Method and appliance for reducing and eliminating local areas of overheating in sensitive loads of dielectric materials

#It is known that electromagnetic fields can be used for thawing, warming and treating different loads consisting of dielectric materials. Examples of such dielectric materials are proteins, wood pulp, alcohols and salts dissolved in water. Examples of electromagnetic fields include microwaves, (frequencies above 900 MHz) and radio fields (frequencies below 900 Mhz). There are many examples of demanding medical and industrial applications requiring a fast and homogenous warming (i.e., even field distribution). One example is a bag with 250 ml frozen blood plasma intended for transfusion, another example is a bag of frozen stem cells, but it can also be about controlling different chemical processes such as the acetylating of wood.

#A common problem of warming with microwaves is that the wavelength is short, at 2500 MHz, (the commercial microwave frequency) the wavelength is 12 cm in vacuum/air and in most dielectric loads the wavelength is 2-5 cm. At frequencies used regularly in microwave products hotspots are common due to reflection and interference. A high frequency will also result in development of superficial energy.

#The energy development in a dielectric material is determined by following relationship. W=∈′*tan(δ)*f*E2

#Having thus described embodiments of the invention in general terms, reference will now be made to the accompanying drawings, where:

#FIG. 1 provides a flow diagram illustrating a method for reducing overheating of areas in a dielectric load, in accordance with several embodiments of the present invention;

#FIG. 2 provides a flow diagram illustrating a method for reducing overheating of areas in a dielectric load, in accordance with several embodiments of the present invention; and

#Embodiments of the present invention now may be described more fully hereinafter with reference to the accompanying drawings, in which some, but not all, embodiments of the invention are shown. Indeed, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the disclosure may satisfy applicable legal requirements. Like numbers refer to like elements throughout.

#With reference to FIG. 3, elements of FIG. 3 will be referenced as necessary throughout the specification.

#In reference to FIG. 1, to master the problems with the previously described edge effects, the load 302 and the surrounding dielectric material 306 are exposed to an electric/electromagnetic field at frequencies below 900 MHz, still better below 300 MHz, as illustrated in block 104 of FIG. 1. Further described by block 106, the field is moved more or less continuously relative to the load 302. In this way zones in the load 302, with higher field strength, are moving around in the load 302 and the risk for local overheating is eliminated. This can be accomplished in different ways.