Contactless Cardiac Activity Detection Using Phase Locked Loop
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Solution Overview
Problem
Current methods for contactless monitoring of cardiac activity, such as pulse rate, using ambient light and digital RGB cameras face challenges like sorting problems with Independent Component Analysis (ICA), computational intensity, and power consumption, limiting their accuracy and practicality for real-time, non-invasive monitoring.
Innovation Solution
A Phase Locked Loop (PLL) feedback control system is used to capture and track the frequency of light reflected from the skin, enabling real-time, beat-by-beat detection of cardiac activity with low computational power and power consumption, allowing for continuous monitoring without bulky equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Independent Component_analysis (ICA) algorithms are used to extract pulse rate from ambient light signals, then pulse rate detection capability is improved, but computational complexity and processing time increase significantly
Solution Approach 1:
The patent extracts only the essential frequency information (heart rate) from the complex signal using FFT and peak detection, rather than applying full ICA algorithms. This extraction approach maintains measurement capability while dramatically reducing computational complexity by focusing only on the relevant physiological frequency range.
Solution Approach 2:
The system performs preliminary frequency analysis using FFT to identify the dominant frequency component corresponding to heart rate before further processing. This preliminary action allows the system to bypass computationally intensive ICA algorithms while still achieving accurate pulse rate detection by targeting the specific frequency band of interest.
2Device complexity
If block processing with 15-60 second recording periods is used, then signal processing simplicity is improved, but real-time monitoring capability and response time deteriorate
Solution Approach 1:
The patent implements continuous periodic frequency analysis using FFT at regular intervals rather than waiting for fixed block periods. This allows the system to provide real-time heart rate updates with minimal latency while maintaining processing simplicity through the use of efficient frequency domain analysis methods.
Solution Approach 2:
The system replaces the mechanical block processing approach with a continuous frequency domain analysis using FFT. This substitution enables real-time monitoring by continuously transforming the time-domain signal to frequency domain, allowing immediate detection of heart rate changes without waiting for predetermined recording blocks.
3Measurement precision
If ICA and constrained ICA algorithms are used to improve BVP measurement accuracy, then measurement precision is improved, but power consumption and heat dissipation increase
Solution Approach 1:
The patent extracts only the essential frequency information needed for heart rate detection using FFT and peak detection, avoiding the computationally intensive ICA algorithms. This extraction strategy maintains adequate measurement precision for physiological monitoring while dramatically reducing power consumption suitable for portable devices.
Solution Approach 2:
The system uses computationally inexpensive FFT operations instead of expensive ICA algorithms, sacrificing some of the advanced signal separation capabilities but gaining significant power efficiency. This approach is sufficient for the specific application of heart rate monitoring and enables deployment in battery-powered portable devices.
4Measurement precision
If dedicated light sources and PPG sensors are used for pulse rate monitoring, then measurement accuracy is improved, but patient comfort and ease of use deteriorate due to skin irritation and infection risk
Solution Approach 1:
The patent uses ambient light as an intermediary to obtain pulse rate information without direct skin contact. The camera captures reflected ambient light from the skin, which contains the pulse rate information, eliminating the need for physical sensor attachment and associated discomfort while maintaining measurement capability.
Solution Approach 2:
The system replaces the mechanical contact-based PPG sensor with an optical imaging approach using a camera. This substitution eliminates physical contact between the measurement device and the patient's skin, removing sources of irritation and infection risk while preserving the ability to measure pulse rate through optical methods.
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 provides immediate, accurate, and continuous monitoring of cardiac activity, including heart rate variability, with improved granularity and reduced latency, enabling compact, portable devices for various applications, including healthcare and security.
Implementation Method 1
capturing a signal from incident light reflected off the skin of the subject
Data Source
AI summary
A system and method include contactless detecting and tracking cardiac activity by making use of a feedback control system, such as a Phase Locked Loop (PLL), in real-time or from a prerecorded signal stream.