Electrolyte Concentration Measurements in DI Water with 0.125 g/L Resolution by means of CSRR-Based Structures

In this paper, it is demonstrated that NaCl concentration measurements in DI water, with resolution as small as 0.125 g/L, are possible. The sensor consists of a pair of identical (and uncoupled) mirrored CSRR-loaded lines equipped with fluidic channels, one for the reference liquid (the solvent, i.e., DI water), and the other one for the liquid under test, LUT (the NaCl solution). The cross-mode transmission coefficient of the structure, very sensitive to asymmetries caused by the presence of solute in the LUT channel, is the considered output variable. The most relevant characteristic of the reported sensor is the small resolution (0.125 g/L). Nevertheless, the measured sensitivity for small concentrations of NaCl is as high as 0.034 (g/L)
^-1
, and the input dynamic range is at least 60 g/L. Therefore, the reported CSRR-based fluidic sensor is found to be competitive, and it is of special interest in applications where solute content in extremely diluted solutions must be determined.