The processing methods, strengthening methods, water-proof coating procedures, and some ways to improve the transmission of microwaves have been reviewed in relation to fused silica ceramics and their composites for radome applications. Fused silica ceramics are characterized by a residual porosity (up to 18%), low dielectric constant (3.06-3.32), low loss tangent (0.00053-0.0065), excellent thermal properties, but low mechanical strength (37-65 MPa). To achieve higher mechanical strength and better transmission efficiency, new randome materials would be those engineered composites consisting, for instance, of a dense layer-porous core structure, a continuous fiber reinforcement, a multilayered structure, and/or frequency selective surface (FSS) layer (s)/metamaterials.

Abstract-We present a generally symmetrical circuit model to describe all kinds of metamaterials with effective permittivity and permeability. The model is composed of periodic structures whose unit cell is a general T-type circuit. Using the effective medium theory, we derive analytical formulations for the effective permittivity and effective permeability of the circuit model, which are quite different from the published formulas [1,2]. Rigorous study shows that such a generally symmetrical model can represent right-handed materials, left-handed materials, pure electric plasmas, pure magnetic plasmas, electric-type and magnetic-type crystal bandgap materials at different frequency regimes, with corresponding effective medium parameters. Circuit simulations of real periodic structures and theoretical results of effective medium models in this paper and in [1] and [2] are presented.The comparison of such results shows that the proposed medium model is much more accurate than the published medium model [1,2] in the whole frequency band.

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The effect of the presence of fillers on the thermal properties of a high performance elastomer was investigated in this work. The characterization of the specific heat capacity (Cp), the specific heat flow and the glass transition temperature of a polyurea elastomer reinforced with two different classes of fillers, i.e. short glass fibers and alumina nanoparticles, was conducted by using a differential scanning calorimeter (DSC). We present and discuss the results of the experimental characterization carried out on the reinforced material. The results are compared to those obtained by testing the pure polymer.

We investigated a novel artificial metamaterial that includes two plates of quartz glass dielectric material and a Ag microstructure sandwiched between the two plates. The Ag grid layer was designed and subsequently prepared by tape casting and screen printing. The transmission characteristics of this metamaterial were able to be controlled by adjusting the geometry parameters of the Ag grid such as the width of the strip and the size of the unit cell. Our work has demonstrated the possibility that the ceramic metamaterial can be used as a transmission material capable of work at high temperatures below the melting point of the metal.