A Complementary Split Ring Resonator Sensor Optimized for Maximizing the Dip and Q-value in S21 Frequency Characteristics

A modified complementary split ring resonator (CSRR) sensor with a high quality factor (Q-value) and sensitivity is developed for the purpose of fluidic dielectric characterization, such as glucose monitoring. The microstrip transmission line and the CSRR sensor are formed on the front and backplane of a printed circuit board (PCB), respectively. The CSRR sensor consists of two straight-line inductors, which are placed perpendicular to a microstrip line, and a single ring-shaped capacitor. The width of the microstrip line (MSL) is widened, even though the characteristic impedance is reduced to less than 50 $\Omega$. S21 measurements on the fabricated PCB showed that the dip was −56 dB at 6.14 GHz, in the absence of a glucose aqueous solution on the CSRR sensor. Changes in S21 dip frequency and the amount of dip were approximately 100 MHz and 3 dB, respectively, for five different concentrations of glucose aqueous solution, namely 0, 1, 3, 5, and 10 wt%.