Metamaterial Thermal Sensor Membrane for Sub-7.5µm IR Detection
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Solution Overview
Problem
Conventional uncooled passive infrared sensors, such as microbolometers, have limited sensitivity and resolution, and are unable to detect IR radiation wavelengths below 7.5µm, which restricts their use in multispectral and high-speed applications, and are costly compared to cooled thermal and photon detector imagers.
Innovation Solution
The use of metamaterial structures with spaced-apart openings in the IR absorbing membrane of thermal sensor pixels, which improves IR absorption characteristics by reducing thermal mass and conductance, allowing for enhanced sensitivity and the ability to detect wavelengths below 7.5µm, while maintaining a low production cost similar to conventional microbolometers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional microbolometer membranes are used, then the device structure is simple and manufacturing is easy, but the sensitivity and IR absorption are insufficient
Solution Approach 1:
The patent applies porous metamaterial structures to the IR absorbing membrane, where the membrane contains an array of holes or voids arranged in specific patterns. This porous configuration increases the effective surface area for IR absorption and reduces thermal mass, thereby enhancing sensitivity and detection capability without significantly complicating the manufacturing process
Solution Approach 2:
The patent employs composite membrane structures combining different materials with complementary properties. The membrane integrates IR-absorbing materials with thermally isolating materials, creating a composite structure that optimizes both thermal absorption efficiency and thermal isolation performance, leading to improved sensitivity
2Adaptability or versatility
If conventional microbolometer membranes are used, then the manufacturing cost is low, but the detection wavelength range is limited to 7.5-14μm
Solution Approach 1:
The patent modifies key parameters of the membrane structure, including hole size, hole spacing, hole depth, and pattern geometry, to tune the IR absorption characteristics. By adjusting these parameters, the membrane can be optimized for different wavelength ranges within and beyond the conventional 7.5-14μm band, enabling broader spectral detection while maintaining compatibility with standard microbolometer fabrication processes
3Speed
If the membrane thermal mass is reduced to improve sensitivity, then the response time decreases, but the thermal isolation becomes more difficult to maintain
Solution Approach 1:
The porous metamaterial structure reduces thermal mass through the hollow voids while the strategic placement and sizing of holes maintain structural integrity. The patterned configuration ensures that thermal pathways are optimized for rapid heat dissipation from the absorbing region while preserving thermal isolation from the substrate
Solution Approach 2:
The composite membrane structure incorporates materials with optimized thermal properties, where certain regions have high thermal conductivity for rapid heat dissipation while other regions maintain low thermal conductivity for effective isolation from the substrate, achieving both fast response and stable thermal isolation
4Measurement precision
If cryogenically cooled detectors are used, then the detection sensitivity and spectral discrimination are high, but the device cost and complexity increase significantly
Solution Approach 1:
The porous metamaterial membrane achieves enhanced IR absorption efficiency that approaches or exceeds that of cooled detectors, while maintaining the uncooled operational mode. The increased surface area and optimized thermal properties enable high sensitivity detection without requiring complex cryogenic cooling systems
Solution Approach 2:
The composite membrane structure optimizes the balance between thermal absorption and thermal isolation, achieving detection performance comparable to cooled detectors while remaining uncooled. This eliminates the need for expensive and complex cryogenic cooling infrastructure
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 modified thermal sensors exhibit improved IR radiation absorption, increasing sensitivity by at least a factor of 2.5 and enabling multispectral imaging capabilities, including detection of methane leaks, with a reduced production cost and smaller footprint compared to cryogenically cooled systems.
Implementation Method 1
IR absorbing material membrane modified using metamaterials technology... significantly improved absorption of IR radiation
Implementation Method 2
the reduced thermal mass and conductance of the modified membrane that is produced by the openings
Implementation Method 3
the reduced thermal mass and conductance of the modified membrane that is produced by the openings
Implementation Method 4
the membrane is coupled to the reflector in a manner that forms an associated Fabry-Perot cavity that resonates when exposed to IR radiation having certain frequencies (wavelengths)
Implementation Method 5
a resistance of the membrane changes in accordance with changes in the cavity's resonant state
Data Source
Figure 1
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Figure 4~5
AI summary
A thermal sensor includes an array of pixels, each having a membrane mounted on legs over a reflector, forming a Fabry-Pérot cavity. Each membrane includes an infrared (IR) absorbing material that defines multiple spaced-apart openings separated by micron-level distances that decrease thermal capacity and increase IR absorption of the membrane. Regular pitch distances between adjacent openings provides narrowband IR absorption, with pitch distances below 7.1µm facilitating the detection of IR radiation wavelengths below 7.5µm. Multispectral thermal imaging is achieved by arranging the pixels in repeated groups (superpixels), where each superpixel detects the same set of IR radiation wavelengths. Thermal imaging devices include thermal sensors, IR lenses and device control circuitry arranged in a camera-like manner. A methane leak detection system utilizes two multispectral imaging devices positioned to image a wellhead from two directions, and a system controller that generates spatial and spectral information describing methane plumes using the image data.