US3748423A

US3748423A - Microwave oven interpose system for control of environmental radiation

Info

Publication number: US3748423A
Application number: US00124842A
Authority: US
Inventors: D Haagensen
Original assignee: Matsushita Electric Industrial Co Ltd
Current assignee: Panasonic Holdings Corp
Priority date: 1971-03-16
Filing date: 1971-03-16
Publication date: 1973-07-24
Anticipated expiration: 1990-07-24
Also published as: GB1378687A; DE2212552B2; FR2130293B1; JPS5148577B1; DE2212552A1; FR2130293A1; DE2212552C3; NL7203010A; NL155165B

Abstract

A deflector device is mechanically connected to the access door of a microwave oven. When the door is opened a deflecting plate, which is a part of the device, is automatically shifted into the waveguide to divert power from the main transmission path leading to the heating cavity to an alternate path having a termination medium associated therewith which absorbs the diverted power. The deflecting plate is retracted or withdrawn when the oven door is closed so that there can then be a resumption of normal power flow to the cavity.

Description

United States'Patent [1 1 Haagensen [11] 3,748,423 July 24,1973

[ MICROWAVE OVEN INTERPOSE SYSTEM FOR CONTROL OF ENVIRONMENTAL RADIATION [75] Inventor:

[73] Assignee: Matsushita Electric Industrial Co.,

Ltd., Osaka, Japan [22] Filed: Mar. 16, 1971 [21] Appl. No.: 124,842

Duane B. IIaagensen, Edina, Minn.

[52] US. Cl. 2l9/10.55, 333/98 S [51] Int. Cl. 1105b 9/06 [58] Field of Search 219/1055; 333/98 S, 333/7 [56] References Cited UNITED STATES PATENTS 3,480,753 11/1969 Wilson et al 219/1055 2,629,048 2/1953 Dyke et al. 333/98 S 3,581,038 5/1971 Williams 219/1055 FOREIGN PATENTS OR APPLICATIONS Great Britain 333/98 S OTHER PUBLICATIONS Microwave Duplexers, Smullin and Montgomery, MIT Radiation Series No. 14, page 406, Mar. 2, 1948 Primary Examiner-J. V. Truhe Assistant Examiner-Hugh D. Jaeger Attorney-Bugger, Peterson, Johnson & Westman [5 7] ABSTRACT A deflector device is mechanically connected to the access door of a microwave oven. When the door is opened a deflecting plate, which is a part of the device, is automatically shifted into the waveguide to divert power from the main transmission path leading to the heating cavity to an alternate path having a termination medium associated therewith which absorbs the diverted power. The deflecting plate is retracted or withdrawn when the oven door is closed so that there can then be a resumption of normal power flow to the cavity.

25 Claims, 7 Drawing Figures PAIENTED 3. 748.423

SHEET u or 4 BY FMW Attorneys MICROWAVE OVEN INTERPOSE SYSTEM FOR CONTROL OF ENVIRONMENTAL RADIATION BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates generally to microwave ovens, and pertains more particularly to an interpose system which diverts microwave power in a direction such that it will not enter the cooking cavity when the access door of the oven is opened.

2. Description of the Prior Art The use of door interlocks to prevent an unsafe operating condition to occur in a microwave oven is generally known to those skilled in the art. Briefly, these interlocks constitute simple electrical switches that open the power supply circuit if the door is opened while the oven is cooking. Such interlocks, however, depend upon some form of contact engagement being broken, or conversely a contact engagement effected, to initiate the disabling action; usually, these contact arrangements are positioned so as to be actuated by a movement of the door handle or the door itself.

The effectiveness of the type of interlock systems alluded to above has been evaluated and the results appear in a report dated October, 1970 prepared by the Department of Health, Education and Welfare entitled Laboratory Testing and Evaluation of Microwave Ovens. Most of the 14 ovens tested were regarded in the report as subject to suggested interlock improvements" inasmuch as with only minor adjustments, which could be accomplished from outside the oven cabinet, the interlocks could be adversely affected sufficiently to allow the oven to operate with the door open. The arms or push-type rods used as the trigger mechanisms for the interlock switches, or the actual switches themselves, were positioned where they could be bent or adjusted to different positions, or simply defeated if the operator chose to do so.

The interlock evaluation included tests which measured the possible radiation exposure a person could be subjected to if the door interlocks failed. The potential radiation exposure as measured at 30 centimeters from the oven front in most cases was above 500 milliwatts per square centimeter and in some instances was over 1,000 mw/cm, a level sufficient to produce serious injury. Since none of the ovens provided for a condition in which the oven continued to operate with the door open, it was recommended that: A suggested improvement for all microwave ovens is that a warning be delivered with the oven stating that a dangerous situation exists if the oven continues to cook with the door open and that the interlocks should not be adjusted or tampered with except by authorized personnel." The remissness of merely a warning notice as a solution to a problem of this nature is easily recognized.

Although not specifically mentioned in the report, it is known that a hazardous situation can occur when the interlock switch circuitry electrically freezes. In this instance the switch simply does not function even though from all outward appearances it seems to be operating normally. Also not specifically mentioned was the effect normal use of the oven may have on these interlock switches. Misalignment of the critical switch contact points due to wear, faulty or shorted electrical wiring, or introduction of foreign objects that hamper the operation of the interlock switch are only a few ex amples of possible effects that may arise through continued use of the oven.

SUMMARY OF THE INVENTION Accordingly, an important object of the present invention is to provide a microwave oven with an interpose deflection system which minimizes the likelihood of any adverse flow of microwave radiation into the environment.

A more specific object of the invention is to provide a microwave oven with an alternate transmission path via which the microwave energy is diverted and which includes dissipative means so that the microwave radiation is safely terminated without escape to the ambient surroundings. More specifically, an aim of the invention is to provide a microwave oven with a heat resistant absorptive material acting in concert with a deflector device for the purpose of terminating the adverse flow of microwave radiation. It is within the purview of the invention to utilize absorptive material that is heat sensitive, thereby enabling an appropriate signal means, such as a thermostatic switch, to be utilized for alerting the operator of the oven that a hazardous condition has arisen.

A further object is to provide an interpose system for diverting microwave energy from the cooking cavity which is independent of any electrical controls normally associated with the microwave radiation. Stated somewhat differently, the usual switch interlocks actuated by the access door movement can still be employed and the interpose system serves as a backup arrangement to assure the prevention of microwave radiation into the environment should there be a failure or malfunction of the electrical controls. Also, the incorporation of my invention into microwave heating apparatus in no way interferes with the use of conventional door seals that have heretofore been utilized for the purpose of minimizing radiation where the door is not completely closed. Consequently, it is an aim of the present invention to provide a microwave oven radiation control system that cannot be affected by any electrical failure of the oven. More specifically, my invention does not rely on any electrical contact being established, such as by the actuation of a switch, either into an open or closed position.

Yet another object of the invention is to provide a microwave oven having an environmental control system that is entirely contained within the cabinet of the oven so that it cannot be easily altered or adversely affected by any external means.

Still further, another object of the invention is to provide amicrowave oven with radiation control means which progressively decreases the amount of energy or power entering thecavity of the oven as the access door is opened, this being irrespective of the operation of any other door interlocks that might be present.

Briefly, my invention provides for the protection of the environment from hazardous microwave radiation through the use of an interpose deflection device at a location within the waveguide which, in effect, blocks the normal transmission path of microwave energy in a microwave oven, instead diverting the energy over an alternate path involving openings in the form of slots provided in the waveguide so that the diverted energy will be directed to an isolated environment in the outer cabinet of the oven where the energy can be safely terminated. The deflection device, although actuated repeatedly each time the access door is opened, is primarily designed to function in the event the supply of power to the magnetron is not stopped by the interruption of an electrical circuit as the oven door is opened. Since this device is not contact dependent or electrically dependent in any way, it provides a fail-safe control of undesirable or dangerous microwave radiation.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a front elevational view of a conventional microwave oven;

FIG. 2 is a sectional view taken in the direction of line 2-2 of FIG. 1 for the purpose of depicting certain parts of the oven prior to incorporating therewith additional components exemplifying my invention, the view being on a larger scale than that of FIG. 1;

FIG. 3 is a still larger scale view corresponding generally to FIG. 2 (the stirrer having been omitted) but with my interpose system added thereto, although the system is ineffectual at this time because the access door is closed;

FIG. 4 is a view corresponding to FIG. 3 but with my system rendered operable by reason of the door being open;

FIG. 5 is a fragmentary perspective view ofa portion of my invention, the position of the deflecting plate corresponding to that appearing in FIG. 4;

FIG. 6 is a sectional view taken in the direction of line 66 of FIG. 4, and

FIG. 7 is a view taken in the direction of line 77 of FIG. 4.

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 components associated therewith which illustrate my invention are all of metal, preferably aluminum, unless otherwise mentioned.

Referring now in detail to the drawings, a typical microwave oven has been designated generally by the reference numeral 10. FIG. 1 provides a basis for the sectional views hereinafter referred to. It will be seen, though, that the oven 10 comprises a cabinet 12 and FIG. 2 will be of benefit in understanding that the cabinet has a top wall 12T, a bottom wall 128, a rear wall 12R, two side walls 12S (only one of which is visible in FIG. 2) and a front wall 12F. The front wall 12F, of course, appears in FIG. 1 and it will be appreciated that certain trim material, usually stainless steel, is utilized that need not be discussed as far as understanding the present invention is concerned. Also, the usual control panel 13 is provided in the upper portion of this wall 12F.

From FIG. 2 it will be seen that there is an inner housing labeled 14 having a top wall l4T, a bottom wall 14B, a rear wall 14R, two side walls 14S (only one being seen in FIG. 2, though) and a front wall 14F. The front wall 14F contains the access opening 16 through which articles to be heated can be placed in the cavity 18 within the inner housing 14. It will be appreciated, owing to the size of the inner housing 14, that a void or space 19 exists between it and the outer cabinet 12.

Functioning as the microwave generator in the present instance is a magnetron 20, a portion 22 of which projects upwardly into one end of a waveguide designated generally by the reference numeral 24. It will be appreciated that the waveguide 24 provides a primary transmission path through which the energy from the magnetron 20 travels to the cooking cavity 18.

Although of conventional configuration, it will be helpful to describe in detail the portions of the waveguide 24 because my interpose system is intimately associated therewith, as will become evident as the description progresses. Therefore, the waveguide 24 includes a horizontal top wall 26 which extends forwardly and meets a sloping or inclined wall 28, the wall 28 having a horizontal flange 30 extending along its foremost or lower edge. Actually, the flange 30 rests on a marginal portion of the top wall 14T of the inner housing 14. In a parallel relationship beneath the top wall 26 is a horizontal bottom wall 32 which extends forwardly to a downwardly sloping wall 34 having a horizontal flange 36 at its lower or foremost edge. Also, laterally spaced side walls 38 connect between the

walls

26, 28 and the

walls

32, 34. Additionally, the waveguide 24 has a closed end 40 and an open end at 42. The open end 42 is modified somewhat in practicing the present invention, but a description of the modified opening is better reserved for later explanation.

As is customary, a stirrer 44 functions to distribute the microwave energy throughout the cavity 18 as it leaves the open end 42 of the waveguide 24. For the sake of completion, it can be simply stated that the stirrer 44 includes a motor 46, a drive shaft 48 extending downwardly through a hole in the top wall 141' and fanlike blades 50 carried at the lower end of the shaft 48.

A door 52, having a hinge 53 at its lower edge, functions to close the access opening 16 during an actual cooking operation. However, the usual window or screen 54 permits the cooking operation to be viewed while the door is closed. A handle 55 is provided so that the door 52 may be swung downwardly about the hinge 53 into an open position. At each side of the door 52 is a limiter arm 56, the limiter arm 56 in each instance being shown pivotally attached to the door 52 by means of a pin 58 that is received in a hole formed in the door side; it will be understood that a rather schematic and simple means has been shown and that more practical arrangements are employed in actual practice. Near the end of the limiter arm 56 which is opposite the end where the pin 58 is present is formed a notch 60 which rides over and engages a latch roller 62 mounted on a pin 64, the pin 64 being affixed to the side wall 12S. Thus, there are two such pins 64 projecting inwardly, each rotatably carrying a roller 62.

From FIGS. 3 and 4, it will be further discerned that the limiter arms 56 each contain a hole at 66. Through the agency of a coil spring 68 located at each side of the oven, there being a hook 70 engaged through the hole 66 and a book 72 which is anchored to the bottom wall 128 of the cabinet 12, the opening and closing of the door 52 is facilitated. Thus, once the door 52 is opened, the tension or force exerted by each coil spring 68, as seen in FIG. 4, assists in keeping the door in its open position, yet when the door is closed, the springs (see FIG. 3) help in maintaining the closed condition thereof.

Prior to describing the deflector device which has been indicated generally by the reference numeral 74, and which plays a very important role in the practicing of my invention, it will be well to refer to a pair of openings in the form of

slots

76 and 78 which are in longitudinal alignment but spaced slightly from each other to provide a bridging section 80 that acts as a transverse short to prevent propagation of the fundamental energy through the slots or

openings

76, 78. More precisely, without the bridging section 80, there would be a relatively long opening in the

waveguide walls

26 and 28. However, the presence of the bridging section 80 limits the escape of energy via this path during normal operation of the oven, as explained immediately above. With respect to the slot 76, close perception will indicate that a portion of this slot is formed in the top wall 26 and a second portion in the sloping wall 28; therefore, it will be well to designate the portion of the slot 76 contained in the top wall 26 by the reference character 76a and the remainder of the slot by the reference character 76b, the portion 26b residing in the sloping wall 28 as is fairly apparent from FIGS. 3 and 4, although resort can additionally be made to FIG. 6 for this showing.

Although the

slots

76, 78 and the bridging section 80 cooperate in diverting energy from the waveguide 24 over a second or alternate transmission path, the positive elements included in the device 74 contributing to the diversion will now be referred to. Therefore, the first such element is a plate or blade 82 having a shank portion 84 with

arcuate strip portions

86 and 88 extending therefrom, there being an arcuate slot 90 between the

strip portions

86 and 88. The slot 90, quite obviously, is of a size so as to permit movement of the plate or blade 82 inwardly without interference from the bridging section 80 that has been referred to. In other words, the

arcuate strip portions

86, 88 straddle the bridging portion 80 when the plate or blade 82 is shifted from an ineffectual position to an effectual position as will presently become clear.

While not, strictly speaking, a part of the deflector device 74, nonetheless a plate 92 will be described. The plate 92 is provided with a marginal portion 94 that is fixed to the bottom wall 32 of the waveguide 24, as by screws 96. From FIG. 7 it will be perceived that the plate 92 is formed with a slot 98, thereby providing a pair of parallel leg portions 100 to either side of the slot. In this way, the slot 98 accommodates the lower extremity of the arcuate strip portion 86 of the plate or blade 82. It will be recognized that the plate 92 functions to confine the microwave power to a more restricted opening at 42. This is important in order that a more complete diversion of the energy that would normally flow from the magnetron 20 to the cavity 18 will be achieved.

The deflector device 74 also includes a shaft 102 that is journaled on a pair of laterally spaced bearing supports 104. It will be appreciated that by reason of the shaft 102 and the fact that the plate or blade 82 is fixedly carried thereon, any rotation of the shaft 102 will be transformed into a swinging movement of the plate or blade 82 that actually performs the deflecting function.

At this time reference will be made to mechanical linkage, generally denoted by the numeral 106, that connects the door 52 to the device 74, more specifically to the shaft 102 of the device 74. The purpose of the linkage 106 is to cause the plate or blade 82 to be advanced or injected into the waveguide 24 when the door 52 is opened and to be withdrawn or retracted when the door is closed. Accordingly, the shaft 102 is equipped with a crank arm 108 that is at one side of the oven 10, more specifically in that portion of the void 19 residing between the righthand side walls 12S, 14S, and any swinging movement of the arm 108 is in this way transmitted to the shaft 102. A crank pin 112 is free to move within the slot 110 so as to transmit motion from an extension 56a integrally disposed on the righthand limiter arm 56, the pin 112 being carried on this extension 56a. Stated somewhat differently, the pin arrangement permits the door 52 to be swung about its pins 58 (see the pin 58 in FIG. 2) with the consequence that the crank pin 112 traverses a circumferential arc having a different radius from the radius associated with the crank arm 108, the slot 110 simply permitting movement of the pin 112 therein.

Consequently, by reason of the foregoing linkage, the crank arm 108 can be swung from the position which it assumes when the door 52 is fully open, as illustrated in FIG. 4, to the position in which it appears in FIG. 3 when the door 52 is completely closed. This angular movement between the positions of the crank arm 108 in FIG. 3 and that of FIG. 4 is approximately 40, yet when correlated with the movement of the plate or blade 82 results in the

arcuate strip portions

86, 88 being fully inserted or injected into the waveguide 24 in the first instance and fully retracted therefrom in the second instance.

It will be appreciated that the access opening 16 may have the usual resilient radiation seal associated therewith. Inasmuch as such a seal does not play a role in the practicing of the present invention, no need exists for picturing such a seal. However, it is contemplated that the power supplied to the magnetron 20 will be interrupted when the door 52 is opened. As already explained, a number of switching arrangements have been utilized, but reliance. on these switches for failsafe operation simply cannot be made and this is the salient reason for the present invention. The diversion of microwave energy flowing from the magnetron 20 through the waveguide 24 into the cooking cavity 18, when following the teachings of my invention, is added assurance that a dangerous radiation situation will not occur, even though the switch arrangement becomes defective or is maladjusted. Consequently, a microswitch 1 14 appears in FIGS. 3 and 4, being spring biased into an open or disabling position when the limiter arm extension 56a is moved forwardly or toward the front of the oven 10, as it does when the door 52 is opened in that the extension 56a is an integral part of the arm 56 which is best seen in FIGS. 2 and 3. In this regard the microswitch 114 is provided with an arm 116 that is engaged by the extension 560 to force the switch contacts (not shown) closed to complete the energizing circuit to the magnetron 20. It is not believed necessary to show the conductors or wires extending from the switch 114 to the low voltage power supply (which is also not shown) for the magnetron 20; it should suffice to state, particularly inasmuch as this is a conventional arrangement, that the switch 114, as indicated above, simply opens or disconnects the power supply so that the magnetron 20 ceases to supply microwave energy to the waveguide 24.

It has already been stated that the various parts exemplifying the invention, as well as those concerned with the conventional portions of a microwave oven, are metal, preferably aluminum. With respect to the plate or blade 82, it should be pointed out that this member is preferably copper, although aluminum or other metal can be used. It might be explained at this stage of the description that the slots or

openings

76 and 78 are approximately one-eighth inch in width and the thickness of the plate or blade 82 is approximately one-sixteenth inch. Consequently, when the

arcuate strip portions

86, 88 of the plate or blade 82 are fully inserted into the waveguide 24, there will be a space flanking the sides of these

portions

86, 88 via which microwave energy exits from the waveguide.

At this time, attention is directed to power termination means collectively identified by the reference numeral 118. More specifically, however, the means 118 is composed of two

blocks

120 and 122 of microwave absorbing material, the block 120 (appearing in phantom outline in FIG. and in section in FIG. 6) being fixedly secured along one side of the slot 76 and the slot 78 by means of an angle member 124 anchored to the sloping wall 28 of the waveguide 24 by screws 126, additional screws 128 extending into the block 120. The other block 122 is similarly held at the other side of these slots. Consequently, when the

portions

86, 88 are inserted into the waveguide 24, they act as antennae to feed the microwave energy through the

waveguide slots

76, 78 and the diverted energy is dissipated in the

blocks

120 and 122. Actually, the

blocks

120 and 122 constitute a highly dissipative ceramic load such as silicon carbide, a typical chemical analysis of such material that has been found satisfactory in practice being:

Silicon 66.6-68.l% Carbon 23.7-24.3% N 5.5-7.5% 0 l.0-2.0%

Although not essential for an appreciation of what occurs, it might be well to list the physical properties of the above-described material which are:

Bulk Density 2.6 gms/cc Apparent Porosity 13.8% Water Absorption 5.3% Modulus of Rupture 6000 psi at room temperature Modulus of Rupture 7500 psi at 1250C Maximum Operating 2800F Temperature OPERATION From the foregoing description, it should be readily apparent that the magnetron provides the microwave power that is fed through the waveguide 24 into the cavity 18. More specifically, energization of the magnetron 20 causes a wave to be propagated in the waveguide 24, the dimensions thereof being such that it will support only a TE mode at the frequency generated by the magnetron 20. The energy in the waveguide 24 is directed, quite obviously, through the region adjacent the open end 42 as restricted by the plate 92. The region near the open end 42 is really a transition section with respect to the cavity 18. Hence, the cutoff wavelength for propagation within the waveguide 24 can be determined by the formula where:

A cutoff wavelength m and n are mode designation subscripts of the TE,,, mode a height of the waveguide b width of the waveguide A waveguide, as is generally recognized, constitutes an efficient means of propagating microwave energy .from a magnetron or other high frequency source to the cooking cavity of a microwave oven. The present invention does not to any noticeable extent lessen the efficiency.

Normally, the magnetron 20 would not be energized when the microwave oven door 52 is opened. Reliance would be made upon the actuation of the switch 114 so as to break or interrupt the power supply to the magnetron 20. However, in order to take into account possible faults in such safety devices used to prevent this type of happening, the switch 114 being only an example, the present invention provides for the actuation of the deflector device 74, more precisely the movement of the plate or blade 82 thereof, into the waveguide 24 adjacent the open end 42.

The insertion or injection of the

arcuate strips

86 and 88 belonging to the plate or blade 82 substantially changes the dimension b, that is the width, of the waveguide 24. Since the effective electrical width corresponding to the b in the formula given above has been reduced, the propagation efficiency of the waveguide 24 must likewise be reduced. Consequently, the antenna effect derived from the inserted

strip portions

86 and 88 in conjunction with the

slots

76 and 78 cause the microwave power to be diverted from its normal or primary course outwardly through the

openings

76, 78 into the void or space 19 between the inner housing 14 and the encompassing cabinet 12. Owing to the fact that the cabinet 12 is of metal, preferably aluminum as already explained, the void 19 would not normally allow microwave energy to be radiated into the environment. The invention, however, does not rely upon the confinement of the microwave energy within the cabinet 12 by virtue of the walls thereof; instead, the termination means 118 is instrumental in absorbing the energy as it exits through the

slots

76 and 78.

The mass of the

blocks

120 and 122 is susceptible to variation, depending to some extent on the size of the oven itself, and also on the proven reliability of electrical safety controls that are embodied in a particular oven. Nonetheless, the size of the

blocks

120 and 122 should be sufficient to take care of whatever emergency might arise. An alarm operating on a temperature sensitive principle can be incorporated into the oven 10, the heat from either or both of the

blocks

120 and 122 affecting the detector.

In actual practice, blocks of the above-identified ceramic material have been 1 inch wide, 2 and 4 inch long and l and :4 inch high. The

slots

76, 78 would have a combined length approximating that of the length of the

blocks

116, 118. Once again, though, the selection of such dimensions would be well within the ability of a person skilled in the microwave oven art.

The actual operation of the mechanical linkage 106 is believed so obvious as not to warrant any description thereof. It is simply connected between the door 52 and the device 74 so that when the door is opened, the

strip portions

86, 88 are progressively swung downwardly or injected into the waveguide 24 via the

slots

76, 78. When the door 52 is closed, the reverse of this occurs with the

strip portions

86 and 88 then being retracted or withdrawn. Consequently, it is thought obvious that no reliance is made on any of the customary electrical safeguards, the injection and retraction of the deflecting plate or blade 82 being instead accomplished mechanically.

RADIATION TEST RESULTS Although extensive tests were made under various operating conditions, only a summary thereof is believed necessary in order to appreciate the benefits to be derived from the practice of my invention. Accordingly, the radiation survey and sequence of operation included the following modes of operation:

Test Conditions l. Oven without magnetron interpose circuit Oven door open (interlocks faulted) Oven load 275cc of water 2. Oven with magnetron interpose circuit Oven door open (interlocks faulted) Oven load 275cc of water Without the use of this invention (test condition 1) the radiation levels measured were in excess of 20 milliwatts per square centimeter at a distance of 60 centimeters from the front of the oven. Due to the high level of radiation, measurements closer to the oven would have resulted in possible injury to the operator and/or burn out of the monitoring equipment. With the installation of my magnetron interpose system the radiation level at the same distance, i.e. 60 centimeters, was reduced to 2 milliwatts per square centimeter. Furthermore, the microwave energy absorbed sufficiently increased the temperature of the ceramic load to trigger a thermostatic switch, capable of preventing further operation of the oven.

The deactivation of the microwave transmission path into the environment accomplished exclusively in a passive circuit, constitutes a major contribution to consumer protection.

I claim:

1. Microwave heating apparatus comprising means providing a cooking cavity having a movable door for preventing access to said cavity in one position and permitting access thereto in a second position, means for normally delivering microwave power along one path to a location within said cavity, means for diverting at least some of the power traversing said first path along a second path to a location outside said cavity, means controlled by said door causing said diverting means to divert at least some of the power traversing said first path along said second path to said outside location when said door is moved from its said one position to its said second position, and means outside said cavity for receiving the power diverted along said second path to said location, said receiving means preventing entry of said diverted power into said cavity.

2. Microwave heating apparatus in accordance with claim 1 in which said diverting means includes a movable deflecting member shiftable from a nondiverting position to a diverting position by said door controlled means.

3. Microwave heating apparatus in accordance with claim 1 in which said receiving means includes an absorptive member located with respect to said second path for terminating at least a portion of the power traversing said second path.

4. Microwave heating apparatus comprising a housing having a cooking cavity therein and an access opening through which an article to be heated is inserted, a microwave generator, a waveguide for delivering microwave power from said generator to said cavity, termination means externally of said waveguide and said cavity, a movable door for opening and closing said access opening, means for diverting at least some of the power flowing through said waveguide to said termination means to reduce the amount of power entering said cavity, and means mechanically interconnecting said door and diverting means so that when said door is opened said diverting means reduces the amount of power flowing through said waveguide and when said door is closed said diverting means allows normal flow of power through said waveguide into said cavity.

5. Microwave heating apparatus in accordance with claim 4 in which said diverting means includes a deflector device.

6. Microwave heating apparatus in accordance with claim 5 in which said deflector device includes a shiftable member mounted for movement into and out of said waveguide to reduce the amount of power flowing into said cavity when moved into the waveguide and to permit normal flow of power through said waveguide into said cavity when moved out of the waveguide.

7. Microwave heating apparatus in accordance with claim 6 in which said deflecting member constitutes a plate or blade movable into said waveguide through a slot in one wall thereof.

8. Microwave heating apparatus in accordance with claim 7 in which said waveguide has a second slot in said one wall longitudinally aligned with said first slot, a section of said one wall extending therebetween to provide a transverse short and thus prevent propagation of the fundamental power through said slots during normal flow of microwave power, said deflecting member having two portions with one of said portions being movable into said waveguide through the first slot and the second portion being movable into said waveguide through said second slot.

9. Microwave heating apparatus in accordance with claim 8 in which said termination means includes absorptive material disposed externally of said waveguide in adjacency with said slots.

10. Microwave heating apparatus in accordance with claim 9 in which said absorptive material constitutes a pair of blocks, one block extending along one side of said slots and the other block along the other side thereof.

l1. Microwaveheating apparatus in accordance with claim 10 including a plate fixedly attached at one edge thereof to the interior of said waveguide, said fixed plate projecting from one side of said waveguide toward the other sidethereof and having a slot extending from the free edge thereof in the direction of its said one edge, said slot being alignedwith the first slot in said waveguide so that said first portion extends into said slot when said deflecting plate is moved into said waveguide through said slots.

12. Microwave heating apparatus in accordance with claim 8 in which said deflecting member is pivotally mounted for rotation, said portions thereof having an arcuate configuration with an arcuate slot therebetween so that said transverse waveguide portion is received in said arcuate slot when said deflecting plate is injected into said waveguide, said second portion residing in a proximal relationship with the free edge of said fixed plate when said deflecting plate is fully injected.

13. Microwave heating apparatus in accordance with claim 4 in which said termination means includes a member for absorbing at least some of the power diverted by said diverting means.

14. Microwave heating apparatus in accordance with claim in which said deflector device is movable in a direction parallel to the direction of power flow.

l5. Microwave heating apparatus in accordance with claim 7 in which said slot is longitudinally oriented in a direction parallel to the direction of power flow.

16. Microwave heating apparatus comprising a metallic cabinet, a housing at least partially contained in said cabinet having a portion thereof spaced from said cabinet so as to provide a void therebetween, said housing having a cooking cavity therein and an access opening through which an article to be heated is inserted, a microwave generator, a waveguide for delivering microwave power from said generator to said cavity, a movable door for opening and closing said access opening, means for diverting at least some of the power flowing through said waveguide into said void to reduce the amount of power entering said cavity, and means mechanically interconnecting said door and diverting means so that when said door is opened said diverting means reduces the amount of power flowing through said waveguide and when said door is closed said diverting means allows normal flow of power through said waveguide into said cavity, said cabinet joining said housing peripherally of said access opening so as to prevent escape of microwave power from said void in the region of said access door.

17. Microwave apparatus in accordance with claim 16 in which said diverting means includes a member movable into said waveguide to reduce the electrical width of said waveguide.

18. Microwave apparatus in accordance with claim 17 in which said movable member constitutes a blade, said waveguide having a slot in one wall thereof via which said blade is insertable into said waveguide, said blade being movable between a position in which it is substantially contained in said void and withdrawn from the waveguide when said door is closed and a second position in which it is substantially contained in said waveguide when said door is open.

19. Microwave heating apparatus in accordance with claim 18 including absorptive material contained in said void.

20. Microwave heating apparatus in accordance with claim 19 in which said absorptive material constitutes a pair of blocks, one block extending along one side of said slot and the other block along the other side thereof.

2]. Microwave heating apparatus in accordance with claim 20 in which said one wall contains a second slot, said slots being longitudinally oriented in the direction of power flow through said waveguide, and said blade being composed of two integral sections thereof so that one section moves through one of said slots and the second section thereof moves through the other of said slots when said blade is inserted into said waveguide.

22. Microwave heating apparatus comprising a housing having a cooking cavity therein and an access opening through which an article to be heated is inserted, a movable door for opening and closing said access opening, a metallic cabinet having a portion thereof joined to said housing periphally of said access opening and having a second portion thereof spaced from said housing to form a void therebetween, said second portion of said cabinet forming said void preventing the escape of microwave power from said void, a microwave generator, a waveguide for delivering microwave power from said generator to said cavity, at least a portion of said waveguide residing in said void, means mechanically connected to said door for diverting at least some of the power flowing through said waveguide into said void when said door is open, and termination means outside of said cooking cavity but within said void for absorbing at least some of the power diverted into said void.

23. Microwave heating apparatus in accordance with claim 22 in which the portion of said waveguide residing in said void has a slot oriented in the direction of waveguide power flow via which the diverted power flows, and said diverting means includes a blade member movable into said waveguide through said slot when said access door is open, and said termination means includes absorptive material in said void.

24. Microwave heating apparatus in accordance with claim 23 in which said waveguide portion includes a second slot oriented in the direction of waveguide power flow and longitudinally spaced from said first slot, said blade member having portions thereof movable through both of said slots into said waveguide, said absorptive material extending along both sides of both slots.

25. Microwave heating apparatus comprising means providing a heating cavity, means for normally delivering microwave power along one path to a location within said cavity, a mechanical interpose system for diverting at least some of the power traversing said first path along a second path to a location electromagnetically isolated from said cavity so that the diverted power does not enter the cavity, said cavity means having an access opening through which an article to be heated is inserted, a movable door for opening and closing said acess opening, means connecting said mechanism interpose system with said door so that said mechanical interpose system is operated to divert at least some of the power traversing said path when said door is opened, and means for preventing said diverted power from entering said cavity and also from flowing in the direction of said access opening and door.

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Claims

11. Microwave heating apparatus in accordance with claim 10 including a plate fixedly attached at one edge thereof to the interior of said waveguide, said fixed plate projecting from one side of said waveguide toward the other side thereof and having a slot extending from the free edge thereof in the direction of its said one edge, said slot being aligned with the first slot in said waveguide so that said first portion extends into said slot when said deflecting plate is moved into said waveguide through said slots.

14. Microwave heating apparatus in accordance with claim 5 in which said deflector device is movable in a direction parallel to the direction of power flow.

15. Microwave heating apparatus in accordance with claim 7 in which said slot is longitudinally oriented in a direction parallel to the direction of power flow.

21. Microwave heating apparatus in accordance with claim 20 in which said one wall contains a second slot, said slots being longitudinally oriented in the direction of power flow through said waveguide, and said blade being composed of two integral sections thereof so that one section moves through one of said slots and the second section thereof moves through the other of said slots when said blade is inserted into said waveguide.