Multiple-Path Herriot Cell for High-Dynamic-Range Trace Gas Detection
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Solution Overview
Problem
Gas detection sensors are limited in their dynamic range, with decreasing the lower detection limit often causing an increase in the upper limit, making them ineffective for detecting trace gases like methane and other pollutants over a wide concentration range.
Innovation Solution
A modified Herriot cell with two detectors and a partially transmissive facet (PTF) allows for a single beam to travel different path lengths, enabling a high dynamic range (HDR) by increasing the lower detection limit with one detector and the upper detection limit with the other, using photodetectors to sense gases like hydrogen disulfide, methane, sulfur oxide, and carbon dioxide.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a single optical path length is used in the detector, then the device complexity is reduced, but the measurement precision for trace gases across a wide concentration range deteriorates
Solution Approach 1:
The optical path is segmented into two distinct path lengths (first optical path length and second optical path length) within the same Herriot cell. The first path length is optimized for detecting lower concentration trace gases, while the second path length is optimized for detecting higher concentration trace gases. This segmentation allows the detector to maintain high measurement precision across a wide dynamic range without requiring multiple separate devices.
Solution Approach 2:
The patent introduces a temporal dimension by sequentially switching between two different optical path lengths. Instead of using multiple simultaneous optical paths, the system alternates between first and second optical path lengths at different time intervals, allowing both path lengths to coexist in a single optical configuration without spatial complexity.
2Measurement precision
If the lower detection limit is decreased, then the upper detection limit also decreases, limiting the dynamic range
Solution Approach 1:
The system dynamically switches between two different optical path lengths based on the expected concentration range of the target gas. By making the optical path length adjustable and time-dependent, the detector can adapt to varying gas concentrations, maintaining optimal detection sensitivity across a wide dynamic range from parts per billion to parts per million levels.
Solution Approach 2:
The patent changes the optical path length parameter to resolve the trade-off between lower and upper detection limits. By using a first optical path length for low concentration detection and a second optical path length for high concentration detection, the system achieves both a low lower detection limit and a high upper detection limit, expanding the overall detection range.
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 system achieves a high dynamic range (HDR) by simultaneously decreasing the lower detection limit and increasing the upper detection limit, effectively detecting trace gases across multiple orders of magnitude, suitable for industrial and environmental applications.
Implementation Method 1
A modified Herriot cell with two detectors and a partially transmissive facet (PTF) allows for a single beam to travel different path lengths, enabling a high dynamic range (HDR) by increasing the lower detection limit with one detector and the upper detection limit with the other, using photodetectors to sense gases like hydrogen disulfide, methane, sulfur oxide, and carbon dioxide.
Data Source
AI summary
Systems, devices, and methods including a modified Herriot cell comprising: a laser configured to generate a single beam; a partially transmissive region (PTR) disposed in at least one of: a first mirror and a second mirror, where a first portion of the single beam is received through the PTR, and where a second portion of the single beam is reflected by the PTR; a first detector disposed proximate the PTR, where the first detector receives the first portion of the beam, and where the first portion of the beam has traveled a first path length from the laser to the first detector; and a second detector disposed proximate the exit hole, where the second detector receives the second portion of the beam, and where the second portion of the beam has traveled a second path length from the laser to the second detector.