Resonance-Based Microwave Transducer for Contactless Salinity Detection

This study presents the development and validation of a microwave transducer for contactless salinity measurement. The proposed transducer is realized in microstrip technology and based on two split-ring resonators (SRRs). The device, which operates in the frequency range from 1 to 3 GHz, is fabricated by inkjet printing of a silver-based ink on a Rogers RO4003C substrate. The sensor design consists of two SRRs coupled by means of interdigitated capacitors. Salinity sensing is accomplished by tracking the main characteristics of two resonances. Tests at salinity levels of 0, 7.5, 15, 22.5, and 30 ppt confirm the sensor ability to discriminate between these levels. Based on these promising results, the sensor shows great potential in many fields of research. As an example, it could be used for aquaculture applications, given the strong influence of water salinity on marine ecosystems, and for climate change research, helping to understand salinity shifts in coastal waters due to global warming. Furthermore, an application could be considered in the smart agriculture field, where high salinity levels of irrigation water can lead to soil degradation.