Researchers are interested in developing devices that can help in these dangerous situations, but most sensors are not sensitive or fast enough to find and process specific odours while flying through the patchy plumes these sources create.
The Smellicopter from a team led by the University of Washington uses the live antenna from a Manduca sexta hawkmoth to navigate toward odours. Smellicopter can reportedly sense and avoid obstacles as it travels through the air and the team’s results are published in IOP Bioinspiration & Biomimetics.
"Nature really blows our human-made odour sensors out of the water," said lead author Melanie Anderson, a UW doctoral student in mechanical engineering. "By using an actual moth antenna with Smellicopter, we're able to get the best of both worlds: the sensitivity of a biological organism on a robotic platform where we can control its motion."
The moth uses its antennae to sense chemicals in its environment and navigate toward sources of food or potential mates.
"Cells in a moth antenna amplify chemical signals," said co-author Thomas Daniel, a UW professor of biology who co-supervises Anderson's doctoral research. "The moths do it really efficiently - one scent molecule can trigger lots of cellular responses, and that's the trick. This process is super-efficient, specific and fast."
Researchers placed moths in a fridge to anesthetise them before removing an antenna. Once separated from the live moth, the antenna stays biologically and chemically active for up to four hours.
By adding wires into either end of the antenna, the researchers were able to connect it to an electrical circuit and measure the average signal from all the cells in the antenna. The team then compared it to a typical human-made sensor by placing both at one end of a wind tunnel and wafting odours - a floral scent and ethanol - that both sensors would respond to. The antenna reacted more quickly and took less time to recover between puffs.
To create Smellicopter, the team added the antenna sensor to a commercially available quadcopter and placed two plastic fins on the rear to help it be constantly oriented upwind.
"From a robotics perspective, this is genius," said co-author and co-advisor Sawyer Fuller, a UW assistant professor of mechanical engineering. "The classic approach in robotics is to add more sensors, and maybe build a fancy algorithm or use machine learning to estimate wind direction. It turns out, all you need is to add a fin."
The team created a "cast and surge" protocol for the drone that mimics how moths search for smells. Smellicopter begins its search by moving to the left for a specific distance. If nothing passes a specific smell threshold, Smellicopter then moves to the right for the same distance. Once it detects an odour, it changes its flying pattern to surge toward it.
Four infrared sensors help Smellicopter to avoid obstacles; if something comes within about 20cm of the drone it changes direction by going to the next stage of its cast-and-surge protocol.
"So, if Smellicopter was casting left and now there's an obstacle on the left, it'll switch to casting right," Anderson said in a statement. "And if Smellicopter smells an odour but there's an obstacle in front of it, it's going to continue casting left or right until it's able to surge forward when there's not an obstacle in its path."
Rather than GPS, Smellicopter uses a camera to survey its surroundings, which is said to make the drone well-suited for exploring indoor or underground spaces like mines or pipes.
During tests in the UW research lab, Smellicopter was naturally tuned to fly toward smells that moths find interesting, such as floral scents. Researchers hope that future work could use the moth antenna sense other odours, such as the exhaling of carbon dioxide from someone trapped under rubble, or the chemical signature of an unexploded device.