Design of Bridge Type C-Band Planar RF Sensor for Detection of Solute Concentration Level in Water

In this paper, a planar Micro-strip-based bridge topology CSRR is proposed for the detection of various solute concentrations in water sample. The designed bridge topology CSRR (B-CSRR) sensors resonates at 5.18 GHz with a Q-factor of 170, which exhibits a fractional sensitivity (10.17%). To avoid the contamination of test liquids, use of the thin Teflon layer is incorporated on top of the sensor region. The numerical analysis of the sensors for various scenarios including the sensor loaded with several lossy samples are carried out and accordingly shift in resonant frequency is recorded. The optimized design topology helps to attain better electric field confinement at the resonant frequency, which eventually leads to improved dielectric sensitivity. In the next part, an equivalent circuit of the proposed sensor is developed using the Advanced Design System (ADS) software. Afterwards, the designed sensor is fabricated on 0.8mm thick Taconic TLY-5 substrate (
$\boldsymbol {\varepsilon }_{r}$
= 2.2). Finally, the measurement of B-CSRR sensor is carried out for different solute concentration in pure water, which is in present scenario are salt and detergent concentration, respectively. The developed sensor is found to be quite sensitive which produces a substantial change in the measured insertion loss even for small variation in solute concentration. For instance, a typical 2% variation in detergent, and salt concentration leads to nearly 1.5 dB, and 2.0 dB, change in measured S21.