Proof of concept for a permittivity detector based on the leaky wave radiation of a CRLH transmission line

A permittivity detector based on a 2D metamaterial implemented as a composite right/left-handed (CRLH) transmission line is presented. The leaky wave radiation exhibited by the CRLH lines is used as the operational principle of permittivity detection. A CRLH line consisting of interdigital electrodes as capacitive elements and short-circuited stubs as inductive elements is designed and fabricated on FR4 substrate. S₂₁ parameter measurements of the implemented CRLH line are performed in the presence of air and three gases: carbon dioxide (CO₂), nitrogen (N₂) and oxygen (O₂). Differences in S₂₁ measurements of the three gases with respect to air, are used as evidence of the occurrence of leaky wave radiation. Quantification of such differences allows detecting the presence of a particular gas. The S₂₁ measurements are compared with those of an implemented conventional transmission line (right-handed or RH transmission line), used as reference. The permittivity sensing capacity of the CRLH line is demonstrated. It is shown that the two RH lines used as access lines to the detector do not contribute to this sensing property.