Smart Ring PPG Sensor Array Assembly and Signal Fidelity
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Solution Overview
Problem
Wearable devices with PPG sensors face challenges in achieving high signal fidelity and low power consumption due to factors like motion artifacts, reduced blood perfusion, and the small AC component of the PPG signal.
Innovation Solution
The design of smart rings incorporates multiple PPG sensors around the ring's perimeter, with a printed circuit board (PCB) and an outer metal shell that functions as an antenna for Bluetooth-low-energy communications. The assembly process involves a U-shaped inner ring with optical ports, a metal rim for electrical connection, and a method to ensure a smooth, rigid structure for optimal performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple PPG sensors are integrated around the ring perimeter, then measurement precision and signal fidelity are improved, but device complexity increases
Solution Approach 1:
The ring is divided into multiple sensing zones with individual PPG sensors distributed around the perimeter, allowing each sensor to independently capture pulse signals from different segments of the finger. This segmentation enables the system to aggregate data from multiple locations, improving overall signal fidelity while maintaining manageable complexity through modular sensor units.
Solution Approach 2:
The patent transitions from a single-point PPG measurement to a distributed spatial array of sensors around the ring perimeter. This dimensional expansion from one measurement point to multiple spatial locations enables capture of pulse signals from different finger segments, improving measurement precision through spatial diversity.
2Measurement precision
If transmissive PPG method is used for accurate oxygen saturation monitoring, then measurement precision is improved, but power consumption increases
Solution Approach 1:
The system employs reflective PPG sensing as a partial solution that consumes less power, accepting that it provides adequate but not optimal oxygen saturation measurements. By using reflective PPG from the ring's inner surface, the system achieves acceptable measurement precision while significantly reducing power consumption compared to continuous transmissive PPG operation.
Solution Approach 2:
The patent changes the optical measurement parameter from transmissive to reflective PPG mode. This parameter change allows the system to operate with lower power consumption while maintaining sufficient measurement accuracy for practical applications, particularly for continuous monitoring where power management is critical.
3Use of energy by moving object
If reflective PPG is used for lower power consumption, then power consumption is reduced, but measurement precision deteriorates due to motion artifacts and reduced blood perfusion
Solution Approach 1:
The system incorporates motion detection sensors that continuously monitor finger movement and provide feedback to the PPG processing system. When motion artifacts are detected, the system adjusts its signal processing algorithms to compensate for the artifacts, maintaining measurement precision while continuing to operate in low-power reflective PPG mode.
Solution Approach 2:
The patent introduces motion sensors as intermediary devices that detect and characterize motion artifacts. These sensors act as mediators between the physical motion and the PPG signal processing, allowing the system to identify and correct for motion-induced distortions in the reflected light signals, thereby maintaining measurement accuracy.
4Measurement precision
If the ring structure is made rigid for optimal sensor performance, then measurement precision is improved, but ease of manufacture decreases
Solution Approach 1:
The ring structure is segmented into modular components including the outer shell, inner ring, PCB assembly, and sensor modules. Each component can be manufactured separately with optimized processes, then assembled together to form the complete rigid structure. This segmentation maintains the required rigidity for sensor performance while significantly improving ease of manufacture.
Solution Approach 2:
The patent employs a nested assembly structure where the PCB and sensors are mounted on an inner ring that fits within the outer shell. The U-shaped cross-section design allows the PCB to be inserted and secured within the ring structure. This nesting approach enables precise sensor positioning and rigid structural integrity while simplifying the manufacturing and assembly process.
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 design enhances the quality and reliability of PPG measurements by minimizing motion artifacts and improving signal fidelity, while also reducing power consumption and enabling accurate oxygen saturation monitoring.
Implementation Method 1
an outer metal shell that functions as an antenna for Bluetooth-low-energy communications
Implementation Method 2
The technology behind these sensors is called photoplethysmography (PPG), which is an optical measurement technique used to detect blood volume changes in living tissues
Data Source
AI summary
A ring for photoplethysmographic (PPG) sensing performs transmissive PPG and/or reflective PPG. In particular, a ring and assembly methods therefor are described including for example connecting a rim to an inner ring via a bonding process, laying a printed circuit board (PCB) on the inner ring, aligning optical sensors of the PCB with ports of the inner ring, providing electrical connections between contact points on the PCB and the rim, and inserting an assembly including the ring, inner ring and PCB into an outer shell.