Simple and Accurate Time-Domain Free-Space Method for Dielectric Constant Determination of Solid Materials With No Thickness Information

A simple yet accurate free-space microwave method is proposed for the determination of the dielectric constant ( $\varepsilon _{r}$ ) of solid materials from uncalibrated reflection measurements (metal termination only and sample terminated in the same metal termination) using time-domain analysis without requiring an thickness (d) information. In comparison to similar free-space methods in the literature, the method has the advantages that: 1) it is resistant to any measurement error arising from the angle misalignment problem; 2) it is relatively weakly influenced by dispersion effects in comparison to other similar methods in the literature; and 3) it does not suffer from any air gap between the sample rear face and the metal termination. Different numerical analyses are performed for validation and accuracy comparison under different cases: 1) increase in loss; 2) angle misalignment effect; and 3) presence of noise. Uncalibrated free-space measurements of three low-loss dielectric samples [polyethylene (PE), polypropylene (PP), and polyoxymethylene (POM)] are conducted to compare our method with other similar methods in the literature.