We think of Wi-Fi as primarily bathing our homes and offices in a comfy, invisible blanket of data and internet access, but just as a blanket can take on the shapes of the bodies it covers, the microwave radiation sent out from a hotspot can be used to generate a three-dimensional image of the surrounding environment and the things and people in it.

Researchers at the Technical University of Munich have come up with a process that creates a holographic image of a space from the microwave radiation of a Wi-Fi signal bouncing off people and objects. The scientists say their method could be used in automated industrial settings, to track objects moving through a facility, for example.

"Using this technology, we can generate a three-dimensional image of the space around the Wi-Fi transmitter, as if our eyes could see microwave radiation," says Friedemann Reinhard, director of the Emmy Noether Research Group for Quantum Sensors at TU Munich.

We've seen similar approaches use Wi-Fi to see through walls, even distinguishing human figures on the other side and performing head counts of people in an open area. But the TU Munich scientists say they've gone a step further: using Wi-Fi and even cellular signals to image an entire space with holographic processing.

Simulation of a warehouse using the Wi-Fi imaging system(Credit: Friedemann Reinhard/Philipp Holl / TUM)

Reinhard concedes that this new ability to use Wi-Fi to essentially spy on entire rooms and buildings does raise questions of privacy.

"After all, to a certain degree even encrypted signals transmit an image of their surroundings to the outside world," he says. "However, it is rather unlikely that this process will be used (to look) into foreign bedrooms in the near future. For that, you would need to go around the building with a large antenna, which would hardly go unnoticed."

The holographic imaging system requires simply one fixed and one movable antenna, but researcher Philipp Holl says a larger number of antennas could replace the movable antenna for higher-resolution images closer to that of video.

"Future Wi-Fi frequencies, like the proposed 60 gigahertz IEEE 802.11 standard will allow resolutions down to the millimeter range," Holl adds.

Potential future applications for this "Wi-Fi vision" include embedding microwave image data into camera images, allowing for easy tracking of lost items. Imagine taking a photo of a room and being able to see in the image that a lost object is hidden under a piece of furniture, for example.

The researchers also hope that the technology could advance to be useful in rescue operations to help reach victims buried by an avalanche or a collapsed building. They also hope to learn about materials that are more translucent or transparent to microwaves to provide better privacy protection or allow for better tracking of equipment in factory floors.

The research was published in the most recent issue of Physical Review Letters.

Source: TU Munich

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