Dielectric Resonance Contribution to Microwave Heating of SiCw-Alumina Composites

Rosario A. Gerhardt, GA Tech Research Corporation - GA Institute of Technology, DMR 0604211

The addition of silicon carbide whiskers to aluminum oxide creates a ceramic composite having a large dielectric loss at microwave frequencies. This property of the material has enabled a novel application in microwave heating and cooking which has already been FDA approved and commercialized by the PI’s collaborator, Advanced Composite Materials LLC in Greer, SC. The dielectric loss is directly proportional to the microwave-heating rate of the material. However, the science behind the technology-enabling dielectric loss was lacking. Investigations with PhD student Brian Bertram show the existence of a resonance in the microwave band which seems to provide a significant contribution to the loss in the form of a peak. The resonance character is established through the shape of the dielectric constant and loss curves. The resonance is attributed to the SiC whiskers, because the peak grows and shifts to lower frequency as whisker content increases. At similar frequencies, measurements on SiC wafers (not shown) displayed even more prominent resonances.

Fig. Frequency-dependencies of the dielectric constant (top) and dielectric loss (bottom) of alumina-SiCw composites. The shapes of these curves indicate that the SiCw are responsible for a resonance which contributes to microwave heating.

From Structural Ceramics to the Food Industry Rosario A. Gerhardt, GA Tech Research Corporation - GA Institute of Technology, DMR 0604211

Advanced Composite Materials, LLC (ACM, LLC, http://www.acm-usa.com/), a company that has benefited from Prof. Gerhardt’s NSF funded research, won a 2008 Kitchen Innovations Award for their new products which are revolutionizing microwave cooking. These innovative Silar® microwave heatable oven grills and flatstones are made of a unique class of advanced composite ceramic materials which provide for extremely fast convection cooking inside microwave ovens. Microwaves heat these materials much faster than the foods which they contact. Thus it is possible to cook higher quality foods evenly, uniformly and faster than any other inserts allow. Results include full size pizzas with crispy crusts in 80 seconds (vs. ~10 minutes).

IM: The extremely fast heating rates of these ceramics results from the incorporation of ACM-fabricated silicon carbide. Use of silicon carbide from other manufacturers results in inferior heating. The microwave heating of these ceramics is directly related to their dielectric properties. As the previous slide indicates, the composites show a dielectric resonance which is directly responsible for the fast heating observed. Prof. Gerhardt is continuing to explore how the processing, microstructure, and composition of these ceramic composites affect their dielectric properties.

BI: Silar® Microwave Grills and Flatstones have revolutionized microwave cooking. Silar® changes the speed-quality cooking paradigm, providing higher quality foods cooked even faster. They are FDA-approved.

Transformative: This technology has the potential to make a major impact on the fast-food and restaurant industries by minimizing time and energy costs.

Benefit to Society: The benefit to society is a higher quality of life and cutting down on energy costs. The Silar product is a major portion of ACM, LLC, already a world leader in silicon carbide technology. They manufacture and sell silicon carbide products, including whiskers and fibers, along with press-ready ceramic blends and solid ceramic composites containing silicon carbide.

Silar ® Rods

food

air heatingconvection

microwave

Conduction (from Silar)

Microwave Oven with Silar insert showing different heating

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