US3670134A - Microwave oven no-load sensor - Google Patents

Microwave oven no-load sensor Download PDF

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Publication number
US3670134A
US3670134A US109818A US3670134DA US3670134A US 3670134 A US3670134 A US 3670134A US 109818 A US109818 A US 109818A US 3670134D A US3670134D A US 3670134DA US 3670134 A US3670134 A US 3670134A
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United States
Prior art keywords
energy
waveguide
ferrimagnetic
section
generator
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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
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US109818A
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English (en)
Inventor
Arnold M Bucksbaum
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Goodman Co LP
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Amana Refrigeration Inc
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    • 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
    • H05B6/70—Feed lines
    • H05B6/707—Feed lines using waveguides
    • 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
    • H05B6/70—Feed lines
    • H05B6/705—Feed lines using microwave tuning
    • 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
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B40/00—Technologies aiming at improving the efficiency of home appliances, e.g. induction cooking or efficient technologies for refrigerators, freezers or dish washers

Definitions

  • the invention relates generally to no-load sensing and protection means for high frequency heating apparatus.
  • the energy generator comprises the magnetron crossed field oscillator of radar system fame.
  • the text Microwave Magnetrons by G. B. Collins, Radiation Laboratory Series, Vol. 6, McGraw-I-Iill Book Company, Inc. 1948 provides details of the construction and operation of such devices.
  • Such sources operate at allocated frequencies of 915 or 2,450 megahertz.
  • Other generators include vacuum tube devices and klystrons. These sources, as well as accompanying high voltage circuits, are relatively costly.
  • the materials to be cooked or heated absorb high frequency electrical energy within the enclosure when the generator is matched'to a load.
  • the absence of such a load or a mismatch condition results in the reflection of energy back to the source often with catastrophic results.
  • Means for prevention of damage by automatic sensing of no-load or severe mismatch condition, such as metallic objects, are therefore of great value.
  • U.S. Pat. No. 2,498,719 issued to P. L. Spencer provides a circuit-controlling means for detecting and continuously monitoring the standing wave amplitudes within the launching section. The occurrence of standing wave peaks within the section in excess of a predetermined value triggers gas-filled electrical discharge devices to energize control relays opening the contacts serially connecting the generator to a voltage source.
  • any high power reflected energy is diverted laterally to a waveguide branch including the energy absorbing means.
  • a magnetic circuit is provided in one. embodiment within a reduced cross-sectional area of the launching section by completely disposing a magnet member within a recessed region in a waveguide wall opposite to the ferrimagnetic body.
  • a pedestal member of a magnetizable material concentrates the flux lines perpendicular to the face of the ferrimagnetic body for more efficient saturation. The disposition of the pedestal member adjacent to the ferrimagnetic member also results in improved heat conduction for more efiicient circulator action.
  • another magnetic field producing member may be supported adjacent the ferrimagnetic material to further enhance saturation.
  • the reduced cross-sectional area in the region of the ferrimagnetic member results in a concentration of the fields established by the electromagnetic wave energy. Coupled with the concentration means for the disposition of the magnetic fields correspondingly lower costs will result through elimination of the need for plural ferrimagnetic members in most applications as well as the smaller volume requirement for complete saturation.
  • FIG. 1 is a perspective view of the embodiment of the invention with a portion of the upper wall broken away to reveal internal structure;
  • FIG. 2 is a vertical cross-sectional area of the illustrative embodiment of the invention.
  • FIG. 3 is a cross-sectional area taken along the line 3--3 of FIG. 2;
  • FIG. 4 is a detailed crosssectional view taken 44 of FIG. 3;
  • FIG. 5 is a cross-sectional view of an alternative embodiment of the invention.
  • FIG. 6 is a vertical cross-sectional view taken along the line 6-6 of FIG. 5;
  • FIG. 7 is a cross-sectional view of the illustrative magnetic concentrator member of the invention.
  • FIG. 8 is a cross-sectional view of an alternative embodiment of the waveguide launching section.
  • FIG. 9 is an enlarged cross-sectional view of the overall magnetic circuit configuration of the invention.
  • the high frequency heating apparatus 2 is illustrated in FIG. 1.
  • a microwave frequency magnetron is commonly employed as the energy generator to radiate at 2,450 megahertz corresponding to a wavelength of approximately 5 inches in space.
  • the term microwave refers to electromagnetic energy in that portion of the spectrum having wavelengths of from 30 centimeters to l millimeter.
  • Rectangular parallelepiped conductive walls 4 define heating enclosure 6 having an access opening with a door 8 incorporating a perforated panel 10. The perforations extend over the major portion of the access opening to prevent the escape of electromagnetic energy during the operation of the apparatus.
  • Handle 12 provides for the manual operation of the door.
  • Panel 14 adjacent the access opening houses the electromagnetic energy generation means and associated circuitry including a high voltage source together with actuating controls.
  • an energy generator of the magnetron type indicated by a block 16 is coupled to a high voltage supply including all the well-known components incorporated in such apparatus.
  • the electromagnetic wave energy is fed from the source 16 by means of an antenna probe 20 within dielectric dome member 22 extending into launching waveguide section 24 adapted to propagate the desired frequency within the heating enclosure 6.
  • Waveguide 24 is closed at one end by wall member 26 which may include perforations 28 to facilitate cooling of the enclosed components by circulation of air under pressure.
  • the open inner end 30 is oriented within the heating enclosure.
  • the electromagnetic energy is uniformly radiated by means of a stirrer 32 of the type described in US. Pat. No. 2,813,185 issued to Robert V. Smith.
  • the stirrer 32 comprises a plurality of vane members 34 rotatably actuated by fractional horsepower motor means 36.
  • the articles to be treated are positioned within the enclosure 6 on'a dielectric plate member 38 spanning the bottom wall 40 and supported by shoulders 42.
  • the plate permits the distribution of the electromagnetic wave energy on all sides of the articles to be heated by reflection from the surrounding conductive walls.
  • dielectric members are also designed to absorb some of the electromagnetic wave energy in the event that an extreme mismatch condition occurs which could damage the generator.
  • a circulator 46 is provided within the launching section including, first, branch lines 48, 50 and 52 of, illustratively, a rectangular cross-sectional area.
  • a ferrimagnetic element 54 having a disc configuration is supported within the junction region common to all the waveguide sections. The element is supported from the upper broad wall of the waveguide launching section 24 with an intermediately disposed concentrator member 56 of a material such as iron forming substantially a pedestal affixed to the ferrimagnetic element.
  • Magnetic plate member 58 also of irons abuts the outer wall of the waveguide section and is joined to pedestal 56.
  • a permanent magnet member 60 is submounted within the confines of the wall structure defined in the launching waveguide section 24 within a portion of reduced cross-sectional area provided by a recessed wall 62.
  • Securing plate member 64 of any desired meta] abuts the magnet 60.
  • a recessed screw member 66 aids in affixing the pedestal element 56 to the upper wall of the waveguide section.
  • Laterally disposed branch section 52 houses energy absorbing means such as a load of, for example, silicon carbide material.
  • the no-load sensing and protection circulator46 will be described utilizing the magnetic field concentration means 56 as well as the reduced cross-sectional area for the disposition of ferrimagnetic element 54.
  • the energy launched from the generator enters waveguide section 48 having a full height dimension of, illustratively,
  • the circulator including the ferrimagnetic element is, however, provided in reduced height branch waveguide members matched to the launching section by a suitable one step one-quarter wavelength transformer 70 utilizing well-known techniques.
  • a suitable one-quarter wavelength transformer 70 utilizing well-known techniques.
  • one inch high guide was selected for the branch members 50 and 52 and in the region for the disposition of the circulating ferrimagnetic element a still further reduction in cross-sectional area is provided by recessed wall surface 62 housing magnet 60.
  • the dielectric constant characteristics of the ferrimagnetic material for element 54 as well as diameter and height are determined by magnetic field saturation requirements and the preferred orientation in accordance with circulator concepts. It is suggested that in the propagation of electromagnetic energy in the TE mode in rectangular waveguide the bodies of the applicable material be magnetized in a direction parallel to the electric field (E) vector or parallel to the narrow walls.
  • E electric field
  • the proper electron spin motion for nonreciprocal propagation of electromagnetic waves is realized when the ferrimagnetic bodies are displaced from the center or longitudinal axis 72 shown in FIG. 3. This determination may possibly be explained by the so-called field-displacement effect for ferrite isolators described by B. Lax and K. J.
  • Return reflected energy however, has an entirely different energy profile configuration with the maximum point shifted toward the narrow waveguide walls. Any such energy will contact the offset saturated magnetized ferrimagnetic body and be diverted to branch waveguide 52 where the energy absorbing load is situated. Adverse energy reflections are thereby prevented from being introduced in the path of the generator waves.
  • a ferrimagnetic material of superior quality is of a nickelaluminum-feriite combination or magnesium ferrite.
  • the energy absorbing means 68 are disposed a discrete distance from the junction where the circulator element is placed. Conventionally, a one-half guided wavelength dimension M2) is preferred for reflectionless matching and low VSWR. Silicon carbide which has a high degree of thermal lag is ideally suited for the absorbing material.
  • Magnet member 60 is shown submounted relative to the ferrimagnetic element 54 in the reduced cross-sectional region adjacent to wall 62 in the substantially one-half height waveguide.
  • Pedestal member 56 will aid in directing the magnetic field flux lines substantially perpendicular to the face of the element 54.
  • a further feature of the invention resides in the conduction of thermal energy generated in the ferrimagnetic material by the circulator action by means of the heat sink action of the abutting pedestal member 56. This will prevent the magnetic material from rapidly reaching the Curie temperature point where magnetization is destroyed.
  • the combination of the ferrimagnetic element, submounted magnet member, and pedestal concentrator in the reduced cross-section area waveguide and junction region also virtually eliminates the need for reactive circuit matching structure such as iris'es at the input and output ends of circulator 46.
  • reactive circuit matching structure such as iris'es at the input and output ends of circulator 46.
  • a single magnet 60 will suffice in most applications.
  • a second magnet member 76 indicated by dotted lines may be positioned adjacent to plate member '58.
  • FIGS. 5 and 6 another variation of the invention is shown.
  • the waveguide branch 50 has a width of, illustratively, 4.3 inches, dimension a, as shown in FIGS. 3 and 4.
  • the narrowing of waveguide branch 52 will lengthen this portion of the overall circulator by lengthening the onehalf wavelength for the placement of the energy absorbing load 68.
  • the height of the energy absorbing load 68 may also be suitably adjusted to match VSWR of the waveguide branch 52 to the remainder of the energy launching means.
  • FIG. 6 a stream of coolant indicated generally by lines 78 are shown directed toward the passages 28 in end ,wall 26 to assist in the operation of the illustrative embodiment of the invention by providing additional cooling for the ferrimagnetic element and absorbing means.
  • FIG. 7 a slightly enlarged cross section of the magnetic pedestal member 56 is shown to assist in the conduction of thermal energy as well as direction of the magnetic field flux lines.
  • a notched edge 80 is shown disposed around the perimeter of the member 56 to assure better contact with the upper broad walls of the rectangular waveguide launching section 24.
  • FIG. 8 another modification of the invention is shown incorporating a launching waveguide section 82 which is provided with rounded corners 84 to form a waveguide launching section.
  • a three-sided substantially U-shaped member from a sheet metal may be stamped to provide the passageway 86 when suitably joined by welding or soldering as at 88 to the upper wall 4 of the oven enclosure. This structure will not only provide for a simplified and compact structure but will lower the overall cost of the oven apparatus.
  • FIG. 9 the idealized magnetic circuit is disclosed utilizing the components of the invention to provide for the concentration of the launched wave energy as well as magnetic flux lines in the region of the ferrimagnetic element.
  • the components previously described have been similarly numbered.
  • the most efficient operation of the resultant circulator will follow with the magnetic lines 90 provided by the magnetic member being oriented perpendicular to the face of the magnetic member being oriented perpendicular to the face of the ferrimagnetic element 54.
  • the flux lines lines therefore, are at right angles to the magnetic vector of the launched microwave energy indicated by the arrow 92 moving along the waveguide section 50.
  • This arrangement will provide for enhancement of the attenuation of the reflected returning energy as well as the lowest insertion loss for the energy initially launched from the microwave energy generator.
  • the arrangement also discourages any fringing flux lines from arising which will result in inefficient operation and the requirement for larger bodies of the ferrimagnetic material to be disposed within the waveguide section.
  • High frequency heating apparatus comprising:
  • said coupling means for coupling said energy from said generator to said enclosure; said coupling means having a passage therethrough with a section thereof of reduced cross-sectional area;
  • nonreciprocal transmission means including a magnetized ferrimagnetic material dis osed within said reduced cross-sectional area to receive and propagate in a direction away from said generator energy reflected from said enclosure;
  • High frequency heating apparatus comprising:
  • means for coupling said energy from said generator to said enclosure including a waveguide transmission line
  • said coupling means having a passage therethrough with a section thereof of reduced cross-sectional area
  • a circulator including a member of a ferrimagnetic material disposed within said reduced cross-sectional area to receive and propagate in a direction away from said generator energy reflected from said enclosure;
  • said magnetizing means include a permanent magnet member mounted opposite to the ferrimagnetic member.
  • said magnetizing means include a submounted permanent magnet member disposed in said reduced cross-sectional area.
  • said magnetizing means include a magnet member disposed opposite to the ferrimagnetic material member and mounted wholly within the plane defined by the outer confines of said waveguide line.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Constitution Of High-Frequency Heating (AREA)
  • Control Of High-Frequency Heating Circuits (AREA)
US109818A 1971-01-26 1971-01-26 Microwave oven no-load sensor Expired - Lifetime US3670134A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US10981871A 1971-01-26 1971-01-26

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US3670134A true US3670134A (en) 1972-06-13

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US109818A Expired - Lifetime US3670134A (en) 1971-01-26 1971-01-26 Microwave oven no-load sensor

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US (1) US3670134A (en, 2012)
JP (1) JPS5216255B1 (en, 2012)
AU (1) AU465174B2 (en, 2012)
BE (1) BE778305A (en, 2012)
CH (1) CH536060A (en, 2012)
DE (1) DE2202276C3 (en, 2012)
FR (1) FR2123334B1 (en, 2012)
GB (1) GB1362076A (en, 2012)
IT (1) IT948203B (en, 2012)
NL (1) NL7201054A (en, 2012)

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3764770A (en) * 1972-05-03 1973-10-09 Sage Laboratories Microwave oven
US3783221A (en) * 1970-12-31 1974-01-01 J Soulier Device for adjusting the microwave energy applied to a band or a sheet to be treated in a resonant cavity furnace
US3886497A (en) * 1973-03-26 1975-05-27 Microwave Dev Lab Inc Waveguide circulator having single gyromagnetic element
US3928824A (en) * 1973-08-30 1975-12-23 Oki Electric Ind Co Ltd Waveguide circulator
US4097709A (en) * 1975-12-17 1978-06-27 Elektromaschinen Ag Oven
US4197442A (en) * 1977-02-10 1980-04-08 U.S. Philips Corporation Temperature supervising system
US4276462A (en) * 1978-01-02 1981-06-30 Husqvarna Aktiebolag Microwave heating apparatus
US4286135A (en) * 1979-10-09 1981-08-25 Raytheon Company Compact microwave isolator
US4341937A (en) * 1980-11-28 1982-07-27 General Electric Company Microwave oven cooking progress indicator
EP0274164A1 (en) * 1987-01-08 1988-07-13 Philips Norden AB A microwave oven
US5459303A (en) * 1994-03-02 1995-10-17 Goldstar Co., Ltd. Method of preventing no-load operation of microwave oven
US5550355A (en) * 1993-06-29 1996-08-27 Samsung Electronics Co., Ltd. Microwave oven driving control method and apparatus thereof
US6166364A (en) * 1999-07-28 2000-12-26 Samsung Electronics Co., Ltd. Microwave oven having a microwave detecting device
US6452141B1 (en) * 2001-06-30 2002-09-17 Samsung Electronics Co., Ltd. Microwave oven with magnetic field detecting device
US20120241445A1 (en) * 2009-09-01 2012-09-27 Lg Electronics Inc. Cooking appliance employing microwaves
US20170099705A1 (en) * 2014-05-26 2017-04-06 Electrolux Appliances Aktiebolag Microwave oven with a waveguide including a reflector element
US9930732B2 (en) * 2010-10-22 2018-03-27 Whirlpool Corporation Microwave heating apparatus and method of operating such a microwave heating apparatus
CN113124429A (zh) * 2019-12-31 2021-07-16 广东美的白色家电技术创新中心有限公司 微波炉及检测微波炉中负载信息的方法

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5893189A (ja) * 1981-11-26 1983-06-02 松下電器産業株式会社 高周波加熱装置
KR0140461B1 (ko) * 1994-07-12 1998-06-01 김광호 전자렌지
KR100208693B1 (ko) * 1996-12-27 1999-07-15 전주범 개선된 구조를 갖는 전자렌지용 도파관

Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3437777A (en) * 1966-06-17 1969-04-08 Tokyo Shibaura Electric Co Microwave heating apparatus

Family Cites Families (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE1299738B (de) * 1966-05-21 1969-07-24 Philips Patentverwaltung Mikrowellenzirkulator mit einer Hohlleiterserienverzweigung

Patent Citations (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3437777A (en) * 1966-06-17 1969-04-08 Tokyo Shibaura Electric Co Microwave heating apparatus

Cited By (22)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3783221A (en) * 1970-12-31 1974-01-01 J Soulier Device for adjusting the microwave energy applied to a band or a sheet to be treated in a resonant cavity furnace
US3764770A (en) * 1972-05-03 1973-10-09 Sage Laboratories Microwave oven
US3886497A (en) * 1973-03-26 1975-05-27 Microwave Dev Lab Inc Waveguide circulator having single gyromagnetic element
US3928824A (en) * 1973-08-30 1975-12-23 Oki Electric Ind Co Ltd Waveguide circulator
US4097709A (en) * 1975-12-17 1978-06-27 Elektromaschinen Ag Oven
US4197442A (en) * 1977-02-10 1980-04-08 U.S. Philips Corporation Temperature supervising system
US4276462A (en) * 1978-01-02 1981-06-30 Husqvarna Aktiebolag Microwave heating apparatus
US4286135A (en) * 1979-10-09 1981-08-25 Raytheon Company Compact microwave isolator
US4341937A (en) * 1980-11-28 1982-07-27 General Electric Company Microwave oven cooking progress indicator
EP0274164A1 (en) * 1987-01-08 1988-07-13 Philips Norden AB A microwave oven
US5550355A (en) * 1993-06-29 1996-08-27 Samsung Electronics Co., Ltd. Microwave oven driving control method and apparatus thereof
US5459303A (en) * 1994-03-02 1995-10-17 Goldstar Co., Ltd. Method of preventing no-load operation of microwave oven
US6166364A (en) * 1999-07-28 2000-12-26 Samsung Electronics Co., Ltd. Microwave oven having a microwave detecting device
EP1073316A3 (en) * 1999-07-28 2002-02-06 Samsung Electronics Co., Ltd. Microwave oven waveguide with microwaves sensor
US6452141B1 (en) * 2001-06-30 2002-09-17 Samsung Electronics Co., Ltd. Microwave oven with magnetic field detecting device
US20120241445A1 (en) * 2009-09-01 2012-09-27 Lg Electronics Inc. Cooking appliance employing microwaves
US9930732B2 (en) * 2010-10-22 2018-03-27 Whirlpool Corporation Microwave heating apparatus and method of operating such a microwave heating apparatus
US11277890B2 (en) 2010-10-22 2022-03-15 Whirlpool Corporation Microwave heating apparatus and method of operating such a microwave heating apparatus
US20170099705A1 (en) * 2014-05-26 2017-04-06 Electrolux Appliances Aktiebolag Microwave oven with a waveguide including a reflector element
US10506672B2 (en) * 2014-05-26 2019-12-10 Electrolux Appliances Aktiebolag Microwave oven with a waveguide including a reflector element
CN113124429A (zh) * 2019-12-31 2021-07-16 广东美的白色家电技术创新中心有限公司 微波炉及检测微波炉中负载信息的方法
CN113124429B (zh) * 2019-12-31 2023-10-31 广东美的白色家电技术创新中心有限公司 微波炉及检测微波炉中负载信息的方法

Also Published As

Publication number Publication date
AU3767372A (en) 1973-07-12
CH536060A (de) 1973-04-15
DE2202276B2 (de) 1974-12-12
GB1362076A (en) 1974-07-30
BE778305A (fr) 1972-05-16
AU465174B2 (en) 1975-09-18
IT948203B (it) 1973-05-30
FR2123334A1 (en, 2012) 1972-09-08
DE2202276A1 (de) 1972-08-03
JPS5216255B1 (en, 2012) 1977-05-07
NL7201054A (en, 2012) 1972-07-28
DE2202276C3 (de) 1975-08-07
FR2123334B1 (en, 2012) 1974-12-13

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