Electromagnetic wave sensing of NO3 and COD concentrations for real-time environmental and industrial monitoring

A novel electromagnetic sensor for real-time analyte composition analysis operating at GHz frequencies is reported. The sensing element in a form of a gold pattern, printed on Rogers substrate, connected to a Vector Network Analyser, and emits an electromagnetic field which interacts with the sample under test. This results in unique microwave spectra, which are specific to the analyte solution. The developed system confirmed the viability of using microwaves for real-time NO3 and chemical oxygen demand (COD) monitoring as the reflected signals represented by S11 parameters were unique for each solution type and concentration, with clearly observed shifts in the resonant frequencies peaks and their amplitudes when placed in direct contact with 30 μl of each solution. The system would be of benefit to a broad range of environmental and industrial process monitoring applications, as it provides real-time information of both the solution type and its concentration, without the need for using additional chemicals for testing. Moreover, the reported microwave sensing technique offers a cost-effective and sustainable approach to current laboratory based methods of aqueous solutions analysis, since the sensors are robust and reusable.