Wearable health devices like smartwatches, earbuds, and fitness trackers have become part of daily life. While they offer useful features, their ability to monitor vital signs accurately—especially during everyday movement—remains limited. A new research initiative led by Assistant Professor Dong Ma at Singapore Management University (SMU) aims to change that. His work focuses on unlocking the full potential of photoplethysmography (PPG) in wearable healthcare.
Understanding PPG and Its Challenges
PPG is a non-invasive optical technique used widely in clinical environments. It measures vital signs like pulse rate and blood oxygen levels by shining light into the skin and recording the reflected signal. Since its introduction in the 1930s, PPG has become standard in hospitals — most commonly seen in clip-on oximeters.
In recent years, consumer devices have incorporated PPG to provide health data on the go. However, these devices face serious limitations. Unlike controlled clinical settings, real-world use introduces factors such as movement, changing posture, and environmental interference — all of which can distort the PPG signal and reduce accuracy.
“Any factor that affects the light’s propagation path will distort the PPG signal and impair performance,” explained Professor Ma.
Addressing Motion and Posture Issues
Professor Ma emphasized that daily activities like walking or shifting posture cause subtle movements between the skin and the sensor. This results in misalignment and noise, which interfere with accurate readings.
“When posture changes, the contact pressure between the skin and sensor changes too, which can deform the skin and degrade the signal,” said Professor Ma.
While research on improving signal quality has been ongoing for decades, Ma points out two major hurdles: motion artifacts often overpower the intended blood pulse signals, and when the sensor shifts too much, meaningful signals may vanish entirely.
The Role of Transparent Pressure Sensors
To tackle these challenges, Ma’s team proposes incorporating contact pressure (CP) as a critical factor in PPG monitoring. They’ve developed a transformation model that reconstructs distorted PPG signals using CP data. However, to bring this solution to wearable devices, they will need transparent pressure sensors—a technology that doesn’t yet exist commercially.
“Transparent pressure sensors are technically possible, and my proposal could drive their development,” Ma explained. “I am seeking collaborations to create these sensors and integrate them into wearable devices.”
Toward Real-World Applications
While current wearables provide heart rate and oxygen saturation reliably at rest, more advanced metrics like heart rate variability, blood pressure, breathing rate, and vascular health are still limited to stationary measurements. Professor Ma’s research could help overcome these limitations, making wearables viable for real-time, active monitoring.
This research is especially timely for Singapore:
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The country is approaching super-aged nation status.
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Cardiovascular disease caused over 31% of all deaths in 2022.
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Over 400,000 Singaporeans live with diabetes, conditions that require daily health monitoring.
“Wearable healthcare technologies can play a vital role in elderly care and promoting overall wellbeing,” said Professor Ma.
A Vision for the Future
With global populations aging and health management becoming more critical, physiological sensing through wearables offers significant potential. Professor Ma believes this area holds vast opportunities for innovation.
“Physiological sensing reflects how the human body truly functions. As health awareness grows worldwide, I see more needs and challenges to explore in the future,” he concluded.
