Front Lens Shutter Mount for IR Imaging Uniformity
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Solution Overview
Problem
Uncooled IR imaging systems face challenges with spatial non-uniformity due to DC background signals, temperature differences, and imperfections in the focal plane array (FPA) caused by the conventional shutter placement, which affects signal-to-noise ratio and dynamic range.
Innovation Solution
A shutter is positioned in front of the lens, allowing internal radiant flux to reach the FPA during calibration and generating a spatially uniform reference image signal, which is then used to correct open-state image signals for external scene radiation, compensating for pixel-to-pixel non-uniformities and offsets between shutter states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the shutter is positioned at the rear of the lens block (conventional placement), then the calibration can be performed, but spatial non-uniformity occurs due to temperature differences between the shutter and internal housing, and blemishes in the FPA sensing window are more pronounced
Solution Approach 1:
The shutter is inverted from its conventional position at the rear of the lens block to a position in front of the lens. This inversion allows the shutter to block external radiation before it enters the optical path, while still permitting internal radiant flux to reach the FPA during calibration, thereby eliminating spatial non-uniformity and reducing the impact of FPA sensing window imperfections
Solution Approach 2:
The shutter acts as an intermediary element positioned in front of the lens that mediates between external radiation and the internal optical path. During calibration, it allows internal flux to pass through to the FPA, and during operation, it blocks external radiation, thereby controlling the radiation environment and improving image uniformity
2Object-generated harmful factors
If DC background signals are removed by AC coupling or subtraction methods, then the DC background is eliminated, but the signal-to-noise ratio is not improved and may be degraded
Solution Approach 1:
The system performs preliminary calibration by capturing a reference image with the shutter closed (blocking external radiation) before actual imaging. This reference image contains only internal radiant flux and is used to correct subsequent open-shutter images, thereby removing DC background signals while preserving the signal-to-noise ratio through proper calibration rather than simple subtraction
3Object-affected harmful factors
If the FPA is cooled to cryogenic temperatures, then background noise is reduced and high signal-to-noise ratio is achieved, but the system becomes expensive and complex
Solution Approach 1:
The patent replaces the mechanical cryogenic cooling system with an optical calibration approach. By positioning the shutter in front of the lens and using reference image calibration, the system achieves uniformity correction without requiring complex cooling mechanisms, thereby reducing system complexity while maintaining acceptable 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
This configuration reduces non-uniformities and noise, improving the signal-to-noise ratio and dynamic range by allowing internal flux to be accounted for during calibration, thereby enhancing image uniformity and reducing thermal noise.
Implementation Method 1
a lens that is configured to focus light or radiation onto a focal plane array (FPA)
Implementation Method 2
A shutter is interposed between the lens and the FPA, and operates to prevent a scene from imaging on the FPA
Implementation Method 3
Microbolometers are another type of IR FPA, which operate near room temperature
Implementation Method 4
A thermoelectric cooler can be attached to the back of the FPA, and a temperature controller and sensing scheme is employed to stabilize the temperature of the FPA and its housing at room temperature
Implementation Method 5
A shutter is positioned in front of the lens, allowing internal radiant flux to reach the FPA during calibration and generating a spatially uniform reference image signal
Data Source
AI summary
An imaging system comprising a lens, a detector array (e.g., focal plane array), a signal processing module and a shutter, wherein the shutter is positioned in front of the lens (between the lens and the scene being imaged). This front lens shutter mount configuration allows offset correction to compensate for internal radiant flux and other deficiencies associated with conventional systems.