A New Frontier: Wi-Fi Signals that Can “See” Through Walls

Wi-Fi signals are not just for providing internet connectivity or streaming movies; recent experiments have revealed that they possess the remarkable ability to identify shapes through solid walls. Despite previous demonstrations of Wi-Fi’s capacity to detect movement through barriers, it has struggled to perceive stationary objects. However, researchers from the University of California Santa Barbara (UCSB) have developed a novel approach to overcome this limitation by focusing on the edges of objects, mimicking the way a person outlines a drawing.

The UCSB researchers employed a Wi-Fi setup that concentrated on the geometric edges of objects using the Geometrical Theory of Diffraction (GTD). GTD explains the behavior of waves as they encounter object edges, resulting in wave interference or diffractions. By applying GTD to Wi-Fi signals, which form shapes known as Keller cones as they diffract around the edges of objects, the researchers were able to gradually reveal a scene by interpreting the composition and direction of these cones.

The system, named Wiffract, created by the UCSB team, consists of three Wi-Fi transmitters that emit signals and a mobile receiver for capturing the signals as they rebound. While it is well known that Wi-Fi waves can penetrate walls, they are also influenced as they encounter objects. The researchers used complex mathematical calculations and educated assumptions to determine the shapes associated with the Keller cones. By utilizing data from edges with strong readings, the scientists enhanced the system’s ability to detect edges with weaker signals, such as those located farther away from the transmitters or concealed behind obstacles.

To overcome the challenge of detecting edges with weaker Wi-Fi signals, the researchers employed Bayesian information propagation. This statistical technique is analogous to solving a jigsaw puzzle: leveraging the known positions of some puzzle pieces to determine the location and shape of missing pieces. By identifying high-confidence edge points through an imaging kernel, the researchers were able to propagate their information to neighboring points using Bayesian information propagation algorithms. While the system still requires fine-tuning, it already demonstrates the ability to recognize larger letters.

The possibilities for utilizing Wi-Fi signals that can “see” through walls are vast. One potential application is in disaster rescue scenarios, where the technology could help locate individuals trapped behind debris or collapsed structures. By visualizing the interior of rooms without a direct line of sight, Wi-Fi-based monitoring systems could also enhance smart home security and surveillance. These systems could offer an additional layer of protection by detecting intruders or unusual activities within the home.

The groundbreaking experiments conducted by the UCSB researchers have unlocked a new frontier in utilizing Wi-Fi signals. By focusing on the edges of objects and leveraging the Geometrical Theory of Diffraction, Wi-Fi signals are now capable of transcending the limitations of solid walls. While the technology still requires further refinement, it holds enormous potential in various domains, from disaster management to everyday home security. As advancements continue, Wi-Fi signals may become an integral part of our lives, “seeing” the unseen and creating a world where walls are no longer barriers to perception.


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