Multi-Path PPG Sensor Layout for Motion Artifact Isolation
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Solution Overview
Problem
Existing PPG sensors face challenges in accurately measuring heart rate and other physiological metrics due to motion artifacts and varying signal quality caused by changes in the location and orientation of the sensor on the body, leading to reduced accuracy during activities involving motion.
Innovation Solution
The use of multiple source-detector pairs with independently addressable combinations to acquire PPG signals, which are processed to isolate the cardiac component by removing the motion component, and selecting the highest-quality signal for estimation based on spatial information and quality metrics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single source-detector pair is used for PPG measurement, then the device complexity is low, but the measurement precision deteriorates during motion due to motion artifacts
Solution Approach 1:
The patent divides the single PPG measurement function into multiple source-detector pairs, each capturing signals from different spatial locations. This segmentation allows the system to isolate cardiac signals from motion artifacts by comparing signals across multiple channels, thereby improving measurement precision during motion without requiring a completely complex new sensor architecture
Solution Approach 2:
The patent combines multiple PPG signals from different source-detector pairs through signal processing algorithms. By merging these signals and applying motion artifact removal techniques, the system achieves higher measurement precision while keeping the overall device complexity manageable through shared electronics and processing
2Measurement precision
If multiple source-detector pairs are used to remove motion artifacts, then the measurement precision improves, but the device complexity increases
Solution Approach 1:
The patent extracts the motion component from the PPG signals by analyzing temporal and spatial variations across multiple source-detector pairs. By separating and removing the motion artifact component, the system improves physiological metric accuracy while managing processing complexity through targeted extraction rather than complete signal reconstruction
Solution Approach 2:
The patent introduces intermediate processing stages that handle motion artifact removal between signal acquisition and final physiological metric calculation. This intermediary approach allows complex processing to be broken down into manageable steps, improving accuracy without overwhelming system complexity
3Measurement precision
If green light wavelength is used for PPG measurement, then the hemoglobin absorption is high improving signal quality, but the adaptability to different measurement conditions is reduced
Solution Approach 1:
The patent implements multiple light sources with different wavelengths (including green and infrared) that can be selectively activated based on measurement conditions. This multi-functional approach allows the system to maintain high signal quality by using green light when appropriate while adapting to different skin tones, motion levels, and measurement scenarios by switching to infrared or combining wavelengths
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Improves the accuracy of heart rate and other physiological metric estimations by effectively isolating cardiac signals from motion artifacts, especially during physical activities, using multiple light paths and spatially informed signal processing techniques.
Implementation Method 1
A PPG sensor may be utilized to detect the volumetric change in blood vessels. A PPG sensor usually includes a light source, typically a light-emitting diode (LED), and a light-sensitive sensor, typically a photodiode. Blood passing through the vasculature between the light source and the sensor will modulate the light path between the two, resulting in a deviation in the current produced by the photodiode.
Implementation Method 2
Many wearable PPG devices use green light, as the hemoglobin absorption of light is up to 20 times greater at green wavelengths than at IR wavelengths.
Data Source
AI summary
Systems, devices, and methods for tracking one or more physiological metrics (e.g., heart rate, blood oxygen saturation, and the like) of a user are described. For example, one or more light sources and one or more light detectors may be positioned on a wearable device such that light can be emitted towards the user's skin and further such that light reflected back to the wearable device can be measured and used to generate values for the one or more physiological metrics.