A Permittivity and Conductivity Sensor Based on Microstrip Transmission Line With Defective Ground for Detection of Urea in Saline

A permittivity and conductivity sensor is designed, analyzed, and fabricated, employing a microstrip transmission line with a defective ground. The defective ground consists of two circular rings, creating an electromagnetic band gap. To further enhance the sensor’s performance, a dumbbell-shaped complementary split-ring resonator (CSRR) is incorporated into the gap to create a narrow passband. Extensive simulations are performed to evaluate the sensor’s performance across a wide range of permittivity and conductivity values. Parameters of the sensor are optimized to maximize sensitivity. The sensor is constructed using an FR4 substrate and tested with urea solution in saline to assess its efficiency. Experimental results confirm the simulations. Frequency shifts of 39 MHz for distilled water and 44 MHz for saline is observed. These shifts are more prominent for urea in saline, indicating its higher conductivity and permeability. Additionally, a linear relationship between the frequency shift and urea concentration is observed, further affirming the sensor’s potential for accurate detection.