Heeju Park/Cornell University

Embroidered optical fibers of the compression shirt track respiration rate, which has been researched to be more accurate than heart rate.

October 18, 2023

Cornell Researchers Create New Smart Shirt, Utilize Innovative Fiber Optic Embroidery

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An advancement in wearable technology, powered by Cornell researchers, transforms a simple shirt into a health and fitness tracker. Prof. Heeju Park, human centered design, and Jeyeon Jo grad created a compression shirt that uses embroidered optical fibers to provide real-time respiratory rate monitoring. The new smart shirt primarily benefits those with respiratory disorders, but may also appeal to athletes and anyone wishing to track the rhythm of their breathing. 

“Wearable technology isn’t really comfortable. Nobody wants to wear an ugly, uncomfortable, heavy garment with dangling electronics and wires,” Park said. “So my intention was to create a garment that provides a useful function, but at the same time is just normal clothing.”

The fitted nature of the shirt around the ribcage enables it to accurately and rapidly measure respiratory rate, which refers to the number of breaths a person takes per minute — a key health indicator separate from heart rate. 

“Though a health concern, heart rate is predictable. You usually know if you have high blood pressure and just need to monitor it,” Park said. “But a change in respiratory rate signals a sudden, serious issue in the respiratory system.”

For example, in certain cases of sleep apnea, the muscles around the throat can temporarily relax, narrowing the airway and temporarily cutting off breathing. While a heart rate sensor wouldn’t identify the problem since the heart is still beating, a smart shirt would detect the absence of breathing and immediately alert the individual or their caregiver. 

Optical fibers — flexible plastic strands about as thick as human hair — incorporated into the shirt detect changes in light intensity to determine whether the chest has expanded or contracted. Unlike other bulky and rigid electronic sensors, the optical fibers are flexible, virtually unnoticeable and can be easily stitched into a shirt as a part of its conventional production. 

Park compared optical fibers to a computer cord, pulling both ends outwards until taut and then moving his hands together until the cord relaxes and bends.

“Compression reduces the light passing through the fiber optic from one end to the other,” Park said. “If the fiber is under a lot of stress from being stretched, just poking it will decrease the amount of light that reaches the end.”

The optical fiber straightens and bends with every inhale and exhale. The shape affects how much light is detected by the microcontroller at the end of the fiber. A curved optical fiber causes a weaker light intensity, indicating a contraction of the chest and the exhalation of the wearer. A straight optical fiber causes a stronger light intensity, signaling that the chest has expanded and the wearer has inhaled. 

The flexibility of a fiber optic strand enables it to measure the most subtle expansions and contractions of the chest, but this flexibility also means it can easily lose its original form.

“If I stretch the fiber optic on a piece of fabric and then allow it to release, it won’t always go back to its original shape,” Park said. “That was a big problem, because the fiber optic couldn’t function as a sensor anymore.” Instead of returning to its symmetrical curves, the strand bent unpredictability, weakening its ability to accurately measure light intensity.  

To address this unpredictability, Park stitched the fiber optic strands into a nylon casing. The embroidered enclosure acts like a tunnel, gently guiding the movement of the strand as it straightens and curves with an individual’s breaths. The casing also prevents the fragile threads from rubbing against other layers of clothing.

Park and Jo filed a patent application for the embroidery of the fiber optic sensor and are now expanding this technology to other wearable devices. With support from the Cornell Technology Licensing Office IGNITE fund, they recently developed a smart shoe insole capable of real-time gait monitoring. 

“Now the optical fiber is not a stretch sensor but a compression sensor. As the wearer takes a step, we are able to monitor which fiber optics are compressed more, compressed less or not compressed,” Park said. 

By monitoring the sequence of foot pressure, the smart insole can tell the wearer if they tend to overpronate or underpronate, which refers to the way the foot rolls inwards or outwards. Excessive pronation in either direction can increase the risk of ankle sprains and cause foot and back pain. These gait-monitoring insoles can also be used by children with cerebral palsy or autism who may walk on their tiptoes. 
“If you think about walking, it’s a lifetime exercise. It’s a daily routine,” Park said. “[Wearable technology] can be more practical than an LED flashing on your jacket. It offers a kind of home care — a remote health care.”

Ellie VanHouten can be reached at [email protected]