QWIP Thermography Camera for SF6 Leak Detection
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Solution Overview
Problem
Conventional thermographic leak detection systems are limited in detecting compounds with absorption bands above 5.0 μm, such as sulfur hexafluoride (SF6), due to the spectral responsivity range of InSb focal plane arrays contributing dark current signal noise and the lack of focal plane arrays capable of imaging beyond 5.0 μm.
Innovation Solution
A portable infrared thermography camera with a focal plane array comprising quantum well infrared photo sensors (QWIP) tuned to a spectral responsivity peak in the 10.4 to 10.8 μm range, combined with an optical band pass filter limiting the spectral bandwidth to 10.3 to 10.8 μm, and a refrigeration device cooling the system to less than 65° K to reduce thermal noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If InSb focal plane arrays are used for thermographic imaging, then the system can detect compounds with absorption bands below 5.0 μm, but the spectral responsivity range contributes dark current signal noise and cannot image compounds with absorption bands above 5.0 μm
Solution Approach 1:
The patent changes the spectral responsivity parameter of the focal plane array by using QWIP technology with specific quantum well layer thicknesses (5-20 nm) and barrier layer structures to tune the detection wavelength range to 10.4-10.8 μm, enabling detection of SF6 and other compounds with absorption bands above 5.0 μm while minimizing dark current noise through optimized quantum confinement dimensions
Solution Approach 2:
The patent employs composite material structures in the focal plane array, combining quantum well layers made of GaAs with AlGaAs barrier layers to create a multi-layer composite that provides both the desired spectral response for long-wavelength infrared detection and reduced dark current through the composite structure's unique electronic properties
2Adaptability or versatility
If the spectral bandwidth is widened to detect more compound types, then the detection versatility improves, but the signal noise increases and image contrast decreases
Solution Approach 1:
The patent applies local quality by using a narrow optical band pass filter (10.3-10.8 μm) that is specifically tuned to match the absorption bands of target compounds like SF6, allowing the system to optimize detection sensitivity for specific compounds without capturing irrelevant spectral information that would increase noise and reduce image contrast
Solution Approach 2:
The patent optimizes the spectral bandwidth parameter by selecting a narrow filter range (10.3-10.8 μm) that balances versatility across multiple compounds with the need for high signal-to-noise ratio, achieving both broad detection capability and high image quality through precise spectral parameter selection
3Measurement precision
If the refrigeration device cools the focal plane array to reduce thermal noise, then the signal noise decreases and image quality improves, but the device complexity and power consumption increase
Solution Approach 1:
The patent changes the temperature parameter of the focal plane array by implementing a refrigeration device that cools the array to cryogenic temperatures (typically 77 K or lower), dramatically reducing thermal noise and improving signal-to-noise ratio for detecting weak infrared signals from gas leaks
Solution Approach 2:
The patent replaces active mechanical cooling systems with passive cryogenic cooling approaches, using pre-cooled focal plane arrays that maintain low temperatures through thermal isolation and cryogenic heat sinks, reducing mechanical complexity while maintaining low noise performance
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 camera effectively detects invisible gas plumes containing compounds like SF6, ammonia, and uranyl fluoride by enhancing image contrast and reducing signal noise, allowing for the visualization of leaks in real-time.
Implementation Method 1
a focal plane array, (FPA), (108) ... configured to provide a spectral responsivity profile having a peak responsivity in the wavelength range 10.4 to 10.8 μm
Implementation Method 2
Each sensor element of the FPA (108) generates an analog photo current value according to a photo current responsivity profile in response to an irradiance generated by the spectrally filtered scene image
Implementation Method 3
an optical band pass filter (110) positioned between the lens (104) the FPA (108) for optically filtering radiation collected by the lens to narrow the spectral bandwidth of the focused image formed on the FPA (108) to the wavelength range 10.3 to 10.8 μm
Implementation Method 4
a refrigeration device configured to cool the FPA (108) and the optical band pass filter (110) to an operating temperature of less than 65° K.
Implementation Method 5
cooling the focal plane array and the optical filter, (cold filter), to 77 to 100° K., during operation, in order to reduce thermal energy from radiating from the focal plane array and the optical filter
Implementation Method 6
A lens (104) forms an image of a survey scene (106) onto a focal plane array, (FPA), (108)
Data Source
AI summary
A portable camera system (100) includes a lens (104) for forming a focused image of a survey scene (106) onto a focal plane array (108). The focal plane array (108) comprises a cooled two dimensional array of quantum well infrared photo detectors, (QWIP) having a peak spectral responsivity in the wavelength range of 10.4 to 10.8 μm. The camera includes a cooled band pass optical filter (110) having a peak spectral transmittance approximately centered at a wavelength of 10.57 μm and a full width half maximum spectral transmittance bandwidth of approximately 10.3 to 10.7 μm. The camera system (100) is usable to detect an invisible gas plume in a video image of a survey scene if the gas plume contains sulfur hexafluoride (SF6), ammonia, (NH3), Uranyl Fluoride (U2O2F2), or any other gas having an absorption band that that at least partially falls within the wavelength band 10.3 to 10.8 μm.