Microwave Reflectance and Transmittance Properties of Conductive Composite Materials

This study investigates the microwave electromagnetic shielding properties of secondary use composite materials used as ingredients in shielding materials. Materials investigated include: waste tire crumb rubber (CR), metallurgical slag (MS) and commercial lightweight expanded clay aggregate (LECA). These materials were tested in a powder form in bulk conditions. The investigation also included core-shell type spheres - expanded polystyrene (EPS) coated by MS (MS@EPS), diameter 4.0-5.0 mm and coating thickness 150 μm. A setup of radiofrequency generating and metering instruments were utilized to measure the reflective and transmission properties of the innovative material. The radiofrequency field tests were done at 2.4 GHz frequency (WiFi network frequency). Reflection and transmission characteristics of the material were measured by free space method. Reflection and transmission coefficients (from 0 to 1) were calculated to each tested sample. The measurements results show full transmission properties for CR and MS@EPS. In case of LECA 91% of the radiation passed through the material while 15% of reflection was measured. The applications of prospective shielding materials innovative material may include shielding smart electrical systems and smart meters from an unwanted electromagnetic interference that may affect the work of the meters or the nearby electronic equipment.