GATE Electronics and Communications (EC) 2018 Solved Paper

A uniform plane wave traveling in free space and having the electric field.
$\overrightarrow{\mathit{E}}=\left(\sqrt{2}{\hat{\mathit{a}}}_{\mathit{x}}-{\hat{\mathit{a}}}_{\mathit{z}}\right)\cos \left[6\sqrt{3}\mathit{\pi }\times {10}^8\mathit{t}-2\mathit{\pi }\left(\mathit{x}+\sqrt{2}\mathit{z}\right)\right]\frac{\mathit{V}}{\mathit{m}}$
is incident on a dielectric medium (relative permittivity > 1, relative permeability = 1) as shown in the figure and there is no reflected wave.

The relative permittivity (correct to two decimal places) of the dielectric medium is
___________.