Multi-Wavelength PPG Sensing for Motion Artifact Cancellation
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Solution Overview
Problem
Conventional optical heart rate detection devices struggle with motion artifacts caused by simple muscle activities, such as wrist movement, which conventional methods like using an acceleration detector fail to address, leading to degraded detection accuracy.
Innovation Solution
A heart rate detection device employing a light source that emits multiple wavelengths and a light detector to sense light from the skin, combined with a processor that performs vector operations on registered and current light detection signals to eliminate motion artifacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If an acceleration detector is used to denoise optical physiological detection signals, then detection accuracy is improved for strong movements, but detection accuracy deteriorates for simple muscle activities because the acceleration detector cannot generate usable results
Solution Approach 1:
The patent segments the light detection into multiple wavelength channels (e.g., red and infrared LEDs) to separately capture different types of signals. By dividing the detection function across multiple wavelength-specific detectors, the system can independently analyze and process signals from different sources, enabling it to handle both strong movements and simple muscle activities effectively
Solution Approach 2:
The patent changes the detection parameter from single-wavelength to multi-wavelength detection. By using light sources emitting at different wavelengths (e.g., 650nm red LED and 940nm infrared LED) and analyzing their respective absorption characteristics, the system can distinguish between motion artifacts and actual physiological signals across different movement intensities
2Measurement precision
If multiple wavelengths of light are used to illuminate the skin surface, then motion artifact cancellation is improved, but device complexity increases due to multiple light sources and detectors
Solution Approach 1:
The patent merges multiple light sources and detectors into a single integrated physiological detection device. The multi-wavelength light sources (e.g., red and infrared LEDs) and corresponding detectors are combined in one unit that can be worn on the body, allowing motion artifact cancellation through software processing while maintaining a compact, wearable form factor
Solution Approach 2:
The patent replaces complex mechanical motion sensing systems (like acceleration detectors) with an optical-based system that uses multiple wavelengths. By substituting mechanical measurement approaches with optical absorption spectroscopy, the system achieves motion artifact cancellation through biochemical principles rather than mechanical complexity
3Ease of operation
If conventional optical detection is used during exercises, then portability is improved, but detection accuracy deteriorates due to noise from relative movement between device and skin surface
Solution Approach 1:
The patent implements a feedback mechanism where the system continuously monitors signals at multiple wavelengths and uses this information to dynamically adjust processing parameters. The multi-wavelength detection provides real-time feedback about motion artifacts, allowing the system to compensate and maintain accurate physiological measurement even during portable use
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
The device achieves high detection accuracy by effectively removing motion artifacts from muscle activities, even when the device is not moving relative to the skin, with low power consumption and improved signal processing efficiency.
Implementation Method 1
a light source configured to emit light covering multiple wavelengths to illuminate a skin surface of a user, and a light detector configured to sense emergent light from the skin surface
Implementation Method 2
the processor configured to perform a vector operation between a predetermined intensity distribution of multiple light colors and current light detection signals of the multiple light colors so as to eliminate the motion artifact in detected photoplethysmogram (PPG) signals
Data Source
AI summary
There is provided a physiological detection device including a white light source, a molding and a pixel array. The white light source is configured to emit white light having a color temperature between 2800K and 3200K. The molding is formed upon the white light source and configured to constrain an emission angle of the white light between 60 and 80 degrees. The pixel array is covered by a filter layer having a passband between 570 nm and 620 nm configured to filter the white light.