Sensitivity Enhancement of a Complementary Split-Ring Resonator as a Dielectric Sensor Using Nonzero-Offset Coupling

In this paper, a novel technique based on nonzero-offset coupling for sensitivity enhancement of a complementary split-ring resonator as a dielectric sensor is proposed. Changing the offset between the central island of CSRR and the microstrip line makes the overall system sensitive to changes near the sensor, which adds a new degree of freedom for sensitivity enhancement since the sensitivity of such a system is related to the coupling capacitance and inductance. The resonator is designed by etching out a ring with a split in the ground plane and then inductively excited by connecting the resonator's island to TL using a plated via. As a dielectric sensor, the sensing mechanism is based on measuring the relative changes in the resonance frequency in respect of a reference case. The sensor is used to detect a dielectric slab with a thickness of 3 mm and width and length of 22.5 mm, where the relative permittivity of the slab is varied from 1 to 11 with a variation of 0.5. The proposed sensor is evaluated using a numerical simulation (HFSS). Based on the numerical results, the enhanced sensitivity is 44.38%, 15.45%, and 6.54 % when detecting the slab with the dielectric constant of 1.5, 2, and 10, respectively. Since the sensor has many features such as high sensitivity, simplicity in the sensing mechanism, and low-cost fabrication using printed circuit board technology, the sensor can be attractive for sensing-system designers, making it an ideal candidate for biomedical and industrial applications.