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With the growing demand for vital signs monitoring using wearables, there is a gap between what is offered and the desire for clinical accuracy. Advancements in electronic miniaturization, materials and signal processing have increased possibilities for wearable technology. Optical sensing using photoplethysmography (PPG) is prominent within the field of wearable healthcare due to the non-invasive and versatile nature of the modality. Different aspects related to cardiovascular health can be screened and monitored with PPG, such as oxygen saturation (SPO2), heart rate (HR), heart rate variability (HRV) and possibly blood pressure. Although the principles and possibilities for vital sign monitoring with PPG are present, there is only sparse evidence of clinically relevant signals from commercial optical sensors. Furthermore, there is still a big challenge regarding motion artifact within a wearable device. Currently three wavelengths are commonly used within commercial wearables; green (550nm), red (660nm) and infrared (850nm). There is increased research on including shorter wavelengths (blue) potentially providing increased robustness to motion artifacts during wear.
Within this study, the design challenges for a universal wearable optic patch for improved signal accuracy were investigated. A dual-photodiode and multi-wavelength flexible wearable optic patch was fabricated using hybrid printed electronics. The design was evaluated as a function of patch-skin contact pressure during motion. Our preliminary results show a more robust PPG signal with increased patch-skin contact pressure. In addition, this study demonstrates the capability of our wearable and flexible optical patch at measuring simultaneous multi-wavelength PPG.
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