Microwave Door Quarter-Wave Trap for Leakage Shielding
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Solution Overview
Problem
Existing microwave cooking appliances face challenges in maintaining effective microwave shielding against changes in the door gap, particularly due to thermal movements and manufacturing tolerances, and are sensitive to oblique incidence of microwave radiation, which affects the leakage radiation and compactness of the quarter-wave trap design.
Innovation Solution
A microwave cooking appliance with a profile-like latch structure forming a quarter-wave trap, featuring electrically conductive metal tongues and a choke profile, where the metal tongues are separated by a microwave entry slot covered by a transparent cover, providing a high degree of insensitivity to door gap changes and oblique incidence, and allowing for a compact design that increases cooking space volume without compromising shielding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional quarter-wave trap is used to seal the door gap, then microwave shielding is provided, but the shielding effect is sensitive to changes in door gap due to thermal movements and manufacturing tolerances
Solution Approach 1:
The quarter-wave trap is divided into multiple segments: a stationary part attached to the door flange and a movable part attached to the door. This segmentation allows each part to accommodate different portions of the door gap variation, maintaining shielding effectiveness across a range of gap sizes without requiring precise manufacturing tolerances.
Solution Approach 2:
The latch structure incorporates a movable part that can dynamically adjust its position relative to the stationary part, allowing the quarter-wave trap to adapt to thermal expansions and manufacturing variations. This dynamic configuration maintains the quarter-wave path length despite changes in the overall door gap.
2Reliability
If a larger quarter-wave trap is used to improve shielding, then microwave leakage is reduced, but the device occupies more space inside the door
Solution Approach 1:
The latch structure is integrated into the door assembly in a nested manner, with the quarter-wave trap components fitting within the existing door flange and door structure. This nesting allows the shielding function to be achieved without adding external protrusions that would reduce the cooking chamber volume.
Solution Approach 2:
The quarter-wave trap utilizes the depth dimension of the door flange and door rather than extending outward, creating the shielding path within the existing thickness of the door assembly. This dimensional utilization maintains cooking space while providing effective shielding.
3Reliability
If the quarter-wave trap is designed for normal incidence, then shielding is effective at perpendicular angles, but leakage radiation increases at oblique incidence angles
Solution Approach 1:
The latch structure with its stationary and movable parts creates an asymmetric configuration that provides multiple reflection paths for microwave radiation. This asymmetry disrupts the coherent reflection that occurs at oblique angles, reducing leakage radiation in directions other than normal incidence.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution ensures a stable and effective microwave shielding effect, reducing leakage radiation and accommodating variations in door gap and incidence angles, while enabling a more compact and efficient use of cooking space.
Implementation Method 1
the latch structure forms, with an electrically conductive door flange, a quarter-wave trap for microwaves surrounding the feed opening
Implementation Method 2
The lambda quarter traps are located behind a cover that protects them from dirt or mechanical damage
Implementation Method 3
The microwave entry slot is in particular covered by a microwave-transparent cover
Data Source
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AI summary
A microwave cooking device (71) has a door (72) that covers a feed opening (3) of a cooking chamber (4) in the closed state and has a profiled trap structure (77), which together with an electrically conductive door flange (7) forms a lambda quarter-wave trap that frames the feed opening (3). The trap structure has a profiled metal choke section (78) with an open face (9) which lies opposite the door flange and into which an inner metal tongue (10) protrudes on the lateral interior and an outer metal tongue (73) protrudes on the lateral exterior, said metal tongues being electrically connected to the profiled choke section and being separated from each other by a microwave entry slot (75). The profiled choke section is surrounded on the exterior in a lateral direction by a parallel overlapping region (15) which protrudes in the direction of the door flange and which has a cover surface (16) that faces the door flange and is made of an electrically conductive material, said cover surface having the same shape as the door flange region covered by the cover surface and being spaced therefrom. The invention can be used in particular on microwave domestic appliances, for example independent microwave cooking devices or baking ovens and/or steam cooking devices with a microwave function.