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Publication numberUS3835280 A
Publication typeGrant
Publication dateSep 10, 1974
Filing dateFeb 1, 1973
Priority dateFeb 1, 1973
Publication numberUS 3835280 A, US 3835280A, US-A-3835280, US3835280 A, US3835280A
InventorsBrandberg L, Gades L, Gorman R
Original AssigneePillsbury Co
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Composite microwave energy perturbating device
US 3835280 A
Abstract
For the purpose of concentrating microwave energy to a central point or other desired location in a microwave oven, a composite signal perturbating device is placed in the oven. It consists of a sheet of a low loss dielectrical material together with a layer of microwave reflecting material. The device is placed on the floor of the oven and on the opposite side of the product heated from the source of microwave energy. The low loss dielectric consists, for example, of a flat sheet of dielectric material having two sheets of aluminum foil imbedded therein as concentric rings positioned in a plane parallel to the floor of the oven chamber and spaced from about 3/4 of an inch to one inch below the product that is to be heated.
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United States Patent [191 Gades et al.

[11] 3,835,280 [451 Sept. 10,1974

[ COMPOSITE MICROWAVE ENERGY PERTURBATING DEVICE l/l970 Brumfield et al. 2l9/l0.55

Primary Examiner-J. V. Truhe Assistant Examiner-Hugh D. Jaeger Attorney, Agent, or Firm-James V. Hermon; Michael D. Ellwein; Ronald E. Lund [5 7] ABSTRACT For the purpose of concentrating microwave energy to a central pointor other desired location in a microwave oven, a composite signal perturbating device is placed in the oven. It consists of a sheet of a low loss dielectrical material together with a layer of microwave reflecting material. The device is placed on the floor of the oven and on the opposite side of the product heated from the source of microwave energy. The low loss dielectric consists, for example, of a flat sheet of dielectric material having two sheets of aluminum foil imbedded therein as concentric rings positioned in a plane parallel to the floor of the oven chamber and spaced from about /1 of an inch to one inch below the product that is to be heated.

5 Claims, 4 Drawing Figures 1 COMPOSITE MICROWAVE ENERGY PERTURBATING DEVICE FIELD OF THE INVENTION The present invention relates to microwave cooking and more particularly to an improved energy concentrator for facilitating the cooking of foods in microwave ovens.

THE PRIOR ART In spite of the demand for a popcorn product which can be freshly popped in a microwave oven and served while it is piping hot, someofthe commercially available ovens have been unsuited for this purpose. For example, numerous attempts have been made by us to satisfactorily pop packages of unpopped popcorn in the Model 500 oven manufactured by the Litton Industries, 360 North Cresent Drive, Beverly Hills, Calif, 90210. It was found by us that only about 25 percent of the kernels would pop on the average while the other 75 percent remained unpopped. This kind of performance is, of course, totally unsatisfactory for commercial acceptance.

It has been proposed to package food products such as TV dinners and frozen foods and the like in boxes formed in part of a microwave reflective material such as aluminum foilhaving holes in selected areas. The microwave energy appears to enter the holes and is reflected about within the package by the aluminum foil thereby facilitating the heating of the food product. In addition to increasing the cost of the package, the use of perforated'aluminum foil layers or strips as a part of the package itself was evaluated by us and found to be unsatisfactory for the purposes of the present invention. US. Pat. No. 3,271,552 describes a heating apparatus for concentrating microwave energy at desired points in a microwave oven and includes spaced parallel strips of conductive material formed into the side walls of the package containing the food product to be heated. These strips are one half wavelength in length to obtain maximum re-radiating characteristics. In another form of the invention, an insulating block of a low dielectric constant material is as mounted in the oven. Vertical re-radiating elements such as metal rods are placed on each side of the block. We found that the reradiation of energy is unsatisfactory in some instances because of localized heating and the possibility for arcing to occur. Inaddition, it is expensive to provide conductive materialas a part of the package containing the food product.

OBJECTS OF THE INVENTION The primary objects of the invention are to provide (a) a simple and reliable method of concentrating microwave energy in a microwave oven such as the Litton Industries Inc. 500 oven whereby products which are difficult-to properly preparebecause they are relatively sensitive to the distribution microwave energy can be cooked satisfactorily e.g., so that when popcorn is popped 80 percent of the kernels pop when the invention is used in a Litton Model 500 oven, (b) to provide a durable and unitary article which functions both as an energy concentrator andas a support for the popcorn or other material being heated, (c) a. device which is capable of functioning by two different methods of operation to concentrate the microwave'energy at the point where it is most needed, ((1) a compact, unitary microwave energy concentrator and combination shelf which is capable of operating successfully over extended periods of time without reflecting excessive amounts of microwave energy back to the magnatron and (e) to provide an energy concentrator of the type described which can be left in the oven at all times-- even during the heating of foods which are less critical than popcorn concerning the concentration of microwave energy.

THE FIGURES FIG. 1 is a side elevational view partly in section of a microwave oven and concentrator in accordance with the invention showing a popcorn product in the oven as it appears after being popped.

FIG. 2 is a partial horizontal sectional view taken on Line 22 of FIG. 1 on a slightly reduced scale.

FIG. 3 is a partial perspective view of the concentrator and food product before heating.

FIG. 4 is a partial vertical sectional view taken on Line 44 of FIG. 3 on a slightly enlarged scale.

SUMMARY OF THE INVENTION A composite microwave signal perturbating device is provided which consists of a low loss dielectrical element p.g., a plane or sheet together with microwave reflecting body bonded thereto. The device is placed in the oven and on the opposite side of the produce being heated from the source of microwave energy. The device is preferably composed of a sheet of low loss dielectric material having the layer of microwave reflecting material imbedded therein e.g., as a series of concentric rings positioned in a plane parallel to the floor of the oven chamber and spaced preferably from about A of an inch to 1 inch below the product which rests on the upper surface of the dielectric material.

DESCRIPTION OF THE PREFERRED EMBODIMENT As seen in FIGS. 1 and 2 the composite energy concentrator 10 is generally rectangular as seen in plan view and consists of two sheets of a low loss dielectric material such as a plastic resin which can be subjected to microwave energy without damage such as melting, warpage, or carbonization. Polypropelene is an example of such a material. For convenience the low loss dielectric material will be referred to as a ballast. The ballast is composed of an upper rectangular plate 12 and a lower rectangular plate 14. The ballast is preferably slightly smaller than the door of the oven so that it can be introduced and removed as needed. A sheet eleven inches square is typical. When polypropelene is used, the upper sheet is i of inch thick and the lower sheet is of an inch. Thus, the package 30 resting on the ballast 10 is held at an elevation of about 1 Vs inches above the floor of the oven. We have found that during a typical heating period of 2 minutes the temperature of the composite sheet is raised from about to about F.

While the reason for the effectiveness of the ballast for improving the concentration of microwave energy is not known with certainity, it is believed to improve the matching of the impedance of the cavity with the impedance of themagnatron thereby assuring maximum energy absorption within the chamber. The dielectric constant of the ballast should be that of low loss dielectric. While a variety of substances can be used, some of the most suitable are dimensionally stable polemeric resinous materials such as polypropelene and teflon. The dielectric constants of these materials range from about 2 to about 3.2. Polyethylene has also been found suitable but does not have quite as good dimensional stability under typical conditions of use. Polystyrene appears to be effective electrically but does not have the desired temperature stability. The same is true of acrylic resins such as polymethylmethacrylate. Glass has too high a dielectric constant and will not function for the purposes of the invention. Other suitable materials will be apparent to those skilled in the art. When polypropelene is used, the entire ballast 10 should weigh about 5 pounds when used in a Litton 500 oven.

As best seen in FIGS. 2 and 4, there is laminated between the sheets 12 and 14 a pair of rings 24 and 26 of microwave reflective material formed from mil. aluminum foil sheets each .1 inch wide and having outside diameters of 6 and 10 inches respectively. Sheets 12 and 14 can be bonded together in any suitable manner as for example by a resinous adhesive having a dielectric constant about the same as the material from which the sheets 12 and 14 are constructed. One example is an epoxy adhesive.

Refer now to FIGS. 1 and 2 for a description of the oven itself. The oven indicated generally by the numeral 40 includes an outside housing 42, a microwave generator including a magnatron (not shown) connected by means of a waveguide 50 to a distributing device for uniformly supplying the microwave energy to the interior of the oven, in this case a mode stirer 48 which communicates with the interior oven chamber through an inlet 49. The operation of the oven is regulated by a means of exterior control 52 of a suitable known construction. As mentioned above, the oven itself is entirely conventional and is best exemplified by oven model 500 manufactured by the Litton Industries Inc. of Calif.

The concentrator 10 has general application but is especially useful for popping frozen packages of popcorn in ovens as low as 500 watts measured output. In this application the popcorn package usually includes a flexible and expandable container body such as a gussetted bag formed from two plys of paper. The charge of popcorn in the package is uniformly mixed with about 1 to 5 parts by weight of shortening for each eight parts of corn. The shortening can include any edible cooking oil or plastic fat, whether solid or liquid and includes both hydrogenated and non-hydrogenated shortenings. Any of a variety of edible animal or vegetable oils or plastic fats can be used with those of vegetable origin being referred because of their lower melting points. The package also contains salt for flavoring.

The flexible popcorn package which is designated 39 consists of paper walls with longitudinally extending gussets on each side to provide a sizeable expansion volume. The bottom and top is sealed tightly by transverse seals 34 and 36. The package preferably consists of two layers of flexible sheet material. One preferred outer sheet material is bleached kraft paper. A suitable liner (not shown) consists of glasine paper.

After the package has been filled with a charge of popcorn, the top is sealed at 36. The charge of unpopped corn and shortening 32 at the center portion of the package 30 can be best seen in FIGS. 3 and 4.'The block of popcorn and shortening 32 is made of about one to five parts of a shortening for each eight parts of corn.

After the package is filled and sealed as shown in FIG. 3, it is preferably placed in refrigerator or frozen storage until it is ready to be used. When the popcorn is to be popped, the package is placed on the center of the concentrator 10 within the cooking chamber 41 of the microwave oven 40. As microwave energy is supplied to the chamber, the package 30 is expanded by steam and then becomes filled with the popped corn 39 as shown in FIG. 1.

It is believed that the outstanding performance re sults made possible through the invention are due in large part to the concentration of microwave energy in the vicinity of the popcorn. During heating, the shortening provides a heat transfer medium for conducting heat evenly between the individual kernels in spite of the presence of hot or cool spots in the package. The package, in addition to being flexible and expandable is relatively leak proof at least during the period of time the product is being cooked.

While the invention has been described in connection with popping popcorn, it is applicable to a variety of other foods. The invention will be better understood by reference to the following example:

Example 1 A concentrator was made of about 5 pounds of polypropelene having the dimensions given above and was placed in a Litton 500 oven. A gussetted paper bag as depicted in the figures is formed from Kraft paper and includes a glasine paper lining having the dimensions 7 X 10 inches with 2 inch deep gussets. The bag is filled with 120 grams of a uniform mixture of popcorn, coconut oil and salt. Forty grams of the shortening and salt mixture consisting of 30 grams coconut oil, 10 grams of super fine granulated salt and grams of yellow hybrid popcorn. After the corn and shortening is placed in the pouch it is sealed transversely at the top. The package is then frozen. Later upon being placed in a microwave oven of a capacity of 1,200 watts running at about 950 watts for one minute and 45 seconds using the concentrator described above, about 22 percent or less of the popcorn will remain unpopped. The resulting popcorn will be crisp and will have a very appealing flavor and texture. The amount of burned kernels will be less than 5 percent and the corn will not be appreciably scorched. The bag can be handled immediately and the volume of popped corn will be about 2,800 cc. or more with a volume ratio of popped to unpopped kernels of about 35 or above.

In a comparative test, otherwise identical except without the concentrator 10, the volume of popped corn was 400 cc. and the percent of unpopped kernels was 80 percent. I

The mechanism by which the energy density is concentrated above the center of the unit 10 is not known with certainty but it appears to result in part from the mass of low loss dielectric material and in part from the reflective material. As a result of tests run in the development of the invention, the best results were obtained in most Litton model 500 ovens when the concentrator had an inner foil ring with an outside diameter of about 6 inches and about 60 percent of the center is cut out. Optimum results were also obtained with the top of the when the concentrator shown in the figures is used, the 0 ratio of transmitted power to reflected power is improved, i.e., raised which is desirable not only from the standpoint of heating the product but also because it would appear to reduce damage to the magnatron which results from reflected energy.

We claim:

1. A composite microwave energy perturbating device useful in concentrating microwave energy in a zone located in approximately the center thereof comprising a sheet of a low loss dielectric material of an appropriate size to fit within the oven and to rest on the bottom thereof during operation, said sheet including upper and lower substantially parallel surfaces and vertical side edges which are substantially less than the width and breadth of the sheet and a plurality of concentric rings of electrically conductive microwave reflective sheet material mounted upon the perturvating device and positioned in a plane substantially parallel to the upper surface thereof thereby concentrating the microwave energy at a point near the center of the concentric rings.

2. The apparatus of claim 1 wherein the concentric rings of said sheet material are embedded within the dielectric material in spaced relationship from both of the upper and lower surfaces thereof.

3. A microwave concentrator for facilitating the heating of food products placed within a microwave oven containing a source of microwave energy, an oven chamber and a means for supplying microwave energy from the source to the chamber, said concentrator comprising:

a. a body of low loss dielectric material having a mass on the order of more than one pound and being resistant to damage by microwave energy when subjected thereto,

b. said dielectric material comprising a sheet of a dielectric substance having flat upper and lower surfaces of substantial width, the height of the sheet between the upper and lower surfaces being substantially less than the width thereof,

c. a sheet of conductive microwave reflective material bonded to said dielectric material,

(1. said sheet of conductive microwave reflective material comprising a ring-shaped endless strip of reflective material located in a plane parallel to the bottom of the oven and to the upper and lower surfaces of the dielectric sheet material,

e. said microwave reflective material being bonded to the dielectric sheet and having its center located approximately in the center of the dielectric sheet material.

4. The concentrator of claim 3 wherein there are a plurality of said ring-shaped strips of reflective material positioned concentric with one another and each is bonded to the dielectric material.

5. The apparatus according to claim 3 wherein the microwave reflective material comprises a sheet of relatively thin metal foil lying in a plane substantially parallel to the upper and lower surfaces of the dielectric sheet.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3490580 *Jul 29, 1968Jan 20, 1970Brumfield Robert CContainers and process for asepsis
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3934106 *Aug 14, 1974Jan 20, 1976Raytheon CompanyMicrowave browning means
US4103431 *Aug 10, 1976Aug 1, 1978Levinson Melvin LMicrowave drying
US4126776 *Jun 4, 1976Nov 21, 1978Chemetron CorporationMethod of preparing food items for subsequent rethermalization in a microwave oven
US4126777 *Jun 4, 1976Nov 21, 1978Chemetron CorporationMethod of automatically rethermalizing previously prepared food for consumption
US4132811 *Dec 3, 1976Jan 2, 1979The Pillsbury CompanyFood package for assuring uniform distribution of microwave energy and process for heating food
US4156806 *Dec 30, 1977May 29, 1979Raytheon CompanyConcentrated energy microwave appliance
US4219573 *Feb 26, 1979Aug 26, 1980The Pillsbury CompanyMicrowave popcorn package
US4292332 *Jan 19, 1978Sep 29, 1981Mcham David EContainer for prepackaging, popping and serving popcorn
US4320274 *Jan 14, 1980Mar 16, 1982Rte CorporationCooking utensil for uniform heating in microwave oven
US4450180 *Jul 7, 1980May 22, 1984Golden Valley Foods Inc.Package for increasing the volumetric yield of microwave cooked popcorn
US4477705 *Jun 1, 1982Oct 16, 1984Plastics, Inc.Microwave oven popcorn popper, steamer and roaster
US4499356 *Apr 4, 1983Feb 12, 1985Matsushita Electric Industrial Co., Ltd.Microwave heater having a device for thawing frozen cakes
US4548826 *Feb 17, 1984Oct 22, 1985Golden Valley Foods Inc.Method for increasing the volumetric yield of microwave cooked popcorn
US4553010 *Jul 5, 1983Nov 12, 1985James River-Norwalk, Inc.Packaging container for microwave popcorn popping and method for using
US4584202 *Mar 29, 1984Apr 22, 1986Waldorf CorporationMicrowave popcorn package
US4642434 *Nov 14, 1985Feb 10, 1987Golden Valley Microwave Foods Inc.Microwave reflective energy concentrating spacer
US4678882 *Jan 3, 1986Jul 7, 1987James River-NorwalkPackaging container for microwave popcorn popping
US4698472 *Sep 8, 1986Oct 6, 1987Golden Valley Microwave Foods Inc.Microwave heating stand with electrically isolated reflector
US4735513 *Jun 3, 1985Apr 5, 1988Golden Valley Microwave Foods Inc.Flexible packaging sheets
US4851246 *Jul 6, 1987Jul 25, 1989General Mills, Inc.Dual compartment food package
US4861958 *Aug 15, 1988Aug 29, 1989James River-Norwalk, Inc.Packaging container for microwave popcorn popping
US4878765 *Mar 28, 1988Nov 7, 1989Golden Valley Microwave Foods, Inc.Flexible packaging sheets and packages formed therefrom
US4917907 *Aug 14, 1987Apr 17, 1990Campbell Soup CompanyPie having a microwave brownable crust and method of baking same
US4973810 *Jul 3, 1989Nov 27, 1990General Mills, Inc.Microwave method of popping popcorn and package therefor
US5244682 *Nov 19, 1991Sep 14, 1993Ab Specialty Packaging, Inc.Cooking apparatus and process for cooking food therewithin
US5317120 *Jan 13, 1993May 31, 1994The Proctor & Gamble CompanyMicrowave susceptor package having an apertured spacer between the susceptor and the food product
US5326576 *Apr 20, 1992Jul 5, 1994A B Specialty Packaging, Inc.Container apparatus
US5397879 *Nov 17, 1993Mar 14, 1995National Presto Industries, Inc.Microwave corn popper device and method
US5593610 *Aug 4, 1995Jan 14, 1997Hormel Foods CorporationContainer for active microwave heating
US5650084 *Oct 2, 1995Jul 22, 1997Golden Valley Microwave Foods, Inc.Microwavable bag with releasable seal arrangement to inhibit settling of bag contents; and method
US5690853 *Sep 27, 1995Nov 25, 1997Golden Valley Microwave Foods, Inc.Treatments for microwave popcorn packaging and products
US5695673 *Feb 23, 1995Dec 9, 1997National Presto Industries, Inc.Microwave cooking device including susceptor retainer and method
US5770839 *Jun 20, 1996Jun 23, 1998Union Camp CorporationMicrowaveable bag for cooking and serving food
US5773801 *Oct 1, 1996Jun 30, 1998Golden Valley Microwave Foods, Inc.Microwave cooking construction for popping corn
US5935477 *Jul 22, 1996Aug 10, 1999Kontract Product Supply Inc.Continuous microwave cooking grill having a plurality of spaced segments
US5958482 *Oct 20, 1997Sep 28, 1999General Mills, Inc.Easily expandable nontrapping flexible paper microwavable popcorn package
US5994685 *Nov 18, 1997Nov 30, 1999Golden Valley Microwave Foods, Inc.Treatments for microwave popcorn packaging and products
US6066346 *May 22, 1998May 23, 2000General Mills, Inc.Easily expandable, nontrapping, flexible paper, microwave package
US6100513 *Aug 17, 1999Aug 8, 2000Conagra, Inc.Treatment for microwave package and products
US6150646 *Aug 26, 1997Nov 21, 2000Graphic Packaging CorporationMicrowavable container having active microwave energy heating elements for combined bulk and surface heating
US6229131Apr 13, 1999May 8, 2001Kontract Product Supply, Inc.Microwave cooking grill and steamer
US6306448Jul 15, 1999Oct 23, 2001General Mills, Inc.Easily expandable, nontrapping, flexible paper, microwave package
US6396036Nov 16, 2000May 28, 2002Conagra, Inc.Microwave packaging having patterned adhesive; and methods
US6410065Jun 23, 1992Jun 25, 2002Nottingham-Spirk Design Associates, Inc.Expansible food container
US6660983Aug 31, 2001Dec 9, 2003General Mills, Inc.Easily expandable, nontrapping, flexible paper, microwave package
US6677563Dec 14, 2001Jan 13, 2004Graphic Packaging CorporationAbuse-tolerant metallic pattern arrays for microwave packaging materials
US6733807Jan 15, 2002May 11, 2004General Mills, Inc.Easily expandable, nontrapping, flexible paper, microwave package
US6951999Feb 25, 2004Oct 4, 2005General Mills, Inc.Easily expandable, nontrapping, flexible paper, microwave package
US7435436 *Nov 18, 2002Oct 14, 2008Conagra Foods Pdm, Inc.Microwave popcorn package
US8026464Feb 28, 2005Sep 27, 2011Nestec S.A.Multi-purpose food preparation kit
US8146748 *May 19, 2008Apr 3, 2012Shurtech Brands, LlcPackaging compression wrap
US8525087May 25, 2011Sep 3, 2013Nestec S.A.Multi-purpose food preparation kit
US8610039Sep 13, 2010Dec 17, 2013Conagra Foods Rdm, Inc.Vent assembly for microwave cooking package
US8613249Aug 3, 2007Dec 24, 2013Conagra Foods Rdm, Inc.Cooking apparatus and food product
US8729437Jan 7, 2008May 20, 2014Con Agra Foods RDM, Inc.Microwave popcorn package, methods and product
US8735786Sep 14, 2009May 27, 2014Conagra Foods Rdm, Inc.Microwave popcorn package
US9079704Nov 23, 2010Jul 14, 2015Conagra Foods Rdm, Inc.Microwave cooking package
US20040096550 *Nov 18, 2002May 20, 2004Schilmoeller Lance BernardMicrowave popcorn product, packaging and methods
US20040217112 *Feb 25, 2004Nov 4, 2004Monforton Randal JEasily expandable, nontrapping, flexible paper, microwave package
US20040234653 *May 22, 2003Nov 25, 2004Cogley Paul A.Susceptor tray and mirowavable dough products
EP0317203A1 *Nov 11, 1988May 24, 1989Alcan International LimitedImprovements in microwave heating
WO1987002334A1 *Oct 17, 1986Apr 23, 1987Hunt Wesson Beatrice IncMicrowave interactive package containing stainless steel and method of making same
Classifications
U.S. Classification219/728, 219/732, 219/745, 423/234, 426/234, 426/111
International ClassificationA23L1/18, B65D81/34
Cooperative ClassificationB65D2581/3421, B65D81/3469, B65D2581/3472, B65D2581/3489, A23L1/1815
European ClassificationA23L1/18C6B, B65D81/34M2P