Li-Fi in the ER

Visible light communication could reduce interference with medical equipment

2 min read
Li-Fi in the ER
Photo: Alamy

Imagine if you could eliminate the tangle of wires that snake across a hospital patient’s body so machines can monitor his or her vital signs. Sounds like a great idea. But wirelessly transmitting data from the patient to the machines cluttering hospital rooms creates the risk of electromagnetic interference. So one group of researchers in South Korea is proposing that some machines use Li-Fi instead.

The team used visible light communications, also known as Li-Fi, to transmit readings from an electroencephalograph (EEG) over a distance of about 50 centimeters. “It’s a very much friendlier means of transmitting biomedical signals in a hospital,” says Yeon Ho Chung, an engineer at Pukyong National University in Busan. The group described their work in the IEEE Sensors Journal.

The signals from an EEG, which measures brain activity, are relatively weak ones, Chung says, with power ranging from 0.5 to 100 millivolts, and frequencies between 0.5 and 45 hertz. The faintness of the signals required the engineers to first amplify them enough to drive the red, green, and blue LEDs they were using to transmit their data.

Transmitting over a single channel produced a reading that was distorted at some points by bit errors. To counter that, the team used color filters and photodiodes matched to each of the three LED colors. Comparing the signals at each of the three photodiodes allowed them to select the bits that were most likely to be correct. Keeping the error rate low, Chung says, is critical to getting useful readings of brain activity—particularly since the electrical activity in the brain can produce a complex signal. “You have to be very accurate. You can’t make any mistakes in transmitting.”

Other researchers at Pukyong have already demonstrated Li-Fi transmission of electrocardiogram readings; Chung’s team is looking into using it for electrooculography, which measures eye movement and could be used by paralyzed people to control computers.

Wireless transmission from medical devices frees up patients so they can move around rather than being tethered to one spot. And using light rather than radio frequencies avoids interference on a crowded radio spectrum.

Groups around the world are exploring Li-Fi as a means of boosting data rates and transmitting more information between computers without worrying about the limitations of radio. Others are developing optical transmission schemes that rely instead on infrared light. “There’s actually vast opportunities in visible light communications,” Chung says. “We see really great potential in this.”

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Metamaterials Could Solve One of 6G’s Big Problems

There’s plenty of bandwidth available if we use reconfigurable intelligent surfaces

12 min read
An illustration depicting cellphone users at street level in a city, with wireless signals reaching them via reflecting surfaces.

Ground level in a typical urban canyon, shielded by tall buildings, will be inaccessible to some 6G frequencies. Deft placement of reconfigurable intelligent surfaces [yellow] will enable the signals to pervade these areas.

Chris Philpot

For all the tumultuous revolution in wireless technology over the past several decades, there have been a couple of constants. One is the overcrowding of radio bands, and the other is the move to escape that congestion by exploiting higher and higher frequencies. And today, as engineers roll out 5G and plan for 6G wireless, they find themselves at a crossroads: After years of designing superefficient transmitters and receivers, and of compensating for the signal losses at the end points of a radio channel, they’re beginning to realize that they are approaching the practical limits of transmitter and receiver efficiency. From now on, to get high performance as we go to higher frequencies, we will need to engineer the wireless channel itself. But how can we possibly engineer and control a wireless environment, which is determined by a host of factors, many of them random and therefore unpredictable?

Perhaps the most promising solution, right now, is to use reconfigurable intelligent surfaces. These are planar structures typically ranging in size from about 100 square centimeters to about 5 square meters or more, depending on the frequency and other factors. These surfaces use advanced substances called metamaterials to reflect and refract electromagnetic waves. Thin two-dimensional metamaterials, known as metasurfaces, can be designed to sense the local electromagnetic environment and tune the wave’s key properties, such as its amplitude, phase, and polarization, as the wave is reflected or refracted by the surface. So as the waves fall on such a surface, it can alter the incident waves’ direction so as to strengthen the channel. In fact, these metasurfaces can be programmed to make these changes dynamically, reconfiguring the signal in real time in response to changes in the wireless channel. Think of reconfigurable intelligent surfaces as the next evolution of the repeater concept.

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