Temperature Invariant Mid-Infrared Filter Using Lead Chalcogenide
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Solution Overview
Problem
Conventional mid-infrared filters exhibit significant shifts in optical properties and reduced transmissivity with temperature variations, limiting their accuracy and reliability in harsh environments such as the petrochemical and hydrocarbon industries.
Innovation Solution
A narrow bandpass filter with a wavelength transmission band that remains substantially temperature invariant over a wide range, achieved by controlling the ratio of low to high refractive index materials and using PbTe-based or PbSe-based interference filters, which minimizes band shifts and transmissivity reductions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional mid-infrared filters are used, then the filter can operate in harsh environments, but the optical properties shift significantly with temperature variations
Solution Approach 1:
The patent changes the material parameters by using lead chalcogenide materials (PbTe, PbSe, PbS) with specific refractive index characteristics that have low temperature coefficients. This material parameter change enables the filter to maintain stable optical properties across wide temperature ranges while operating in harsh environments
Solution Approach 2:
The patent employs composite multilayer structures combining different lead chalcogenide materials with varying refractive indices. This composite approach creates interference filters where the temperature-induced optical property shifts are minimized through the complementary thermal-optical characteristics of the constituent materials
2Adaptability or versatility
If the filter operates over a wide temperature range, then the sensor can be used in various downhole and subsea conditions, but the wavelength transmission band shifts
Solution Approach 1:
The patent selects materials with specific refractive index temperature dependencies. The lead chalcogenide materials are chosen because their refractive indices change minimally with temperature, allowing the filter to cover wide temperature ranges from -25°C to 200°C while maintaining accurate wavelength transmission
Solution Approach 2:
The patent converts the typically harmful thermal expansion and refractive index changes into a beneficial design feature by selecting materials whose thermal-optical properties naturally compensate for each other in the multilayer structure, making the wavelength transmission invariant across temperature changes
3Ease of manufacture
If conventional filter materials are used, then the filter can be manufactured with standard materials, but transmissivity reduces with increasing temperature
Solution Approach 1:
The patent uses composite multilayer structures of lead chalcogenide materials that can be deposited using standard thin-film techniques. The composite design maintains high transmissivity across temperature ranges by compensating for thermal effects through the interference properties of the layered structure
Solution Approach 2:
The patent changes from conventional dielectric materials to lead chalcogenide materials with superior thermal-optical stability. This parameter change in material selection enables manufacturing with adapted techniques while achieving stable transmissivity across temperature variations
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 solution significantly reduces temperature-induced shifts in the filter's optical properties, maintaining accuracy and reliability across varying temperatures, from -25 to 200°C, enhancing the use of mid-infrared sensing techniques in temperature-fluctuating conditions.
Implementation Method 1
the filter may in some embodiments comprise a substrate, formed of Si, SiO2, Al2O3, Ge, ZnSe and/or the like and at each opposing side of the substrate alternating high and low refractive index layers may be formed
Data Source
AI summary
A narrow bandpass filter that may be used in a mid-infrared sensor for monitoring a species, which may be a component of a fluid or a solid material. The filter comprises a cavity comprising a low refractive index material. By providing a high ratio of low refractive index material in the filter with respective to high refractive index material, the filter is configured so that wavelength transmission remains constant with varying temperature. Materials used for the low and/or high refractive index provide a temperature invariant filter that transmits mid-infrared spectra without serious degradation.