PPG Sensor Time Calibration via Optical Mediator
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Solution Overview
Problem
Existing PPG sensor systems face challenges in achieving accurate pulse delay measurements due to the need for precise time synchronization between independent devices, which is difficult to achieve manually and requires complex electrical communication, limiting their ability to provide millisecond-level accuracy.
Innovation Solution
A sensor system comprising two PPG sensors with a monitoring system for optical calibration signals, allowing for time calibration without external synchronization, using direct optical coupling or a docking station to align light sources and detectors, enabling independent units to synchronize their timing for accurate pulse delay measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If manual time synchronization is used between independent PPG devices, then device complexity is reduced, but measurement precision deteriorates due to inability to achieve millisecond-level accuracy
Solution Approach 1:
The patent introduces an optical calibration signal as an intermediary carrier to transfer timing information between independent PPG devices. The calibration signal travels through the same optical path as the physiological light, allowing time synchronization without electrical communication or shared clock references, thus maintaining device independence while achieving millisecond-level precision.
Solution Approach 2:
The patent replaces manual time synchronization (mechanical/system-level operation) with automated optical signal-based synchronization. The system automatically detects the calibration signal, calculates time offsets, and adjusts timing parameters without manual intervention, achieving both simplicity and precision.
2Measurement precision
If electrical communication is used for time synchronization between PPG devices, then measurement precision improves to millisecond-level accuracy, but device complexity increases due to requirement for shared timing references
Solution Approach 1:
The optical calibration signal serves as a mediator that eliminates the need for electrical communication infrastructure. By embedding timing information in optical pulses that travel through the measurement path, the system achieves synchronization without requiring shared clock references, wireless communication modules, or complex electrical synchronization protocols.
Solution Approach 2:
The optical calibration signal performs multiple functions simultaneously: it serves as both the synchronization reference and the measurement carrier. The same optical path used for physiological measurement is also used for timing calibration, eliminating the need for separate synchronization hardware and reducing overall system complexity.
3Measurement precision
If optical calibration signals are used for time synchronization, then measurement precision improves without increasing device complexity, but the system requires direct optical coupling between devices
Solution Approach 1:
The docking station with optical elements (mirrors, lenses, or optical fibers) acts as an intermediary that establishes the optical coupling between devices. This intermediary component simplifies the setup process by providing a standardized interface that automatically aligns the optical paths, making the system easy to operate despite the requirement for optical coupling.
Solution Approach 2:
The docking station pre-establishes the optical coupling pathway before measurement begins. By configuring the optical elements in advance and providing a fixed mechanical interface, the system eliminates the need for manual alignment during operation, making setup straightforward while maintaining the required optical coupling for precision synchronization.
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
Enables accurate pulse delay measurements by calibrating the relative timing between PPG sensors to the millisecond level, allowing for precise pulse wave velocity calculations without the need for shared timing references or electrical communication.
Implementation Method 1
The LED and sensor are placed such that the LED directs light into the skin of the user, which is reflected or transmitted, and detected by the sensor
Implementation Method 2
using direct optical coupling or a docking station to align light sources and detectors
Data Source
AI summary
A sensor system comprises first and second PPG sensors. A monitoring system monitors detection by at least one of the first and second detectors an optical calibration signals, for performing time calibration between the first and second PPG sensors. This system makes use of two PPG sensors. To enable these sensors to be independent units, rather than being fully integrated into a combined system, a calibration system is provided. Based on detected optical signals, the behavior over time of each PPG sensor can be monitored and thus calibration can take place.