U.S. patent number 3,845,266 [Application Number 05/377,663] was granted by the patent office on 1974-10-29 for microwave cooking utensil.
This patent grant is currently assigned to Raytheon Company. Invention is credited to Palmer P. Derby.
United States Patent |
3,845,266 |
Derby |
October 29, 1974 |
MICROWAVE COOKING UTENSIL
Abstract
A utensil is disclosed for microwave cooking including a load
supporting means of a nonpermeable nondissipative material having a
plurality of frequency responsive impedance matching energy
transparent structures to expose a load to varying degrees of
heating. Exterior load surfaces are differentially heated to
achieve a browned and seared appearance in the areas of intense
heating. Numerous configurations include slots, holes and slots,
rectangular and diamond shaped openings. A body member having an
energy transparent low loss region is provided to space the load
from the oven enclosure conductive walls. A conductive cover is
included in an alternative embodiment to enhance browning and
searing.
Inventors: |
Derby; Palmer P. (Weston,
MA) |
Assignee: |
Raytheon Company (Lexington,
MA)
|
Family
ID: |
23490040 |
Appl.
No.: |
05/377,663 |
Filed: |
July 9, 1973 |
Current U.S.
Class: |
219/728; 426/243;
219/729; 219/745; 219/732 |
Current CPC
Class: |
H05B
6/688 (20130101); H05B 6/64 (20130101); H05B
6/705 (20130101); H05B 6/725 (20130101); H05B
6/6426 (20130101); H05B 6/6494 (20130101); Y02B
40/00 (20130101); Y02B 40/146 (20130101) |
Current International
Class: |
H05B
6/80 (20060101); H05B 6/64 (20060101); H05b
009/06 () |
Field of
Search: |
;219/10.55 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truhe; J. V.
Assistant Examiner: Jaeger; Hugh D.
Attorney, Agent or Firm: Rost; Edgar O. Pannone; Joseph D.
Murphy; Harold A.
Claims
1. In combination:
an enclosure;
means for energizing said enclosure with microwave electromagnetic
energy;
energy coupling means for supporting a load within said
enclosure;
said load supporting means comprising a means of a nonpermeable,
nondissipative material having a plurality of spaced energy
transmission structures arranged to provide areas of high energy
penetration with substantially no attenuation to cause elevated
temperatures to heat the
2. The combination according to claim 1 wherein said energy
transmission structures comprise frequency responsive energy
transparent areas arranged
3. The combination according to claim 1 wherein said structures
comprise
4. The combination according to claim 1 wherein said structures
comprises
5. The combination according to claim 1 wherein said structures
comprise a
6. The combination according to claim 1 wherein said structures
comprise
7. The combination according to claim 1 wherein said structures
comprise openings having a diamond shaped configuration in said
supporting means.
8. A utensil for cooking with microwave heating apparatus
comprising:
a body member having a microwave energy transparent low loss
region; and
a load supporting surface of a nontransparent, nondissipative
material having a plurality of spaced frequency responsive
impedance matching energy transmission structures arranged in an
array to provide a
9. A utensil according to claim 8 wherein said supporting surface
is of a
10. A utensil according to claim 8 wherein said body member
energy
11. A utensil according to claim 8 wherein said supporting surface
comprises a grille including interconnected elongated metal rods
having predetermined spacings for maximum energy transmission at
the microwave
12. A utensil according to claim 8 wherein said supporting surface
comprises a slotted metallic plate member with the slot dimensions
and spacings being determined to provide maximum energy
transmission at the
13. A utensil according to claim 8 wherein said supporting surface
comprises a metallic plate member having a plurality of slots with
the dimensions and spacings being determined to provide maximum
energy
14. A utensil according to claim 8 and a cover of a metallic
material to enclose a load disposed on said supporting surface.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a utensil for microwave cooking.
2. Description of the Prior Art
The preparation of food by microwave energy has become popular in
recent years due to the fast preparation times available to the
user. The microwave heating apparatus includes the magnetron which
is operated at conventional domestic low frequency line voltages.
The energy is fed within a conductive wall oven enclosure through a
waveguide transmission line and the energy is distributed in a
plurality of energy modes by such means as a mode stirrer. The
frequencies of operation are assigned by federal regulatory bodies
and, typically are 915 .+-. 13MHz and 2,450 .+-. 50MHz. For the
purposes of the present description of the invention the term
"microwave" is defined as electromagnetic energy radiation having
wavelengths in the order of 1 meter to 1 millimeter and frequencies
in the order of 300MHz to 300GHz.
The load placed in the oven enclosure becomes heated due to the
interaction of the microwave fields within the material. In
accordance with the so-called dielectric heating phenomena, the
molecules tend to oscillate under the influence of the high
frequency electromagnetic energy fields. The friction created by
the molecular movement causes the material to be heated. All
materials have varying energy propagating characteristics and,
therefore, the depth of penetration and surface coloration vary
which requires consideration, particularly, in the preparation of
the edible product loads. Because of the depth-of-penetration
limitations it is sometimes difficult to achieve a seared or
browned surface on such materials as steaks, fowl, roasts and the
like. Some microwave oven apparatus incorporate an electric or gas
broiling element. Certain food additives may be coated on the load
prior to cooking of selected materials having higher energy
absorbing characteristics which will lead to a more rapid heating
of the exterior surfaces while the remainder of the food load
achieves the desired tenderness. Another factor to be considered is
the selection of a cooking utensil since microwave energy is
substantially shielded and reflected by conductive metallic
materials and, therefore, microwave energy transparent materials,
such as glass or plastic are preferred for microwave cooking.
Exemplary of some of the attempts in the prior art to evolve the
browning and searing characteristics will now be enumerated. U.S.
Letters Pat. 2,830,162, issued Apr. 8, 1958, to D. A. Copson, et
al., and assigned to the assignee of the present invention,
utilizes a container constructed of a ferromagnetic-like material
with the container absorbing the microwave energy when heated. The
material is responsive to the electromagnetic energy impinging
thereon up to the Curie temperature point and, thereafter, it
becomes substantially nonresponsive and pervious to the energy. The
ferromagnetic materials sustain alternating electric and magnetic
fields and, characteristically, have high energy loss at
temperatures below the Curie point. Examples of such materials from
which the food container is fabricated include alloys of manganese,
tin, copper or manganese, aluminum and copper, as well as, alloys
of iron and sulphur, such as pyrrhotite. Additionally,
ferroelectric materials such as zircomates of lead and barium and
titanates of lead, barium and strontium may be utilized. The
browning or searing surface conditions desired have been
significantly improved by the disclosed utensils which, however,
like the addition of the additional broiling elements, can be
costly in the implementation.
Another example of prior art utensils is found in U.S. Letters Pat.
3,219,460 issued Nov. 23, 1965, to E. Brown which discloses a
container of a dielectric material, such as paper, plastic or
Pyrex, having an electrically conductive shielding material such as
aluminum wrapped completely around the side and bottom surfaces. In
addition, numerous designs include a crisscross, strip or other
geometric pattern in aluminum foil covering the dielectric
container to prevent the transmission of energy in certain
compartments while permitting such energy to be readily introduced
in other compartments to thereby provide for selective heating in
the shielded and unshielded areas of the specific food products
therein contained. Such microwave cooking utensils may also be
costly and expensive in reduction to practice.
U.S. Letters Pat. 3,302,632 issued Feb. 7, 1967 to E. C. Fichtner
also discloses a plastic-type material containing different foods
in different cooking areas with the container having a microwave
regulating material embedded in the walls to alter the microwave
conductivity and permit microwave transmission in certain wall
portions while providing different microwave cooking rates in other
areas. In this embodiment certain materials, such as metallic
particles, are embedded in selective compartments to alter the
microwave transparency characteristics. Both of the embodiments
using plastic materials with either an outer conductive coating or
embedded metallic particles, lend themselves ideally to the
preparation of frozen foods, such as TV dinners with the cost of
the disposable container reflected in the relatively high cost of
such prepared frozen meals.
Another method and apparatus for use in microwave cooking is
disclosed in U.S. Letters Pat. 3,591,751 issued July 6, 1971 to C.
E. Goltsos which discloses the use of a plurality of metal rods
each having a length that is a multiple of a half wavelength of the
microwave energy with the rods supporting, or being disposed, in
close proximity to the food load. The requirement for the half
wavelength metal rods causes these elements to become highly heated
to red heat and to thermally transfer this heat to the supported
food load by conduction. This prior art teaching may lead to rather
cumbersome structures within the oven enclosure and, due to the
high energy absorption by such elements, caution is required in the
removal of the utensil to prevent unnecessary burns.
All the foregoing prior art embodiments designed to provide
selective heating have been reasonably successful and will be found
reduced to practice in numerous embodiments. A need, however,
exists for a simple, less costly, microwave cooking utensil which
will not be subject to cracking, due to overheating or uncontrolled
temperature rise during operation and be relatively simple to use
and store similar to conventional cooking utensils utilized with
standard electric or gas cooking appliances.
SUMMARY OF THE INVENTION
In accordance with the invention a microwave cooking utensil is
disclosed having a member of a microwave permeable material, such
as glass or Pyrex or Pyroceram, having a thickness selected to
provide for the coupling of energy reflected from the oven
enclosure wall into the utensil. The article to be heated is
supported on a member having a plurality of spaced energy frequency
responsive impedance matching structures to permit coupling of
energy into the load. The heating pattern results in browning and
searing in the areas of intense energy transmission. The load
supporting member comprises a nondissipating nonpermeable material
having a perforated pattern or array of slots, holes and slots and
the like achieve a desired microwave transparency. A cover of a
conductive material may be provided, completely enveloping the load
during operation, to further enhance the outer surface coloration.
Since the utensil is primarily nonabsorbing and nondissipative very
little thermal heating will be achieved. The transfer of energy
relies principally on adjustment of the energy coupling
characteristics to differentially heat the load to cause elevated
temperatures through the microwave transparent structures. The
utensil is easily removed, cleaned and stored.
BRIEF DESCRIPTION OF THE DRAWINGS
Details of the illustrative embodiments of the invention will be
described with reference to the accompanying drawings, wherein:
FIG. 1 is an isometric view of an oven enclosure with the
embodiment of the invention disposed therein;
FIG. 2 is a vertical cross-sectional view of a microwave oven
apparatus with the distribution of the microwave energy within the
oven enclosure shown diagrammatically;
FIGS. 3-7, inclusive, represent embodiments of the load supporting
member to achieve numerous heating patterns.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A typical microwave oven apparatus 10 is illustrated in FIG. 2. Top
and bottom conductive walls 12, as well as sidewalls 14 define the
oven enclosure 16 having an access opening 18 closed by means of
door assembly (not shown) which may be side or bottom-hinged. A
casing member 20 provided with a control panel member 22 surrounds
the oven enclosure as well as the energy generator, controls and
electrical apparatus. The control panel member 22 provides for
mounting timers 24 and 26, as well as start, stop and light buttons
28, 30 and 32.
Magnetron energy generator 34 is of the well known type, as
described in the text "Microwave Magnetrons," Radiation Laboratory
Series, Vol. 6, by G. B. Collins, McGraw-Hill Book Co., Inc., 1948
and U.S. Pat. No. 3,531,613 issued Sept. 29, 1970 to C. P.
Domenichini, et al., and assigned to the assignee of the present
invention. The generated energy is coupled to the oven enclosure by
means of antenna 36 extending into the launching rectangular
waveguide section 38. The waveguide launching section is closed at
one end by a terminating wall 40, spaced a predetermined dimension
from the antenna 36, for optimum launching and direction of the
energy. The opposing end of the waveguide launching section is
provided with an open end 42. The launched energy, diagrammatically
represented by the waves 44, is distributed within the enclosure in
a multimode heating pattern accomplished by such well-known means
as a mode stirrer 46 having a plurality of paddle members 48
actuated by motor 50. The rotation of the stirrer results in the
reflection of the energy waves which bounce off the conductive
walls at the ceiling, back side and bottom of the oven enclosure.
Load 52 is supported in a microwave energy permeable container 54
such as, a dish of a dielectric material which is in turn supported
on a plate 56 of a similar material. The spacing of the glass plate
56 from bottom wall 12 provides for the reflections of the waves 44
from the bottom wall member to enter and be absorbed by the load
52. The distribution and reflection of the waves 44 provides for
substantially uniform energy distribution throughout the load 52
with a minimum of hot spots. The absorption of the microwave energy
results in the conversion of a molecular movement within the load
into heat for cooking. Substantially uniform cooking is achieved in
this manner commencing from the outer surface into the interior of
the load. In products where a searing or browning of the outer
surfaces is desired such as in roasts, steaks or loads of a
relatively large mass, the continued cooking with microwaves to
achieve the outer surface coloration may result in the interior
being overcooked and the loss of nutrient values. Taste as well as
appeal is also improved by proper outer surface preparation.
Referring next to FIGS. 1 and 3 the utensil 60 embodying the
invention is shown disposed within the oven enclosure 16 comprising
a body member having a microwave permeable material region 62. The
thickness of this region is selected to provide a spacing between
an exemplary load 64, such as, illustratively, a steak, and bottom
wall 12 to assure that the bouncing microwave energy waves will be
coupled into the utensil. Region 62 is fabricated from any of the
dielectric or ceramic materials which are transparent to the
microwave energy or the utensil 60 may be provided with legs.
The load 64 is supported on a nonpermeable, nondissipative material
surface 66 having a plurality of spaced frequency responsive energy
transmission structures, such as perforation 68. The array of
perforations 68 is selected to provide for differential heating by
intense transmission rather than absorption and conduction by the
microwaves entering through the transparent opening 68 to thereby
establish a searing or browning condition by reason of the
penetrating concentrated energy. The load support surface 66 may be
fabricated of stainless steel which is easy to clean; has a
pleasing appearance and relatively long life. The spacings between
the perforations 68 are selected to provide for the maximum
coupling of the electromagnetic waves radiation within the
enclosure into the load without materially heating the intervening
portions of plate 68. The transfer of energy is thereby
accomplished not by thermal absorption and conduction by surface 66
but rather an arrangement where the spaces provide for little or no
attenuation of the energy. This array is selected based on the
anticipated varying dielectric constant load characteristics
relative to the impedance characteristics of the waves within the
enclosure at the operating frequency.
Referring to FIG. 4 another arrangement of the load supporting
surface is shown comprising a grille 70 formed by a grid
arrangement of elongated rods 72 and 74 interconnected in a
mutually perpendicular manner. This arrangement would provide for
intense heating by coupling energy in accordance with teachings in
the microwave transmission art, such as delay lines of the
ladder-type or meander lines.
In FIG. 5 the so-called dumbbell resonant iris arrangement 80 is
shown comprising holes 82 and interconnecting slots 84. This
arrangement is similar to that found in the waveguide transmission
art to provide combined inductances and capacitances in iris
members utilized as impedance matching structures for devices such
as those shown and described in the text "Microwave Duplexers"
Radiation Laboratory Series, Vol. 14 by L. D. Smullin and C. G.
Montgomery, McGraw-Hill Book Co., Inc., New York, 1948, Page 70.
Other examples of resonant openings are discussed in this text as
well as the H-shaped arrangement 90 shown in FIG. 6 comprising
parallel elongated slots 92 interconnected by a mutually
perpendicular elongated slot 94. The provision of these resonant
structures which are highly pervious to the microwaves assures the
provision of the desired heating patterns in accordance with the
invention.
In FIG. 7 a portion of a load support surface 100 is illustrated
comprising diagonally arranged rods 102 and 104 in a substantially
crisscross pattern to provide diamond shaped openings.
Cover 110 of a conductive material shown in FIG. 1 having a handle
112 provides for the further enclosing of the load supported on a
surface having an array of microwave energy resonant structures
comprising perforations, slots, square, diagonal or circular
openings. The coupling of the energy through the body member region
62 or legs and surface 66 openings will be further amplified by
this cover to enhance browning and searing. The cover will also
prevent splattering on the oven walls.
There is thus disclosed an efficient microwave cooking utensil
incorporating a nondissipative, nonpermeable support surface having
a plurality of spaced energy transmission structures adapted to
provide a selected differential heating pattern with a minimum of
attenuation through the structure openings. The utensil is easy to
clean, as well as, to store, and provides for substantial searing
or browning by the intense penetration of the microwave energy in
selected regions of the load. Since numerous modifications,
variations and alterations will be evident of those skilled in the
art, the foregoing description is intended to be interpreted
broadly rather than in a limiting sense.
* * * * *