On the subject of THz and drones.
A pair of drones can use Wi-Fi signals to see through walls.
Researchers at UC Santa Barbara were able to create three-dimensional images of the objects behind a brick wall in a series of experiments with the
The two flying machines work in tandem. In the demonstration, they fly around a four-sided brick building. One drone transmits a continuous Wi-Fi
signal, while the other, on the opposite side of the house, measures its power after it passes through.
No, really. You can see through walls using drones and Wi-Fi
Researchers explore 3D imaging using drones
By Katyanna Quach 20 Jun 2017 at 23:51 19 Reg comments SHARE ▼
Video Drones can perform three-dimensional imaging of objects through walls using Wi-Fi, a team of researchers demonstrated for the first time.
Chitra Karanam, a PhD student, and Yasamin Mostofi, a professor at the department of electrical and computer engineering at the University of
California, Santa Barbara, presented their results [PDF] at the Association for Computing Machinery/Institute of Electrical and Electronics Engineers
International Conference on Information Processing in Sensor Networks.
“Our proposed approach has enabled unmanned aerial vehicles to image details through walls in 3D with only Wi-Fi signals. This approach utilizes
only Wi-Fi RSSI measurements, does not require any prior measurements in the area of interest and does not need objects to move to be imaged,”
Mostofi said on Monday.
RSSI stands for received signal strength indicator. A drone beams radio waves at 2.4GHz, and another drone on the other side of the wall measures the
power of the signals.
The researchers used two 3D Robotics RTF X8+ drones, measuring 40 x 40cm (15.7 x 15.7in) and weighing 3.5kg (7.7lb) each.
The strength of the received signal drops by a certain level depending on the presence of objects through the wall, Mostofi explained to The
“3D imaging is harder than 2D, since there are a lot more unknown areas. We approximate the wave model and solve Maxwell’s equations that describe
the propagation of the Wi-Fi waves. Next, the signals are compressed to form an image,” she said.
Just like pixels make up a two-dimensional image, voxels describe a patch of three-dimensional space. The final step is to use the voxels to build a
model of the interior hiding behind the walls.
Both drones are always parallel with one another and travel in a zig-zag motion. They hover outside the 10-cm (4-in) brick walls, sweeping the area at
different angles to try to get a good picture inside.
But it’s not possible to catch everything, and the researchers have to fill in the blanks by employing a bit of nifty guesswork during the modelling
“Each voxel looks at its neighbors’ image decisions. For instance, if a voxel’s own decision is that this voxel should be empty but then the
neighbors’ decisions are all full (non-empty), then the voxel may want to revise its decision since there should be a spatial correlation.
“So the belief propagation method is a way of doing this iterative update. At some point, the image will converge to something and will not change
any more. That is the final imaging result we produce, and its quality has improved a lot beyond that initial processing phase,” said Mostofi.
Some of the clear structure like edges are lost. But the drone manages to estimate the length of objects to a pretty good accuracy – a wall that is
actually 1.48 metres is measured as 1.5 metres.
It’s not the first time Wi-Fi has been used for imaging. A group from MIT used it to capture human motion behind a wall. But the UC Santa Barbara
group are the first to do this with drones, they claim.
The brick wall scenario is simple, and a lot of problems have to be solved before drones can be used for more complex situations like
search-and-rescue operations, structural modelling to monitor the state of buildings and bridges, or inspecting potential archaeological sites.
There’s definitely room for improvement, Mostofi said. Issues such as interference from other Wi-Fi networks or needing better image processing
methods will need to be addressed before it’s applicable in the real world
Ultrafast wi-fi, which is 100 times quicker than today’s mobile networks is on the horizon, after scientists proved they could send complex data
using high-frequency radiation.
The researchers sent video signals using terahertz, rather than traditional microwaves, at speeds of 50 gigabytes per second. Most wireless networks
only operate at top speeds of 500 megabytes a second.
The breakthrough could lead to high-speed streaming on the go.
“We showed that we can transmit separate data streams on terahertz waves at very high speeds and with very low error rates,” corresponding author
Professor Daniel Mittleman, from Brown University, said in a statement. “This is the first time anybody has characterized a terahertz multiplexing
system using actual data, and our results show that our approach could be viable in future terahertz wireless networks.”
The multiplexer uses a single guideline to transmit both signals at the same time. The guideline has a slit cut into it and some of the signals will
leak out of it. The angle at which they leak out depends on the frequency of the signal so the two signals won’t interfere with each other. So
currently, the angle of the receiver is very important to keep the error rate down.
“If the angle is a little off, we might be detecting the full power of the signal, but we’re receiving one sideband a little better than the
other, which increases the error rate,” Mittleman explained. “So it’s important to have the angle right.”
edit on 11-4-2018 by AdamE because: (no reason given)