Abstract

The change in capacitance of a sensor is linearly proportional to ice thickness provided that the ice thickness is significantly less than the distance between the conductive electrodes. By employing sensors with different electrodes, the sensitivity to ice may be traded off against the ability to measure greater ice thickness. A sensor with small spacing between electrodes will exhibit a large change in capacitance when covered by a thin layer of ice, however, the capacitance change will be linear only for very thin layers of ice. A sensor with greater spacing between electrodes is less sensitive to ice accretion but has a correspondingly greater ice thickness measurement range. Accordingly, sensor (55) is relatively sensitive and is employed to determine whether or not ice or water is present. This is accomplished by circuit (60) determiniSTATEMENT REGARDING GOVERNMENT FUNDED RESEARCHThis invention was made with Government support under NAS1-18421, NAS2-12890 and NAS3-25618 awarded by the National Aeronautics and Space Administration. The Government has certain rights in this invention.

Other References

• Olsson et al., "Assessment of the Piezo-Electric Foil as a Mean of Monitoring the Wall Turbulence", The Aeronautical Research Institute of Sweden (FFA), Stockholm, Document No. FFATN 1985-60, 1985, pp. 1-30
• A. Bertelrud, "Use of Hot film Sensors and Piezoelectric Foil for Measurement of Local Skin Friction", The 12th International Congress on Instrumentation in Aerospace Simulation Facilities (ICIASF), Williamsburg, Va., Jun. 22-25, 1987, pp. 1-5 (FIGS. 1-22)
• W. B. Scott, "New Stall Detection System Measures Intensity of Turbulent Airflow Over Wing", Aviation Week & Space Technology, Jan. 11, 1988, pp. 57-59
• W. B. Scott "Air Force Funding Joint Studies to Develop `Smart Skin` Avionics", Aviation Week & Space Technology, Apr. 18, 1988, pp. 65
• Wusk et al. "An Arrayed Hot-Film Sensor for Detection of Laminar Boundary-Layer Flow Disturbance Spatial Characteristics", AIAA/NASA/AFWAL Sensors & Measurement Technologies Conference, Atlanta, Ga., Sep. 1-9, 1988, pp. 1-11
• J. S. Heyman and R. S. Rogowski "Fiber Optic Sensor Technology An Opportunity for Smart Aerospace Structures," AIAA/NASA/AFWAL Conference on Sensors and Measurements Techniques for Aeronautical Applications, Atlanta, Ga., Sep. 7-9, 1988, pp. 1-5
• Regowski et al. "The Evolution of `Smart` Composite Material", NASA Tech. Briefs, Oct. 1988, pp. 20-22
• Goldberg and Lardiere, Jr., "Developments in Expulsive Separation Ice Protection Blankets", AIAA, 27th Aerospace Sciences Meeting, Reno, Nev., Jan. 9-12, 1989, pp. 1-5
• Eric H. Urruti and John F. Wahl "Coatings Affect Fiber Performance in Smart-Skin Sensing", Laser Focus World, Jan. 1990, pp. 165-17