Ear-Worn Optical Sensor Layout for Motion-Resistant PPG
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Solution Overview
Problem
Hearing devices with optical sensors face movement artifacts due to user movements, leading to degraded PPG data quality and reduced reliability of physiological information, especially when positioned outside the ear canal, and manufacturing variations cause measurement uncertainties, necessitating cumbersome calibration.
Innovation Solution
A hearing device with dual photodetectors at different distances from a light source to account for spatial relationships, reducing movement artifacts and eliminating common disturbances, while allowing access to various tissue layers and analytes without individual calibration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the optical sensor is placed outside the ear canal, then it is easier to accommodate the sensor and obtain physiological information about tissue outside the ear canal, but movement artifacts increase and data quality degrades
Solution Approach 1:
The patent divides the optical sensing function into multiple photodetectors positioned at different locations on the housing. By segmenting the sensing array and placing photodetectors at multiple positions (including outside the ear canal), the system maintains versatility in tissue monitoring while compensating for movement artifacts through spatial diversity. The processing unit combines signals from multiple photodetectors to maintain data quality regardless of sensor position.
2Device complexity
If a single photodetector is used, then the device complexity is reduced, but measurement precision decreases due to movement artifacts and manufacturing variations
Solution Approach 1:
The patent merges the measurements from multiple photodetectors positioned at different distances from the light source. The processing unit combines the optical signals detected by each photodetector, taking into account their respective spatial relationships to the light source. This combining approach eliminates common disturbances and movement artifacts that affect all detectors equally, while maintaining measurement precision without requiring complex individual calibration for each photodetector.
Solution Approach 2:
The patent introduces a processing unit that acts as an intermediary between the multiple photodetectors and the final measurement output. This processing unit receives signals from all photodetectors, applies appropriate processing that accounts for their spatial positions and manufacturing variations, and produces a corrected measurement. The processing unit eliminates the need for individual calibration by using the relative spatial relationships as a reference framework.
3Measurement precision
If multiple photodetectors at different distances are used, then measurement accuracy improves by accounting for spatial relationships, but device complexity increases
Solution Approach 1:
The patent changes the spatial parameter (distance from light source) of the photodetectors to improve measurement precision. By positioning photodetectors at different known distances from the light source, the system creates a spatial reference framework that enables accurate tissue property measurement without individual calibration. The processing unit uses these known spatial parameters to correct for manufacturing variations and eliminate the need for complex calibration procedures.
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
Enhances the accuracy and reliability of physiological data by minimizing movement artifacts and eliminating the need for calibration, providing precise measurements of tissue properties and analyte concentrations.
Implementation Method 1
The light source is used to illuminate tissue inside the ear canal and the photodetector detects the light returning from the tissue at the device. Based on the detected light, it is possible to determine changes in light absorption caused by the blood flowing through the tissue during a heartbeat sequence.
Implementation Method 2
Based on the detected light, it is possible to determine changes in light absorption caused by the blood flowing through the tissue during a heartbeat sequence.
Data Source
AI summary
A hearing device includes a housing configured to be worn at an ear of a user; an output transducer configured to provide an audio signal to the user; a light source configured to provide light emitted from a light emission area at the housing, the light illuminating an illumination volume extending into tissue at the ear when the housing is worn at the ear; and a first photodetector configured to detect a first light intensity of light arriving from a first acceptance volume extending into tissue at the ear when the housing is worn at the ear such that a part of the emitted light scattered by the tissue into the first acceptance volume is contributing to the first light intensity, the first acceptance volume including a first reception area at the housing having a first distance from the light emission area.