QWIP Infrared Camera for SF6 Detection via Bandpass Filtering
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Solution Overview
Problem
Conventional thermographic leak detection systems are limited in detecting gases with absorption bands outside the 3.0-5.0 μm range, such as sulfur hexafluoride (SF6) at 10.57 μm, due to broad spectral responsivity of InSb focal plane arrays, which increases dark current noise and reduces image contrast, and are not adaptable to detect compounds with absorption bands above 5.0 μm.
Innovation Solution
An infrared camera system utilizing a focal plane array with quantum well infrared photo detectors (QWIPs) tuned to a specific spectral bandwidth, coupled with an optical band pass filter to filter radiation to a narrow wavelength range corresponding to the absorption band of target gases, such as 10.3-10.8 μm, to enhance detection of gases like SF6, ammonia, and uranyl fluoride.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If InSb focal plane arrays are used for thermographic detection, then the detection range covers 3.0-5.0 μm, but the broad spectral responsivity increases dark current noise and reduces image contrast
Solution Approach 1:
The patent applies local quality by making the focal plane array's spectral responsivity non-uniform across the spectrum. Specifically, it enhances responsivity at the target gas absorption wavelength (e.g., 10.57 μm for SF6) while suppressing responsivity at other wavelengths. This is achieved through optical band pass filters that selectively transmit only the desired wavelength range to the detector, thereby reducing dark current noise from out-of-band radiation while maintaining detection capability at the target wavelength.
Solution Approach 2:
The patent changes the spectral responsivity parameter of the focal plane array by introducing optical band pass filters with specific transmission characteristics. These filters are designed to transmit only a narrow bandwidth centered at the target gas absorption wavelength, thereby transforming the broad spectral responsivity of InSb detectors into a narrowband responsivity profile that matches the absorption spectrum of the target gas, reducing noise while maintaining detection precision.
2Adaptability or versatility
If conventional thermographic cameras are used, then they can detect gases with absorption bands in the 3.0-5.0 μm range, but they cannot detect gases with absorption bands above 5.0 μm such as SF6 at 10.57 μm
Solution Approach 1:
The patent implements dynamics by making the spectral detection range adjustable and reconfigurable. Instead of being fixed to the 3.0-5.0 μm range, the system can be adapted to detect gases at various wavelengths above 5.0 μm (such as SF6 at 10.57 μm) by changing the optical band pass filter configuration. This dynamic adaptability allows the same hardware platform to target different gas absorption bands while maintaining detection precision through optimized filter selection for each specific application.
3Adaptability or versatility
If the spectral bandwidth is broadened to detect more gas types, then versatility improves, but dark current noise increases and image contrast decreases
Solution Approach 1:
The patent applies segmentation by dividing the broad spectral range into multiple narrow bandwidth segments, each optimized for detecting specific gas types. Instead of using a single broad spectral response, the system employs multiple optical band pass filters, each targeting a specific gas absorption band (e.g., one filter for methane at 3.3 μm, another for SF6 at 10.57 μm). This segmentation allows the system to maintain high image contrast and low noise for each specific detection task while retaining versatility through filter interchangeability.
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 effectively increases image contrast and detects gases with absorption bands outside the conventional range by reducing dark current noise and improving spectral responsivity, allowing for the detection of gases like SF6 and ammonia with enhanced accuracy.
Implementation Method 1
an optical band pass filter to filter radiation to a narrow wavelength range corresponding to the absorption band of target gases
Implementation Method 2
a focal plane array with quantum well infrared photo detectors (QWIPs) tuned to a specific spectral bandwidth
Data Source
AI summary
An infrared camera system is provided to detect absorption of infrared radiation in a selected spectral bandwidth. In one example, an infrared camera system includes a lens adapted to receive infrared radiation from a survey scene comprising one or more gasses. The infrared camera system also includes a focal plane array comprising a plurality of quantum well infrared photo detectors (QWIPs). The QWIPs are tuned to detect a limited spectral bandwidth of the infrared radiation corresponding to at least a portion of an infrared absorption band of the one or more gasses. The infrared camera system also includes an optical band pass filter positioned substantially between the lens and the focal plane array. The optical band pass filter is adapted to filter the infrared radiation to a wavelength range substantially corresponding to the limited spectral bandwidth of the QWIPs before the infrared radiation is received by the focal plane array.