Abstract:
This invention provides a cooking system capable of using microwave energy to heat food quickly and efficiently and form a crusty surface. The cooking system may include a base underneath a heating element that absorbs the microwave energy to generate thermal energy. The cooking system may also include a cover that covers a tray that is adapted to sit on top of the heating element. The cover may tightly close the tray that is adapted to hold food. The tray may be conductive to thermal energy so that the thermal energy from the heating element may be conducted to the tray to bake the side of the food that is on the tray.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Related Applications  
           [0002]    This application claims priority to two Korean Patent Applications: (1) Korean Patent Application No. 2002-0015998, filed May 24, 2002, entitled COOKER HAVING A CERAMIC HEATING ELEMENT; and (2) Korean Patent Application No. 2002-0016610, filed May 30, 2002, entitled CERAMIC HEATING ELEMENT AND COOKER FOR USE IN MICROWAVE RANGE, which are both incorporated by reference.  
           [0003]    2. Field of the Invention  
           [0004]    This invention provides a cooking system capable of thermal heating food using a microwave oven to quickly cook the food without making the food soggy, and in particular, the cooking system may be adapted to cook a pizza.  
           [0005]    3. General Background  
           [0006]    Microwave ovens are popular because they cook food quickly. They are also efficient in their use of electricity because a microwave oven heats only the food rather than containers such as glass. A microwave oven uses microwaves to heat food. These are radio waves having frequency of about 2,500 megahertz (2.5 gigahertz). Radio waves in this frequency range are absorbed by water, fats, and sugars, and as they are absorbed they are converted into atomic motion causing heat. Microwaves in this frequency range have another interesting property: they are not absorbed by most plastics, glass, or ceramics. Metal reflects microwaves, which is why metal pans do not work well in a microwave oven.  
           [0007]    When backing a cake using a conventional convection oven, the outside of the cake may burn before the inside even gets warm because the heat migrates, by conduction, from the outside of the food toward the middle. The air surrounding the food is hot and dry causing moisture within the food to evaporate, which forms a crispy, and brown surface while the inside is moist.  
           [0008]    In microwave cooking, the radio waves penetrate the food and excite water and fat molecules where the friction between the molecules generates heat within the food. As such, there is no heat having to migrate toward the interior by conduction. Rather, heat is generated everywhere all at once because the molecules are all excited together. There are limits, of course. Radio waves penetrate unevenly in thick pieces of food so that molecules in the middle of the food may not be excited. Hot spots may also form where there is microwave interference. Unlike convection oven, however, air within the microwave oven is at room temperature so that the surface of the food does not get crusty or become brown. There are certain foods, however, where having a crusty surface is desirable, such as the bottom of a pizza. Therefore, there is a need for a cooking system that is capable of cooking food quickly and efficiently using microwave energy and forming a crusty surface.  
         INVENTION SUMMARY  
         [0009]    This invention provides a cooking system capable of using microwave energy to heat food quickly and efficiently and form a crusty surface. The cooking system may include a base underneath a heating element that absorbs the microwave energy to generate thermal energy. The cooking system may also include a cover that covers a tray that is adapted to sit on top of the heating element. The cover may tightly close the tray that is adapted to hold food. The tray may be conductive to thermal energy so that the thermal energy from the heating element may be conducted through the tray to bake the side of the food that is on the tray. 
       
    
    
     BRIEF DESCRIPTION OF THE FIGURES  
       [0010]    [0010]FIG. 1 is an expanded perspective view of a cooking system.  
         [0011]    [0011]FIG. 2 is an assembled perspective view of a cooking system.  
         [0012]    [0012]FIG. 3 is a cross-sectional view of a tray in the cooking system.  
         [0013]    [0013]FIG. 4 is a perspective view of a heating element that is beaded.  
         [0014]    [0014]FIG. 5 is a cross-sectional view of the cooking system to illustrate its operational functions. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    [0015]FIG. 1 illustrates a cooking system  10  capable of using microwave energy to heat food quickly and efficiently and form a crusty surface. The cooking system  10  includes a base  12  adapted to receive a heating element  14  that absorbs microwave energy and produces thermal energy. The cooking system  10  may also include a tray  16  so that the heating element  14  may be placed between the tray  16  and the base  12 . The cooking system also includes a cover  18  that may be placed over the tray  16 . The cover  18  may form a seal around the rim of the tray  16  that is adapted to receive a cooking object or food for heating. FIG. 2 illustrates an assembled cooking system  10  that may be placed into a microwave oven for cooking food. Once the microwave oven is turned on, the heating element  14  absorbs the microwave energy and generates thermal energy or heat that is conducted through the bottom of the tray  16  and heats up the food in the tray. As such, the food in the microwave may be cooked with a combination of thermal energy and microwave energy.  
         [0016]    The base  12  may be adapted for microwave oven usage. The base  12  may include a plurality of legs  22  that projects from the frame  20  to provide a footing for the base  12 . The base  12  may also include a rib  24  that has a circular or round-shape formed on the circumference of the frame  20  and recessed or adapted to receive the heating element  14 . In this regard, the tray  16  may have a concaved shape bottom  30  adapted to receive cooking objects or items like pizza. A rib hole  26  may be formed within the base  24  so that the bottom side of the heating element  14  may absorb the microwave energy radiating from the microwave oven through the rib hole.  
         [0017]    The legs  22  may be wrapped with an insulating cab  28  to protect the glass tray usually provided within microwave ovens. The insulating cab  28  may be made of silicon rubber material (Silicon). Accordingly, as the base  12  is placed on top of the heat-resisting glass resting on a turntable within the microwave oven, the cabs may prevent the cooking system from slipping as the heat-resisting glass turns. In a fully extend position, the legs  22  may have a certain height so that the distance between the heating element  14  and the heat-resisting glass is such that the heat from the heating element does not damage the heat-resisting glass.  
         [0018]    The heating element  14  generates heat when it is subjected to microwave energy generated from the microwave range. The heating element may have a variety of shapes, such as a circular disk having a certain thickness, rectangular shape, diamond shape, or star shape. In particular, the circular disk shape as illustrated in FIG. 1 may have substantially flat upper and lower surfaces  15  and  17 , respectively. The thickness “t” of the circular disk  14  may be between about ⅛ inches and about ¾ inches. The circular disk-heating element  13  may equally receive the microwave energy on the lower surface  17  to generate heat on the entire part of the heating element  14 . The heat generated from the heating element  14  may then emit evenly through the upper surface  15  of the heating element  14 . For additional heating capacity, a plurality of heating elements may be stacked on top of each other. For instance, another heating element may be placed on top of the heating element  14  to form a double stack of the heating elements.  
         [0019]    The heating element  14  may be comprised of Al 2 O 3 , SiO 2 , SiC, and MgO, and may also include clay and binder. For example, the heating element  14  may be comprised of the following elements by weight: Al 2 O 3 —about 10% to about 20%; SiO 2 —about 20% to about 30%; SiC—about 20% to about 60%; MgO—about 1% to about 10%; Clay—about 1% to about 10%; and Binder—about 1% to about 10%.  
         [0020]    The addition of Al 2 O 3  and SiO 2  into the composition of the heating element  14  may be used to lower the intensity and the temperature of plasticity at the time of manufacturing the heating element  14 . With regard to SiC, the temperature of plasticity may be ascended or descended by controlling the amount of SiC&#39;s content because SiC converts the microwave energy to heating-energy by absorbing microwaves. When more SiC&#39;s are used, the efficiency may increase as the temperature of plasticity rises, on the other hand, when the amount of SiC&#39;s is less, the efficiency may decrease as the temperature of plasticity drops. Put differently, the heating capacity of the heating element  14  may correspond to the amount of SiC&#39;s content used in the composition of the heating element and, therefore, the amount of SiC&#39;s content used may be predetermined to formulate a heating element  14  with a desirable heating capacity. The amount of SiC&#39;s used, however, may correlate to the manufacturing cost of the heating element so that heating capacity of the heating element  14  may need to be balanced with production cost. With regard to other elements, MgO, clay, and binder may be added at the time of manufacturing in order to efficiently operate the temperature of plasticity and formation.  
         [0021]    The heating element  14  based on the composition discussed above may be manufactured in the temperature range of 1300˜1400° C. after the heating element is formed as a certain shape. A typical microwave oven may operate at about 2,500 megahertz. The heating element  14  may absorb microwave energy from such a microwave oven and generate the temperature range of about 200° C. to about 300° C.  
         [0022]    [0022]FIG. 3 illustrates a cross-sectional view of the tray  16  along the bottom where coating layers may be formed on the outer surfaces  30  and  32  and on the inner surfaces  34  and  36 . The coating layers may provide non-stick, chemical resistance, and insulation with a predetermined amount of coating layers. The efficiency of insulation may be improved with the ceramic layer on the outer surfaces  30  and  32  of the tray  16 . Moreover, the ceramic layer may also prevent the sparks from occurring within the microwave oven as the tray rotates. The ceramic layer may be formed and coated with organic chemical components, including SiO 2  line, and Al 2 O 3  line ceramic, and organic/inorganic complex Hybrid paints manufactured by simultaneous Copolymerization of inorganic chemical components and organic chemical components including non-adhesive function. These inorganic chemical components may be consolidated in OH system by mutual condensation of Colloidal Solution, —(O—X—O—X—OH)-Group and OH-Group by repulsive power of static electricity—dispersed in water, and Silane chemical components. As such, the ceramic layer may have such characteristics as heat-resistance, high-solidity, and acid-resistance, like traditional ceramic materials, as well as the efficiency of non-stick that is the strength of fluorine materials.  
         [0023]    [0023]FIG. 4 illustrates a heating element  14  that may be adapted to conduct heat more evenly. The heating element  14  may be beaded to form a waffle like configuration. In this regard U.S. Pat. No. 4,927,991 issued to Wendt et al. is incorporated by reference into this application. This way, the heating element placed about the middle part of the tray  16  may more evenly transfer heat to the bottom of the tray  16 .  
         [0024]    [0024]FIGS. 1, 2, and  5  illustrate the cover  18  having a lip  40  that may flange down or form on the edge of the lower part of the cover  18 . The lip  40  may be provided with insulating materials  42  along the outer surface area of the lip  40  to substantially prevent sparks from occurring as the cover touches the inner surface of the microwave oven as the cooking system  10  rotates. A variety of insulating materials may be used such as silicon rubber. As further illustrated in FIG. 5, insulating material  44  may be provided in the inner surface of the cover  18  around the lip  40  so that once the cover  18  is placed over the tray  16 , a seal may be formed between the lip  40 , and the tray  16 , then a space  46  is formed between the cover  18  and the tray  16 . Besides the insulating material, the coating layer  30  may also prevent the sparks from occurring within the microwave oven.  
         [0025]    The cover  18  may also have a hole  48  with a predetermined diameter that allows certain amount of moisture and heat within the space  46  to exhaust through the hole  48 , while cooking the food  50 . The size of the hole may determine the amount of moisture and heat that may exhaust through the hole  48 . The hole  48  may be formed in the center of the cover  18  so that microwave energy may enter the space  46  through the hole  48 , but substantially blocked along the outer perimeter portion of the cover  18 . The size of the hole  48  may be varied through an apparatus such as a fan or sliding cover that may be formed on the interior side of the cover  18 , or any other method known to one skilled in the art.  
         [0026]    The cover  18  may substantially prevent certain portions of the food such as the outer crust area of a pizza from directly being exposed to the microwave that may dry the crust. The cover may also insulate or block the heat in the outer perimeter of the cover to enhance the thermal effect to efficiently cook the food. With the hole  48  about the center of the tray  18 , moisture is able to escape so that the food does not become soggy around the center, and may be exposed to more microwave energy to cook more along the center. For example, when heating or cooking a pizza using a microwave oven, one of the problems is that the middle of the pizza may be soggy and the crust of the pizza may be dry. With the cooking system  10  such a problem may be minimized because the hole  48  allows the moisture to escape so that the middle of the pizza does not become soggy. The crust of the pizza may also not become dry because the cover  18  insulates the moisture within the space  46  around the crust of the pizza.  
         [0027]    [0027]FIG. 5 illustrates one of many ways to assemble the cooking system  10 . The heating element  14  may be placed on top of the rib  24  of the base  12 . Then, the tray  16  may be placed on the upper part of the frame  20 , and food may be placed into the tray  16 . The cover  18  may be placed over the tray  16  to enclose the food. The cooking system may be then placed into a microwave oven for heating or cooking. In most instances, the cooking system  10  may be placed onto a glass table that turns once the microwave oven is turned on. As the microwave oven radiates microwave energy in all directions within the oven, at least a portion of the microwave energy may reflect off the bottom side  19  of the microwave oven towards the heating element  14  through the rib hole  26  of the base  12 , and other portion of the microwave energy may radiate directly to the cover  18 . The heating element  14  may then convert the microwave energy to thermal energy that may generate temperatures in the range of about 200° C. to 300° C. The thermal energy may be then conducted to the tray to cook the food via thermal energy so that when cooking a pizza, the bottom of the pizza may be crusty rather than soggy.  
         [0028]    The moisture that is developed in the space  46  near the hole  48  may evaporate through the hole  48 . The amount of evaporation may be controlled through varying the size of the hole  48  so that the appropriate level of humidity may be maintained within the space  46  to prevent the food such as a pizza from burning. Microwave energy that is radiated onto the cover  18  may be blocked to substantially prevent the food in certain areas, such as along the perimeter of the cover  18 , from being overcooked or burned.  
         [0029]    As described above, the cooker for use in microwave range can efficiently cook the object, properly placed in a microwave, by using the heat generated from the Heating