US3716688A

US3716688A - Reflector and waveguide applicator

Info

Publication number: US3716688A
Application number: US00193907A
Authority: US
Inventors: R Johnson
Original assignee: Microdry Corp
Current assignee: MICRODRY Inc A CORP OF KENTUCKY; Microdry Corp
Priority date: 1971-10-29
Filing date: 1971-10-29
Publication date: 1973-02-13
Anticipated expiration: 1990-02-13

Abstract

In a waveguide applicator using a water load termination for absorbing remnant power after the material being processed leaves the applicator, a metallic gate is interposed between the water load and the location at which the product exits the applicator. One edge of the gate is hinged about a broadwall of the guide, and this edge is in continuous electrical contact with the broadwall. The gate is adjustable for selective reflection of power back through the guide to make a second pass in processing the material, thereby enhancing the system''s efficiency.

Description

United States Patent n 1 Johnson [451 Feb. 13, 1973 [54] REFLECTOR AND WAVEGUIDE APPLICATOR [75] Inventor: Ray MQJohnson, Danville, Calif.

[73] Assignee: Microdry Corporation, San Ramon,

Calif.

[22] Filed: Oct. 29, I971 [21] Appl. No.: 193,907

[52] US. Cl ..219/l0.55, 333/985 [51] Int. Cl. ..II05b 9/06 [58] Field of Search ..219/l0.55; 333/985 [56] References Cited UNITED STATES PATENTS 3,597,565 8/1971 Johnson ..2l9/l0.55

FOREIGN PATENTS OR APPLICATIONS 826,760 7/1957 Great Britain ..333/98 S OTHER PUBLICATIONS Microwave Duplexers, Smullin and Montgomery, MIT Radiation, Series No. 14, page 406, March 1948 Primary Examiner-.1. V. Truhe Assistant Examiner-Hugh D. Jaeger Att0rneyCarl C. Batz s7 9 ABSTRACT In a waveguide applicator using a water load termination for absorbing remnant power after the material being processed leaves the applicator, a metallic gate is interposed between the water load and the location at which the product exits the applicator. One edge of the gate is hinged about a broadwall of the guide, and this edge is in continuous electrical contact with the broadwall. The gate is adjustable for selective reflection of power back through the guide to make a second pass in processing the material, thereby enhancing the system's efficiency.

11 Claims, 10 Drawing Figures FIG. 2

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' INVENTOR: RAY M-JOHNSON am' flau gm QJZ'ZM Qafhmz 4%7444a 5 PATENTED FEB! 3 I973 SHEET 30F 3 RiA Y w 4mm INVENTOR:

N1- JOHNSON REFLECTOR AND WAVEGUIDE APPLICATOR BACKGROUND OF THE INVENTION The present invention relates to microwave applicators; and more particularly, it relates to a waveguide microwave applicator designed for treating food products, although the invention is not so limited.

Systems which treat materials or food products with microwave energy may be classified either as multimode cavities or waveguide applicators. In a mu]- timode cavity, a number of different modes are excited within a metallic cavity so as to distribute the microwave energy throughout the space enclosed by the cavity. In a waveguide, the microwave energy is preferably maintained in a preselected mode or modes, and then transmitted through the waveguide. Microwave applicators may be further classified as continuous operation or batch type ovens. The present invention, therefore, relates to a continuous microwave waveguide applicator.

A number of continuous microwave waveguide applicators are known, including those disclosed in my applications Ser. No. 100,395, filed Dec. 21, 1970, for Continuous Microwave Heating or Cooking System and Method", which is a continuation application of my earlier filed application, Ser. No. 816,722, filed Apr. 16, 1969; Ser. No. 817,097, filed Apr. 17, 1969,

now U.S. Pat. No. 3,597,565 for Wave Guide Applicator and Method"; and Ser. No. 816,500, filed Apr. 16, 1969, for System and Method for Heating Material Employing Oversize Wave Guide Applicator".

In a microwave applicator of the type discussed above, the metallic walls of the applicator form a wave'guide,that is, the microwave energy is propogated, ideally, maintained only in predetermined modes. The waveguide defines a heating or treating section through which the product is passed continuously, and downstream of the treating section, the remnant microwave energy is preferably absorbed in a power termination, such as water load wherein water is continuously fed through the waveguide to absorb the remnant power.

It is desirable in some cases to use waveguide applicators, as distinguished from multimode cavities because the design can be treated more analytically. That is, the particular modes of the waves are predetermined, and knowing the excitation frequency, many of the design parameters can be solved through the application of classical waveguide theory; whereas in a multimode cavity, most of the engineering problems have to be solved empirically.

One of the problems, however, that is encountered in a waveguide applicator is that of reflections. Normally, the energy source is a magnetron tube which generates the electrical power at the desired microwave frequency. Magnetrons have been developed for producing power in the amounts required, but a common characteristic of a magnetron is that it is highly sensitive to reflective power. That is, any power that is fed back into its output port, as by reflection, places stress on the tube and greatly reduces its life cycle. Hence,-rather than to risk reflection of microwave power back to the source, most microwave applicators, whether a multimode cavity or waveguide type, are designed to absorb remnant power. This, of course, contributes to inefficiency in operating the system.

SUMMARY OF THE INVENTION In the present system, a microwave waveguide applicator is excited in the Tlil mode, where m is an integer. The material being treated is passed-continuously through the waveguide from an input aperture to an exit aperture. The microwave energy is passed into the treating zone and through it to a termination area where it is absorbed by a water load termination.

lnterposed between the water load and the treating zone is a metallic gate or flapper which is adapted to be selectively located at one of a number of positions including a fully open position, a closed position and intermediate positions to reflect a desired amount of energy back to the treating zone to enhance the efficiency of operation of the system.

One edge of the gate is hinged about a broadwall of the guide, and the hinged edge is in continuous electrical contact with the broadwall.

In a preferred embodiment, the waveguide applicator is formed in two side sections separable about a longitudinal vertical center plane so that the sections may be separated for cleaning the interior. In this case, the gate is also formed in two side sections so that it separates along the separation plane of the waveguide when the waveguide is broken down for cleaning. A mechanism is provided for returning the gate to its open position whenever the waveguide is separated for cleaning, so that when it is put together, the opposing ends of a split shaft on which the gate is mounted are in alignment when the side sections of the guide are placed together.

The gate itself is preferably made of stainless steel; and it contains a plurality of apertures to permit air to pass through it if it is desired in purging the treating area with air.

The mechanism which permits adjustment of the gate also prevents the gate from reaching a fully closed position or even having its distal end come within arching distance of the broadwall opposite the broadwall to which the gate is hinged.

Thus, the present invention provides for the selective reflection of power back through the treating zone while, at the same time, permitting selection of the amount of reflected power so that the power that the reflected power that ultimately reaches the source will be a minimum. Under conditions of full load, for example, the efficiency of the system can be raised from approximately per cent to about 96 per cent while permitting operation of the magnetron well within its design range.

Other features and advantages of the present invention will be apparent to persons skilled in the art from the following detailed descriptionof a preferred embodiment accompanied by the attached drawing wherein identical reference numerals will refer to like parts in the various views.

THE DRAWING FIG. 1 is a perspective view of a waveguide applicator incorporating the present invention;

FIG. 2 is a transverse cross sectional view of the system of FIG. 1 taken through the sight line 2-2 FIG. 4 is a detailed view of a portion of the reflector in exploded relation;

FIG. 5 is a side cross sectional view of the elements of FIG. 4 in assembled relation;

FIG. 6 is a top fragmentary view of the elements of FIG. 4 in assembled relation;

FIG. 7 is a detailed fragmentary view in perspective showing the structure of the split shaft;

FIGS. 8 and 9 are side views of the adjusting plate showing the reflector respectively in an open and a closed position; and

FIG. 10 is a side view of a portion of the waveguide of FIG. 1 with the side sections separated for cleaning and showing the reflector returned to its open position.

DETAILED DESCRIPTION Referring first to FIG. 1, reference numeral 10 generally designates a source of the product being treated. In the illustrated embodiment, the product is bacon, and the source 10 may be a slicer providing the bacon in individual drafts of slices in shingled relation as at 11, which are transported from the source 10 by means of a conveyor 12 to a waveguide applicator generally designated by reference numeral 13.

The bacon is fed into the applicator through a rejection filter generally designated 14; and it exists from the waveguide applicator 13 as at 15 for packing or for treatment in a subsequent applicator, if desired.

Briefly, the microwave energy is generated in a source 16 and fed to the applicator via a rectangular waveguide 17, through a tapered input section 18 and into the treating zone 19. The microwave energy is then routed to a termination section generally designated by reference numeral 20 which contains a conduit 21 through water is continuously forced for absorbing remnant energy which is not absorbed by the bacon in the treating zone 19. Forced air may be fed through an input conduit 23 in the direction of the arrow, and thence through the tapered input section l8,'the treating zone 19, and the termination section 20 where exits through a conduit 24 to purge the treating zone of cooking gases or vapor.

Referring now to FIG. 2, the treating zone 13 has a V-shaped cross section including an upper broadwall having first and second

inclined sections

25 and 26 and a lower broadwall having opposing

inclined sections

27 and 28. Sidewalls 30 and 31 connect respectively the outboard ends of the broadwalls, and the center portions of the lower, inclined

broadwall sections

27, 28 may be slightly separated as at 32 to define a drainage slot.

As seen in FIG. 1, at the downstream end of the treating zone 19, there is an upwardly turned waveguide connecting section 33 which connects the treating zone with the vertical termination section 20. The product exits through one broadwall of the connecting section 33. The entire waveguide, including input rejection filter 14, input section 18, treating section 19, and termination section 20 are formed in symmetrical side sections which are provided with opposing center flanges for securing the sections together while permitting separation for cleaning.

Additional details of waveguide applicators of this general type may be found in my above-described patent applicationspThe connecting waveguide 33 of the treating chamber 19'i s also divided into first and second side sections denoted 33A and 338 respectively in FIG. 2. Similarly, the termination section 20 is divided into side sections 20A and 208. The connection between the connecting waveguide 33 and the termination section 20 is by means of horizontal peripheral abutting flanges located on each section adjacent the junction. The peripheral flange for the connecting portion 33 is shown in plan view in FIG. 3, and the two flange portions for the

sides

33A, 33B are labeled respectively 33C and 33D.

It will be observed that in plan view, the connecting portion 33 forms a rectangular waveguide, the upper and lower walls as viewed in FIG. 3 being broadwalls and the two narrower walls being sidewalls. Adjacent the lower broadwall in FIG. 3, the

flanges

33D and 33C are milled to form grooves denoted respectively 35 and 36. These grooves are aligned, and they are adapted to receive a split shaft generally designated by reference numeral 38 and including first and

second side sections

39 and 40.

As best seen in FIG. 7, the inboard end of the shaft section 39 is provided with a rectilinear cavity 39A adapted to receive a mating male member 40A formed at the inboard end of the shaft section 40 so that both shaft sections turn in unison. The central portion of the split shaft 38 is supported by a grooved double flange member generally designated by reference numeral 41 which is secured to the side of the connecting portion 33.

A reflective gate or flapper", as it is sometimes called, is welded to the split shaft 42 in two side sections designated 41 and 43 in FIG. 3, and welded respectively to the

sections

39, 40 of the split shaft. When the

side sections

39, 40 of the shaft 38 are con nected together, the

gate sections

42, 43 are aligned. Both

sections

42, 43 of the gate are apertured as at 44 to permit passage of purging gases and cooking products from the treating zone.

Locating pins 45 center the shaft 38 in the

side grooves

35, 36.

Referring now to FIGS. 4 and 5, a strip of finger stock is generally designated by reference numeral 47, and it includes a plurality of curved fingers 48 adapted to cradle and hold the section 39 of the shaft 38 to maintain the shaft in electrical continuity. with the flange 33D. A similar section of finger stock 49 is adapted to hold and cradle the section 40 of the shaft 38 in electrical connection with the flange 33C. The flat portions of the finger stock are attached to their associated sections of the peripheral flanges by means of screws, commonly designated 50. Thus, as the shaft 38 is rotated about its axis to adjust the position of the reflector plate, the reflector plate. remains in continuous electrical contact with the walls of the waveguide via the fingers 48 of the finger stock 47, the flat portion thereof, and the peripheral connecting flange of the waveguide.

The outboard end of the section 39 of the split shaft 38 extends beyond the peripheral flange 33, as seen in FIG. 3, and is provided with an index plate 52 which extends toward the opposite broadwall and has a generally wedge-shaped configuration, as seen in FIGS. 8 and 9. The index plate 52 is provided with a handle 53 for rotating the plate together with the split shaft 38 about the axis of that shaft. The portion of the plate 52 which is remote from the shaft 38 is provided with a plurality of apertures 54 arranged on an are centered at the axis of the shaft 38.

Referring back to FIG. 3 now, a pin 55 has first and second

reduced end portions

56 and 57, and the reduced end portion 57 is provided .with an even further reduced portion 58 for fitting into and aligning with one of the apertures 54 of the index plate 52. The

reduced end portions

56, 57 of the pin 55 are held in associated apertures of

brackets

59 and 60 which are secured to the left section 33B of the connecting portion of the waveguide. Connected to the right-hand section 33A of the connecting waveguide 33 is a stop member 62 which engages the reduced portion 56 of the pin 55 and prevents further rightward motion of the pin. The pin 55 is biased in a rightward direction by means of a coil spring 63 which is interposed between the brackets 60 and a shoulder 64 at the base of the reduced portion 57 of the pin 55.

Referring now to FIGS. 8 and 9, the

reflector plates

42, 43 are curved to assume the shape of the upward curve of the connecting waveguide 33. It will be observed that the weight of index plate 52 acts as a force to pivot or bias the

reflector plates

42, 43 in a downward or open position, as shown in FIG. 8. The reflector plate is set to an intermediate position, as shown in FIG. 9, simply by pulling the handle 53 slightly outwardly so as to disengage the reduced tip 58 of the pin 55 from the apertures 54 and then adjusting the plate 52 so that one of the apertures 54 become aligned with the reduced end tip 58 of the pin 55. The aligned aperture is then fit over the reduced end tip 58, and the

reflector plate

42, 43, is held in place.

When it is desired to disassemble the waveguide for cleaning, the flanges which connect the side sections of the waveguide are disconnected, and the spring 63 urges the pin 55 rightward because the stop 62 no longer engages the reduced end portion 56 of the pin 55'. This disengages the other reduced end tip 58 from its associated aperture 54, and the weight of the index plate 52 and reflector plate return both sections of that reflector plate to their open position. Thus, when the sides of the waveguide are re-assembled after the cleaning, the inboard ends of the split shaft are aligned so that the male portion 40A of the shaft section 40 will be received within the cavity 39A of the shaft section 39.

As can be seen in FIG. 9, even though the right-hand edge of the

reflector plate

42, 43 is always maintained in electrical continuity with the right broadwall, even in its open position, the distal end of the reflector plate is spaced at least about one inch from the opposing broadwall in order to prevent arcing. This, nevertheless, permits reflection of at least about 90 per cent of the remnant energy back through the product for a second pass in treating the product. For example, without the reflector plate of the present invention, the system described in my above-referenced patent has been found to be about 85 per cent efficient under full load; and with the reflector plate described herein, efficiency is increased to about 96 per cent. The remaining reflective power, less than 4 per cent, is within the permissible reflection limit acceptable to the source magnetron without damage.

Although the invention has been disclosed in one practice the inventive principle; and it is, therefore, in-

tended that all such modifications and substitutions be covered as they are embraced within the spirit and scope of the appended claims.

I claim:

1. In a microwave waveguide applicator providing a treating zone for a material and passing microwave energy through said treating zone to a termination section, the improvement comprising: reflector plate means of conductive material; a waveguide connecting said treating zone to said termination section; and hinge means for connecting one end of said plate to one wall of said waveguide for pivotal motion between a first position in which said reflector plate means does not reflect microwave energy and a second position in which said reflector plate means reflects at least a portion of said microwave energy back through said treatmg zone.

2. The system of claim 1 wherein said hinge means maintains electrical continuity between said reflector plate means and the walls of said waveguide.

3. The system of claim 2 further including index means connected to said hinge means for selectively setting the placement of said reflector plate means to thereby reflect a predetermined amount of remnant power back to said treating zone while permitting the remainder of said power to pass to said termination section.

4. The system of claim 1 wherein said plate means includes a metallic apertured plate conforming to the shape of the waveguide wall to which it is attached when said plate is in said open position.

5. A method of treating a material with microwave energy comprising: propagating microwave energy through a treating zone defined by a generally rectangular waveguide to a termination section; passing material through said treating zone; and selectively reflecting within acceptable limits a predetermined portion of said energy from a location between said zone and said section back through said zone while maintaining the power reflected back to the source.

6. A microwave system for treating material comprising: waveguide applicator means providing a treating zone of generally rectangular cross section and having opposing broadwalls; source means for exciting said applicator means in a TE, mode; means for moving said material through said treating zone; a termination section; waveguide means having opposing broadwalls and receiving remnant power passing through said treating zone and connecting with said termination section; and reflector means including a reflector plate connected at one end to one of the broadwalls of said waveguide means for hinging movement between a first position wherein said reflector plate lies adjacent said one broadwall and permits unreflected passage of power from said treating zone to said termination section, and

. a second position wherein said reflector plate is inclined relative to the direction of power flow to reflect at least a portion of said power back to said treating zone to further treat said material.

7. The system of claim 6 wherein said waveguide applicator means is formed of symmetrical side sections connected together along a vertical center plane by means of abutting flanges whereby said applicator means may be separated for cleaning; and wherein said reflector plate comprises first and second side sections connected respectively to separable sections of said waveguide, said reflector means including a split shaft journaled in said waveguide for pivotal motion about an axis transverse of the direction of power flow through said waveguide and including first and second mating side shaft sections rigidly connected respectively to said side sections of said reflector plate.

8. The system of claim 7 wherein said side plate sections are each apertured for permitting passage of gas between said treating zone and said termination section.

9. The system of claim 7 wherein said applicator means further includes a connector waveguide interposed between said treating zone and said termination section, said termination section and said connecting waveguide each including peripheral abutting flanges for connecting to each other, said system further including conductive finger stock defining a plurality of extending, curved fingers for cradling said shaft sections and for forming continuous electrical contact between said shaft sections and said peripheral abutting flanges.

10. The system of claim 7 wherein said reflector means further includes index plate means connected to said reflector plate and defining a plurality of apertures, said system further comprising a holding member connected to said waveguide and adapted to be received in one of the apertures of said index plate for holding said reflector plate in a predetermined reflective position.

11. The system of claim 10 further comprising spring means for urging said holding means out of engagement with said index plate when the side sections of said applicator means are separated, whereby said index plate and said reflector plate return :to their open positions under gravity.

Claims

1. In a microwave waveguide applicator providing a treating zone for a material and passing microwave energy through said treating zone to a termination section, the improvement comprising: reflector plate means of conductive material; a waveguide connecting said treating zone to said termination section; and hinge means for connecting one end of said plate to one wall of said waveguide for pivotal motion between a first position in which said reflector plate means does not reflect microwave energy and a second position in which said reflector plate means reflects at least a portion of said microwave energy back through said treating zone.

6. A microwave system for treating material comprising: waveguide applicator means providing a treating zone of generally rectangular cross section and having opposing broadwalls; source means for exciting said applicator means in a TEmo mode; means for moving said material through said treating zone; a termination section; waveguide means having opposing broadwalls and receiving remnant power passing through said treating zone and connecting with said termination section; and reflector means including a reflector plate connected at one end to one of the broadwalls of said waveguide means for hinging movement between a first position wherein said reflector plate lies adjacent said one broadwall and permits unreflected passage of power from said treating zone to said termination section, and a second position wherein said reflector plate is inclined relative to the direction of power flow to reflect at least a portion of said power back to said treating zone to further treat said material.