Patent Publication Number: US-10764970-B2

Title: Multiple cavity microwave oven insulated divider

Description:
BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The invention relates generally to a microwave oven having multiple cooking cavities, and more specifically to the insulated divider of a microwave oven having multiple cooking cavities. 
     Description of the Related Art 
     Traditional microwave ovens usually comprise a single cooking cavity in which a foodstuff to be cooked is placed. The number of foodstuffs that can be prepared at the same time in such traditional microwave ovens is therefore limited and inadequate for many users. For example, preparing different foodstuffs that require different cooking parameters in a single cavity microwave oven may require the time to cook them sequentially rather than concurrently because of the different cooking parameters. Out of this need, microwave ovens with multiple cooking cavities were developed. One problem is that microwaves emitted into one cavity may interfere with microwaves emitted into another cavity. 
     SUMMARY OF THE INVENTION 
     In one aspect, the invention relates to a radio frequency heating apparatus that has a cavity dividable into at least two sub-cavities, a removable partition for thermally insulating the at least two sub-cavities, a rail provided along a boundary of the cavity for supporting the removable partition, and at least one radio frequency generator configured to transmit radio frequency radiation into at least one of the at least two sub-cavities. The rail or a perimeter of the partition is corrugated with a set of grooves or ridges. The dimensions of the corrugations are selected based on the frequency of transmitted radio frequency radiation between the two sub-cavities. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings: 
         FIG. 1  is a perspective view of a microwave oven according to an embodiment of the invention. 
         FIG. 2  is an enlarged front view of a partition for use in the microwave oven of  FIG. 1  according to an embodiment of the invention. 
         FIG. 3  is a perspective view of the partition of  FIG. 2  with an enlarged view of the corrugations of the partition according to an embodiment of the invention. 
         FIG. 4  is a schematic cross-sectional view of the contacting surfaces of the partition of  FIGS. 2 and 3  against the rail of the microwave oven according to an embodiment of the invention. 
         FIG. 5  is an enlarged front perspective view of the rail of the microwave oven according to an embodiment of the invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Turning now to the drawings and to  FIG. 1  in particular, there is shown a perspective view of a radio frequency heating apparatus in the form of a microwave oven  100  according to an embodiment of the invention. The microwave oven  100  includes a cabinet  120  defining a cooking cavity  112  and a removable partition  114  that extends laterally between two side walls  124 ,  126  of the cavity  112 . The removable partition  114  divides the cooking cavity  112  into at least two sub-cavities, illustrated herein as a first sub-cavity  116  and a second sub-cavity  118 . The removable partition  114  is supported by lateral rails  128 , shown in  FIG. 2  as attached to and protruding from the side walls  124 ,  126  of the cavity  112 . While the illustrations herein show two sub-cavities  116 ,  118 , it is also contemplated that the cooking cavity  112  of the microwave oven  100  could be divided into any suitable number of sub-cavities, each sub-cavity being defined by a suitable arrangement of partitions  114 . Microwave energy may be selectively introduced to the first and second sub-cavities  116 ,  118  through at least first and second wave guides (not shown) corresponding, respectively, to the first and second sub-cavities  116 ,  118 . Each wave guide may be supplied microwaves from a separate microwave generator including but not limited to a magnetron or a solid state radio frequency (RF) device to independently cook foodstuffs located in the two sub-cavities  116 ,  118 . Furthermore, the electric field of the supplied microwaves can be perpendicular to the upper surface of the partition  114 . 
     The microwave oven  100  further includes a door  200 . The door  200  is provided with a choke frame  220  which encompasses a first pane of glass  224  and a second pane of glass  226  which correspond, respectively, to the first and second sub-cavities  116 ,  118 . The first and second panes of glass  224 ,  226  are constructed in such a way, that they are optically transparent but not transparent to microwaves. Furthermore, the first and second panes of glass  224 ,  226  are separated by the choke frame  220 . A hinge  228  mounted to one side of the door  200  and to the cabinet  120  pivotally connects the door  200  to the cabinet  120 . 
     The hinge  228  allows the door  200  to pivotally move between a first open position, best seen in  FIG. 1 , for simultaneous access to the first and second sub-cavities  116 ,  118  and a second closed position (not shown) for preventing simultaneous access to the first and second sub-cavities  116 ,  118 . When the door  200  is in the second position, the choke frame  220 , and particularly the area of the choke frame  220  between the first and second panes of glass  224 ,  226  is in communication with the removable partition  114  in such a manner so as to attenuate microwave transmission between the first and second sub-cavities  116 ,  118 . Furthermore, the choke frame  220  is also is in communication with the cooking cavity aperture perimeter  122  in such a manner so as to attenuate microwave transmission between the cooking cavity  112  and the door  200 . In the case that there are more than two sub-cavities  116 ,  118  within the microwave oven  100 , the choke frame  220  can be designed in such a way that it contacts all of the partitions  114  necessary to separate into the desired number of sub-cavities. Further details of the structure of the door  200  and choke frame  220  that may be used in the embodiment are disclosed in International Publication No. WO 2015/099648, published Jul. 2, 2015, which is incorporated herein by reference in its entirety. 
     According to one embodiment, the removable partition  114  may be arranged at half of the height of the cooking cavity  112 , thereby enabling the division of the cooking cavity into the two sub-cavities  116 ,  118  essentially identical in size (or volume). However, according to another embodiment, the partition  114  may be arranged such that the cooking cavity  112  may be divided in different manners (e.g. at one third or two third of the height or, in other cases, at one fourth or three fourths of the height), thereby resulting in sub-cavities  116 ,  118  of different sizes/volumes. 
       FIG. 2  shows an enlarged front view of the removable partition  114  positioned within the microwave oven  100  according to an embodiment of the invention. The removable partition  114  is constructed in such a way that it attenuates the transmission of microwaves between the first and second sub-cavities  116 ,  118 . The removable partition  114  may have a lower layer  130  that is a thermally insulating layer, as well as a dielectric upper layer  132 , where the lower and upper layers  130 ,  132  are separated by an air gap. The air gap between the lower and upper layers  130 ,  132  increases thermal attenuation. The dielectric upper layer  132  is supported by the lower layer  130  and is suitable for cooking a foodstuff placed directly on the upper layer  132 . By spacing the upper layer  132  a suitable distance away from the lower layer  130 , which is not transparent to microwaves, efficient microwave cooking of foodstuff placed directly on the upper layer  132  can be achieved. One example of a suitable structural lower layer  130  for a removable partition  114  is disclosed in U.S. Patent Application No. 2013/0153570, published Jun. 20, 2013, which is incorporated herein by reference in its entirety. It is contemplated herein that the lower layer  130  may essentially form a trapezoidal box with rectangular top and bottom surfaces and side in the form of sloped surfaces  134  that angle inwardly, away from the side wall  126  of the cooking cavity  112 , from the top surface to the bottom surface of the lower layer  130 . It is illustrated herein that the angle of the sloped surfaces  134  of the lower layer  130  are roughly 45°, but any suitable angle that allows the removable partition  114  to stay in place, for example between 5° and 85°, is also considered. 
     On the sloped surfaces  134  of the lower layer  130 , along the perimeter of the partition  114 , are provided a set of grooves or ridges  136 . In an exemplary embodiment, the set of ridges  136  is provided as a series of semi-circular corrugations protruding out from the sloped surface  134  of the lower layer  130  of the removable partition  114  and protruding towards the side wall  126  of the cooking cavity  112 . In an exemplary embodiment, the lower layer  130  and the corrugated ridges  136  are formed of a single, common material. Non-limiting examples of suitable materials for the lower layer  130  of the partition  114  include aluminum or sheet steel. It is contemplated that the upper layer  132  of the partition  114  is formed of a type of glass, including, but not limited to, borosilicate. The lower and upper layers  130 ,  132  can be attached to each other by any suitable method, including, but not limited to, gluing the lower and upper layers  130 ,  132  to one another in such a way that the air gap is sufficiently maintained. 
     The removable partition  114  is supported by a rail  128  that is attached to the side wall  126  of the cooking cavity  112 . The rail  128  protrudes from the boundary or side wall  126  of the cooking cavity  112  such that a sloped or angled surface  137  of the rail  128  angles outwardly from the side wall  126  from the topmost part to the lowermost part of the rail  128 , and the angled surface  137  of the rail  128  is sloped relative to the boundary of the cavity  112 . The angle of the angled surface  137  of the rail  128  as it protrudes from the side wall  126  of the cooking cavity  112  is the same as the angle of the sloped surface  134  of the lower layer  130  of the partition  114  as it angles away from the side wall  126  of the cooking cavity  112 , such that when the removable partition  114  is laid on and supported by the angled surface  137  of the rail  128 , the two surfaces can contact and complement one another. The angled surface  137  of the rail  128  is illustrated herein as being provided with a set of grooves or ridges  138  in a complementary pattern to the grooves or ridges on the sloped surface  134  of the lower layer  130  of the partition  114 , such that the ridges  136 ,  138  on one of the surfaces are received in the grooves or ridges  136 ,  138  of the complementary surface. It is also contemplated that the angled surface  137  of the rail  128  could be completely smooth or flat and have no grooves or ridges  138 . Furthermore, it is also possible that the angled surface  137  of the rail  128  could have protruding ridges  138  and the sloped surface  134  of the lower layer  130  of the partition  114  could have complementary inwardly protruding ridges  136 , in the opposite configuration from what is illustrated herein. Further, it is contemplated that the sloped surface  134  could be completely smooth or flat and have no grooves or ridges  136 , while the angled surface  137  of the rail  128  has protruding ridges  138 . It is contemplated that the rail  128  is formed of the same material as the lower layer  130  of the partition  114  and the ridges  136 , although any suitable material can alternatively be used. 
       FIG. 3  shows a perspective view of the removable partition  114 , as well as an enlarged view of the sloped surface  134  of the partition  114 . While it is illustrated here that the ridges  136  are provided on all sloped surfaces  134  of the partition  114 , it is also contemplated that the ridges  136  could occupy any suitable amount of the perimeter of the partition  114 . For example, the ridges  136  can be provided only on certain sides of the partition, or, within a single sloped surface  134 , the ridges  136  can be provided only on a portion or multiple discrete portions of the sloped surface  134 , rather than being provided along the entire length of the sloped surface  134 . 
       FIG. 4  illustrates a schematic, cross-sectional view of an embodiment of the interface where the ridges  138  on the rail  128  are adjacent to and oriented so as to be facing the sloped surface  134  of the lower layer  130  of the partition  114 . It is shown herein that the ridges  138  of the rail  128  and the ridges  136  of the partition  114  are arranged in such a way as to be complementary to one another. For example, the ridges  138  of the rail  128  are aligned such that each of the ridges  138  can at least partially receive each of the ridges  136  of the sloped surface  134  of the lower layer  130  of the partition  114 . Conversely, the ridges  136  of the lower layer  130  of the partition  114  are aligned such that each of the ridges  136  is at least partially received within, and can further come into contact with, a ridge  138  of the angled surface  137  of the rail  128 . Having this complementarity of profile between the rail  128  and the partition  114  allows for a plurality of potential contact points to create a reliable electrical connection between the rail  128  and the partition  114  in order to optimize and maximize the thermal attenuation between the two sub-cavities  116 ,  118 , as well as ensuring that the partition  114  stays in the desired position. The complementary arrangement of the ridges  138  of the rail  128  and the ridges  136  of the lower layer  130  of the partition  114  also allows for thermal expansion of the partition  114  during cooking processes. While the rail  128  and the lower layer  130  of the partition  114  are illustrated herein as being spaced apart from one another in order to easily view the complementarity of the two separate components, it is understood that, when the partition  114  is in its position and being supported by the rail  128 , the sloped surface  134  of the lower layer  130  of the partition  114  and the angled surface  137  of the rail  128  can come into physical contact with one another. During the course of thermal expansion of the partition  114  during cooking processes, the partition  114  is allowed to move slightly vertically along the angled surface  137  of the rail  128  in order to accommodate the expanded size of the partition  114 . It is also contemplated that the ridges  136  of the lower layer  130  of the partition  114  could be slightly narrower than the ridges  138  of the rail  128  so that there is also some allowance for horizontal movement of the partition  114  during the course of thermal expansion. 
       FIG. 5  illustrates an enlarged front perspective view of the angled surface  137  of the rail  128 . The distance A between the peaks, or the pitch, of adjacent ridges  138  must be determined in such a way that attenuation of the transmission of microwaves between the two sub-cavities  116 ,  118  is maximized. For example, if the distance A between ridges is too large, the electrical field components will be able to pass between the sub-cavities  116 ,  118 , reducing efficiency. Ensuring that the distance A is sufficiently small enough so that the ridges  136 ,  138  can act as waveguides can be accomplished by calculating the maximum value of the distance A in order for the ridges  136 ,  138  to act as effective waveguides. Generally the maximum width of the waveguide can be represented in the following equation:
 
 A=c/ 2 fc   TE10 ,  (1)
 
where, A=width of the waveguide, or distance A between the peak or pitch of adjacent ridges, c=speed of light in the vacuum, and fc TE10 =cut-off frequency, which is the upper limit of the working frequency of the microwave oven  100 . In this way, the dimensions of the corrugations are selected on the basis of a cut-off frequency of transmitted radio frequency radiation between the two sub-cavities  116 ,  118 .
 
     It is contemplated herein that the transmitted microwave bandwidth of the microwave oven  100  is 2.5 GHz, in which case equation (1) provides a value of A=6 cm, indicating that the pitch or distance A of not more than 6 cm for a microwave oven  100  with a working frequency of 2.5 GHz is required for optimal function. Placing the ridges  136 ,  138  at a pitch or distance A of less than 6 cm will result in even greater attenuation of transmission of microwaves, but it is understood herein that any distance A that is less than or equal to 6 cm would be effective within the scope of the invention for a microwave oven  100  with a transmitted microwave bandwidth of 2.5 GHz. It is also contemplated that the invention can be applied with microwave ovens having transmitted microwave bandwidths of any suitable value, and that equation (1) can be used to determine a suitable distance A between ridges  136 ,  138  for the partition  114  and/or the rail  128 . For example, the bandwidth of frequencies between 2.4 GHz and 2.5 GHz is one of several bands that make up the industrial, scientific and medical (ISM) radio bands. In another embodiment, the transmission of other microwave frequency bands is contemplated and may include non-limiting examples contained in the ISM bands defined by the frequencies: 13.553 MHz to 13.567 MHz, 26.957 MHz to 27.283 MHz, 902 MHz to 928 MHz, 5.725 GHz to 5.875 GHz and 24 GHz to 24.250 GHz. 
     The embodiments described above provide for a variety of benefits including the attenuation of microwave transmission between multiple cavities in a microwave oven such that foodstuffs contained in different cooking cavities may be cooked at the same time and independently of each other resulting in more even cooking and reduced cooking time. 
     While the invention has been specifically described in connection with certain specific embodiments thereof, it is to be understood that this is by way of illustration and not of limitation, and the scope of the appended claims should be construed as broadly as the prior art will permit.