US3525841A - Door seal for microwave ovens - Google Patents

Door seal for microwave ovens Download PDF

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Publication number
US3525841A
US3525841A US772982A US3525841DA US3525841A US 3525841 A US3525841 A US 3525841A US 772982 A US772982 A US 772982A US 3525841D A US3525841D A US 3525841DA US 3525841 A US3525841 A US 3525841A
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United States
Prior art keywords
cavity
electromagnetic wave
wave energy
door
attenuating
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Expired - Lifetime
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US772982A
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English (en)
Inventor
Duane B Haagensen
Samuel G Sweet
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Northrop Grumman Guidance and Electronics Co Inc
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Litton Precision Products 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
    • H05B6/76—Prevention of microwave leakage, e.g. door sealings
    • H05B6/763—Microwave radiation seals for doors

Definitions

  • This invention relates to microwave ovens and more particularly to a novel door seal for preventing the escape of electromagnetic wave energy from such ovens.
  • electromagnetic Wave energy may be utilized for heating foodstuff or other lossy dielectric materials.
  • the foodstuff or other materials are placed in a cavity of a microwave oven and are exposed to electromagnetic wave energy that is supplied by a suitable source, e.g., a magnetron.
  • a movable door is provided for such ovens. 'I'he interior surface of the movable door completes the cavity to ensure proper heating of the foodstuff and prevents the wholesale escape of electromagnetic wave energy from the oven.
  • door seals must be provided to prevent any further leakage of electromagnetic wave energy from the oven.
  • microwave oven manufacturers have utilized various types of door seals.
  • microwave ovens featured direct contact between the inside surface of the metallic door and the front surface of the metallic housing, with the addition of spring biasing of the door to maintain the door seal.
  • the spring biasing method did not prove satisfactory over a period ⁇ of time, in some cases, because of warping of the metallic surfaces or other damage thereto, and in other cases, because of the deterioration of the springs. In either case, arcing between the respective surfaces of the door and the housing and excessive leakage from the oven occurred, unless proper maintenance procedures were strictly observed.
  • the cavity presented a short circuit which was reflected back as a short circuit between the parallel plate transmission line formed by the interior surface of 3,525,841 Patented Aug. 25, 1970 ICC door and front surface of the housing.
  • electromagnetic wave energy was blocked from leaving the oven cavity.
  • warping of the metallic surfaces or eventual wearing of the non-metallic spacers caused arcing between the metallic surfaces.
  • the burning out of the rubber seal occurred.
  • ⁇ It is another object of the present invention to provide an improved door seal for microwave ovens which includes novel cavity means for preventing the escape of electromagnetic wave energy from such ovens and rcduces the Weight of the door of such ovens.
  • the present invention provides an improved ⁇ door seal for microwave ovens comprising a plurality of spacers to provide a gap for preventing arcing of electromagnetic wave energy between the respective surfaces of the door and the housing of the oven, the gap ensures a port of entry for the electromagnetic wave energy, and a combination of an lattenuating cavity and an absorption cavity provides a volumetric resonant cavity that presents high impedance to electromagnetic wave energy within the attenuating cavity and a terminating impedance to electromagnetic wave energy within the absorption cavity.
  • FIG. 2 isa cross sectional view of the microwave oven taken along the line 2 2 of FIG. l;
  • FIG. 3 is an alternate embodiment of the present invention in which the cavities have a vaporized metallic coating thereon;
  • FIG. 4 is an enlarged view of one of the corners of the door of the microwave oven of FIG. 1 with part of the door cut away to show the elements of a door seal in accordance with the present invention.
  • FIG. 2 illustrates a door seal for preventing the escape of electromagnetic wave energy from the microwave yoven 10.
  • the door seal is located completely around the perimeter of the interior surface of the door 12.
  • the door 12 is constructed of metal castings '116 and 18, preferably aluminum to maintain a light weight door which may be held together by a number of conventional means, such as, a screw 19.
  • the spaces 27 located between metal castings 16 and :18 house the mechanism, not shown, for operating the handle 13, or are empty so as to reduce the weight of the door 12.
  • the housing 11 having three surfaces 11b, 11C and 11d.
  • the surface 11b and the window 14 dene the location of a microwave oven cavity 111a, or the interior of the microwave oven 10.
  • the numeral 17 designates the exterior panel of the door 12.
  • an attenuating cavity 24 which is filled with a dielectric, preferably polypyroleyne. Utilization of the polypyroleyne filler in the attenuating cavity 24 allows the cavity to be physically smaller than if the cavity only contained air and further provides for attenuating any electromagnetic wave energy entering the attenuating cavity 24.
  • an absorption cavity 22 which is filled with an electromagnetic wave energy absorbing material, for example, ferrite.
  • the numeral 23 defines the surface of the absorption cavity 22 that is adjacent the attenuating cavity 24.
  • a retaining strip 20 is affixed between the metal castings 16 and 18 and retains the ferrite in the cavity 22, as shown. 'Ihe retaining strip 20 includes spacers 21 at the four corners of the door 12, as illustrated in FIGS. 2 and 4. The four spacers 21 ensure that a proper gap is maintained between the interior surface of the door 12 and the surface 11c of the housing 11.
  • the attenuating cavity 24 and the absorption cavity 22 provide a volumetric resonant cavity such that there is a high impedance to electromagnetic wave energy within the attenuating cavity 24 for attenuating such electromagnetic wave energy, and there is a terminating impedance to electromagnetic wave energy within the absorption cavity 22 for absorbing such electromagnetic wave energy.
  • a port of entry 26, which has been established by the four spacers 21, ensures that a physical opening of such a capacitance to provide minimum impedance to electromagnetic wave energy is maintained.
  • the establishment of a transmission line into the volumetric resonant cavity, or resonant cavity choke is such, that it allows purposeful capacity transmission into the volumetric resonant cavity.
  • the surface 11C of the .housing 11 and the interior surface of the window 14 define a gap which establishes the port f entry 26. Since an electromagnetic wave energy pattern is established within the cavity 11a, a portion of the. electromagnetic wave energy will travel to the port of entry 26. Any electromagnetic wave energy within the cavity 11a that is directed thereto is allowed to enter. Upon entering the attenuating cavity 22, the electromagnetic wave energy therein will be attenuated. A major portion of this attenuated electromagnetic wave energy will then enter the absorption cavity 24 which maintains a terminating impedance to absorb such electromagnetic energy.
  • the present invention provides a port of entry 26 which allows electromagnetic wave energy to enter; therefore, eliminating the possibility of arcing. It was found that if the absorption cavity 22 is placed as near as possible to a port of exit 25, maximum absorption of any attenuated electromagnetic wave energy attempting to leave said attenuating cavity 24 is accomplished by the absorption cavity 22.
  • the constructed door seal which was maintained entirely around the interior perimeter of the door 12, included the cavity 24 having a polyproleyne filler therein, with the polyproleyne filler 'being of the following dimensions at the following respective surfaces: 2411:.480, +1100, .005 inch; 240:.900, -[-.000, 005 inch; 24d:.590; and 25:.240 inch.
  • the ferrite material in cavity 22 had a width of .1251.015 inch at surface 23 and a depth of .30811020 inch.
  • the opening is .0153005 at the port of entry 26
  • no arcng is experienced and the port of entry 26 thereby established allows the electromagnetic wave energy to enter the attenuating cavity 24.
  • one of the standard operating frequencies for magnetrons employed in microwave ovens is 2450 megacycles per second.
  • the door seal in accordance with the present invention provides a volumetric resonant cavity exhibiting broad 'band characteristics that effectively prevents the escape of electromagnetic wave energy from the microwave oven 10.
  • FIG. 3 illustrates another embodiment in accordance with this invention wherein the attenuating cavity 24 and the absorption cavity 22 may be provided with a vaporized coating of conductive material 28, for example, aluminum, that the volumetric resonant cavity will be effective and at the same time will enable the elimination of a substantial portion of the metal casting 18 so as to provide a relatively light weight door.
  • conductive material 28 for example, aluminum
  • Microwave oven apparatus comprising:
  • heating cavity located within said housing, said heating cavity having an opening therein;
  • a movable door mounted to said housing, said movable door in the closed position completing with said heating cavity an effective heating cavity for said electromagnetic wave energy supplied to said heating cavity;
  • spacing means for providing a physical gap between said movable door and the surface immediately adjacent said movable door, said gap having a port of entry to allow electromagnetic wave energy to enter said gap;
  • volumetric resonant cavity means located adjacent said gap and in proximity of the entire perimeter of the interior surface of said movable door for ensuring an electrical opening of such a capacitance that minimum impedance to said electromagnetic wave energy occurs at said port of entry
  • said volumetric resonant cavity means includes attenuation cavity means for attenuating said electromagnetic wave energy entering said gap, said attenuating cavity means having a port of exit
  • said volumetric resonant cavity means further includes absorption cavity means having a surface abutting said attenuating cavity means for absorbing said attenuated electromagnetic wave energy, said absorption cavity means being located in proximity of said port of exit of said attenuating means.
  • volumetric resonant cavity means comprises:
  • Microwave oven apparatus as recited in claim 2 wherein said dielectric materaial is polyproleyne and said absorption material is ferrite.
  • Microwave oven apparatus as recited in claim 1 wherein said volumetric resonant cavity means is located within said movable door.
  • Microwave oven apparatus as recited in claim 1 wherein said volumetric resonant cavity means comprises in combination:
  • a vaporized coating of conductive material enclosing said dielectric material and said absorption material except at the surface of said dielectric that is exposed to said gap.
  • Microwave oven apparatus as recited in claim 5 wherein said dielectric material is polyproleyne, said absorption material is ferrite, and said conductive material is aluminum.
  • Microwave oven apparatus as recited in claim 1 wherein the width of said port of entry is approximately .015 inch.
  • Microwave oven apparatus comprising:
  • heating cavity located within said housing, said heating cavity having an opening therein;
  • a movable door mounted to said housing, said movable door in the closed position completing with said heating cavity an effective heating cavity for said electromagnetic wave energy supplied to said heating cavity;
  • spacing means for providing a gap between said mofvable door and the surface immediately adjacent said movable door, said gap having a port of entry ofI a width of approximately .015 inch to allow electromagnetic wave energy to enter said gap;
  • volumetric resonant cavity means located adjacent said gap and including polyproleyne filled attenuating cavity means and ferrite filled absorption cavity means, for attenuating and absorbing said electromagnetic wave energy traveling through said gap and that enters said volumetric lresonant cavity, said ferrite being located in close proximity of said gap and having a surface abutting said polyproleyne.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Electric Ovens (AREA)
  • Constitution Of High-Frequency Heating (AREA)
US772982A 1968-11-04 1968-11-04 Door seal for microwave ovens Expired - Lifetime US3525841A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US77298268A 1968-11-04 1968-11-04

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US3525841A true US3525841A (en) 1970-08-25

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US (1) US3525841A (US20020051482A1-20020502-M00012.png)
JP (1) JPS4834263B1 (US20020051482A1-20020502-M00012.png)

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3651300A (en) * 1971-01-25 1972-03-21 Matsushita Electric Ind Co Ltd Microwave heating apparatus with radiation control and monitoring
US3666904A (en) * 1971-04-12 1972-05-30 Bowmar Tic Inc Microwave oven and door structure for minimizing leakage
FR2133848A1 (US20020051482A1-20020502-M00012.png) * 1971-04-19 1972-12-01 Matsushita Electric Ind Co Ltd
US3742176A (en) * 1969-06-26 1973-06-26 Tdk Electronics Co Ltd Method for preventing the leakage of microwave energy from microwave heating oven
US3809843A (en) * 1970-06-01 1974-05-07 Gen Corp Microwave heating apparatus
JPS49104037U (US20020051482A1-20020502-M00012.png) * 1972-12-26 1974-09-06
US3835283A (en) * 1970-03-03 1974-09-10 Matsushita Electric Co Ltd Partition and front wall forming choke structure for a microwave oven
JPS49111242U (US20020051482A1-20020502-M00012.png) * 1973-01-22 1974-09-24
US3866009A (en) * 1969-06-26 1975-02-11 Tdk Electronics Co Ltd Seal means for preventing the leakage of microwave energy from microwave heating oven
US3879595A (en) * 1973-01-08 1975-04-22 Tappan Co Microwave oven door seal
US4041266A (en) * 1972-10-25 1977-08-09 Chemetron Corporation Sensor and tray arrangement
US4046983A (en) * 1975-09-03 1977-09-06 Tdk Electronics Co., Ltd. Microwave heating oven having seal means for preventing the leakage of microwave energy
US4166207A (en) * 1977-05-31 1979-08-28 Whirlpool Corporation Microwave generating device--door seal
US4471194A (en) * 1971-05-20 1984-09-11 Matsushita Electric Industrial Co., Ltd. Electromagnetic energy seal for high frequency heating apparatus
FR2595450A1 (fr) * 1986-03-07 1987-09-11 Bosch Siemens Hausgeraete Dispositif d'etancheite de porte pour four a micro-ondes

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPH0261795U (US20020051482A1-20020502-M00012.png) * 1988-10-31 1990-05-08

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2958754A (en) * 1958-12-15 1960-11-01 Gen Electric Electronic ovens
US3182164A (en) * 1962-02-28 1965-05-04 Raytheon Co Electromagnetic energy seal
US3196242A (en) * 1961-10-25 1965-07-20 Philips Corp High-frequency oven door seal
US3249731A (en) * 1963-11-14 1966-05-03 Westinghouse Electric Corp Oven
US3351730A (en) * 1964-03-10 1967-11-07 Philips Corp Energy seal for microwave ovens

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2958754A (en) * 1958-12-15 1960-11-01 Gen Electric Electronic ovens
US3196242A (en) * 1961-10-25 1965-07-20 Philips Corp High-frequency oven door seal
US3182164A (en) * 1962-02-28 1965-05-04 Raytheon Co Electromagnetic energy seal
US3249731A (en) * 1963-11-14 1966-05-03 Westinghouse Electric Corp Oven
US3351730A (en) * 1964-03-10 1967-11-07 Philips Corp Energy seal for microwave ovens

Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3742176A (en) * 1969-06-26 1973-06-26 Tdk Electronics Co Ltd Method for preventing the leakage of microwave energy from microwave heating oven
US3866009A (en) * 1969-06-26 1975-02-11 Tdk Electronics Co Ltd Seal means for preventing the leakage of microwave energy from microwave heating oven
US3835283A (en) * 1970-03-03 1974-09-10 Matsushita Electric Co Ltd Partition and front wall forming choke structure for a microwave oven
US3809843A (en) * 1970-06-01 1974-05-07 Gen Corp Microwave heating apparatus
US3651300A (en) * 1971-01-25 1972-03-21 Matsushita Electric Ind Co Ltd Microwave heating apparatus with radiation control and monitoring
US3666904A (en) * 1971-04-12 1972-05-30 Bowmar Tic Inc Microwave oven and door structure for minimizing leakage
FR2133848A1 (US20020051482A1-20020502-M00012.png) * 1971-04-19 1972-12-01 Matsushita Electric Ind Co Ltd
US4471194A (en) * 1971-05-20 1984-09-11 Matsushita Electric Industrial Co., Ltd. Electromagnetic energy seal for high frequency heating apparatus
US4041266A (en) * 1972-10-25 1977-08-09 Chemetron Corporation Sensor and tray arrangement
JPS49104037U (US20020051482A1-20020502-M00012.png) * 1972-12-26 1974-09-06
US3879595A (en) * 1973-01-08 1975-04-22 Tappan Co Microwave oven door seal
JPS49111242U (US20020051482A1-20020502-M00012.png) * 1973-01-22 1974-09-24
US4046983A (en) * 1975-09-03 1977-09-06 Tdk Electronics Co., Ltd. Microwave heating oven having seal means for preventing the leakage of microwave energy
US4166207A (en) * 1977-05-31 1979-08-28 Whirlpool Corporation Microwave generating device--door seal
FR2595450A1 (fr) * 1986-03-07 1987-09-11 Bosch Siemens Hausgeraete Dispositif d'etancheite de porte pour four a micro-ondes

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Publication number Publication date
JPS4834263B1 (US20020051482A1-20020502-M00012.png) 1973-10-19

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