Alcan International Limited

Hormel Foods Corporation

Bryan C Hewitt

Melville D Ball

Claude P Lorenson

Richard M Keefer

Phillip L Minerich

Cindy M Lacroix

Christine E Gallerneault

An microwave container with synergistic active elements provides more uniform heating than prior art containers, and is more tolerant of variations in food product, load and heating conditions. The active elements (which are conductive and microwave opaque) include an annular ring in the base of the container, a band extending from the base of the side walls up the walls to a level approximately even with the anticipated fill level in the container, a lip extending from the bottom of the side walls onto the base, and at least one, preferably three cooperative active elements in the lid of the container. These containers can be used for thawing and cooking frozen, uncooked meats and other foods, with which prior art containers produced unsatisfactory results.

Container for active microwave heating

A microwave tunnel oven receives a series of packages each comprising a container and a load in the container to be heated by microwave energy. The oven has a conveyor with a series of carriers each for receiving one of the packages and conveying it through the oven. The improvement comprises modifying the microwave field in the load during its irradiation in the oven in a manner to generate higher order modes of microwave energy in the load to enhance the uniformity of heating throughout the load. The structure for achieving the field modification is divided into two parts, one part being formed on the conveyor and the other part being formed either on the package or on a subsidiary conveyor that extends parallel to the main conveyor.

Microwave tunnel oven having means for generating higher order modes in

A container for heating a substance, e.g. food, in a microwave oven has a bottom transparent to microwave energy. The container is supported on a stand that contains one or more electrically conductive plates (or apertures in an electrically conductive sheet) that generate at least one mode of microwave energy of higher order than the fundamental modes. The stand also serves to support the container above the higher order mode generating plates (or apertures) so that the undersurface of the substance is spaced from them by a uniform predetermined distance. The arrangement has the known features of 'bottom heating', i.e. taking advantage of the natural heat flow in the substance, while achieving more uniform heating of the substance by virtue of the higher order mode or modes. As an alternative to or in addition to the generation of higher order modes, the stand may embody elements that modify the microwave pattern in a manner than enhances the coupling of microwave energy into the undersurface of the substance to be heated.

Microwave heating device with microwave distribution modifying means

A product comprises a shallow container and a load located therein for heating by microwave energy. This product is designed either to be used with, or itself to incorporate, a structure for generating or enhancing at least one mode of the microwave energy of an order higher than a fundamental mode that is determined by boundary conditions resulting from the lateral dimensions of either the container of the load or both. The invention resides in controlling the depth of the load in the container in such a manner that, upon irradiation of the product with the microwave energy, the power absorbed by the load from a higher order mode is at or near a maximum value, while preferably the power absorbed by the load from the fundamental mode is at or near a minimum value. Since uneven heating would ordinarily be associated with the predominance of a fundamental mode, the result of this invention is to increase the intensity of a higher order mode relative to the fundamental mode intensity, and thus provide improved microwave heating uniformity.

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Kingston, Canada

Bryan C Hewitt