Compact and sensitive half-mode SIW microwave sensor based on CCSRR for biomedical applications

Abstract

This paper presents a compact and sensitive half-mode substrate integrated waveguide microwave sensor (HMSIW) for characterization of liquid samples. The sensor comprises a circular complementary split ring resonator (CCSRR) to provide high concentration electric field distribution around the sensing area. Variations in the refractive index of the MUTs cause shifts in the sensor's resonance frequencies and the transmission zero. Sensitivity performance was evaluated using water-ethanol solutions of varying concentrations, demonstrating sensitivities of approximately 3.1 $\left(\frac{\mathrm{MHz}}{{{∆\epsilon }^{\prime }}_r}\right)$ and 2.9 $\left(\frac{\mathrm{MHz}}{{{∆\epsilon }^{\prime }}_r}\right)$ at resonance frequency (S₁₁) around 5.6 GHz and transmission zero (S₂₁) 6.66 GHz, respectively. Additionally, parametric analyses of material synthesis, electric field distribution, and CCSRR length are provided to demonstrate the adaptability and performance of the proposed sensor. This concept is compact (11×12×1.524 mm³), cost-effective, reusable, easy to fabricate, non-invasive and it supports quick and easy replacement of the infusion tube and real-time monitoring. A strong correlation was observed between the measured and simulated results. While primarily designed for analyzing aqueous solutions, this sensor could be further adapted for other liquids, such as oils, using the principles outlined in this study.