Free space microwave measurement for detecting corrosion under a thin paint of aluminium panel

This paper presents a free space microwave measurement methods which are non-destructive and noncontact to determine the corrosion under a thin paint on aluminium panel. For free space microwave measurements techniques, the measured parameters are reflection coefficients S₁₁, transmission coefficients S₂₁, dielectric constants, loss factors, and complex permittivity as a function of frequencies. This paper is focusing on metal backed method in order to detect corrosion under thin paint on Aluminium panel. The metal backed method will measure the free space reflection coefficients, S₁₁ only. In order to obtain smaller errors of dielectric constant, it is required that the sample thickness to be close to odd multiples of quarter wavelength. The results of the complex permittivity of the samples were calculated from measured reflection coefficient S₁₁ at frequency range of 8 GHz-12 GHz.