Abstract:
An “Adaptable Ceramic Based Microwave Absorbing Heater” simple to manufacture with efficiency to capture and store enough microwave energy in typically one to 1.5 minutes in a 1200 W microwave oven to keep food or beverages hot at the table when the heater is used in a “Heat Retentive Plate” or “Heat Retentive Coffee Mug” and other dinnerware. The heater can also be used for scorching or browning food and in other industrial applications.

Description:
RELATED APPLICATIONS  
       [0001]     The present application is related to U.S. application Ser. No. 11/248,713, filed Oct. 12, 2005, for “INTEGRATED MICROWAVEABLE HEAT STORAGE DEVICE”, by Juan J. Ramirez, included by reference herein.  
         [0002]     The present application is related to U.S. Provisional Patent Application No. 60/663,052, filed Mar. 8, 2005, by Juan J. Ramirez, included by reference herein.  
         [0003]     U.S. Ser. No. 11/248,713 Patent pending “Integrated Microwaveable Heat Storage Device” by Juan J. Ramirez (Who is also the Applicant for this patent) discloses a ceramic based microwave absorbing heater specially developed for the “Integrated Microwaveable Heat Storage Device” which also has other potential applications. The Inventor claims the priority date of this invention, since it was not allowed by the Examiner for considering it to be a different invention.  
         [0004]     This is a Divisional Application that claims the filing date of the parent case U.S. Ser. No. 11/248,713 and the filing date of the Provisional Patent Application 60/663,052. 
     
    
     FIELD OF THE INVENTION  
       [0005]     The present invention relates to microwave absorbing heaters, and more particularly, to ceramic based microwave absorbing heaters used to absorb microwaves in a common microwave oven in order to scorch food and/or store heat to maintain food hot at the table. The inventor developed this heater while working on the Integrated Microwaveable Heat Storage Device (Patent pending U.S. Ser. No. 11/248,713). This is a divisional application of that parent application and the Inventor claims the filing date of that parent case.  
       BACKGROUND OF THE INVENTION  
       [0006]     During the development of the “Integrated Microwaveable Heat Storage Device” (Patent pending U.S. Ser. No. 11/248,713), the Applicant found the need to develop a “low cost”, “low tech” (Simple technology) ceramic based “microwave absorbing heater” capable of absorbing and storing relatively large amounts of microwave energy in a short period of time (Typically one to 1.5 minutes), in order to store this energy as thermal energy or heat and radiate in the infrared wave length in a confined cavity according to the Laws of physics for radiation of hot bodies.  
         [0007]     Applicant could not find any microwave absorbing heater with high absorption capacity and enough thermal mass for the purpose mentioned above, which besides that is a low cost, “low tech” (Simple technology) and easy to manufacture heater.  
         [0008]     Some Microwave Absorbing Materials Found are:  
         [0009]     Microwave absorbing films which obviously do not have the thermal mass required to store heat.  
         [0010]     Porous structures which have the same problem: Not enough thermal mass.  
         [0011]     Materials that require nano-particles with complex manufacturing processes such as in U.S. Pat. No. 6,986,942 by Mayes.  
         [0000]     Other Concepts or Microwave Absorbing Materials Found are:  
         [0012]     Arrays of metal plates like in U.S. Pat. No. 6,756,932 by Barker, which are not suitable for microwave ovens or to be used inside a ceramic plate.  
         [0013]     Materials made out of plastic which would not resist the heat. See: Emmerich U.S. Pat. No. 6,420,688  
         [0014]     Materials for shielding electronic components like in Allen U.S. Pat. No. 6,410,847.  
         [0015]     Materials for microwave oven doors see: Osepchuk U.S. Pat. No. 5,981,927.  
         [0016]     Materials using complex icosahedral molecules designed for particular purposes (Low weight, impedance tuning), see: U.S. Pat. No. 5,574,077 by Dougherty.  
         [0017]     Materials for insulating hand held telephones, see: Luxon U.S. Pat. No. 5,507,012.  
         [0018]     Materials for reducing the radar signature of planes: Grant U.S. Pat. No. 5,415,364  
         [0019]     Materials used as susceptors for pizza, popcorn etc. (A susceptor absorbs microwaves and releases heat they are usually films).  
         [0020]     Materials used to suppress EMI (Electromagnetic interference, see: Catt U.S. Pat. No. 5,397,854.  
         [0021]     Materials made of glass micro spheres (With a complex manufacturing process). See: Japka U.S. Pat. No. 5,326,640.  
         [0022]     Materials used as thermo plastic or thermosetting adhesives, see: Johnson, U.S. Pat. No. 5,238,975.  
         [0023]     Materials used as heater but with porosity not suitable to store thermal energy, See: Inukai, U.S. Pat. No. 5,189,273.  
         [0024]     Materials for absorbing frequencies of 2500-6000 MHz (A very particular range of frequencies): Hahn, H1, 002  
         [0025]     Materials comprising two layers of microwave absorbing material separated by one layer transparent to microwaves, See: Emslander, U.S. Pat. No. 4,962,000 and;  
         [0026]     Materials designed to absorb radar signals used by police, See: Eubanks, U.S. Pat. No. 4,791,419.  
       DISADVANTAGES OF THE EXISTING MATERIALS OR PRIOR ART  
       [0027]     The materials found are films with not enough thermal mass, porous structures (Same problem, not enough thermal mass to store heat), some use nano-particles (Very small particles with complex manufacturing processes), use complex polar molecules, or are for a very specific use such as suppressing EMI, reducing the radar signature of a plane, etc. They rely basically on the property of polar molecules to get excited by a variable electromagnetic field. Although those materials may perform well for their intended purpose, there is still the need for a heater with enough thermal mass for other purposes, such as the “Integrated Microwaveable Heat Storage Device” and other Industrial applications.  
         [0028]     Most of the microwave absorbing materials mentioned above rely on a single phenomenon: Agitation of polar molecules to create heat.  
       WORKING PRINCIPLE  
       [0029]     The present invention uses three different phenomena:  
         [0030]     1) Agitation of polar molecules: Metal oxides on the surface of the metal particles and metal oxides contained in the clay body itself, plus . . .  
         [0031]     2) Induction heating: Minute electrical currents are generated on the surface of the metal particles by induction. And . . .  
         [0032]     3) A parasitic current that is formed within the body of the heater due apparently to the presence of minute contents of carbon and other impurities in the clay body.  
         [0033]     While Applicant finds explanation to the effectiveness of the heater in these three phenomena, he does not wish to be bound by this.  
         [0034]     It is therefore an object of the invention to provide a simple but efficient microwave absorbing heater with relatively high thermal mass to absorb and store the microwave energy as heat and radiate in the infrared zone of the electro magnetic spectrum (Or radiated heat). Simply put: It is a rigid microwave absorbing material whose absorption capacity can be regulated, and can be shaped as wished, can be preheated in a microwave oven and radiates heat (Infrared radiation).  
         [0035]     It is another object of the invention to provide a microwave absorbing heater to be used in. “Heat Retentive Plates” 
         [0036]     It is another object of the invention to provide a microwave absorbing heater to be used in “Heat Retentive Coffee Mugs”.  
         [0037]     It is another object of the invention to provide a heater to be used in “Heat Retentive Tortilla Warmers”, “Gravy Boats” and any other “Heat Retentive Dinnerware” 
         [0038]     In general it is another object of the invention to provide a low cost, “low tech” (Simple technology), efficient, easy to manufacture and shape microwave absorbing heater to be used in any application that requires an efficient heater with relatively high thermal mass.  
         [0039]     Other potential Industrial applications are: welding plastics, curing adhesives (The heater can be shaped using molds or by any other well known method used in the ceramic industry.) etc. The absorption characteristics can be regulated easily by changing the percentage of metal particles in the mix. The emissivity can be controlled by optionally glazing the heater, changing the color of the surface with a coat of “slip” (Clay in creamy consistency) or paint of different color and/or changing the finish of the surface.  
       SUMMARY OF THE INVENTION  
       [0040]     In accordance with the present invention, there is provided an “Adaptable Ceramic Based Microwave Absorbing Heater” with efficiency to capture enough microwave energy in typically one to 1.5 minutes in a 1200 W microwave oven to keep food or beverages hot at the table when the heater is used in a “Heat Retentive Plate”, “Heat Retentive Coffee Mug”, gravy boat or any other embodiment of the “Integrated Microwaveable Heat Storage Device” as well as many other potential Industrial applications.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0041]     A complete understanding of the present invention may be obtained by reference to the accompanying drawings, when considered in conjunction with the subsequent, detailed description, in which:  
         [0042]      FIG. 1  is a cross section view of a disk shaped “adaptable microwave absorbing heater” used in a “heat retentive disk” made out of ceramic, the disk can be used inside a regular plastic tortilla warmer or a pizza bag to put heat inside, instead of relying just in insulation;  
         [0043]      FIG. 2  is a cross section view of a convex (to create thermal gradient) disk shaped “adaptable microwave absorbing heater” used in a “heat retentive plate” the rim of the plate remains cool for easy handling;  
         [0044]      FIG. 3  is a cross section view of a “adaptable microwave absorbing heater” used to scorch food in a microwave oven, the drawing is just an schematic, obviously, the food will scorch better if little pieces are distributed on the surface of the heater, for this application the heater should be glazed;  
         [0045]      FIG. 4  is a cross section view of a heater used in a ceramic tortilla warmer; and  
         [0046]      FIG. 5  is a temperature v. time chart that shows how the delay action and the maximum temperature reached in a “heat retentive plate can be controlled by the percentage of iron in the mix of the heater, although there are many other factors, such as internal gaps, thicknesses, thermal masses, etc. The point here is that the “heater is easily adaptable to the desired performance, hence the name: “Adaptable Microwave Absorbing Heater”. The heater is also very adaptable in shape, thermal mass, emissivity, etc. 
     
    
       [0047]     For purposes of clarity and brevity, like elements and components will bear the same designations and numbering throughout the Figures.  
       DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0048]      FIG. 1  is a cross section view of a disk shaped “adaptable microwave absorbing heater” used in a “heat retentive disk” made out of ceramic  10 . This is the figure chosen to explain the components of the heater.  
         [0049]      FIG. 2  is a cross section view of a convex (to create a thermal gradient) disk shaped “adaptable microwave absorbing heater” used in a “heat retentive plate”.  
         [0050]      FIG. 3  is a cross section view of an “adaptable microwave absorbing heater” used for scorching food in a microwave oven.  
         [0051]      FIG. 4  is a cross section view of a heater used in a tortilla warmer.  
         [0052]      FIG. 5  is a temperature v. time chart view of the delay action and the maximum temperature reached in a “heat retentive plate can be controlled by the percentage of iron in the mix of the heater although there are many other factors, such as internal gaps, thicknesses, thermal masses, etc. The point here is that the “heater is easily adaptable to the desired performance, hence the name: “Adaptable Ceramic Based Microwave Absorbing heater”. It is also very adaptable in shape, thermal mass etc.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0053]     My preferred embodiment of the “Adaptable Ceramic Based Microwave Absorbing heater” is a mixture of red earthenware clay with uniformly dispersed iron shavings (Just two components) preformed as required and fired in a kiln to the recommended pyrometric cone range for red earthenware which is very wide: cone 06 to cone 02 (1828 degrees F. to 2016 degrees F.).  
         [0054]      FIG. 1  shows one of the simplest applications of the Microwave absorbing heater in a Microwaveable heat storage device. The fact that the heater is encapsulated in a sealed cavity limits the radiation of the heater according to the laws of physics for hot body radiation.  
         [0055]     The heater is simply a rigid microwave absorbing material made out of clay (Red earthenware) and metal particles  12  (Preferably iron) uniformly dispersed, the preferred ceramic  10  is red earthenware since it already contains ferric oxides which are polar molecules that get excited in a variable electromagnetic field such as the one produced by a microwave oven.  
         [0056]     Traces of carbon  14  in the mix provide a path for a parasitic current inside the heater (Optionally other impurities can be used in place of or in addition to carbon to create a conductive path). Carbon does not need to be added in the preferred embodiment which uses iron particles. Since iron contains some carbon.  
         [0057]     The use of Paper fiber  18  is optional to provide mechanical strength to the heater while handling (Before firing) in the manufacturing process.  
         [0058]     The heater can also optionally be sealed using glaze  16  to: add thermal mass, control the emissivity and keep moisture from penetrating the heater.  
       How to Make  
       [0059]     The iron particles (Shavings) can be incorporated to the clay by any well known mechanical mixing process in the dinnerware industry. They can be uniformly dispersed even by hand to make prototypes by wedging, which is also a very well known process for potters. The same thing can be done with the paper fiber  18  and it can be done at the same time the iron particles are mixed. After the mix is dry enough, it can be fired in a kiln by any well known method, firing the heater(s) at a relatively low temperature to get rid of the water that is physically attached to the mix, then continue firing at medium temperature to get rid of the water that is attached chemically, and finally continue firing until the desired pyrometric cone temperature is reached. All these are well known methods for the skilled in the art.  
       The Iron Particles  
       [0060]     Iron particles (Shavings) of the appropriate size can be obtained from brake shops where they are discarded as scrap, they can be obtained from recycling companies and also larger size shavings obtained at machine tool shops can be milled in a ball mill to the appropriate mesh size preferably no larger than mesh size 12 more preferably no larger than 16 mesh size, and most preferably no larger than 20 mesh size. My preferred percentage in the mix goes from 10 to 20% by volume (It all depends on the application, so a fixed percentage cannot be specified). The amount of Iron in the mix has a direct impact in the maximum temperature reached and how fast it reaches the maximum temperature.  
       The Paper Fiber  18  (Optional)  
       [0061]     The paper fiber  18  can be obtained from scrap paper or carton, soaked in water, then shredded and blended to a pulpy consistency, pressed to discard excess of water and incorporated to the clay body by any well known mechanical means (The ceramic  10  before being fired is called clay). My preferred percentage of paper fiber  18  in the mix is 5% to 15% by volume. The percentage of paper fiber  18  used has a direct impact on how easily the heater can be handled (Before firing it) without damaging it.  
         [0062]      FIG. 1  is a simple application of the heater in a heat retentive disk that can be used inside a pizza bag or a common tortilla warmer to put heat inside it. Normally tortilla warmers work just by trying to insulate the tortillas and keeping the heat in the tortillas from escaping, unfortunately, tortillas do not have enough thermal mass (They cannot store a lot of heat), by putting one of these disks inside, the difference is great. This is a totally different approach: Adding heat and releasing it slowly instead of trying to insulate and keep the small amount of heat stored in the tortillas from escaping.  
         [0063]      FIG. 2  this is a very good application: A heater inside a heat retentive plate: Plate, (Container), Heater and Base cooperate to embody a Heat Retentive Plate that can be preheated for typically just one to 1.5 minutes to keep food hot at the table. Plates are particularly difficult to insulate due to their shape and large surfaces, many attempts have been made, none of them is practical enough to be used at home or in restaurants on a regular basis. This is a totally new approach: Putting heat inside the plate. In this case the heater is precisely shaped to create a thermal gradient and avoiding thermal shock, as well as allowing the plate to be handled safely by the rim.  
         [0064]      FIG. 3 a  heater being used to scorch food. One big disadvantage of microwave ovens is that they are not good for scorching or browning, by using a heater of the appropriate characteristics regarding to the content of iron particles (Preferably thick and glazed) the advantages of microwave cooking can be combined with the advantages of the heater for browning or scorching, giving a common microwave oven new capabilities at a very low price.  
         [0065]      FIG. 4 a  heater inside a ceramic tortilla warmer, the application is obvious: Storing and radiating heat.  FIG. 5  shows how the percentage of iron in the mix has a direct impact on how fast the heater gets hot also in the thermal mass of the heater (There are many other factors that affect the temperature chart on the surface of a plate)  
         [0066]     Since other modifications and changes varied to fit particular operating requirements and environments will be apparent to those skilled in the art, the invention is not considered limited to the example chosen for purposes of disclosure, and covers all changes and modifications which do not constitute departures from the true spirit and scope of this invention.  
         [0067]     Having thus described the invention, what is desired to be protected by Letters Patent is presented in the subsequently appended claims.