Multiple Fabry-Perot Filters for Gas Analysis Spectrometer
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Solution Overview
Problem
Current spectrometric methods for gas analysis, such as FTIR and NDIR, are costly, inflexible, and limited in spectral resolution due to the use of single Fabry-Pérot filters, which restricts the ability to selectively detect multiple gas components with high accuracy.
Innovation Solution
A spectrometer employing a filter arrangement with multiple Fabry-Pérot filters, allowing for adjustable mirror spacings and electrostatic or piezoelectric control, enabling flexible tuning of frequency properties and achieving high spectral resolution by combining filters with varying full widths at half maximum and free spectral ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a single Fabry-Pérot filter with high full width at half maximum is used, then the free spectral range is large, but the spectral resolution is reduced and multiple absorption lines cannot be selectively detected
Solution Approach 1:
The patent divides a single Fabry-Pérot filter into multiple filters with different full widths at half maximum. Each filter segment handles specific spectral regions, allowing the system to achieve both large free spectral range and high spectral resolution simultaneously by combining the capabilities of individual filter segments.
Solution Approach 2:
The patent introduces an additional dimension by varying the full width at half maximum across multiple filters rather than relying on a single filter parameter. This dimensional expansion allows independent optimization of free spectral range and spectral resolution through the ensemble of filters with different characteristics.
2Measurement precision
If a single Fabry-Pérot filter with reduced full width at half maximum is used, then the spectral resolution is high, but the free spectral range becomes too small to cover multiple absorption lines
Solution Approach 1:
The patent segments the spectral coverage task across multiple filters. Filters with narrow full width at half maximum provide high spectral resolution for specific absorption lines, while the collection of filters collectively covers a broad free spectral range, eliminating the need to compromise between resolution and range.
Solution Approach 2:
The filter arrangement achieves multi-functionality by combining filters with different full widths at half maximum. The system can selectively detect multiple gas components with different spectral requirements using the same filter arrangement, making it universally applicable to various gas analysis scenarios.
3Device complexity
If NDIR with optical band pass filters is used, then the system is simple, but it requires a separate filter for each gas component reducing flexibility
Solution Approach 1:
The patent creates a universal filter arrangement that can detect multiple gas components with a single system configuration. By using Fabry-Pérot filters with tunable mirror spacings, the same physical apparatus can selectively analyze different gases by adjusting the filter parameters, eliminating the need for separate dedicated filters for each gas component.
Solution Approach 2:
The patent introduces dynamic adjustability to the filter system through electrostatic or piezoelectric control of mirror spacings. This allows real-time tuning of the Fabry-Pérot filters to adapt to different gas components and spectral regions, providing flexibility without requiring physical replacement of filter components.
4Reliability
If mechanical choppers are used for light modulation, then lock-in methods can be applied, but the system requires large construction space and is susceptible to interference
Solution Approach 1:
The patent replaces mechanical choppers with electrostatic or piezoelectrically controlled Fabry-Pérot filters for light modulation. This substitution eliminates moving mechanical parts, reduces construction space requirements, and improves reliability by using field-based control mechanisms instead of mechanical rotation and stabilization systems.
Solution Approach 2:
The patent uses dynamically controllable Fabry-Pérot filters that can be rapidly tuned through electrostatic or piezoelectric actuation to achieve light modulation. This dynamic control provides the necessary modulation for lock-in detection methods without requiring mechanical choppers, thereby reducing system complexity and improving reliability.
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 allows for cost-effective, compact, and robust gas analysis with high spectral resolution, enabling the detection of multiple gas components with improved signal-to-noise ratio and reduced maintenance, while maintaining optical throughput and flexibility.
Implementation Method 1
By means of constructive and destructive interference only those wavelengths are transmitted which correspond to the resonance condition
Implementation Method 2
A Fabry-Pérot filter is an optical resonator which is formed by two part transparent mirrors
Implementation Method 3
electrostatic or piezoelectric control
Implementation Method 4
electrostatic or piezoelectric control
Implementation Method 5
the gases show a characteristic absorption at frequencies which correspond to the spectral lines of its molecules
Data Source
AI summary
A spectrometer (10) for gas analysis is provided, the spectrometer comprising a measurement cell (28) having a gas to be investigated, a light source (12) for the transmission of light (14) into the measurement cell (28) on a light path (16), a filter arrangement (22) having a Fabry-Perot filter (24a-c) in the light path (16), in order to set frequency properties of the light (14) by means of a transmission spectrum of the filter arrangement (22), as well as a detector (36, 38) which measures the absorption of the light (14) by the gas (30) in the measurement cell (28). In this connection the filter arrangement (22) has a plurality of Fabry-Perot filters (24a-c) arranged behind one another in the light path (14) and a control unit (44) for the filter arrangement (22) is provided in order to change the transmission spectrum by setting at least one of the Fabry-Perot filters (24a-c).