Ice detection technology developed by researchers at the University of Toronto could speed up the de-icing process for aircraft and other aerospace vehicles, helping to prevent costly flight delays.
In a paper published in the journal Advanced Materials , researchers from the Durable Repellent Engineered Advanced Materials (DREAM) Laboratory describe how their triboelectric nanogenerator (TENG) sensor can detect ice forming, melting and detaching on surfaces - and provide this information in real time using very little energy.
The lab is led by Kevin Golovin, an associate professor of mechanical and industrial engineering in the Faculty of Applied Science & Engineering.
"To the best of our knowledge, this is the first triboelectric ice-sensing system of its kind to be described in scientific literature," says postdoctoral researcher Kamran Alasvand Zarasvand, lead researcher and author of the paper.
"The TENG sensor consists of two layers: a metal electrode and a thin dielectric plastic coating. When another material makes contact with this coating and then separates, they exchange a charge, producing a sharp electrical signal. The signal changes depending on what event occurs - so ice forming generates one signal pattern, while ice melting and detachment create a different one."
Most existing ice-sensing systems can only detect ice at a localized point, meaning ice forming just a few centimetres away from the sensor can go unnoticed. Alasvand Zarasvand says that since the triboelectric sensor, by contrast, is much more reliable because it forms a continuous layer over the surface.
"It's extremely lightweight: just two thin layers, simple to fabricate and can be applied to any surface - even complex geometries, such as aircraft wings or wind turbine blades."
The sensor can also detect ice cracking or detaching from the surface.
"Based on the signal and temperature, we can also distinguish between types of precipitation, such as rime ice - a type that forms as planes fly through fog or clouds - or freezing rain, which is most dangerous for aircrafts," Alasvand Zarasvand says.
"Ice can damage vehicles like planes in a number of ways, leading to them being grounded or needing maintenance, and to increased costs and delays for travellers."
Because the coating is lightweight and versatile, it can be applied to many surfaces - including small drones, where Alasvand Zarasvand sees significant potential.
"Drone crashes in cold weather are common. Drones used for commercial inspections of power lines or delivering aid to remote regions need reliable ice detection," he says. "Our system responds in less than a millisecond, so drones can land before icing causes a crash."
Unlike larger aircraft that undergo extensive real-world testing, Alasvand Zarasvand says that most current drone blade testing for icing is done under simulated conditions. The blades are attached to a rotary hub in an icing wind tunnel where they accrue ice on the entire surface - but that doesn't match real flight conditions.
"A drone is highly sensitive to icing and will crash long before that much ice builds up."
If we can avoid the need for emergency landings for aircraft vehicles and the need for de-icing fluid, then it's a real impact
To more accurately evaluate the impact of ice on a drone and the effectiveness of the sensors, Alasvand Zarasvand flew the drone in front of a nozzle system that sprayed water at known temperatures while keeping the environment below freezing. Once ice began to form, it didn't take long for the drone to crash.
"One of the surprises in our research was just how vulnerable the drones were under cold weather conditions. Even a very thin line of ice on a drone blade caused crashes."
Another feature that sets the new sensor apart is its heating potential. Alasvand Zarasvand hopes that the electrode layer can also act as an electrothermal de-icing system to melt ice once it's detected.
"Once the system detects ice forming, a heating function could be switched on until the sensor detects that the ice has melted," he says. "It's an energy saver, not having to constantly have heating on."
Currently, de-icing planes with fluid is both costly and time consuming. Wintertime travellers often find their flights delayed while the aircraft is coated in de-icing solution, which is toxic to wildlife.
Alasvand Zarasvand hopes his system can save airlines and passengers time and money - while offering a safer and more environmentally friendly way to detect and remove ice.
"If we can avoid the need for emergency landings for aircraft vehicles and the need for de-icing fluid, then it's a real impact," he says.
More research is planned, including outdoor drone tests, integrating heating and sensing, and adapting the system for different applications.
"With something like a drone, you really have to focus on making the sensors lightweight, whereas if you're creating the coating for a wind turbine, that isn't as big of a concern," he says.
"What we have is the first step, and now that we know this system works, it will be exciting to take it further."
