US3629537A - Microwave oven door seal having dual cavities fed by a biplanar transmission line - Google Patents

Microwave oven door seal having dual cavities fed by a biplanar transmission line Download PDF

Info

Publication number
US3629537A
US3629537A US70641A US3629537DA US3629537A US 3629537 A US3629537 A US 3629537A US 70641 A US70641 A US 70641A US 3629537D A US3629537D A US 3629537DA US 3629537 A US3629537 A US 3629537A
Authority
US
United States
Prior art keywords
door
wall
section
opening
transmission line
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
US70641A
Other languages
English (en)
Inventor
Duane Buford Haagensen
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.)
Panasonic Holdings Corp
Original Assignee
Matsushita Electric Industrial Co Ltd
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 Matsushita Electric Industrial Co Ltd filed Critical Matsushita Electric Industrial Co Ltd
Application granted granted Critical
Publication of US3629537A publication Critical patent/US3629537A/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
    • H05B6/76—Prevention of microwave leakage, e.g. door sealings
    • H05B6/763—Microwave radiation seals for doors

Definitions

  • ABSTRACT A microwave oven door seal is established when [45] Patented Dec. 21, 1971 an access opening of a heating cavity is closed by a door.
  • A'ssignee m m mu-1 m-l m 1 seal includes a biplanar transmission line which extends in a K'doma. O k Japan first direction from'within the heating cavity to a point outside the heating cavity.
  • the biplanar transmission line turns and extends in a second direction away from the acl l MICROWAVE VEN DOOR SEAL HAVING DUAL cess opening.
  • a first electromagnetic wave filter is fed by the CAV ITIES FED BY A BIPLANAR TRAN MI first portion of the biplanar transmission line and a second electromagnetic wave filter is fed by the second portion of the 26 (,lalms, lDrawlng Flgs. biplanar transmission line for reducing the amount of elecs21 u.s.
  • the filters are cavities which are located along the biplanar Field of Search 219/1055 transmissim and are design OccuPY minimum of space to provide room for an observation window in the door.
  • the present invention relates to a heating cavity for subjecting products to electromagnetic wave energy. More particularly, it relates to a microwave oven door seal having dual electromagnetic wave energy seals fed by a biplanar transmission line which extends around an access opening of the heating cavity to limit the leakage of such energy from the heating cavity.
  • the maximum permissible radiation from a new microwave oven would be 1.0 milliwatt per square centimeter and that from any microwave oven (independently of the duration of use thereof) would be 5.0 milliwatts per square centimeter.
  • compression seal plates have been used.
  • these seals require excessive pressure across the two surfaces to be sealed and the pressure spring used therein may wear or break, rendering the seal ineffective.
  • the compression seal plates are generally thin and fragile, they are easily broken by cooking utensils.
  • the size of the seal is compatible with an objective of maximizing the area of an observation window in the door.
  • a device to absorb microwave energy during no-load operation of the oven may be located at the high impedance location so that the volume of the heating cavity need not be reduced to provide no-load protection.
  • the door in a second embodiment of the present invention is mounted so that it extends from the opposite side toward the one side at an obtuse angle relative to a wall at the one side of the heating cavity.
  • an object of the present invention is to provide a new and improved microwave oven door seal.
  • Another object of the present invention is to limit the amount of electromagnetic wave energy which leaks from a microwave oven when the oven door is closed and during an initial portion of the opening movement of the door.
  • a further object of this invention resides in the provision of a microwave energy door seal which is effective to limit the amount of microwave energy which leaks from a microwave oven and which occupies a minimum amount of space so that other features, such as an observation window for viewing a product in the oven, may have an increased and more functional size.
  • Still another object of the present invention is to provide a transmission line which commences within and extends out of a microwave oven cavity in more than one plane for feeding microwave energy to a pair of compact microwave energy filters, wherein the transmission line and the filters are effective to limit the amount of such microwave energy that leaks from the microwave oven.
  • An additional object of the present invention resides in the provision of an obtuse angular relationship between a first wall of a microwave heating cavity and the closed position of an inner wall of a microwave oven door, wherein the angular relationship positions the elements of a door seal for predetermined movement during the initial opening of the door so that the effectiveness of the seal remains relatively constant during such opening of the door.
  • FIG. 1 is a perspective view of a first embodiment of a microwave oven which may include a door seal embodying the principles of the present invention to limit the amount of radiation which is transmitted past a door and is emitted from a heating'cavity of the oven;
  • FIG. 2 is another perspective view of the oven depicted in FIG. 1 showing the door in an open position to expose the heating cavity;
  • FIG. 3 is vertical sectional view of the microwave oven shown in FIG. 1 illustrating the door seal including a biplanar transmission line and first and second filter cavities fed by the transmission line;
  • FIG. 4 is an enlarged view of a portion of FIG. 3 showing the details of one of the door seals
  • FIG. 5 is a top partial sectional view of a modified heating cavity structure in conjunction with a door provided with a door seal;
  • FIG. 6 is a partial vertical sectional view illustrating a first filter cavity provided in the wall of an outer housing rather than in the door;
  • FIG. 7 is a partial vertical sectional view of the first filter cavity containing a block of material for attenuating microwave energy during no-load operation of the microwave oven;
  • FIG. 8 is a perspective view of a second embodiment of the microwave oven of the present invention showing a slanted cavity frame and a door in the open position;
  • FIG. 9 is a vertical cross-sectional view of the oven of FIG. 8 showing the door in a closed position wherein an inner wall thereof extends at an obtuse angle relative to a given wall of the heating cavity;
  • FIG. 10 is a partial vertical sectional view of the oven shown in FIG. 9 illustrating successive positions of the door as the door is opened, wherein the length and the width of a first portion of the transmission line decrease as the door is opened.
  • a microwave oven 10 embodying the principles of the present invention is shown including an enclosure or outer housing 12 containing a heating chamber or cavity 14 and a power source 16 connected to a waveguide 18 for supplying electromagnetic wave energy to the heating cavity 14 for heating a product (not shown) received in the heating cavity 14.
  • a door 20 is shown provided with a handle 22 for opening the heating cavity to receive the product. When the door 20 is closed, an electromagnetic wave energy door seal 24 is effective to limit the amount of electromagnetic wave energy which leaks from the heating cavity 14 as the product is heated.
  • the door is also shown having a frontal face 26 which borders a window or screen 28 which is perforated to minimize the radiation of electromagnetic energy while permitting the product to be observed during heating.
  • the width 30 of the frontal face 26 is minimized so that the observation screen 28 may have a maximum area for a given overall height 32 and width 34 of the door 20. Further, according to another object, the door seal 24 is provided while retaining a maximum amount of the heating cavity depth 36.
  • FIG. 2 a first embodiment of the present invention is shown including the outer housing 12 and the heating cavity 14 received therein.
  • the door 20 is shown in an open position to expose an opening 38 at one side of the outer housing 12.
  • the opening 38 permits access to the heating cavity 14 for placing products (not shown) in the heating cavity 14.
  • the door 20 is provided with an inner wall 40 which is positioned in the heating cavity when the door is closed (FIG. 3).
  • the perimeter 42 of the inner wall 40 is spaced from the sidewalls 44 of the enclosure 12 by a selected gap 46.
  • the electromagnetic wave energy seal 24 is provided for limiting the amount of energy which leaks through the gap 46 and out of the oven 10 when the door 20 is closed and the electromagnetic wave energy is supplied to the heating cavity 14.
  • the seal 24 includes a first portion 48 of a biplanar transmission line 50 which has an origin 52 adjacent the perimeter 42 of the inner wall 46.
  • the first portion 48 extends out of the heating cavity and feeds a second portion 54 of the transmission line 50.
  • the second portion 54 extends along a cavity frame or border member 56 of the enclosure in a plane other than that of the first portion 48 so that the transmission line 50 is biplanar.
  • the seal 24 also includes dual, first and second electromagnetic wave filters 58 and 60, respectively which are located along the biplanar transmission line 50 such that a low electrical impedance appears at the origin 52 of the biplanar transmission line 50. More particularly, a first opening 62 is provided in the first portion 48 of the transmission line 50 at a first distance 64 of less than one-quarter wavelength from the origin 52; whereas a second opening 66 is provided in the second portion 54 of the transmission line 50 at a second distance 68 of about an odd number of one-quarter wavelengths from the origin.
  • a partition 70 is provided in the first filter 58 to establish therein a selected electrical length 72 extending from the first opening 62 to a terminating surface 74 of the first filter 58 such that the sum of the first distance 64 from the origin 52 to the first opening 62 plus the selected electrical length 72 equals about an even multiple of onequarter wavelength.
  • the second distance 68 from the origin 52 to the second opening 66 equals about one-quarter wavelength and the total distance from the origin 52 to a closed end or terminating surface 74 of the first filter 58 equals about one wavelength.
  • the enclosure 12 contains an inner, rear wall 76 and four of the inner sidewalls 44 which extend forwardly from the rear wall 76.
  • the upper sidewall may be referred to as the top wall 78 and the lower sidewall may be referred to as the bottom wall 80.
  • the sidewalls 44 and the rear wall 76 mutually intersect to define the heating cavity.
  • Each of the sidewalls 44 extends forwardly from the rear wall 76 to a terminus 82 which fonns a perimeter 84 of the access opening 38.
  • a dashed line 86 is shown in FIG. 2 to define an outer portion 88 of each of the sidewalls 44.
  • the outer portion 88 extends rearwardly from each terminus 82 for a selected distance 90.
  • the enclosure 12 has been described as having planar walls, it is to be understood that the present invention may also be provided on an enclosure formed from one or more arcuate walls.
  • the present invention may be used in conjunction with an enclosure 92 having a single wall structure as shown in FIG. 5.
  • a rear wall 94 and sidewalls 96 form both a housing and define a heating cavity 98.
  • forward ends 100 of the sidewalls 96 have a border section or cavity frame 102 provided with a return lip 104 which extends back into the heating cavity 98.
  • An inner surface 106 of the lip 104 defines the perimeter of an access opening 108 and also corresponds to the outer portion 88 of the sidewalls 44 shown in FIG. 2.
  • the cavity frame 56 has an inner perimeter which is coextensive with the termini 82 of the sidewalls 44. Further, the cavity frame 56 extends from the inner perimeter thereof in a plane other than that of the sidewalls 44. As shown in FIG. 2, the cavity frame 56 surrounds and provides an outer border for the access opening 38.
  • the door 20 is mounted on a hinge 1 which extends along a lower portion 1 12 of the enclosure 12. If it is desired to move the door relative to the enclosure 12 in a different manner, the hinge 110 may be provided on the left or right side of the enclosure, for example. Alternatively, the door 20 may be secured to the enclosure 12 in such a manner that it moves in a rectilinear, rather than arcuate, path away from the cavity frame 56.
  • the door 20 may be rotated counterclockwise on the hinge 110 into the closed position shown in FIGS. 3 and 4.
  • the inner wall 40 is received in the heating cavity 14 and extends across the access opening 38.
  • the central area of the inner wall 40 of the door 20 is provided in a well-known manner with many small diameter cylindrical apertures 114 which form the screen 28 to permit visual observation of the product in the heating cavity 14 without permitting more than a minute amount of electromagnetic energy to be transmitted from the heating cavity 14.
  • the inner wall 40 extends across and closes the access opening 38 except for the gap 46. Because the seal 24 causes a low electrical impedance to appear at the origin 52 of the transmission line 50, the amount of electromagnetic wave radiation which is transmitted through the transmission line 50 and out of the oven 10 is less than the maximum value of 1.0 milliwatt per square centimeter permitted under the proposed radiation standards.
  • the biplanar transmission line 50 includes a first transmission line element 116 extending from each side of the perimeter 42 of the inner wall 40 of the door 20.
  • Each of the first elements 1 16 extends generally parallel to the outer portion 88 of the sidewall 44 opposite thereto and is spaced therefrom by the width of the gap 46.
  • the first elements 116 extend out of the heating cavity 14 and past the plane 118 of the cavity frame 56 by an amount equal to the width of the gap 46 whereupon each intersects a second transmission line element 120.
  • Each of the second elements 120 extends in parallel, overlapping relationship with the cavity frame 56.
  • the first transmission line elements 116 and the portions 88 of the sidewall 44 opposite thereto form the first portion 48 of the transmission line 50 having a width equal to the width of the gap 46.
  • the first portion 48 extends from each side of the inner wall 40 of the door 20 and has a length which is less than an odd multiple of one-quarter wavelength as measured from the origin 52 of the transmission line 50.
  • the first and second portions 48 and 54, respectively, of the transmission line 50 extend in different planes.
  • the biplanar arrangement permits the width 122 and the height 124 of the access opening 38 to be maximized for a given height 32 and width 34 of the enclosure 12 without significantly reducing the usable depth 36 of the heating cavity 14.
  • the biplanar arrangement uses a minimum amount of the width 30 of the frontal face 26 of the door 20 so that the area of the observation screen 28 is maximized for a given width and height of the door 20.
  • the first opening 62 is in the form of a slot which extends through each first transmission line element 116 at the first distance 64 from the origin 52 so that electromagnetic wave energy is fed from the transmission line 50 into the first filter 58.
  • the first filter 58 is provided with a cavity 126 defined by respective surfaces 128 and 130 of the inner wall 40 and the first element 116.
  • a cavity wall 132 mounted opposite to the first opening 62 is provided with a surface 134 which extends from the inner wall surface 128 to a surface 136 of the frontal face 26 of the door 20.
  • the electrical length from the origin 52 to the terminating surface 74 of the first cavity 126 must be equal to about an even multiple of onequarter wavelength so that a low electrical impedance appears at the terminating surface 74 of the first filter cavity 126.
  • the partition 70 is mounted to the closed end 74 of the first cavity 126.
  • the partition 70 extends generally parallel to the cavity wall 132 and defines a serpentine or tortuous electrical path 138 within the first cavity 126.
  • the path 138 defined by the partition 70 has the selected electrical length 72 from the first opening 62 to the terminating surface 74 so that the selected electrical length 72 plus the first distance 64 are equal to about an even multiple of onequarter wavelength.
  • at least one high impedance appears along the electrical path 138 inside the first cavity 126 between the first opening 62 and the terminating surface 74.
  • the second opening 66 is in the form of a slot which extends through each second transmission line element 120 at the distance 68 from the origin 52 so that electromagnetic wave energy is fed from the transmission line 50 into the second filter 60.
  • the second filter 60 is provided with a second cavity 140 defined by a surface 142 of the second element 120 and by a surface 144 of a cavity wall 146 which is opposite to the surface 142.
  • the frontal face 26 extends around a corner toward the cavity frame 56 to provide a terminating surface 148 for closing the second filter cavity 140.
  • the second distance 68 is about an odd multiple of one-quarter wavelength. Because the second cavity 60 is closed ended, the distance from the second opening 66 to the terminating surface 148 is selected such that a low electrical impedance also appears at the terminating surface 148.
  • the distance 68 (the sum of distances 64 and 150) is an odd multiple of one-fourth wavelength and that the sum of the distance 64 and the length 72 is about an even multiple of one-fourth wavelength.
  • the distance 64 may be 0.5 units, for example, and the distance 68 may be 1 unit.
  • the partition 70 will be effective to reduce the door depth and the width 30 of the frontal face 26 required for the seal 24. With these distances selected, it may be understood that the following relationships result:
  • the physical length of 3.5 units is less than 3.5 times 1.25 inches, which is the numerical value of one-fourth wavelength in air at 2,450 megacycles per second.
  • the actual physical length of the path 138 from the opening 62 to the terminating surface 74 is 10 cm., for example.
  • the door depth can be as short as 4 cm. plus the thickness of the sheet metal used to fabricate the door.
  • the dual filters 58 and 60 of the first embodiment are shown in a different arrangement which permits an even smaller door face width 30 and a resulting greater area for the observation screen 28.
  • the heating cavity 14 is shown defined by the inner door wall 40 and the side wall 44.
  • the origin 52 of the biplanar transmission line 50 is adjacent the intersection of the inner door wall 40 and the first section 1 16.
  • the transmission line 50 extends from the origin 52 along the first portion 48 and the second portion 54.
  • a first opening 62' extends through the wall 44 to permit electromagnetic wave energy to enter a cavity 126' of the first filter 58 which is provided in a space 151 between the inner walls 44 and outer walls 154.
  • the first cavity 126 is defined by a surface 156 of a wall 158 and a surface 160 of a wall 162 opposite to the first opening 62'.
  • a terminating surface 74' is provided in the first cavity 126' and supports a partition 70' for defining the electrical path 138. It may be understood that because the first cavity 126' is provided in the space 151, the width 30 of the frontal face 26 is decreased so that the area of the observation screen 28 may be increased.
  • the second filter 60 is similar to the second filter described above in reference to FIGS. 3 and 4. Also, the spacing of the first and second openings 62 and 66, respectively, as well as the dimensions of the cavities 126' and 140 are similar to those described above.
  • FIG. 7 a view similar to FIG. 4 but reduced in size illustrates the door seal 24 provided with facilities 166 to protect the oven 10 in the event the power source 16 supplies electromagnetic wave energy to the heating cavity 14 when no product or load is in the heating cavity to absorb such energy.
  • the door is shown in the closed position with the biplanar transmission line 50 and the dual filters 58 and 60 positioned to limit the amount of radiation emitted from the heating cavity 14.
  • a product or other lossy material is placed in the heating cavity 14 and absorbs a major portion of the electromagnetic wave energy which is supplied to the heating cavity.
  • only a minute amount of input energy leaks into the transmission line 50 past the low impedance which appears at the origin 52.
  • the microwave oven 10 when only a small amount of energy is absorbed by a product in the heating cavity or when there is no lossy material in the heating cavity 14, the microwave oven 10 is said to be operating at no-load.” Under such no-load conditions, a substantial amount of electromagnetic wave energy may leak past the origin 52 and into the transmission line 50. To render the seal effective in reducing the amount of electromagnetic wave energy which leaks completely out of the oven 10, the high impedance which exists in the cavity 126 of the first filter $8 is used to advantage. In particular, it may be recalled that because of the location of the first opening 62 relative to the origin 52, one or more high impedances appear within the first cavity 126. A block 168 of material having selected properties is mounted within the first cavity 126 at the location of one of such high impedances.
  • the material selected resists deterioration at high temperatures such as 1,200 F. for example, and is electrically lossy.
  • high-temperature resistant silicone carbide high-temperature resistant silicone carbide, water extended polyethylene and silicone rubber graphite. These materials may be used in their commercially available forms.
  • the block 168 mounted at the location of one of the high impedances is effective to absorb the electromagnetic wave energy which leaks into the biplanar transmission line 50. As a result, a substantial portion of the electromagnetic wave energy supplied to the heating cavity 14 is absorbed so that only a limited amount of such energy is emitted from the oven 10.
  • FIGS. 8-10 there is shown a second embodiment of the present invention.
  • the advantages of the second embodiment are particularly significant in the event the microwave oven is not equipped with a safety lock (not shown) for the door, for example.
  • the door 20 may be held tightly closed by the lock and the lock must be secured before the power source 16 can be conditioned for operation.
  • some manufacturers provide microwave ovens with a device (not shown) which interrupts or prevents the operation of the power source 16 in the event the door 20 is open more than a very slight amount. After a period of usage, the part of such devices which senses the position of the door 20 may wear or otherwise require adjustment.
  • the device may permit the power source 16 to continue to operate even though the door 20 is open to such an extent that conventional energy seals around the door are no longer effective and allow as much as 200 milliwatts per square centimeter, for example, of energy to leak from the microwave oven 10.
  • the second embodiment overcomes this disadvantage by providing a door seal which is effective over a greater range of door movement than conventional door seals.
  • the second embodiment of the present invention is shown provided on a microwave oven 180.
  • the oven 180 is similar in design to the oven 10 in that it is provided with an outer housing 182 which defines a heating cavity 184. Also, electromagnetic wave energy is supplied from the source 16 to the heating cavity 184 through the waveguide 18.
  • the oven 180 is provided with a heating cavity frame 186 and a door 188 which are mounted in a new relationship with respect to the walls 44 of the oven 180. This new relationship enhances the effectiveness of the radiation seal provided by a top section 190 of the first portion 48 of the biplanar transmission line 50 and the first filter 58 as the door 188 is opened. More particularly, as shown in FIG.
  • the door 188 in its closed position the door 188 slants or slopes toward the rear wall 76 of the oven 180 and is positioned at an acute angle relative to a vertical line 192.
  • the door 188 also extends toward the top wall 78 at an obtuse angle therewith and extends away from the bottom wall at an acute angle.
  • the length 194 (FIG. 10) of the top section 190 of the first portion 48 of the transmission line 50 decreases.
  • the first portion 48 of the transmission line 50 consists of inductive and capacitive elements, thus, the capacitance thereof increases as the width of the gap 46 decreases.
  • the increase in the capacitance decreases the length 194 of the top section 190 which is required to produce a given resonant frequency for the top section of the transmission line. Therefore, with the door 188 mounted to the bottom of the enclosure 182 at the obtuse angle relative to the outer portion 88, it may be appreciated that as the door 188 is initially opened, the decrease of the width of the gap 46 across the top section 190 is counteracted by the decrease in the length 194 of the top section 190 so that the resonant frequency of the top section of the transmission line 50 remains relatively constant during the initial open ing movement of the door 188.
  • the top section 190 of the first portion 48 of the transmission line 50 and the first filter 58 will continue to limit the amount of electromagnetic wave energy which leaks out of the heating cavity 184.
  • the provision of such improved radiation seal along the top section 190 of the transmission line 50 decreases the likelihood that excessive radiation will be emitted in the event the door is opened before a door actuated safety switch (not shown) interrupts operation of the power source 16.
  • the outer housing 182 is shown containing the rear wall 76 and the sidewalls 44 which extend vertically between the top and bottom walls 78 and 80, respectively.
  • the housing 182 is truncated so that the inner wall 40 of the door 188 will be positioned at an acute angle with respect to the top wall 78.
  • the top wall 78 extends forwardly from the rear wall 76 a shorter distance than the bottom wall 80 extends forwardly from the same wall.
  • a terminus 196 of the bottom wall 80 is spaced from the rear wall 76 by a greater distance than the spacing of a terminus 198 of the top wall 78 from the rear wall 76.
  • the termini 196 and 198 cooperate with termini 200 of the sidewalls 44 to form the perimeter of a tilted access opening 202.
  • the outer portion 88 of each of the top, bottom and sidewalls 78, 80 and 44 respectively extends from the perimeter of access opening 202 rearwardly to the dashed line 86 as shown in FIG. 8.
  • the cavity frame 186 has an inner perimeter 204 which is coextensive with the perimeter of the tilted access opening 202.
  • the cavity frame 186 is positioned at an acute angle relative to the vertical line 192 and extends from the inner perimeter 204 to the outer housing 182. Further, the cavity frame 186 extends at an acute angle relative to the outer portion 88 and at an obtuse angle relative to the bottom wall 80.
  • the hinge 110 is shown mounting the door 188 for rotary movement from the closed position shown in FIG. 9 to the open position shown in FIG. 8.
  • the hinge 110 is designed to stop the rotation of the door when it is in closed position with the inner wall 40 thereof at the acute angle relative to the vertical line 190.
  • the inner wall 40 closes the access opening 202 except for the gap 46 which exists between the perimeter 42 of the inner wall 40 and the top, bottom and sidewalls 78, 80 and 44, respectively.
  • the oven 188 is provided with the biplanar transmission line 50 which includes the first portion 48 and the second portion 54 extending around the four sides of the door 188.
  • the first portion 48 includes one of the first transmission line elements 116 extending from each side of the perimeter 42 of the inner wall 40. Because the inner wall 40 is not perpendicular to the top wall 78, a top transmis sion line element 206 intersects the inner wall 40 at an acute angle.
  • the top element 206 extends generally parallel to the outer portion 88 of the top wall 78, which is opposed thereto and is spaced therefrom by the width of the gap 46 when the door 188 is in the closed position (FIG. 9').
  • the first transmis sion line element 206 extends out of the heating cavity 184 and intersects the respective second transmission line element 120. As shown in FIG. 9, in the closed position of the door 188, the second position of the door 188, the second transmission line element 120 is spaced from the cavity frame 186 by the width of the gap 46 and extends at an acute angle relative to the vertical line 192 in parallel relationship with the cavity frame 186, which is overlapped thereby form the second portion 54 of the biplanar transmission line 50.
  • the first and second filters 58 and 60 are mounted in the door 188 and cooperate with the transmission line 50 so that a low impedance appears at the origin 52 of the gap 46 when the door 188 is closed.
  • FIG. 10 where the initial opening movement of the door 188 is shown in successive steps.
  • the sloped cavity frame 186 and the outer portion 88 are shown in cross section, whereas (for the closed l 0 position of the door) the first and second transmission line elements 206 and 120, respectively, are shown in solid lines.
  • the gap 62 and the length 194 of the first portion 48 of the transmission line 50 are also shown for the door 188 in the closed position.
  • the top transmission line element 206 and the other structure of the door assume the dashed line position in which the width of the gap 46 has decreased to a smaller gap 220 and the length 194 of the first portion 48 of the transmission line 50 has shortened to a length 222.
  • the resonant frequency of the top section 190 of the transmission line 50 remains relatively constant during the de picted initial opening movement of the door 188.
  • the top section 190 of the first portion 48 of the transmission line 50 and the first filter 58 fed thereby will continue to limit the amount of electromagnetic wave energy which leaks through the top section 190 out of the heating cavity 184.
  • a microwave oven door 20 having a biplanar transmission line 50 extending across the upper section of the cavity frame 56 was found to limit the leakage of electromagnetic wave radiation to less than 1.0 milliwatt per square centimeter measured at the appropriate distance from the door 20 for the electromagnetic wave frequency (2,450 megacycles per second) used with the door 20 in its normal closed position.
  • the door constructed had a cavity frame 56 having a width of 1.156 inches and a length of 17.0 inches.
  • the gap was 0.125 inches between the cavity frame 56 and the second element and between the outer portion 88 of the top wall 78 and the first element 116.
  • the inner wall 40 extended 1.875 inches into the heating cavity 14 past the access opening 38.
  • the cavities 126 and 140 were constructed from metal having a thickness of 0. inch.
  • the first distance 64 was 0.875 inch and the size of the first opening 62 was 0.25 inch by the width of the cavity frame 56.
  • the door 20 was constructed to illustrate the radiation sealing effect without minimizing the size of the seal, thus the second distance 68 was selected to be about three-fourths of l wavelength in air. However, to shorten the physical length 212 of the second cavity and permit use of a standard test door, the second cavity 140 was filled with polypropylene which decreased the distance 68 to 3,563 inches. However, the data taken are still representative of the improved sealing characteristics of the oven 10 shown in FIG. 4.
  • the size of the second opening 66 was 0.1875 inch and the distance 212 was 0.938 inch, and the internal depth of the second cavity 140 was 0.406 inch.
  • the first cavity had an internal depth of 0.75 inch, and a length of 1.75 inches.
  • the terminating surface 74 was located 0.625 inch from the surface 136 and the partition 70 had a length of 1.0 inch.
  • the width 214 of the electrical path 138 was 0.406 inch and the width 216 of such path 138 was 0.250 inch.
  • the length of the partition 70 was 1.0 inch.
  • the power source 16 provided electromagnetic wave energy at the frequency of 2,450 megacycles per second, the door 20 was in its closed position and the amount of radiation was measured with a sensitive radiation detector.
  • the constructed door 20 was found to effectively prevent the electromagnetic wave energy from being emitted from the heating cavity 14 through the gap 46 and out of the oven 10.
  • heating cavity having an access opening, said heating cavity being defined by at least one wall
  • a door movable into a position for closing said access opening, said door having a first section, when said door is closed said first section extending through said access opening into said heating cavity to form a first portion of a biplanar transmission line, said first portion of said biplanar transmission line having an origin adjacent the inner end of said first section;
  • said door having a second section extending from the outer end of said first section in overlapping relationship with said member to form a second portion of said biplanar transmission line;
  • a first electromagnetic wave filter provided in one of said walls and said first section, said first filter having a first opening extending through said one of said wall and said first section, said first opening being located at a given distance from said origin;
  • a second electromagnetic wave filter provided in one of said member and said second section, said second filter having a second opening formed through said one of said member and said second section and spaced from said origin by about an odd number of one-fourth wavelengths.
  • said given distance is less than one-fourth wavelength
  • said first and second openings are located in difierent planes and are spaced from each other by less than one-fourth wavelength.
  • said first filter includes a terminating surface and a side surface opposite to said one of said wall and said first section for defining one side of a transmission path from said first opening to said terminating surface;
  • a partition is mounted in said first filter for defining the other side of said path so that the distance from said origin through said first opening and along said path to said terminating surface is about an even multiple of onefourth wavelength.
  • said distance from said origin to said terminating surface is about 1 wavelength.
  • said first filter is provided in said wall and said first opening.
  • said second filter is provided in said member and said second opening extends through said member to said second filter.
  • said first filter is provided in said first section and said first opening extends through said first section to said first filter
  • said second filter is provided in said second section and said second opening extends through said second section to said second filter.
  • said first filter is provided in said wall and said first opening extends through said wall to said first filter
  • said second filter is provided in said second section and said second opening extends through said second section to said second filter.
  • heating cavity having an access opening, said heating cavity being defined by at least one wall
  • a door having a first section extending from an origin within said cavity along said wall and through said access opening out of said heating cavity, said first section and said wall defining a first part of a biplanar transmission line;
  • a first electromagnetic wave filter provided in said first section and having a first opening thereto formed through said first section at a first distance from said origin;
  • said door having a second section extending from said first section in overlapping relationship with said member, said second section and said member defining a second part of said biplanar transmission line;
  • a second electromagnetic wave filter having a second opening formed through said second section at a second distance of about an odd number of one-fourth wavelengths from said origin.
  • a microwave oven according to claim 8 in which:
  • said first filter includes a cavity having a partition mounted therein to establish in said cavity a selected electrical length such that the sum of said first distance plus said selected length equals about an even multiple of onefourth wavelength.
  • a microwave oven according to claim 9 in which:
  • said second distance equals about one-fourth wavelength
  • said sum of said first distance and said selected electrical length equals about one wavelength.
  • said first section extends from said origin to said second section for a distance less than one-fourth wavelength.
  • a microwave oven according to claim 1 l in which:
  • said first filter includes a cavity having a terminating surface
  • a partition is mounted within said cavity, said partition being efiective to define a biplanar path from said first opening'to said terminating surface, the distance from said origin through said first opening and along said path to said terminating surface being equal to about an even number of one-fourth wavelengths.
  • said one wall and said first section establish a low electrical impedance at said origin during the operation of said oven
  • said first filter includes a cavity having a terminating surface spaced an even number of one-quarter wavelengths from said origin such that a high electric impedance appears at a selected location within said cavity during the operation of said oven;
  • heat-resistant means are mounted in said first cavity at said selected location, said means being electrically lossy for absorbing electromagnetic wave energy during no-load operation of said oven.
  • said heat-resistant means are fabricated from a material taken from the group consisting of high-temperature silicon carbide, water extended polyethylene, and silicone rubber graphite.
  • a microwave oven comprising a heating cavity defined by a plurality of intersecting sidewalls and a rear wall;
  • a cavity frame secured to said sidewalls and extending in a plane other than that of said sidewalls, said frame being v rovided with an aperture to permit access to said heating cavity;
  • a door having an inner wall, said inner wall being received within said heating cavity for closing said heating cavity when said door is in a closed position, the perimeter of said inner wall being spaced from said sidewalls by a selected gap when said door is in said closed position, said door having a first transmission line element extending from said perimeter of said inner wall along a portion of said sidewalls and out of said heating cavity for a selected distance, said door having a second transmission line element extending from the outer end of said first element across said cavity frame, said second element being spaced from said cavity frame by said selected gap when said door is in said closed position;
  • said first element and said portion of said sidewalls forming a first section of a biplanar transmission line, said line having an origin adjacent the perimeter of said inner wall;
  • said second element and said cavity frame forming a second section of said biplanar transmission line
  • a first filter cavity having a first opening extending through said first element, said first opening being spaced from said origin by a first distance;
  • a second filter cavity having a second opening extending through said second element, said second opening being spaced from said first opening by a second distance;
  • the sum of said first and second distances being about an odd multiple of one-fourth wavelength.
  • said sum of said first and second distances is equal to about one-fourth wavelength.
  • a microwave oven including a heating cavity defined by a rear wall and a plurality of sidewalls, said sidewalls defining an access opening, a frame extending from a first of said sidewalls on one side of said access opening to a second of said walls on a second opposite side of said access opening, the improvement in said oven which comprises:
  • said door being provided with a first side and a second side, said first side of said door having a first section extending along said first wall into said heating cavity when said door is in said closed position to form a first transmission line element, said first section being spaced from said first wall by a gap having a predetermined width when said door is in said closed position to form a first portion of a biplanar transmission line, said first side of said door having a second section overlapping said frame when said door is in said closed position to form a second portion of said biplanar transmission line;
  • a pair of electromagnetic wave filters a first of said filters having a first opening extending through one of said first wall and said first section and the other of said filters having a second opening extending through one of said frame and said second section;
  • said mounting means is also effective to mount said door in said closed position so that said door is tilted at a second angle relative to said second wall, said second angle being acute.
  • said frame includes a top portion adjacent said first sidewall and spaced from said rear wall by a first distance, a bottom portion adjacent said second sidewall and spaced from said rear wall by a second distance, and side portions connecting said top and bottom portions, id first distance being shorter than said second distance so that said heating cavity is truncated;
  • said mounting means is provided adjacent said bottom portion of said frame so that said door slopes toward said rear wall when said door is in said closed position.
  • said first section and said first wall define a first transmission line having an origin at the end of said first section, said origin being received in said heating cavity when said door is in said closed position;
  • said first opening is spaced from said origin by less than onequarter wavelength.
  • a partition is mounted in said first of said filters to define therein a given electrical length such that the total distance from said origin to said first opening plus said given electrical length equal about an even number of onequarter wavelengths.
  • said total distance equals about one wavelength
  • the distance from said origin to said second opening equals about one-quarter wavelength.
  • heating cavity defined by at least a first wall and a second wall opposite to said first wall, said heating cavity having an access opening between said first wall and said second wall;
  • a frame secured to said first and second walls and extending in a plane other than the planes of said first and second w l a door mounted adjacent said second wall for movement into a position for closing said access opening, said door having an inner wall extending toward said first wall at a selected obtuse angle when said door is in said closed position, said angle being measured relative to the plane defined by said first wall;
  • said door having a first transmission line element extending from the end of said inner wall for a given length in opposed relationship to said first wall, said first element extending out of said heating cavity;
  • said door having a second transmission line element extending along said frame
  • said first wall and said first element forming a first transmission line having a given width and said given length when said door is in said closed position;
  • a pair of filter cavities mounted in said door, a first of said cavities having a first opening thereto formed in said first element, a second of said cavities having a second opening thereto formed in said second element;
  • said first element being movable toward said first wall to decrease both said given width and said given length of said first transmission line as said door moves from said closed position so as to decrease said obtuse angle.
  • said door is pivotally mounted to said second wall such that said first element moves in an arcuate path during said movement of said door.
  • a rear wall extends between said first wall and said second wall
  • said first and second walls extend different distances from said rear wall to said door when said door is in said closed position:
  • a heating cavity defined by top, bottom side and rear walls, said bottom wall terminating at a given vertical plane and said top wall terminating at a location spaced toward said rear wall from said given plane so that said cavity is truncated;
  • a cavity frame secured to and extending outwardly from said top, bottom and sidewalls at the truncated end of said cavity, said frame having an aperture to permit access to said cavity;
  • a closure member having top, bottom and side portions, said bottom portion being mounted adjacent said bottom wall for pivotal movement, said closure member being movable into a closed position so that a first section thereof overlaps said cavity frame to form a first transmission line element and a second section of said member extends into said heating cavity along said top, bottom and sidewalls to form a second transmission line element;
  • a top part of said second section being spaced from said top wall by a gap having a selected width and length when said closure member is in said closed position;
  • closure member having a closure wall bounded by said top, bottom and side portions, said closure wall sloping toward said rear wall when said closure member is in said closed position;

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Constitution Of High-Frequency Heating (AREA)
  • Electric Ovens (AREA)
US70641A 1970-09-09 1970-09-09 Microwave oven door seal having dual cavities fed by a biplanar transmission line Expired - Lifetime US3629537A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
US7064170A 1970-09-09 1970-09-09

Publications (1)

Publication Number Publication Date
US3629537A true US3629537A (en) 1971-12-21

Family

ID=22096521

Family Applications (1)

Application Number Title Priority Date Filing Date
US70641A Expired - Lifetime US3629537A (en) 1970-09-09 1970-09-09 Microwave oven door seal having dual cavities fed by a biplanar transmission line

Country Status (6)

Country Link
US (1) US3629537A (de)
JP (1) JPS5145341B1 (de)
DE (1) DE2144548C3 (de)
FR (1) FR2107439A5 (de)
GB (1) GB1368105A (de)
NL (1) NL161961C (de)

Cited By (23)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3736398A (en) * 1971-11-15 1973-05-29 Litton Systems Inc Method and means for controlling electromagnetic wave energy leakage in microwave ovens
US3809843A (en) * 1970-06-01 1974-05-07 Gen Corp Microwave heating apparatus
US3835283A (en) * 1970-03-03 1974-09-10 Matsushita Electric Co Ltd Partition and front wall forming choke structure for a microwave oven
US3955060A (en) * 1974-08-14 1976-05-04 Philip Morris Incorporated Microwave oven construction
US3985993A (en) * 1974-08-29 1976-10-12 U.S. Philips Corporation Sealing arrangement in a microwave oven
US4013861A (en) * 1975-08-13 1977-03-22 The Frymaster Corporation Microwave oven door seal
US4059742A (en) * 1975-07-09 1977-11-22 Litton Systems, Inc. Microwave seal for combination cooking apparatus
US4081647A (en) * 1976-05-10 1978-03-28 Roper Corporation Energy seal for a microwave oven
US4122323A (en) * 1977-09-22 1978-10-24 General Electric Company Phase shift device for microwave oven door seal
US4166207A (en) * 1977-05-31 1979-08-28 Whirlpool Corporation Microwave generating device--door seal
US4211910A (en) * 1977-12-21 1980-07-08 Matsushita Electric Industrial Co., Ltd. High frequency heating apparatus with improved door arrangement
US4347420A (en) * 1979-09-11 1982-08-31 Matsushita Electric Industrial Co., Ltd. Microwave seal structure in microwave oven
US4449025A (en) * 1980-10-03 1984-05-15 Matsushita Electric Industrial Co., Ltd. Door seal construction for high frequency heating appliance
US4471194A (en) * 1971-05-20 1984-09-11 Matsushita Electric Industrial Co., Ltd. Electromagnetic energy seal for high frequency heating apparatus
US4475023A (en) * 1981-09-25 1984-10-02 Hitachi Heating Appliances Co., Ltd. Microwave heating apparatus with fundamental and second higher harmonic chokes
WO2006131725A1 (en) * 2005-06-06 2006-12-14 Glen Dimplex Home Appliances Limited Choke system and oven
CN100365344C (zh) * 2006-02-28 2008-01-30 王宝根 带微波吸收腔的新型微波炉
US20110290230A1 (en) * 2010-05-26 2011-12-01 Lg Electronics Inc. Door choke and cooking apparatus including the same
USD762086S1 (en) * 2014-11-13 2016-07-26 Lg Electronics Inc. Oven range
USD762415S1 (en) * 2014-11-13 2016-08-02 Lg Electronics Inc. Oven range
US20180153002A1 (en) * 2016-11-30 2018-05-31 Illinois Tool Works Inc. Rf choke and interface structures for employment with an rf oven
EP3612006A4 (de) * 2017-04-12 2020-03-04 LG Electronics Inc. -1- Kochgerät
US10873996B2 (en) * 2016-11-30 2020-12-22 Illinois Tool Works, Inc. Oven door assembly for an RF oven

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2122059B (en) * 1982-05-28 1985-08-07 Tdk Electronics Co Ltd An absorber device for microwave leakage
SE452389B (sv) * 1983-03-15 1987-11-23 Philips Norden Ab Tetningsanordning vid mikrovagsugnar
JPS60174308U (ja) * 1984-04-25 1985-11-19 株式会社ヨコオ フレキシブルアンテナのエレメント
DE102004052798B4 (de) * 2004-11-02 2006-08-31 Electrolux Home Products Corp. N.V. Garofen
DE102007043483B4 (de) * 2007-09-12 2009-07-09 Rational Ag Abdichtungsvorrichtung zum Verringern eines Mikrowellenaustrittes aus einem Gargerät und Gargerät mit zumindest einer solchen Abdichtungsvorrichtung

Citations (4)

* 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
US3197600A (en) * 1959-05-25 1965-07-27 Miwag Mikrowellen A G Door for microwave ovens
US3249731A (en) * 1963-11-14 1966-05-03 Westinghouse Electric Corp Oven

Patent Citations (4)

* 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
US3197600A (en) * 1959-05-25 1965-07-27 Miwag Mikrowellen A G Door for microwave ovens
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

Cited By (28)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
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
US4471194A (en) * 1971-05-20 1984-09-11 Matsushita Electric Industrial Co., Ltd. Electromagnetic energy seal for high frequency heating apparatus
US3736398A (en) * 1971-11-15 1973-05-29 Litton Systems Inc Method and means for controlling electromagnetic wave energy leakage in microwave ovens
US3955060A (en) * 1974-08-14 1976-05-04 Philip Morris Incorporated Microwave oven construction
US3985993A (en) * 1974-08-29 1976-10-12 U.S. Philips Corporation Sealing arrangement in a microwave oven
US4059742A (en) * 1975-07-09 1977-11-22 Litton Systems, Inc. Microwave seal for combination cooking apparatus
US4013861A (en) * 1975-08-13 1977-03-22 The Frymaster Corporation Microwave oven door seal
US4081647A (en) * 1976-05-10 1978-03-28 Roper Corporation Energy seal for a microwave oven
US4166207A (en) * 1977-05-31 1979-08-28 Whirlpool Corporation Microwave generating device--door seal
US4122323A (en) * 1977-09-22 1978-10-24 General Electric Company Phase shift device for microwave oven door seal
US4211910A (en) * 1977-12-21 1980-07-08 Matsushita Electric Industrial Co., Ltd. High frequency heating apparatus with improved door arrangement
US4347420A (en) * 1979-09-11 1982-08-31 Matsushita Electric Industrial Co., Ltd. Microwave seal structure in microwave oven
US4449025A (en) * 1980-10-03 1984-05-15 Matsushita Electric Industrial Co., Ltd. Door seal construction for high frequency heating appliance
US4475023A (en) * 1981-09-25 1984-10-02 Hitachi Heating Appliances Co., Ltd. Microwave heating apparatus with fundamental and second higher harmonic chokes
WO2006131725A1 (en) * 2005-06-06 2006-12-14 Glen Dimplex Home Appliances Limited Choke system and oven
CN100365344C (zh) * 2006-02-28 2008-01-30 王宝根 带微波吸收腔的新型微波炉
US20110290230A1 (en) * 2010-05-26 2011-12-01 Lg Electronics Inc. Door choke and cooking apparatus including the same
US9179506B2 (en) * 2010-05-26 2015-11-03 Lg Electronics Inc. Door choke and cooking apparatus including the same
USD762086S1 (en) * 2014-11-13 2016-07-26 Lg Electronics Inc. Oven range
USD762415S1 (en) * 2014-11-13 2016-08-02 Lg Electronics Inc. Oven range
US20180153002A1 (en) * 2016-11-30 2018-05-31 Illinois Tool Works Inc. Rf choke and interface structures for employment with an rf oven
CN110521281A (zh) * 2016-11-30 2019-11-29 伊利诺斯工具制品有限公司 用于射频烤箱的射频阻流器和界面结构
US10873996B2 (en) * 2016-11-30 2020-12-22 Illinois Tool Works, Inc. Oven door assembly for an RF oven
US10912166B2 (en) * 2016-11-30 2021-02-02 Illinois Tool Works, Inc. RF choke and interface structures for employment with an RF oven
CN110521281B (zh) * 2016-11-30 2022-06-03 伊利诺斯工具制品有限公司 一种烤箱和用于烤箱的射频阻流器
EP3612006A4 (de) * 2017-04-12 2020-03-04 LG Electronics Inc. -1- Kochgerät
US11589431B2 (en) 2017-04-12 2023-02-21 Lg Electronics Inc. Cooking appliance

Also Published As

Publication number Publication date
NL161961C (nl) 1980-03-17
JPS5145341B1 (de) 1976-12-03
DE2144548A1 (de) 1972-03-16
GB1368105A (en) 1974-09-25
NL7112263A (de) 1972-03-13
DE2144548C3 (de) 1978-12-07
NL161961B (nl) 1979-10-15
DE2144548B2 (de) 1978-04-27
FR2107439A5 (de) 1972-05-05

Similar Documents

Publication Publication Date Title
US3629537A (en) Microwave oven door seal having dual cavities fed by a biplanar transmission line
US2958754A (en) Electronic ovens
US3678238A (en) High frequency heating apparatus
US4471194A (en) Electromagnetic energy seal for high frequency heating apparatus
US3767884A (en) Energy seal for high frequency energy apparatus
US3654417A (en) Microwave oven including air flow system
US4677251A (en) Voltage dividing shielded door seal
US4013861A (en) Microwave oven door seal
US3182164A (en) Electromagnetic energy seal
JP2005106461A (ja) オーブンドアの電磁波遮蔽装置
US3525841A (en) Door seal for microwave ovens
US4053731A (en) Microwave energy oven seal
US3196242A (en) High-frequency oven door seal
CA1224536A (en) Microwave oven door seal
US3835283A (en) Partition and front wall forming choke structure for a microwave oven
CA2054047A1 (en) Microwave shielding device for a door of a microwave oven
US3624335A (en) Microwave oven
US3879595A (en) Microwave oven door seal
RU2134495C1 (ru) Микроволновая печь (варианты)
US4868359A (en) Radiation sealed door in a microwave heating apparatus
US4347420A (en) Microwave seal structure in microwave oven
GB2161347A (en) Microwave oven door
GB1348846A (en) High-frequency heating equipment
US3633564A (en) High-frequency sealing device
US3511959A (en) Microwave cavity having a varied impedance transmission line microwave energy seal around the access door opening