Capnometer Fresnel Reflector Heating Uniformity
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Solution Overview
Problem
Capnometers using reflecting geometry face challenges with uneven heating, gas trapping, and limited range of gas concentration measurement due to spherical/elliptical curved mirrors, which also hinder the use of a replaceable breath tube.
Innovation Solution
A capnometer employing a Fresnel reflector or reflective diffractive optical elements, such as Fresnel zone plates, with a flatter geometry to improve heating uniformity, reduce dead space, and allow for a replaceable breath tube, enabling broader gas concentration measurement ranges and higher temporal resolution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If spherical/elliptical curved mirrors are used in a reflecting geometry capnometer, then the device can achieve high temporal resolution and high accuracy over a specific concentration range, but the mirrors are difficult to heat uniformly to prevent condensation and cause gas to be trapped in the apex which reduces temporal resolution
Solution Approach 1:
The patent replaces spherical/elliptical curved mirrors with a planar (flat) reflector geometry. This fundamental geometric change eliminates the curvature-related problems of non-uniform heating and gas trapping in apices, while maintaining the reflecting geometry's advantages of low cost and compact form factor. The planar surface allows uniform heat distribution across the reflector area.
2Speed
If spherical/elliptical curved mirrors are used in a reflecting geometry capnometer, then the device can achieve high temporal resolution, but the curvature causes gas to be trapped in the apex that reduces the temporal resolution of the system
Solution Approach 1:
The patent eliminates the curved apex geometry by using a planar reflector, which removes the dead space volume where gas would be trapped. This directly improves temporal resolution by ensuring complete gas flow through the measurement region without stagnation zones.
3Measurement precision
If spherical/elliptical curved mirrors are used in a reflecting geometry capnometer, then the device can achieve high accuracy over a specific concentration range, but the single path length means the sensor is suited to a narrow range of gas concentration measurement
Solution Approach 1:
The patent divides the optical path into multiple segments by introducing additional reflectors or using a multi-path configuration. This creates multiple gas sampling paths with different effective lengths, allowing the sensor to accurately measure a broader range of gas concentrations by selecting or combining signals from different path lengths.
Solution Approach 2:
The patent transitions from a single-dimensional optical path to a multi-dimensional path configuration using the planar reflector geometry. This allows light to traverse the gas sample volume through multiple reflections, effectively creating multiple path lengths within a compact structure and expanding the measurable concentration range.
4Speed
If spherical/elliptical curved mirrors are used in a reflecting geometry capnometer, then the device can achieve high temporal resolution, but the curved system does not lend itself to introducing a replaceable breath tube
Solution Approach 1:
The patent replaces the curved mirror system with a planar reflector configuration that provides straight, accessible optical paths. This geometry easily accommodates the introduction of replaceable breath tubes without interfering with the optical measurement system, enabling both high temporal resolution and ease of operation with disposable components.
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 capnometer achieves improved heating efficiency, reduced power consumption, and increased accuracy with a broader range of gas concentration measurements, while maintaining high temporal resolution and allowing for easy replacement of the breath tube to prevent contamination.
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
Measurements of concentration of certain gases in breath can be made using non-dispersive infrared techniques. The most common is the measurement of carbon dioxide using the 4.26 μm absorption band
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. The reflector is selected from a Fresnel reflector and a reflective diffractive optical element, such as a Fresnel zone plate.