Humidity Sensitive Flexible Microwave Absorbing Sheet Using Polyaniline–Polytetrafluoroethylene Composite

Abstract

Pelletized or powdered polyaniline composite, a potential candidate for microwave absorbers, was synthesized in the sheet form for the first time, and its absorption characteristics along with structural, electrical and mechanical properties are presented. Enhanced microwave absorption behavior of this novel, thin, flexible, lightweight sheet in hydrous environment was analyzed for various humidity-dependent sensor and electromagnetic applications. The preparation method of protonated chlorine-doped polyaniline (PANI), and its synthesis in the sheet form using polytetrafluoroethylene (PTFE) are discussed. The surface and structural morphology were characterized by XRD and SEM, which reveal the granular, macro-porous and polycrystalline structure of the material. A transmission–reflection-based waveguide technique was used for obtaining the permittivity of sheets in the frequency range of 3–9 GHz by employing the Nicholson–Ross algorithm, and it was verified by cavity perturbation method. The temperature stability of the PANI–PTFE conducting sheet was checked using four-probe method. Conductivity enhancement of the sheet in hydrous environment was studied using a humidity chamber. The microwave absorption studies at various humidity conditions were carried out using waveguide method which also illustrated its potentiality as a humidity sensor. The mechanical strength of the proposed conducting polymer sheet was tested by standard load–extension procedure. To make this PANI–PTFE polymer material suitable for anechoic chamber-like applications, it was impregnated in polyurethane foam and its humidity-related microwave absorption studies were carried out using free space method.