Variable Aperture Sensor for Pulse Oximetry
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Solution Overview
Problem
Pulse oximeters face challenges in accommodating varying tissue site characteristics, such as thickness and opacity, which affect light absorption and detector output, leading to inconsistent measurements across different tissue sites.
Innovation Solution
A variable aperture sensor with rotatable jaws and a movable slide or shutter mechanism that adjusts the optical radiation received by the detector, allowing for compensation of tissue site variations by altering the aperture size or shutter opening to maintain an optimal operating point within the detector's dynamic range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If the aperture size is increased to allow more light to reach the detector, then the detector signal strength is improved, but the detector may saturate and lose measurement precision
Solution Approach 1:
The patent implements a variable aperture mechanism that can dynamically adjust its opening size based on the specific tissue site being measured. The aperture includes a movable element that changes the effective aperture area, allowing the system to optimize light transmission for each measurement site while preventing detector saturation. This dynamic adjustment capability resolves the contradiction by making the aperture size adaptable rather than fixed.
Solution Approach 2:
The patent changes the physical parameter of aperture area to control light transmission. By varying the aperture area between a first size (allowing more light) and a second size (allowing less light), the system can prevent detector saturation while maintaining sufficient signal strength. This parameter change approach directly addresses the contradiction between maximizing light intensity and maintaining measurement precision.
2Illumination intensity
If the drive current to emitters is increased to compensate for high absorption sites, then the light intensity is improved, but the detector dynamic range is reduced
Solution Approach 1:
The patent introduces an intermediary element (the variable aperture) between the tissue site and the detector. This aperture acts as a mechanical mediator that controls light transmission independently of the emitter drive current. By using the aperture as an intermediary, the system can compensate for high absorption sites without needing to increase emitter current, thereby preserving detector dynamic range and avoiding the trade-off between light intensity and adaptability.
3Measurement precision
If the gain at the front-end is increased to accommodate low signal sites, then the detector sensitivity is improved, but the measurement reliability deteriorates due to noise amplification
Solution Approach 1:
The patent applies preliminary action by adjusting the aperture size before the light reaches the detector. By optimizing the aperture area in advance, the system ensures that the detector receives an appropriate signal level that maximizes sensitivity without requiring excessive front-end gain amplification. This preliminary optimization of light transmission prevents noise amplification issues that would occur with high gain settings, thereby maintaining measurement reliability while improving sensitivity.
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 solution ensures consistent and accurate oxygen saturation measurements across different tissue sites by dynamically adjusting the light intensity incident on the detector, thereby improving the reliability and precision of pulse oximetry readings.
Implementation Method 1
The emitters 110 are positioned to project light through the blood vessels and capillaries of the tissue site 10, and the detector 120 is positioned so as to detect the emitted light as it emerges from the tissue site 10
Implementation Method 2
The variable aperture is disposed in the second jaw and configured to adjust the amount of the optical radiation received by the detector
Data Source
AI summary
A variable aperture sensor has a first jaw and a second jaw that are rotatably attached. An emitter is disposed in the first jaw, and a detector is disposed in the second jaw. The jaws are adapted to attach to a tissue site so that the emitter transmits optical radiation into the tissue site and the detector receives optical radiation through a variable aperture after absorption by the tissue site. The variable aperture is disposed in the second jaw and configured to adjust the amount of the optical radiation received by the detector.