Proof-of-concept microwave sensor on flexible substrate for real-time water composition analysis

This paper reports on the development of a novel proof-of-concept type sensor for real-time monitoring of water composition. In particular, the change in the electromagnetic wave signal in microwave frequency range is used as an indicator of water purity. The sensing element was designed on a flexible substrate to provide for a long-term usage since this configuration is less prone to failure due to mechanical damage. This allows for a broad range of applications where a sensor could be mounted on any curved surface or even just placed bended in a tube or water pipe. Inderdigitated Silver metal pattern printed on this substrate acted as a sensor. The developed system confirmed the viability of using microwaves for real-time water purity monitoring as the corresponding spectra for air, deionised and tap water were unique and clearly depicted a shift in the resonant frequencies of the sensor when it was placed in contact with water samples.