Infrared Sensor Radiation Trap Stray Absorption
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Solution Overview
Problem
Infrared sensor assemblies face issues with stray radiation reaching the sensor element due to high refractive indices of materials used for lenses and windows, causing multiple reflections and thermal distortions, which affect measurement accuracy.
Innovation Solution
The implementation of a radiation trap between the first and second optical elements, designed to absorb stray radiation and prevent multiple reflections, while ensuring IR radiation passes through the optical elements only once, thereby reducing stray radiation influence and maintaining thermal homogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If optical elements (lenses, windows) with high refractive index materials are used to protect and focus IR radiation, then optical performance is improved, but multiple reflections occur causing stray radiation to reach the sensor element
Solution Approach 1:
A radiation trap is introduced as an intermediary component between the optical element and the sensor element. This radiation trap absorbs stray IR radiation that would otherwise reflect multiple times and reach the sensor, thereby eliminating the harmful effect while preserving the optical element's protective and focusing functions
Solution Approach 2:
The high refractive index materials that cause strong reflections are converted from a harmful source into a manageable phenomenon. The radiation trap is specifically designed to absorb the reflected radiation, transforming the harmful multiple reflections into a controlled absorption process that improves overall measurement accuracy
2Measurement precision
If optical elements are placed in front of the sensor element to define field of view, then field of view control is improved, but thermal behavior differences cause additional thermal effects that distort measurements
Solution Approach 1:
The radiation trap serves as a thermal intermediary between the optical element and sensor element. It absorbs stray radiation and prevents it from reaching the sensor, thereby reducing thermal effects caused by uneven heating of optical elements while maintaining field of view control
Solution Approach 2:
The harmful thermal effects are extracted from the measurement path by removing the stray radiation that causes uneven heating. The radiation trap selectively absorbs only the stray radiation outside the intended field of view, allowing the optical element to maintain its field of view defining function without introducing thermal distortion
3Object-affected harmful factors
If the housing is designed to protect the sensor element, then protection is improved, but the housing itself may be heated unevenly causing thermal effects that distort measurements
Solution Approach 1:
The radiation trap acts as a thermal mediator within the housing structure. It absorbs stray radiation before it can contribute to uneven heating of the housing and sensor assembly, thereby maintaining the protective function of the housing while minimizing thermal distortion effects
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 significantly increases measurement accuracy by minimizing the impact of stray radiation and maintaining a restricted field of view, with approximately 95% of IR radiation originating from the intended field of view, reducing measurement distortion to less than 5%.
Implementation Method 1
A radiation trap is arranged between the first optical element and the second optical element and is configured to absorb a first portion of IR radiation incident the second optical element
Implementation Method 2
IR-transparent materials often used for lenses and windows have relatively high refractive indices n (e.g., silicon n≈3.46, germanium n≈4.0, polyethylene n≈1.7), which may produce strong reflections on the interfaces
Implementation Method 3
The thermal behavior of the optical elements of the infrared sensor assembly differs from that of the actual sensor element (e.g., thermopile chip), i.e., the optical elements heat up (cool down) in relation to the actual sensor element
Data Source
AI summary
An infrared (IR) sensor package includes a heat sink defining a first interior space and a radiation trap adjacent the first interior space. An IR sensor having a radiation-sensitive region which detects IR radiation is arranged within the first interior space of the heat sink. A first optical element and a second optical element are arranged at respective ends of the radiation trap. The radiation trap is configured to allow for the passage of a first portion of IR radiation incident the second optical element, through the first optical element, and into communication with the IR sensor element, and to absorb a second portion of IR radiation incident the second optical element.