A Watch on the Watch
SARINA TRACY, SARINA.TRACY@PHOTONICS.COM
Whether we use our fingertips to count the pulses thumping in our wrists after a run, or guess our hydration by the amount of water left in our bottles at the end of the day, we’ve all monitored our bodies from time to time – and it can be sketchy at best.
For many, however, there is no room for error – biometric monitoring can be a matter of life or death. And to maintain the most accurate readings of glucose, pulse or hydration, people are often tied to invasive or bulky machines such as glucose monitors, pulse oximeters or echocardiography equipment. Now, researchers have found a noninvasive way for people to independently monitor their physiological parameters by renovating a common accessory: the wristwatch.
Two groups of investigators have developed their own wearable biometric watches that use scattered light to monitor the body’s processes. These models can accurately monitor the body in motion, differing from past models that become sensitive to error when the person is walking or playing sports.
Photo courtesy of Optical Society.
Dr. Zeev Zalevsky of Israel’s Bar-Ilan University and colleagues have created a glucose- and dehydration-monitoring watch. The glucose sensor is the first wearable device that can measure glucose concentration directly and noninvasively, the researchers said. “Glucose is the holy grail of the world of biomedical diagnostics,” he said, “and dehydration is a very useful parameter in the field of wellness, which is one of our main commercial aims.”
The biometric watch consists of a laser that generates a wavefront of light onto a patch of skin above an artery, a camera that measures changes in backscattered light, and a magnet. The watch produces speckle when laser light is reflected from an uneven surface or is scattered from an opaque material. Because the technology uses scattered light, movement has no influence on its abilities.
Zalevsky’s watch harnesses magnets to uncover glucose information. Unlike other chemicals present in the blood, glucose exhibits a Faraday effect. When in the presence of a magnetic field, the glucose molecules affect the polarization of the wavefront by influencing the speckle patterns. By analyzing the changing patterns, glucose concentration can be measured. Muscle weakness, a main sign of dehydration, also can alter the strength of the signals, which indicate the relative dehydration level of the user as they fluctuate over time.
When the surface material is moving, such as blood flowing through the circulatory system, the speckle pattern changes as the flow changes, said biomedical engineer Mahsa Nemati, a graduate student at the Delft University of Technology in the Netherlands. Nemati and her team also designed a watch using the speckle effect, but they focused on pulse monitoring. “The speckle change technique can be used to make heartbeat detection a bit more robust to errors, which they are prone to at the moment,” Namati said.
Nemati and her colleagues found that speckle changes can be used to accurately measure flow pulsations of the artery, with just a couple of image pixels sufficient to extract heart rate. “Biometric monitoring can prevent many serious health issues by providing an early warning,” she said. “It is also a good technique to keep an eye on patients in ambulatory situations. … Sophisticated optics is not necessary to implement this, so the costs for devices can be kept low. Another advantage is that the devices can be noncontact or far from the sample.”
Both researchers are looking toward commercialization, with Zalevsky’s team expecting a commercial biometric watch to reach the market within two to three years. Namati’s team is currently working with companies to integrate its motion-friendly pulse monitoring technique into existing sensors for clinical and athletic applications.
“A biometric watch will allow people to be able to monitor their health situation outside the hospital scenario,” Nemati said. “They can have a better quality of life while being able to keep a check on some health issues they have.”