Abstract: Active elements are described which modify the heating of foodstuffs and other microwave-heatable loads and which are responsive to changes of load dielectric properties with temperature or as a result of changes of state, composition or density during heating, to the presence of absence of loads, and to the presence or absence of adjacent dielectric materials. The active elements, which may be looped slots or strips, are constituted so as to be or become resonant or non-resonant during microwave heating of the load in response to the presence or absence of the load or the presence or absence of adjacent dielectric material. The elements conveniently may be constructed of electroconductive metal or artificial dielectric material.

Abstract: Active elements are described which modify the heating of foodstuffs and other microwave-heatable loads and which are responsive to changes of load dielectric properties with temperature or as a result of changes of state, composition or density during heating, to the presence of absence of loads, and to the presence or absence of adjacent dielectric materials. The active elements, which may be looped slots or strips, are constituted so as to be or become resonant or non-resonant during microwave heating of the load in response to the presence or absence of the load or the presence or absence of adjacent dielectric material. The elements conveniently may be constructed of electroconductive metal or artificial dielectric material.

Abstract: A method and device for enhancing the heating of a surface layer of an article being heated by microwave energy is characterized by directing the energy through the surface layer into a main portion of the article in such a manner that the modes of the energy are in cut-off in the surface layer.

Abstract: A susceptor for use in the heating of a foodstuff or other material in a microwave oven is constructed to have at least two regions (12,14) which are each adapted to couple with and absorb microwave energy for the generation of heat in such regions, which heat is then radiatively and conductively transferred to the material. The invention is characterized by one such region (12) having a different lossiness from the other (14), the regions being contiguous with each other. They preferably have a stepwise discontinuity of lossiness between them, which causes higher order mode or modes of microwave energy to be generated or accentuated. The susceptor may be a separate panel or may be a wall component, e.g. the bottom, of a container or utensil, or a removable cover therfor.

Abstract: A container for holding a body of material such as foodstuff to be heated in a microwave oven, including a dielectric lid and/or other dielectric wall structure with at least two ontiguous dielectric wall portions of respectively different electrical thickness for cooperatively modifying the microwave electric field patterns that would obtain in the body during such heating if the lid and/or other dielectric wall structure were of uniform electrical thickness or were absent. At least one of the portions, preferably the portion of higher electrical thickness, may be so constituted as to undergo a change in dielectric constant during the microwave heating, thereby to alter the heating distribution in the body as heating proceeds.

Abstract: A container for holding material such as foodstuff to be heated in a microwave oven, including an open-topped tray and a lid for covering the tray to form a closed cavity, wherein at least one surface of the container has one or more electrically conductive plates and/or microwave-transparent apertures for generating a microwave field pattern having a higher order than that of the fundamental modes of the container, such that the field pattern so formed propagates into the contained material to thereby locally heat the material.

Abstract: A container for containing a material to be heated in a microwave oven, having at least one stepped structure protruding into or out of the container from a surface thereof, this structure including a side wall or side walls that define boundary conditions that generate a microwave field pattern within the container having a higher order than that of the fundamental mode of the container.

Abstract: A container for holding a body of material to be heated in a microwave oven, the container having at least one surface provided with a structure for generating within the container a microwave energy mode of a higher order than that of the container fundamental modes, wherein the mode generating structure has a periphery formed with a multiplicity of protuberances distributed around its perimeter for diffusing the heating effect of the higher order mode microwave energy.

Abstract: For determining doneness of a body of food or other material heated in a microwave oven, a device including an indicator that changes appearance at a predetermined temperature, mounted on an outwardly-facing major surface of a thin-gauge metal element which is disposed in the oven so as to receive heat from the body. The metal element may be mounted on the lid or other wall of a container holding the body in the oven; the lid may be microwave-transmissive and may hold the metal element spaced above the body. The indicator may include a substance that melts at the predetemined temperature to reveal an underlying color or pattern on the metal element surface. In use, the device is placed in a microwave oven together with the body and is observed visually, for detection of the change of appearance, which occurs when the indicator reaches a temperature corresponding to adequate doneness of the body.

Abstract: A novel cover arrangement is described for use with foodstuff holding pans to be heated in a microwave oven. The cover is one which in terms of microwave energy, does not transmit reflected energy. Thus, the cover acts in a manner analogous with non-reflecting coatings in optics and permits passage of the microwave radiation into the container holding the foodstuff, while substantially preventing escape of microwave radiation reflected from the foodstuff surface and container bottom. In this manner the microwave energy is retained and concentrated within the container, resulting in more efficient and uniform heating of the foodstuff. The novel cover is particularly valuable when used with aluminum foil pans, which without the cover of this invention seriously reflect microwave radiation.