Planar Microwave Sensor for Localized Ice and Snow Sensing

Ice and snow accretion on aircraft surfaces imposes operational and safety challenges, severely impacting aerodynamic performance of critical aircraft structures and equipment. For optimized location-based ice sensing and integrated ‘smart’ de-icing systems of the future, microwave resonant-based planar sensors are presented for their high sensitivity and versatility in implementation and integration. Here, a conformal, planar complementary split ring resonator (CSRR) based microwave sensor is presented for robust detection of localized ice and snow accretion. The sensor has a modified thick aluminum-plate design and is coated with epoxy for greater durability. The fabricated sensor operates at a resonant frequency of 1.18 GHz and a resonant amplitude of -33 dB. Monitoring the resonant frequency response of the sensor, the freezing and thawing process of a 0.1 ml droplet of water is monitored, and a 60 MHz downshift is observed for the frozen droplet. Using an artificial snow chamber to create falling snow, a 1 mm thick accretion of snow shows a 35 MHz downshift in resonant frequency. The proposed sensor system can be extended using a novel radar-inspired method of Time-Domain Reflectometry (TDR). TDR based ice/snow sensors can be implemented in an array or network structure for reliable, local and distributed ice and snow accretion monitoring on aircraft structures. Applying Time-Domain Reflectometry (TDR) methods, three identical sensors with the same resonant frequency are monitored over an approximate length of 10 m and localized sensing of water is presented. This novel method offers a pathway towards implementation of large network-based resonant-microwave sensors for future reliable integrated localized icing and snow accretion rate-measurement sensors.