Abstract:
A microwave intensification system includes a base frame having a plurality of support members, a microwave transparent, central vessel, and at least one dielectric unit positioned within the central vessel. A cooking surface is formed by covering the dielectric unit with a protective covering. In operation, a food item is placed within a processing container and positioned on the cooking surface over the dielectric unit. The processing container is sized such that an overlap exists between the container and the dielectric unit in order to balance the exposure of the food item to a microwave energy field. With this arrangement, the food item can rapidly undergo a cooking process in a manner wherein central and edge portions of the food item are exposed to a uniform cooking process thereby increasing the quality of the final product.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/552,196 entitled “Microwave Intensification System For Rapid, Uniform Processing of Food Items” filed Mar. 12, 2004. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention pertains to the art of cooking appliances and, more particularly, to a microwave energy intensification system for use in a microwave cooking appliance for rapidly and uniformly processing a food item. 
     2. Discussion of the Prior Art 
     In general, high-speed microwave processing or cooking of certain types of food items will result in poor food quality due to uneven cooking. Typically, central and outer sections of a food item may not be heated to the same temperature for the same time period. This is particularly true when cooking food items having different densities, such as a combination egg and meat filled product. 
     Safety concerns relating to contamination from pathogenic microorganisms require that certain food items be heated above 165° F. (74° C.) prior to human consumption. In particular, dairy and meat items must be pasteurized or cooked for a prescribed period above approximately 165° F. (74° C.) or else a consumer runs the risk of consuming a food item contaminated with a pathogenic bacteria. Unfortunately, when exposing a food item to the pasteurization process, the temperature distribution within a food item, in particular a combination food item, is not uniform. As is often the case, targeting 165° F. (74° C.) throughout a particular food item results in the outer edge portions of the food item achieving temperatures well beyond the targeted value. Consequently, the edges of the food item are generally over cooked and the central portion under cooked. Actually, if the edges of the food item are not allowed to “burn” for a sufficient time period, the central portions may not achieve the targeted temperature value. In this case, the consumer may still be exposed to harmful pathogenic microorganisms. 
     Various methods have been proposed in the prior art to more uniformly cook a food item. However, most of the methods proposed inherently involve various tradeoffs which negatively impact cooking efficiency, food costs and processing times. Proposed methods include processing the food for longer time periods at reduced power levels, reformulating the food items, and using a single mode microwave oven design, all of which necessarily increase cook times and/or add significant costs which, in the highly competitive field of microwave cooking, is not acceptable. 
     Based on the above, there exists a need in the art for a microwave intensification system which will provide for a uniform cooking environment for food items. More specifically, there exists a need for a microwave intensification system which will enable a food item to be uniformly cooked to a targeted temperature zone without detrimentally affecting the overall quality of the final food product. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to a microwave intensification system for a cooking appliance including an oven cavity and a microwave generator. More specifically, the microwave intensification system constructed in accordance with the present invention includes a base frame portion having a plurality of support members and a microwave transparent central vessel supported by the base frame above a bottom surface of the oven cavity. 
     In accordance with a preferred embodiment of the present invention, at least one dielectric unit is positioned within the central vessel. In one form of the invention, the dielectric unit is formed from Alumina Oxide. In another form, the dielectric unit is formed from Zirconia. The unit preferably has a dielectric constant in the range of 6-12 and a dielectric loss tangent of between 0.0001 and 0.01. However, it should be understood that the dielectric constant could be as high as 20. Most preferably, the dielectric unit will have a dielectric constant of intermediate value between that of the particular food item and free space or air. The dielectric unit could take the form of a disk, a powder or a slurry so long as the qualities of the dielectric unit, i.e., the dielectric material, functions to shorten the wavelength of the microwave energy field at an interface between the unit and the food item. The shorter wavelength increases the number of energy nodes and produces a higher energy field concentration which, in turn, establishes a higher power concentration at the food item. The higher power concentration results in a more even cooking of the food item. Another function of the unit is to help match the incoming energy into the food material, which has a high value of dielectric constant. In theory, the unit should have a dielectric constant which is roughly equal to the square root of the dielectric constant of the food. In any event, when placed in specific proximity to certain food items, the dielectric properties of the dielectric unit balance central portion cooking with outer or edge portion cooking. In part, the dielectric unit helps reduce the field at any sharp corners of the food. With this arrangement, the microwave intensification system establishes a uniform cooking environment which results in a uniformly cooked food item. 
     In accordance with one aspect of the present invention, there could be provided a relatively thin dielectric cover layer or sheet between the dielectric unit(s) and the food. One function of this cover sheet is to act as a protective coating. Preferably, the protective coating is formed from a silicone rubber and defines a cooking surface onto which the food item is placed. Actually, the material of the cover sheet can be any microwave transparent material, preferably an FDA food grade material, that will protect the dielectric material from spills and various food debris that may accumulate on the surface during a cooking process. In a more preferred form of the invention, the food items are stored within a food processing container which is sized so that the food overlaps the dielectric unit onto which it is placed. More specifically, the food overlaps the dielectric unit, preferably about ½-¾ inches (1.27-1.91 cm), such that the food item is exposed to a more balanced microwave energy field. 
     In a more preferred embodiment, at least first and second dielectric units are positioned within the central vessel and covered with a microwave transparent protective covering to form first and second heating zones. In still another form of the invention, a plurality of central vessels are supported within the base frame. With this arrangement, multiple food items, each designed to undergo a similar cooking process, can be handled simultaneously. Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments when taken in conjunction with the drawings wherein like reference numerals refer to corresponding parts in the several views. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an upper perspective view of a microwave intensification system constructed in accordance with the present invention positioned within a microwave oven cavity; 
         FIG. 2  is a partially exploded, perspective view of the microwave intensification system of  FIG. 1 ; 
         FIG. 3  is a perspective view illustrating a pair of food processing containers positioned on a support surface of the microwave intensification system of  FIG. 1 ; 
         FIG. 4  is a perspective view of a microwave intensification system constructed in accordance with a second embodiment of the present invention; 
         FIG. 5  is a perspective view of a microwave intensification system constructed in accordance with a third embodiment of the present invention; and 
         FIG. 6  is a partial exploded view of a microwave intensification system constructed in accordance with a fourth embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With initial reference to  FIG. 1 , a cooking appliance constructed in accordance with the present invention is generally indicated at  2 . Although the actual cooking appliance to which the present invention may be incorporated may vary, the invention is shown in connection with cooking appliance  2  depicted as a single wall oven. However, it should be understood that the present invention is not limited to this particular model type and can be incorporated into various types of microwave oven configurations, e.g., cabinet mounted ovens, dual wall oven units, and free standing units. In the embodiment shown, cooking appliance  2  includes an oven  4  having associated therewith an oven cavity  6 . In a manner known in the art, oven  4  is provided to perform a combination microwave/convection cooking process. However, it should be recognized that the present invention can be employed in any type of cooking appliance employing microwaves as an energy source. As shown, cooking appliance  2  includes an outer frame  12  which supports oven cavity  6  within associated structure, such as a wall, kitchen cabinetry or the like. 
     In a manner known in the art, a door assembly  14 , which is adapted to pivot at a lower portion  18 , is mounted to frame  12  to selectively provide access to oven cavity  6 . In a manner also known in the art, door  14  is provided with a transparent zone  22  for viewing the contents of oven cavity  6  while door  14  is closed. In addition, a seal and microwave choke (not shown) are provided about a peripheral edge portion of door assembly  14  to prevent both oven gases and microwaves from escaping from within oven cavity  6 . 
     As best seen in  FIG. 1 , oven cavity  6  is defined by a smooth bottom portion  27 , an upper portion  28 , opposing side portions  30  and  31  and a rear portion  33 . Preferably, arranged on each opposing side portion  30  and  31  are a plurality of vertically spaced and fore-to-aft extending rack support guides indicated generally at  34  and  35 . Arranged above oven cavity  6  is a microwave applicator or power source generally indicated at  37 . Microwave applicator  37  includes a waveguide  39  having arranged thereon a microwave emitter or magnetron  40 . As further shown in  FIG. 1 , cooking appliance  2  includes a convection heating system indicated generally at  45 . Preferably, convection heating system  45  includes an inlet vent cover  47  arranged on rear portion  33  of oven cavity  6 , a fan assembly  49 , and first and second outlet vents  51  and  52  arranged on opposing sides of vent cover  47 . Finally, cooking appliance  2  includes an upper control panel  60  arranged above oven cavity  6  and carried at least partially by frame  12 . In the embodiment shown, control panel  60  includes first and second rows of oven control buttons  62  and  63  for programming, in combination with a numeric pad  65  and a display  66 , particular cooking operations for oven  4 . Since the general programming and operation of cooking appliance  2  is known in the art and does not form part of the present invention, these features will not be discussed further here. 
     In general, the structure described above with respect to cooking appliance  2  is already known in the art and does not constitute part of the present invention. Therefore, this structure has only been described for the sake of completeness. Instead, the present invention is particularly directed to a microwave intensification system  90  and, more particularly, to a microwave intensification system  90  including a base unit or central vessel  95  supported within oven cavity  6  by a support frame  99 . Microwave intensification system  90  is adapted to establish a uniform cooking environment for a food item undergoing a microwave cooking process, particularly a food item positioned within a food processing container, such as those indicated at  103  and  104 . 
     With particular reference to  FIG. 2 , base unit  95  includes a lower section  110  having a hollow interior portion  112  extending to an upper section  115 . In accordance with this preferred form of the invention, base unit  95  is formed from a microwave transparent material, such as PTFE, polypropylene or polyethylene. As shown, upper section  115  includes a supporting surface  118  which, in the embodiment shown, extends about hollow interior portion  112 . Projecting from a peripheral edge of supporting surface  118  is an upstanding ledge portion  120 . In the embodiment shown, upstanding ledge portion  120  includes first and second container spacers  124  and  125  that project from upstanding ledge  120  toward hollow interior portion  112  along supporting surface  118 . As will be discussed more fully below, spacers  124  and  125  function to position food items in a particular relationship upon supporting surface  118 . 
     In accordance with a preferred form of the invention, arranged within hollow interior portion  112  are first and second dielectric units  126  and  127 . Preferably, dielectric units  126  and  127  are formed from Alumina oxide (AL 2 O 3 ) or Zirconia having a dielectric constant in the range of 6-12 and a loss tangent preferably as low as possible. However, it should be understood that the dielectric constant could be as high as 20. More preferably, dielectric disks  126  and  127  are formed from a material having a dielectric constant less than that of the food product to be heated and a dielectric loss tangent below 0.01. In further accordance with the invention, dielectric units  126  and  127  could take the form of disks, a powder or even a slurry so long as a close relationship is established between the dielectric constant of units  126  and  127  and the food item. With this arrangement, the particular qualities of the dielectric material function to shorten the wavelength of the microwave energy field creating localized field concentrations which, in turn, result in a more uniform heat distribution within the food item. 
     As shown, first and second dielectric units  126  and  127  are maintained in a spaced relationship by a spacer assembly  133 . More specifically, spacer assembly  133  includes first and second spacer elements  136  and  137  separated by an intermediate web portion  139 . With this arrangement, food containers, such as indicated at  103  and  104  in  FIG. 1 , are located by spacers  124  and  125  over dielectric units  126  and  127  respectively. Preferably, each food container  103  and  104  is positioned such that ½to ¾ inches (1.27-1.91 cm) of the container  103 ,  104  overlaps a respective one of disks  126  and  127 . Finally, a protective cover or grease shield  144  is positioned over disks  26  and  127  to prevent grease and other food byproducts from entering interior portion  112  or accumulating on first and second dielectric disks  126  and  127 . Preferably, cover  144  is formed from a molded silicone rubber or similar microwave transparent material and is arranged upon an inner ledge (not labeled) of supporting surface  118  such that it can be easily removed for cleaning. 
     As best seen in  FIGS. 2 and 3 , support frame  99  of intensification system  90  includes a base section  155  defined by opposing side support members  156  and  157  interconnected through a front support member  159  and a rear support member  160 . As shown, support frame  99  further includes a plurality of vessel support members  167 - 170  which are respectively secured to front support member  159  and rear support member  160  and project inward toward a center of base section  155 . More specifically, vessel support members  167 - 170  interconnect with a vessel support ring (not shown) which is adapted to snap-fittingly receive central vessel  95 . In a preferred form of the invention, side support members  156  and  157 , front support member  159 , rear support member  160  and vessel support members  167 - 170  are formed from metallic wire. However, it should be understood that various other materials usable in a microwave and high heat environment could also be employed. 
     At this point, it should be understood that the number and size of base units  95  capable of being supported within support frame  99  can vary in accordance with the invention while still enabling support frame  99  to facilitate the loading and unloading of food items into cooking appliance  2 . To this end,  FIG. 4  shows a support frame  99   a  constructed in accordance with a second embodiment of the present invention. As shown, support frame  99   a  includes a base section  155  constructed in a corresponding similar to that shown in  FIGS. 1-3 . However, vessel support members  167 - 170  are replaced by a pair of vessel support members  180  and  181  which are arranged parallel to one another and extend from front support member  159  to rear support member  160 . With this arrangement, a plurality of vessels, such as those indicated at  95   a ,  95   b  and  95   c , are capable of being simultaneously supported by support frame  99   a  thereby increasing the number of food items capable of being processed at a given time period. 
     Referring to  FIG. 5 , a central vessel  193  is shown constructed in accordance with a third embodiment of the present invention. As illustrated, central vessel  193  includes a lower section  196  interconnected to an upper section  199 . Upper section  199  includes a support surface  203  having an upstanding peripheral wall portion  204  including opposing side sections  205  and  206  interconnected by a rear section  207 . Support surface  203  is divided into four quadrants by a first wall portion  209  extending from approximately a midpoint of rear wall  207  to a front edge of support surface  203 , and a second wall portion  210  interconnecting approximate midpoints of opposing side walls  205  and  206 . With this arrangement, four cooking zones  212 - 215  are established upon support surface  203 . In a manner similar to that described with reference to central vessel  95 , each respective cooking zone  212 - 215  includes an associated central portion  218 - 221  below which is arranged a corresponding dielectric unit (not shown). With this arrangement, a plurality of food containers can be supported by central vessel  193  for simultaneous processing in microwave oven  4 . 
       FIG. 6  shows another preferred embodiment of the invention illustrating a central vessel  293  utilized in combination with support frame  99 . In accordance with this embodiment, central vessel  293  includes a base  300  which is preferably formed from a microwavable plastic material. As shown, support base  300  includes an upper surface portion  305  and a lower surface portion  310 . Surface portions  305  and  310  are vertically spaced such that an upstanding wall  315  is defined. In the most preferred embodiment, upstanding wall  315  includes an angled, lead-in section  320 . Lower surface portion  310  is formed with a first countersunk portion  325  and a second, countersunk portion  330 . Countersunk portion  330  extends about countersunk portion  325  so as to essentially define a ledge about countersunk portion  325  as clearly shown in this figure. 
     This embodiment of the microwave energy intensification system of the invention further includes one or more dielectric units  335 - 337  which are either sized so as to be recessed within countersunk portion  325  or otherwise used to fill countersunk portion  325 . Arranged atop dielectric units  335 - 337  is a spacer or protective cover  340 . Protective cover  340  is sized so as to seat upon the ledge defined by countersunk portion  330 , with an upper surface (not separately labeled) of protective cover  340  being substantially flush with lower surface portion  310 . Protective cover  340  is thereafter secured within countersunk portion  330  through, for example, a sonic welding process. In accordance with the invention, protective cover  340  need not be employed. In addition, dielectric units  335 - 337  could project slightly above lower surface  310 , for example, 40/1000 inch (1.02 mm) such that the food item is only separated from dielectric units  335 - 337  by a bottom surface of a tray or other form of packaging material as will be detailed more fully below. Alternatively, dielectric units  335 - 337  could be inserted from an underside portion of central vessel  293  and made substantially flush with lower surface portion  310 , preferably while being encapsulated within support base  300 . 
     Furthermore, this embodiment is shown to employ a food tray  350  within which is arranged food items  370 - 372 . Food tray  350  is formed from a microwave safe material and, although not shown, can be compartmentalized. In the preferred embodiment shown, food tray  350  is sized so as to be positioned upon lower surface  310  against portions of upstanding wall  315 , with at least a portion of food tray  350  being arranged over protective cover  340  and dielectric units  335 - 337 . This arrangement has been found to be particularly advantageous when food items  370 - 372  are from different food groups and therefore it is desired to subject these food groups to different levels of microwave cooking. For example, with food item  370  constituting a meat, food item  371  constituting a starch and food item  372  constituting a vegetable, the microwave intensification developed through the use of the dielectric units  335 - 337  can be easily concentrated on one of more of the food groups, such as food item  370 , by properly positioning food tray  350  against upstanding wall  315 , with angled portion  328  functioning to guide food tray  350  to the proper corner position on lower support surface  310 . 
     Although described with reference to preferred embodiments of the invention, it should be readily understood that various changes and/or modifications can be made to the invention without departing from the spirit thereof. For instance, while the microwave intensification system of the invention is shown mounted in a convection/microwave oven, it should be readily understood that the present invention is equally adaptable to standard microwave oven applications. In addition, while the food items are shown being processed within covered food processing containers, other types of containers, including those without covers, are equally acceptable. Also, while the dielectric units are described as being provided with a protective cover, it should be realized that the protective cover itself is optional. In general, the invention is only intended to be limited by the scope of the following claims.