Sapphire Optical Sampling Cell for Bubble-Free IR Analysis
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Solution Overview
Problem
Conventional liquid transmission cells for optical measurements are prone to air bubble trapping, difficult to fill and clean, especially with viscous samples, and have alignment and temperature control issues, making accurate measurements challenging, particularly in near and mid-infrared regions.
Innovation Solution
An optical sampling arrangement featuring a smoothly curved concave cavity in one element and a shallower convex surface on another, allowing for precise and bubble-free sample placement, with elements made of transparent materials like sapphire, and a hinged design for easy pathlength adjustment and cleaning, along with a sealed housing for temperature control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional liquid transmission cells are used, then optical measurements can be made, but air bubbles are trapped and measurement accuracy deteriorates
Solution Approach 1:
The cell uses a concave spherical cavity in one window and a convex spherical surface on the other window, creating a curved optical path that prevents air bubbles from forming and interfering with measurements. The spherical geometry ensures bubbles are excluded from the optical path while maintaining a sealed sample environment.
2Ease of manufacture
If conventional liquid transmission cells are used, then optical measurements can be made, but cleaning becomes difficult especially with viscous samples
Solution Approach 1:
The concave spherical cavity and convex spherical surface create smooth curved surfaces without crevices or corners where viscous samples could accumulate. This geometry allows easy cleaning by simply wiping the surfaces, as there are no trapped areas for residue to hide in.
3Manufacturing precision
If conventional liquid transmission cells are used, then optical measurements can be made, but pathlength reproduction becomes inaccurate when cells are disassembled and rebuilt
Solution Approach 1:
The spherical cavity and convex surface are designed with precise radii of curvature that determine the sample pathlength. When the windows are assembled, the spherical geometry ensures consistent contact and reproducible pathlength regardless of minor assembly variations, making it easy to disassemble and rebuild while maintaining precision.
4Temperature
If conventional liquid transmission cells are used, then optical measurements can be made, but temperature control and stabilization becomes difficult
Solution Approach 1:
The cell design merges the sample containment function with thermal management by using a compact sealed structure where the sample is contained in a small volume between the two windows. This reduces thermal mass and allows more efficient temperature control and stabilization compared to larger conventional cells.
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 enables easy filling and cleaning, accurate and reproducible pathlengths, and effective temperature stabilization, allowing for precise optical measurements with viscous samples, including semi-solids, while minimizing interference and requiring minimal solvent and parts, thus improving measurement accuracy and safety.
Implementation Method 1
at least one of the first and second elements being transparent to optical radiation such that optical radiation can be directed through the thickness of the liquid sample
Implementation Method 2
One or both elements may be of sapphire. The concave cavity and the convex surface formation are preferably part spherical.
Data Source
AI summary
An infra-red liquid sampling cell has a sapphire base plate with a part-spherical concave recess. A sapphire upper plate is hinged relative to the base plate larger radius of curvature than the recess. When the upper plate is lowered into contact with the base plate its convex surface contacts the liquid sample thereby excluding air bubbles and, when in contact with the edge of the recess, produces a well-defined sample thickness. An infra-red source directs radiation down through both plates and the liquid sample to a detector.