Abstract:

Detecting the onset of ice formation on fixed wing and rotary wing aircraft before and during flight is very important. The experimental results of using a new type of piezoelectric sensor oscillator will be presented. The d15 coefficient of PZT (lead zirconate titanate) is exploited by poling a thin rod (1.3-mm-diam) specimen of PZT along its length direction, and the rod specimens reelectroded diametrically. Two rods were attached to an aluminum plate, and an oscillator circuit was set up using an amplifier and a frequency counter. The plate mode determines the oscillation frequency. Since this is a shear mode, the frequency is unchanged if there is a thin layer of water on the plate. The water is then frozen and a jump in the oscillation frequency is noted at the onset of freezing. Shear waves can couple to ice in solid form, and this changes the dispersion relation, and hence the plate mode frequency. Results are presented showing the sensitivity of the measurement, repeatability, effect of temperature and ice thickness. This is proposed as a reliable, inexpensive sensor arrangement for detecting the onset of ice formation on aircraft.