US3436508A - Cabinet and door construction for microwave heating appliances - Google Patents

Cabinet and door construction for microwave heating appliances Download PDF

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Publication number
US3436508A
US3436508A US574475A US3436508DA US3436508A US 3436508 A US3436508 A US 3436508A US 574475 A US574475 A US 574475A US 3436508D A US3436508D A US 3436508DA US 3436508 A US3436508 A US 3436508A
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door
cabinet
radiation
construction
lip
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US574475A
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English (en)
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Karl Fritz
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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

  • the present invention relates to microwave ovens, and more particularly to a cabinet and door construction for microwave ovens.
  • Heating by microwaves is particularly suitable to defrost frozen food and to obtain quick and uniform heating throughout the food.
  • Microwave ovens are, however, expensive; the frequency used is required to be high, in the order of 20 cm. or less and the frequency band width must be small. Lowering the frequency could effect economy, but it is then difficult to provide a radiation tight door closure.
  • Frequencies having a wavelength in the order of 30 to 40 cm. have the advantage that the surface layer of the food within the cabinet is penetrated better, apart from the fact that the cost of the apparatus is lower. If the wave length of the radiation Within the cabinet is, however, of about the same order of magnitude as a dimension of the space itself, the first harmonic will be the primary radiation therein. It is diflicult to manufacture doors, particularly in mass production, which seal such longer wave radiation to the inside of the cabinet and effectively prevent escape of any radiation to the outside. The amount of permissible stray radiation is very small, without exceeding safety and interference limits; it may be only as little as watts. These safety and manufacturing difliculties have heretofore prevented acceptance of microwave ovens utilizing such higher frequencies.
  • a radiation monitoring arrangement may readily be combined with the door construction to give an alarm when the radiation leaking to the outside of the cabinet exceeds a predetermined and safe limit.
  • the cabinet is formed with a lip surrounding the door opening, which lip extends inwardly, preferably in the form of a truncated cone or pyramid, like a funnel; the door fits into the truncated funnel, with matching sides, spaced a very small distance apart.
  • the spacing may be determined by 3,436,508 Patented Apr. 1, 1969 a plastic coating, applied to the door or to the cabinet lip.
  • a metallic contact is provided by the door against the cabinet on the outside, that is beyond the termination of the parallel sides of door projection and lip.
  • the door projection and the lip together form a wave guide having a characteristic impedance to 1,000 times, that is 2 to 3 orders of magnitude (on a decimal scale) lower than the internal impedance of the cabinet.
  • a discontinuity of impedance is formed within the cabinet in the region of the juncture of door projection and lip, which discontinuity will cause reflection, rather than penetration into the low impedance wave guide.
  • Such penetration as does occur will be of such low power that the metallic contact at the outside of the wave guide, between door and cabinet, can readily short circuit the still transmitted radiation.
  • the door is suspended by means of a linkage arrangement, for example a parallelogram arrangement to provide for parallel seating at the final point of travel of the door within the lip.
  • a linkage arrangement for example a parallelogram arrangement to provide for parallel seating at the final point of travel of the door within the lip.
  • the polarization of waves leaving the interior of the cabinet is normally approximately vertical to the surface of the door or its frame. It is therefore simple to provide an antenna, such as a wire or a number of wires looped around the door, mounted in an insulating material, such as a plastic head or strip, to pick up radiation leaking beyond the seal. These monitoring wires, acting like antennas, are then connected to an alarm device, for example over an amplifier.
  • the alarm device can give an audible, visual, or other signal to warn of excessive radiation beyond the cabinet, and further may actuate a safety switch to disconnect the radiation generator and prevent damage or hazards.
  • the spacing between the internally projecting lip surrounding the door opening, and the matching projecting portions of the door itself, may be in the order of 1 mm. or so; if a plastic liner is used, either on the door or on the lip, the resistance of the wave guide formed by door and lip will be in the order of about 1 ohm or less.
  • the wave resistance of the cabinet iself may vary from about 100 ohms to an average of several hundred ohms to in excess of thousand ohms. Thus, severe discontinuities of resistance will occur just at the point where reflections are desired, and little radiation will escape in the space formed by the wave guide between door and cabinet.
  • FIG. 1 is a cross sectional view illustrating the door construction, and adjacent parts of the cabinet, in section;
  • FIG. 2 is a view similar to FIG. 1, showing an alternative embodiment of door construction, with the door partly open;
  • FIG. 3 is a pictorial view of a cabinet with a door of a construction similar to FIG. 1;
  • FIG. 4 is a schematic circuit diagram of the control circuit.
  • the base of the door 2 is projecting from the side flanges 2, by having inwardly tapering or slanting walls 2" so that the entire construction is in the form of a truncated, closed funnel.
  • the flange 2' is formed with an inwardly extending projection 3, extending on all sides of the flange 2. Projection 3 comes to a point 4.
  • a seal 5 shown as a plastic seal with metallized surface, or covered with flexible wire netting, and further on the side against a metal strip '8, connected to the housing 1 of the cabinet.
  • Strip 8 may be a single unit, or formed with a spring overlay to make good electrical contact with projection 3.
  • the door opening of cabinet 1 matches the truncated funnel shape of the door.
  • a lip formed by a pair of slanting walls 6, 6 surrounds the door opening; between the walls 6, 6, which may be formed by folded material so as to present a re-entrant fold, insulating material 7 may be located which may be a dissipating substance.
  • the door is supported on door hinges; a bracket 22 (FIG. 1, FIG. 3) extends from the cabinet to hold the hinge mechanism.
  • the link 20, extending generally perpendicularly from base 2 of the door, and hinged at 10 thereto, is hinged at 11 to a second link 21, again extending perpendicular to link 20.
  • Link 21 is hinged at 12 to bracket 22.
  • a spring 24 is further provided, shown connected with hinge 12 in order to keep the door in a closed position.
  • a cover plate 14 closes off the mechanism, to which a handle may be attached.
  • FIG. 3 shows the door construction with cover plate 14 and handle 15 removed.
  • FIG. 2 shows an alternative form of door holding construction, using a parallelogram arrangement, having pivot points 30, and 31, 31, hinged at 33 to a link 35 which, in turn, is hinged at 32 to the door bracket 22.
  • a spring 34 again tends to hold the door in closed position.
  • the arrangement can function as a toggle to snap shut.
  • FIG. 2 also shows an embodiment in which the door opening is defined by a single wall '6, rather than by the double, re-entrant construction including walls 6, 6' of FIG. 1.
  • the sidewalls 2" of the door and wall 6 (or 6) of the cabinet are separated by a small distance, for example in the order of 1 mm. or so. This separation can be obtained, for example by covering either the door sidewalls 2", or the cabinet door opening wall 6 (or 6') by a thin plastic liner, shown at 16 in FIG. 2 (and omitted from FIG. 1 for purposes of clarity).
  • "Separating walls 2" and 6, rather than providing a short-circuited electrical contact, will form between walls 2" and 6 a wave guide having a characteristic impedance very much less than the characteristic impedance of the interior of the cabinet. A severe discontinuity will thus result at the edge of the thus formed wave guide indicated at D (FIG.
  • the walls 6 (or 6) of the cabinet form a lip extending around the door opening, converging at an angle to match the angle of convergence of the sum of the funnel shaped projecting section of the door.
  • the dielectric 7 within the re-entrant portion 6, 6' can act as a dissipating section to dissipate radiation along the wave guide formed therebetween, for any radiation not reflected at point D and reaching point E within the door and the cabinet structure.
  • a single Wall 6, to which a dielectric such as plastic coating 16 is applied, both for spacing as well as for mechanical sealing purposes will suflice.
  • the energy reaching point B is usually so low that it can readily be short-circuited by contact between projection 3 and cabinet contact member 8.
  • said radiation pickup means includes a loop of conductors located on the cabinet just beyond the outer edge of the door opening and surrounding said door opening.
  • a construction as claimed in claim 1 including alarm means connected to said radiation pickup means, said alarm means being operative upon detection of radiation in excess of a predetermined level by said radiation pickup means.
  • a construction as claimed in claim 4 wherein a first link is provided extending generally perpendicular to the door and mounted for limited swinging movement thereon; a second link extending generally parallel to said door and mounted for limited swinging movement with respect to said first link at one end thereof, and secured for swinging movement at the other end thereof to said cabinet.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Electric Ovens (AREA)
US574475A 1965-08-26 1966-08-23 Cabinet and door construction for microwave heating appliances Expired - Lifetime US3436508A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DEF0046989 1965-08-26
DEF0030213 1965-08-26

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US3436508A true US3436508A (en) 1969-04-01

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US574475A Expired - Lifetime US3436508A (en) 1965-08-26 1966-08-23 Cabinet and door construction for microwave heating appliances

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CH (1) CH442563A (enrdf_load_html_response)
SE (1) SE325351B (enrdf_load_html_response)

Cited By (9)

* 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
DE2224165A1 (de) * 1972-05-18 1973-11-29 Zanussi A Spa Industrie Sicherheitseinrichtung gegen unerwuenschte ausstrahlung aus ukw geraeten
US3956608A (en) * 1971-10-19 1976-05-11 U.S. Philips Corporation Energy seal for a microwave oven
FR2399780A1 (fr) * 1977-08-01 1979-03-02 Bosch Siemens Hausgeraete Four a micro-ondes comportant une porte du type a tiroir
US4211910A (en) * 1977-12-21 1980-07-08 Matsushita Electric Industrial Co., Ltd. High frequency heating apparatus with improved door arrangement
FR2449849A1 (fr) * 1979-02-23 1980-09-19 Pruines Iseco De Systeme de securite pour porte de four a micro-ondes
EP0287549A1 (de) * 1987-04-14 1988-10-19 Helmut Dr. Katschnig Vorrichtung zum Erhitzen von Gegenständen und Organismen
US4982053A (en) * 1988-01-13 1991-01-01 The Marconi Company Limited Closure arrangement including a radio frequency seal
US6462320B1 (en) * 1996-05-17 2002-10-08 Technology Finance Corporation (Proprietary) Limited Dielectric heating device employing microwave heating for heating or cooking substances

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB587361A (en) * 1944-08-18 1947-04-23 Standard Telephones Cables Ltd Improvements in or relating to apparatus for heating by high frequency electric currents
US2512751A (en) * 1946-08-01 1950-06-27 Girdler Corp Dielectric heating system having provision for selection of preset electrode spacings
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
US3219747A (en) * 1963-02-08 1965-11-23 James H Mcadams Shielding arrangement with wave guide below cutoff

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB587361A (en) * 1944-08-18 1947-04-23 Standard Telephones Cables Ltd Improvements in or relating to apparatus for heating by high frequency electric currents
US2512751A (en) * 1946-08-01 1950-06-27 Girdler Corp Dielectric heating system having provision for selection of preset electrode spacings
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
US3219747A (en) * 1963-02-08 1965-11-23 James H Mcadams Shielding arrangement with wave guide below cutoff

Cited By (10)

* 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
US3956608A (en) * 1971-10-19 1976-05-11 U.S. Philips Corporation Energy seal for a microwave oven
DE2224165A1 (de) * 1972-05-18 1973-11-29 Zanussi A Spa Industrie Sicherheitseinrichtung gegen unerwuenschte ausstrahlung aus ukw geraeten
FR2399780A1 (fr) * 1977-08-01 1979-03-02 Bosch Siemens Hausgeraete Four a micro-ondes comportant une porte du type a tiroir
US4211910A (en) * 1977-12-21 1980-07-08 Matsushita Electric Industrial Co., Ltd. High frequency heating apparatus with improved door arrangement
FR2449849A1 (fr) * 1979-02-23 1980-09-19 Pruines Iseco De Systeme de securite pour porte de four a micro-ondes
EP0287549A1 (de) * 1987-04-14 1988-10-19 Helmut Dr. Katschnig Vorrichtung zum Erhitzen von Gegenständen und Organismen
US5098665A (en) * 1987-04-14 1992-03-24 Helmut Katschnig Device for heating of articles and organisms
US4982053A (en) * 1988-01-13 1991-01-01 The Marconi Company Limited Closure arrangement including a radio frequency seal
US6462320B1 (en) * 1996-05-17 2002-10-08 Technology Finance Corporation (Proprietary) Limited Dielectric heating device employing microwave heating for heating or cooking substances

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SE325351B (enrdf_load_html_response) 1970-06-29
CH442563A (de) 1967-08-31

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