US2820127A - Microwave cookers - Google Patents

Description

Jan. 14, 1958 Filed March 50, 1953 [6 will 1/ 11 H. F. ARGE NTO ETAL MICROWAVE COOKERS 3 Sheets-Sheet l .t In

I l g m Q) I l i I a l l g I l l I 0 l I I U] Q m! In INVENTORS .-HENRY FT ARGENTO DUANE 3. HA eels/sew TTORNE Y H. F. ARGENTO ET AL 2,820,127

Jan. 14, 1958 MICROWAVE COOKERS s Sheets-Sheet 2 Filed March 30, 1953 N v s E R0 m m N m NE 0 E6 T vmM 4M m H u and w Jan. 14,1958

H. F. ARGENTO ETAL MICROWAVE COOKERS Filed March so, 1952; ,5 Sheets-Sheet s as Q 6 4/ FIG. 5?

IN VEN 70/25 HENRY F. ARGENTO r DLMNE B. HAAGENSEN T laws-V MICROWAVE COOKERS Henry Fr Argento,-Newtonville, and Duane B. Haagensen, Wayland,. Mass., assignors to Raytheon Manufacturing .Company, Newton, Mass., a corporationof Delaware Application March 30, 1953, Serial No. 345,372 14 Claims. Cl. 219-1055) zThis is a continuation-in-part of application, Serial No. 1.63-,'902,"fi1ed May 24, 1950.

This invention relates to microwave electron-discharge apparatua and more particularly to electronic cooking devices wherein microwaves areused to rapidly heat a body byabsorption of the microwave energy'in the body.

lnmicrowave cookers of the type generally utilized commercially, a cavity is energizedfrom a suitable source of microwaves such as, for example, a magnetron, and the body to be cooked is placedin'the cavity. Serious difiiculty arises due to'the fact that the load impedance presented to the source, for example, the magnetron, varies overwide ranges for different conditions of operation of the device. For example, when the cavity .is empty, the load impedance presented to the magnetron will normally be considerably different from the load impedance ,presented to the magnetron if a body to be heated is placed in the cavity. Further, this load impedance will vary with diiferent types of bodies to be heated and different sizes of a given body.

.For example, the magnetron may be matched to the cavity for one set of conditions for a particular type and size of body positioned therein so that the standing wave ratio is reduced to a suitably low value, for example, less than two. However, if the body is removed, the change inthe impedance of the cavity'will cause the standing wave ratio to increase beyond the allowable limits. As a result, an undesirably large amount of energy is fed back into the magnetron and may build up therein to'a point where the magnetron is damaged, for example, by overheating.

This invention discloses a structure whereby the standing wave ratio in a microwave cooker may be kept with in reasonable values for all conditions of operation thereof.

Briefly, the invention consists of positioning a'plurality of slots in one side of the cavity, and dimensioning the cavity such that when said cavity is unloaded waves will be propagated in said cavity in a particular mode which will cooperate with the slots, to pass energy out of the cavity through the slots thus preventing its'refiection back tofthe magnetron. When the cavity is loaded byplacing therein a body to be heated, the dimensions of the cavity are such that it will support a different mode of propagation wherein e'nergywill not be'coupled outthrough the slots and thus will build up in the cavity and be absorbed the body to'be heated. The magnetron is then'matched tojthecavity for its loaded condition, and if the cavity becomes'rnismatched to the magnetron for any reason as,'for. example, if the load in the form of the body to be heated is. removed from the cavity, the mode of propagation," in the cavity will change to pass energy out through theslots in the side thereof.

1 addition, this invention discloses the use'of 'a tapered By the use a suitable match may be accomplished between a cavity and the magnetron over a relatively wide" range of "frequencies, thereby eliminating the necessity of manufacturing the magnetrons to a close frequency "tolerance. 'In addition," the tapered transition section has'been'found to reduce the standing wave ratioreflected"'back tothe magnetron which may be encountered under conditions of varying load.

This invention further discloses means for decreasing energy which may be fed back to the -iriagnetron from the cavity. This comprises an iris in*the wave guidei 'said iris being,'for example, a slot. It has'beenfound-that"by rotating the axis of the slot slightly, the standing wave-ratio encountered for various loads-may be 'reduc'ed.

'This invention further discloses means for I positioning the body to be heated in the electronic -cooker with-relativeaccuracy, thereby insuring that-a particular "size' and type of body will present substantially the same impedance'tothe magnetron whenever thatipartic'ular type or body is heated in the electronic cobker. Thisco'mprises a cylindrical container extending through the 'cavity, the ends of said cylindrical containerbeing covered'with-removable shield members. Said cylindrical container is transparent to the energy in the cavity whereby, whena body is placed in said cylindrical container, energy iirsaid cavity will pass through said cylindrical-container'and will be absorbed by said body.

Other-and further advantages of this invention will be apparent as the description thereof progresses, reference being hadto the accompanying drawings, wherein:

Fig. 1 illustrates a longitudinal, cross-sectional view-of amicrowave cooker embodying this invention;

Fig. 2 illustrates an elevation view of the device shown in Fig. 1 taken along line 2-2 of Fig. l; V

Fig. 3 illustrates a longitudinal, cross-sectional view of the device shown in Fig. 1, taken at right angles to the plane of Fig. 1, along line 33 of Fig. l; w h

Fig. 4 illustrates a transverse, cross-sectional view of the device shown in Fig. 1 taken along line 4- 465 Fig. 1;

Fig. 5 illustrates a partial longitudinal cross-sectional view of a further embodimentof this inventiearafid v Fig. 6 illustrates a transverse cross-seetienat view or the embodiment illustrated in Fig. 5 'taken' aleng'i'ine 6- 6 of Fig. 5.

Referring now to the drawings, there is strewn-anagratron 10 which may be of any desired type, such as a standard commercial package magnetron. 'Magnetron 10 may generate any desired frequency, preferably, however, within the microwave spectrum, the output thereof being coupled through a probe 11 into a wave guide secti6fi 12. While the wave guide section may be ofany'desired shape, as shown here, it is rectangular in form' with the probe 11 extending perpendicular to the wider sides of theguide. One end of guide 12 terminates ina plate 13-which completely blocks the guide. The distance to plate 13 from probe 11 is adjusted to produce the desired impedance match between the probe 11, the guide 12,"and the :load fed by the guide 12. As shown here, the probe 11 is on the order of an eighth of a wave lengthlong, and the distance between probe 11 and end plate 1-3 is somewhat in excess of a quarter wave length of a wavepropag'ated in guide 12. p v

The other'end of the guide 12 from the plate'13] feeds a-cavity 14 in which the body to be heated is placed. The coupling between the wave guide 12 andthe cavity 14 comprises a tapered transition section 15 formed by causing the wider walls 16 of guide 12 to diverge, while keeping the narrower walls 17 of guide 12 auniform distance apart. As shown here, the wide walls diverge until the narrower walls have become greater in width than the wider walls, at which point they are attached to the. cavity with the top and bottom ofthe cavity being made up of the walls 16 of guide 12 which diverged,

and the sides of the cavity being made up of continuations of the walls 17 of the cavity which did not diverge.

The cavity is closed by an end plate 18 extending between the walls 16 and the walls 17 at right angles thereto. End plate 18 has a plurality of slots 19 cut therein, said slots being parallel to walls 16 and being on the order of one-half of a free space wave length long. Extending through cavity 14 is a glass cylindrical container 20 whose axis is parallel to walls 17. Cylindrical container 20 extends out through the walls 16 of the cavity 14 and is rigidly held with respect to cavity 14 by upper and lower retainer rings 21 bolted to the walls 16 of the cavtiy. Each end of cylinder 20 is covered by a cover plate 22 pivotally attached to its respective retainer ring 21, for example, by a bolt 23 such that the plate 22 may be swung away from the end of cylinder 20 to allow the insertion of a body to be heated therein. As shown here, for example, the body to be heated may be a frankfurter 24 positioned in a roll 25, the entire food body being packaged, for example, in a cellophane wrapper 26. The diameter of cylinder 20 is made just large enough to take the frankfurter and roll assembly such that said assembly, when dropped into cylinder 20, will always be positioned subtsantially in the same place in cavity 14. As shown here, upper container ring 21 has a plurality of shallow cuts 27a therein which act as vents to allow any cooking vapors to escape from cylinder 20 during the cooking process when the covers 22 close the ends of cylinder 20.

The operation of the device will now be described. With the food body positioned in cylinder 20 and the covers 22 closing the ends thereof, energization of the magnetron 10 causes a wave to be propagated in guide 12, the dimensions thereof being such that it will support only a TE mode at the frequency generated by the magnetron. The energy in guide 12 is fed through the transition section 15 to the cavity 14. Since the cavity 14 has a dimension parallel to the radiator 11 of magnetron 10 or parallel to the E-lines of propagation which is considerably greater than the width of the narrow sides of guide 12, the cavity 14 will support propagation therein in the TE mode. This mode is set up in cavity 14 and excludes the TE mode since current losses in the cavity walls are lower for the TE mode. The cutoff wave length for these modes may be determined by the formula where:

The transition between the TE mode of propagation in wave guide 12 and the TE mode set up in cavity 14 occurs in the tapered transition section 15. For TE propagation, the slots 19 are positioned in walls 17 at points of zero current flow in said walls, and hence no energy is coupled to these slots. However, if the magnetron is energized when the cylinder 29 is empty, the cavity 14 will not support a TE mode since the effective electrical height corresponding to b in Equation 1 thereof has been reduced by reducing the dielectric constant of the space in cylinder 20. This decreases t of'Equation l to below the wave length used and, therefore, operation in the TE mode ceases. Hence, the

positioned at high current points and each slot behaves as a coupling iris coupling energy out of cavity 14. Normally, magnetron 10 will not be energized when the cylinder 20 is empty, and hence the undesirably high standing wave ratio would not be encountered. However, if magnetron 10 were accidentally energized when cylinder 20 does not contain a body to be heated, or, if for any other reason, the cavity 14 is mismatched to the magnetron 10 such as, for example, the body to be heated has an undesirably low dielectric constant, or is not of the correct size, the cavity 14 will not support the higher mode and will radiate the lower mode out through the slots 19.

Positioned in the wave guide 12 at the junction of wave guide 12 and tapered transition section is an iris comprising a plate 27 substantially closing the guide 12. Plate 27 has a slot 28 therein, said slot being on the order of a half wave length long. While maximum coupling through slot 28 occurs when said slot has its axis parallel to the wider sides 16 of guide 12, it has been found that by orienting the axis slightly, the standing wave ratio may be further reduced for variations in the food body to be heated, for example, due to varations in the tem-- perature of the food body when ti is placed in the cylinder as well as variations in the size and composition thereof. While the wave guide tapered transition section and cavity may be of any desired dimensions, it has been found that satisfactory dimensions of the device are as follows. The distance from probe 11 to iris 28 may be on the order of a guide wave length. The length of the tapered transition section 15 and the distance from the junction of section 15 and cavity 14 and the end plate 18 may each be on the order of a half of a guide wave length long. Referring now to Figs. 5 and 6, there is shown a further modification of the invention which may be useful for heating oblong food products, such as sandwiches, positioned in cardboard cartons. The wave guide structure 12 is similar to that shown in Figs. 1 through 4 and may utilize a similar magnetron microwave source, which has not been shown in Figs. 5 and 6. The tapered portion 15 is similar to that shown in Figs. 1 through 4, except that it tapers outwardly in both planes, such that the cook: ing cavity proper indicated at 30 has a transverse cross section which is shown here as being substantially square. The opposite end of the cooking cavity from thatfed by the tapered transition 15 is closed by a metallic plate 31 having a slot 32 therein. Slot 32 is positioned transverse to the electrostatic field in the cavity and is shown here as being adjacent the upper edge of the plate 31 Positioned inside the cavity proper is a container for holding the food during the application of the heat thereto. The container comprises a pair of dielectric members 33 which are held to the metallic side walls 34 of cavity 30 by means of screws 35. Members 33 have their inner surfaces bowed slightly such that they are thicker toward the center of the cavity 30 than toward the edge. The result is that the field intensity pattern in the cavity 30, which tends to be concentrated toward the center of the cavity is deformed slightly toward the side walls.

Attached across the front and rear edges of the members 33 are dielectric plates 36. Plates 36 are relatively energy propagated in cavity 14 is in the lower or TE thin and serve the purpose of holding the food package in the desired position in the cavity 30. Plates 36 are fastened to members 33 by means of screws 37. Plates 36 extend substantially entirely to the upper and lower walls of the cavity 30, but are spaced slightly therefrom. Attached to plates 36 outside the space containing the food package are dielectric matching members 38. Metabers 38 are attached to plates 36 by means of screws 39 and are similar in shape to members 33. The members 38 are substantially the same height as the plates 36 and have a width which covers substantially the middle third 4. brine plates 36. Memberess'weia gmieker towardthe center of the"cavity sd' tnantoward the edges; tend to diminish the concentration of energyat this point inthe center of the cavity,- ther'ebyfproviding a more uniform heatingindicative of thei'space'occupied by'the food body.

1 In order to get the food'pa'ckag'e into and out of the cavity, there is provided an aperture inthe' upper Wall of cavity 30, which is" covered by a metallic door 40 pivoted at the rear edge of the aperture on a pivot pin 41 andretained'in a closed pos'itio'nby' a spiral spring 42 wound around pivot '41. When a food body is placed on door 40 of sufficient-weight, it 'causes'thedoor to'open downwardly, thereby allowing the food body to drop into the space between the plates" 36.

Thebottom of thefoo'd body, which'fnay be illustrated hereinas asandw'ich 43 positioned in a cardboard box 44, restson a metallic semi-cylindrical projection 45, which extends upwardly froma'lowe'r door 46' covering an aperture in the lower Wall of cavity 30." The lower door is pivoted on a p'ivot 47 and'ope'nsa predetermined time after the food body has been introduced into the cavity 3'0, thereby releasing the food body from the cavity following heating of the food body to the desired temperature.

In operation, the foodbody absorbs a largeportion of the-energy fed into the cavity 30 and also tends to concen trate the intensity of the field pattern in the center of the'cavity, since it has a relatively higher dielectric con stant than the'remaining open spa'cesof the cavity. As a result, relatively little energy is coupled out" through the'slot'32. However, if the cavity 30 is energized with out a food body therein or with a food body therein which absorbs very little energy, the' field pattern shifts somewhat such that there" is a greater relative concentration of energy in the region of the'slot 32 and the over-all intensity of the field pattern increases due to the lack of absorption of the energy within the cavity. As a result, a substantially larger amount of energy is coupled out through the slot 32 when there is no food body within the cavity than when there is a food' body within the cavity. As a result, the impedance load presented to the magnetron-by the cavity and'associated wave guide structure' remains substantially more constant than would be the case without slot 32. This allows normal operation of the magnetron'closer to its maximum rated value without danger of destruction of the magnetron due to large changes in the loadimpedance.

' As in the-case of'slots 19 in Figs. 1 through 4,-the slot 32 is made substantially resonant at the operating frequency of the magnetron by making the length ofthe slot'substantially a half-wave length of said frequency. While the mode pattern within the cavity is relatively complex, it appears to be'basicallya TE mode, both when the food body isout of the cavity.

This completes'the description of the specific embodimerit of' the invention disclosed herein. However, many modifications thereof will be apparent to persons skilled in the art. For example, other shapes and sizes could be used for the cavity 14, the tapered transition section 15, and'the guide '12, and other sources of energy could be used besides the magnetron without departing from the spirit and scope of this invention. Therefore, it is desired that the invention be not limited by the particular details described herein, except as defined by the appended claims.

What is claimed is:

1. An electronic cooker comprising an enclosure defining a cavity, means for radiating electromagnetic wave energy into said cavity, means for positioning a body to be heated in said cavity comprising a cylinder transparent to said energy and extending through said cavity, and coupling means for coupling said energy out of said cavity under normal operating conditions when said body is not positioned in said cavity, said coupling means being inoperative--to"couple energy out of said cavity when said bodyi's po'sit'ion'ed insaid'cav'ity.

2'; A'n' e'lectronic cooker comprising an enclosurefde fininga cavity, means for radiating electromagnetic wave energy into said cavity, means'for positioninga'l'oss'ydb electric body to'be heated in said cavity comprising-a cylinder transparent to said energy and extending'thr'ough said cavity, and'energy coupling apertures in said cavity for coupling energy out of said cavity when said body is not positioned in said cavity and for substantially pre venting energy from escaping from said cavity when said body ispositioned therein.

3. An electronic cooker comprising an enclosure defin ing asubstantially closed cavity, means for radiating electromagnetic wave energy into said cavity comprising a wave guide coupled to said cavity through a tapered transition section, means for positioning a lossy dielectric body to be heated in said cavity, an'dat-least one'energ'y couplings'lot in the wall of said cavity for allowing'energy to escape from said cavity when said body is not pasttioned'in said cavity and substantially preventing energy from escaping from said cavity when said body is po'si= ti'oned therein.

4. An electronic cooker comprising an enclosure deaning a cavity, means for radiating electromagnetic wave energy into said cavity comprising a signal wave tran s mission system coupled to said cavity through a tapered transition section, means for positioning a body tobe heated in said cavity comprising a cylinder transparent to said'energy and extending through said cavity, the ends of said cylinder being covered by electrically conductive shields, and an energy coupling slot in the wall of said cavity for allowing energy to escape from said cavity when said body is not positioned in said cavity and substantially preventing, energy from escaping from said cavity when said body is positioned therein.

5. A microwave cooker comprising an enclosure defin= ing a cavity, means for radiating microwave energy into said cavity, means for positioning a body to be-he'a t'ed in'said cavity, said cavity being structurally dimensioned to 'support one mode pattern of propagation of saidenei'gy when said body is not in said cavity, and another mode pattern of propagation of said energy when said body in said cavity, and an uncovered energy coupling slot in the wall of said cavity, said slot being operative to couple said energy out of said cavity when'said body is not positioned in said cavity, said slot being inoperative to couple energy out of said cavity when said 'b'odyis positioned in said cavity.

6. A microwave cooker comprising an enclosuredefining a cavity, means for radiating microwave'energy into said cavity, means for positioning a body to be heated'in said cavity, said cavity being structurally dimensioned to support one mode pattern of propagation of saidenergy when'said body is not in said cavity, and another mode pattern of propagation of said energy when said body'is in said cavity, and an uncovered energy coupling slot in the wall of said cavity, said slot being on the order of one half of a free space wavelength long at the frequency of said energy, said slot being operative to couple Said energy out of said cavity when said body is not positioned in said cavity, said slot being inoperative to couple energy out of said cavity when said body is positioned in said cavity.

7. An electronic cooker comprising an enclosure defining a cavity, means for radiating microwave energy into said cavity, means for positioning a body to be heated in said cavity comprising a cylinder transparent to said energy and extending through said cavity, the ends of said cylinder being covered by electrically conductive shields, and an energy coupling slot in the wall of said cavity for allowing energy to escape from said cavity when said body is not positioned in said cavity and substantially preventing energy from escaping from said cavity when said body is positioned therein.

7 38. An electronic cookercomprising an enclosure defining a cavity, means for radiating microwave'energy into said-cavity, means for positioning a body to be heated in said cavity comprising a cylinder transparent to said energy and extending through said cavity, and an energy coupling slot in the wall of said cavity for allowing energy to escape from said cavity when said body is not positioned in said cavity and substantially preventing energy from escaping from said cavity when said body is positioned therein. 1

9. A microwave cooker comprising an enclosure defining'a cavity, means for radiating microwave energy into said cavity, means for positioning a body to beheated in said cavity, said cavity being structurally dimensioned to support one mode pattern of propagation of said energy when said body is not in said cavity, and another mode pattern of propagation of said energy when said body is in said cavity, means for reducing energy which may be fed back to said radiating means, and an uncovered energy coupling slot in the wall of said cavity, said slot being operative to couple said energy out of said cavity when said body is not positioned in said cavity, said slot being inoperative to couple energy out of said cavity when said body is positioned in said cavity.

10. A microwave cooker comprising an enclosure defining a cavity, means for radiating microwave energy into said cavity, means for positioning a body to be heated in said cavity, said cavity being structurally dimensioned to support one mode pattern of propagation of said energy when said body is not in said cavity, and another mode pattern of propagation of said energy when said body is in said cavity, means positioned between said cavity and said radiating means for reducing energy which may be fed back to said radiating means, and an uncovered energy coupling slot in the wall of said cavity, said slot being operative to couple said energy out of said cavity when said body is not positioned in said cavity, said slot being inoperative to couple energy out of said cavity when said body is positioned in said cavity.

11. A microwave cooker comprising an enclosure defining a cavity, means for radiating microwave energy into said cavity, means for positioning a body to be heated in said cavity, said cavity being structurally dimensioned to support one mode pattern of propagation of said energy whensaid body is not in said cavity, and another mode pattern of propagation of said energy when said body is in said cavity, a plate having a slot therein positioned between said cavity and said radiating means, and an uncovered energy coupling slot in the wall of said cavity, said slot being operative to couple said energy out of said cavity when said body is not positioned in said cavity,

said slot being inoperative to couple energy out of said cavity when said body is positioned in said cavity.

12. A microwave cooker comprising an enclosure defining a cavity, means for radiating microwave energy into said cavity, means for positioning a body to be heated in said cavity, said cavity being structurally dimensioned to support one mode pattern of propagation of said energy when said body is not in said cavity, and another mode pattern of propagation of said energy when said body is in said cavity, a plate having a slot therein positioned between said cavity and said radiating means, said slot having its axis angularly displaced with respect to a longitudinal line across the surface of said plate, and an uncovered energy coupling slot in the wall of said cavity, said slot being operative to couple said energy out of said cavity when said body is not positioned in said cavity, said slot being inoperative to couple energy out of said cavity when said body is positionedin said cavity.

13. An electronic cooker comprising an enclosure define ing a cavity, means for radiating electromagnetic wave energy into said cavity comprising a signal wave transmission system coupled to said cavity through a tapered transition section, means for positioning a body to be heated in said cavity comprising a cylinder transparent to said energy and extending through said cavity, the ends of said cylinder being covered by electrically conductive shields, means positioned between said cavity and said radiating means for reducing energy which may be fed back to said radiating means, and an energy coupling slot in the wall of said cavity for allowing energy to escape from said cavity when said body is not positioned in said cavity and substantially preventing energy from escaping from said cavity when said body is positioned therein.

14. An electronic cooker comprising an enclosure defining a cavity, means for radiating electromagnetic wave energy into said cavity, means for positioning a body to be heated in said cavity, said cavity being structurally dimensioned to support a TE mode of propagation of said energy when said body is not in said cavity, and a TE mode of propagation of said energy when said body is in said cavity, and coupling means for coupling said energy out of said cavity when said body is not positioned in said cavity, said coupling means being inoperative to couple energy out of said cavity when said body is positioned in said cavity.

References Cited in the file of this patent UNITED STATES PATENTS 2,373,233 Dow et a1 Apr. 10, 1945 2,401,425 Hershberger June 4, 1946 2,408,425 Jenks et al Oct. 1, 1946 2,410,109 Schelleng Oct. 29, 1946 2,467,230 Revercomb et al Apr. 12, 1949 2,472,196 Cork June 7, 1949 2,480,682 Stiefel Aug. 30, 1949 2,500,676 Hall et al Mar. 14, 1950 2,500,752 Hanson et al. Mar. 14, 1950 2,549,131 Rideout Apr. 17, 1951 2,549,511 Nelson Apr. 17, 1951 2,557,180 Fiskc June 19, 1951 2,560,859 Gutton et al July 17, 1951 2,560,903 Stiefel July 17, 1951 2,595,748 Andrews May 6, 1952 2,599,033 Wild June 3, 1952 2,605,356 Ragan July 29, 1952 2,618,777 Ashmead Nov. 18, 1952 2,626,316 Gibson Jan. 20, 1953 2,650,291 Kinn Aug. 25, 1953 2,720,629 Edson et al Oct. 11, 1955 U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,820,127 January 14, 1958 Henry F. Argento et a1.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 24, for "ti" read it column 5, line 54, after is insert in the cavity and when the food body is Signed and sealed this 25th day of February 1958.

(SEAL) Atteet:

KARL ROBERT c. WATSON Atteeting Officer I Conmissioner of Patents U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OF CORRECTION Patent No, 2,820,127 January 14, 1958 Henry F. Argento et al.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 24, for "ti" read it column 5, line 54, after "is insert in the cavity and when the food body is Signed and sealed this 25th day of February 1958.

(SEAL) Attest:

KARL Ho ROBERT c. WATSON Attesting Officer Comnissioner of Patents

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