System and method for simultaneous high-sensitivity measurement of methane and ethane via laser absorption spectroscopy in an open-air configuration
Inventors
Frish, Michael B. • Chen, Shin-Juh • AUBUT, Nicholas F. • Wainner, Richard T.
Assignees
Heath Consultants Inc • Physical Sciences Inc
Publication Number
US-12228501-B2
Publication Date
2025-02-18
Expiration Date
2042-10-04
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Abstract
A system for measuring a target gas via laser absorption spectroscopy in an open-air configuration, comprising a mid-infrared distributed feedback interband cascade laser (mid-IR DFB-ICL) having a wavelength selected to correspond with a spectral absorption line of the target gas and first electronic circuitry to control the laser temperature, current and modulation frequency. The mid-IR DFB-ICL is mounted to a heat sink. The system includes an optical component that projects a beam of the mid-IR DFB-ICL onto a distal backscattering directionally-reflective target and an optical receiver assembly that receives a fraction of the laser light that is backscattered from the directionally-reflective target and focuses the collected light onto an uncooled photodetector having a spectral bandwidth and optical configuration selected to optimize signal-to-noise response to received laser light. The optical receiver assembly comprises a primary mirror for receiving laser light backscattered from the directionally-reflective target and focusing the collected light onto the uncooled photodetector.
Core Innovation
The invention provides a compact, high-sensitivity, fast-response open-air sensor system for the simultaneous detection and measurement of methane and ethane gas via laser absorption spectroscopy. It utilizes mid-infrared distributed feedback interband cascade lasers (mid-IR DFB-ICLs) with wavelengths selected to correspond to spectral absorption lines of the target gases. The system projects the laser beams onto a distal backscattering directionally-reflective target, and an optical receiver assembly collects the backscattered light and focuses it onto an uncooled photodetector.
The core of the innovation is the simultaneous measurement of ppb-level concentrations of methane and ethane with high speed using mid-IR backscatter TDLAS, operating near room temperature. The system enables rapid detection and discrimination of natural gas leaks by employing two lasers, each tuned for a specific spectral feature of either methane or ethane, and separates their signals using frequency multiplexing. It solves the problem of selectivity by choosing wavelengths with minimal cross-sensitivity to other ambient gases, such as water and carbon dioxide.
The invention addresses the issue of detecting small, diluted, or distant emissions with a high probability of detection and minimal false positives, particularly useful for mobile leak survey vehicles. By not using extractive sample cells, it avoids dilution and delays, enabling fast temporal resolution of plume concentration and accurate discrimination between natural gas and biogenic methane sources. The system’s electro-optic package is designed to be compact, robust, and suitable for mounting onto survey vehicles.
Claims Coverage
The patent contains two independent claims: one for a system measuring a target gas via laser absorption spectroscopy in an open-air configuration, and another for a system simultaneously measuring methane and ethane in an open-air configuration. There are a total of two core inventive features.
System for open-air laser absorption spectroscopy using mid-IR DFB-ICL and uncooled photodetector
A system comprising: - A mid-infrared distributed feedback interband cascade laser (mid-IR DFB-ICL) with wavelength selected for a specific spectral absorption line of the target gas. - First electronic circuitry to control the laser’s temperature, current, and modulation frequency. - A heat sink for the mid-IR DFB-ICL. - A distal backscattering directionally-reflective target. - An optical component for projecting the laser beam onto the target. - An optical receiver assembly that receives and focuses backscattered laser light onto an uncooled photodetector.
System for simultaneous methane and ethane measurement using dual mid-IR DFB-ICLs and frequency-multiplexed detection
A system comprising: - A first mid-IR DFB-ICL for ethane and a second mid-IR DFB-ICL for methane, each with wavelengths corresponding to target gas spectral absorption lines. - Separate electronic circuitry to control each laser's temperature, current, and modulation frequency. - A heat sink serving both lasers. - A distal backscattering directionally-reflective target. - Individual optical components to project beams from each laser onto the target. - An optical receiver assembly focusing the backscattered light onto an uncooled photodetector. - Differentiated modulation frequencies for methane and ethane lasers to enable frequency-multiplexed detection.
The independent claims cover a system that precisely measures target gases in open-air environments using mid-IR DFB-ICL technology and uncooled photodetectors, and extend to simultaneous measurement and differentiation of methane and ethane with frequency-multiplexed detection using dual lasers.
Stated Advantages
Provides high sensitivity and fast response for simultaneous detection of methane and ethane, with better than 100 ppb limit of detection at a 10 Hz rate.
Enables discrimination between natural gas leaks and biogenic methane sources by concurrent measurement of both methane and ethane.
Uses a compact, lightweight, and battery-operated package suitable for mounting on natural gas leak survey vehicles.
Avoids sampling delays and dilution associated with extractive analyzers by using an open-air path to directly sense gas plumes.
Reduces false detections and increases probability of detecting small or intermittent gas leaks, even from distant or wind-dispersed sources.
Documented Applications
Detection of natural gas leaks from pipelines and related gas infrastructure during mobile survey using vehicles.
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