A Dual-Mode Split-Ring Resonator to Eliminate Relative Humidity Impact

In this letter, a compact resonant-based dual-mode microwave sensor is proposed, aimed to eliminate the erroneous effect of relative humidity (RH) in microwave chemical sensing within the uncontrolled environment. A single split-ring resonator (SRR) is employed as the sensor core and the first resonance (f
₁
~ 0.552 GHz) and the second resonance (f
₂
~ 1.03 GHz) of the resonator are utilized to calibrate the potential measurement error arising from ambient RH. Simulations of the sensor's design and sensitivity using the finite-element method were performed and presented, which are further confirmed by measurements for resonant profile variation considering RH change of 5%-70%. Using the proposed technique, SRR size reduction of 50% is achieved. In addition, common chemical materials of methanol, ethanol, 2-Isopropanol (IPA), and heptane are successfully detected, achieving clear distinction from the impact of external humidity.