US3296405A - Microwave oven - Google Patents

Description

n-3,1961 B. R. MCAVOY Em 3,296 5 MICROWAVE OVEN Filed Dec. 23. 1963 2 Sheets-Sheet 1 MICROWAVE GENERATOR WAVEGUIDE OVEN Fig. l

INVENTORS Bruce R. Mc Avoy and BY Thaddeus A. Osiol. RM? KM ATTORNEY Jan. 3, 1967 R. McAVOY ETAL 3,296,405

MICROWAVE OVEN Filed Dec. 23. 1965 2 Sheets-Sheet 2 Fig.5.

Fig.8.

United States Patent 3,296,405 MICROWAVE OVEN Bruce R. McAvoy, Pittsburgh, and Thaddeus A. Osial,

Penn Hills, Pa., assignors to Westinghouse Electric Corporation, Pittsburgh, Pa, a corporation of Pennsylvania Filed Dec. 23, 1963, Ser. No. 332,748 6 Claims. (Cl. 219-1055) This invention relates to heating of materials by ex posure to electromagnetic radiation and concerns especially distribution of microwave energy for uniform heating thereby in an oven or similar enclosure.

Increase in temperature of materials exposed to electro magnetic radiation in the microwave portion of the spectrum (from about one thousand to three hundred thousand megacycles per second, corresponding to wavelengths of from about thirty centimeters to one millimeter) is a familiar, phenomenon. Microwave generators operating in the low midportion of this range are used to provide energy to cooking ovens or the like. However, the pattern of radiation established in an oven, for example,

. resembles standing waves to such an extent that the food or other material to be heated is affected non-uniformly. For this reason it is customary to stir the pattern or mix the modes by means of a rota-ting fan having electrically conductive blades to reflect the radiation intermittently. However, the added initial cost and upkeep of such a device are unwelcome, and there is a great need for improvement.

A primary object of the present invention is assurance of heating uniformity in a microwave oven or the like without use of moving blades therein.

Another object is coupling of microwave energy from a waveguide into an oven or similar enclosure by stationary means effective to smooth or even out the energy pattern therein.

A further object is accomplishment of the previous objects without significantly decreasing the useful volume of the oven or like enclosure.

Other objects of this invention, together with means and methods for attaining the various objects, will be apparent from the following description and the accompanying diagrams.

FIG. 1 is a block diagram of microwave heating apparatus;

FIG. 2 is a perspective view, partly diagrammatic, of components of the preceding view constructed according to one embodiment of the present invention;

FIG. 3 is a view similar to FIG. 2 but with the components constructed according to another embodiment of this invention;

FIG. 4 is a diagrammatic representation of electrical elements encountered in the practice of the invention;

FIG. 5 is a perspective view, on an enlarged scale, of a portion encircled and designated V in FIG. 2;

FIG. 6 is a front sectional elevation of a portion of the apparatus of FIG. 3, with a diagrammatic representation of electrical wiring added, taken as indicated at VIVI on FIG. 7;

FIG. 7 is a side sectional elevation of the portion of ap aratus shown in FIG. 6, taken at VII-VII thereon; and

FIG. 8 is a perspective view of a part of the portion of apparatus shown in FIGS. 6 and 7.

In general, the objects of the present invention are accomplished, in apparatus for heating materials by exposure to microwave energy in an enclosure supplied therewith from a source outside the enclosure, by means for conducting the energy from the source and coupling it into the enclosure at a plurality of locations therealong, microwave switching means for varying the coupling impedance at the respective locations, and means for actuating the switching means variously from time to time and thereby varying the energy input to the enclosure at the respective locations so as to modify the energy pattern in the enclosure. The invention contemplates use of semiconductor (ferro electric) diodes as, or in, the microwave switching means.

FIG. 1 shows, in the form of a block diagram, the interconnection of a microwave generator to an oven or the like by means of a waveguide. Specific constructions useful according to the present invention are shown in the subsequent views.

FIG. 2 shows, in perspective, an oven 11 viewed from below and a waveguide 12 viewed from above, spaced from one another along phantom lines indicating the manner of assembling the one to the other. The bottom wall or floor of the oven has a pair of circular openings or ports 13 therein spaced similarly to and opposite a pair of like openings 14 in a terminal portion 15 of the waveguide, which is joined to the major portion 16 thereof. Shown schematically across openings 14 are a pair of diodes 18 (one across each of the openings). An encircled portion marked V, including one such diode, is shown considerably enlarged in FIG. 5, which also shows a collar 17 surrounding and defining the opening 14 across which the diode 18, at the end of an electrical lead 19, extends to terminate against the inside wall of the collar. This completes the illustration of a first structural embodiment, as compared with a second embodiment illustrated in FIGS. 3, 6, 7, and 8.

FIG. 3 shows, in like manner as FIG. 2, an oven 21 viewed from below and a waveguide 22 viewed from above, spaced from one another along phantom assembly lines. Rectangular opening 23 in the bottom wall or floor 31 of the oven is the same size, shape, and orientation as opposing rectangular aperture 24 near the end of the waveguide. Intruding upward into the oven is a structure having a rectangular roof 26 supported on a pair of trapezoidal end walls 25, '25. Defined thereby and by the floor of the oven alongside the opening 23 are a pair of oblique rectangular ports 27, 27' crossed by a pair of diodes 28, 28', shown schematically. Further details of this embodiment appear in FIGS. 6, 7, and 8.

FIG. 6 shows in front sectional elevation, and FIG. 7 in side sectional elevation, a bot-tom portion of the oven 21 and terminal portion of the waveguide 22 assembled to one another, together with a diagrammatic showing of associated electrical wiring (in FIG. 6). FIG. 8 shows, in perspective, the structure composed of roof 26 and supporting end walls 25, 25 intruding upward from the floor of the oven, shown in front elevation in FIG. 6 and'side sectional elevation in FIG. 7. The intruding structure is made of electrically conductive material as are the bottom or floor 31, walls, and top or root (not shown) of the oven.

The oven 21 has a false bottom or floor 32 of dielectric material, which is essentially transparent to microwave radiation, extending from side to side a short distance above the roof 26 of the intruding structure. The diodes 28, 28 extend obliquely upward from their leads 29, 29' to cross the ports 27, 27', which they bisect laterally, and terminate in tapered ends abutting the opposite edges of the roof 26. The leads 29 and 29' terminate at respective terminals a and b, across which a varying electrical potential (indicated piotorially by a sine wave) is impressed; lead 39 from the bottom or floor 31 of the oven is grounded, as indicated, at terminal 0 located midway (electrically) between the other two. Although not so shown. like wiring is suitable for the previously described and illustrated embodiment. In either event the leads to the diodes may be brought out of. the oven cavity through a capacitive bypass to minimize leakage of microwave energy from the oven interior.

Although not indicated in FIG. 6, each of the diode leads 29, 2? will have, as indicated in the schematic diagram in FIG. 4, a lead resistance R a lead inductance L which must be considered together with a. junction resistance R and a junction capacitance C attributatahle to the connection of the diode to the oven. R L and C though variable as a matter of design, are substantially constant in any single design, while R is adapted to vary between two markedly different values depending upon the diode biasing.

When either diode is biased in the forward direction RJ is small, effectively shunting C and the diode (with lead) impedance is accounted for by R and L When the bias is in the reverse direction, however, R, is quite large so that Q, must be considered. The inductive reactance.

of the lead may make only a negligible contribution to the total impedance, or it may be adjusted to provide series resonance with the junction capacitance.

When a diode is forward-biased, microwave energy passes through the input port bridge thereby without significant attenuation; however, when the diode is reversebiased, relatively little microwave energy passes through the port and into the oven. Accordingly, alternating the bias of the respective diodes at a frequency low with respect to that of the microwave energy (e.g., ordinary power frequencies of 50 or 60 c.p.s.) elfectively switches the input energy from one input port to another. As desired, the pattern of energy in the oven is mixed or stirred thereby to eliminate standing waves, evening out the heating effect upon exposed foodstuffs or the like.

The microwave switching means utilized according to this invention may (and presumably will) be conventional. Junction (ferro-electric) diodes having a power rating sufficiently high to handle the applied load are satisfactory. They may be made of any appropriate semiconducting material adapted to such use, and their selection and incorporation into the apparatus of this invention will be well within the ability of persons having ordinary skill in the art.

The apparatus of this invention may .be modified by alteration in size, shape, number, and state of subdivision or combination of parts or otherwise while retaining benefits and advantages of the invention as defined in the claims.

We claim as our invention:

1. In a microwave oven or the like having an external source of microwave energy, a channel-like indentation open to the exterior and having oblique opposite side walls with a separate opening in each of said opposite sidewalls thereof adapted to admit microwave energy to the oven interior, separate electronic microwave switching means at each opening adapted to vary the impedance presented to incident microwave energy, means for conducting microwave energy from the external source to the channel-like indentation, and means for controlling said switching means to alternately substantially pass, and alternately substantially attenuate, the microwave energy at each said separate opening.

2. In a microwave oven or the like having an external source of microwave energy, a channel-like indentation open to the exterior, with oblique sidewalls, and with a separate opening in each of a pair of the oblique sidewalls thereof adapted to admit microwave energy to the oven interior, wave-guide means for conducting microwave energy from the external source to the channel-like indentation, separate electronic microwave switching means including semiconductor diodes at the respective openings adapted to vary the impedance presented to incident microwave energy, and means for biasing the respective diodes alternately forward and backward at a relatively low frequency to alternately substantially pass to said oven interior, and alternately substantially attenuate, the microwave energy at each said opening.

3. In apparatus for heating materials by exposure to microwave energy in an enclosure supplied therewith from a source outside the enclosure,

single passage means for conducting the energy from the source and coupling it into the enclosure at a plurality of separate but closely adjacent inlet locations to said enclosure, said enclosure being of substantially greater dimensional extent that said passage means,

separate electronic microwave switching means at each said inlet location for varying the coupling impedance at each said location,

means for actuating each said separate switching means at its respective location to substantially block and alternately substantially pass microwave energy to said enclosure,

said separate switching means being actuated alternately with respect to each other to switch the input of said energy between said inlet locations to modify correspondingly the energy pattern in said enclosure.

4. An apparatus according to claim 3,

said conducting means is in the form of a rectangular waveguide.

5. An apparatus according to claim 3,

each said microwave switching means comprises a semiconductor diode, and

said means for actuating said switching means includes means for biasing each said diode alternately forward and 'backwardly,

6. An apparatus according to claim 5,

sad biasing means includes a source of relatively lowfrequency alternating potential, series load resistance and a ground connection for the enclosure to which one side of said diodes is connected.

References Cited by the Examiner UNlTED STATES PATENTS 2,790,054 4/1957 Haagensen 21910.55 3,014,188 12/1961 Chester et al. 33383 3,017,585 1/1962 Luke 333-7 3,127,494 3/1964 Kellough et al. 219-10255 3,178,659 4/1965 Smith et al. 333-7 RICHARD M. WOOD, Primary Examiner.

ANTHONY BARTIS, Examiner.

L. HJBENDER, Assistant Examiner.

Claims (1)

1. IN A MICROWAVE OVEN OR THE LIKE HAVING AN EXTERNAL SOURCE OF MICROWAVE ENERGY, A CHANNEL-LIKE INDENTATION OPEN TO THE EXTERIOR AND HAVING OBLIQUE OPPOSITE SIDE WALLS WITH A SEPARATE OPENING IN EACH OF SAID OPPOSITE SIDEWALLS THEREOF ADAPTED TO ADMIT MICROWAVE ENERGY TO THE OVEN INTERIOR, SEPARATE ELECTRONIC MICROWAVE SWITCHING MEANS AT EACH OPENING ADAPTED TO VARY THE IMPEDANCE

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