Scientists Successfully Generate Holographic Images Using Radio Waves

Your wireless router may reveal your information in ways you never expected. For the first time, physicists used a radio wave from aWiFi transmitter  to encode a three-dimensional image of a real object in a hologram, similar to the image of Princess Leia projected by the robot R2D2 in the movie Star Wars. In principle, this technology allows outsiders to “see” inside a room through Wi-Fi signals scattered in the room, but some scientists say such espionage is easier said than done.

Friedemann Reinhard, a quantum sensing expert at the Technical University of Munich, Germany, said the idea was born a few years ago. “At lunchtime, we discussed what the world would see from the eyes of WiFi.” He said, “Obviously, if you want to see the world from the eyes of WiFi, then you have to make a hologram.”

The camera generates an image by collecting the light reflected by the object and focusing it onto a screen to produce a two-dimensional model of higher or lower intensity. In contrast, holograms make more use of the natural properties of light waves. Lasers are usually used. The laser is split and half of it reflects the object onto a photographic film. The other half of the light (reference light) is directly incident on the film. Like equally spaced water waves, the light waves in the reference beam arrive in a flat wave. In contrast, the light reflected by the object is modified by it, so that some of the waves reach the film earlier and some arrive later, depending on where they are bounced off. The associated interference of the two beams forms a bright and dark spot – a hologram.

Such two-dimensional images appear to be random and completely different from the object itself. Just as light waves are scattered or diffracted in a manner that initially reflects from the object’s wavefront, the three-dimensional phantom of the object can be recovered by emitting another beam of light, such as reference light, on the film.

Now, Reinhard and Philipp Holl, graduate students of the Munich University of Technology, use a radio wave from a WiFi router instead of a laser to form a hologram of a thin aluminum cross with a width of about 1 meter. The results were recently published in the Physical Review Letter.

This experiment does not rely on any of the tens of billions of digital information encoded in the WiFi signal, in fact, these signals are clean, “coherent” waves. However, the researchers did not record the key interference patterns on the photographic film but instead reconstructed the object in the computer with a WiFi transmitter. They placed a WiFi transmitter 0.9 meters behind the cross in the room. They then placed a standard WiFi receiver 1.4 meters in front of the cross and slowly moved it back and forth to form a “virtual screen” instead of a photographic film. Moreover, they did not separate the reference light that directly reached the screen but placed another fixed receiver outside a few meters away, where the transmitter could be seen directly.

For each point on the virtual screen, the researchers compared the signals arriving at the two receivers simultaneously and made a hologram through the delay caused by the aluminum cross. Virtual holograms are not as traditional, because researchers cannot recover images by illuminating more radio waves. Instead, scientists use computers to pull radio waves back on the screen at the right time to where the wavefront hits the object. The cross then popped out.

“Obviously from the image, there is a cross there,” said Neal Patwari, an electrical engineer at Utah University in Salt Lake City. “This is impressive.” But he said that this approach may not be good in a messy environment. Play a role.

In addition, the receiver and the object are in the same room, where the cross is easily visible. In principle, Reinhard said that the WiFi receiver can be placed outside the room to image objects inside the house. However, Mark Coates, a computing engineer at McGill University in Montreal, Canada, who did not participate in the study, warned that this could be difficult, especially if there were metal studs on the wall. “Basically, there are so many light waves coming from so many directions, this technology will be very challenging,” Coates said.

Reinhard’s main idea is to put a series of WiFi sensors on the ceiling of a factory to create a hologram that better tracks RFID tags. Patwari suggests that other researchers have developed a simpler way to track the movement of people in the building using off-the-shelf WiFi signals. Such RF tracking technology will start soon, Patwari predicts: “In the next 5 to 10 years, people will use WiFi more for positioning than for communication.”

From:http://www.hj-antenna.com/