Microwave absorption properties of flexible zinc oxide sheet

This paper presents the fabrication and microwave absorption properties of low-cost flexible light-weight zinc oxide (ZnO) sheet. The elastomers, films and foams used as microwave absorbers are made of lossy materials impregnated on low density matrixes which are thicker, heavier and expensive in wide frequency ranges. The prepared ZnO sheet in polytetrafluoroethylene (PTFE) matrix and isopropyl alcohol (IPA) as binder is characterized using XRD which showed the crystalline structure of ZnO in the sample. The microwave characterization is done using waveguide method by placing the sheet samples of different thickness (1 mm and 2 mm) perpendicular to the direction of propagation of power inside the rectangular wave-guides with operating frequency ranges of 5 - 7 GHz and 7 - 9 GHz connected to a Vector Network Analyzer (VNA). Transmission (S21) and reflection (S11) coefficients are analyzed in the above frequency ranges. The reflection coefficients show no remarkable variation throughout the measured frequency range whereas the transmission coefficients exhibit noticeable drop in the transmitted power around 5 - 15 dB at certain frequencies. As the thickness of the sample increases, the absorption level also increases. The absorption of microwave power is observed to be maximum at 8 - 9 GHz frequency range. Absorption properties of conducting ZnO sheet may find applications in the design of novel type of microwave absorbers.