Reflecting Geometry Capnometer for Stable CO2 Measurement
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Solution Overview
Problem
Existing capnometers face issues with output drifts due to temperature changes and contamination, leading to instability in CO2 level measurements, particularly in non-dispersive infrared techniques using single collimated emission and detection.
Innovation Solution
A capnometer employing a reflecting geometry with a mid-IR semiconductor emitter and detector, along with a reflector, to measure CO2 levels in exhaled and inhaled gases, allowing for improved signal-to-noise ratio and reduced contamination risks through a breath tube design and optical layer coatings.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If single collimated emission and detection is used, then device complexity is reduced, but measurement stability deteriorates due to output drifts from temperature changes and component instability
Solution Approach 1:
The optical path is divided into multiple segments with multiple reflectors creating distinct reflection paths. This segmentation allows the system to achieve stable measurements by comparing signals from different path lengths while maintaining relatively simple optical components at each segment.
Solution Approach 2:
Multiple reflectors are introduced as intermediary elements to create multiple reflection paths between the emitter and detector. These intermediaries enable the system to obtain stable reference signals without requiring complex optical systems, as each reflector is a simple passive element.
2Measurement precision
If longer sampling length is used, then signal-to-noise ratio is improved, but device dimensions increase
Solution Approach 1:
Instead of increasing the linear distance between emitter and detector, the patent uses multiple reflectors to create an extended optical path through folding reflections. This transforms the problem from a one-dimensional length issue to a multi-dimensional spatial arrangement, achieving long sampling length within a compact device footprint.
3Measurement precision
If transmissive optics and beam splitter optics with filters are used, then measurement accuracy is improved, but power consumption and production cost increase
Solution Approach 1:
The patent extracts and removes complex transmissive optics, rotating elements, and beam splitter optics with filters from the system. By using only simple reflectors and a straightforward emitter-detector arrangement, the system achieves measurement accuracy through multiple path comparison while eliminating the power consumption and cost associated with complex optical components.
4Device complexity
If windows enclosing the gas sample are used, then optical path is defined, but contamination of windows occurs leading to measurement instability
Solution Approach 1:
The patent applies local quality by using anti-contamination coatings specifically on the reflector surfaces that are exposed to the gas sample. This localized protection maintains measurement stability without requiring complete sealing of the optical path, thus avoiding the complexity and contamination issues of enclosed windows while protecting only the critical reflective surfaces.
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
The reflecting geometry capnometer provides stable and accurate CO2 level measurements with low power consumption and cost-effective production, achieving high temporal resolution and minimizing contamination impacts on measurement accuracy.
Implementation Method 1
a mid-IR semiconductor emitter configured to provide IR light at a wavelength in the range 3-5 μm
Implementation Method 2
a reflector to reflect said IR light emitted by said emitter; wherein said emitter, said detector and said reflector are arranged such that said IR light emitted by said emitter passes through said air flow region via said reflector to said detector
Implementation Method 3
a mid-IR semiconductor detector to detect said IR light
Implementation Method 4
Non-dispersive infrared (IR) techniques utilise the 4.26 μm absorption band of CO2
Data Source
AI summary
We describe a capnometer for detecting a concentration of a component in a gas, wherein said gas is inhaled and/or exhaled by a patient, said capnometer comprising: an air flow region through which said gas passes to and/or from said patient's lung; a mid-IR semiconductor emitter configured to provide IR light at a wavelength in the range 3-5 μm; a mid-IR semiconductor detector to detect said IR light; a reflector to reflect said IR light emitted by said emitter; wherein said emitter, said detector and said reflector are arranged such that said IR light emitted by said emitter passes through said air flow region via said reflector to said detector.