Patent Application
20100243646
The subject matter disclosed herein relates to microwave ovens, and, more specifically, to an electronic mode stirrer used to enable an improved distribution of wave patterns to cause even heating within such ovens.
In microwave ovens, cold spots or small spatial regions may occur, where heating is uneven or lesser than in other regions of the oven, due to a low density of signal energy. These cold spots are the result of multipath interference between wave patterns. Corresponding regions or volumes of food or other items placed at these cold spots may be underheated or undercooked as compared to other parts of the same food or items. Food is thus often turned or otherwise moved physically in microwave ovens. One other technique that may be used to reduce these effects of a multipath-induced heating deficiency is referred to as mode stirring. This technique can be performed in a variety of ways such as through incorporation of a moving reflector near the point where wave patterns are emitted. The moving reflector changes the standing wave patterns and spatially perturbs the nulls in the wave patterns. Mechanical mode stirring arrangements may, however, include a costly and noisy mechanical apparatus to drive the reflector. This mechanical system may entail extra manufacturing time and components in addition to moving parts that may require maintenance later in the life of the microwave oven.
The invention provides a system that includes a mode stirrer comprising a scatterer with a radar cross section. Further, the radar cross section is configured to change when exposed to electromagnetic waves to reduce a destructive interference condition within a structure where the electromagnetic waves are directed. A method is also provided that includes emitting electromagnetic waves from a magnetron and receiving the electromagnetic waves in a scatterer. The method also includes varying a radar cross section of the scatterer in response to exposure to the electromagnetic waves.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
In addition, the mass 30 may be placed upon or in a piece of cookware 32 or a tray. The cookware 32 or tray may be removed from the microwave system 10 following the heating of the mass 30 for reuse and cleaning. The piece of cookware 32 may be placed on a platform 34, which may be used elevate the mass 30 during a heating operation of the microwave system 10. In presently contemplated embodiments, the electronic mode stirrer assembly 12 may be located in or on a structure within the microwave, including the piece of cookware 32, the removable tray, or the platform 34. The platform 34 may be coupled to microwave oven floor 36. Alternatively, the electronic mode stirrer assembly 12 may be alternatively located on the wall 38 of the oven. Further, a plurality of electronic mode stirrer assemblies 12 may be located throughout the structure of the microwave system 10 inside the microwave cavity 28. Specifically, an electronic mode stirrer assembly 12 may be coupled to the wall 16, the wall 38, the ceiling 26, the floor 36 and/or structures coupled to these surfaces. The electronic mode stirrer assembly 12 may be located on brackets 14 and/or platform 34 in order to more efficiently perturb electromagnetic wave patterns within the cavity 28.
As depicted, the microwave system 10 may also include an outer structure or casing 40, which may shield objects from exposure to the electromagnetic waves generated by the magnetron 18. As illustrated, the bracket 14 may be spaced a distance 42 from the wall 16 in order to more efficiently perturb the electromagnetic waves using the electronic mode stirrer assembly 12. Similarly, the platform 34 may be spaced a height 44 from the floor 36. For example, distances 42 and 44 may be approximately one-half of the wavelength of the electromagnetic waves emitted by the magnetron 18, such as approximately 10 cm (2.5 inches). As described in detail below, the electronic mode stirrer assembly 12 may be used to perturb the electromagnetic wave patterns within the cavity 28, thereby ensuring a more uniform heating of objects within the microwave system 10, while doing so in a manner to enhance reliability and simplify manufacturing of the microwave system 10.
Alternatively, the assembly 66 may include a structural member 68, which may be included as a portion of bracket 14 and/or platform 34. Specifically, the member 68 may be a component of the platform 34, where a plate of food may be placed for heating by the microwave system 10. A length 70 of the scatterer 58 may be determined in relation to a wavelength of the electromagnetic energy generated by the magnetron 18. Specifically, for optimal perturbation and distribution of the electromagnetic waves, the distance 70 may be between about 25% and about 75% of the wavelength of the electromagnetic waves. For example, for a microwave system 10 that generates waves at a frequency of 2.45 GHz, the wavelength may be approximately 20 cm (5 inches). Accordingly, in the example, the length 70 may be approximately about 5-7.5 cm (2 to 3 inches). Specifically, length 70 may be about 10 cm (2.5 inches).
In another embodiment, the tray 68 may include a single scatterer 58, or two or more scatterers 58. In addition, the tray 68, including a plurality of scatterers 58 may be placed in the microwave system 10 which also includes a plurality of scatterers 58, each coupled to interior portions of the microwave cavity 28. Alternatively, the scatterers 58 may be located on, or embedded in, an adhesive member, such as a sticker, which is able to withstand heating when coupled to a structure that is exposed to electromagnetic waves within the microwave system 10. For example, the sticker, including scatterers 58, may be placed on the wall 16, a plate or the bracket 14 within the microwave cavity 28.
As discussed above, the scatterer 58 is configured to vary its radar cross section due to properties and materials of the connector 64, conductors 60 and 62. Specifically, the connector 64 may connect the conductors 60 and 62 as the scatterer 58 cools down, thereby increasing the radar cross section of the scatterer 58. Further, as microwave energy from the magnetron is received by the conductors 60 and 62, the scatterer 58 is heated, thereby expanding the connector 64 to disconnect the conductors 60 and 62 thereby, decreasing the radar cross section of the scatterer 58. As the radar cross section of the scatterer 58 increases and decreases the re-radiation of electromagnetic waves by the scatterer 58 changes, thereby disturbing a wave pattern to vary the distribution of electromagnetic energy, and heat, through the microwave cavity 28.
For the embodiments discussed above, the conductors 60 and 62 may be made of a conductive material such as copper or aluminum. Further, the conductors 60 and 62 may be thin as compared to length 70. For example, in an embodiment where the length 70 is 10 cm (2.5 inches), the conductors 60 and 62 may be about 0.1 inch wide. The connector 64 may be composed of a matrix material, such as a polymer or silicone matrix. The matrix material may have a high thermal coefficient of expansion and may include small metallic grains that are conductive within the matrix. The metallic conductive grains may be composed of copper or zinc. These properties enable the connector 64 to expand and contract to allow the radar cross section of the scatter to vary. Specifically, when the matrix is cooled the metal particles may touch as the matrix contracts, thereby forming an electrical connection between the conductors 60 and 62. When conductors 60 and 62 are electrically connected, the scatterers 58 have a high radar cross section. As electromagnetic waves are received by the conductors 60 and 62, the conductors 60 and 62 are heated, thereby expanding the matrix, causing a disconnect between the adjacent metal particles, which reduces the radar cross section. The alternating high and low radar cross section of the scatterers 58 causes a perturbance in the electromagnetic waves within the microwave cavity 28, thereby distributing the waves more evenly to reduce nulls within the microwave system 10.
Alternatively, the conductors 60 and 62 may be connected by the connector 64 that includes an insulating material located between a pair of conductor plates, where the conductor plates are each coupled to conductor 60 or 62. The conductor plates and insulated dielectric material are located within the connector 64, where the plates function as plates of a capacitor. Accordingly, when current flows through the conductors 60 and 62, the dielectric material is heated causing a separation of one of the plates from the dielectric material. This reduces the capacitive coupling and the current flow through the assembly. According, the radar cross section of the scatterer 58 is reduced. In addition, when the current flow is reduced, the material cools and the previously separated conductor plate comes back into contact with dielectric material, reforming a capacitive coupling of the two conductor plates, thereby providing a conductive path. After cooling, the radar cross section is larger for the assembly, enabling the scatterer to re-radiate the electromagnetic waves, causing a perturbation in the wave patterns within the microwave cavity 28
Technical effects of the invention include reduced complexity in microwave systems and improved heating distribution within microwave cavities. The embodiments enable a perturbation or disruption of microwave patterns within a microwave cavity to reduce or eliminate cold spots or nulls. In addition, the components utilized as a mode stirrer, to perturb wave patterns, may reduce production costs and manufacturing complexity. Further, it may improve reliability and quality by eliminating mechanical parts that may be used for mode stirring assemblies.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
