Researchers at the University of Washington have developed a tiny new sensor that can be carried around on a small drone or even the back of an insect – and then dropped on demand to track the environment for years at a time.
Obviously there are a few main features that this kind of system needs. The sensor needs to be very lightweight, it needs to be securely attached to its transport until a “drop” command is issued, then it needs to be able to survive a fall from a high place, and finally it has to be able to run for a decent amount of time.
The team addressed all of those points with the design. The whole sensor system weighs just 98 milligrams, which they describe as about one 10th the weight of a jellybean. That makes it small enough for a tiny drone or a moth to carry without too much trouble.
The sensor is secured with a magnetic pin and a thin coil of wire. When it’s time to drop, a command is sent via Bluetooth that triggers a current to run through the wire, generating a magnetic field that pops the pin out and releases the sensor.
To survive the freefall, the sensor is made with the battery in one corner. Being the heaviest component, that makes it spin and – coupled with the tiny overall weight – slows its fall speed to 11 mph (17.7 km/h) at most. That lets it land safely from as high as 72 ft (22 m). And then its real work begins.
Once safely on the ground, the sensor can then … well, sense, taking stock of its surroundings by gathering data in things such as temperature and humidity. The electronic systems in the package allow it to wirelessly transmit data up to 0.6 mi (1 km), while the battery can run for up to 2.5 years.
The system was tested using drones measuring just 28 mm (1.1 in) wide, and on the backs of live moths, with each having their own advantages. The drones can obviously be controlled more directly, but they have limited battery lives – the moths, on the other hand, can fly for hours and fit into much smaller spaces.
The team says that this system could be used to deliver the sensors throughout an area that needs to be studied over a relatively long time, such as a forest or farm.
Intriguing as the idea is, we can foresee some logistical issues that may need to be addressed. How well do the sensors withstand the elements? Will they stay in place, if they’re just lying on the ground? And how much might they interfere with the natural environment?
The researchers acknowledge that there’s still more work to do in developing the system. They say that they need to work out a way to collect the sensors after their batteries die, and they could eventually be made to run off solar cells instead.
It may be a little difficult to see a specific use case for this technique, but it’s nevertheless an intriguing idea.
The research was presented at MobiCom 2020 in September, and the team demonstrates the technology in the video below.
Dropping Sensors From Live Moths
Sources: University of Washington, Sensordrop project page