Design of Slotted Microwave Sensor for Evaluation of Water Quality

In this paper, a planar Micro-strip based Slotted topology CSRR is proposed for water quality assessment. The modelled Slotted topology CSRR (S-CSRR) sensor resonates at 4.14 GHz with a Q of 226 and fractional sensitivity of 9.5%. The advantage of a Slotted structure is its improved coupling with incident E-field of the Sample Under Test (SUT) and its improved notch level in case of high loss samples like water
$({\varepsilon} \mathbf{r}=\mathbf{80})$
. The detection of lossy liquid like water is carried out by the inclusion of a thin Teflon layer placed on top of the ground etched sensor. The equivalent circuit of the proposed sensor is further optimized in ADS software. The sensor is fabricated on a 0.8mm thick Taconic TLY-5 substrate
$({\varepsilon} \mathbf{r}=\mathbf{2.2})$
. Finally, the measurement of the S-CSRR sensor is carried out for different solute concentrations of dissolved salt, detergent and sugar variants respectively in pure water for its quality assessment. With the developed sensor, it was observed that even for a slight change in solute concentration there is a significant shift in S
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dB level of 0.7 dB, 0.9 dB, and 0.05 dB for unit percentage change in detergent, salt, and sugar solution respectively in the measured values.