US 3436507 A
Description (OCR text may contain errors)
April 1, 1969 H. A. PUSCHNER 3,436,507
DEVICE FOR HEATING NONMETALLIC MATERIALS, MORE PARTICULARLY FOODSTUFF-S BY MICROWAVE ENERGY IN A CAVITY RESONATOR Filed June 10. 1966 9%WAM United States Patent US. Cl. 219-1055 5 Claims ABSTRACT OF THE DISCLOSURE A microwave oven is fed from the top through an input coupling system connecting the heating chamber with the microwave generator. A sealed stirrer is in the heating chamber supported for rotation coaxially to the input coupling system and has a primary radiator and an array of secondary radiators so that rotation of the stirrer keeps the field in the oven essentially uniform.
The invention relates to a device for heating nonmetallic materials, more particularly foodstufis, by microwave energy in a cavity resonator.
In such devices the cavity resonator serves as the heating chamber and a coupling system is provided which connects the heating chamber with the microwave generator, an oscillation-type converter being provided which rotates in the heating chamber. Hitherto, the converter has been provided apart from the coupling system, on the assumption that by this an especially uniform field distribution and uniform heating of the material would be achieved. Practice has shown however that with such an arrangement, undesirably high field strength differences occur in the heating chamber which cause nonuniform heating and necessitate correspondingly longer heating times in order to bring the entire material to the desired final temperature.
The present invention is based on the consideration that an arrangement of the converter apart from the coupling system results in an operative mechanism which is difiicult to supervise and is independent of the otherwise usual geometric relationships. Starting from this consideration, in a device constructed according to the invention, the converter is arranged to rotate coaxially to the input coupling system. As a result of this, by suitably distributing the secondary radiators of the oscillation-type converter relative to the coupling system, it is possible to produce a desired field distribution and to achieve excitation of only such oscillation modes which result in superimpositions of the desired field distribution in the chamber.
A particularly advantageous utilisation of the coaxial arrangement of the input coupling system and oscillationtype converter is achieved if the wave coming from the coaxial input is coupled to the oscillation-type converter through a coaxial conical transition. The oscillation-type converter can consist of a number of secondary radiators and the polarisation of the secondary radiators can be distributed over all three space coordinates of the cavity resonator. I 1
3,436,507 Patented Apr. 1, 1969 In order to make the invention clearly understood, reference will now be made to the accompanying diagrammatic drawings which are given by way of example and in which:
FIG. 1 illustrates a cavity resonator with an input coupling system and an oscillation-type converter; and
FIG. 2 is a plan view of FIG. 1.
The illustrated device comprises a heating chamber 1 in which foodstuff to be heated can be placed. The heating chamber has a door 2 at its front side.
The heating chamber 1 is formed as a cavity resonator for the microwave energy which is used, and for this purpose is provided with a wall 2 which consists of metal or which is provided with a metallic cladding. In the centre of the top, as an input coupling system, a coaxial line with an outer conductor 4 and an inner conductor 5 is provided. In the chamber 1, a conical transition 6 of metal is connected to the inner conductor 5, its base surface carrying a circular plate 7 with a plurality of secondary radiators '8 which are in the form of narrow metal strips. The plate 7 which consists of nonmetallic material, with the metal transition cone 6 connected to the inner conductor 5, serves as an oscillation-type converter and is arranged for rotation.
1. A device for heating nonmetallic materials, such as foodstuffs, by microwave energy, comprising a cavity resonator serving as a heating chamber, a microwave generator, an input coupling system connecting the heating chamber with the microwave generator, and field stirring means rotatably disposed in the heating chamber, means for supporting said field stirring means for rotation coaxially to the said input coupling system, said field stirring means including a primary radiator and an array of secondary radiators.
2. A device according to claim 1, wherein said primary radiator includes a conical transition member disposed coaxially to the input coupling system and arranged for coupling a wave from the input coupling system to said primary and secondary radiators.
3. A device according to claim 1, wherein the secondary radiators are carried by a nonmetallic and circular plate carried by said conical transmission memher.
4. A device according to claim 1, wherein the polarisation of the secondary radiators is distributed over all three space coordinates of the cavity resonator.
5. A device according to claim 3, wherein the secondary radiators are in the form of narrow metal strips.
References Cited UNITED STATES PATENTS 2,748,239 5/1956 Long et a1 219-10.55 2,961,520 11/1960 Long 219--10.55 3,364,332 1/1968 Sven-Olov Reftmark FOREIGN PATENTS 1,482,777 5/1967 France.
RICHARD M. WOOD, Primary Examiner. L. H. BENDER, Assistant Examiner.