Capacitive Impedance Water Ice Sensor (CIWIS)

The CIWIS is configured to detect ice, water, and other material accretion on an aircraft's surface using a capacitive sensor comprised of metal traces on a printed circuit board (PCB) with a dielectric surface covering. The traces are on the bottom side of the PCB for protection from the elements experienced on the top side. It drives the sensor with a sinusoidal signal and monitors the sensed sinusoidal signal from the sensor. By electronically measuring the RMS voltage of both the drive and sensed signal as well as the phase shift introduced by the sensor, the CIWIS can determine the impedance of the sensor and any material deposition. When a material is present on the surface, this introduces another capacitor in parallel with the air and PCB, with that material being another dielectric. Water and ice exhibit frequency-dependent permittivity that introduces a phase shift unlike that of a typical capacitor. CIWIS leverages these differences, distinguishing materials by the unique RMS levels and phase shifts they produce in the sensor. For ice, this effect occurs at approximately 10 kHz. While NASA originally developed the CIWIS to detect ice on aircraft, it may also be useful to sense the presence of water and other contaminants in pharmaceutical production; condensation in heating, ventilation, and air conditioning (HVAC) systems; and ice accumulation on cryogenic equipment. This technology is available for patent licensing, and is rated at a Technology Readiness Level or TRL of 5 , meaning it has been developed and validated in an industrially relevant environment and is ready for a prototype demonstration. Ice accumulation on an aircraft’s surface poses a serious safety risk, causing stalls and crashes due to the distortion of the smooth flow of air necessary to maintain lift. There are a variety of sensors commonly used to identify materials collecting on the surface of an aircraft, however, they all have operational limitations. Vibrating sensors are not able to detect small amounts of accumulation, optical sensors can be blocked by dirt or debris, and magnetostrictive sensors require precise calibration and have limited range. Engineers at NASA’s Glenn Research Center have developed a novel method for detecting ice or other material accumulation on the surface of aircraft. The Capacitive Impedance Water Ice Sensor (CIWIS). CIWIS works by measuring the impedance of accumulation using the phase of a smart capacitive sensor. This allows users to accurately determine when ice, water, or other materials are on the surface of an aircraft.