Real-Time Phase Transition Sensor Based on Latent Heat Driven FBG for Submillimeter Ice Accretion Monitoring

We present a comprehensive experimental validation of a latent heat based phase transition sensor employing Fiber Bragg Gratings (FBGs) for sub-millimeter ice detection. While the sensing principle itself leverages the well-known exothermic signature of water-to-ice freezing, our work demonstrates its performance across a range of practical conditions. Using a commercial refrigerator (Panasonic NR-A195L/2014, –18°C setpoint, ±0.5°C stability) and a Micron Optics SM-130 interrogator (1 pm resolution, 1 kHz sampling), we evaluated 3D printed water column holders with depths from 5 mm down to 500 μm. Through targeted signal processing, we successfully isolated both the icing and deicing spectral signatures. The sensor reliably produced the characteristic icing spectral signature for columns ≥ 500 μm, establishing this as the system's minimum detectable thickness. Five consecutive freeze and thaw cycles confirmed negligible drift and stable onset amplitudes. Crucially, we introduce a fog-immunity protocol using an ultrasonic mist maker to show that sub threshold frost does not trigger false positives. These novel experimental structures and validation procedures substantiate the FBG phase-transition sensor's robustness and specificity, paving the way for reliable real-time icing surveillance in aerospace, renewable-energy, and power-transmission applications.