Sensing System for Mixed Inorganic Salt Solution Based on Improved Double Label Coupling RFID

As a crucial part in sewage, high-salt wastewater contains abundant corrosive components and heavy metal elements, which makes it difficult for invasive monitoring. Therefore, based on coupling radio frequency identification (RFID) tags, this article proposes a noninvasive monitoring method for concentration of inorganic salt in sewage. In this method, the Cole–Cole model and slit cylindrical capacitance (SCC) model are combined to explore the relationship between capacitance of RFID and concentration of inorganic salt in sewage pipeline. A new efficient Levenberg–Marquardt (NELM) algorithm is used for regression between relative permittivity and concentration of inorganic salt categorically. Then, measurement data are processed under modified relative permittivity mixing rule of electrolyte and solvent. Finally, the concentration of each component in the multicomponent inorganic salt wastewater is obtained. Experimental results show that the maximal relative error (MRE) and average relative error (ARE) of single inorganic salt solution are 1.1% and 0.5%, while mixed solution are 2.6% and 1.89%. Such results indicate significant improvement compared with previous works. Great potential of RFID in working sewage monitoring is sufficiently confirmed.