An Accurate Permittivity Measurement Using Interferometric Phase Noise Averaging for Terahertz Imaging

We propose a permittivity measurement system that uses an interferometric phase noise averaging method with multiple tones with an optimal frequency interval. The permittivity is measured by a free space method using terahertz continuous waves at around 300 GHz. To reduce measurement error, interferometric phase noise caused by reflected waves is effectively suppressed by using multiple tones with an optimal interval and a linear approximation. Simulations show that the maximum measurement error can be reduced to 0.34%, which is one-eighth compared to the conventional method using multifrequency phase unwrapping. Permittivity imaging of chocolate containing a piece of a plastic shows that the proposed method can reduce measurement error to less than one-fourth compared with that of the conventional method and that a clearer permittivity image can be acquired.