Miniature Gas Sensor Folded Optical Path
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Solution Overview
Problem
Existing gas sensors using the NDIR technique face challenges in miniaturization and alignment precision, with limited possibilities for compact design due to the need for precise alignment of light sources and detectors, and most light rays making only a single reflection before reaching the detector.
Innovation Solution
A gas sensor design featuring a substrate with an objective, eyepiece, relay lens, and reflective surfaces that fold the optical path through successive reflections, allowing for a compact configuration with a longer optical path length, reduced dimensions, and relaxed alignment constraints, using MEMS technology for the light source and detector.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a cavity with parallel flat surfaces and lateral surface is used with light source at one focus and detector at the other focus of an ellipse, then the optical path length is increased through reflection, but the alignment precision requirement becomes very strict and miniaturization possibilities are restricted
Solution Approach 1:
The patent introduces a folding optic system that reflects the light beam multiple times between the light source and detector, effectively extending the optical path in three-dimensional space while maintaining a compact physical footprint. The folding mirrors create a folded optical path that traverses the cavity multiple times, achieving long optical path length without requiring a long linear distance between components.
Solution Approach 2:
The optical components including folding mirrors, beam splitters, and detectors are integrated into a compact nested arrangement where the light beam folds back on itself multiple times within a small volume. This nesting allows the optical path to be contained within a minimal space while achieving the required path length for sensitive detection.
2Volume of moving object
If a folding optic system with multiple reflections is implemented, then the optical path length is extended within compact dimensions, but the device complexity increases
Solution Approach 1:
The patent combines multiple optical functions into integrated components. The folding mirrors serve dual purposes of extending the optical path and defining the measurement volume. Beam splitters are positioned to simultaneously direct light to reference and measurement paths. This merging of functions reduces the number of separate components needed and simplifies the overall system architecture.
Solution Approach 2:
The folding optic system is designed so that the same optical components serve multiple functions: the folding mirrors extend the path length while also confining the beam within the measurement cavity; the beam splitters create reference and measurement paths using the same optical element; the detector array processes multiple beam paths simultaneously. This multi-functionality reduces component count and system complexity.
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 design achieves a more compact gas sensor with a longer optical path while simplifying production and reducing alignment requirements, enabling precise gas concentration measurements with improved miniaturization and efficiency.
Implementation Method 1
an objective situated on the substrate, adapted to collect a light beam emitted by the light source
Implementation Method 2
reflective surfaces known as return surfaces, situated facing said substrate; the light beam emitted by the light source propagates by successive reflections from the objective to the eyepiece
Implementation Method 3
at least one relay lens, arranged on a reflective surface known as intermediate surface formed on the substrate, and comprising at least one field lens adapted to deviate the rays of the light beam emitted by the light source
Implementation Method 4
an eyepiece situated on the substrate, adapted to collect an incident light beam to focus it on the detector
Implementation Method 5
The detector 16 makes it possible to express, in an electric signal, the light intensity of the incident light beam
Implementation Method 6
The light beam is partially absorbed by said gas. The absorption wavelength depends on the nature of the gas
Implementation Method 7
Beer-Lambert's law links: the light intensity at the absorption wavelength before partial absorption by said gas (l0); the light intensity at the absorption wavelength after partial absorption by said gas (l); the length of the optical path travelled in the gaseous medium (lg); the concentration of gas in the medium (C)
Data Source
AI summary
A gas sensor (20) comprising a substrate (231); an objective (211) situated on the substrate (231), adapted to collect a light beam (212, 213) emitted by a light source (210); an eyepiece (250) situated on the substrate (231), adapted to collect an incident light beam to focus it on a detector (251); return reflective surfaces (281, 282), situated facing said substrate; and at least one field lens (221), arranged on an intermediate reflective surface (222) formed on the substrate (231), and adapted to deviate the rays (213) of the light beam emitted by the light source, to bring them closer to the optical axis of the eyepiece (250).