32 nd URSI GASS, Montreal, 19-26 August 2017 Characterization and Design of Elastomeric Magnetodielectric Materials for Radar Absorber Structures Akin Dalkilic*, Doganay Dogan , and M. Erim INAL ASELSAN Inc., Radar, Electronic Warfare and Intelligence Systems Division, Ankara, Turkey, http://www.aselsan.com.tr Abstract Radar absorbing materials (RAMs) are widely used in order to reduce the radar cross section (RCS) of military platforms requiring low observability. In this work, nitrile based elastomer material which exhibits dielectric properties only is filled with carbonyl iron powder at different concentration ratios. As a result, a material library consisting of magnetodielectric materials with different complex dielectric and magnetic coefficients is obtained. Using the material library, RAMs exhibiting desired absorption characteristics in 2-18 GHz frequency range are synthesized, produced and measured. The expected and measured reflection characteristics are observed to show good agreement. 1. Introduction Radar absorbing materials (RAMs) constitute one of the major solutions to reduce the radar cross section (RCS) of various military systems, like planes, ships and submarines. RCS reduction can be obtained in different ways, such as diffraction of the electromagnetic wave to different directions, transformation of electromagnetic energy to heat via absorbing and active cancellation of reflected wave with an inverse-phased radiation. Radar absorbing materials transform most of the electromagnetic energy of the incident wave into heat energy because of their lossy nature and provide absorption at specific microwave frequencies depending on the dielectric and magnetic properties. In Section 2 of the paper, material characterization technique for carbonyl iron deposited elastomers is explained. The design procedure, production and measurement steps are demonstrated in Section 3 and 4, respectively. 2. Material Characterization In this work, nitrile based elastomeric dielectric material is used as the carrier for the carbonyl iron filler which is preferred for its certain magnetic properties [1],[2]. First, a material library is constructed from nitrile elastomers with carbonyl iron filler at different weight ratios. The members of the material family are pure and 20%-80% (at a step of 10%) carbonyl iron filled nitrile elastomers (see Figure 1). The characterization of materials in terms of complex permittivity (ε) and permeability (μ) coefficients is accomplished using free space and waveguide material measurement setups which are shown in Figure 2. For the characterization between 5.8-18 GHz, free space measurement setup is used while waveguide setup is utilized in 2-5.8 GHz frequency range. Figure 1. Nitrile elastomers filled with carbonyl iron powder at different weight ratios changing from 20% to 80%. Figure 2. Free Space (on the left) and Waveguide (on the right) Material Characterization Setups The results of the material measurements given in Figure 3 reveal that the magnetization of the nitrile based elastomer is enhanced as the weight ratio of the carbonyl iron filler in the carrier matrix increases. Figure 3. Variation of real and imaginary parts of averaged permeability (μ) for different carbonyl iron concentrations 0 10 20 30 40 50 60 70 80 0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 Weight Ratio (%) μ' μ"