Integrated PbSe Detector and Bandpass Filter for Capnometer
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Solution Overview
Problem
Existing capnometers are bulky, have multiple components, and suffer from reflection loss and temperature variability issues, which affect the accuracy and sensitivity of carbon dioxide measurement in respiratory gases.
Innovation Solution
A compact capnometer design with an integrated lead selenide (PbSe) detector and bandpass filter, where the bandpass filter is disposed on top of or between the PbSe layer to reduce reflection loss and temperature variability, and a thermoelectric cooling system for precise temperature control, enhancing sensitivity and accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a separate PbSe detector and bandpass filter are used, then temperature control is achieved, but device size and component count increase
Solution Approach 1:
The patent combines the bandpass filter and PbSe detector into a single integrated component where the filter is deposited directly on the detector surface. This merging eliminates the need for separate temperature control systems for each component while maintaining precise temperature control for the integrated unit, thereby reducing device complexity and component count while preserving measurement precision.
Solution Approach 2:
The integrated component serves multiple functions simultaneously: the bandpass filter isolates the CO2-sensitive infrared spectral range while the PbSe layer detects the transmitted light intensity. Both functions are achieved within a single component that requires only one temperature control system, making the device more universal and less complex while maintaining precise temperature control for accurate measurements.
2Measurement precision
If a separate PbSe detector and bandpass filter are used, then temperature monitoring is achieved, but device volume increases
Solution Approach 1:
By merging the filter and detector into a single integrated component, the patent reduces the overall volume required for temperature monitoring and control. The integrated structure allows both functions to share the same thermal environment and control system, significantly reducing the capnometer volume while maintaining accurate temperature monitoring capability.
3Measurement precision
If standard PbSe detector configuration is used, then detection capability is achieved, but reflection loss occurs
Solution Approach 1:
The integration of the bandpass filter directly on the PbSe detector surface creates an optimized optical interface that reduces reflection loss. The filter material and configuration are specifically designed to minimize reflections at the air-detector interface while maintaining infrared detection capability, thereby reducing energy loss without compromising detection precision.
4Measurement precision
If separate filter and detector are used, then spectral isolation is achieved, but measurement consistency varies with temperature
Solution Approach 1:
By combining the filter and detector into a single integrated component, the patent ensures that both elements experience identical temperature conditions. This eliminates measurement consistency issues that arise from temperature differences between separate components, as the integrated structure maintains stable spectral isolation characteristics across varying ambient temperatures through unified thermal control.
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 solution results in a more compact, sensitive, and accurate capnometer with reduced components and improved temperature control, leading to better measurement consistency and reduced reflection loss.
Implementation Method 1
The PbSe film exhibits photoconductivity for infrared light in the wavelength range of 3 to 5.5 microns
Implementation Method 2
a bandpass filter having a pass band in the 3-5.5 micron range is used to isolate the CO2-sensitive infrared spectral range
Implementation Method 3
CO2 absorbs significantly in the infrared, with an absorption peak at about 4.26 micron
Implementation Method 4
a thermoelectric cooling system for precise temperature control
Data Source
Figure 1
Figure 2~4
AI summary
A capnometer (10) includes an integrated device (30, 30A, 30B) comprising a substrate (40), a lead selenide (PbSe) layer (42) or other infrared light absorbing layer disposed on the substrate, and a bandpass filter layer (50) disposed on the substrate. A temperature sensor tracks temperature of the device. A CO2 measurement cell (20) has light source (28) arranged to emit light (L) that passes through a flow path (F) and then through the bandpass filter layer of to reach the PbSe or other infrared light absorbing layer. Electronics (32) connected with the PbSe or other infrared light absorbing layer measure a photoconductivity signal. The electronics includes signal processing circuitry to convert the photoconductivity signal to a carbon dioxide partial pressure or concentration value. The electronics also includes the temperature sensor to enable accurate and fast temperature control of the device and instant temperature compensation for the temperature change.