Biosignal Sensor Polarizer Configuration for Motion Noise Reduction
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Solution Overview
Problem
Biosignal sensors face noise interference due to changes in position and angle between the skin and the sensor caused by user motion, which degrades the accuracy of biometric information obtained.
Innovation Solution
The biosignal sensor employs a light-emitting element and a photo-detective element with polarizers arranged in specific perpendicular orientations to selectively transmit and block light, reducing noise by stabilizing the DC component affected by skin motion, and includes a phase retarder to enhance light conversion efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional biosignal sensor is used without polarizers, then the device structure is simple, but noise increases due to position changes between skin and sensor caused by user motion
Solution Approach 1:
The patent introduces polarizers as intermediary optical elements between the light source and detector. These polarizers modulate the light signal based on skin motion, converting mechanical displacement into optical signal variations that can be distinguished from noise, thereby improving reliability without fundamentally changing the sensor structure
Solution Approach 2:
The patent changes the optical parameters of the system by introducing polarized light and analyzing polarization state changes. By measuring changes in polarization parameters caused by skin motion, the system can differentiate between actual biosignals and noise, improving signal stability while maintaining a relatively simple sensor structure
2Measurement precision
If polarizers are added to reduce noise, then measurement precision improves, but light loss increases
Solution Approach 1:
The patent employs periodic modulation of light polarization states through the polarizers. By using alternating polarization orientations and analyzing the periodic variations in the detected signal, the system achieves high measurement precision while recovering and utilizing the light that would otherwise be blocked, thereby reducing overall light loss
3Measurement precision
If multiple photo-detective elements are used to detect biosignals, then measurement precision improves, but device complexity increases
Solution Approach 1:
The patent divides the detection function into multiple specialized photo-detective elements, each responsible for detecting specific polarization components or spatial regions. This segmentation allows precise measurement of different signal characteristics while organizing the complexity into manageable, functionally distinct modules that can be systematically analyzed and processed
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
This configuration effectively reduces noise and improves the accuracy of biometric information by stabilizing the DC component and increasing signal efficiency, even during skin motion, while maintaining high light efficiency without significant light loss.
Implementation Method 1
a first polarizer configured to selectively transmit light in a first polarization direction
Implementation Method 2
a second polarizer configured to selectively transmit light in a second polarization direction, the first polarization direction and the second polarization direction being perpendicular to each other
Implementation Method 3
a photo-detective element configured to detect a biosignal from light reflected from a target that is external to the biosignal sensor
Data Source
AI summary
A biosignal sensor includes a light-emitting element, a photo-detective element configured to detect a biosignal from light reflected from an in-vivo target, a first polarizer configured to selectively transmit light in a first polarization direction, and a second polarizer configured to selectively transmit light in a second polarization direction. The light-emitting element includes a first light-emitting element overlapped with the first polarizer in a vertical direction, the photo-detective element includes a first photo-detective element overlapped with the second polarizer in the vertical direction, the first light-emitting element and the first photo-detective element are parallel to each other along a first direction that is perpendicular to the vertical direction, and the first polarization direction and the second polarization direction are perpendicular to each other.