Microwave cooking device with a lambda quarter-wave trap

Abstract

A microwave cooking appliance includes a door which covers a loading opening of a cooking chamber when closed, and has a profiled trap structure to form with an electrically conductive door flange a lambda quarter-wave trap that frames the loading opening. The trap structure includes a metal choke profile with an open face opposite the door flange, inner and outer metal tongues protruding into the open face laterally on an inside and outside, respectively. The metal tongues are connected electrically to the choke profile and separated from one another by a microwave entry slot covered by a microwave-transparent cover. The choke profile is framed laterally on the outside by a parallel overlap region which protrudes from the door flange and has a cover surface facing the door flange at a distance and made of electrically conductive material and having a same shape as a door flange region it covers.

Claims

1. A microwave cooking appliance, comprising: a door configured to cover a loading opening of a cooking chamber in a closed state, the door having a profiled trap structure configured to form in the closed state together with an electrically conductive door flange a quarter-wave trap that frames the loading opening; the profiled trap structure including a metal choke profile with an open face opposite the door flange, an inner metal tongue protruding into the open face laterally from an inner side of the choke profile, and an outer metal tongue protruding into the open face laterally from an outer side of the choke profile, with the inner and outer metal tongues connected electrically to the choke profile and separated from one another by a microwave entry slot; the choke profile being framed laterally on the outside by a parallel overlap region which protrudes continuously in a stepped manner from the outer metal tongue in the direction of the door flange; the parallel overlap region having a cover surface which faces the door flange at a gap distance when the door is in the closed state, is made of electrically conductive material, and has a profile corresponding to the door flange; and a microwave-transparent cover in direct contact with the inner metal tongue and the outer metal tongue and covering the microwave entry slot.

2. The microwave cooking appliance of claim 1, wherein at least one of the inner and outer metal tongues is configured to extend into a hollow space formed by the choke profile.

3. The microwave cooking appliance of claim 1, wherein at least one of the inner and outer metal tongues is toothed with a row of teeth in a profile direction, with the teeth being separated from one another by separating slots.

4. The microwave cooking appliance of claim 3, wherein the teeth are bent in a direction of a hollow space formed by the choke profile on at least one face adjoining a corresponding one of the separating slots.

5. The microwave cooking appliance of claim 3, wherein the teeth are bent in a direction of a hollow space on a face adjoining the microwave entry slot.

6. The microwave cooking appliance of claim 3, wherein at least some of the separating slots are straight and at least some of the teeth have a rectangular basic shape.

7. The microwave cooking appliance of claim 3, wherein at least some of the teeth have a ring shape.

8. The microwave cooking appliance of claim 7, wherein at least some of the ring-shaped teeth are interrupted.

9. The microwave cooking appliance of claim 1, wherein the microwave-transparent cover is a self-supporting cover, and further comprising a permanently elastic, temperature-resistant and grease-resistant sealing compound to fasten the microwave-transparent cover to the trap structure.

10. The microwave cooking appliance of claim 1, wherein the cover surface of the parallel overlap region protrudes over the microwave-transparent cover.

11. The microwave cooking appliance of claim 1, wherein the cover surface of the parallel overlap region is arranged flush with the microwave-transparent cover.

12. The microwave cooking appliance of claim 1, wherein the microwave-transparent cover covers both the microwave entry slot and a viewing window of the door.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The properties, features and advantages of the present invention described above and the manner in which they are achieved will become clearer and more readily understandable in conjunction with the schematic description of an exemplary embodiment that follows, described in more detail in conjunction with the drawings.

(2) FIG. 1 to FIG. 3 show a sectional side view of a detail of a respective microwave cooking appliance according to a first to third exemplary embodiment, each with a different embodiment of the trap structure;

(3) FIG. 4 to FIG. 5 show an oblique view from below of a detail of a respective microwave cooking appliance in particular according to the first or second exemplary embodiment with a comb-type trap structure;

(4) FIG. 6 to FIG. 7 show an oblique view from below of a detail of a respective microwave cooking appliance according to a fourth or fifth exemplary embodiment, each with a different embodiment of the trap structure; and

(5) FIG. 8 to FIG. 10 show diagrams showing the shielding effect of a microwave cooking appliance with an inventive lambda quarter-wave trap compared with the prior art DE 102 56 624 B4.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS OF THE PRESENT INVENTION

(6) FIG. 1 shows a sectional side view of a detail of a microwave cooking appliance 1 according to a first exemplary embodiment with a door 2, which in the illustrated closed state covers a loading opening 3 of a cooking chamber 4. The cooking chamber 4 is delimited by a cooking chamber wall or muffle 5.

(7) The door has a profiled trap structure 6, shown here on an upper edge of the door 2. When the door 2 is in the closed state, the trap structure 6 together with an electrically conductive door flange 7 forms a lambda quarter-wave trap that frames the loading opening 3.

(8) The trap structure 6 has a metal choke profile 8 that is C-shaped in cross section and has an open face 9 opposite the door flange 7. An inner metal tongue 10 protrudes into the open face 9 laterally on the inside and an outer metal tongue 11 protrudes into the open face 9 laterally on the outside. The metal tongues 10 and 11 here are embodied here as a single piece with the choke profile 8 and separated from one another by a microwave entry slot 12. In a first variant the metal tongues 10 and/or 11 can be configured continuously or without interruption or in a strip in a profile direction perpendicular to the plane of the page. In a second variant the metal tongues 10 and/or 11 can be configured in the manner of a comb or teeth in the profile direction.

(9) The microwave entry slot 12 is covered by a microwave-transparent cover in the form of a glass plate 13 made of hardened glass shown by way of example. This prevents any ingress of steam and dirt into a hollow space 14 formed by the choke profile 8.

(10) The choke profile 8 is framed laterally on the outside by a parallel overlap region 15 protruding in the direction of the door flange 7, produced here in one variant as a single piece with the choke profile 8. The parallel overlap region 15 has a cover surface 16 facing the door flange 7 and made of electrically conductive material, which is shaped in the same manner as the region of the door flange it covers (specifically vertically flat here) and arranged at a distance from the door flange 7. The door flange 7 and cover surface 16 therefore form a door gap 17.

(11) The glass plate 13 here is configured flush with the cover surface 16. The glass plate 13 has a viewing grid 18 that does not allow the passage of microwaves in its region opposite the loading opening 3 and can be formed for example in the manner of a printed metal grid. The glass plate 13 is fastened to the trap structure 6 by means of a permanently elastic, temperature-resistant and grease-resistant bonding agent (adhesive) or sealing compound 19. To this end the sealing compound 19 is introduced here into a lateral space between an edge of the glass plate 13 and the parallel overlap region 15.

(12) FIG. 2 shows a sectional side view of a detail of a microwave cooking appliance 21 according to a second exemplary embodiment with a door 22. The door 22 is configured in a similar manner to the door 2, but with the outer metal tongue 23 of a trap structure 26 being partially bent into a hollow space 25 formed by a choke profile 24 in cross section. The metal tongue 23 is therefore kinked or bent in cross section. This allows the choke profile 24 and therefore the hollow space 25 to be smaller but still maintain the same shielding effect, in this instance having a smaller height than the hollow space 14.

(13) In a first variant the metal tongues 10 and/or 23 can be configured continuously or without interruption in the profile direction perpendicular to the plane of the page. In a second variant the metal tongues 10 and/or 23 can be configured in the manner of a comb or teeth in the profile direction.

(14) FIG. 3 shows a sectional side view of a detail of a microwave cooking appliance 31 according to a third exemplary embodiment with a door 32. The door 32 is configured in a similar manner to the door 2, but with the inner metal tongue 33 of a trap structure 36 now being partially bent into a hollow space 35 formed by a choke profile 34 in cross section.

(15) In a further variant (not shown) both metal tongues can be bent into the hollow space.

(16) FIG. 4 shows an oblique view from below of a detail of the microwave cooking appliance 1 according to its second variant with a glass plate 13 shown partially masked. The outer metal tongue 11 of the trap structure 6 here is toothed or provided with a row of teeth 44 in a profile direction P, said teeth 44 being separated from one another by straight separating slots 45. The teeth 44 each have a rectangular shape with a width of 4 mm in the profile direction P, while the separating slots 45 have a width of 2 mm.

(17) FIG. 5 shows a view like the one in FIG. 4 of a microwave cooking appliance 21 according to its second variant. The door 22 has an outer metal tongue 23 with teeth 54, which are separated from one another by separating slots 55. Some of the teeth 54 are bent in the direction of the hollow space 25 of the choke profile 24, about a bending line B extending in the profile direction P. In other words the teeth 54 are bent in the direction of the hollow space 25 on or along a face adjoining the microwave entry slot 12.

(18) FIG. 6 shows a view like the one in FIG. 4 of a microwave cooking appliance 61 according to a fourth exemplary embodiment. A door 62 is configured in a similar manner to the door 43, but the outer metal tongue 63 of a trap structure 67 now has teeth 64, some of which are bent in the direction of a hollow space 65 of a choke profile 66, about a bending line C extending perpendicular to the profile direction P. In other words the teeth 64 are bent in the direction of the hollow space 65 on at least one face adjoining a separating slot 68.

(19) FIG. 7 shows a view like the one in FIG. 4 of a microwave cooking appliance 71 according to a fifth exemplary embodiment. A door 72 is configured in a similar manner to the door 42 but the outer metal tongue 73 now has teeth 74, which have an elliptical ring shape. The teeth 74 here all have a respective interruption 76 at their end facing the microwave entry slot 75.

(20) However in other variants the interruptions can be present at a different point on the teeth, in some instances a different point in the profile direction. The ring-shaped teeth can also be without interruption in one variant.

(21) Apart from the connection between the elliptical teeth 74 and the remainder of the trap structure 77 by way of respective webs as shown in FIG. 7, the teeth 74 for example can also be connected (Fig.) by way of a common continuous web or without a web with a direct connection to the trap structure 77, in particular to the choke profile 78 or the parallel overlap region 15.

(22) The trap structure 77 with elliptical teeth 74, generally ring-shaped toothing, compensates for the effect of an obliquely incident electromagnetic wave much more effectively than the trap structures 6, 26, 36, 46, 56 and 67 that do not have a ring shape.

(23) FIG. 8 shows a graph of an attenuation in dB on the y-axis against a frequency in GHz on the x-axis for a microwave cooking appliance with characteristic attenuation curves F1 and F2 for the prior art DE 102 56 624 B4 and with characteristic attenuation curves F3 and F4 for a lambda quarter-wave trap according to the present invention, e.g. according to the exemplary embodiment in FIG. 4.

(24) The attenuation curves F1 and F3 show the instance of an “ideal” door gap of 1 mm, in other words a door gap, with which an active frequency of the microwave trap or trap structure has been made to correspond to a working frequency of the microwave cooking appliance. However in practical applications the door gap will have different dimensions, its widening representing the critical instance. The causes are numerous and can be due to manufacturing tolerances or thermal movement of the appliance during heating operations for example. In actual use such a change in the door gap and different angles of incidence θ of the microwave radiation above all contribute to an unwanted change in shielding properties. A lambda quarter-wave trap shields leaked microwave radiation particularly reliably if it is particularly insensitive to changes, in particular increases, in the door gap due to its structure. Increased stability in respect of change is demonstrated primarily by a small change in the attenuation characteristic—in particular by a small displacement of the frequency position of maximum attenuation. The attenuation curves F2 and F4 show the instance of a door gap that is 1 mm wider (in other words a total of 2 mm wide).

(25) The attenuation properties are practically identical for the ideal gap of 1 mm, as shown in the attenuation curves F1 and F3. In particular the positions of maximum attenuation are located at the same microwave frequency of approx. 2.455 GHz.

(26) When the door gap is opened an additional 1 mm, the attenuation curves F2 and F4 in contrast show significant differences. The attenuation curve F4 for the lambda quarter-wave trap according to the present invention advantageously shows a much smaller displacement of the frequency position for maximum attenuation than the attenuation curve F2 according to the prior art.

(27) FIG. 9 shows a graph of a frequency displacement for the position of maximum attenuation in GHz on the y-axis against an increase in the door gap in mm on the x-axis for the prior art DE 102 56 624 B4 (curve G1) and for the lambda quarter-wave trap from FIG. 8 (curve G2).

(28) In the prior art the ideal active frequency is displaced much further when the door gap increases than with the lambda quarter-wave trap according to the present invention. The fact that the lambda quarter-wave trap according to the present invention responds much less to changes in the door gap means that the door can be opened more before the leaked radiation reaches an unreliably high level. This means there is greater stability in respect inter alia of thermal movement and manufacturing tolerances, which has clear advantages for the production process among other things.

(29) FIG. 10 shows a graph of an attenuation in dB on the y-axis against a frequency in GHz on the x-axis with characteristic attenuation curves H1 and H2 for the prior art DE 102 56 624 B4 and with characteristic attenuation curves H3 and H4 for a lambda quarter-wave trap with a trap structure 77 according to FIG. 7. While the attenuation curves H1 and H3 describe the attenuation with a small angle of incidence θ=7°, the attenuation curves H2 and H4 describe the attenuation with a large angle of incidence θ=40°. The smaller the displacement of the ideal active frequency when the angle of incidence θ of the microwave radiation from the cooking 4 chamber changes, the more reliably the lambda quarter-wave trap or the choke profile can ensure a low level of leaked radiation.

(30) The trap structure 77 from FIG. 7 with elliptical or generally ring-shaped toothing compensates for the effect of an obliquely incident electromagnetic microwave much more effectively than the prior art. The lower level of sensitivity to changes in the angle of incidence θ means that this embodiment demonstrates a particularly reliable attenuation function as a microwave trap.

(31) The present invention is of course not restricted to the exemplary embodiment shown.

(32) Features of the various exemplary embodiments can therefore be combined in any manner. For example elliptical teeth can also be bent into a hollow space and/or different types of teeth can be present on a metal tongue.

(33) Generally “one”, etc. can refer to a single one or a multiple, in particular in the sense of “at least one” or “one or more”, etc., unless this is specifically excluded, for example by the expression “just one”.

(34) A number can also refer to just the cited number as well as to a standard tolerance range, unless this is specifically excluded.

LIST OF REFERENCE CHARACTERS

(35) 1 Microwave cooking appliance 2 Door 3 Loading opening 4 Cooking chamber 5 Muffle 6 Trap structure 7 Door flange 8 Choke profile 9 Open face of choke profile 10 Inner metal tongue 11 Outer metal tongue 12 Microwave entry slot 13 Glass plate 14 Hollow space 15 Parallel overlap region 16 Cover surface 17 Door gap 18 Viewing grid 19 Sealing compound (adhesive) 21 Microwave cooking appliance 22 Door 23 Outer metal tongue 24 Choke profile 25 Hollow space 26 Trap structure 31 Microwave cooking appliance 32 Door 33 Inner metal tongue 34 Choke profile 35 Hollow space 36 Trap structure 44 Tooth 45 Separating slot 54 Tooth 55 Separating slot 61 Microwave cooking appliance 62 Door 63 Outer metal tongue 64 Tooth 65 Hollow space 66 Choke profile 67 Trap structure 68 Separating slot 71 Microwave cooking appliance 72 Door 73 Outer metal tongue 74 Tooth 75 Microwave entry slot 76 Interruption 77 Trap structure 78 Choke profile B Bending line C Bending line F1-F4 Attenuation curves G1-G2 Curves for a position of maximum attenuation H1-H4 Attenuation curves P Profile direction