U.S. patent number 3,789,179 [Application Number 05/305,956] was granted by the patent office on 1974-01-29 for microwave oven with premixing of wave energy before delivery to its heating cavity.
This patent grant is currently assigned to Matsuhita Electric Industrial Co., Ltd.. Invention is credited to Duane B. Haagensen.
United States Patent |
3,789,179 |
Haagensen |
January 29, 1974 |
MICROWAVE OVEN WITH PREMIXING OF WAVE ENERGY BEFORE DELIVERY TO ITS
HEATING CAVITY
Abstract
An antenna protrudes into the interior of a semicyclindrical
coupling and distribution structure extending from the rear of the
heating cavity. Contained in the structure is a rotatable reflector
unit composed of a horizontal flat arm and a curved vane depending
downwardly therefrom. The end of the arm remote from the vane is
mounted for rotation about a vertical axis at a location between
the antenna and the heating cavity, the arm having a length such
that the vane passes between the antenna and the semicircular rear
wall of the structure during each revolution. The vane's radius of
curvature is less than the radius of curvature of the wall so that
the distance or spacing of the vane is continually varying with
respect to the wall as well as continually varying with respect to
the antenna, thereby causing considerable mode alterations or
premixing of the microwave energy prior to its delivery into the
heating cavity. Additional dispersion of the energy is effected as
it enters the cavity by means of an inclined dispersive plate
extending into the cavity from the opening or window through which
the energy is introduced. In this way, the vertical dimension of
the cavity is substantially reduced and at the same time the usable
space therein is maximized by reason of the externally located
coupling structure, which modulates the wave pattern of the energy
entering the cavity.
Inventors: |
Haagensen; Duane B. (Edina,
MN) |
Assignee: |
Matsuhita Electric Industrial Co.,
Ltd. (Osaka, JA)
|
Family
ID: |
23183095 |
Appl.
No.: |
05/305,956 |
Filed: |
April 3, 1972 |
Current U.S.
Class: |
219/751 |
Current CPC
Class: |
H05B
6/74 (20130101) |
Current International
Class: |
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.
Attorney, Agent or Firm: Peterson; Stuart R.
Claims
I claim:
1. A microwave oven comprising a heating cavity, means providing
microwave energy including a fixedly located antenna spaced from
said cavity, means for directing energy radiated from said antenna
into said cavity including a revolvable reflector member movable
relative to said antenna in an eccentric path about said antenna
and varying in distance with respect to said antenna.
2. A microwave oven in accordance with claim 1 including a fixedly
located reflector member having at least a portion thereof spaced
farther from said cavity than from said antenna, said eccentric
path passing between said portion and also varying in distance with
respect to said fixed reflector member.
3. A microwave oven in accordance with claim 2 in which said
antenna is mounted on a vertical axis and said revolvable reflector
member is rotated about a second vertical axis located between said
antenna and said cavity.
4. A microwave oven in accordance with claim 3 in which said
revolvable member constitutes a vane.
5. A microwave oven in accordance with claim 4 in which said vane
is curved.
6. A microwave oven in accordance with claim 5 in which said vane
constitutes a segment of a cylinder.
7. A microwave oven in accordance with claim 6 in which the radius
of said cylinder is equal to the radius of rotation of said
vane.
8. A microwave oven in accordance with claim 7 in which said fixed
reflector member constitutes a vertical wall.
9. A microwave oven in accordance with claim 8 in which said wall
is curved.
10. A microwave oven in accordance with claim 9 in which said wall
has a radius of curvature greater than said radius of rotation so
that said vane passes between said wall and said antenna during a
portion of each revolution.
11. A microwave oven in accordance with claim 10 in which said wall
is semicircular.
12. A microwave oven in accordance with claim 11 in which the ends
of said semicircular wall extend to said cavity.
13. A microwave oven in accordance with claim 12 in which said
cavity is formed in part by a vertical wall, said semicircular wall
extending to said cavity wall.
14. A microwave oven in accordance with claim 13 in which said
cavity wall has an elongated opening through which microwave energy
is delivered into said cavity.
15. A microwave oven in accordance with claim 14 in which said
opening extends between locations near the ends of said
semicircular wall.
16. A microwave oven in accordance with claim 15 including an
inclined dispersive plate extending along one edge of said
opening.
17. A microwave oven in accordance with claim 16 in which said
opening is near the upper edge of said cavity wall and said
dispersive plate is connected to said cavity wall between said
opening and the upper edge thereof, said dispersive plate angling
downwardly and inwardly into said cavity.
18. A microwave oven comprising means forming a heating cavity
having front, rear, side, top and bottom walls, said front wall
having an access opening via which articles to be heated are
inserted into said cavity, said rear wall having a horizontal
window via which microwave energy is delivered into said cavity,
means forming a coupling and distribution structure extending from
the rear wall of said cavity including a curved vertical wall, a
top wall and a bottom wall, an antenna projecting upwardly through
the bottom wall of said structure into the interior thereof, said
antenna being located nearer to said curved wall than to said rear
cavity wall, a horizontal arm rotatable at one end about a vertical
axis located between said antenna and the rear wall of said cavity,
and a curved vertical vane extending downwardly from the other end
of said arm, said arm having a length such that said vane passes
between said curved wall and said antenna during rotation of said
arm in an eccentric path.
19. A microwave oven in accordance with claim 18 in which said arm
constitutes a flat strip.
20. A microwave oven in accordance with claim 19 in which said flat
strip resides in a horizontal plane, said curved wall also residing
in a vertical plane, the radius of curvature of said wall being
greater than the curvature of said vane.
21. A microwave oven in accordance with claim 20 in which said
opening in the cavity rear wall is nearer the upper edge thereof,
the top wall of said structure being substantially co-planar with
the top wall of said cavity and the bottom wall of said structure
residing in a plane above the bottom wall of said cavity and in a
proximal relation with the lower edge of said opening.
22. A microwave oven in accordance with claim 21 including a flat
dispersive plate inclining downwardly into said cavity from said
rear cavity wall from a height between the upper edge of said
opening and the top wall of said cavity.
23. A microwave oven comprising a heating cavity, a coupling and
distribution structure for feeding microwave energy into said
cavity including first reflector means fixedly located with respect
to said cavity, an antenna for introducing microwave energy into
the interior of said structure in a spaced relationship with said
first reflector means, and second reflector means movable relative
to said first reflector means and relative to said antenna in a
path in which the spacing of said second reflector means with
respect to said first reflector means continually changes and also
in which the spacing of said second reflector means with respect to
said antenna continually changes, said second reflector means
passing between said antenna and said first reflector means during
a portion of its travel in an eccentric path.
24. A microwave oven in accordance with claim 23 in which said
first and second reflector means each includes a curved
surface.
25. A microwave oven in accordance with claim 24 in which the
curved surface of said first reflector means has a radius of
curvature greater than the radius of curvature of the curved
surface of said second reflector means.
26. A microwave oven in accordance with claim 25 in which said
second reflector means includes a flat surface generally
perpendicular to the curved surface thereof.
27. A microwave oven in accordance with claim 26 including means
for rotating said second reflector means about an axis parallel to
said antenna and located between said antenna and said cavity.
28. A microwave oven in accordance with claim 27 in which said
cavity has a window via which microwave energy is delivered
thereinto, and means associated with said window for dispersing at
least a portion of the energy passing through said window.
29. A microwave oven in accordance with claim 28 in which said
dispersive means is contained within said cavity and is located in
a proximal relation with said window.
30. A microwave oven in accordance with claim 29 in which said
dispersive means constitutes a plate angling downwardly and
inwardly from the upper edge of said window into said cavity.
31. A microwave oven in accordance with claim 30 including a
perforated cover plate of low loss dielectric material extending
between the lower edge of said dispersive plate and the lower edge
of said window.
32. A microwave oven comprising a heating cavity, means providing
microwave energy including a fixedly located antenna spaced from
said cavity, first reflective means fixedly located with respect to
said antenna and with respect to said cavity, second reflective
means, and means successively positioning said second reflective
means between said antenna and said cavity and between said antenna
and said first reflective means in an eccentric path.
33. A microwave oven in accordance with claim 32 in which said
first and second reflective means each include concave surface
portions facing in the direction of said antenna.
34. A microwave oven in accordance with claim 33 in which the
concave portion of said first reflective means constitutes a
cylindrical segment having one radius and the concave portion of
said second reflective means constitutes a cylindrical segment
having a lesser radius than said one radius.
35. A microwave oven in accordance with claim 33 in which said
second reflective means is revolved about an axis offset from said
antenna in the direction of said cavity.
36. A microwave oven comprising a heating cavity, an antenna spaced
from said cavity, an arcuate reflector, and means moving said
reflector in an eccentric path about said antenna, said reflector
passing between said antenna and cavity in one position and to the
other side of said antenna in a second position.
37. A microwave oven in accordance with claim 36 including an
additional arcuate reflector, said first reflector passing between
said antenna and said second reflector in said second position.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to microwave heating apparatus,
and pertains more particularly to a microwave oven having reduced
volumetric dimensions consistent with the material to be
heated.
2. Description of the Prior Art
Past attempts to improve the distribution of electromagnetic energy
within microwave heating compartments have been only partially
successful. For example, a mode stirrer with multiple fan-like
blades has been installed inside the heating cavity for the purpose
of continually changing the concentration of the electrical fields
propagated therein. Provided the cavity Q is high in such
instances, that is if all the cavity dimensions are large compared
to the freespace wavelength of the microwave energy, some degree of
uniformity is realized in the heating pattern; however, when this
type of stirrer is used with a smaller heating cavity, its
effectiveness becomes noticeably impaired. Moreover, since the mode
stirrer occupies a portion of the heating cavity, the useful
cooking space is diminished. In general, the cavity size in such
prior art situations is out of proportion with respect to the items
to be heated.
With a realization of these disadvantages, attempts have been made
heretofore to reduce the volume of the cooking cavity or
compartment, yet still provide an adequate heating pattern therein.
A plurality of mode stirrers, revolving food trays, and a host of
other devices have been conceived and tried, but all have included
some drawback as far as their practical application is concerned.
In this regard, either the device did not suitably accomplish its
intended purpose or the apparatus was so complicated as to render
it impractical. Additionally, such devices were designed for use
within the heating cavity, thereby reducing the useful cooking
space.
SUMMARY OF THE INVENTION
Accordingly, an important object of the present invention is to
provide a microwave oven in which an article may be uniformly
heated. In this regard, an aim of the invention is to provide an
effective R.F. input transition device for dispersion of the wave
energy into the heating cavity.
Another object is to provide a compact oven, especially with
respect to its vertical dimension. In this regard, it is planned
that the transition and dispersive device be located externally of
the heating cavity, thereby providing more usable space within the
cavity. Specifically, it is within the purview of the invention to
eliminate the need for installing a conventional mode stirrer
within the usable oven cavity space.
Also, an object is to provide a microwave oven that will be easier
to clean inasmuch as there is no internally positioned stirrer
which can become spattered with food particles.
Another object is to provide a microwave oven in which not only the
vertical dimension of the heating cavity is reduced but in which
the entire height of the oven is decreased in that the present
invention obviates the need for locating a waveguide above the
heating cavity. Stated somewhat differently, an aim of the
invention is to minimize not only the cavity height but the overall
height of the microwave oven.
A further object of the invention is to provide a microwave oven
having a power input structure whereby relatively equal R.F. fields
are transmitted longitudinally across the input opening to the oven
cavity.
Still further, the invention has for an object the provision of a
microwave oven utilizing an R.F. input transmission device which
transmits the microwave energy into the heating cavity by means of
multiple transmission paths having relatively large phase
variations determined by an eccentric mechanical and electrical
placement of a moving reflective system.
Yet another object of the invention is to provide a microwave oven
having a power input transmission system associated therewith which
substantially prevents arcing or high voltage stationary standing
wave points within or about the microwave oven input structure,
thereby enabling the use of mechanically compact R.F. input
components.
A still additional object is to provide a microwave oven utilizing
an R.F. input structure presenting a suitable cross sectional area
in which a portion of the air used to cool the magnetron is further
routed through the coupling structure and the cavity to prevent
objectionable vapor condensation within the oven.
While it is contemplated that my coupling device, even though
employing movable parts, will be long-lasting, nonetheless it is
planned that such parts will be readily accessible for whatever
maintenance or replacement proves necessary.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view taken from the rear of a microwave
oven equipped with my coupling and distribution structure, a
portion of the top wall of the structure being broken away in order
to reveal certain parts and their relationship with each other;
FIG. 2 is a vertical sectional view taken in the direction of line
2--2 of FIG. 1, and
FIG. 3 is a horizontal sectional view taken in the direction of
line 3-3 of FIG. 2 in order to show to better advantage the orbital
path taken by the curved reflecting vane with respect to the
antenna, the view also illustrating the vane's radius of curvature
with respect to the radius of curvature of the rear wall of the
structure.
DESCRIPTION OF THE PREFERRED EMBODIMENT
It will be of assistance to explain at the outset that the
following detailed description of the microwave oven and the
coupling structure associated therewith are all of metal,
preferably aluminum, unless otherwise mentioned.
Referring now in detail to the drawings, the microwave oven
exemplifying my invention has been designated generally by the
reference numeral 10. It includes a cabinet 12 which is typical
other than that the dimensions thereof have been reduced as will
become evident during the ensuing description. To facilitate the
description, it will be observed that the cabinet comprises a front
wall 14, a rear wall 16, side walls 18, a top wall 20 and a bottom
wall 22. These walls 14-22 form a heating cavity labeled 24 in FIG.
2. The top wall 20 has a panel 21 containing small perforations or
holes 23 of size to permit the passage of cooling air but providing
a high impedance to the passage of microwave energy. As is
conventional with microwave ovens, there is an access opening 26 in
the front wall 14 having a door 28 hinged at 30. Within the cavity
24 is a cooking tray 32 having an article or "load" 34 thereon
which is to be heated. As already explained, the construction up to
this point has dealt with conventional details other than that the
dimensions of the cabinet can be reduced, particularly its height,
thereby providing a more compact oven than heretofore.
A rectangular coupling opening or window 36 is provided in the rear
cavity wall 16, the opening being in the upper half of the rear
wall 16. Also, as seen in FIGS. 1 and 2, there is a dispersive
plate 38 extending across the upper edge of the opening 36, the
inclined plate angling downwardly into the cavity 24. A cover plate
31 of low loss dielectric material, such as polypropylene, is
attached to the plate 38 at 33 and to the wall at 35, the plate 31
having perforations or holes 37 to permit passage of air. The cover
plate 31 functions as a shield to prevent spattered food particles
from passing through the coupling opening 36. Also, it precludes
the possibility of any articles (or a portion of a given article)
being inserted through the opening 36 into the premixing structure
yet to be described. Although the microwave energy delivered to the
cavity 24 via the opening 36 is premixed, as will become clearer
during the subsequent description, nonetheless the plate 38
performs an additional dispersive function which promotes uniform
heating of the article or load 34 within the cavity 24.
A coupling and distribution structure denoted generally by the
reference numeral 40 is semicylindrical, being comprised of a
semicircular vertical rear wall 42 having its ends extending from
locations near the ends of the elongated opening 36. There is also
a top wall 43 and a bottom wall 44, the three walls forming a
hollow enclosure in which the R.F. energy is premixed before
entering the cavity 24. By means of a flange 39 and screws 41, the
structure 40 is removably attached to the wall 16.
A source of microwave energy in the form of a magnetron 46 is
provided. The bottom wall 44 has a number of perforations or holes
47 through which a portion of the cooling air for the magnetron 46
is forced into the structure 40, the air flowing through this
structure, the holes 37 in the cover plate 31, and through the
cavity 24; finally exiting via the earlier-mentioned holes 23.
There is a conventional antenna 48 associated with the magnetron 46
and there is also the usual enclosing dome 50. The antenna 48
protrudes into the interior of the structure 40 through a circular
opening 52 formed in the bottom wall 44. It will be apparent that
the antenna 48 is located on a vertical axis that is fixed with
respect to the rear wall 16 of the cavity 24. More will be said
later on concerning this spacing.
Also located at a fixed distance from the rear wall 16 and at a
fixed distance from the antenna 48 is a stub shaft 56 of a low loss
dielectric microwave material, such as polypropylene, that projects
downwardly through the top wall 43. The stub shaft 56 rotates in a
counterclockwise direction as indicated by the arrow 58, being
driven by a motor 60.
Attached to the stub shaft 56 by a member 54 is a rotatable
metallic reflector unit 61 comprising a strip or flat arm 62 having
a depending curved vane 64 at its free end. As best understood from
FIG. 3, the arm 62 has an arcuate length such that it will traverse
a circular path 66 passing between the antenna 48 and the rear wall
42. Also from FIG. 3 it should be apparent that the radius of
curvature of the vertically oriented vane 64 is less than the
radius of curvature of the rear wall 42. More specifically, the
vane 64 has a radius of curvature corresponding to the radius of
the circular path 66, whereas the rear wall 42 has a radius of
curvature corresponding to approximately half the length of the
rectangular opening 36 in the rear wall 16. It will be recognized
that a plurality of reflective surfaces are provided by the walls
42, 43 and 44. Additionally, the arm 62 and the vane 64 provide
still additional reflective surfaces.
PHYSICAL DIMENSIONS
Although perhaps better appreciated from the operational
description yet to be presented, nonetheless at this stage it will
be helpful to give certain dimensions of the oven 10 that have
proved advantageous in actual practice.
The heating cavity 24, it can be explained, has a vertical height
of 5.75 inches. From the front of the cavity, that is from the
front wall 14, to the rear thereof, that is to the rear wall 16, is
13.5 inches. The cavity has a width of 14.0 inches, that is from
side wall 18 to side wall.
Considering now the dispersive plate 38, it can be explained (as
seen from FIG. 2) that this plate has a height of 1.5 inches, the
plate being inclined at an angle such that its lower edge is 0.625
inch from the opening 36 in the rear wall 16. The lower edge, owing
to the angulation of the plate 38, is perpendicularly spaced 1.25
inches in a vertical direction beneath the top wall 20.
Continuing with the dimensional description, the width of the arm
or strip 62 is 0.5 inch and the length thereof 2.5 inches. As far
as the vane 64 is concerned, it will be noted from FIG. 3 that it
subtends an arc which is 4.5 inches in length. The vertical height
of the vane 64 is approximately 1.25 inches.
The coupling and distribution structure has an overall height of
approximately 2.25 inches. Its diameter is 9.0 inches, thus making
its radius 4.5 inches.
As far as the radiating antenna 48 is concerned, the vertical axis
on which it is located is spaced approximately 1.75 inches from the
rear wall 42 of the structure 40, being also centrally disposed
with respect to this wall 42. The antenna 48 is 2.75 inches from
the cavity wall 16. The glass dome 50, which encloses the antenna
48 protrudes into the interior of the structure 40 to a height of
approximately 1.9 inches.
Continuing further with the dimensional description, the centerline
of the shaft 56 is situated at a distance of approximately 1.8
inches from the rear wall 16 containing the opening 36. As already
mentioned, the width of the arm or strip 62 is 0.5 inch and its
length 2.5 inches; however, the arm 62 is attached to the shaft 56
so that the effective radius of rotation of its free end is 2.0
inches. As far as the vane 64 is concerned, which is integral with
the free end of the arm 62, it can be explained that it subtends an
arc of 4.5 inches, having a vertical height of 1.25 inches.
OPERATION
It will be assumed that the magnetron 46 is connected to a power
source (not shown) and therefore is able to generate high frequency
energy in the form of microwaves. These waves are radiated by the
antenna 48 into the interior of the coupling and distribution
structure 40. With the drive motor 60 energized, it follows that
the unit 61 is rotated in the direction denoted by the arrow 58.
Although the vane 64 traverses a predetermined arc as indicated by
the reference numeral 66 in FIG. 3, owing to the location of the
shaft 56, the vane 64 continually changes its position with respect
to the fixedly located antenna 48. Consequently, the spacing or
distance between the vane 64 and the antenna 48 is continually
changing. In other words, the energy waves emitted by the antenna
48, or at least a portion of the radiated energy, is always
received and concurrently reflected by the vane 64 and the radial
arm 62 to which it is integrally attached. Since the vane 64 is
continually changing its relationship with respect to the antenna
48, the amount of wave energy received and reflected continually
varies in the direction of reflection.
Additionally, the vane 64 is continually changing as far as its
spacing is concerned with respect to the curved wall 42 of the
structure 40. Inasmuch as the wall 42 has a semicircular
configuration, almost an infinite number of reflective points are
presented.
Consequently, the microwave energy is reflected by any of the
surfaces provided by the structure 40 and the resulting multiple
reflections influence the energy propagation paths into the cavity
24. In other words, a state of wave disparity is produced within
the structure 40 which causes the microwave energy to enter the
cavity 24 through the opening or window 36 in a diverse order,
thereby producing relative uniformity as far as the heating pattern
within the cavity 24 is concerned. The continuous change in phase
relationship of the various reflective surfaces due to the orbital
path traveled by the vane 64, this being derived from the eccentric
arc indicated by the numeral 66 in FIG. 3, results in an
interesting and novel concept. Also peculiar to the arrangement is
the disseminative properties of the structure 40 in which mode
mixing occurs before the energy reaches the heating cavity 24. The
vane 64 is never in the same phase with respect to the antenna 48
during any one revolution. Additionally, there exists considerable
disparity between the vane 64 and the curved wall 42 as the vane 64
revolves inharmoniously about the antenna 48.
Although effectively mixed by the time the wave energy reaches the
opening or window 36, nonetheless there is a predominantly vertical
polarization of the electric field due to the vertical orientation
of the antenna 48. The dispersive plate 38, which functions as a
baffle, effectively turns or rotates the electric field so that a
portion of the energy enters the cavity 24 with its electric field
horizontally polarized, the plate 38, as its name implies, further
contributing to the dispersive action that has already been
provided by the structure 40 and the interplay of the parts
constituting the structure 40 and the components contained therein.
In other words, the plate 38 changes the regularity of the cavity
24 and further enhances the distributive characteristics thereof.
The member 38 further has the effect of making the opening 36 of an
irregular nature. In actual practice, this causes the microwave
energy to enter the cavity 24 at different levels relative to the
vertical height. Consequently, the plate 38, in combination with
the multiple reflections of a discordant nature which have occurred
within the structure 40, provides an omni-directional energy feed
into the cavity 24, thereby producing a highly uniform energy
pattern within the heating cavity which contributes appreciably to
the uniform heating of the article or load 34.
REPRESENTATIVE TEST DATA
Although many experiments were conducted under a plurality of
operating conditions with the described microwave heating cavity 24
and dispersive coupling system 40, 61, only exemplary results are
deemed necessary to realize the advantages to be gained by
practicing the teachings of my invention. Accordingly, the amount
of power coupled to water loads ranging from 200 to 900cc in a
1,000cc dielectric bowl of a conventional nature was measured. The
energy source or magnetron 46 used had an average output power into
a matched load of approximately 600 watts. The results are listed
below:
Test Conditions
a. water load: varied 200-900cc
b. original temperature: 20.degree.-21.degree. C
c. heating time: 70 seconds
Test Results
Water Load Approximate Power to Water Load 200cc 492 watts 300cc
414 watts 400cc 500 watts 500cc 450 watts 700cc 525 watts 900cc 540
watts
Tests were performed with a relatively flat plastic container (7
.times. 7 .times. 1.5 inches) equally divided into 12 thermally
insulated sections or cubicles. Placing this container in
approximately the center of the heating cavity 24 with about 37cc
of water in each section, the following results were obtained:
Test No. 1
Test Conditions
a. water load: approximately 450cc/12
b. original temperature: 20.degree. - 21.degree. C
c. heating time: 70 seconds
Test Results
power output--446 watts
maximum difference in heating pattern -- 10.degree. C
average temperature increase-- 16.5.degree. C
Test No. 2
Test Conditions
a. water load: 720cc/12
b. original temperature: 21.degree. C
c. heating time: 100 seconds
Test Results
power output-- 470 watts
maximum difference in heating pattern-- 14.degree. C
average temperature increase-- 16.degree. C
Test No. 3
Test conditions
a. water load: 700cc -- dielectric bowl
b. original temperature: 22.degree. C
c. heating time: 140 seconds
Test Results
power output -- 473 watts
It will be obvious to those skilled in the microwave heating art
that the plastic walls dividing the container into the 12 sections
or cubicles provided inherent thermal barriers, owing to their
relatively low heat transfer coefficient, against the conduction of
any appreciable amount of heat from one section or cubicle to
another. This resulted in the 10.degree. C and 14.degree. C
temperature differences listed in Tests Nos. 1 and 2, respectively.
Such temperatures, it will be appreciated, would not occur when
heating a unitary load.
Under the test conditions the magnetron 46 necessarily operated at
a lower rate of efficiency, a phenomenon common to all microwave
heating cavities wherein multiple load variations are experienced.
However, as the test results clearly illustrate, the new dispersive
coupling system comprising the structure 40 and unit 61 produced
satisfactory heating over the range of loads and varied test
conditions.
* * * * *