
said source of microwave energy comprises a magnetron coupled to a coaxial transmission line through a waveguide.
said source of microwave energy comprises a magnetron coupled to a coaxial transmission line through a waveguide.
. 3. The combination in accordance with Claim 1 wherein:
said ports have dimensions substantially greater than those producing cut-off of transmission at the frequency of said microwave energy.
said ports have dimensions substantially greater than those producing cut-off of transmission at the frequency of said microwave energy.
. 4. The combination in accordance with Claim 1 wherein:
said radiation from said ports being through solid material which is transparent to said microwave energy.
said radiation from said ports being through solid material which is transparent to said microwave energy.
. 5. A microwave oven comprising:
an enclosure comprising a cavity for supporting a body to be heated and having an access opening and a closure member;
means for simultaneously supplying a plurality of different patterns of microwave energy having different polarizations to said en-closure in directions predominantly parallel to a common axis through a multi-port rotating radiator comprising a source of microwave energy coupled to said multi-port rotating radiator;
said ports being positioned at different distances -from the axis of rotation of said radiator; and said radiator having a plenum supplied with microwave energy from said source through a coaxial line whose inner conductor supports said radiator and whose inner and outer conductors extend into said plenum.
an enclosure comprising a cavity for supporting a body to be heated and having an access opening and a closure member;
means for simultaneously supplying a plurality of different patterns of microwave energy having different polarizations to said en-closure in directions predominantly parallel to a common axis through a multi-port rotating radiator comprising a source of microwave energy coupled to said multi-port rotating radiator;
said ports being positioned at different distances -from the axis of rotation of said radiator; and said radiator having a plenum supplied with microwave energy from said source through a coaxial line whose inner conductor supports said radiator and whose inner and outer conductors extend into said plenum.
6. The microwave oven in accordance with Claim 5 wherein:
said plenum comprises waveguide sections of differing lengths extending in at least three different directions from a common junction.
said plenum comprises waveguide sections of differing lengths extending in at least three different directions from a common junction.
7. The microwave oven in accordance with Claim 6 wherein:
the outer conductor of said coaxial line extends into said plenum through the bottom of said enclosure.
the outer conductor of said coaxial line extends into said plenum through the bottom of said enclosure.
8. The microwave oven in accordance with Claim 5 wherein:
the standing wave ratio on said coaxial line is substantially the same for substantially all rotary positions of said radiator.
the standing wave ratio on said coaxial line is substantially the same for substantially all rotary positions of said radiator.
9. The microwave oven in accordance with Claim 8 wherein:
said coaxial line is coupled to a waveguide through a transition comprising a sheet metal conical member surrounding the central conductor of said coaxial line and spaced from the ends of said waveguide by a distance greater than one-half the wavelength of said microwave energy in said guide.
said coaxial line is coupled to a waveguide through a transition comprising a sheet metal conical member surrounding the central conductor of said coaxial line and spaced from the ends of said waveguide by a distance greater than one-half the wavelength of said microwave energy in said guide.
10. In combination:
an enclosure comprising a cavity for supporting a body to be heated;
a source of microwave energy;
means for simultaneously radiating a plurality of different patterns having different polarizations of microwave energy from said source into said cavity in directions predominately parallel to a common axis through a multi-port radiator while rotating said radiator about an axis positioned at different distances from said ports;
said radiator comprising a plenum supplied by a coaxial line whose central and outer conductors extend into said plenum; and electrical resistive heater means positioned in said enclosure in a region spaced from said radiating means for heating the interior of said oven and extending through the enclosure wall surrounded by choke means electrically bonded to said wall.
an enclosure comprising a cavity for supporting a body to be heated;
a source of microwave energy;
means for simultaneously radiating a plurality of different patterns having different polarizations of microwave energy from said source into said cavity in directions predominately parallel to a common axis through a multi-port radiator while rotating said radiator about an axis positioned at different distances from said ports;
said radiator comprising a plenum supplied by a coaxial line whose central and outer conductors extend into said plenum; and electrical resistive heater means positioned in said enclosure in a region spaced from said radiating means for heating the interior of said oven and extending through the enclosure wall surrounded by choke means electrically bonded to said wall.
11. The combination in accordance with Claim 10 wherein:
said source of microwave energy is a magnetron coupled to said radiator through a structure comprising a coaxial transmission line whose central conductor supports said radiator.
said source of microwave energy is a magnetron coupled to said radiator through a structure comprising a coaxial transmission line whose central conductor supports said radiator.
12. The combination in accordance with Claim 10 wherein:
said body to be heated is supported on a metal rack above said radiator with the apertures in said rack being substantially greater than those producing cut off of transmission at the frequency of said microwave energy.
said body to be heated is supported on a metal rack above said radiator with the apertures in said rack being substantially greater than those producing cut off of transmission at the frequency of said microwave energy.
13. The combination in accordance with Claim 10 wherein:
said radiator comprises a plenum supplied by a coaxial line whose central conductor is electrically connected to conductive surface of said plenum containing said ports and whose outer conductor extends into said plenum.
said radiator comprises a plenum supplied by a coaxial line whose central conductor is electrically connected to conductive surface of said plenum containing said ports and whose outer conductor extends into said plenum.
14. The combination in accordance with Claim 13 wherein:
radiation from said ports being through a solid material which is transparent to said microwave energy.
radiation from said ports being through a solid material which is transparent to said microwave energy.
15. The method of heating a body comprising the steps of:
supplying microwave energy to an enclosure containing said body from a source of microwave energy comprising coupling said source to a rotat-ing radiator having a plurality of radiating elements positioned at different distances from an axis of said radiator and a coaxial line whose inner con-ductor supports said radiator and whose outer conductor extends into said enclosure; and rotating said radiator about said axis.
supplying microwave energy to an enclosure containing said body from a source of microwave energy comprising coupling said source to a rotat-ing radiator having a plurality of radiating elements positioned at different distances from an axis of said radiator and a coaxial line whose inner con-ductor supports said radiator and whose outer conductor extends into said enclosure; and rotating said radiator about said axis.
16. The method in accordance with Claim 15 wherein:
said step of coupling said source to a rotating radiator comprises coupling said source to a plenum having ports forming said radiating elements.
said step of coupling said source to a rotating radiator comprises coupling said source to a plenum having ports forming said radiating elements.
17. The method in accordance with Claim 15 wherein:
said step of coupling said source to a rotating radiator comprises coupling the outer conductor of said coaxial line to the bottom wall of a plenum of said radiator.
said step of coupling said source to a rotating radiator comprises coupling the outer conductor of said coaxial line to the bottom wall of a plenum of said radiator.
18. The method in accordance with Claim 15 wherein:
the standing wave ratio between said source and said radiator is substantially the same for the majority of the rotary positions of said radia-tor.
the standing wave ratio between said source and said radiator is substantially the same for the majority of the rotary positions of said radia-tor.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US84786377A | 1977-11-02 | 1977-11-02 | |
| US847,863 | 1977-11-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1118844A true CA1118844A (en) | 1982-02-23 |
Family
ID=25301681
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000312734A Expired CA1118844A (en) | 1977-11-02 | 1978-10-05 | Combination microwave oven with a multi-port radiator |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPS54113549A (en) |
| AU (1) | AU520687B2 (en) |
| CA (1) | CA1118844A (en) |
| CH (1) | CH639807A5 (en) |
| DE (2) | DE2845145A1 (en) |
| FR (1) | FR2408271A1 (en) |
| GB (1) | GB2007477A (en) |
| NL (1) | NL7810707A (en) |
Families Citing this family (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CA1105567A (en) * | 1976-12-23 | 1981-07-21 | Raytheon Company | Radiating mode stirrer for microwave heating system |
| AU518080B2 (en) * | 1977-11-25 | 1981-09-10 | Raytheon Company | Primary choke system |
| CA1125378A (en) * | 1978-04-03 | 1982-06-08 | Bernard J. Weiss | Combination microwave oven control system |
| JPS55146895A (en) * | 1979-05-04 | 1980-11-15 | Matsushita Electric Ind Co Ltd | Heating cooking oven |
| US4350859A (en) * | 1980-05-05 | 1982-09-21 | Raytheon Company | Microwave oven feed system |
| DE3028078C2 (en) * | 1980-07-24 | 1988-09-08 | Bosch-Siemens Hausgeräte GmbH, 7000 Stuttgart | Microwave oven |
| DE3028352C2 (en) * | 1980-07-25 | 1982-10-14 | Bosch-Siemens Hausgeräte GmbH, 7000 Stuttgart | Microwave oven |
| AU531450B2 (en) * | 1980-08-28 | 1983-08-25 | K.K. Toshiba | High frequency heating device |
| US4430538A (en) | 1980-08-28 | 1984-02-07 | Tokyo Shibaura Denki Kabushiki Kaisha | High-frequency heating device |
| SE439092B (en) * | 1980-10-07 | 1985-05-28 | Philips Norden Ab | INPUT AND EQUIPMENT IN MICROWAVE OVEN |
| JPH07107874B2 (en) * | 1985-05-16 | 1995-11-15 | 株式会社東芝 | High frequency heating cooker |
| CA1262374A (en) * | 1985-06-24 | 1989-10-17 | Ryuji Igarashi | High-frequency heating apparatus having a rotating waveguide |
| CN107467094A (en) * | 2017-09-22 | 2017-12-15 | 长齐胜餐饮管理（深圳）有限公司 | Microwave hot air combined roasting plant and burn cured baking method |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2912554A (en) * | 1959-04-03 | 1959-11-10 | Gen Electric | Electronic oven shelf arrangement |
| JPS4837532B1 (en) * | 1969-12-01 | 1973-11-12 | ||
| US3746823A (en) * | 1972-02-28 | 1973-07-17 | L Whiteley | Electronic cooking appliance |
| SE369026B (en) * | 1973-03-07 | 1974-07-29 | Husqvarna Vapenfabriks Ab | |
| GB1543980A (en) * | 1975-05-19 | 1979-04-11 | Matsushita Electric Ind Co Ltd | Microwave heating apparatus |
| US4028521A (en) * | 1976-02-26 | 1977-06-07 | Roper Corporation | Antenna construction for microwave oven |
-
1978
- 1978-10-05 CA CA000312734A patent/CA1118844A/en not_active Expired
- 1978-10-16 AU AU40745/78A patent/AU520687B2/en not_active Expired
- 1978-10-17 DE DE19782845145 patent/DE2845145A1/en not_active Withdrawn
- 1978-10-17 DE DE19787830898 patent/DE7830898U1/en not_active Expired
- 1978-10-23 CH CH1093978A patent/CH639807A5/en not_active IP Right Cessation
- 1978-10-26 FR FR7830447A patent/FR2408271A1/en not_active Withdrawn
- 1978-10-26 NL NL7810707A patent/NL7810707A/en not_active Application Discontinuation
- 1978-11-02 JP JP13569978A patent/JPS54113549A/en active Pending
- 1978-11-02 GB GB7842976A patent/GB2007477A/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| GB2007477A (en) | 1979-05-16 |
| AU520687B2 (en) | 1982-02-18 |
| JPS54113549A (en) | 1979-09-05 |
| CH639807A5 (en) | 1983-11-30 |
| AU4074578A (en) | 1980-04-24 |
| DE7830898U1 (en) | 1980-04-10 |
| FR2408271A1 (en) | 1979-06-01 |
| DE2845145A1 (en) | 1979-05-03 |
| NL7810707A (en) | 1979-05-04 |
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| MKEX | Expiry |