Wearable PPG Sensor with Transparent Optical Path for Motion Robustness
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional wearable devices for monitoring vital signs suffer from limited motion robustness and calibration dependency on measurement location due to reliance on a well-defined light path through the skin, which is disrupted by motion and varies with different body locations.
Innovation Solution
A wearable device with an optical emitter and sensor arranged to minimize the optical path-length between them, allowing for direct contact or close proximity, and a processing unit to derive physiological information from the time-varying amplitude of light scattered from the skin, using a configuration that resembles camera-based PPG measurement to reduce motion influence and calibration dependencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional contact sensors are used with a well-defined light path through the skin, then signal strength is improved, but motion robustness deteriorates
Solution Approach 1:
The patent changes the optical path configuration from a deep penetration path through the skin to a shallow path measuring primarily skin surface blood flow. This parameter change in measurement depth allows the system to maintain strong signals while becoming insensitive to motion artifacts that affect deeper tissue measurements.
Solution Approach 2:
The invention extracts the measurement from the deeper tissue layers and isolates it to the skin surface level. By measuring only the superficial blood flow in the skin and not the deeper pulsating vessels, the system removes the source of motion-related signal variations while maintaining measurement quality.
2Adaptability or versatility
If conventional pulse oximeters are used at different body locations, then adaptability is improved, but measurement precision deteriorates due to calibration dependency
Solution Approach 1:
The patent creates a universal measurement approach that works consistently across different body locations by measuring skin surface blood flow, which has similar characteristics regardless of location. This eliminates the need for location-specific calibration functions while maintaining measurement accuracy across forehead, wrist, finger, and other sites.
Solution Approach 2:
The invention changes the measurement parameter from deep tissue oxygen saturation (which varies by location and requires calibration) to skin surface blood flow characteristics (which are location-independent). This parameter transformation enables consistent measurements across diverse measurement sites without recalibration.
3Reliability
If camera-based remote PPG is used, then motion robustness is improved, but device complexity increases
Solution Approach 1:
The patent employs simple, inexpensive optical components (LEDs and photodetectors) arranged in a compact configuration, replacing complex camera systems. This disposable-like simplicity in component selection achieves motion robustness without the high complexity and cost of camera-based solutions.
Solution Approach 2:
The invention extracts only the essential function of light emission and detection needed for PPG measurements, removing the unnecessary complexity of imaging systems. By taking out just the core photodetection capability and eliminating camera mechanics, the system achieves motion robustness with minimal device complexity.
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 solution enhances motion robustness and calibration stability, achieving stronger signal strength and location-independent measurements, similar to camera-based systems, while maintaining the advantages of contact sensors by ensuring a controlled light path and homogeneous illumination.
Implementation Method 1
an optical sensor for receiving light scattered back from the subject's skin in response to the emission of light into the subject's skin
Implementation Method 2
Photoplethysmography (PPG) is an optical measurement technique that evaluates a time-variant change of light reflectance or transmission of an area or volume of interest. PPG is based on the principle that blood absorbs light more than surrounding tissue
Data Source
AI summary
The present invention relates to a wearable device for acquiring physiological information of a subject. To combine the advantages of a contact sensor and a contactless sensor, the wearable device comprises an optical emitter (10) for emitting light into the subject's skin, an optical sensor (20) for receiving light scattered back from the subject's skin in response to the emission of light into the subject's skin, the received light representing or allowing the derivation of physiological information of the subject, and a carrier (30) for being held at the subject's skin and for carrying said emitter (10) and said sensor (20) such that a light receiving area (12), at which the emitted light enters the subject's skin, substantially corresponds to a light reflecting area (22), at which at least part of the scattered light leaves the subject's skin and is received by said optical sensor, the optical sensor (20) is arranged between the optical emitter (10) and the light receiving area (12) and is at least partially transparent for the light emitted by the optical emitter or the optical emitter (10) is arranged between the optical sensor (20) and the light reflecting area (22) and is at least partially transparent for the light reflected from the light reflecting area.