US3872276A - Including a semiresonant slotted mode stirrer - Google Patents

Including a semiresonant slotted mode stirrer Download PDF

Info

Publication number
US3872276A
US3872276A US339539A US33953973A US3872276A US 3872276 A US3872276 A US 3872276A US 339539 A US339539 A US 339539A US 33953973 A US33953973 A US 33953973A US 3872276 A US3872276 A US 3872276A
Authority
US
United States
Prior art keywords
disc
oven
cavity
energy
plane
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 - Lifetime
Application number
US339539A
Other languages
English (en)
Inventor
Richard P Corcoran
Alfred E Hirtler
Robert F Mittel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Philips North America LLC
US Philips Corp
Original Assignee
US Philips Corp
Priority date (The priority date 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 date listed.)
Filing date
Publication date
Application filed by US Philips Corp filed Critical US Philips Corp
Priority to US339539A priority Critical patent/US3872276A/en
Priority to DE19742409199 priority patent/DE2409199C3/de
Priority to GB888974A priority patent/GB1463826A/en
Priority to SE7402971A priority patent/SE387216B/xx
Priority to CA194,234A priority patent/CA996638A/en
Priority to JP49026133A priority patent/JPS5219331B2/ja
Priority to FR7407932A priority patent/FR2220959B1/fr
Application granted granted Critical
Publication of US3872276A publication Critical patent/US3872276A/en
Anticipated expiration legal-status Critical
Expired - Lifetime legal-status Critical Current

Links

Images

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
    • H05B6/74—Mode transformers or mode stirrers

Definitions

  • the disc is rotated so that the segments pass by the microwave energy coupling aperture for the oven.
  • the oven combination produces a more uniform microwave energy distribution within the oven cavity and also improves the matching of the microwave generator to the cavity load so that the generator operates in the load region most suitable to the application.
  • This invention relates to a microwave oven and more particularly to a microwave oven having an improved field stirrer which produces a more uniform distribution of microwave energy within the oven enclosure.
  • microwave energy can be used successfully for heating or cooking various dielectric materials, especially for cooking foodstuffs in a rapid and economical manner.
  • the amount of heat developed in the work material is a function of the intensity and frequency of the electromagnetic field and the electrical properties of the material.
  • a suitably dimensioned closed metal cavity into which microwave energy can be introduced makes a good microwave oven.
  • Microwave energy coupled into the cavity produces a pattern of standing waves.
  • a problem inherent in this type of oven is that the intensity of the electric field is not constant throughout the cavity. This may give rise to an unequal distribution of heat'within the work material.
  • the cavity can be dimensioned for a so-called multi-mode operation and the field patterns within the cavity can be periodically shifted in position so that a more uniform distribution of heat is achieved in the work material. If the cavity is properly dimensioned, a small change in the microwave generator frequency cancause a changeover to a different mode or field pattern in the cavity. A change in the shape of the cavity, or a change in boundary effects, also can be used to switch modes in the cavity.
  • the stirrer is generally a propeller type fan having a plurality of radially disposed metal fan blades which are rotated by a motor.
  • the stirrer fan is mounted within the oven cavity so as to intercept a substantial portion of the microwave energy radiated from the generator and to deflect the energy impinging upon the fan blades towards the oven load.
  • the blade rotation influences the generator frequency and also changes the mode pattern within the cavity by changing the boundary effects.
  • One such field stirrer is described in US. Pat. No. 2,8l3,l85. Although the use of known field stirrers improves the en ergy distribution'within the cavity, there is still room for further improvement, especially in ovens designed to accomodate a wide variety of load materials and of widely varying shape and size.
  • Another object of the invention is to provide a new and improved form of field stirrer for use in a microwave oven to produce a more uniform distribution of the electromagnetic energy in the oven cavity.
  • a further object of the invention is to provide a microwave oven with a field stirrer that can be readily adjusted to match a wide variety of oven loads.
  • the microwave oven of the subject invention includes a novel field stirrer arrangement that comprises a circular sheet metal disc having a plurality of radially extending slots arranged around its periphery. The ends of the segments formed by the slots can be bent at the same or different angles.
  • the disc is mounted directly on a revolving metal or dielectric shaft or by means of dielectric spacers on a revolving shaft so that the segments pass in front of a coupling aperture in the oven by means of which the microwave energy is introduced into the oven cavity.
  • the bent ends of the segments formed by the slots reflect the microwave energy coming from said aperture at different angles depending upon the degree of bend in the different segments.
  • the angle of bend also is used to perform a secondary function in that it influences the matching of the microwave generator, for example, a magnetron; to the load, i.e. the microwave oven cavity.
  • the slots in the disc also serve a dual function in that when cut to the proper depth, the slots and the segments produced thereby form semiresonant elements which couple to the microwave fields in the cavity and reradiate some ofthe energy in various directions in the oven cavity.
  • the slots, or semiresonant elements are analagous to short circuited sections of two wire transmission lines in which the metal surrounding the slot constitutes the inductance and the opposite walls of the slots act as the plates of a capacitor. Surface currents are induced in the metal disc which causes coupling between the various slots.
  • the rotating stirrer interacts with fields of different frequencies to a greater or lesser extent. The rotating stirrer thus provides an active function because of the direct interaction of the fields and the semiresonant elements.
  • the slots and the segments formed thereby also affect the matching of the microwave generator to the load. Since the disc is made of sheet metal, it is possible to readily adjust or vary the number of slots, the width and the depth of the slots, the angle of bend in the ends of the segments, the position ofthe stirrer, etc. so that the microwave generator can be made to operate in the most advantageous region (sink region) of its load (Reike) diagram, thus producing the greatest overall efficiency of operation for the entire microwave oven system. Alternately, the microwave generator may be operated away from the sink region to gain additional stability of operation in those applications where the generator is consistently lightly loaded.
  • the distribution of microwave energy to the load obtained with the oven of the present invention has been found to be substantially uniform.
  • the stirrer used herein also serves to excite several modes in the oven. By periodically changing the field distribution or mode pattern inside the oven, the energy distribution is made uniform throughout the oven thereby producing uni form heating in all parts of the oven.
  • FIG. 1 illustrates a sectional view of a preferred embodiment of a microwave oven according to the invention
  • FIGS. 2 and 3 together illustrate the details of the new and improved field stirrer construction
  • FIGS. 4A-7D are sectional view of the field stirrer of FIG. 2,
  • FIG. shows a portion of a second embodiment of the field stirrer
  • FIGS. 6A and 6B are sectional views of the stirrer of FIG. 5 that help to illustrate the construction thereof.
  • a hollow rectangular thin walled metallic enclosure or cavity 1 is adapted to serve as a microwave oven for heating or cooking foodstuffs, or the like.
  • the dimensions of the oven are preferably large compared with the wavelength of the microwave energy supplied by a magnetron 2 to the oven cavity.
  • the microwave energy generated by the magnetron is coupled into the oven cavity by means of a waveguide section 3 and a rectangular or other suitable coupling aperture 4 formed ina metal wall 5.
  • the microwave energy is supplied to the oven cavity through the back wall 6 of the oven.
  • a shelf 7 is secured to the oven walls and is located near the bottom'wall 8 of the oven.
  • the shelf is made of any material that is transparent or semi-transparent to microwave energy and is adapted to support a heating load 9, e.g., an article of food to be cooked.
  • the shelf may be partially composed of a lossy dielectric material to insure that the cavity has some load in the event that the oven is operated without its normal load. This serves to protect the magnetron from damage due to excessive amounts of reflected microwave energy.
  • an opening 10 is provided in the front wall 11 of the oven.
  • the opening 10 is covered by a hinged metal door 12 having means, not shown, for sealing the opening against the leakage of microwave energy when the door is closed. When the door is closed, the oven cavity is entirely closed except for the coupling aperture 4 through which the-microwave heating energy enters the cavity.
  • Theshaft 14 is mounted for rotationin a bearing 15 secured in the top wall 16 of the oven.
  • the shaft and stirrer are rotated by .means of a motor 17 to which the shaft is coupled.
  • the shaft and stirrer are preferably symmetrically located in the top wall 16 of the oven. As the stirrer is rotated by the motor the end segments or fins pass in front of the coupling aperture 4 to provide the above described desirable"stirring action on the microwave field within the oven cavity.
  • the stirrer 13 is a thin circular sheet metal disc having a plurality of-radially extending'slots l8 symmetrically arranged about the periphery of the disc to form a plurality of segments 19.
  • the ends 20 of the segments can all be bent up or down at the same angle.
  • the fins or segment ends 20 are bent at different angles. In one embodiment of to bend all of the fins downward at the same angle or at different angles. It is furthermore possible to bend some ofthe fins up and others down. This feature of the invention is best illustrated in FIGS. 5 and 6 wherein the end segment 20,, is bent up and the end segment 20,, is bent down.
  • the optimum configuration of the fins will vary with the dimensions and shape of the various oven cavities. Since the stirrer is made of a thin sheet metal, the best configuration of the fins can be readily adjusted by test or service personnel for each individual oven.
  • the height of the shaft 14 (FIG. 1) also can be adjusted to provide optimum performance of any given oven cavity.
  • the slots and segments form semireso nant elements to which some of the energy from the microwave generator couples directly, as well as coupling to fields in the oven cavity. This coupled energy is then reradiated from the rotating stirrer which acts as a moving virtual source to improve the energy distribution in the oven cavity.
  • the invention provides a large degree ofdesign flexibility for the designer of microwave ovens.
  • the invention produces a more uniform energy distribution pattern in the oven cavity and improves the matching of the microwave generator to the cavity load.
  • the novel stirrer makes it possible to load the magnetron tube near its sink region, a very desirable feature from the viewpoint of overall system efficiencyv
  • One embodiment of the invention which was tested and found to produce good overall results had the following approximate dimensions.
  • the diameter of the stirrer disc was 13 inches and it was 0.04 inches thick.
  • the radial distance from the center of the disc to the interior end ofthe slot was 2 inches and to the fin it was 5 inches.
  • the slot was 3 4 inches long and 4 inch wide.
  • the shaft 14 extended 4 of an inch down from the top wall 16 of the oven.
  • the oven was l4 inches high, 15 inches deep and 16 inches wide.
  • the coupling aperture was a rectangular opening 1 inch by 4 inches symmetrically located at the top of the back wall and equally distant from the ovenside walls.
  • the waveguide section was 2 inches high, 4 inches wide and 6 inches long.
  • a microwave oven comprising a substantially closed metallic cavity adapted to hold an energy absorbing load, an aperture in a wall of said oven for cou pling microwaveenergy into the oven cavity, means for generating and coupling microwave energy to said aperture, a field' stirrer rotatably mounted in the cavity and comprising a thin metal disc having a plurality of radial slots arranged about its periphery to form a plurality of segments with the outer ends of at least some of said segments being bent out of the plane of the disc whereby said slots and-se gments form semiresonant elements which couple to the R.F. fields in the oven and reradiate the energy in various'directions, and means ,for rotating said disc so that the bent ends pass near i 4.
  • a mircowave oven as claimed in claim 2 wherein the bending angle of the end segments varies progressively about the disc periphery.
  • a microwave oven as claimed in claim 1 wherein said aperture is located in a side wall of the cavity near the top wall and said stirrer is mounted on a vertical shaft extending from said cavity top wall.
  • a microwave oven comprising a substantially closed metallic cavity adapted to hold an energy absorbing load, means for supplying microwave energy into the oven cavity, a field stirrer rotatably mounted within the cavity and comprising a thin metal circular disc having a plurality of radial slots therein to form rainteract. with the energy supplied to the oven cavity thereby to produce a cyclically repetitive distribution of energy within the cavity which is substantially uniform in the region of the cavity to be occupied by the load.
  • a microwave oven as claimed in claim 9 wherein said fins are uniformly disposed about the disc periphery and at least some of which are inclined at different angles to the plane of the disc.
  • a microwave oven comprising a substantially closed metallic cavity adapted to hold an energy absorbing load, means for supplying microwave energy into the oven cavity, a field stirrer rotatably mounted in the cavity and comprising a thin metal circular disc having a plurality of radial slots symmetrically arranged about its periphery to form a plurality of segmentswith the outer ends of at least some of said segments being bent out ofthe plane of the disc, said slots being dimensioned so as to form semiresonant elements to which energy from said energy supplying means is coupled directly and then is reradiated to the oven cavity, and means for rotating said disc so as to intercept and interact with the energy from said energy supplying means and the energy within the fields in the oven cavity thereby to improve the energy distribution within said I the same angle to the plane of the disc.

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Constitution Of High-Frequency Heating (AREA)
  • Electric Ovens (AREA)
US339539A 1973-03-09 1973-03-09 Including a semiresonant slotted mode stirrer Expired - Lifetime US3872276A (en)

Priority Applications (7)

Application Number Priority Date Filing Date Title
US339539A US3872276A (en) 1973-03-09 1973-03-09 Including a semiresonant slotted mode stirrer
DE19742409199 DE2409199C3 (de) 1973-03-09 1974-02-26 Mikrowellenherd
GB888974A GB1463826A (en) 1973-03-09 1974-02-27 Microwave oven
SE7402971A SE387216B (sv) 1973-03-09 1974-03-06 Mikrovagsugn med en feltomrorare, som innefattar en tunn metallskiva med ett flertal radiella spar
CA194,234A CA996638A (en) 1973-03-09 1974-03-06 Microwave oven field stirrer
JP49026133A JPS5219331B2 (enrdf_load_stackoverflow) 1973-03-09 1974-03-06
FR7407932A FR2220959B1 (enrdf_load_stackoverflow) 1973-03-09 1974-03-08

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US339539A US3872276A (en) 1973-03-09 1973-03-09 Including a semiresonant slotted mode stirrer

Publications (1)

Publication Number Publication Date
US3872276A true US3872276A (en) 1975-03-18

Family

ID=23329496

Family Applications (1)

Application Number Title Priority Date Filing Date
US339539A Expired - Lifetime US3872276A (en) 1973-03-09 1973-03-09 Including a semiresonant slotted mode stirrer

Country Status (6)

Country Link
US (1) US3872276A (enrdf_load_stackoverflow)
JP (1) JPS5219331B2 (enrdf_load_stackoverflow)
CA (1) CA996638A (enrdf_load_stackoverflow)
FR (1) FR2220959B1 (enrdf_load_stackoverflow)
GB (1) GB1463826A (enrdf_load_stackoverflow)
SE (1) SE387216B (enrdf_load_stackoverflow)

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3993886A (en) * 1974-08-30 1976-11-23 U.S. Philips Corporation Supply wave guide system in microwave ovens
US4092513A (en) * 1977-01-31 1978-05-30 Litton Systems, Inc. Stirrer hub assembly
US4327266A (en) * 1980-09-12 1982-04-27 Amana Refrigeration, Inc. Microwave ovens for uniform heating
US4342896A (en) * 1976-12-23 1982-08-03 Raytheon Company Radiating mode stirrer heating system
US4410779A (en) * 1978-04-03 1983-10-18 Raytheon Company Combination microwave oven control system
US4429204A (en) 1981-06-19 1984-01-31 Whirlpool Corporation Bushing mounted stirrer shaft
US4463239A (en) * 1982-12-06 1984-07-31 General Electric Company Rotating slot antenna arrangement for microwave oven
US4642435A (en) * 1985-12-26 1987-02-10 General Electric Company Rotating slot antenna arrangement for microwave oven
US6614011B2 (en) * 1999-12-07 2003-09-02 Sanyo Electric Co., Ltd. Microwave oven including antenna for properly propagating microwaves oscillated by magnetron
US20060101794A1 (en) * 2004-11-12 2006-05-18 Gregoire Daniel J Diesel particulate filter system with meta-surface cavity
US20060102621A1 (en) * 2004-11-12 2006-05-18 Daniel Gregoire Meta-surface waveguide for uniform microwave heating
US20090095749A1 (en) * 2007-10-15 2009-04-16 E. I. Du Pont De Nemours And Company Microwave Field Director Structure Having Metal Vanes
US20090095743A1 (en) * 2007-10-15 2009-04-16 E. I. Du Pont De Nemours And Company Molded Microwave Field Director Structure
US20090095748A1 (en) * 2007-10-15 2009-04-16 E. I. Du Pont De Nemours And Company Microwave Field Director Structure Having V-Shaped Vane Doublets
US20090095745A1 (en) * 2007-10-15 2009-04-16 E. I. Du Pont De Nemours And Company Microwave Field Director Structure Having Vanes With Inner Ends Wrapped With A Conductive Wrapper
US20130126521A1 (en) * 2007-10-15 2013-05-23 E I Du Pont De Nemours And Company Microwave field director structure with vanes having a conductive material thereon
CN108180515A (zh) * 2017-12-29 2018-06-19 广东美的厨房电器制造有限公司 微波加热器具

Families Citing this family (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4430538A (en) 1980-08-28 1984-02-07 Tokyo Shibaura Denki Kabushiki Kaisha High-frequency heating device
AU531450B2 (en) * 1980-08-28 1983-08-25 K.K. Toshiba High frequency heating device
JPS57189493A (en) * 1981-05-15 1982-11-20 Matsushita Electric Ind Co Ltd High frequency heater
EP2230882B1 (en) 2009-03-19 2015-06-17 Topinox Sarl Microwave cooking appliance and method of operating it

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3626136A (en) * 1969-05-14 1971-12-07 Sanyo Electric Co High-frequency heating apparatus
US3716687A (en) * 1970-08-18 1973-02-13 Hirst Microwave Ind Ltd Method and apparatus for cooking

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2920174A (en) * 1957-06-28 1960-01-05 Raytheon Co Microwave ovens
US3526737A (en) * 1967-03-20 1970-09-01 Varian Associates Microwave heating apparatus

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3626136A (en) * 1969-05-14 1971-12-07 Sanyo Electric Co High-frequency heating apparatus
US3716687A (en) * 1970-08-18 1973-02-13 Hirst Microwave Ind Ltd Method and apparatus for cooking

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3993886A (en) * 1974-08-30 1976-11-23 U.S. Philips Corporation Supply wave guide system in microwave ovens
US4342896A (en) * 1976-12-23 1982-08-03 Raytheon Company Radiating mode stirrer heating system
US4092513A (en) * 1977-01-31 1978-05-30 Litton Systems, Inc. Stirrer hub assembly
US4410779A (en) * 1978-04-03 1983-10-18 Raytheon Company Combination microwave oven control system
US4327266A (en) * 1980-09-12 1982-04-27 Amana Refrigeration, Inc. Microwave ovens for uniform heating
US4429204A (en) 1981-06-19 1984-01-31 Whirlpool Corporation Bushing mounted stirrer shaft
US4463239A (en) * 1982-12-06 1984-07-31 General Electric Company Rotating slot antenna arrangement for microwave oven
US4642435A (en) * 1985-12-26 1987-02-10 General Electric Company Rotating slot antenna arrangement for microwave oven
US6614011B2 (en) * 1999-12-07 2003-09-02 Sanyo Electric Co., Ltd. Microwave oven including antenna for properly propagating microwaves oscillated by magnetron
GB2359972B (en) * 1999-12-07 2005-03-02 Sanyo Electric Co Microwave oven including antenna for properly propagating microwaves oscillated by magnetron
US7091457B2 (en) * 2004-11-12 2006-08-15 Hrl Laboratories, Llc Meta-surface waveguide for uniform microwave heating
US20060102621A1 (en) * 2004-11-12 2006-05-18 Daniel Gregoire Meta-surface waveguide for uniform microwave heating
US20060101794A1 (en) * 2004-11-12 2006-05-18 Gregoire Daniel J Diesel particulate filter system with meta-surface cavity
US7303603B2 (en) 2004-11-12 2007-12-04 General Motors Corporation Diesel particulate filter system with meta-surface cavity
US20090095745A1 (en) * 2007-10-15 2009-04-16 E. I. Du Pont De Nemours And Company Microwave Field Director Structure Having Vanes With Inner Ends Wrapped With A Conductive Wrapper
US20090095743A1 (en) * 2007-10-15 2009-04-16 E. I. Du Pont De Nemours And Company Molded Microwave Field Director Structure
US20090095748A1 (en) * 2007-10-15 2009-04-16 E. I. Du Pont De Nemours And Company Microwave Field Director Structure Having V-Shaped Vane Doublets
US20090095749A1 (en) * 2007-10-15 2009-04-16 E. I. Du Pont De Nemours And Company Microwave Field Director Structure Having Metal Vanes
US20130126521A1 (en) * 2007-10-15 2013-05-23 E I Du Pont De Nemours And Company Microwave field director structure with vanes having a conductive material thereon
US8455802B2 (en) * 2007-10-15 2013-06-04 E I Du Pont De Nemours And Company Microwave field director structure having vanes with inner ends wrapped with a conductive wrapper
US8461498B2 (en) * 2007-10-15 2013-06-11 E I Du Pont De Nemours And Company Microwave field director structure having V-shaped vane doublets
US8487225B2 (en) * 2007-10-15 2013-07-16 E I Du Pont De Nemours And Company Microwave field director structure having metal vanes
US8735785B2 (en) * 2007-10-15 2014-05-27 E I Du Pont De Nemours And Company Molded microwave field director structure
US8785827B2 (en) * 2007-10-15 2014-07-22 E I Du Pont De Nemours And Company Microwave field director structure with vanes having a conductive material thereon
CN108180515A (zh) * 2017-12-29 2018-06-19 广东美的厨房电器制造有限公司 微波加热器具

Also Published As

Publication number Publication date
DE2409199B2 (de) 1977-03-24
SE387216B (sv) 1976-08-30
JPS507139A (enrdf_load_stackoverflow) 1975-01-24
CA996638A (en) 1976-09-07
GB1463826A (en) 1977-02-09
DE2409199A1 (de) 1974-09-12
FR2220959A1 (enrdf_load_stackoverflow) 1974-10-04
FR2220959B1 (enrdf_load_stackoverflow) 1979-01-05
JPS5219331B2 (enrdf_load_stackoverflow) 1977-05-27

Similar Documents

Publication Publication Date Title
US3872276A (en) Including a semiresonant slotted mode stirrer
US2813185A (en) Heating devices
US3692968A (en) Electronic oven
KR100396765B1 (ko) 전자렌지의 균일가열구조
US4596915A (en) Microwave oven having resonant antenna
US4335290A (en) Microwave oven blower radiator
US4342896A (en) Radiating mode stirrer heating system
US3746823A (en) Electronic cooking appliance
US4421968A (en) Microwave oven having rotating conductive radiators
US2888543A (en) Electronic heating apparatus
US4463239A (en) Rotating slot antenna arrangement for microwave oven
US2827537A (en) Electronic heating apparatus
JPH0467317B2 (enrdf_load_stackoverflow)
US4327266A (en) Microwave ovens for uniform heating
US4350859A (en) Microwave oven feed system
US4343976A (en) Energy feed system for a microwave oven
CA1263452A (en) Rotating slot antenna arrangement for microwave oven
JPS6029840Y2 (ja) マイクロ波加熱装置
US4695693A (en) Triangular antenna array for microwave oven
CA1134449A (en) Microwave oven having rotating conductive radiators
EP0240271B1 (en) Microwave oven with microwave stirrer
US3626136A (en) High-frequency heating apparatus
US3364331A (en) Energy distribution system
US3430022A (en) Microwave oven
US4412117A (en) Microwave oven feed system