Vehicle Occupant PPG Monitoring Under Ambient Light Variation
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Solution Overview
Problem
Existing methods for monitoring physiological parameters of vehicle occupants using photoplethysmography are hindered by variations in ambient illumination, which degrade signal quality and make real-time monitoring difficult.
Innovation Solution
A monitoring system with a pulsed light source and a time-of-flight camera uses synchronized shutter periods to isolate the component due to ambient illumination, allowing for the determination of physiological parameters through photoplethysmography by subtracting this component from acquired images.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If continuous illumination is used for photoplethysmography, then the physiological signal can be continuously captured, but ambient illumination variations degrade the signal quality and measurement reliability
Solution Approach 1:
The patent applies periodic action by using a pulsed light source that emits light in periodic intervals rather than continuously. The light source is activated during a first time interval to capture the physiological signal, then deactivated during a second time interval to eliminate ambient illumination interference. This periodic activation pattern allows the system to repeatedly capture clean photoplethysmography signals while blocking harmful ambient light variations.
Solution Approach 2:
The patent segments the illumination and measurement process into distinct time intervals. The first time interval is dedicated to emitting the light pulse and capturing the reflected light containing the physiological signal. The second time interval is dedicated to eliminating ambient illumination. This temporal segmentation separates the useful signal capture from the harmful ambient light exposure, improving measurement reliability.
2Measurement precision
If ambient illumination is not blocked, then the image sensor receives sufficient light for image acquisition, but the signal to noise ratio decreases making physiological parameter detection difficult
Solution Approach 1:
The system uses periodic action to create optimal signal to noise ratio conditions. During the first time interval when the light source is active, the sensor captures the strong reflected light signal from the subject. During the second time interval when the light source is off, ambient illumination is eliminated. By processing the difference between these periodic measurements, the system achieves high signal to noise ratio for physiological parameter detection.
Solution Approach 2:
The patent applies preliminary anti-action by proactively blocking ambient illumination during the measurement process. The shutter or light source control is configured to eliminate ambient light during the critical measurement intervals, preventing the degradation of signal to noise ratio before it can occur. This preemptive blocking ensures optimal detection conditions for physiological parameters.
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 approach enhances the reliability and accuracy of physiological parameter determination by minimizing the impact of ambient illumination, enabling real-time monitoring and three-dimensional reconstruction of the occupant's face, thus improving the effectiveness of photoplethysmography in vehicle environments.
Implementation Method 1
the light received by the image sensor in the first acquisition period and the second acquisition period comprising a component due to ambient illumination and a component due to the light pulse emitted by the pulsed light source
Implementation Method 2
an image acquisition device such as a time of flight camera, said image acquisition device comprising an image sensor and a shutter configured for allowing light to pass towards the image sensor during a first acquisition period in which the pulsed light source emits a light pulse
Implementation Method 3
the processing unit being configured for determining a physiological parameter of the occupant by photoplethysmography on the basis of the acquired images
Data Source
AI summary
The monitoring system (1) comprises:a light source (3),an image acquisition device (5) comprising a shutter (11) which allows light to pass during a period (P1) when the source is active and during a period (P2) when the source is inactive, the light received by a sensor (9) comprising a component (Ca) due to ambient illumination and a component (Ci) due to the light source;a processing unit (7) configured for determining a physiological parameter of the occupant by photoplethysmography.The shutter (11) allows light to pass during a third period (P3), said light comprising the component (Ca) due to ambient illumination and the processing unit (7) being configured for subtracting this component (Ca) from the light received (9) during the other two periods for the purpose of isolating the component (Ci) due to the source in acquired images.