Miniature ice detection sensor systems for aerospace applications

Ice detection systems using microfabricated diaphragms as sensing elements and portable capacitance detection circuitry are presented. Finite element analysis (FEA) is used to optimize the sensor geometry for enhanced sensitivity to ice accretion. The sensors are fabricated by bulk micromachining and wafer bonding of silicon and glass substrates. During operation, actuation forces are applied electrostatically to cause diaphragm deformation. Accumulation of ice on a diaphragm leads to an increase in its effective stiffness. Therefore, for a given actuation voltage, an ice-covered diaphragm exhibits a smaller deflection than a corresponding ice-free diaphragm. This deflection is measured using a customized, portable, high-sensitivity, differential capacitance measurement circuit. The sensors are operated with the diaphragms in their stiffness-sensitive mode, enabling discrimination between ice and water (or deicing fluids) films. Calibration experiments reveal that the miniature ice detection sensor system can successfully detect ice and water film thicknesses between approximately 0.5-1.5 mm. Finally, dynamic testing indicates that adhesion of ice to silicon is poor when the sensor is driven continuously.