Ricocheting radio waves monitor the tiniest movements in a room

August 06, 2018

DURHAM, N.C. -- 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.
-end-
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://journals.aps.org/prl/accepted/b307fY31A5a13c5579fc4252303f8b2e5e024fc00

Duke University

Related Healthcare Articles from Brightsurf:

How to protect healthcare workers from COVID-19
Researchers are developing simple and inexpensive tools--like a DIY ventilator--to treat patients more effectively and prevent disease transmission in hospitals.

Healthcare as a climate solution
Although the link may not be obvious, healthcare and climate change -- two issues that pose major challenges around the world -- are in fact more connected than society may realize.

Healthcare's earthquake: Lessons from COVID-19
Leaders and clinician researchers from Beth Israel Lahey Health propose using complexity science to identify strategies that healthcare organizations can use to respond better to the ongoing pandemic and to anticipate future challenges to healthcare delivery.

Poor women in Bangladesh reluctant to use healthcare
A study, published in PLOS ONE, found that the women living in Dhaka slums were reluctant to use institutionalised maternal health care for fear of having to make undocumented payments, unfamiliar institutional processes, lack of social and family support, matters of honour and shame, a culture of silence and inadequate spousal communication on health issues.

Women and men executives have differing perceptions of healthcare workplaces according to a survey report in the Journal of Healthcare Management
Healthcare organizations that can attract and retain talented women executives have the advantage over their peers, finds a special report in the September/October issue of the Journal of Healthcare Management, an official publication of the American College of Healthcare Executives (ACHE).

Greater financial integration generally not associated with better healthcare quality
New findings from a Dartmouth-led study, published in the August issue of Health Affairs, show that larger, more integrated healthcare systems do not generally deliver better quality care, and that there is significant variation in quality scores across hospitals and physician practices, regardless of whether they are independent or owned by larger systems.

Wearable sensor may help to assess stress in healthcare workers
A wearable biosensor may help monitor stress experienced by healthcare professionals, according to a study published in Physiological Reports.

Healthcare innovators focus on 'quality as a business strategy' -- update from Journal of Healthcare Quality
Despite two decades of effort -- targeting care processes, outcomes, and most recently the value of care - progress has been slow in closing the gap between quality and cost in the US healthcare system.

How runaway healthcare costs are a threat to older adults and what to do about it
Empowering Medicare to directly negotiate drug prices, accelerating the adoption of value-based care, using philanthropy as a catalyst for reform and expanding senior-specific models of care are among recommendations for reducing healthcare costs published in a new special report and supplement to the Winter 2019-20 edition of Generations, the journal of the American Society of Aging (ASA).

How can healthcare achieve real technology driven transformation?
Real transformation in healthcare through the adoption of artificial intelligence (AI), robotics, telecommunications, and other advanced technologies could provide significant improvements in healthcare quality, productivity, and access.

Read More: Healthcare News and Healthcare Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.