US3209113A - Furnace for high-frequency heating with the aid of oscillations of very high frequency - Google Patents

Furnace for high-frequency heating with the aid of oscillations of very high frequency Download PDF

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Publication number
US3209113A
US3209113A US195798A US19579862A US3209113A US 3209113 A US3209113 A US 3209113A US 195798 A US195798 A US 195798A US 19579862 A US19579862 A US 19579862A US 3209113 A US3209113 A US 3209113A
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United States
Prior art keywords
waveguide
open end
waveguide system
wall portion
parabolic
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Expired - Lifetime
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US195798A
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English (en)
Inventor
Verstraten Jan
Timmerma Franciscus Hendricus
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US Philips Corp
North American Philips Co Inc
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US Philips Corp
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    • 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
    • H05B6/788—Arrangements for continuous movement of material wherein an elongated material is moved by applying a mechanical tension to it
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01Q—ANTENNAS, i.e. RADIO AERIALS
    • H01Q13/00—Waveguide horns or mouths; Slot antennas; Leaky-waveguide antennas; Equivalent structures causing radiation along the transmission path of a guided wave
    • H01Q13/02—Waveguide horns

Definitions

  • the invention relates to a furnace for high-frequency heating of substances by means of electromagnetic energy of very high frequency, for example, energy in the decimeter or centimeter range.
  • This furnace comprises a very high frequency generator and a waveguide system bounded by two parallel closing Walls.
  • the output circuit of the very high frequency generator is connected to the waveguide system for guiding the very high frequency energy to the outlet port of the waveguide system along which the objects to be heated are conveyed in a direction which is substantially at right angles to the two parallel closing walls of the waveguide system.
  • the device described yielded excellent results, but it has been found that, when the dimensions of the waveguide system were reduced, for example, in order to reduce the dimensions of the outlet port and to raise the concentration of power thereat, practical difliculties arose.
  • Applicants have found that with such a high-frequency heating furnace the advantages of the uniform heating and the attenuation of the stray radiation projecting beyond the waveguide system Were disturbed, which was found by experiments to be due to the fact that the reduction of the dimensions adversely affects the satisfactory operation of the radiation system of the heating furnace formed by the linear radiator and the reflector due to the surroundings, particularly the objects to be heated.
  • the invention has for its object to provide a different structure of a device of the kind set forth, in which, while the advantages of uniform heating and reduced stray radiation are maintained, an appreciably greater freedom in the choice of the dimensions of the high-frequency furnace is obtained, so that apart from a mechanically rugged structure a marked increase in power concentration at the outlet port can be realized.
  • the device according to the invention is characterized in that the two parallel boundary Walls of the waveguide system are bounded in the plane remote from the outlet port by a semi-parabolic cylindrical surface, the generatrices of which are at right angles to the parallel boundary walls, and by a boundary surface of waveguide horn, arranged at the side of the outlet port of the waveguide system in the focal line of the semi-parabolic cylindrical surface, which horn radiates very high-frequency oscillations from the ultrahigh-frequency generator towards the semi-parabolic surface.
  • the horn is furthermore bounded by the parallel boundary surfaces of the Waveguide system and by a boundary surface leading to the outlet port and intercepting direct radiation from the waveguide horn towards the outlet port of the waveguide system.
  • FIG. 1 shows in a perspective view one embodiment of a high-frequency heating furnace according to the invention.
  • FIG. 2 is a cross sectional view of the high-frequency heating furnace of FIG. 1 and FIG. 3 shows a further development of the device according to the invention.
  • the high frequency heating furnace shown in a perspective view in FIG. 1, having a power of, for example, 5 kw., comprises a magnetron generator 1 which is capable of producing oscillations having a wavelength of, for example, 12 cms.
  • the output circuit of the magnetron generator 1 is connected via a coaxial conductor 2 and by means of a rectangular waveguide 3 with a waveguide system 6.
  • Waveguide system 6 is bounded by two parallel boundary walls 4, 5, for guiding the oscillations produced towards the outlet port 7 of the waveguide system 6.
  • the boundary walls 4, 5 are partly omitted in order to show the interior of the waveguide system 6.
  • the objects 8 to be heated for example, deepfrozen meals
  • conveyer belt 9 which is driven by driving rollers (not shown).
  • the rectangular waveguide 3 has connected therewith the tuning means 10, which may be constructed in known manner.
  • the two parallel boundary walls 4, 5 are closed in the plane remote from the outlet port 7 by a semi-parabolic cylindrical surface 11, the generatrices of which are orthogonal to the parallel boundary surfaces and by a boundary surface 12 of a waveguide horn 13, arranged at the side of the outlet port 7 of the waveguide system 6 in the focal line of the semi-parabolic cylindrical surface 11, which horn radiates the oscillations from the magnetron generator 1 towards the parabolic cylindrical surface.
  • the waveguide horn is bounded by the parallel boundary surfaces 4, 5 of the waveguide system 6 and a boundary surface 14 leading to the outlet port and intercepting direct radiation from the waveguide horn 13 towards the outlet port 7.
  • the output circuit of the magnetron generator 1 is coupled with the waveguide 3 by means of a linear radiator 15, which is arranged parallel to the generatrices of the semiparabolic cylindrical surface 11 and hence at right angles to the axis of the parabola.
  • the waveguide 3 is connected via a coupling piece 16 with the opening of the waveguide horn 13. If desired, the magnetron generator 1 may be coupled in a different manner with the waveguide 3, for example, by a loop coupling.
  • the waveguide system is connected with a pass channel 17 of conductive material surrounding the conveyor belt 9.
  • the pass channel 17 is bent over in a direction away from the conveyor belt 9 and shaped in the form of a rectangular trough 18, which is partly filled with absorbing material 20 (see FIG. 2) for absorbing the radiation from the magnetron generator 1 passing the conveyor belt 9, so
  • the opening of the waveguide horn 13, measured from the center of the radiation mouth, may be about 120.
  • the direction of radiation of the waveguide horn 13 is directed away from the outlet port 7.
  • the waveguide horn is particularly directed towards the semi-parabolic cylindrical surface and it has been found that a direct coupling of the objects to be heated with the waveguide horn 13 is thereby considerably reduced. Without adversely affecting the uniform electromagnetic field produced at the area of the outlet port 7, the dimensions of the waveguide system 6 can then be considerably reduced, for instance in order to reduce the width of the outlet port 7 in order to raise the power concentration at this area, which is illustrated in the cross sectional view of FIG. 2.
  • the height of the waveguide system 6, measured from the conveyor belt 9, is 30 cms. and the width of the outlet port 7 is 30 cms.
  • the distance between the two boundary walls 4, 5 is 4.3 cms.
  • the power concentration at the outlet port 7 amounts to 42 w./cm.
  • the device described has the practically important advantage that the radiation projecting beyond the high-frequency furnace is considerably reduced.
  • the direction of the electric field vector E of the field irradiated by the linear radiator 15 is parallel to the generatrices of the semi-parabolic cylindrical surface 11 and therefore it has a course at the outlet port 7 of the waveguide system 6 indicated in FIG. 1 by the broken arrows 19.
  • the energy vector is at right angles tothe electric field vector E and has therefore substantially no component in the pass direction of the conveyor belt 9, so that from the waveguide system 6 only stray radiation can emanate, which is, moreover, attenuated in the pass channel 17, for example, by a factor of about 26 db.
  • the length of the pass channel 17 is 28 cms. and the height 5 cms.
  • the high-frequency heating furnace according to the invention has a rugged mechanical structure and a freedom of dimensions and, moreover, produces a uniform heating while the stray radiation projecting beyond the waveguide system 6 is considerably attenuated.
  • FIG. 3 shows a further development of the high-frequency heating furnace according to the invention, in which elements corresponding with those of FIG. 1 are designated by the same reference numerals, to which an accent is added.
  • the stray radiation projecting beyond the pass channel 17 is found to be substantially the same as that of the In the high-frequency furnace concerned the maximum power of the stray radiation outside the furnace at the area of the operator is found to be less than 8 mw./cm.
  • the two waveguide systems 6' and 6 are arranged at a given distance from each other, so that time periods with high-frequency heating and without high-frequency heating alternate, which is advantageous for various uses, for example, for high-frequency heating of frozen meals from 20 to a temperature of C.
  • time period without heating the heat produced during the preceding period is capable of spreading over the object 8 to be heated, which is conducive to a uniform heating, since owing to local variations of the dielectric constant of the objects 8 to be heated local irregularities in the high-frequency heating may occur.
  • this is, for example, the case at the thawing instants of the frozen meals.
  • the uniformity of the heating was further improved by arranging, in the first place, the waveguide horns 13' and 13" of the waveguide systems each on one side of the pass channel 17 and, furthermore, by connecting the two waveguide systems 6 and 6 in opposite senses with the common pass channel 17, the
  • the high-frequency furnace has an important increase in efficiency, since the objects 8 to be heated pass by the outlet ports 7' and 7 of the waveguide systems 6' and 6" in different heating stages, so that these objects constitute different loads for the magnetron generators 1' and 1".
  • an improvement in efiiciency of, for example, 30% is obtained.
  • a high-frequency heating furnace which is distinguished by a considerable increase in efi'iciency and an improvement in the heating process and which exhibits a considerable increase in output power (10 kw.) and a minimum stray radiation.
  • High frequency heating apparatus comprising a high frequency generator and a waveguide system, said waveguide system comprising an enclosure having an open end and comprising first and second substantially parallel spaced apart wall portions, a third wall portion having a substantially parabolic contour arranged at right angles to and bounding said first and second wall portions and extending substantially from one end of the said open end to a predetermined point of said first and second wall portions remote from said open end, said parabolic portion defining a focal line at a position at one side of said open end, energy radiating means disposed at said focal line and arranged to radiate the high frequency energy towards said parabolic surface, means for coupling said generator to said radiating means, a fourth wall portion bounding said first and second Wall portions and extending between said radiating means and said predetermined point, a fifth wall portion forming a boundary surface extending between said radiating means and said open end and arranged to intercept the portion of direct energy radiation emanating from said radiating means towards said open end of said enclosure, and means for supporting objects to be heated at said open end of said
  • High frequency heating apparatus comprising a high frequency generator and a waveguide system, said waveguide system comprising an enclosure having an open end and comprising first and second substantially parallel spaced apart wall portions, a third wall portion having a substantially parabolic contour arranged at right angles to and bounding said first and second wall portions and extending substantially from one end of the said open end to a predetermined point of said first and second wall portions remote from said open end, said parabolic portion defining a focal line positioned to one side of said open end, waveguide radiating means arranged to radiate the high frequency energy towards said parabolic surface and located in said focal line, means for coupling said energy from said generator to said waveguide means, a fourth wall portion bounding said first and second wall portions and extending between said waveguide radiating means and said predetermined point, said fourth wall portion forming an extension of one wall of said waveguide radiating means, a fifth wall portion extending between said radiating means and said open end, and means for supporting objects to be heated at said open end of said enclosure.
  • High frequency heating apparatus comprising a high frequency generator and a waveguide system, said waveguide system comprising first, second, third and fourth wall portions defining an enclosure having an open end, said first wall portion comprising a portion of a parabolic cylindrical surface which defines a focal line located at one side of said open end, said second and third wall portions forming two parallel boundary surfaces enclosing the ends of said parabolic surface and substantially at right angles thereto, and said fourth wall portion forming said enclosure with said first, second and third wall portions, waveguide means for radiating the high frequency energy towards said parabolic surface and located substantially in the focal line of said parabolic cylindrical surface, means for coupling said energy from said genera tor to said waveguide means, said fourth wall portion forming an extension of one wall of said waveguide means, said waveguide system further comprising a fifth wall portion extending between the radiating end of said waveguide means and the open end of said waveguide system so as to intercept the direct energy radiation from said waveguide means towards said open end, and means for supporting objects to be heated at said open end
  • High frequency heating apparatus comprising a high frequency generator and a waveguide system, said waveguide system comprising first, .second, third and fourth wall portions defining an enclosure having an outlet port, said first wall portion comprising a semi-parabolic cylindrical reflecting surface, said second and third wall portions comprising two spaced parallel plates enclosing the ends of said parabolic surface and substantially at right angles thereto, and said fourth wall portion bounding said second and third Wall portions and forming said enclosure with said first, second and third wall portions, waveguide means having an open end facing said parabolic surface and located at the side of the outlet port of said waveguide system and in the focal line of the parabolic cylindrical surface, means for coupling said generator to said waveguide means, said fourth wall portion extending between said waveguide means and one end of said parabolic surface, a fifth wall portion extending between the open end of said waveguide means and said outlet port, and conveyor means for carrying objects to be heated past said outlet port of the waveguide system.
  • High frequency heating apparatus comprising a high frequency generator and a waveguide system, said waveguide system comprising first, second, third and fourth wall portions defining an enclosure having an outlet port, said second and third wall portions forming two parallel boundary surfaces of said waveguide system, said parallel boundary surfaces being bounded along a portion thereof by said first wall portion comprising a semiparabolic cylindrical surface having generatrices which are at right angles to said parallel boundary surfaces and along another portion thereof by said fourth wall portion, a waveguide horn located to the side of said outlet port and in the focal line of the parabolic cylindrical surface, said fourth wall portion forming a boundary surface of said waveguide horn which extends to one end of said parabolic surface, waveguide means for coupling the high frequency energy from said generator to said waveguide horn, said waveguide means being positioned so that the electric field vector of the electromagnetic energy supplied to said waveguide horn is parallel to the generatrices of said semi-parabolic cylindrical surface, said waveguide horn being further bounded by said second and third parallel boundary walls of the waveguide system and
  • Apparatus as described in claim 6 further comprising means for enclosing said outlet port comprising a rectangular trough composed of a conductive material and providing aligned openings in said second and third wall portions, a radiation absorbing material disposed in said enclosing means, said conveyor means comprising a conveyor belt member extending through said aligned openings for supporting objects to be heated at said outlet port, and shield means enclosing said conveyor belt at portions thereof adjacent said aligned openings.
  • High frequency heating apparatus comprising high frequency generator means and a plurality of waveguide systems, each of said waveguide systems comprising an enclosure having an open end and comprising first and second substantially parallel spaced apart wall portions, a third wall portion comprising a semi-parabolic cylindrical reflecting surface arranged at right angles to and bounding said first and second wall portions and extend ing substantially from one end of the said open end to a predetermined point of said first and second wall portions remote from said open end, said parabolic portion defining a focal line positioned to one side of said open end, waveguide means for radiating the high frequency energy towards said parabolic surface and located to one side of said open end and substantially in the focal line of said parabolic cylindrical surface, means for coupling said energy from said generator to said waveguide means, a fourth wall portion bounding said first and secondwall portions and extending between said waveguide radiating means and said predetermined point, said fourth wall portion forming an extension of one wall of said waveguide radiating means, a fifth wall portion forming a boundary surface extending between said waveguide radiating
  • said hollow channel member comprises at least first and second boundary surfaces disposed on opposite sides of said conveyor means and having at least one aperture in each of said boundary surfaces, predetermined ones of said waveguide systems being arranged on different sides of said conveyor means so that each of said openings of said waveguide systems is associated with a predetermined one of said apertures.
  • Apparatus as described in claim 12 wherein a first and second one of said waveguide systems are arranged in side by side relationship with one parallel boundary wall of said first waveguide system in contact with one of the parallel boundary walls of said second waveguide system.
  • Waveguide systems are spaced apart along the length direction of said conveyor means by predetermined distances sufficient to allow the heat developed in said objects in the preceding waveguide system to be uniformly distributed in said objects during its travel between successive waveguide systems.
  • High frequency heating apparatus comprising a high frequency generator and a waveguide system, said waveguide system comprising first, second, third and fourth wall portions defining an enclosure having an outlet port in a given plane, said first wall portion comprising a portion of a parabolic cylindrical surface which defines a focal line located at one side of said open end, said second and third wall portions forming two parallel boundary surfaces enclosing the ends of said parabolic surface and substantially at right angles thereto, and said fourth wall portion forming said enclosure with said first, second and third wall portions, waveguide means for radiating the high frequency energy towards said parabolic surface and located substantially in the focal line of said parabolic cylindrical surface, means for coupling said energy from said generator to said waveguide means, said waveguide system further comprising a fifth wall portion forming a boundary surface extending between the radiating end of said waveguide means and the open end of said waveguide system, said fifth wall portion extending parallel to the plane of said outlet port and spaced inwardly from said plane in the interior of said waveguide system thereby to intercept the direct

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Constitution Of High-Frequency Heating (AREA)
US195798A 1961-07-17 1962-05-18 Furnace for high-frequency heating with the aid of oscillations of very high frequency Expired - Lifetime US3209113A (en)

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NL267183 1961-07-17

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US (1) US3209113A (ja)
BE (1) BE620304A (ja)
CH (1) CH417798A (ja)
DE (1) DE1265320B (ja)
GB (1) GB959242A (ja)
NL (2) NL267183A (ja)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3474209A (en) * 1967-04-10 1969-10-21 Rca Corp Dielectric heating
US3710064A (en) * 1971-06-03 1973-01-09 Mac Millan Bloedel Ltd Microwave drying system
US5973306A (en) * 1996-07-11 1999-10-26 Lg Electronics Inc. Microwave oven with an outer and an inner housing and a waveguide for directing microwave energy with the inner housing

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2327700A1 (fr) * 1975-10-09 1977-05-06 Meisel Nicolas Four tunnel a micro-ondes pour le traitement en continu de produits alimentaires
JPS58176896A (ja) * 1982-04-10 1983-10-17 豊田合成株式会社 マイクロ波加熱装置

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB600101A (en) * 1945-09-29 1948-03-31 Alfred Brian Pippard Improvements in or relating to electromagnetic horns
FR1255297A (fr) * 1959-05-01 1961-03-03 Philips Nv Four haute fréquence pour chauffage à l'aide d'oscillations à ultra-hautes fréquences
US3027442A (en) * 1960-02-29 1962-03-27 Philips Corp High-frequency furnaces
US3102181A (en) * 1959-05-01 1963-08-27 Philips Corp High-frequency heating furnaces operating with very high frequencies

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB600101A (en) * 1945-09-29 1948-03-31 Alfred Brian Pippard Improvements in or relating to electromagnetic horns
FR1255297A (fr) * 1959-05-01 1961-03-03 Philips Nv Four haute fréquence pour chauffage à l'aide d'oscillations à ultra-hautes fréquences
US3102181A (en) * 1959-05-01 1963-08-27 Philips Corp High-frequency heating furnaces operating with very high frequencies
US3027442A (en) * 1960-02-29 1962-03-27 Philips Corp High-frequency furnaces

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3474209A (en) * 1967-04-10 1969-10-21 Rca Corp Dielectric heating
US3710064A (en) * 1971-06-03 1973-01-09 Mac Millan Bloedel Ltd Microwave drying system
US5973306A (en) * 1996-07-11 1999-10-26 Lg Electronics Inc. Microwave oven with an outer and an inner housing and a waveguide for directing microwave energy with the inner housing

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Publication number Publication date
BE620304A (ja)
NL113972C (ja)
NL267183A (ja)
CH417798A (de) 1966-07-31
GB959242A (en) 1964-05-27
DE1265320B (de) 1968-04-04

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