Abstract:
In one embodiment, a method includes emitting electromagnetic radiation from a magnetron and receiving the electromagnetic radiation in a scatterer. The method also includes varying a radar cross section of the scatterer in response to exposure to the electromagnetic radiation.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    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. 
         [0002]    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. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0003]    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. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    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: 
           [0005]      FIG. 1  is a sectional schematic diagram of a microwave oven and electronic mode stirrer in accordance with an embodiment of the invention; 
           [0006]      FIG. 2  is a detailed schematic diagram of the electronic mode stirrer, along with a magnetron and mass, in accordance with an embodiment of the invention; 
           [0007]      FIG. 3  is a detailed schematic diagram of the components included in an electronic mode stirrer in accordance with an embodiment of the invention; 
           [0008]      FIG. 4  is a top view of an electronic mode stirrer system, in the form of a cooking platform, in accordance with an embodiment of the invention; 
           [0009]      FIG. 5  is a top view of an electronic mode stirrer system, in the form of a piece of cookware, in accordance with an embodiment of the invention; and 
           [0010]      FIG. 6  is a side view of the piece of cookware shown in  FIG. 5  in accordance with an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0011]      FIG. 1  is a sectional schematic view of an embodiment of a microwave system  10  that includes an electronic mode stirrer assembly  12 . As depicted, the electronic mode stirrer assembly  12  enables an improved distribution of heating energy throughout the microwave system by perturbing microwave patterns to remove nulls or cold spots. The microwave system  10  also includes a bracket  14  which may be coupled to a wall  16 . Further, the electronic mode stirrer assembly  12  may be located on or embedded in the bracket  14 . For example, the electronic mode stirrer assembly  12  may be located on a sticker or decal that may be coupled to the bracket  14  via an adhesive. In the microwave system  10 , a magnetron  18  generates electromagnetic waves, which are emitted from a feeder  20 . After being emitted from the feeder  20 , the electromagnetic waves travel through a wave guide  22  in a direction  24  within the microwave system  10 . In addition, the electromagnetic waves may reflect off of members within the structure of the microwave system  10 , including the wall  16  and a ceiling  26 . Further, as the electromagnetic waves reflect off of structures within microwave system  10 , a wave pattern may be established within the structure of a microwave cavity  28 . Accordingly, cold spots or nulls within the cavity  28  may be reduced or eliminated by the electronic mode stirrer assembly  12 , which is configured to disrupt wave patterns within the structure, thereby ensuring more even heating of a mass  30  (e.g., food) to be heated by the microwave system  10 . The electronic mode stirrer assembly  12  is configured to perturb or disrupt the electromagnetic wave patterns within the cavity  28 , in order to more evenly distribute the electromagnetic energy, thereby ensuring a more even cooking or heating of the mass  30 . 
         [0012]    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 . 
         [0013]    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 . 
         [0014]      FIG. 2  is a detailed illustration of the electromagnetic waves generated by the magnetron  18  and their relationship with electronic mode stirrer assembly  12 . In the diagram of  FIG. 2 , the magnetron  18  is shown emitting a ray  52  of electromagnetic energy from feeder  20 , to a mass  30  located within the microwave system  10 . In addition, a ray  54  of electromagnetic energy may encounter the electronic mode stirrer assembly  12 . As described in detail below, the electronic mode stirrer assembly  12  includes one or more scatterers with a variable or changing radar cross section, configured to perturb the electromagnetic waves and their patterns within the cavity  28 . As depicted, the ray  54  is re-radiated by the electronic mode stirrer assembly  12 , which is depicted by a ray  56 . Rays  52  and  56  may both encounter the mass  30 , wherein the magnitude of the re-radiated magnetic wave in ray  56  is different from the magnitude of the electromagnetic energy of ray  52 . Further, the phases of the electromagnetic energy within rays  52  and  56  may differ, enhancing the perturbation of the wave patterns in the microwave cavity  28 . 
         [0015]      FIG. 3  is a schematic diagram of an exemplary embodiment of a scatterer  58 . The scatterer  58  includes conductors  60  and  62 , which may be configured to have a relatively small radar cross section at or near the frequency of the electromagnetic energy of ray  56 . The conductors  60  and  62  are each coupled to a connector  64 . The connector  64  may be configured to connect and disconnect the conductors  60  and  62  when the scatterer  58  is cooled and heated, respectively. For example, the scatterer  58  may receive electromagnetic energy, thereby heating the conductors  60  and  62 , causing the connector  64  to disconnect the conductors  60  and  62  due to expansion caused by the heating. Accordingly, the radar cross section of the scatterer  58  is reduced when the conductors  60  and  62  are disconnected. Further, when the scatterer  58  is cooled and the conductors  60  and  62  are disconnected, the cooling of the connector  64  may electrically join the conductors  60  and  62 , thereby increasing the radar cross section of the scatterer  58 . Therefore, the scatterer  58  may alternate between a relatively small and larger radar cross section as the scatterer  58  is heated and cooled, respectively. 
         [0016]      FIG. 4  is top view of an embodiment of an electronic mode stirrer assembly  66 . As depicted, the electronic mode stirrer  66  includes a plurality of scatterers  58 . The scatterers  58  are configured to be in different rotational orientations with respect to one another. The differing orientations may be used to improve the perturbation of electromagnetic waves by each of the scatterers  58 . For example, the electronic mode stirrer assembly  66  may include a tray  68 , wherein the scatterers  58  are located on, or embedded in, the tray  68 . Further, a piece of food may be placed on the tray  68  inside the microwave cavity  28 , to be heated by the microwave system  10 . Moreover, the tray  68  may be removed from the microwave to be cleaned and reused for additional heating processes within the microwave system  10 . 
         [0017]    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). 
         [0018]    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 . 
         [0019]      FIG. 5  is a top view of an embodiment of a piece of cookware, such as a plate  72 , that includes the scatterers  58 . As depicted, two scatterers  58  are located on or embedded in the plate  72 . Alternatively, as few as one or as many as ten or more scatterers  58  may be located in the plate  72 . The scatterers  58  are arranged in different orientations with respect to one another, thereby increasing the perturbation of electromagnetic waves within the microwave system  10 . For example, the scatterers  58  may be on or embedded inside the plate  72 , wherein a piece of food or mass  30  may be placed on the plate  72  and heated inside the microwave cavity  28 . 
         [0020]    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 .  FIG. 6  is a side view of the plate  72  shown in  FIG. 5 , including a plurality of scatterers  58 . As depicted, the scatterers  58  are embedded within the plate  72 , which may be placed inside the microwave system  10  for heating of the mass  30  using the scatterers  58  to insure a more uniform heating process. 
         [0021]    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 . 
         [0022]    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   
         [0023]    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. 
         [0024]    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.