WO1991003140A1 - Applicateur de micro-ondes - Google Patents

Applicateur de micro-ondes Download PDF

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Publication number
WO1991003140A1
WO1991003140A1 PCT/AU1990/000353 AU9000353W WO9103140A1 WO 1991003140 A1 WO1991003140 A1 WO 1991003140A1 AU 9000353 W AU9000353 W AU 9000353W WO 9103140 A1 WO9103140 A1 WO 9103140A1
Authority
WO
WIPO (PCT)
Prior art keywords
microwave
applicator
waveguide
applicator according
waveguides
Prior art date
Application number
PCT/AU1990/000353
Other languages
English (en)
Inventor
Geoffrey Edward Beard
Original Assignee
James Hardie & Coy Pty. Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by James Hardie & Coy Pty. Limited filed Critical James Hardie & Coy Pty. Limited
Publication of WO1991003140A1 publication Critical patent/WO1991003140A1/fr

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Classifications

    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/78—Arrangements for continuous movement of material
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/70—Feed lines
    • H05B6/705—Feed lines using microwave tuning
    • H—ELECTRICITY
    • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
    • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
    • H05B6/00—Heating by electric, magnetic or electromagnetic fields
    • H05B6/64—Heating using microwaves
    • H05B6/70—Feed lines
    • H05B6/707—Feed lines using waveguides
    • H05B6/708—Feed lines using waveguides in particular slotted waveguides

Definitions

  • This invention relates to a microwave applicator for applying microwave radiation to materials by passing the material through a microwave field.
  • microwave energy is particularly suited to this application since the temperature required to cure some coatings is sufficiently high to damage the substrate. It has been found that microwave energy can be used to cure the coatings without any damaging effect on the substrates. Additionally, the conventional drying apparatus used for continuous curing processes occupies an extremely large area and requires enormous quantities of energy. Disclosure of the Invention
  • this invention consists in a microwave applicator comprising a hollow rectangular applicator waveguide, two centrally disposed longitudinally extending slots respectively formed in the opposing major sides of said applicator waveguide to allow material to be passed through the applicator waveguide; and two antenna means respectively associated with said applicator waveguide and symmetrically disposed on opposite sides of said slots to supply in phase microwave radiation substantially uniformly along the length of said applicator waveguide and excite in said applicator waveguide odd order microwave propagation modes so that a surface current minimum substantially coincides with the centres of said slots.
  • the applicator waveguide and antenna means are configured to excite substantially only the TE propagation mode in the applicator waveguide.
  • the dimension of the rectangular waveguide, in the direction of the minor transverse axis is preferably less than half of one wavelength of the microwave radiation in air.
  • the antenna means are preferably slotted hollow rectangular waveguides of the kind disclosed in United States patent 4,160,145.
  • the antenna waveguides preferably share a common wall with the applicator waveguide, -the energy coupling tuned slots being formed in this wall.
  • the antenna waveguides and applicator waveguide are formed by a removable septum fitted into a rectangular structure.
  • the opening through the applicator waveguide is sealed from the remainder of the interior of the applicator waveguide by substantially microwave transparent sheet material such as teflon.
  • substantially microwave transparent sheet material such as teflon.
  • the sealing material is also effective in isolating the material to be irradiated from any arcing that may occur in the waveguides.
  • Microwave radiation is preferably supplied to the antenna waveguides by way of a power splitter and appropriate waveguides.
  • Phase equalisation is preferably effected by respective path length adjustment, for example by the narrowing of the longer wave guide along an appropriate length for increasing the phase velocity by a predetermined amount along that length.
  • one or more quarter wavelength chokes are provided adjacent the marginal edges of the slots outside the applicator waveguide to reduce radiation leakage.
  • a water load is also preferably positioned adjacent the chokes to further reduce radiation.
  • the microwave applicator of this invention is suitable for use with microwave radiation of any frequency and in particular the commonly use 2450 Mhz and 915 Mhz frequency bands. It will be appreciated that the waveguides and other transmission components have to be dimensioned to suit the operating frequency.
  • FIG. 1 is a schematic partly cut away perspective view of a microwave applicator according to this invention.
  • Figure 2 is a schematic perspective view showing part of the arrangement of figure 1 in greater detail and including representative graphs of field magnitude and surface current.
  • FIG. 3 is a schematic partly cut away perspective view of a microwave applicator according to the invention including a narrowing of one of the feeder waveguides.
  • the microwave applicator 1 of this invention comprises a two part waveguide housing 2 separated by passage 3.
  • a main applicator waveguide 4 of hollow rectangular form is formed in two parts each respectively disposed in the two parts of the housing 2.
  • Passage 3 passes through the centre of waveguide 4 by virtue of two centrally disposed and longitudinally extending slots (not shown in detail) respectively formed in the opposing sides of the waveguide.
  • the interior of passage 3 is lined by sheet teflon barriers 5 which is substantially transparent to microwave radiation. These barriers seal the passage 3 from the interior of waveguide 4 and are provided mainly to prevent any material entering the waveguide or fouling the waveguide as it passes through passage 3. (Barriers 5 are not shown in Figure 2).
  • Microwave radiation is supplied to waveguide 4 by means of two antenna waveguides 6 and 7 respectively disposed on opposite sides of passage 3 formed by the slots in the waveguide 4.
  • the antenna waveguides share a common wall 8 with the applicator waveguide 4 which wall is formed in two parts.
  • a series of tuned slots 9 (figure 2) spaced apart by three quarters of a wavelength are provided to couple the microwave radiation into waveguide 4.
  • Wall 8 is removable to permit variation in the nature of the tuned slots 9 without reconstruction of the waveguides.
  • the slots are arranged in the same manner as described in U.S. 4,167,145 so as to provide a substantially uniform distribution of microwave energy along the length of waveguide 4.
  • the waveguide antenna 6 and 7 are symmetrically disposed and the dimensions of the waveguide 4 are chosen to excite only odd order microwave propagation modes in the waveguide 4.
  • the dimension of the waveguide 4 in the direction of the minor transverse axis is less than one half of one wavelength or, for 2,450 Mhz radiation, about 60 mm. It is preferred that the configuration is such as to substantially excite only the TE mode by suitable choice of the waveguide dimensions.
  • the surface current in the waveguide 4 is at a minimum at the centre of the longitudinally extending slots.
  • Two one quarter wavelength deep slots 10 which act as chokes short-circuitry are provided adjacent each edge of the slots in the waveguide 4 to reduce radiation leakage.
  • the chokes 10 extend right around the inside of passage 3 although this cannot be seen from Figure 1. It is preferred that a water load (not shown) is positioned adjacent each set of chokes 10 to further reduce radiation leakage. Plates 11 and 12 at each end of housing ports 2 maintain the spaced-apart relationship and plate 11 provides a short circuit to both the applicator waveguide 4 and antenna waveguides 6 and 7. Plate 12 provides a short circuit to applicator waveguide 4 but pierced by feeding waveguides 13 and 14 which couple to antenna waveguides 6 and 7 respectively.
  • Microwave radiation is provided by substantially conventional magnetron and launcher assembly 15 which provides microwave power at 2,450 Mhz and at a power of approximately 5 kW.
  • the launcher (not shown) conforms to the European R26 waveguide type.
  • Magnetron and launcher assembly 15 is connected to a three port 6kW rated R26 circulator 16 of a substantially conventional type.
  • the return port of the circulator 16 is connected to a 6kW water load schematically shown at 17.
  • the output port of the circulator 16 is directed via an R26 directional coupler 18 having a coupling coefficient of -30 dB to a four screw tuner 19.
  • the directional coupler 18 provides for measurement of forward and reflected power in the microwave system by means of power metering terminations 20 and 21 which are connected to conventional 2,450 Mhz microwave power meters (not shown) .
  • the four screw tuner 19 is of a substantially conventional type and is provided to tune the impedance of the circuit to minimise the amount of reflected power. It should be noted that the reflected power is preferably not however reduced to zero since too high a Q for the circuit can result in tuning mismatch due to small frequency variations in the microwave source. In practice the circuit is preferably tuned to have a forward to reflected power ratio of approximately 8 to 10:1.
  • Four screw tuner 19 is connected by waveguide section 22 to a 3 dB power splitter 23 of known type from which feeding waveguides 13 and 14 extend.
  • Feeding aveguides 13 and 14 are half height guides that is, they have a width equivalent to the R26 standard guide but half the height.
  • a teflon block 24 is provided in waveguide 14 to provide for path length adjustment between the radiation travelling to antenna guide 6 and that travelling to antenna guide 7 so that the two- are in phase upon entering waveguides 6 and 7.
  • the microwave applicator is tuned as described above and the material to be irradiated is passed through passage 3 preferably by a conveyor system.
  • the applicator of this invention is particularly suited to applying microwave energy to sheet material, for the curing of surface coatings. It will be apparent that the establishment of the TE 10 mode in the applicator guide 4 results in a maximum of microwave field at the centre of the slot so that the maximum microwave energy is transmitted to the material passing through the passage.
  • the energy distribution in the longitudinal direction of waveguide 4 is substantially a standing wave pattern and preferably multiple applicators according to this invention are provided offset by one quarter of a wavelength to provide a uniform energy distribution.
  • the invention has significant advantage in that a controlled amount of substantially uniform heating power can be applied to material passing through the passage 3 and suitably spaced apart applicators can be used to selectively heat at the required rate.
  • the size of the apparatus required for the application of a given amount of power is also considerably less than that associated with conventional drying tunnels. Additionally, the efficiency of a microwave generator for heating is significantly greater than conventional heating apparatus.
  • a conveyor belt of a suitable material such as teflon which is substantially microwave transparent can pass through the passage 3 to convey relatively small items or particulate materials.
  • suitable control circuitry can be provided to monitor and adjust forward and reflected microwave power by adjustment of the magnetron output and the tuner.
  • suitable dielectric phase delay structures for example teflon, can be provided to match the phase velocities of the microwaves in the antenna guides and applicator guide to improve coupling efficiency and uniformity of the microwave field in the applicator guide.
  • Waveguide 25 provides for both length adjustment between the radiation travelling to antenna guide 6 and that travelling to antenna guide 7 so that the two are in phase upon entering the respective waveguides.

Landscapes

  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Waveguide Aerials (AREA)

Abstract

Applicateur de micro-ondes (1) comportant un guide d'ondes (4) présentant deux fentes opposées pour y permettre le passage du matériau et deux guides d'ondes rectangulaires creux fendus (6, 7) pour fournir en phase un rayonnement à micro-ondes sensiblement uniformément au guide d'ondes (4), pour ainsi exciter dans ce dernier uniquement les modes d'ordre impair de propagation des micro-ondes afin d'établir un courant de surface minimum sensiblement au centre des fentes. Afin de permettre l'excitation uniquement des modes d'ordre impair, la dimension du guide d'ondes (4) dans le sens de l'axe transversal mineur est inférieure à une moitié d'une longueur d'ondes du rayonnement à micro-ondes.
PCT/AU1990/000353 1989-08-18 1990-08-17 Applicateur de micro-ondes WO1991003140A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
AUPJ585489 1989-08-18
AUPJ5854 1989-08-18

Publications (1)

Publication Number Publication Date
WO1991003140A1 true WO1991003140A1 (fr) 1991-03-07

Family

ID=3774121

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/AU1990/000353 WO1991003140A1 (fr) 1989-08-18 1990-08-17 Applicateur de micro-ondes

Country Status (1)

Country Link
WO (1) WO1991003140A1 (fr)

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2278764A (en) * 1993-05-05 1994-12-07 Apv Corp Ltd Microwave ovens
US5536921A (en) * 1994-02-15 1996-07-16 International Business Machines Corporation System for applying microware energy in processing sheet like materials
WO1999042778A2 (fr) * 1998-02-19 1999-08-26 Siemens Aktiengesellschaft Procede et dispositif pour le frittage hyperfrequence de combustible nucleaire
CN115978785A (zh) * 2022-12-19 2023-04-18 四川大学 一种同轴开缝辐射器、连续流液体加热系统及加热方法

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU3605968A (en) * 1967-04-28 1969-10-09 Varian Associates Slotted waveguide applicator
GB1291763A (en) * 1969-01-21 1972-10-04 Varian Associates Microwave applicator employing a flat multimode cavity for treating webs
US4160145A (en) * 1978-02-16 1979-07-03 Armstrong Cork Company Microwave applicator device
GB2067059A (en) * 1980-01-03 1981-07-15 Stiftelsen Inst Mikrovags Method and device for heating by microwave energy

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU3605968A (en) * 1967-04-28 1969-10-09 Varian Associates Slotted waveguide applicator
GB1291763A (en) * 1969-01-21 1972-10-04 Varian Associates Microwave applicator employing a flat multimode cavity for treating webs
US4160145A (en) * 1978-02-16 1979-07-03 Armstrong Cork Company Microwave applicator device
GB2067059A (en) * 1980-01-03 1981-07-15 Stiftelsen Inst Mikrovags Method and device for heating by microwave energy

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB2278764A (en) * 1993-05-05 1994-12-07 Apv Corp Ltd Microwave ovens
GB2278764B (en) * 1993-05-05 1997-03-19 Apv Corp Ltd Microwave tunnel ovens
US5536921A (en) * 1994-02-15 1996-07-16 International Business Machines Corporation System for applying microware energy in processing sheet like materials
WO1999042778A2 (fr) * 1998-02-19 1999-08-26 Siemens Aktiengesellschaft Procede et dispositif pour le frittage hyperfrequence de combustible nucleaire
WO1999042778A3 (fr) * 1998-02-19 1999-11-11 Siemens Ag Procede et dispositif pour le frittage hyperfrequence de combustible nucleaire
US6617558B2 (en) 1998-02-19 2003-09-09 Framatome Anp Gmbh Furnace for microwave sintering of nuclear fuel
CN115978785A (zh) * 2022-12-19 2023-04-18 四川大学 一种同轴开缝辐射器、连续流液体加热系统及加热方法
CN115978785B (zh) * 2022-12-19 2024-03-19 四川大学 一种同轴开缝辐射器、连续流液体加热系统及加热方法

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