Curved Warm Filter for Thermal Imager Radiation Uniformity

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Solution Overview

Problem

Thermal imaging systems face limitations in capturing thermal images across various wavelength ranges due to undesirable effects from reflected infrared radiation, particularly when using flat bandpass filters at ambient temperature, which cause spatial non-uniformities and limit integration time and dynamic range.

Innovation Solution

The implementation of a curved warm filter or a combination of a flat warm filter with lenses to reflect out-of-band infrared radiation uniformly over the field of view of the thermal imager, reducing aberrations and improving image uniformity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Adaptability or versatility

If a flat warm filter is used to provide flexibility in wavelength ranges, then adaptability is improved, but spatial non-uniformities occur in captured thermal images

Engineering Contradiction:

Improvewavelength range flexibilityVSAvoidimage uniformity

Core Design Contradiction:

Adaptability or versatilityVSManufacturing precision

Solution Approach 1:

The patent applies a curved surface to the warm filter instead of a flat surface. This curvature is specifically designed to reflect out-of-band infrared radiation in a uniform distribution across the field of view, thereby maintaining image uniformity while preserving the flexibility of using a warm filter for different wavelength ranges.

Inventive Principle:

Principle #14Spheroidality (Curvature)

Solution Approach 2:

The patent introduces optical elements with specific local properties (curved surfaces, selective reflectivity) at particular locations in the optical path. These localized optical features are designed to redirect reflected radiation uniformly across different regions of the field of view, addressing the non-uniformity problem while maintaining overall system flexibility.

Inventive Principle:

Principle #3Local quality

2Manufacturing precision

If a cold filter is positioned within the IDCA to reduce reflected radiation, then image uniformity is improved, but adaptability to different wavelength ranges is limited

Engineering Contradiction:

Improveimage uniformityVSAvoidwavelength range flexibility

Core Design Contradiction:

Manufacturing precisionVSAdaptability or versatility

Solution Approach 1:

The patent extracts the filter from the cold IDCA environment and positions it externally at ambient temperature. By removing the filter from the cryogenic environment, the system gains flexibility to use different filters for different wavelength ranges, while optical elements are added to compensate for the loss of uniformity control.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The patent introduces optical elements (curved surfaces, lenses) as intermediaries between the warm filter and the thermal imager. These intermediary elements serve to redirect and redistribute the reflected infrared radiation, compensating for the absence of cryogenic cooling and maintaining image uniformity.

Inventive Principle:

Principle #24Intermediary (Mediator)

3Measurement precision

If integration time is increased to improve signal quality, then measurement precision is improved, but temporal noise increases due to reflected radiation

Engineering Contradiction:

Improvesignal qualityVSAvoidtemporal noise

Core Design Contradiction:

Measurement precisionVSLoss of information

Solution Approach 1:

The patent converts the harmful reflected out-of-band radiation into a beneficial uniform distribution across the field of view. By designing optical elements that redistribute reflected radiation uniformly, the system can tolerate longer integration times without accumulating localized noise artifacts, thereby improving signal quality without proportionally increasing temporal noise.

Inventive Principle:

Principle #22Blessing in disguise (Convert harm into benefit)

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 approach enhances thermal image uniformity, increases integration time, and expands the dynamic range of the thermal imager, reducing temporal noise and allowing for the capture of thermal images across different wavelength ranges without significant non-uniformities.

Implementation Method 1

an optical element such as a curved warm filter is provided with a curved concave surface configured to reflect out-of-band radiation back to a thermal imager in a uniform distribution

Methodology Applied

Scientific EffectReflection: Reflection

Implementation Method 2

a thermal imager disposed within the interior volume and configured to capture thermal images

Methodology Applied

Scientific EffectInfrared radiation detection: Infrared Radiation

Implementation Method 3

an integrated dewar cooler assembly (IDCA) configured to maintain an interior volume at a constant temperature

Methodology Applied

Scientific EffectCryogenic cooling: Cryogenics

Data Source

PatentUS20220291047A1Warm filter configuration for reducing effects of reflected infrared radiation systems and methods

Publication Date: 2022.09.15 FLIR SYST AB

AI summary

Various techniques are disclosed to reduce the effect of reflected infrared radiation on cooled thermal imaging systems. In one example, a system includes an integrated dewar cooler assembly (IDCA) configured to maintain an interior volume at a constant temperature. The system also includes a thermal imager disposed within the interior volume and configured to capture thermal images. The system also includes an optical element external to the IDCA and configured to provide reflected infrared radiation in a uniform distribution over a field of view of the thermal imager in response to emitted infrared radiation from the thermal imager. Additional methods, devices, and systems are also provided.