CALIBRATION: IMAGE SYNTHESISING
Generating holograms fromWi-Fimicrowave radiation requires one fixed and onemovable antenna, below; foil cross between viewer and WLAN-
router reconstructed fromthe WLAN-hologram, inset; and a 3D image of a warehouse can be reconstructed fromthe ‘light’ of the WLAN router
3D vision theWi-Fiway J
ust like peering through a window, holograms project a seemingly three- dimensional image.While optical holograms require
elaborate laser technology, generating holograms with themicrowave radiation of aWi-Fi transmitter requiresmerely one fixed and one movable antenna. “Using this technology, we can generate a
three-dimensional image of the space around theWi-Fi transmitter, as if our eyes could seemicrowave radiation,” says Friedemann Reinhard, director of the EmmyNoether Research Group for QuantumSensors at theWalter Schottky Institute of TUMunich in Germany. The researchers envision fields of deployment especially in the domain of Industry 4.0 – automated industrial facilities, in which localising parts and devices is often difficult.
WI-FI CAN PENETRATEWALLS Processes that allow the localisation of microwave radiation, even through walls, or in which changes in a signal pattern signify the presence of a person already exist. The novelty is that an entire space can be imaged via holographic processing ofWi-Fi or cell phone signals. “Of course, this raises privacy questions.
After all, to a certain degree even encrypted signals transmit an image of their surroundings to the outside world,” says Reinhard. “However, it is rather unlikely that this process will be used for the view into people’s houses in the near future. For that, you would need to go around the building with a large antenna, which would hardly go unnoticed. There are simpler ways available!” Hitherto, generating images from
microwave radiation required special- purpose transmitters with large bandwidths. Using holographic data processing, the very small bandwidths of typical householdWi- Fi transmitters operating in the 2.4 and 5GHz bands are sufficient. Even Bluetooth and cell phone signals can be used. The wavelengths of these devices correspond to a spatial resolution of a few centimetres.
40 /// Environmental Engineering /// August 2017 “Instead of a using amovable antenna,
whichmeasures the image point by point, one can use a larger number of antennas to obtain a video-like image frequency,” says Holl. “FutureWi-Fi frequencies, like the proposed 60GHz IEEE 802.11 standard, will allow resolutions down to the millimetre range.” Well-known opticalmethods for image
processing can also be deployed inWi-Fi holography: one example is the dark-field methodology used inmicroscopy, which improves the recognition of weakly diffracting structures. A further process is white-light holography in which the researchers use the remaining small bandwidth of theWi-Fi transmitter to eliminate noise fromscattered radiation.
The concept of treatingmicrowave
holograms like optical images allows the microwave image to be combined with camera images. The additional information extracted fromthemicrowave images can be embedded into the camera image of a smart phone, for example to trace a radio tag attached to a lost item. Currently, research on the transparency of
specificmaterials is lacking. This knowledge would facilitate the development of paint or wall paper translucent tomicrowaves for privacy protection, while transparent materials could be deployed in factory halls to allow parts to be tracked. The researchers also hope that further
advancement of the technologymay aid in the recovery of victims buried under an avalanche or a collapsed building.While conventionalmethods only allowpoint localisation of victims, holographic signal processing could provide a spatial representation of destroyed structures, allowing first responders to navigate around heavy objects and use cavities in the rubble to systematically elucidate the easiest approach to quickly reach victims. EE
German scientists have developed a holographic imaging process that depicts the radiation of a Wi-Fi transmitter to generate 3D images of the surrounding environment. Andy Pye reports
PICTURES: FRIEDEMANN REINHARD/PHILIPP HOLL/TUM
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