Flying Sensors From Potato Starch and Wood Waste
Empa researchers at the Sustainability Robotics laboratory in Dübendorf are developing low-cost, sustainable sensors and flying devices, known as bio-gliders.
They can collect environmental data in an energy-efficient, close-meshed, and autonomous way even in inaccessible regions. Their ingredients include potatoes, wood refuse, and dyer’s lichen.
The innovative devices are inspired by biology, as they are modeled on the flying seeds of the Java cucumber, yet they are also biodegradable. Once a drone has released the smart sensor seeds, they report data on, say, soil moisture and acidity until they eventually decay and become one with the forest floor.
The data from the smart seeds will be used to monitor the condition of the forest soil and its biological and chemical balance, according to Empa researcher Fabian Wiesemüller and Mirko Kovac’s team from the Sustainability Robotics lab. A first sensor is now utilized to perform a traditional litmus test to determine the pH value.
Collecting Data at the Critical Moment
A protective film is applied to the sensor to guarantee that it is protected until it is used and only gathers data at the critical moment. This is a complex “contra hood” that releases the sensor as soon as rain falls, yet takes a robust protective posture during work breaks. However, as soon as the sensor begins to operate, the protective film reacts very quickly. It opens like a flower when there is rain or humidity in the air.
The researchers created this protective mechanism in collaboration with Gustav Nyström’s team from Empa’s Cellulose & Wood Materials department. It is based on nano-fibrillated cellulose from wood residues, which was treated with gelatin to generate a fine polymer coating that responds to air moisture. After the rain clouds have cleared, the polymer bloom closes for about 30 minutes until the next duty cycle.
The polymer film is additionally coated with a very fine layer of shellac, a natural resin-like material excreted by plant lice, to ensure that the “blossom” opens symmetrically. When exposed to moisture, it inhibits the polymer substance from expanding unevenly.
The biosensor’s transport vehicle is a glider made of regular potato starch, which is similar to edible paper. This means that the glider may be easily printed and pressed into the shape of a Java cucumber seed. The glider, with the sensor, weighs only 1.5 grams and has a wingspan of 14 cm.
When the ultralight measuring device reaches the ground, it becomes a race against time. Nature gets to work on it while the sensor detects the pH value every time it rains. Soil organisms have already degraded their wings after seven days in the laboratory. After three weeks, the sensor disintegrates. This is how the bio-glider’s natural components make their way back into nature.