US3478187A - Heating arrangement utilizing microwaves - Google Patents

Heating arrangement utilizing microwaves Download PDF

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US3478187A
US3478187A US673506A US3478187DA US3478187A US 3478187 A US3478187 A US 3478187A US 673506 A US673506 A US 673506A US 3478187D A US3478187D A US 3478187DA US 3478187 A US3478187 A US 3478187A
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microwave
elements
microwaves
heating
power
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US673506A
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Nils Bertil Agdur
Per Olof Gunnar Hedvall
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SKANDINAVISKA PROCESSINSTRUMENT AB
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SKANDINAVISKA PROCESSINSTRUMENT AB
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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
    • 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
    • H05B2206/00—Aspects relating to heating by electric, magnetic, or electromagnetic fields covered by group H05B6/00
    • H05B2206/04—Heating using microwaves
    • H05B2206/046—Microwave drying of wood, ink, food, ceramic, sintering of ceramic, clothes, hair

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  • the structure includes a conductive base plate from which extend a plurality of T-shaped crosssection microwave elements disposed in regular array.
  • the elements are spaced from each other by a distance which is so much smaller than the free-space operating wavelength of the microwaves that the microwaves propagate along the structure with 'a phase velocity which is less than the free-space velocity of the microwaves.
  • the present invention refers to apparatus for heating materials by means of microwave energy from a microwave source.
  • An object of the invention is to provide e.g. the paper and wood industry with a simple and reliable device for heating and for drying of paper, pulp and other cellulose products, wood, glue, dyes etc.
  • the heating (drying) power can be controlled simply and instantaneously by temperature and humidity sensors.
  • Another object of the invention is to provide a simple device for heating, boiling and frying foodstuffs. In such a device the preparation times will be much shorter than for conventional methods.
  • Apparatus according to this invention is characterized in that a microwave source is coupled to a microwave structure having the property that the microwave energy propagates along the structure while remaining concentrated to a narrow region near the structure and in that the material to be heated is placed in or passes this narrow region.
  • FIG. 1 shows a heating device with central microwave I power input
  • FIG. 2 shows a part of the device of FIG. I seen from above and with some field lines indicated
  • FIG. 3 shows a part of the device of BIG. 1 with indicated field lines
  • FIG. 4 shows a modified cross section of the elements for a device according to FIG. 1,
  • FIG. 5 shows the vertical distribution of energy between two elements of the device
  • FIG. 6 shows a modification of the arrangement of FIG. .2,
  • FIG. 7 shows heating device with circumferential power input
  • FIG. 8 shows a modification of the device of FIG. 1 such that the power is fed in at one end of the structure.
  • the device shown in FIG. 1 comprises amicrowave input 10-11 and a microwave structure (heating table) 13-14-15.
  • the input consists of a waveguide 10 and a coupling loop 11 for the microwave power.
  • the heating 3,478,187 Patented Nov. 11, 1969 ICC table consists of a number of mutually similar T-shaped metal elements 14 mounted on a metal base plate 13.
  • the coupling loop 11 has one end directly connected to one of the elements 14, the other end projects into the central part of the waveguide 10.
  • the microwave power from the waveguide 10 is fed into and propagated both ways by the microwave structure formed by the elements 14 and the base plate 13.
  • At either end of this structure there have been placed essentially vertical metal plates 15 furnished with slit-shaped quarter-wavelength chokes 16.
  • the purpose of the metal plates 15 is to reflect back towards the center of the structure that part of the microwave power that has not been absorbed in the material to be heated.
  • the material is passed through the slits 16 and immediately above the elements 14.
  • the energy absorbers 17 can comprise glass tubes with water running through them in which part of the excess microwave power will be absorbed and converted to heat.
  • the elements 14 are elongated and extend perpendicular to the direction of transmission of the microwave power along the microwave structure (heating table) 13 14-15. Further, the elements are arranged in such a way that the distance between corresponding points on adjacent elements is less than half the free-space operating wavelength of the microwaves. This distance can either be constant as shown in FIG. 1 or can increase gradually away from the input (increasing phase velocity) or can decrease gradually (decreasing phase velocity).
  • a microwave structure such as the one shown in FIGS. 1-3 has the property that the microwaves propagate with a phase velocity that is less than the free-space velocity. The microwave energy will then be closely bound to the microwave structure.
  • the field configuration is outlined in FIGS. 2P3.
  • the electric field (solid lines) is mainly concentrated near the gaps between the flanges of adjacent elements, whereas the magnetic field lines (broken lines) mainly close round the webs of the elements 14.
  • the concentration of the electric field-with consequent high energy densityclose to the upper surface of the microwave structure can be made more pronounced by means of elements having sharp edges as shown in FIG. 4.
  • FIG. 5 shows schematically how the electric microwave energy is distributed along a vertical line between two elements of the type shown on the left in the figure. It is seen that the energy is concentrated near. the level of the flanges and decreases exponentially above the structure.
  • the material to be heated is placed on top of the structure (heating table) where it'will be exposed to strong electric fields. Dissipation in the material will causepart of the microwave power to be converted into heat inside the material and the propagating wave will be damped. Because the field concentrates near to the gaps between the elements 14 there exists a risk of local burns in solid materials. This can be avoided if such materials, e.g. paper, are made to move along the structure. If the dielectric constant of the material is greater than that of air, the electric energy will tend to concentrate in the material. The exponential decrease of the energy density will also be less marked and the microwave power can permeate and heat even fairly thick materials.
  • FIG. 6 shows a modified microwave sructure.
  • the elements 64 are essentially rectangular when seen from above.
  • the elements 64 comprise a vertical stern and a horizontal flange so that a vertical section through an element will still be similar to that shown in FIG. 5.
  • the elements 64 are arranged in a regular two-dimensional array on a base plate 13in such'a way that the distance between corresponding points on two diagonally adjacent elements is less than half the free-space operating wavelength of the microwaves.
  • the elements then form a plane microwave structure that allows the microwaves to propagate in several directions with a phase velocity less than the free-space velocity.
  • the field configuration is such that the electric field is concentrated to the region between the edges of the flanges of the T-shaped elements 64 and the magnetic field lines mainly close around the stems of these elements.
  • the embodiment shown in FIG. 7 comprises a number of concentric circular elements 74 with T-shaped cross section.
  • the elements are mounted on a circular base plate 13.
  • a vertical reflector tube 75 is connected to the rim of the base plate.
  • the microwave power is fed in from a circularly cylindrical waveguide 70.
  • the coupling loops 71 have one end connected to the inner wall of the tube 75, the other end projects into the wave-guide 70.
  • one part 82 of the microwave structure (heating table) has a comparatively small curvature and the other part 83 has a greater curvature.
  • the microwave input 80-81 is connected to a reflector at the free end of the second part 83.
  • the elements 84 of the microwave structure 82-83 are T-shaped as in the abovedescribed embodiments.
  • the microwave structure can bemade cylindrical and arranged for internal or external heating of tubes.
  • the shape of the structure may be adapted to suit the material for which it is to be used.
  • the T-shaped elements and base plate need not be made separately but may, for instance, be manufactured by bending (corrugating) sheet-metal, e.g. copper, to obtain the desired profile.
  • bending (corrugating) sheet-metal e.g. copper
  • microwave structure will 'be made up of a continuous copper surface without soldering joints which will decrease the undesirable losses of microwave power.
  • the manufacturing procedure should be both simple and inexpensive.
  • the microwave input can also be modified in several ways.
  • the microwave structure may form an integral part of a microwave generator, for instance a distributed transistor amplifier.
  • Heating apparatus utilizing microwave power comprising a source of microwave power wherein the microwaves have a given operating wavelength, and a microwave structure connected to said source of microwave power, said microwave structure including a plurality of mutually similar microwave elementspaced from each other in a reglar array, the distance between corresponding points of adjust microwave elements being so much smaller than half the free-space operating wavelength of the microwaves and said microwave elements cooperating with each other so that the microwaves propagate along the microwave structure with a phase velocity less than the free-space velocity whereby microwave energy is concentrated in the microwave structure itself and in a region adjacent to the microwave structure.
  • said microwave structure comprises a conductive base plate and the microwave elements are elongate elements made of conductive material and having a generally T-shaped crosssection, the foot of each element being in immediate electric contact with said conductive base plate.
  • Apparatus according to claim 2 wherein the generally T-shaped cross-section of the microwave elements has a gradual transition 'between its cross arm and its long arm and that the cross arm has a sharp edge.
  • said microwave structure comprises a conductive base plate, and said microwave elements are arranged in a two-dimensional array, said elements being made of conductive material and of a substantially T-shaped cross-section having a top flange and a stem, the stems of the elements being in immediate electric contact with the conductive base plate.
  • the microwave structure is bent and comprises at least one part with small curvature and a second part with more pro nounced curvature, said microwave source being connected to the second part.
  • Apparatus according to claim 1 wherein the microwave source is connected to a central part of the microwave structure.
  • the microwave structure includes, along at least one edge, a conductive surface member disposed perpendicular to the direction of propagation of the microwaves for reflecting microwave power toward the material to be heated.
  • microwave structure includes microwave energy absorber means for absorbing such microwave power as has not been absorbed in the material to be heated.

Description

N. B. AGDUR ET AL BEAT ING ARRANGEMENT UT ILI Z ING MICROWAVES' Nov. 11, 1969 Filed ob". e, we?
2 Sheets-Sheet 1 jiii Q n u. n N 9 a t o a V n N u I G T an u 9- qmtnivi.
Nov. 11, 1969 N. B. AGDUR ET AL 3,478,187
HEATING ARRANGEMENT UTILIZING MICROWAYES Filed Oct. 6, 1967 2 Sheets-Sheet 2 1 v l v w ,1 v I u \j g a 1 TJTENTORQ Nu- BG\TH.. RGDQI. PIC. 01.0! umnaQ cram.
N mad $4 United States Patent 0..
3,478,187 HEATING ARRANGEMENT UTILIZING MICROWAVES Nils Bertil Agdur, Danderyd, and Per Olof Gunnar Hedvall, Akersberga, Sweden, assignors to Skandinaviska Processinstrument AB, Stockholm, Sweden, a company of Sweden Filed Oct. 6, 1967, Ser. No. 673,506 Claims priority, application Sweden, Oct. 19, 1966, 14,242/66 Int. Cl. Hb 9/06 US. Cl. 21910.55 12 Claims ABSTRACT OF THE DISCLOSURE There is disclosed a microwave heating apparatus which includes a source of microwave power which generates microwaves having a given operating wavelength. A microwave structure is connected to the source of microwave power. The structure includes a conductive base plate from which extend a plurality of T-shaped crosssection microwave elements disposed in regular array. The elements are spaced from each other by a distance which is so much smaller than the free-space operating wavelength of the microwaves that the microwaves propagate along the structure with 'a phase velocity which is less than the free-space velocity of the microwaves.
The present invention refers to apparatus for heating materials by means of microwave energy from a microwave source.
An object of the invention is to provide e.g. the paper and wood industry with a simple and reliable device for heating and for drying of paper, pulp and other cellulose products, wood, glue, dyes etc. In this device the heating (drying) power can be controlled simply and instantaneously by temperature and humidity sensors. Another object of the invention is to provide a simple device for heating, boiling and frying foodstuffs. In such a device the preparation times will be much shorter than for conventional methods.
Apparatus according to this invention is characterized in that a microwave source is coupled to a microwave structure having the property that the microwave energy propagates along the structure while remaining concentrated to a narrow region near the structure and in that the material to be heated is placed in or passes this narrow region.
The invention will be described in detail in connection with the accompanying schematic drawings, where FIG. 1 shows a heating device with central microwave I power input,
FIG. 2 shows a part of the device of FIG. I seen from above and with some field lines indicated,
FIG. 3 shows a part of the device of BIG. 1 with indicated field lines,
FIG. 4 shows a modified cross section of the elements for a device according to FIG. 1,
FIG. 5 shows the vertical distribution of energy between two elements of the device,
FIG. 6 shows a modification of the arrangement of FIG. .2,
FIG. 7 shows heating device with circumferential power input, and
FIG. 8 shows a modification of the device of FIG. 1 such that the power is fed in at one end of the structure.
The device shown in FIG. 1 comprises amicrowave input 10-11 and a microwave structure (heating table) 13-14-15. The input consists of a waveguide 10 and a coupling loop 11 for the microwave power. The heating 3,478,187 Patented Nov. 11, 1969 ICC table consists of a number of mutually similar T-shaped metal elements 14 mounted on a metal base plate 13. The coupling loop 11 has one end directly connected to one of the elements 14, the other end projects into the central part of the waveguide 10. Thus the microwave power from the waveguide 10 is fed into and propagated both ways by the microwave structure formed by the elements 14 and the base plate 13. At either end of this structure there have been placed essentially vertical metal plates 15 furnished with slit-shaped quarter-wavelength chokes 16. The purpose of the metal plates 15 is to reflect back towards the center of the structure that part of the microwave power that has not been absorbed in the material to be heated. The material is passed through the slits 16 and immediately above the elements 14. To protect the microwave source against excessive reflected powerfor instance when no material to be heated is present in the device-energy absorbers 17 have been placed adjacent to the metal plates 15. The energy absorbers 17 can comprise glass tubes with water running through them in which part of the excess microwave power will be absorbed and converted to heat.
From FIG. 2 it is seen that the elements 14 are elongated and extend perpendicular to the direction of transmission of the microwave power along the microwave structure (heating table) 13 14-15. Further, the elements are arranged in such a way that the distance between corresponding points on adjacent elements is less than half the free-space operating wavelength of the microwaves. This distance can either be constant as shown in FIG. 1 or can increase gradually away from the input (increasing phase velocity) or can decrease gradually (decreasing phase velocity).
A microwave structure such as the one shown in FIGS. 1-3 has the property that the microwaves propagate with a phase velocity that is less than the free-space velocity. The microwave energy will then be closely bound to the microwave structure. The field configuration is outlined in FIGS. 2P3. The electric field (solid lines) is mainly concentrated near the gaps between the flanges of adjacent elements, whereas the magnetic field lines (broken lines) mainly close round the webs of the elements 14. The concentration of the electric field-with consequent high energy densityclose to the upper surface of the microwave structure can be made more pronounced by means of elements having sharp edges as shown in FIG. 4.
FIG. 5 shows schematically how the electric microwave energy is distributed along a vertical line between two elements of the type shown on the left in the figure. It is seen that the energy is concentrated near. the level of the flanges and decreases exponentially above the structure.
The material to be heated (dried) is placed on top of the structure (heating table) where it'will be exposed to strong electric fields. Dissipation in the material will causepart of the microwave power to be converted into heat inside the material and the propagating wave will be damped. Because the field concentrates near to the gaps between the elements 14 there exists a risk of local burns in solid materials. This can be avoided if such materials, e.g. paper, are made to move along the structure. If the dielectric constant of the material is greater than that of air, the electric energy will tend to concentrate in the material. The exponential decrease of the energy density will also be less marked and the microwave power can permeate and heat even fairly thick materials.
FIG. 6 shows a modified microwave sructure. Instead of elongated elements 14 as in FIG. 2 the elements 64 are essentially rectangular when seen from above. The elements 64 comprise a vertical stern and a horizontal flange so that a vertical section through an element will still be similar to that shown in FIG. 5. The elements 64 are arranged in a regular two-dimensional array on a base plate 13in such'a way that the distance between corresponding points on two diagonally adjacent elements is less than half the free-space operating wavelength of the microwaves. The elements then form a plane microwave structure that allows the microwaves to propagate in several directions with a phase velocity less than the free-space velocity. The field configuration is such that the electric field is concentrated to the region between the edges of the flanges of the T-shaped elements 64 and the magnetic field lines mainly close around the stems of these elements.
The embodiment shown in FIG. 7 comprises a number of concentric circular elements 74 with T-shaped cross section. The elements are mounted on a circular base plate 13. A vertical reflector tube 75 is connected to the rim of the base plate. The microwave power is fed in from a circularly cylindrical waveguide 70. The coupling loops 71 have one end connected to the inner wall of the tube 75, the other end projects into the wave-guide 70. The advantage of this circumferential power input is that the attenuation of the microwaves due to energyabsorption in the material will be counteracted by the geometric focussing of the waves.
In the embodiment shown in FIG. 8 one part 82 of the microwave structure (heating table) has a comparatively small curvature and the other part 83 has a greater curvature. The microwave input 80-81 is connected to a reflector at the free end of the second part 83. The elements 84 of the microwave structure 82-83 are T-shaped as in the abovedescribed embodiments. The material to be heated (dried), eg a paper web 89, touches the slightly curved part 82 of the microwave structure.
Many'other possible arrangements come within the scope of the invention as defined in the appended claims. Thus the microwave structure can bemade cylindrical and arranged for internal or external heating of tubes. In general the shape of the structure may be adapted to suit the material for which it is to be used.
Further, the T-shaped elements and base plate need not be made separately but may, for instance, be manufactured by bending (corrugating) sheet-metal, e.g. copper, to obtain the desired profile. In this way microwave structure will 'be made up of a continuous copper surface without soldering joints which will decrease the undesirable losses of microwave power. At the same time the manufacturing procedure should be both simple and inexpensive.
The microwave input can also be modified in several ways. Thus the microwave structure may form an integral part of a microwave generator, for instance a distributed transistor amplifier.
What is claimed is:
1. Heating apparatus utilizing microwave power comprising a source of microwave power wherein the microwaves have a given operating wavelength, and a microwave structure connected to said source of microwave power, said microwave structure including a plurality of mutually similar microwave elementspaced from each other in a reglar array, the distance between corresponding points of adjust microwave elements being so much smaller than half the free-space operating wavelength of the microwaves and said microwave elements cooperating with each other so that the microwaves propagate along the microwave structure with a phase velocity less than the free-space velocity whereby microwave energy is concentrated in the microwave structure itself and in a region adjacent to the microwave structure.
2. Apparatus according to claim 1 wherein said microwave structure comprises a conductive base plate and the microwave elements are elongate elements made of conductive material and having a generally T-shaped crosssection, the foot of each element being in immediate electric contact with said conductive base plate.
3. Apparatus according to claim 2 wherein the generally T-shaped cross-section of the microwave elements has a gradual transition 'between its cross arm and its long arm and that the cross arm has a sharp edge.
4. Apparatus acording to claim 2 wherein the T-shaped elements and the base plate are manufactured integrally by bending sheet-metal to obtain the desired profile.
5. Apparatus according to claim 2 wherein the microwave elements are shaped as concentic circles.
6. Apparatus according to claim 5 wherein the microwave source is connected to the circumference of the circular structure.
7. Apparatus according to claim 1, wherein said microwave structure comprises a conductive base plate, and said microwave elements are arranged in a two-dimensional array, said elements being made of conductive material and of a substantially T-shaped cross-section having a top flange and a stem, the stems of the elements being in immediate electric contact with the conductive base plate.
8. Apparatus according to claim 1 wherein the microwave structure is bent and comprises at least one part with small curvature and a second part with more pro nounced curvature, said microwave source being connected to the second part.
9. Apparatus according to claim 1 wherein the microwave source is connected to a central part of the microwave structure.
10. Apparatus according to claim 1 wherein the microwave structure includes, along at least one edge, a conductive surface member disposed perpendicular to the direction of propagation of the microwaves for reflecting microwave power toward the material to be heated.
11. Apparatus accordin gto claim 10 wherein the conductive surface member includes an opening for passage of the material to be heated.
12. Apparatus according to claim 1 wherein the microwave structure includes microwave energy absorber means for absorbing such microwave power as has not been absorbed in the material to be heated.
References Cited UNITED STATES PATENTS 2,492,187 12/1949 Rusca 219-1061 2,960,777 11/1960 Doll 219-10.61 X 3,205,334 9/1965 'Manwaring 2l9--10.61 3,263,052 7/1966 Jeppson et a1. 21910.61 X 3,271,552 9/1966 Krajewski 2l9-10..55
JOSEPH V. TRUHE, Primary Examiner L. H. Bender, Assistant Examiner
US673506A 1966-10-19 1967-10-06 Heating arrangement utilizing microwaves Expired - Lifetime US3478187A (en)

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Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3555232A (en) * 1968-10-21 1971-01-12 Canadian Patents Dev Waveguides
US3591751A (en) * 1969-09-26 1971-07-06 Teckton Inc Browning apparatus for use in a microwave oven
US3885118A (en) * 1971-04-15 1975-05-20 Husqvarna Vapenfabriks Ab Microwave oven having controlled wave propagating means
US3891818A (en) * 1971-04-15 1975-06-24 Husqvarna Vapenfabriks Ab A filtering device for restrictively propagating incoming high-frequency waves
US4019009A (en) * 1974-02-08 1977-04-19 Matsushita Electric Industrial Co., Ltd. Microwave heating apparatus
US4121078A (en) * 1975-04-30 1978-10-17 Matsushita Electric Industrial Co., Ltd. Microwave heating apparatus
US4329135A (en) * 1980-03-19 1982-05-11 Technics Lambda International Device for the continuous thermal or thermo-chemical treatment of objects by emission of micro-waves
US4816632A (en) * 1987-01-08 1989-03-28 U.S. Philips Corporation Multi-resonant microwave oven having an improved microwave distribution
US4870235A (en) * 1987-06-02 1989-09-26 U.S. Philips Corporation Microwave oven detecting the end of a product defrosting cycle
US4871891A (en) * 1987-06-02 1989-10-03 U.S. Philips Corporation Microwave oven providing defrosting control
US4889966A (en) * 1988-08-08 1989-12-26 Apv Magnetronics Limited Apparatus for heating discrete packages of products using microwaves
US5580595A (en) * 1993-11-01 1996-12-03 Unilever Patent Holdings B.V. Process for the preparation of a food product

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
SE385027B (en) * 1974-09-27 1976-05-31 Mo Och Domsjoe Ab PROCEDURE FOR RELEASING CELLULOSIAN FIBERS

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2492187A (en) * 1945-01-05 1949-12-27 Ralph A Rusca Method and apparatus for electrical heating
US2960777A (en) * 1957-01-07 1960-11-22 Bemberg Ag Device for the removal of liquids adhering to running textile threads
US3205334A (en) * 1963-07-30 1965-09-07 Radio Frequency Company Inc Textile thread heating apparatus
US3263052A (en) * 1963-09-11 1966-07-26 Cryodry Corp Power distribution system for microwave process chambers
US3271552A (en) * 1963-02-01 1966-09-06 Litton Prec Products Inc Microwave heating apparatus

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2492187A (en) * 1945-01-05 1949-12-27 Ralph A Rusca Method and apparatus for electrical heating
US2960777A (en) * 1957-01-07 1960-11-22 Bemberg Ag Device for the removal of liquids adhering to running textile threads
US3271552A (en) * 1963-02-01 1966-09-06 Litton Prec Products Inc Microwave heating apparatus
US3205334A (en) * 1963-07-30 1965-09-07 Radio Frequency Company Inc Textile thread heating apparatus
US3263052A (en) * 1963-09-11 1966-07-26 Cryodry Corp Power distribution system for microwave process chambers

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3555232A (en) * 1968-10-21 1971-01-12 Canadian Patents Dev Waveguides
US3591751A (en) * 1969-09-26 1971-07-06 Teckton Inc Browning apparatus for use in a microwave oven
US3885118A (en) * 1971-04-15 1975-05-20 Husqvarna Vapenfabriks Ab Microwave oven having controlled wave propagating means
US3891818A (en) * 1971-04-15 1975-06-24 Husqvarna Vapenfabriks Ab A filtering device for restrictively propagating incoming high-frequency waves
US4019009A (en) * 1974-02-08 1977-04-19 Matsushita Electric Industrial Co., Ltd. Microwave heating apparatus
US4121078A (en) * 1975-04-30 1978-10-17 Matsushita Electric Industrial Co., Ltd. Microwave heating apparatus
US4329135A (en) * 1980-03-19 1982-05-11 Technics Lambda International Device for the continuous thermal or thermo-chemical treatment of objects by emission of micro-waves
US4816632A (en) * 1987-01-08 1989-03-28 U.S. Philips Corporation Multi-resonant microwave oven having an improved microwave distribution
US4870235A (en) * 1987-06-02 1989-09-26 U.S. Philips Corporation Microwave oven detecting the end of a product defrosting cycle
US4871891A (en) * 1987-06-02 1989-10-03 U.S. Philips Corporation Microwave oven providing defrosting control
US4889966A (en) * 1988-08-08 1989-12-26 Apv Magnetronics Limited Apparatus for heating discrete packages of products using microwaves
US5580595A (en) * 1993-11-01 1996-12-03 Unilever Patent Holdings B.V. Process for the preparation of a food product

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FI53907C (en) 1978-08-10
DE1615118A1 (en) 1970-05-06
FI53907B (en) 1978-05-02
SE311055B (en) 1969-05-27
FR1563678A (en) 1969-04-18
DE1615118C3 (en) 1978-03-09
DE1615118B2 (en) 1977-07-14
GB1162055A (en) 1969-08-20

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