Unlocking Conformal Microwave Split Ring Resonant Sensors for In-Flight Ice Sensing

In-flight ice accretion is an ongoing challenge for airplane safety as it disrupts the aerodynamics of wings, increasing drag and decreasing lift. This work proposes a conformal ice sensing method based on microwave split-ring resonator (SRR) sensors for early ice detection on critical aircraft surfaces. A single-port dual-frequency sensor with SRRs operating at ∼1.95 and ∼2.13 GHz was implemented and integrated on a NACA 0018 airfoil with a chord of 0.25 m. The sensor's performance was experimentally investigated in ice crystal icing (ICI) conditions at the National Research Council's (NRC) Research Altitude Test Facility (RATFac), at a simulated altitude of 19 000 ft, a velocity of 100 m/s and, a total air temperature of +3˚C. The performance of the sensor was evaluated with the resonant frequency parameter to extract correlations in different icing conditions. The sensor was tested in different melt ratio conditions (11%, 13%, 16%, and 25%) at varying accretion time periods, accurately determining the onset of icing, the increase in accretion volume, and its eventual shedding, while successfully differentiating the %melt conditions tested. Additionally, the sensor's response to electrothermal deicing procedures is presented, demonstrating its capability for monitoring the efficiency of deicing procedures and sensing the formation of ice during anti-icing operations.