Search Images Maps Play YouTube News Gmail Drive More »
Sign in
Screen reader users: click this link for accessible mode. Accessible mode has the same essential features but works better with your reader.

Patents

  1. Advanced Patent Search
Publication numberUS3810248 A
Publication typeGrant
Publication dateMay 7, 1974
Filing dateOct 12, 1971
Priority dateOct 19, 1970
Also published asDE2151655A1, DE2151655B2, DE2166290A1, DE2166290B2, DE2166290C3
Publication numberUS 3810248 A, US 3810248A, US-A-3810248, US3810248 A, US3810248A
InventorsPer Olov Risman, Lars Rosengren
Original AssigneeHusqvarna Vapenfabriks Ab
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Microwave heating apparatus
US 3810248 A
Abstract
A microwave heating apparatus is disclosed, the apparatus being provided with a treatment chamber, a microwave source, and a wave guide having a mode converter. A first section of the wave guide connected to the treatment chamber is joined to a second section connected to the microwave source and has a rectangular cross-sectional area with sides approximately equal to a and b under formation of a so-called H-bend, the first section having a cross-sectional area in the form of a rectangle with sides approximately equal to n x a and b, where n = 2, 3, 4, etc., and wherein the H-bend between two outer sides of the respective wave guide sections have a corner-plate parallel to the rectangle side b of the wave guide cross-section areas and form inside obtuse angles with the outer side. The apparatus ensures spreading and distribution of the radiation in the treatment chamber with an even intensity.
Images(2)
Previous page
Next page
Claims  available in
Description  (OCR text may contain errors)

United State sPatent 1 19 1 Ris man et al.

[451 May 7, 1974 MICROWAVE HEATING APPARATUS Primary Examiner-Joseph V. Truhe Assistant Examiner-Hugh D. Jaeger Attorney, Agent, or Firm-Holman & Stern ABSTRACT A microwave heating apparatus is disclosed, the apparatus being provided with a treatment chamber, a microwave source, and a wave guide having a mode converter. A first section of the wave guide connected to the treatment chamber is joined to a second section connected to the microwave source and has a rectangular cross-sectional area with sides approximately equal to a and b under formation of a so-called H- bend, the first section having a cross-sectional area in the form of a rectangle with sides approximately equal to n X a and b, where n 2, 3, 4, etc., and wherein the l-l-bend between two outer sides of the respective wave guide sections have a corner-plate parallel to the rectangle sideb of'the wave guide cross-section areas and form inside obtuse angles with the outer side. The apparatus ensures spreading and distribution of the radiation in the treatment chamber with an even intensity. v

7 Claims, 5 Drawing Figures [75] Inventors: PerOlov G. Risman, Vastra, Sweden; Lars O. Rosengren,

Washington, DC. [73] Assignee: Husgvarna Vapenfabriks Aktiebolag, Huskvarna, Sweden [22] Filed: Oct. 12, 1971 21 Appl. No.: 188,015

[30] Foreign Application Priority Data 00!. 19, 1970 Sweden l4061/70 [52] US. Cl. 219/1055, 333/98 BE [51] Int. Cl. 05b 9/06 1 [58] Field of Search..... 219/1055; 333/21 R, 98 BE [56] References Cited V UNITED STATES PATENTS 3,539,75'l ll/l970 Levinson 2l9/l0.55 2,814,708 1 H1957 Blass 2l9/l0.55 2,673,962 3/l954 Kock 333/98 BE 3,662,141 5/l972 Schauer.... 2l9/l0.55 2,600,566 6/1952 Moffett;...j. 2l9/l0.55 UX 2,909,635 10/1957 Haagensen 2l9/l 0.55

sum 2 or 2 PATENTEDMAY 1 m4 w a m a qd 18 FIGLI' FIG. 5'.

. 1 MICROWAVE IEATING APPARATUS BACKGROUND OF THE INVENTION The present invention relates to a microwave heating apparatus in which microwave energy is conducted from a microwave source to a microwave heating applicator by means of a waveguide, provided with a mode converter.

In microwave heating appliances the need arises-frequently for an extended heating zone in a treatment chamber, in which the article to be heated passes the zone at a specified, desirable speed. The problem arises as to how, from a relatively narrow cross sectional area in, for example, a waveguide, a spreading of the radiation with an even intensity within a large area, determined by the type of the furnace, could be obtained.

PRIoR ART it provides in a narrowoven, the greatest density of radia'tion in the center of the heating zone, since its width corresponds to approximately half the wave length of the microwaves. The result is an uneven heating of the article and, as a consequence thereof, a reduction of the maximum applicable effect. Since the greatest advantage of the microwave heating consists in the short treatment times, there is every reason to attempt to overcome the disadvantage of uneven radiation owing to the TE wave shape by the application of some other wave shape an combination of wave shapes SUMMARY OF THE INVENTION The problem is solved in accordance with the invention in that a more uniform field of radiation is achieved by means of the conversion of at least a portion of the TB wave issuing from the microwave source to waves of a higher order, for example TE By building up the radiation energy of several different wave shapes, the intensity at the outer edges of the treatment chamberbecomes appreciably higher than at radiation with only the TE wave. As a result, the treatment zones become wider and the capacity of the oven is increased. For the conversion, a converter specially designed for the purpose is used, which is very simple and effective. Its principal characteristics for fulfilling the function which leadto the improvement of the microwave oven are defined in such a way that a first section of a wave guide connected to the treatment chamber is joined to a second section connected to the microwave source and having a rectangular cross-section with sides approximativelya and b, under formation of a so-called H-bend, said first section having a crosss'ection in the form of a rectangle with sidesa'pproximatively n a and b where n 2, 3, 4cm, and that said I-I-bend between two outer sides of the respective waveguide sections has a corner-plate parallel to the rectangle side b of the waveguide cross-sections and forming inside obtuse angles with the outer sides. The

' present converter constitutes a substantial part of the microwave system used in the apparatus according to the invention and enables a quite unique type'of applicator.

An example of the realization of a microwave heating appliance provided with a waveguide and modeconverter and an applicator connected thereto, all in accordance with the invention, is described in the following with reference to the enclosed drawings, in

which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing such an appliance in a combination oven-hotplate or surface unit,

FIG. 2 is a detailed view of a waveguide switch used in the appliance according to FIG. 1,

FIG. 3 is a cross-section of a vessel with a base, constituting an absorber, intended to be used on a cooking plate according to FIG. 1,

FIG. 4 shows in a horizontal projection a waveguide with a mode-converter and FIG. 5 shows a vertical projection of the waveguide.

DETAILED DESCRIPTIONVOF THE INVENTION,

The appliance shown in FIG. l'can be used for the warming up of an article in an oven 1 as well as for cooking and roasting in pot or like receptacle on a plate or surface unit 2. The oven has atight-closing door 3 on the frontside and is suitable for being placed on a kitchen range or for being built into a cupboard. The cookingplate is fixedto one side of the oven and has a panel equipped with control knobs 4 and indicator lamps 5. The plate and the oven each form the base for a microwave applicator or radiation surface 6 and re spectively. This is defined as a device which, without being heated itself by the microwaves incident on it from generators, conducts and modifies the field pattern, so that the same is made suitable for absorption by the object or objects which are to be treated by microwaves. A waveguide system conducts the radiation from a magnetron 8 to the respective applicator. The magnetron has an aerial 9 which is located in the end of a main waveguide 10 which is provided with a waveguide switch 11 from which issues a branch waveguide 12. The waveguide switch, which is shown :in FIG. 2,

has a rotary handle 13 which is accessible from the outside and which is used to change over a pivotable plate 14 between a position oblique to the branch conductor and a position parallel with the main conductor. In the first named position, the radiation from the magnetron is reflected into the branch conductor and in the second position the radiation continues in the mainguide. Behind the oven chamber is an apparatus chamber The two waveguides are each by itself provided with mode converters. Such a converter consists for example of a waveguide with a waveguide passage in form of a corner, for example as formed by the main waveguide 10 and a waveguide tube 15 at an angle to the same. The main waveguide according to FIG. 1 is designed as a TE -waveguide and conducts the TE waves emitted by the magnetron to the waveguide corner. This comprises the connection of the tube 15 at an angle with the main guide 10 as well as a corner plate 16 between two outer sides 17, 18 of the respective tubes. The cross-section of the tube 15 defines a rectangle with a long side of approximatelydouble the length of the corobtuse angle'therewith. The plate reflects the TB waves incident from the main guide into the tube with simultaneous conversion of a part of the TE waves to TE waves. The combined radiation of TE and 'TE type, which is obtained in the normal manner by squaring and halving of the amplitude values, is thus sectional area in different parts, than is the case in a pure TE Waveguide.

The converter shown in FIG. 4 constitutes a simple example of how a wave type can be converted, while the principle also comprises multiple and complex con- .vers'ions of thistyp'e. lf, for example, several of the waveguide passages now described arecoupled behind one another, or if a specially wide tube replaces the tube 15, it can be stated in advance that the radiation issuing will include wave shapes TE TE TE wherein, however, certain terms may dominate while others will be wholly excluded. 7

The construction of the converter shown is very simple to realize, since the sides of the waveguides are made up of edge-flanged sheetsand even the corner plate 16 can be made of such sheet, which means that the converter is built only of elements generally used for waveguides. It is also possible to arrange in the waveguide tube a control element for the propagation of the waves; thus two parallel slots 15a are present in the tube 15 on both sides about the central plane. In these slots which are in the proximity of the amplitudes of the TE' -wave so-calledchokes could be arranged,

the size and position of which are such that the characteristic of the waveguide for TE waves is improved.

The tube 15 has on the topside the radiation surface 6 surrounded by a ring or frame 19 and provided with a number of slots 20 in the wall of the tube. As the end ,of tube 21 is closed by a plate 22, the microwave radiation issues through the slots. On top of the radiation surface, suitably fixed on the ring, is placed the load,

that is to say a pot or vessel with an absorber. Such a pot is shown in detail in FIG. 3. The pot is made of metal and is provided with a lid and a handle as well with a collar 23 in the lower portion which fits against the ring 19 when the pot is placed on the radiation surface. Through this the radiation is screened effectively from the surroundings. The base in the pot has two layers, a metal layer 24 and an absorption layer 25.-The metal layer may be very thin and serves on the one hand as a radiation protection in the pot and on the other hand as a roasting surface for the object in the pot. The absorption layer is formed by an active material, for example Fe O or NiFe O coal or a similar material, together with a binder and is placed directly on the metal layer. The two layers are therefore thermally very well attached and the energy taken up in the absorption layer is conducted with very small losses to the metal layer. The two layers have a low heat capacity and therefore heat up quickly when the absorber is exposed to radiation. On the other hand, the base of the vessel will cool down with appreciable delay when the radiation stops. Through this the advantage is obtained, that the cooking intensity, roasting temperature etc. in the pot react directly to a variation in the power supply, which considerably simplifies the setting of the power control when a specified intensity is required. Due to this radiation-protecting metal layer in the pot the same can be used without risk, even when the lid is removed.

The waveguide 12 present in the bottom of the oven together with mode converters is realized in principle similarly to those just described, except that a waveguide section 26 with a width approximately three times the width of the branch waveguide 12 is used. By means of the mode conversions, a portion of the TE wave will here be converted to both TE and TE waves. Thus the radiation surface 7 on this waveguide section can be made larger than the corresponding surface on the waveguide tube 15. The surface 7 is surrounded by a ring 27 and in this is fitted a round absorption plate similar to the one which forms the base of the pot according to FIG. 3. As the oven forms a closed space, no extra radiation protection is required, so that the metal layer on the absorption layer can be excluded on this absorption plate. As a result, the effect alluded to in the introduction is achieved, namely that an article on the plate is warmed up partly through contact pressure on the plate and, partly through microwave radiation which passes through the plate and has an effect on the article. Through the variation of the absorption capacity of the plate, for example with the help of the thickness, it is possible to alter the ratio of transmitted to absorbed radiation effect. A dish can thus be roasted on the surface by the heat which has been absorbed and is given off by the plate, at the same time as the microwave radiation warms the dish homogeneously right through. In this way a considerable amount of time is saved in the preparation without the dish being deprived of the desirable browned surface. Such a preparation which comprises both roasting and microwave heating may also be carried out in a pot such as that shown in FIG. 3, in which, however, the radiation-protecting metal layer 24 has been excluded.

In such a case, however, another radiation-protecting means must be arranged at the top of the pot, for example a lid, which is so equipped that it cannot be removed when the microwave power is switched on. The use of a pot for the preparation has naturally also the advantage that it can easily be removed and cleaned in the normal washing; this solves a considerable problem of hygiene in microwave ovens in general.

The principle of roasting and heating at the same time is in a wider sense also applicable to baking. The baking molds may, for example, be provided with an absorbing layer, which brings about that the mold remains warm so that a crust is formed on its contents, at the same time as a part of the radiation penetrates into the side of the molds and rapid-bakes" the contents.

A combination of oven and cooking plate according to the embodiment shown has the advantage that the scope of application for microwave heating is widened. Furthermore, the expensiveelectronic equipment can be used jointly for oven and plate; It is not to be regarded as essential, however, for the realization of the invention that this combination exists; a microwave heating appliance with an absorber may comprise only a cooking plate, only an oven, or either built into a conventional cooker.

The combination shown and described is thus only a preferred embodiment and should be regarded as one example of the application of the invention. This embodiment represents a basic form of the subject of the invention to which may be added further supplementary devices. Such devices consist, for example, of a temperature protection built into the absorber, which is coupled to a safety switch, which breaks the microwave power when the temperature on the absorber becomes too high. The invention in its entirety is defined in the following claims.

What is claimed is:

l. A microwave heating apparatus'including treatment means, a microwave source connected to a wave guide having a mode converter, said wave guide being provided with first and second sections, said first section having a width ofa and a height of b, said second section having a width equal to n'a' in which n 2,3,4, etc. and a height equal to b, said first section being connected to the microwave source, said second section being connected to said treatment means, said first section being joined to said second section by an- H-bend forming inside obtuse angles between the outer b sides of said first and second sections.

2. The apparatus as claimed in claim 1 in which one of said sides having dimension a of said first section is provided with an aerial inlet to which the microwave source is connected.

3. The apparatus as claimed in claim 1 in which the second section includes an applicator provided with slots through which microwave energy radiates.

4. The apparatus as claimed in claim 3 in which said applicator is arranged on a side dimensioned n'aand is defined by a number of slots therein.

5. The apparatus as claimed in claim 4 further including vessel means including a plate means having a high coefficient of microwave absorption converting microwave energy to thermal energy, and an external holder detachably fitting the vessel means.

6. The apparatus as claimed in claim 5 in which the plate means includes a layer of a high coefficient of microwave absorption.

7. The apparatus as claimed in claim 1 further including a branch section connected to said first section to extend at right angles thereto, said branch section having a width of a and a height of b, said branch section being connected to a further-section having a width approximately three times the width of the branch section, and a height of b, said further section being joined to said branch section by an l-l-bend forming inside obtuse angles between the outer b sides of said branch and said further section, and a switching means at the connection between the branch section and first section movable between a position oblique to the first section and a position parallel with the first section for directing radiation from said microwave source into the branch section and into the first section respectively.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2576862 *Jun 11, 1946Nov 27, 1951Electronic Chemical EngineerinMethod and apparatus for preserving foodstuffs
US2600566 *Nov 23, 1949Jun 17, 1952Moffett Jr Frank WesleyMethod of heating frozen food packages
US2673962 *Jan 18, 1949Mar 30, 1954Bell Telephone Labor IncMode suppression in curved waveguide bends
US2814708 *Jan 5, 1952Nov 26, 1957Raytheon Mfg CoMicrowave ovens
US2909635 *Jul 29, 1957Oct 20, 1959Raytheon CoElectronic oven systems
US3539751 *Oct 26, 1966Nov 10, 1970Levinson Melvin LInsulating implement for use in a microwave oven
US3662141 *Jun 6, 1968May 9, 1972Gen Motors CorpOven shelf adapted to absorb microwave energy and conduct heat to a load
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US4019009 *Feb 6, 1975Apr 19, 1977Matsushita Electric Industrial Co., Ltd.Microwave heating apparatus
US4121078 *Apr 27, 1976Oct 17, 1978Matsushita Electric Industrial Co., Ltd.Microwave heating apparatus
US4198555 *Jan 9, 1978Apr 15, 1980De Pruines Iseco S. A.Cabinet for storing prepared meals on individual trays
US4329557 *Dec 7, 1979May 11, 1982General Electric CompanyMicrowave oven with improved energy distribution
US4354083 *Nov 5, 1980Oct 12, 1982General Electric CompanyMicrowave oven with novel energy distribution arrangement
US4458126 *Mar 30, 1982Jul 3, 1984General Electric CompanyMicrowave oven with dual feed excitation system
US4463239 *Dec 6, 1982Jul 31, 1984General Electric CompanyRotating slot antenna arrangement for microwave oven
US4464554 *Aug 25, 1982Aug 7, 1984General Electric CompanyDynamic bottom feed for microwave ovens
US4695693 *Oct 2, 1986Sep 22, 1987General Electric CompanyTriangular antenna array for microwave oven
US5166487 *Dec 15, 1989Nov 24, 1992Tecogen, Inc.Cooking oven with convection and microwave heating
US5451751 *Jan 22, 1993Sep 19, 1995Kabushiki Kaisha ToshibaHigh-frequency heating apparatus with wave guide switching means and selective power switching means for magnetron
US5874706 *Sep 24, 1997Feb 23, 1999Tokyo Electron LimitedMicrowave plasma processing apparatus using a hybrid microwave having two different modes of oscillation or branched microwaves forming a concentric electric field
US5874715 *Jul 30, 1997Feb 23, 1999Lg Electronics Inc.Heating apparatus in the form of an antenna array plate for a microwave oven
US5990466 *Apr 2, 1998Nov 23, 1999Turbochef Technologies, Inc.Apparatus for supplying microwave energy to a cavity
US6008483 *Oct 9, 1998Dec 28, 1999Turbochef Technologies, Inc.Apparatus for supplying microwave energy to a cavity
US6607920Jan 31, 2001Aug 19, 2003Cem CorporationAttenuator system for microwave-assisted chemical synthesis
US6649889May 23, 2002Nov 18, 2003Cem CorporationMicrowave-assisted chemical synthesis instrument with fixed tuning
US6713739Dec 13, 2002Mar 30, 2004Cem CorporationMicrowave-assisted chemical synthesis instrument with fixed tuning
US6753517Jan 31, 2001Jun 22, 2004Cem CorporationMicrowave-assisted chemical synthesis instrument with fixed tuning
US6886408Jan 31, 2001May 3, 2005Cem CorporationPressure measurement in microwave-assisted chemical synthesis
US6960747 *Nov 7, 2002Nov 1, 2005Personal Chemistry I Uppsala AbMicrowave applicator system
US6966226Jun 8, 2004Nov 22, 2005Cem CorporationPressure measurement in microwave-assisted chemical synthesis
US7092988Apr 30, 2001Aug 15, 2006Jeffrey BogatinRapid cooking oven with broadband communication capability to increase ease of use
US7144739Nov 26, 2002Dec 5, 2006Cem CorporationPressure measurement and relief for microwave-assisted chemical reactions
US7208709May 12, 2005Apr 24, 2007Cem CorporationPressure measurement in microwave-assisted chemical synthesis
US7493362Jul 13, 2006Feb 17, 2009Turbochef Technologies, Inc.Rapid cooking oven with broadband communication capability to increase ease of use
US8224892Dec 24, 2008Jul 17, 2012Turbochef Technologies, Inc.Rapid cooking oven with broadband communication capability to increase ease of use
US9282594Dec 12, 2011Mar 8, 2016Eastman Chemical CompanyWood heater with enhanced microwave launching system
US9456473Dec 12, 2011Sep 27, 2016Eastman Chemical CompanyDual vessel chemical modification and heating of wood with optional vapor
US20040101441 *Nov 26, 2002May 27, 2004Cem CorporationPressure measurement and relief for microwave-assisted chemical reactions
US20040221654 *Jun 8, 2004Nov 11, 2004Jennings William EdwardPressure measurement in microwave-assisted chemical synthesis
US20050210987 *May 12, 2005Sep 29, 2005Jennings William EPressure measurement in microwave-assisted chemical synthesis
DE3310703A1 *Mar 24, 1983Oct 13, 1983Gen ElectricMikrowellenkochgeraet
EP0037643A1 *Mar 12, 1981Oct 14, 1981THORN EMI Domestic Appliances LimitedImprovements in microwave cookers
WO2003040630A2 *Nov 5, 2002May 15, 2003Personal Chemistry I Uppsala AbMicrowave applicator system
WO2003040630A3 *Nov 5, 2002Dec 4, 2003Personal Chemistry I UppsalaMicrowave applicator system
Classifications
U.S. Classification219/746, 219/730, 219/759, 219/750, 333/249
International ClassificationH05B6/64, H05B6/80, H05B6/70
Cooperative ClassificationH05B6/80, H05B6/708
European ClassificationH05B6/70W1, H05B6/80