The team at The University of California Santa Barbara have unveiled drones that use Wi-Fi signals to see through a solid wall.
Yasamin Mostofi, professor of electrical and computer engineering, said: "Our proposed approach has enabled unmanned aerial vehicles to image details through walls in 3D with only Wi-Fi signals. This approach utilises only Wi-Fi [signal strength] measurements, does not require any prior measurements in the area of interest and does not need objects to move to be imaged."
However, Chitra R. Karanam, the lead PhD student on the project, admits it is a "very challenging" concept.
They said: "High-resolution 3D imaging through walls, such as brick walls or concrete walls, is very challenging and the main motivation for the proposed approach."
Whilst Mostofi added: "Enabling 3D through-wall imaging of real areas is considerably more challenging due to the considerable increase in the number of unknowns."
The research team have explained how it works whilst also revealing the drone in action in a series of tests.
They write on their website: "There are four tightly-integrated key components to our proposed approach to enable 3D through-wall imaging. First, we have proposed robotic paths that can capture the spatial variations in all the three dimensions as much as possible while maintaining the efficiency of the operation. Second, we have modelled the 3D unknown area of interest as a Markov Random Field and utilised Loopy Belief Propagation to update the imaging decision of each voxel.
"In order to approximate the interaction of the transmitted wave with the area of interest, we have used the WKB linear wave model. Finally, we have also taken advantage of the compressibility of the information content to image the area with a very small number of WiFi measurements (less than 4%), using sparse signal processing."