Microwave properties of composite films based on thermoplastic polyurethane and oxidized activated carbon

Films of composite materials based on thermoplastic polyurethane with oxidized birch activated carbon (TPU/BAC-HNO3) were obtained with a filler concentration from 0.5 to 30% by mass. The samples were prepared by adding oxidized activated carbon (BAC-HNO3) to a solution of TPU in dimethylformamide (DMF) with subsequent mixing and ultrasonic treatment at a frequency of 20 kHz. The resulting mixture was cast into silicone molds and dried for two days. Before introduction into TPU, activated carbon was oxidized with a 5% nitric acid solution. The morphology of BAC-HNO3 was studied by the SEM method. The films’ average thickness varied from 0.32 to 0.73 mm. The reflection and transmission coefficients of electromagnetic waves interacting with the materials under study were measured depending on the concentration of the BAC-HNO3. It was found that for the given filler concentrations the considered composite materials are radio-transparent with a rather weak dependence of microwave properties on BAC-HNO3 amount. Specifically, the reflection coefficient for the composite films varied from –17.4 to –13.6 dB, and transmission coefficient was within –0.93 to –0.34 dB for the all BAC-HNO3 filler concentrations.