Abstract
Wearable photoplethysmography (PPG) sensors detect a small pulsatile signal against a large non-pulsatile background. The signal quality varies widely across users, activities, and conditions. This publication describes systems and techniques in which the optical geometry of a PPG sensor is adjusted during operation to balance signal quality against power consumption. A voltage-controlled film, for instance, over an emitter and a photodetector changes an effective aperture, and thereby the depth of light penetration and the perfusion index, without moving parts. A control system uses a perfusion index and a motion level to select the aperture size produced by the voltage-controlled film. The system opens the aperture to reduce power when perfusion is high and motion is low, but the system closes the aperture, while increasing drive current, to improve signal quality when perfusion is low or motion is high. The respective apertures over the emitter and the photodetector can also be reduced together to reject contributions from superficial skin layers.
Creative Commons License
This work is licensed under a Creative Commons Attribution 4.0 License.
Recommended Citation
Vavadi, Hamed; Yao, Kaiyuan (Kai); and Trehan, Chintan, "Dynamically Adjustable Photoplethysmography Geometry Based on Perfusion Index and Motion Profile to Balance Accuracy and Power Efficiency", Technical Disclosure Commons, ()
https://www.tdcommons.org/dpubs_series/11385