One advantage of drones is that they can go places where people can't including areas that might be too dangerous such as unstable structures after a natural disaster or a region with unexploded devices.
Researchers are interested in developing devices that can navigate these situations by sniffing out chemicals in the air to locate disaster survivors, gas leaks, explosives, and more. But most sensors are not sensitive or fast enough to find and process specific smells while flying through the patchy odor plumes these sources create.
A team has developed Smellicopter, an autonomous drone that uses a live antenna from a moth to navigate toward smells. It can also sense and avoid obstacles as it travels through the air. By using an actual moth antenna, researchers were able to get the best of both worlds: the sensitivity of a biological organism on a robotic platform on which motion can be controlled.
The moth uses its antennae to sense chemicals in its environment and navigate toward sources of food or potential mates. The team used antennae from the Manduca sexta hawkmoth for Smellicopter. Researchers placed moths in the fridge to anesthetize them before removing an antenna. Once separated from the live moth, the antenna stays biologically and chemically active for up to four hours. That time span could be extended by storing antennae in the fridge.
By adding tiny 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 of 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 smells that both sensors would respond to: a floral scent and ethanol, a type of alcohol. The antenna reacted more quickly and took less time to recover between puffs.
To create Smellicopter, the team added the antenna sensor to an open-source, handheld, commercially available quad-copter drone platform that allows users to add special features. The researchers also added two plastic fins on the back of the drone to create drag to help it be constantly oriented upwind.
Smellicopter doesn't need any help from the researchers to search for odors. 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 odor, it changes its flying pattern to surge toward it.
Another advantage to Smellicopter is that it doesn't need GPS. Instead, it uses a camera to survey its surroundings, similar to how insects use their eyes. This makes Smellicopter well-suited for exploring indoor or underground spaces like mines or pipes.
During tests in the lab, Smellicopter was naturally tuned to fly toward smells that moths find interesting such as floral scents. But researchers hope that future work could have the moth antenna sense other smells such as the exhaling of carbon dioxide from someone trapped under rubble or the chemical signature of an unexploded device.