Love wave surface acoustic wave sensor for ice detection on aircraft.

This paper presents the design, fabrication, experimental results, and theoretical validation of a Love wave surface acoustic wave sensor for detecting the phase change from liquid water to solid ice. The sensing of this phase transition is due to the shear horizontal nature of Love waves which couple to a solid (ice) but not to a liquid (water). An SiO2 film of thickness 3.2 μm deposited on an ST cut quartz wafer via plasma-enhanced chemical-vapor deposition acts as the guiding layer for Love waves. Testing is carried out with the water or ice placed directly in the propagation path of Love waves. An oscillation frequency shift of 2 MHz is observed when water on the sensor is frozen and melted cyclically. The contribution to the frequency shift is explained in terms of the acousto-electric effect (high permittivity and conductivity of water relative to ice), mass loading, and elastic film formation (solid ice). An arrangement for wireless interrogation of the sensor is proposed which is particularly attractive for aircraft and rotorcraft applications obviating the need for complex wiring and local power sources. t