US3370145A - Arrangement in microwave stoves - Google Patents

Arrangement in microwave stoves Download PDF

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Publication number
US3370145A
US3370145A US444548A US44454865A US3370145A US 3370145 A US3370145 A US 3370145A US 444548 A US444548 A US 444548A US 44454865 A US44454865 A US 44454865A US 3370145 A US3370145 A US 3370145A
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US
United States
Prior art keywords
magnetron
stirrer
cavity
opening
waveguide
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
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US444548A
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English (en)
Inventor
Malmquist Leo
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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Publication date
Application filed by US Philips Corp filed Critical US Philips Corp
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Publication of US3370145A publication Critical patent/US3370145A/en
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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
    • H05B6/6402—Aspects relating to the microwave cavity
    • 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 present invention relates to an arrangement in microwave stoves in which a heating cavity is energized by means of a magnetron via a wave guide connection terminating in an opening in one of the walls of the cavity.
  • a microwave stove utilizing a magnetron as the energy source requires on the one hand that the magnetron be loaded such that it operates within a favourable working range, and on the other hand that the energy distribution within the stove cavity be uniform.
  • a stirrer which influences the field pattern within the cavity.
  • the stirrer may, for example, consist of one or more reflecting disks arranged near to the energy feed opening and fixed in an inclined position to a shaft so that upon rotation of the shaft the said disks are brought successively to a position opposite the energy feed opening.
  • Such a stirrer functions on the one hand to periodically change the resonance frequency of the cavity, and on the other hand to reflect the energy coming through the energy feed opening in different directions within the cavity, which functions both have the effect of making the energy distribution within the cavity more uniform.
  • An object of the invention is to produce a more uniform energy distribution in a microwave stove of the kind described than has hitherto been possible by means of commonly used stirrers, which is in principle achieved in that the magnetron is influenced by means of a reflected wave such that it periodically changes its frequency.
  • a reflected wave which returns to a magnetron in a certain phase position may be favourable in that it increases the output power of the magnetron.
  • the phase of the reflected wave at which this effect is maximum is called the sink phase and the corresponding range in the magnetron loading diagram is called the sink range.
  • the reactive matching element is adjusted in relation to the said periodically variable reactan'ce such that the reflected wave from the matching element in the di rection towards the magnetron, in combination with the reflected wave coming from the variable reactance, gives rise to a resulting wave in direction towards the magnetron which causes the magnetron to work substantially in the sink range over the whole variation range of the 3,370,145 Patented Feb. 20, 1968 ICE variable reactance.
  • the magnetron will have an appreciable frequency variation resulting in an even energy distribution in the cavity, but also that the magnetron will always operate with high output power.
  • FIG. 1a shows a schematic diagram of an arrangement according to the invention
  • FIG. 1b shows the field variations in a section of the wave guide in the device according to FIG. 1a (standing wave) and
  • FIG. 2 shows a loading diagram for the magnetron included in the device according to FIG. 1a.
  • reference numeral 1 designates a magnetron which is connected through a wave guide 2 to the heating cavity 3 of a microwave stove.
  • a reactive matching element in the shape of a pin 4 projecting into the wave guide.
  • the pin is displaceable in the length direction of the Wave guide by being arranged in a longitudinal slot in the side wall of the Wave guide.
  • a stirrer in the shape of a rotatable wheel 5 with inclined wings is situated near the energy feed opening in the cavity.
  • a resulting reflected wave in the direction towards the magnetron is produced which gives rise to a standing wave, for example, as shown in FIG. 1b.
  • the reflected wave influences the magnetron so that its working point will be dependent both upon the phase and the magnitude of the reflected wave.
  • the magnitude of the reflected wave is commonly specified by the standing wave ratio, which is the relation between the maximum and minimum field of the standing wave, i.e. the relation v /v in FIG. 1b.
  • the phase of the reflected wave is commonly determined by measuring the distance between the minimum of the standing wave and a reference plane A-A in the magnetron, i.e. the distance d in FIG. 1b expressed in fractions of the wave length of the working frequency.
  • the loading diagram for a magnetron is shown in FIG. 2 and illustrates how the magnetron will respond to different loads resulting in different reflected waves.
  • the input variables in FIG. 2 are on the one hand the said standing wave ratio and on the other hand the distance between the minimum of the standing wave and the reference plane.
  • Loci of points having the same standing wave ratio in FIG. 2 form concentric circles, while loci of points having the same value of the said distance d form radial lines emanating from the centre of the circle diagram.
  • the output magnitudes are the power and frequency of the magnetron.
  • the working point will be the centre point of the circle diagram in FIG. 2. Its frequency is then equal to the working frequency of the magnetron and the output power is, in the example shown, equal to 2 kilowatts. If there is a mismatch in the feeding connection or at the load so that a reflected wave is produced, this mismatch can, according to the diagram, influence the magnetron in different ways dependent upon the phase position in which the reflected wave arrives. Thus if the reflected wave has such a phase position that the standing wave has its minimum at a distance which in FIG.
  • the output power will, according to the diagram, increase with increasing value of the standing wave ratio, i.e. with increased reflected wave.
  • the phase position of the reflected wave is such that the standing Wave has its minimum at, in the example shown, approximately 0.16 A, which is called antisink
  • the output power will instead decrease with increasing value of the standing wave ratio.
  • the magnetron In order to achieve a high output power from the magnetron it is required that the magnetron operate within the sink range and not in the antisink range.
  • this is utilized so that, by means of the matching element 4 in combination with the stirrer 5, it is ensured that the magnetron operates substantially within the sink range at all positions of the stirrer 5.
  • the stirrer will then produce the small variations in the phase position of the reflected wave which are required for achieving the frequency variation of the magnetron and thereby a more uniform energy distribution in the stove.
  • the matching element 4 is adjusted during variation of the reactance 5 such that the working points of the magnetron at the different positions of the reactance 5 will fall within a range lying near to the line designated sink in FIG. 2.
  • a microwave oven comprising a wall structure defining a heating cavity, an opening in one wall of said cavity for supplying microwave energy thereto, a magnetron, a waveguide interconnecting said magnetron with said wall opening, a reactive matching element positioned within said waveguide between the magnetron and the wall opening, and a field stirrer rotatably mounted in said cavity in front of and close to said wall opening so as to reflect a portion of the microwave energy radiated from said opening back towards said magnetron, the reflected wave varying as a function of the movement of the stirrer, said reactive element being located within said waveguide and dimensioned relative to said stirrer so that the reflected waves from said matching element and stirrer produce a resultant wave in the direction towards the magnetron having a given phase variation that corresponds to operation of the magnetron in the sink region of its characteristic diagram, said phase variation producing a substantial variation in the magnetron frequency thereby to improve the field distribution within .said heating cavity.
  • a microwave oven comprising a wall structure defining a heating cavity, one wall of said cavity having an opening therein for supplying microwave energy to said cavity, a magnetron, a waveguide interconnecting said magnetron with said wall opening, a reactive matching element positioned within said waveguide between the magnetron and the wall opening, and variable reactance means comprising a field stirrer rotatably mounted in said cavity adjacent to said wall opening and interposed between said opening and the cavity heating load, said stirrer being arranged to reflect a portion of the radiated microwave energy back towards said magnetron to produce a reflected wave exhibiting a given phase variation which is a function of the position of said stirrer, the position of said matching element within the waveguide and the dimensions thereof being chosen relative to said stirrer so that the reflected waves from said matching element and stirrer produce a resultant wave in said waveguide having a given phase variation, said given phase variation of the resultant wave corresponding to operation of the magnetron in its sink region whereby a substantial variation in the magnetr
  • said reactive matching element comprises a metal pin movably mounted in a longitudinal .slot in one side wall of the waveguide.
  • a microwave oven comprising a wall structure defining a heating cavity, one wall of said cavity having an opening therein for supplying microwave energy to said cavity, a magnetron, a waveguide interconnecting said magnetron with said wall opening, and means for mismatching said magnetron and waveguide to produce a periodically varying reflected wave in which the phase of the reflected wave corresponds to operation of the magnetron in its sink region over the whole variation range of said reflected wave
  • said mismatching means comprising a rotatable field stirrer mounted entirely within said cavity and opposite said wall opening so as to reflect a portion of the radiated energy back towards said magnetron to produce a reflected wave in the waveguide which varies in accordance with the displacement of the stirrer, and an adjustable reactive matching element positioned in said waveguide relative to said stirrer and dimensioned relative thereto so as to cooperate with said stirrer to produce said periodically varying wave.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Constitution Of High-Frequency Heating (AREA)
US444548A 1964-04-07 1965-04-01 Arrangement in microwave stoves Expired - Lifetime US3370145A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE424464 1964-04-07

Publications (1)

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US3370145A true US3370145A (en) 1968-02-20

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US444548A Expired - Lifetime US3370145A (en) 1964-04-07 1965-04-01 Arrangement in microwave stoves

Country Status (6)

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US (1) US3370145A (de)
BE (1) BE662202A (de)
CH (1) CH431756A (de)
DE (1) DE1540978C3 (de)
GB (1) GB1068484A (de)
NL (1) NL139434B (de)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3965325A (en) * 1974-03-23 1976-06-22 Matsushita Electric Industrial Co., Ltd. Microwave oven
US3991295A (en) * 1974-05-20 1976-11-09 Matsushita Electric Industrial Co., Ltd. Microwave oven with symmetrically positioned microwave stirrers
US4133997A (en) * 1977-02-09 1979-01-09 Litton Systems, Inc. Dual feed, horizontally polarized microwave oven
US10004115B2 (en) 2016-06-13 2018-06-19 The Markov Corporation Electronic oven with reflective energy steering
US10009957B2 (en) 2016-03-30 2018-06-26 The Markov Corporation Electronic oven with infrared evaluative control

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR1378280A (fr) * 1963-10-04 1964-11-13 Procédé et dispositif d'excitation d'un four de chauffage à ondes d'hyperfréquence
US3218429A (en) * 1962-03-14 1965-11-16 Electrolux Ab Dielectric heating apparatus

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3218429A (en) * 1962-03-14 1965-11-16 Electrolux Ab Dielectric heating apparatus
FR1378280A (fr) * 1963-10-04 1964-11-13 Procédé et dispositif d'excitation d'un four de chauffage à ondes d'hyperfréquence

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3965325A (en) * 1974-03-23 1976-06-22 Matsushita Electric Industrial Co., Ltd. Microwave oven
US3991295A (en) * 1974-05-20 1976-11-09 Matsushita Electric Industrial Co., Ltd. Microwave oven with symmetrically positioned microwave stirrers
US4133997A (en) * 1977-02-09 1979-01-09 Litton Systems, Inc. Dual feed, horizontally polarized microwave oven
US10009957B2 (en) 2016-03-30 2018-06-26 The Markov Corporation Electronic oven with infrared evaluative control
US10681776B2 (en) 2016-03-30 2020-06-09 Markov Llc Electronic oven with infrared evaluative control
US11632826B2 (en) 2016-03-30 2023-04-18 Markov Llc Electronic oven with infrared evaluative control
US10004115B2 (en) 2016-06-13 2018-06-19 The Markov Corporation Electronic oven with reflective energy steering
US10426000B2 (en) 2016-06-13 2019-09-24 The Markov Corporation Electronic oven with reflective energy steering
US10863593B2 (en) 2016-06-13 2020-12-08 Markov Llc Electronic oven with reflective energy steering

Also Published As

Publication number Publication date
GB1068484A (en) 1967-05-10
CH431756A (de) 1967-03-15
DE1540978C3 (de) 1974-05-09
DE1540978B2 (de) 1973-10-18
NL6504180A (de) 1965-10-08
DE1540978A1 (de) 1970-01-22
BE662202A (de) 1965-10-07
NL139434B (nl) 1973-07-16

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