The idea of using drones for sensor deployment isn’t anything new. One could either simply drop its payload, or use some sort of extension arm to place it on a vertical surface. Both have certain disadvantages, however, such as the need to closely approach the target in the case of an extension arm. Researchers at Imperial College London’s Aerial Robotics Laboratory have instead been exploring a way to shoot “sensor darts” from the aerial robots
Experiments undertaken involve using a spring-loaded launching device with a shape-memory alloy (SMA) trigger, capable of sending these darts from a distance of over three meters. The research paper was based on darts (which the team actually refers to as sensor pods) with penetrating spines for attachment to wood (e.g. trees) though magnets and chemical bonding could be implemented in other settings too.
Darts here are equipped with an Arduino Nano 33 BLE Sense that together form a wireless sensor network for monitoring a variety of conditions — including temperature, atmospheric pressure, and luminosity — in hazardous or inaccessible locations.
The system was tested indoors with an automated setup, as well as directly controlled by an operator in an outdoor environments. It's able to achieve an accuracy of ±10 cm from up to four meters away, and has been successfully demonstrated over 80 times between indoor and outdoor trials. More info is available in the researchers' paper and in Imperial College London's own article here.