Optical Sensor Contact Pressure Evaluation Using Multi-Wavelength PPG
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Solution Overview
Problem
Existing wearable devices with optical sensors, such as smartwatches, face challenges in accurately measuring physiological parameters due to improper contact pressure between the sensor and the skin, leading to poor-quality measurements, which are often resolved with additional equipment integration, user calibration, or imprecise algorithms.
Innovation Solution
A method using optical signals at different wavelengths to evaluate contact pressure by comparing optical data from green and red or green and infrared ranges, calculating a parameter, and adjusting the sensor position based on threshold comparisons to ensure optimal contact pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If contact pressure between optical sensor and skin is increased to improve measurement quality, then measurement precision deteriorates due to poor blood flow and signal quality
Solution Approach 1:
The system continuously monitors PPG signal quality metrics (perfusion index, signal-to-noise ratio, AC/DC ratio) and provides real-time feedback to the user through notifications when contact pressure is suboptimal, enabling dynamic adjustment of wearing conditions to maintain reliable measurements
Solution Approach 2:
The system evaluates multiple PPG parameters across different wavelengths (green, red, infrared) and compares their ratios to determine optimal contact pressure conditions, using parameter thresholds to guide user adjustment of device positioning and contact force
2Measurement precision
If additional equipment (force sensors, multiple wavelengths) is added to evaluate contact pressure, then device complexity increases
Solution Approach 1:
The optical sensor performs multiple functions: it measures physiological parameters (heart rate, blood oxygen saturation) and simultaneously evaluates contact pressure quality by analyzing PPG signal characteristics across different wavelengths, eliminating the need for separate force sensors
Solution Approach 2:
The system uses its own PPG measurement capabilities to self-evaluate the quality of its contact with the skin, analyzing signal metrics such as perfusion index and AC/DC ratios to determine whether contact pressure is adequate without requiring external evaluation equipment
3Measurement precision
If user calibration is required for each individual to optimize measurement, then ease of operation decreases
Solution Approach 1:
The system pre-establishes universal threshold values for PPG signal quality parameters (perfusion index thresholds, AC/DC ratio ranges) that work across different users and conditions, eliminating the need for individual calibration while maintaining measurement accuracy
Solution Approach 2:
The system segments the evaluation into standardized parameter thresholds that can be independently assessed and combined, allowing universal application of quality criteria without requiring user-specific calibration data
4Reliability
If contact pressure is not optimized, then measurement quality deteriorates due to motion artifacts and poor signal
Solution Approach 1:
The system continuously monitors PPG signal quality metrics (perfusion index, signal-to-noise ratio, AC/DC ratio) and provides real-time feedback to the user through notifications when contact pressure is suboptimal, enabling dynamic adjustment of wearing conditions to maintain reliable measurements
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
Enhances measurement robustness by normalizing optical signals to account for external factors, eliminating the need for user calibration and improving measurement quality without additional equipment.
Implementation Method 1
determining first optical data using a first optical signal obtained by the optical sensor at a first wavelength; determining second optical data using a second optical signal obtained by the optical sensor at a second wavelength different from the first
Implementation Method 2
The optical signals may be pulse-modulated optical signals... The optical data includes information about the pulse component of the optical signal
Data Source
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AI summary
The invention particularly relates to a method for evaluating a contact pressure between an optical sensor and the skin of a user, the method comprising: a) determining (502) first optical data, using a first optical signal obtained by the optical sensor at a first wavelength, b) determining (504) second optical data, using a second optical signal obtained by the optical sensor at a second wavelength different from the first wavelength, c) analysing (506) at least one comparison of the first optical data with the second optical data, this analysis generating information relating to the contact pressure between the optical sensor and the skin.