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Robots Use EM Waves to See Through Walls

EM detection can be combined with robots to provide methods for in-wall scanning of unknown areas.

Robots are by now well-established parts of the military electronics landscape, whether on the ground, in the air, or at sea. By combining ground robots with detection systems based on electromagnetic (EM) energy, they can also play quite effective roles in search and rescue, as well as surveillance and security applications. These see-through imaging systems, which are also known as “through-wall imaging,” can work with EM energy as popular as 2.4-GHz Wi-Fi signals and a pair of robots to perform the through-wall detection. Using Wi-Fi received signal strength indicator (RSSI) signals, one of the robots measures the received signal power of the signals transmitted by the other robot to perform imaging of objects through a wall.

A trio of researchers developed both narrowband and ultrawideband (UWB) imaging approaches using commercial transceivers and antennas. The researchers, Saandeep Depatla, Chitra R. Karanam, and Yasamin Mostofi, are all with the University of California at Santa Barbara. Their research was funded by a National Science Foundation Communications, Circuits, and Sensing Systems award. A number of different scenarios were modeled, one in which two unmanned vehicles with RF sensors were used for imaging of a completely unknown area, and another scenario in which the only signal power available for imaging was Wi-Fi signals at 2.4 GHz.

The researchers developed an effective UWB imaging approach based on the use of a commercially available UWB transceiver chipset from DecaWave (model EVK1000 transceiver), coupled with an omnidirectional antenna. Along with comparisons of Wi-Fi and UWB imaging approaches, the researchers show how the use of antenna directionality can improve imaging quality. Having a large number of robot localization positions also helps to minimize the localization errors when determining the positions of the in-wall images.

Experimental scenarios are presented based on the use of two ground robots for in-wall imaging, in one case performing imaging only with Wi-Fi RSSI signals and in another case using only two robots with UWB signals. The researchers note that the availability of small UWB transceiver chipsets makes it possible to add such UWB imaging capabilities to small robotic platforms. By programming the trajectories of the two robots so that their transmit and receive antennas follow a precise path, detailed imaging can be achieved. In addition, the transmit and receive robots can also be used to travel nonspecific patterns and simply perform wireless measurements as they move about an unknown area, in what is referred to as a random motion pattern.

The researchers present results for a number of different unknown areas, showing scanned 2D images for areas of different complexity and size and comparing the effectiveness of the Wi-Fi and UWB imaging approaches. Robotic path planning is a key ingredient in achieving detailed in-wall scans, with semiparallel routes at various angles providing effective results even when tackling complex unknown areas. The robotic in-wall scanning technique clearly has great promise for government and possibly even military search-and-rescue operations.

See “Robotic Through-Wall Imaging,” IEEE Antennas & Propagation Magazine, Vol. 59, No. 5, October 2017, p. 47.

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