Polarization Insensitive X-Band Frequency Selective Surface Sensor for Wireless Thin-Ice Monitoring

Winter ice conditions present major challenges, particularly for cable-supported bridges where ice accumulates on cables, followed by sudden shedding, creating serious hazards for vehicles and pedestrians. This paper presents a passive and flexible frequency selective surface (FSS) ice sensor designed for wireless detection of thin ice layers over large areas. The proposed FSS fabricated on a 0.1 mm thick substrate, comprises an array of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$6 \times 10$</tex> square-shaped unit cells. A horn antenna was used to interrogate the sensor and measure its <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S_{11}$</tex> response, with the design resonant frequency set at 9.38 GHz. Measurement results demonstrated that the microwave FSS sensor achieved a sensitivity of approximately 260 MHz for a 5 mL ice layer covering its surface, highlighting its potential for effective ice monitoring to enhance the safety of cable-supported bridges. Additionally, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$S_{11}$</tex> results showed distinct responses for ice thicknesses up to 3 mm, confirming the sensor's capability to differentiate ice thicknesses within this range.