Electromagnetic interactions with materials: Magneto-dielectric composites design and development of a novel microwave heating device

Electromagnetic interactions with materials dictate their performance for several applications ranging from wireless communications to energy transport. Understanding how these interactions are affected by material properties is essential for improving application performance and was the underlying theme for this work. Projects included the design and fabrication of magneto-dielectric composites and the development of a novel microwave heating device for activated carbon regeneration.;Engineered magneto-dielectric materials differ from conventional electromagnetic materials due to their enhanced magnetic properties; these materials can increase bandwidth and efficiency for a variety of technologies. However, naturally occurring magneto-dielectric materials are often non-magnetic and exhibit a large loss at frequencies greater than 1GHz. The goal of this project was to design and fabricate materials with enhanced dielectric and magnetic properties at GHz frequencies. Preliminary experimental work was focused on investigating polymer composites with spherical iron oxide nanoparticles; very large loadings of iron oxide were necessary to increase the magnetic permeability, at the cost of material integrity. Alternatively, by using frequency selective surface (FSS) layers within a polymer matrix, the design objective was successfully met. The FSS layers were designed as periodic metallic arrays, which acted as "inductive inclusions" within the polymer, collectively causing an effective susceptibility due to the interactions between inclusions and a self inductance of the inclusions, resulting in an enhanced magnetic response. The shape, dimension, and periodicity of the metallic elements of the array were variables for the final design and determined the effective properties and operational bandwidth for the composites. These materials were designed to have a permittivity and permeability greater than 2, with very low loss, from 2-5GHz. The details of the design, fabrication, and characterization of these materials will be presented in this work.;While the focus of the first project was primarily materials design, the second project involved the development of a novel application, based on the dielectric properties of the material. Activated carbon is often used as an adsorbent for applications involving removal of toxic effluents from waste streams and emissions. It has been shown that high power microwave heating is a promising alternative method to heat small volumes of activated carbon. In contrast, some applications may require heating large volumes of carbon with lower power inputs; hence, developing a novel microwave heating applicator would be important for eliminating the problem of "hot spots" found often in conventional microwave cavity heating. An applicator similar to a coaxial transmission line was designed at 2.45GHz to heat activated carbon using under 120 Watts of power; bench-top systems were constructed to analyze the efficiency of the design. An energy balance was used to model the temperature throughout the carbon in the device. Results of the device design, experimentation, and modeling will be discussed.