A Non-specific Microwave Sensor for Water Quality Monitoring

This paper deals with a microwave measurement system for the real-time monitoring of water quality. The sensor is a compact cavity resonator tuned at 1.91 GHz which has been designed by a Finite Element Method code to maximize the Q-factor. The sensing principle relies on the changes of the device response in terms of the transmitted power, resonance frequency, and 3-dB bandwidth. These variations are caused by the change of the permittivity and conductivity of the water sample under test induced by the presence of pollutants. Experiments are carried out in laboratory conditions on water solutions contaminated with different substances. As shown, the system is capable to reliably detect the presence of nitrates and sulfites dissolved in water in concentrations above 10 mg/L. The proposed set-up is portable and thus particularly tailored for its deployment on-field. Moreover, it has reduced cost since it does not necessitate expensive instrumentation such as network analyzers.