US3535483A - Microwave heating apparatus - Google Patents

Microwave heating apparatus Download PDF

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Publication number
US3535483A
US3535483A US863021A US3535483DA US3535483A US 3535483 A US3535483 A US 3535483A US 863021 A US863021 A US 863021A US 3535483D A US3535483D A US 3535483DA US 3535483 A US3535483 A US 3535483A
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United States
Prior art keywords
magnetron
constant
microwave
power
heating
Prior art date
Legal status (The legal status 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 status listed.)
Expired - Lifetime
Application number
US863021A
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English (en)
Inventor
Herbert August Puschner
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Fried Krupp AG
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Fried Krupp AG
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Filing date
Publication date
Priority claimed from DE19671591830 external-priority patent/DE1591830A1/de
Application filed by Fried Krupp AG filed Critical Fried Krupp AG
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Publication of US3535483A publication Critical patent/US3535483A/en
Anticipated expiration legal-status Critical
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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
    • H05B6/782—Arrangements for continuous movement of material wherein the material moved is food

Definitions

  • the apparatus includes a magnetron for generating the microwave heating energy and a source of power for supplying the magnetron with electricity at a constant voltage.
  • the present invention relates to microwave apparatus for heating nonmetallic materials, e.g. foodstuffs in the preparation of packaged foods.
  • the apparatus includes one or more magnetrons for the generation of microwaves or, more particularly, magnetrons for generating continuous waves.
  • Prior art apparatus for heating a material with microwaves has been beset with the problem of maintaining the microwave output power at a constant level. This requirement for a constant output power is critical if the material to be heated is to be heated uniformly.
  • VSWR voltage standing wave ratio
  • a known technique for reducing these variations in output power is to supply the continuous-wave magnetron with a constant anode current.
  • a number of means are available for controlling the anode current. It is possible to employ a controlled rectifier on the high voltage side, or, on the low voltage side, transductor or thyristor control means.
  • the microwave output may still vary as a result of the admissible range of reflection of the high frequency load impedance over a region of about i%, depending on the type of magnetron. These variations, caused by the mismatching of the high frequency load impedance, are too great for many industrial uses.
  • An object of the present invention is to stabilize the power produced by microwave heating apparatus.
  • Power supplies producing a constant output voltage may be manufactured with less expense than the customary power supplies employing a constant current control. This is especially true for microwave generating apparatus of medium to high output power which, as a rule, employs a number of continuous-wave magnetrons. Because of their simpler construction the constant voltage power supplies are also more reliable an easier to maintain.
  • FIG. 1 is a schematic diagram, in elevation, of a continuous-flow heating plant employing a number of microwave generators.
  • FIG. 2 is the generator diagram (Rieke-diagram) of a continuous-wave magnetron operated with a constant anode current regulator.
  • FIG. 3 is the generator diagram of a continuous-wave magnetron operated with a constant input voltage regulator, according to the present invention.
  • FIG. 4 is a schematic diagram of the apparatus, according to the present invention, which generates microwaves for the heating apparatus of FIG..1.
  • FIG. 1 a continuous-flow plant for heating meat 11 with the aid of microwave energy.
  • This type of plant may be used, for example, to heat meat as a part of the process of food packing.
  • the meat 11 is introduced onto the conveyor belt 13 through the tube 12.
  • the microwave energy heats the meat 11 gently yet quickly and uniformly.
  • the heated meat is then dropped into the funnel 21 and is conveyed to the next station for processing.
  • the meat to be heated makes frequent quick changes in its consistency as it passes through the radiation area of each microwave energy source. From the electrical viewpoint, this means that both the magnitude and phase of the load impedance Z of the generator are extremely variable. There are, as a result, strong variations in the amount of power received by the meat.
  • FIGS. 2 and 3 wherein the load impedance is represented in polar coordinates by the phase l/A related to the reference plane of the generator output waveguide, and by s, the voltage standing wave ratio (VSWR), the dashed curve b illustrates one example of the many possibilities for change in the load impedance.
  • I is the distance from the first voltage minimum on the waveguide to the reference plane of the generator output waveguide
  • 7 ⁇ is the wavelength of the waveguide.
  • the advantage of the apapratus according to the present invention may be seen by comparing two diagrams.
  • the generator diagram of FIG. 2 represents the prior art continuous-wave magnetron system which utilizes constant current regulation.
  • the family of curves a are lines of constant output power. If the load impedance Z varies in a manner shown by the dashed curve b, the power output finds a minimum value at point d (P -1.3 kw.) and a maximum value at point 1 (P +0.5 kw.). The percentage variation thus runs from 25% to +10%.
  • Such a variation is inadmissably high for many heating applications since, for example with the continuous-flow heating plants of FIG. 1, it produces a nonuniform temperature distribution within the meat 11 along the direction of flow.
  • FIG. 4 illustrates the preferred embodiment of the circuit according to the present invention.
  • An induction voltage regulator 1 an adjustable transformer which is auto matically regulated by a motor when under load, forms the constant voltage source. This type of regulator is described on pages 365 and 366 of volume 14 of the McGraw-Hill Encyclopedia of Science and Technology (New York, 1960).
  • the primary of the induction regulator 1 is connected directly to the line 2.
  • the secondary which receives a constant three-phase voltage, is connected to a high voltage transformer 3.
  • the transformer 3 feeds a rectifier circuit 4 which, in turn, is connected to the continuous-wave magnetron 5.
  • the magnetron 5 generates microwave energy which is fed via a waveguide 6 to the load 7, such as the load impedance Z.
  • magnetron as used in this application is intended to include all cross-field microwave generating devices known in the art.
  • Apparatus for the microwave heating of a foodstuff of the type which presents, with respect to microwaves, an electrical impedance whose magnitude and phase angle vary by a substantial amount as the foodstuff is heated comprising, in combination: a microwave energy heating source; means for delivering the foodstuff past said source; a magnetron connected to deliver microwave energy to said heating source; and power supply means connected for supplying operating power to said magnetron at a constant voltage, whereby the heating power from said source remains substantially constant as the load impedance presented by the foodstuff varies.
  • said power supply means comprises: a high voltage transformer having a primary winding and a secondary winding; and an induction voltage regulator connected to said primary winding.
  • apparatus for the microwave heating of a foodstuff of the type which presents, with respect to microwaves, an electrical impedance whosemagnitude and phase angle vary by a substantial amount as the foodstuff is heated which apparatus includes a microwave energy heating source and means for' delivering the foodstuff past such source, the improvement comprising: a magnetron connected to deliver microwave energy to said heating source; and power supply means connected for supplying operating power to said magnetron at a constant voltage, whereby the heating power from said source remains substantially constant as the load impedance presented by the foodstuff varies.
  • a method for the microwave heating of a foodstuff of a type which presents, with respect to microwaves, an electrical impedance whose magnitude and phase angle vary by a substantial amount as the foodstuff is heated comprising: causing the foodstuff to flow past a microwave energy source so that the foodstuff constitutes part of the electrical load of the source; delivering microwave heating energy from the source to the foodstuff; generating the microwave heating energy in a magnetron forming part of the energy source; and supplying the magnetron with operating power at a constant voltage for maintaining the output power from the source substantially constant in response to variations in the load impedance presented by the foodstuff.

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  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Constitution Of High-Frequency Heating (AREA)
US863021A 1967-02-10 1969-09-29 Microwave heating apparatus Expired - Lifetime US3535483A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE19671591830 DE1591830A1 (de) 1967-02-10 1967-02-10 Vorrichtung zur Erwaermung von Gut mit einem Mikrowellengenerator
DEB0091122 1967-02-10

Publications (1)

Publication Number Publication Date
US3535483A true US3535483A (en) 1970-10-20

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US863021A Expired - Lifetime US3535483A (en) 1967-02-10 1969-09-29 Microwave heating apparatus

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US (1) US3535483A (enrdf_load_stackoverflow)
FR (1) FR1557959A (enrdf_load_stackoverflow)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3961569A (en) * 1974-08-15 1976-06-08 The United States Of America As Represented By The Secretary Of The Army Apparatus for continuous microwave sterilization of food in pouches
US4198554A (en) * 1977-07-01 1980-04-15 Cober Electronics, Inc. Method and apparatus for microwave vulcanization of extruded rubber profiles
US4286133A (en) * 1979-05-29 1981-08-25 Whirlpool Corporation Bi-rotational microwave oven turntable/rotisserie

Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2648772A (en) * 1949-02-15 1953-08-11 Raytheon Mfg Co Magnetron control circuits
US2847637A (en) * 1956-09-21 1958-08-12 Philamon Lab Inc Voltage regulator for a. c. power supplies
US3263052A (en) * 1963-09-11 1966-07-26 Cryodry Corp Power distribution system for microwave process chambers
US3302060A (en) * 1963-07-17 1967-01-31 Philips Corp Control system for regulating the current in a magnetron tube
US3321314A (en) * 1965-09-20 1967-05-23 Cryodry Corp Process for cooking bacon with microwave energy
US3392309A (en) * 1965-05-24 1968-07-09 Philips Corp Magnetron power supply and cathode heater circuit

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2648772A (en) * 1949-02-15 1953-08-11 Raytheon Mfg Co Magnetron control circuits
US2847637A (en) * 1956-09-21 1958-08-12 Philamon Lab Inc Voltage regulator for a. c. power supplies
US3302060A (en) * 1963-07-17 1967-01-31 Philips Corp Control system for regulating the current in a magnetron tube
US3263052A (en) * 1963-09-11 1966-07-26 Cryodry Corp Power distribution system for microwave process chambers
US3392309A (en) * 1965-05-24 1968-07-09 Philips Corp Magnetron power supply and cathode heater circuit
US3321314A (en) * 1965-09-20 1967-05-23 Cryodry Corp Process for cooking bacon with microwave energy

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3961569A (en) * 1974-08-15 1976-06-08 The United States Of America As Represented By The Secretary Of The Army Apparatus for continuous microwave sterilization of food in pouches
US4198554A (en) * 1977-07-01 1980-04-15 Cober Electronics, Inc. Method and apparatus for microwave vulcanization of extruded rubber profiles
US4286133A (en) * 1979-05-29 1981-08-25 Whirlpool Corporation Bi-rotational microwave oven turntable/rotisserie

Also Published As

Publication number Publication date
FR1557959A (enrdf_load_stackoverflow) 1969-02-21

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