Researchers from the Samsung Advanced Institute of Technology have developed a wearable health-monitoring system that's attached to a user's wrist, and can stretch by as much as 30 percent without adversely affecting display or monitoring performance.
In order to overcome performance issues with current stretchable display technologies that make use of plastic, the team applied a 17 x 7 array of stretchable green or red OLED displays and photoplethysmography sensors to a modified elastomer.
Each display pixel is made up of two OLEDs with the optical sensor mounted inbetween. The light is reflected by the wrist and the sensor "monitors the variation in the reflected light intensity owing to the volumetric changes in the blood vessels according to the cardiac cycle" and the reading is then processed onboard for real-time display via the array.
The elastomer's molecular composition was tweaked by the team to improve thermal resistance, and to make it better suited to manufacture using existing semiconductor production methods. And the size of the OLED/optical sensor array was chosen for clear display of letters and digits.
"We applied an ‘island’ structure to alleviate the stress caused by elongation," said co-first author of the paper, Yeongjun Lee. "More stress was induced in the area of the elastomer, which has a relatively low elasticity coefficient and is thus more likely to become deformed. This allowed us to minimize the stress sustained by the OLED pixel area, which is more vulnerable to such pressure. We applied a stretchable electrode material (cracked metal) that resists deformation to the elastomer area, and this allowed the spaces and wiring electrodes between the pixels to stretch and shrink without the OLED pixels themselves becoming deformed."
The research team tested the prototype system, which is powered by a thin bendable battery, by attaching it to the inner wrist of a user, with the stretchable display portion positioned at the hand end and the more rigid processing module and battery further up the inner arm.
The researchers observed stable heart-rate measurement and display operation even with animated wrist movement, with the signals picked up reported to be 2.4 times stronger than those from a fixed silicon sensor. They managed to stretch the device by up to 30 percent without any performance degradation, and continually operated the device over a thousand repeated stretches.
"The strength of this technology is that it allows you to measure your biometric data for a longer period without having to remove the solution when you sleep or exercise, since the patch feels like part of your skin," said principal researcher, and corresponding author of the paper, Youngjun Yun. "You can also check your biometric data right away on the screen without having to transfer it to an external device. The technology can also be expanded to use in wearable healthcare products for adults, children and infants, as well as patients with certain diseases."
The eventual goal of the research is to commercialize stretchable health monitors, with the team planning to make high-resolution readings of heart rate, oxygen saturation, blood pressure, EMG and so on, possible on a stretchable wearable device. The development of the chemical- and heat-resistance aspects of the modified elastomer, in particular, are seen as major drivers toward this end.
A paper on the development has been published in the journal Science Advances.
Source: Samsung