A Metamaterial-Inspired Wideband Microwave Interferometry Sensor for Dielectric Spectroscopy of Liquid Chemicals

A miniaturized wideband interferometry-based sensor for complex dielectric spectroscopy of liquid chemicals is presented in this paper. Two composite right-/left-hand (CRLH) transmission lines (TLs) are employed in a direct downconversion architecture. The material under test (MUT) is placed in direct contact with the printed interdigital capacitor of the artificial TL as the sensing component. Since the employed CRLH TL provides nonlinear dispersion characteristics, improved sensitivity with wideband (4.2-8 GHz) operation is achieved compared with resonator- or TL-based interferometers. The sensor circuit board is realized based on common printed circuit board technology, and the fluidic polydimethylsiloxane channels are fabricated and bonded to the circuit board using 3-D printing and soft lithography techniques. The measured results of pure liquid chemical characterization suggest the mean squared errors of 1.1% and 1.6% for $\epsilon ^{\prime }-{r}$ and $\epsilon ^{\prime \prime }-{r}$ , respectively, compared with the MUT's theoretical model. Moreover, binary mixture characterization is carried out based on $\epsilon ^{\prime }-{r}$ measurements with an accuracy of 1%.