Radio waves reveal person's presence in a room, even beyond the sensor's line of sight
Relief may be on the horizon for anyone who has ever jumped around a room like a jack-in-the-box to get motion-sensing lights to turn back on, thanks to a new motion sensor based on metamaterials that is sensitive enough to monitor a person's breathing.
In a pair of new studies, researchers from Duke University and Institut Langevin, France, have shown that patterns made by radio waves can detect a person's presence and location anywhere inside a room.
The findings appeared recently in Scientific Reports and Aug. 6 in the Physical Review Letters.
This new motion-sensing technology could lead to new smart home devices for energy savings, security, healthcare and gaming.
"Energy companies don't love infrared motion detectors because they have lots of problems," said David R. Smith, the James B. Duke Professor of Electrical and Computer Engineering at Duke. "The amount of space they can cover is limited, a person has to be within their line of sight to be detected, and probably everyone has had the experience where the lights have gone off because they've sat still for too long. Radio waves can get around all of these limitations."
In their initial paper published earlier this year, the researchers took advantage of patterns created by radio waves bouncing around a room and interfering with themselves. These unique patterns change with the slightest perturbation of the room's objects, allowing a sensitive antenna to detect when something moves in or enters the room. And by comparing how these patterns change over time, they can also be used to detect cyclical movements like a fan blade turning -- or even a person breathing.
In the latest paper, the team shows that with a bit of training, the system can also extract information necessary to locate objects or people in a space. The demonstration system was taught the pattern of radio waves scattered by a triangular block placed in 23 different positions on a floor. That calibration is enough not only to distinguish between the learned 23 scenarios, but to also distinguish the positions of three identical blocks placed in any one of 1,771 possible configurations.
The technology works by taking advantage of the way radio waves behave in an enclosed room. Their ability to continuously reflect off multiple surfaces creates complex interference patterns throughout a room. In the past, this complexity has been an obstacle for systems trying to locate the origin of a signal. But Smith and his colleagues have now shown that this same complexity can be tapped to detect movement and locate objects within a room.
"The complexity of the way radio waves bounce around a room and interfere with themselves creates a sort of fingerprint," explained Philipp del Hougne, a researcher visiting Smith's laboratory from Institut Langevin in Paris, France. "And each time an object within a room moves, even a little bit, that fingerprint changes."
The challenge lies with finding the most efficient way to ink that fingerprint in the first place. It requires a lot of information, del Hougne explained, and there are multiple traditional ways it can be done, but they all have drawbacks.
A large number of antennas could be installed in many places around a room to take multiple measurements, but this would be costly and inconvenient. Another tactic would be to measure many different frequencies, as each bounces around a room in a unique way. This approach, however, would likely create interference with other radio wave signals like Wi-Fi and Bluetooth operating within a room.
The researchers' solution is to dynamically control the shape of the waves using metamaterials -- artificial materials that manipulate waves like light and sound through properties of their structure. A flat-panel metamaterial antenna can shape waves into arbitrary configurations and create many different wave fronts in rapid succession.
"It doesn't even matter what those particular wave shapes are," said Smith. "As long as they're diverse, the detector will pick up enough different patterns to determine if something is there and where it is."
"There are other technologies that could achieve similar wave front shaping capabilities, but they are much more expensive both in cost and energy usage," said Mohammadreza Imani, a postdoctoral fellow in Smith's lab who also worked on the papers. "Studies have shown that the ability to adjust a room's temperature when people leave and come back can reduce power consumption by around 30 percent. But if you're trying to save energy by spending more energy changing the antenna pattern, then you're not helping."
And energy savings may be just the tip of the iceberg. The ability to count the number of people in a room, distinguish body positions and monitor breathing patterns also has potential applications in security, healthcare and gaming.
The French scientists on the project have created a related startup company called Greenerwave.
"While we're definitely still continuing with the energy angle, we'll also see where the research takes us," Smith said.
This work was supported by the Air Force Office of Scientific Research (FA9550-12-1-0491).
CITATIONS: "Dynamic Metasurface Aperture as Smart Around-the-Corner Motion Detector," Philipp del Hougne, Mohammadreza F. Imani, Timothy Sleasman, Jonah N. Gollub, Mathias Fink, Geoffroy Lerosey, and David R. Smith. Scientific Reports, 2018. DOI: 10.1038/s41598-018-24681-9
"Precise localization of multiple noncooperative objects in a disordered cavity by wave front shaping." Philipp del Hougne, Mohammadreza F. Imani, Mathias Fink, David R. Smith, and Geoffroy Lerosey. Phys. Rev. Lett., 2018. LINK: https:/
Ken Kingery | EurekAlert!
Touring IPP’s fusion devices per virtual-reality viewer
07.08.2018 | Max-Planck-Institut für Plasmaphysik
Electron Beam Patterning for high-resolution full-color OLED displays
07.08.2018 | Fraunhofer-Institut für Organische Elektronik, Elektronenstrahl- und Plasmatechnik FEP
You seem to be standing in the plasma vessel looking around: Where otherwise plasmas with temperatures of several million degrees are being investigated, with...
A magneto-plasmonic nanoscale router and a high-contrast magneto-plasmonic disk modulator controlled by external magnetic fields
Plasmonic waveguides open the possibility to develop dramatically miniaturized optical devices and provide a promising route towards the next-generation of...
The first unambiguous observation of a radioactive molecule, 26AlF, was made in the ancient nova-like object CK Vul (or Nova Vul 1670), which - most likely - is a stellar-merger remnant. The eruption of the object was observed between 1670-1672 in Europe. The interest in this object has been recently rejuvenated by the discovery of molecular gas of a very peculiar isotopic composition in the remnant.
The finding was announced by an international research team led by Tomasz Kamiński (CfA), including Karl Menten (MPIfR Bonn).
The variable star CK Vulpeculae (CK Vul) is known as the location of a stellar outbreak, a nova, which was observed by European astronomers in the 17th century...
Scientists from NUST MISIS and colleagues from the University of Bayreuth, the University of Münster (Germany), the University of Chicago (U.S.), and Linköping University (Sweden) have created nitrides, a material previously considered impossible to obtain. More amazing, they have shown that the material can be obtained using a very simple method of direct synthesis. Articles about the revolutionary research results have been published in Nature Communications and Angewandte Chemie International Edition.
Nitrides are actively used in superhard coatings and electronics. Usually, the nitrogen content in these materials is low, and it is therefore difficult to get...
An international group of researchers has achieved the world’s first multi-qubit demonstration of a quantum chemistry calculation performed on a system of trapped ions, one of the leading hardware platforms in the race to develop a universal quantum computer.
The research, led by Cornelius Hempel and Thomas Monz, explores a promising pathway for developing effective ways to model chemical bonds and reactions using...
27.07.2018 | Event News
25.07.2018 | Event News
13.07.2018 | Event News
07.08.2018 | Power and Electrical Engineering
07.08.2018 | Life Sciences
07.08.2018 | Materials Sciences