U.S. patent number 3,746,823 [Application Number 05/229,790] was granted by the patent office on 1973-07-17 for electronic cooking appliance.
Invention is credited to Lloyd L. Whiteley.
United States Patent |
3,746,823 |
Whiteley |
July 17, 1973 |
ELECTRONIC COOKING APPLIANCE
Abstract
A magnetron is coupled to a wave guide having an open end
exciting a transition section which is spproximatelytwo wavelengths
square. The transition section approximately two box is secured
over the microwave cavity which has a circular opening formed in
the top wall thereof. A disk having a plurality of apertures or
slots is rotatably supported beneath the upper cavity wall in close
proximity thereto so that energy is radiated into the cavity in
such a manner as to produce uniform and linear heating throughout
the cavity. The apertures in the disk appear electrically at
multiples of substantially half-wavelengths from the point of the
magnetron coupling when the longder dimension of the apertures are
transverse to the longitudinal dimension of the wave guide.
Inventors: |
Whiteley; Lloyd L. (Minnetonka,
MN) |
Family
ID: |
22862673 |
Appl.
No.: |
05/229,790 |
Filed: |
February 28, 1972 |
Current U.S.
Class: |
219/749; 219/750;
D7/351 |
Current CPC
Class: |
H05B
6/725 (20130101); H05B 6/74 (20130101); H05B
6/705 (20130101); H05B 6/688 (20130101); Y02B
40/00 (20130101); Y02B 40/146 (20130101) |
Current International
Class: |
H05B
6/80 (20060101); H05B 6/74 (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.
Claims
What is claimed is:
1. An electronic cooking appliance comprising:
a. a microwave generator including coupling means for coupling
microwave energy into a wave guide;
b. a microwave cavity constructed and arranged to receive objects
to be heated and having a central opening formed in one wall
thereof;
c. a wave guide transition box disposed over said central opening
in said cavity, said box and said cavity having walls forming a
barrier to the transmission of microwave energy except through said
central opening, said box having a wave guide opening formed in one
wall thereof;
d. a wave guide operably connected between said microwave generator
and the wave guide opening in said wave guide transition box for
conducting microwave energy therebetween;
e. a disk rotatably supported about an axis substantially coaxial
with said central opening and having a periphery extending
outwardly at least to the periphery of said central opening in a
plane substantially coplanar with the wall containing said central
opening, said disk having at least one aperture therein
distributing said microwave energy between said transition box and
said cavity;
f. and motor means operably connected to said disk for rotation
thereof.
2. The structure set forth in claim 1 including:
g. insulated spacers secured around the periphery of said disk and
disposed between said disk and said wall of said cavity, said
spacers eliminating arcing between said disk and said cavity
wall.
3. The structure set forth in claim 1 wherein said central opening
is circular having its center a plurality of substantially
half-wavelengths from said coupling means, said disk having a
greater diameter than said central opening.
4. The structure set forth in claim 1 wherein at least said one
aperture has an elongated shape of which the longer dimension, when
transverse to the longitudinal dimension of said wave guide appears
at multiples of substantially half-wavelengths from said coupling
means.
5. The structure set forth in claim 3 wherein said transition box
is substantially two wavelengths square and has its center
concentric with said central opening.
6. The structure set forth in claim 1 wherein said motor means
drives said disk at a speed less than 100 rpm.
7. The structure set forth in claim 1 including:
h. a tuning element aligned parallel to said axis of rotation for
said disk and disposed in a wall opposite that having said disk
adjacent thereto and disposed to produce low microwave power
variations for different loads placed in said microwave cavity.
8. An electronic cooking appliance comprising:
a. a microwave generator including coupling means for coupling
microwave energy into a wave guide;
b. a microwave cavity constructed and arranged to receive objects
to be heated and having a central opening formed in one wall
thereof;
c. a wave guide transition box disposed over said central opening
in said cavity, said box and said cavity having walls forming a
barrier to the transmission of microwave energy through said
central opening, said box having a wave guide opening formed in one
wall thereof;
d. a wave guide operably connected between said microwave generator
and the wave guide opening in said wave guide transition box for
conducting microwave energy therebetween;
e. a disk rotatably supported about an axis substantially coaxial
with said central opening and having a periphery extending
outwardly at least to the periphery of said central opening, said
disk extending in a plane substantially coplanar with the wall
containing said central opening, said disk having a plurality of
apertures formed therein with elongated shapes of substantially
parallel sides, of which the longer dimension when transverse to
the longitudinal dimension of said wave guide appears at multiples
of substantially half-wavelengths from said coupling means for
distributing said microwave energy between said transition box and
said cavity;
f. and motor means operably connected to said disk for rotation
thereof.
9. The structure set forth in claim 8 wherein said plurality of
apertures have at least two apertures of equal dimensions and at
least one aperture of other dimensions.
10. The structure set forth in claim 8 wherein each of said
plurality of apertures has a ratio of length to width of
approximately 7.68 to 9.25.
11. The structure set forth in claim 8 wherein said plurality of
apertures are constructed and arranged in said disk so that the
longitudinal axes thereof are in non-parallel alignment and the
angles between the same are substantially less than normal to each
other.
12. The structure set forth in claim 11 wherein said plurality of
apertures are constructed and arranged so that they appear
sequentially at multiples of substantially half-wavelengths from
said coupling means.
13. The structure set forth in claim 8 wherein said wave guide has
an open end operably connected to the wave guide opening in said
wave guide transition box, said wave guide opening extending
through a wall substantially parallel to said disk rotational
axis.
14. The structure set forth in claim 8 wherein said disk used with
a microwave generator having a frequency of 2450 .times. 10.sup.6
Hz has apertures specifically constructed and arranged as shown in
FIG. 5 hereof.
15. The structure set forth in claim 8 wherein said plurality of
apertures are disposed in said disk so that the part of said
aperture farthest from the center of said disk is less than a wave
guide width when transverse to the longitudinal axis of said wave
guide.
16. The structure set forth in claim 1 including:
i. a shelf defining a cooking plane disposed below said disk at a
distance representative of substantially a multiple of
half-wavelengths.
17. The structure set forth in claim 8 wherein said wave guide
transition box includes an indented ring portion extending
downwardly from the top of said box in a smooth curve.
Description
BACKGROUND OF INVENTION
Microwave cooking or heating devices have been in existence for
some time incorporating standing waves of high frequency energy
which are directed into the oven cavity and reflected within the
cavity to accomplish the heating or cooking process. Due to the
nature of the standing waves, there are localized areas of high
electric field intensity and localized areas of low electric field
intensity within the oven cavity. Distribution of the microwave
energy in this manner obviously results in relatively hot or cold
spots within the cavity and generally speaking with a large area to
be covered, such as in the baking process, unless the cold and hot
spots are eliminated, the process using microwave energy does not
perform the baking process in an acceptable manner. In fact, the
true test of a microwave oven is to determine if it will bake
rather than merely produce localized heating which may be
acceptable in certain foods such as meats or smaller food items
such as baked potatoes, cupcakes, and the thawing of certain small
frozen foods.
Different approaches have been taken to solve the problem of
production of hot and cold spots ranging from attempts to change
the pattern of the standing waves by electronically varying the
frequency of oscillation of the magnetron used to excite the
cavity, and thus produce standing wave patterns of different
wavelengths, to attempts which make use of certain mechanical mode
stirrers for theoretically causing a change in the geometric space
of the microwave cavity. While it proves to be rather impractical
to change walls of the microwave cavity, the walls may be
electrically deformed or changed through the use of certain devices
such as a mode stirrer assembly which simulates the effects of
deforming or moving the walls. One such approach is disclosed in U.
S. Pat. No. 3,521,019 in which a number of vanes are positioned
adjacent to one of the walls of the cavity so that the spacing
between the vanes which are oriented like a venetian blind is not
greater than one-quarter wavelength of the microwave energy and the
distance between the vanes and adjacent wall when closest to the
wall is no greater than one-quarter wavelength. The inventor making
use of the venetian wave guide technique also recognizes that the
electronic mode of operation may also be changed by providing
multiple inputs to the microwave cavity. It is further recognized
that using more than one input to the cavity does require critical
placement of the wave guides relative to the microwave cavity.
Another approach to changing the reflective configuration within
the cavity has been through the use of bladed stirrers such as
disclosed in U. S. Pat. Nos. 3,431,381; 3,281,567; 3,364,332;
3,505,491; and 3,517,152. Basically, all of these structures have
one thing in common in that they attempt to change the standing
wave patterns within the cavity by reflecting the standing waves
towards the magnetron and thus change the standing wave patterns
within the cavity to distribute the hot and cold spots. They also
recognize that in using such a structure, the greater the area
within the cavity that is affected by the blades, theoretically
there should be a more even distribution of the microwave energy.
For this reason, some of the disclosures are directed to the use of
more than a single stirrer, and some use motors having various
speeds to drive the stirrers so as to create random reflections and
thus tend to avoid introducing secondary or auxiliary hot and cold
spots. This technique is used even more extensively where the
cavity may be thought of as including a double size or being
energized by two different sources of microwave energy.
Other approaches are also taken where it is permissible to allow
the food to be moved within the cavity and such an approach is
disclosed in U. S. Pat. Nos. 3,478,188 and 3,474,212. In each of
these disclosures, the mode of operation is generally made at some
mode other than the dominant mode, or TE.sub.1,0 mode of operation.
However, it must be recognized that each of these ovens is designed
for a particular purpose and does permit a conveyor to move through
the oven. It will also be noted that each of these ovens makes use
of mechanical stirrers on as many as three different walls of the
oven to increase the chances of creating reflective waves within
the cavity. It will also be apparent from the disclosures set forth
thus far, that the stirrers take on a multitude of different
configurations.
Another slightly different approach in an oven utilizing a
conveyor, is found in U. S. Pat. No. 3,263,052 in which the oven or
cavity is some eight feet long and uses a wave guide which is some
5 feet long to excite the oven. Slots are formed in the wave guide
and various reflectors are used between the slots in the wave guide
to improve the standing wave pattern within the cavity. However, it
is obvious that it is impractical to employ an 8 foot long oven
with a conveyor used therewith to attempt to create a condition
which has uniform heating within the cavity.
Another approach to creating an even distribution of the energy
within the cavity is found in U. S. Pat. No. 3,436,507 which
utilizes a circular non-metallic material for supporting certain
narrow metal strips, the entire structure being secured to a
conical transition member extending from the end of a coaxial
coupler, the combination being rotatable. The structure is
apparently designed to again produce reflective waves within the
cavity in such a manner that the standing wave patterns are broken
up. A similar approach is disclosed in U. S. Pat. No. 3,471,671 in
which the disk is driven by an air stream.
Several of the inventors whose disclosures have been made thus far
have taken the position that a moving antenna distribution system
is generally proven to be the least suitable for attempting to
solve the problem of eliminating the hot and cold spots.
Other approaches solving the problem are set forth in U. S. Pat.
No's. 3,474,211 and 3,475,577 in which some form of reflective
element is placed directly in the wave guide and is moved or
rotated to change the standing wave patterns. The one approach is
accomplished through the use of a parabolic shaped wave guide in
which disks are used having radially extending slots to provide
some form of reflective elements. In the latter disclosure,
reflective elements are introduced along the longitudinal axis of
the wave guide and is repeated at distances of half-wavelengths to
produce different reflective waves towards the magnetron. One of
the disclosures additionally introduces a rotating heating plane so
that the food may be rotated within the cavity in an additional
attempt to eliminate hot and cold spots. Movement of the food to be
heated within the oven, both horizontally and vertically is
similarly disclosed in U. S. Pat. No's 3,428,772 and 3,436,506.
U. S. Pat. No. 3,439,143 discloses a microwave oven having a mode
stirrer which is located within the wave guide rather than in the
microwave oven cavity. The inventor there suggests that changes
within the wave guide have a much better chance of providing
uniform distribution of energy within the cavity because the
so-called "paddle wheel" stirrers have a limited effect in
providing uniformity of heating. The disclosure in the latter
reference is directed to placing a rotatable element within the
wave guide between two openings into the cavity such that when a
reflective strip is placed upon the rotatable element, it will
alternately act like a gate in producing an open condition and a
shorted condition thus permitting energy to be alternately applied
through the two openings and thus create a means of changing the
standing wave patterns within the cavity.
Another means of introducing energy in a uniform distribution
within a cavity is disclosed in U. S. Pat. No. 3,493,709 which is
directed to a form of spiral antenna. The inventor there also notes
that in attempting to use a resonant disk antenna having a diameter
which is approximately one-half wavelength and disposed near the
upper wall of the oven, the food would cook at a higher rate around
the periphery of the cavity than in the center thereof. The
inventor considered such an approach to be undsirable.
SUMMARY OF THE INVENTION
This invention relates to the field of electronic cooking
appliances and more particularly to a means of controlling the
microwave radiation between the wave guide and a heating or cooking
cavity.
The present invention recognized the deficiencies which have been
prevalent in the art and from the background of the invention, it
should also be apparent that the problems which various inventors
have attempted to solve still remain. The instant invention makes
use of a magnetron which energized the wave guide in the dominant
mode or the TE.sub.1,0 mode of operation. The wave guide is
connected to a transition wave guide or box along one of the side
walls with the longitudinal axis of the wave guide intersecting the
center point of the transition box. Generally speaking, the
transition section is approximately two wavelengths square. For the
preferred embodiment of the invention, the frequency of operation
of the magnetron is at 2450 .times. 10.sup.6 Hz having a wavelength
of approximately 4.81 inches. A tuning stub is also used at an
appropriate point in the transition section to tune the wave guide
in such a manner that various loadings of the cavity will not
affect the mode of operation of the magnetron.
The heating cavity is located directly below the transition box and
is coupled to the transition box through an opening which is
circular in nature, the upper wall of the cavity and lower wall of
the wall guide transition section being common to each other. A
disk is rotatably secured in close proximity to the lower surface
of the wall just described having the opening formed between the
transition wave guide section or box and the cavity so that it may
be considered that the disk and common wall are coplanar. This disk
is supported for rotation through the use of a non-metallic shaft
which is supported above through the upper edge or wall of the
transition wave guide section or box, the upper portion of the
shaft being driven by a low speed motor which generally operates
between approximately 13 to 18 revolutions per minute. Because it
is generally known that maximum coupling is obtained from a
magnetron to a wave guide in the dominant mode by coupling at
quarter-wavelength point, maximum transfer of energy down the wave
guide would then occur at multiples of half-wavelengths from that
point. The disk is secured within the transition box along the
longitudinal axis of the wave guide at a point representative of
approximately two wavelengths. The disk has a number of apertures
formed therein which are elongated and sequentially oriented
transverse to the longitudinal axis of the wave guide at multiples
of half-wavelengths. That is, regardless of whether the aperture is
nearest the magnetron or rotated to a position which is furthest
from the magnetron, when the apertures are transverse to the
longitudinal axis of the wave guide, they appear electrically at
multiples of half-wave points from the magnetron, and thus would
appear to produce a radiation system permitting maximum power
transfer to the cavity. With this type of system, there is no
reflection of the waves within the cavity back to the magnetron or
within the wave guide. Therefore, it would appear that the
operation of the disk is independent of the size of the cavity. The
load seen by the magnetron may be varied or modified by the
position of the resonant stub and the disk is prevented from arcing
with respect to the wall of the cavity or wave guide transition
section through the use of a plurality of insulated spacers which
prohibit the disk and the other surface from rubbing together.
In keeping with the teachings of the present invention, it is a
general object to provide an electronic cooking appliance which
receives its energy through a rotating disk having at least one
elongated aperture.
It is another object of this invention to provide an electronic
cooking appliance with a cavity having substantially uniform and
linear heating characteristics.
It is still another object of the present invention to provide a
means of energizing an electronic cooking appliance by a rotating
disk having apertures substantially coplanar with a wall of the
cavity.
It is yet another object of this invention to provide a means of
energizing an electronic ooking appliance by a rotating disk having
apertures substantially coplanar with a wall of the larger
dimension of the wave guide.
It is a further object of the invention to provide a means of
energizing an electronic cooking appliance by a rotating disk
having a plurality of elongated apertures, rotatable to appear at
multiples of substantially half-wavelengths from the point of
energizing the wave guide.
It is a still further object of this invention to provide a means
of energizing an electronic cooking appliance by a rotating disk
having a plurality of elongated apertures where the apertures are
constructed and arranged in the disk so that the longitudinal axes
thereof are in non-parallel alignment and the angles between the
same are substantially less than normal to each other.
It is still a further object of this invention to provide a means
of energizing an electronic cooking appliance by a rotating disk
having a plurality of elongated apertures where the apertures are
constructed and arranged so that they appear sequentially at
multiples of substantially half-wavelengths from the coupling
means.
It is still another object of this invention to provide a means of
energizing an electronic cooking appliance by a rotating disk
having a plurality of apertures where the disk forms a part of a
transition wave guide substantially two wavelengths square and has
its center concentric with that of the disk and appearing
substantially two wavelengths from the point of energizing the wave
guide.
These and other objects and advantages of the invention will more
fully appear from the following description made in connection with
the accompanying drawings, wherein like reference characters refer
to the same or similar parts throughout the several views and in
which:
FIG. 1 is a perspective view of the front of an electronic cooking
appliance incorporating the invention;
FIG. 2 is a back perspective view of the electronic cooking
appliance with the outer cover removed;
FIG. 3 is a top plan view of the electronic cooking appliance with
the cover removed exposing the transition section or feedbox and a
portion of the disk;
FIG. 4 is a side elevation view of the electronic cooking appliance
with the cover off as seen looking into the end of the wave
guide;
FIG. 5 is a top plan view of the disk showing all of the details of
the placement and size of the apertures formed therein; and
FIG. 6 is a diagram showing the relationship of the standing wave
patterns in the wave guide and transition box.
FIG. 1 discloses a microwave oven 10 which has a front panel to
which is secured a door 12. The oven has a cabinet cover 13 which
covers the rear portion of the oven. Several oven controls 14 and
15 are also secured to the front panel 11.
FIG. 2 discloses the rear of microwave oven 10 where a magnetron 16
is coupled to a wave guide 17 in the normal manner for a TE.sub.1,0
mode of operation and further includes a shroud or housing 18 which
is used to cool magnetron 16 through the use of a blower 20. A
power supply 21 is secured to the base plate of the oven and a
junction box 22 is secured to the back of the base plate. An oven
cavity 23 is secured in the center of the microwave oven and
secured to the upper portion of the cavity is a microwave
transition section or box 24. A motor 25 is secured to the upper
portion of cavity 23 or the edge of transition section 24 to drive
a pulley 26 through the use of a belt 27. A tuning stub 28 is also
secured in the upper edge of transition section 24, to insure that
a proper standing wave ratio is obtained and that the magnetron 16
operates in the proper mode. A wave guide adaptor 30 also helps
secure wave guide assembly 17 to transition section 24.
As shown in greater detail in FIGS. 3 and 4, wave guide 18 is
secured to the transition box 24 through suitable means such as
bolts 31 which are secured through a side wall of box 24 and wave
guide adaptor 30, bolts 31 being connected to a pair of brackets 32
and 33 which are secured to wave guide 18. Wave guide 18 is
connected in open-end fashion through an opening 34 formed in a
side wall of transition box 24. Wave guide 18 may include a
transition section between wave guide adaptor 30 and a coupling
point 35 which is located axially with the center hole of a
plurality of circular spaced ventilating holes 36. For the
embodiment disclosed, magnetron 16 has an operating frequency of
2,450 .times. 10.sup.6 Hz and the wave guide has a height of 2.25
inches where coupled to the magnetron and is reduced to a height of
1 inch where coupled to transition box 24. The wave guide width is
maintained at 3.75 inches. It will also be generally understood
that the magnetron is coupled to the wave guide at a multiple of a
guarter-wavelength from the closed end of the wave guide. The
distance from the point of coupling to the wave guide from the
magnetron to the end secured to transition box 24 is 5.002
inches.
Pulley 26 is coupled to a shaft 40 which is formed of a
non-metallic material such as polypropylene. A bushing 41 forms a
journal for shaft 40 and is secured in the center at the top of the
transition box 24. Shaft 40 extends downwardly and is connected to
a hub 42 which is secured to a disk 43. The distance from coupling
point 35 to the position of the axis of shaft 40 along a
longitudinal axis of wave guide 18 is approximately two
wavelengths.
A plate 45 forms the upper wall of cavity 23 and has a central
circular opening 46 formed therein. It is through this opening that
shaft 40 extends to secure disk 43 at a position slightly below
that of wall 45. A plurality of insulated spacers 47 are secured
between the bottom surface of plate 45 and disk 43, the spacers
being approximately one-sixteenth inch in thickness and are
disposed between the two surfaces to prevent arcing in the cavity.
For all practical purposes, plate 45 and disk 43 may be considered
to be substantially coplanar. Opening 46 has a smaller diameter
than the diameter of disk 43. In the instant application, the
cavity is 14 inches square and the sides of the transition box 24
which are normal to wave guide 18 are 9.44 inches long and the
sides which are parallel to the longitudinal axis of wave guide 18
are 9.12 inches long, the opening 46 in plate 45 being 8 inches in
diameter. The distance from the top of the transition box to its
base is 2.250 inches, the wave guide opening being 0.498 inches
below the upper surface of the transition box 24. A circular ring
48 is depressed in the top of transition box 24 having an outer
radius of 2.375 inches and an inner radius of 1.60 inches, the
central portion being depressed 0.38 inches, and a sloping portion
49 between the two radii joining the top with a curvature of 0.50
inch radius.
Disk 43 is shown in more detail in FIG. 5 wherein eight holes 50
are equally spaced around the rim of the disk at a diameter of 9
inches, the disk being formed of a metallic material such as
aluminum and having a diameter of 10 inches. Holes 50 are formed in
disk 43 to accomodate the spacers 47 which are generally formed
with a flange so that they may be pressed into holes 50 and held in
place. Disk 43 contains three elongated apertures 51 through 53
having a length of 2.31 inches and a fourth elongated aperture 54
having a length of 1.920 inches, all of the apertures being 0.250
inches wide. A pair of center lines 55 and 56 are representative of
axes which are longitudinally and transversely oriented
respectively with respect to the longitudinal axis of wave guide
18. Thus it will be seen that when aperture 51 is oriented in the
position shown in FIG. 5, and as found in FIG. 3, the midpoint of
the aperture is approximately 1.92 wavelengths from the magnetron
coupling 35. When aperture 51 is rotated 180.degree., it will
appear adjacent to transverse axis 56 and will be approximately
2.05 wavelengths from coupling point 35.
With the disk rotating counterclockwise as seen in FIGS. 3 and 5,
aperture 52 would have been transverse to axis 55 just prior to the
appearance of aperture 51 and in this position, aperture 52 is 1.50
wavelengths from the magnetron coupling point 35. Upon aperture 52
being oriented transverse to longitudinal axis 55 at a point 180
degrees from that shown in FIG. 5, aperture 52 will be
approximately 2.47 wavelengths from coupling point 35.
Aperture 53 will appear electronically at a transverse position
relative to axis 55 prior to apertures 52 and 51 and in so doing,
will be oriented approximately 1.95 wavelengths from magnetron
coupling point 35 and when rotated 180.degree. from such position,
will then appear transverse to longitudinal axis 55 at
approximately 2.02 wavelengths.
Aperture 54 when appearing closest to coupling point 35 and
transverse to axis 55, appears at a position of 1.52 wavelengths
from magnetron coupling 35 and when rotated 180.degree. appears at
a position of 2.46 wavelengths from magnetron coupling point
35.
The results just described are shown diagrammatically in FIG. 6
where it will be observed that each of the transverse appearances
of the apertures 51, 52, 53, and 54 with respect to the magnetron
coupling point 35 is at a multiple of a half-wavelength and thus
maximum transfer of the energy through the apertures is achieved.
In fact, when apertures 51 through 54 are aligned with their
longitudinal axes parallel to the longitudinal axis 55, a minimum
amount of energy will be transferred into cavity 23. With the
microwave energy radiating through apertures 51 - 54, it will be
observed that there is virtually no reflection from cavity 23 back
towards the magnetron such as may be experienced when exciting a
cavity with an open-ended or large aperture or iris formed in a
wave guide. Additionally, cavity 23 then becomes substantially
independent of the frequency for a particular area within the
cavity. It will be observed that FIG. 4 additionally discloses a
front opening 60 which is closed through appropriate electrical
sealing means by door 12 and a cooking or heating plane or shelf 61
is formed above a bottom member 62 of cavity 23. Adequate
ventilation vents 63 may be formed in cavity 23 by the appropriate
forming of small holes in the side walls to allow the escape of
cooking vapors without permitting microwave energy to escape
therethrough. In the instant application, the cooking cavity is
8.875 inches high with the shelf 61 being elevated 1.50 inches
above floor 62, which means that the distance from disk 43 to shelf
61 is also a multiple of substantially half-wavelengths. In the
present invention the distance is approximately one and one-half
wavelengths.
It has also been found that the same principles enumerated herein
are equally applicable to ovens which are generally thought to be
of "double" cavity size, that is, where two different magnetrons
are used to feed the oven cavity. Again, the oven cavity width and
length may be varied without regard to the general requirements of
attempting to maintain some relationship to the operating frequency
or wavelength. Through the use of the apertured disk 43 the
radiation is directed into cavity 23 much like a sprinkler in which
the sprinkler head is rotated so as to "bathe" everything within
the cavity, In fact, tests have been made in which at least 16
containers were placed in the oven in a square pattern, each of the
containers being formed of styrofoam and containing eight ounces of
water. The temperature of the water was measured initially in each
of the containers and after the oven was excited for 11/2 minutes,
the results indicated that after two tests, the difference between
the highest and the lowest temperature was 2.9.degree. F. A similar
test was run on a microwave oven embodying the state of the art at
present using a cavity with a stirrer and after both tests had been
completed, the difference between the highest and the lowest
temperature was 21.degree. F for the first test and 22.degree. F
for the second test. It was also observed that there was more
usable energy in the instant invention than that embodying the
present state of the art, and that the instant invention produced
power which was very close to the rated power rating whereas the
oven embodying the present state of the art was considerably lower
than the rated power.
Other tests involving the use of the 16 containers has provided
additional proof of the principles of operation of the oven. With
aperture 53 aligned transverse to axis 55, readings were taken of
the total temperature rise of the water after 11/2 minutes of
energization, the total being 128.degree. C and this would be
proportional to the radiation entering the cavity. Aperture 53 was
then rotated until it was nearest wave guide 18 and substantially
parallel to axis 55. In this position, the 16 containers
(containing 8 ounces of water each) were again subjected to 11/2
minutes of radiation, and the total temperature rise was found to
be 84.5.degree. C. However, upon moving disk 43 counterclockwise to
a position representative of approximately 6.degree. to 18.degree.
beyond the position of longitudinal axis 55, the magnetron received
reflected waves of such magnitude that different moding occurred
and the amount of radiation passing through slots 51 through 54
would have to be considered at a minimum.
An additional test was developed in which 16 containers were placed
in the oven in a square pattern in the same manner as indicated
previously, each containing 8 ounces of water, and disk 43 was
rotated in the normal manner in a counterclockwise direction at a
speed of approximately 13 rpm, for 11/2 minutes. The total
temperature rise was then recorded as 111 degrees C. What is more
important however, is that the uniformity stated above was
maintained.
To further compare the prior art to that of the instant invention,
sheets of Thermofax paper were inserted in the ovens with a black
backing material being held in close proximity thereto through the
use of a clear plastic holder having sheets of the material both
above and below the Thermofax paper. As a result of energizing the
two different ovens, it was found that the oven employing the
present state of the art produced a hot spot so intense that a hole
approximately 11/2 inches in diameter was burned through the upper
sheet of the plastic material, the Thermofax paper, and the
material was burned through on the back side thereof. Additionally,
there were four other hot spots shown on the paper, all of which
occurred at the end of 45 seconds.
The same test was made of the instant invention and after 3 minutes
of operation, there were no burned spots on the plastic material,
or the Thermofax paper, and there was a more even distribution of
energy indicated from the pattern established on the Thermofax
paper.
From the results of the test just described, it should be apparent
that the maximum transfer of energy is occurring through the
apertures in the disk at a position where the apertures are
transverse to the longitudinal axis of the wave guide and a minimum
amount of energy is transferred to the cavity when the apertures
are aligned substantially parallel to the longitudinal axis of the
wave guide. Thus the description of the principles of operation as
disclosed in FIG. 6 are shown to be correct.
It will of course, be understood that various changes may be made
in the form, details, arrangement and proportions of the parts
without departing from the scope of the invention which consists of
the matter shown and described herein and set forth in the appended
claims.
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