Adjustable Interference Filter for Gas Detection
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Solution Overview
Problem
Existing interference filters for gas detection with infrared light are costly and inefficient for mass-produced CO sensors due to mechanical complexity and energy consumption in achieving correlation and anti-correlation modes, and they struggle with maintaining stability and light throughput.
Innovation Solution
An adjustable interference filter using two silicon discs with an adjustable cavity, allowing for electrostatic or piezoelectric control of the optical path length, enabling fast switching between correlation and anti-correlation modes with high refractive index materials like silicon or Germanium, and incorporating anti-reflection layers for minimal reflection and improved light throughput.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a mechanical interferometer is used to achieve correlation and anti-correlation modes, then the filter can be adjusted between modes, but the device becomes costly and mechanically complex
Solution Approach 1:
The patent replaces the mechanical interferometer system with an electrostatic or piezoelectrically controlled Fabry-Perot filter. The mechanical adjustment mechanism is substituted with electrical control of the cavity thickness, eliminating complex mechanical parts while maintaining the ability to switch between correlation and anti-correlation modes.
Solution Approach 2:
The patent changes the physical parameter used for adjustment from mechanical displacement to electrical field control. By applying voltage to electrostatic actuators or piezoelectric materials, the cavity thickness is precisely controlled, enabling mode switching without mechanical complexity.
2Adaptability or versatility
If thermal modulation is used to change optical wavelength, then the filter can be adjusted, but the response time becomes slow and energy consumption increases
Solution Approach 1:
The patent substitutes thermal modulation with electrostatic or piezoelectric control. Instead of heating silicon discs to change their optical properties, electrical fields or piezoelectric effects are used to adjust the cavity thickness, achieving rapid response times and low energy consumption.
Solution Approach 2:
The patent changes the physical mechanism from thermal expansion to electrostatic/piezoelectric deformation. This parameter change enables fast switching between modes by applying voltage rather than heat, dramatically improving response time.
3Ease of manufacture
If a low refractive index material like air is used in the resonator, then the filter structure is simple, but the light throughput is reduced
Solution Approach 1:
The patent uses composite material structures including high refractive index materials (silicon, germanium) for the resonator walls and electrostatic/piezoelectric materials for actuation. This combination achieves both high light throughput through the high refractive index and precise control through the electrostatic/piezoelectric elements.
Solution Approach 2:
The patent changes the refractive index parameter of the resonator material from low (air) to high (silicon, germanium). This parameter change increases the etendue and light throughput by a factor of up to 10, while the electrostatic/piezoelectric control maintains structural precision.
4Ease of manufacture
If the cavity thickness is fixed, then the filter is simple to manufacture, but it cannot switch between correlation and anti-correlation modes
Solution Approach 1:
The patent transforms the static fixed cavity into a dynamic adjustable cavity. By incorporating electrostatic or piezoelectric actuators, the cavity thickness can be dynamically changed to switch between correlation and anti-correlation modes, maintaining manufacturing simplicity while adding adaptability.
Solution Approach 2:
The patent makes the cavity thickness parameter variable rather than fixed. Electrical control enables precise adjustment of this parameter to achieve different operational modes without complicating the overall manufacturing process.
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 provides a cost-effective, efficient, and stable interference filter that allows for flexible operation in both correlation and anti-correlation modes, enhancing light transmission and reducing the impact of environmental disturbances, thereby improving the accuracy and reliability of gas concentration measurements.
Implementation Method 1
The cavity thickness may be adjusted by means of an electrostatic or piezoelectric actuator
Implementation Method 2
The cavity thickness may be adjusted by means of an electrostatic or piezoelectric actuator
Implementation Method 3
An adjustable interference filter with two parallel silicon surfaces with a distance d between the surfaces
Implementation Method 4
incorporating anti-reflection layers for minimal reflection and improved light throughput
Data Source
Figure 1~2
Figure 3A~3D
Figure 4A~4B
AI summary
The present invention relates to an adjustable interference filter, especially for use in gas detection with infrared light within a chosen range, comprising at least two essentially parallel reflective surfaces separated by a chosen distance defining a cavity delimited by the reflective surfaces between which the light may oscillate, and at least one of said surfaces being semitransparent for transmission of light to or from the cavity. The filter comprises a transparent material with a chosen thickness and having a high refractive index positioned in the cavity, and adjustable separation means for adjusting the cavity length between the reflecting surfaces, so as to obtain a cavity constituted by the transparent, high refractive index material and a an adjustable part.