Folded Metaporous Acoustic Coating for Low-Frequency Absorption
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Solution Overview
Problem
Existing porous materials for noise absorption in aircraft engines are limited by their thickness, which constrains low-frequency absorption, and new engine architectures with low-speed fans require compact acoustic treatments that can absorb low frequencies.
Innovation Solution
An acoustic treatment coating using a metamaterial with a solid structure containing folded cavities and porous material, produced via additive manufacturing, to increase the effective sound path length while maintaining a compact form.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If porous material thickness is increased to absorb low frequencies, then low frequency absorption is improved, but the volume and weight of the acoustic treatment increase
Solution Approach 1:
The patent applies dimensionality change by transforming the linear thickness dimension into a folded three-dimensional path. The porous material is configured in a zigzag or folded pattern that extends the sound propagation path length beyond the physical thickness of the component. This allows low frequency absorption to be achieved with a shorter physical thickness, resolving the contradiction between absorption effectiveness and volume constraints.
Solution Approach 2:
The folded porous material structure nests multiple absorption paths within the limited thickness available in the fan casing. By folding the material back on itself, the design effectively nests the extended absorption path within the constrained spatial envelope, maintaining compact volume while achieving the equivalent absorption performance of a much thicker material.
2Reliability
If porous material thickness is increased to achieve perfect absorption, then absorption effectiveness is improved, but the acoustic treatment becomes incompatible with thin nacelle space
Solution Approach 1:
The invention uses dimensionality change by folding the porous material into a three-dimensional zigzag configuration. This extends the effective absorption path length without increasing the physical thickness of the treatment layer, allowing perfect absorption to be achieved within the thin space constraints of modern nacelle designs.
3Speed
If fan rotation speed is reduced to improve engine architecture, then noise spectrum shifts to lower frequencies, but existing acoustic treatments become ineffective
Solution Approach 1:
The patent applies parameter changes by modifying the physical configuration parameters of the porous material - specifically its geometric arrangement from a simple linear layer to a folded three-dimensional structure. This changes the effective path length parameter, enabling the material to absorb the shifted low frequency noise spectrum generated by slower rotating fans, thereby maintaining absorption effectiveness despite the change in operating conditions.
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 coating effectively attenuates low frequencies with finer absorption peaks over a broader frequency range, optimizing noise absorption without increasing volume.
Implementation Method 1
significant noise absorption is only possible above the visco-inertial transition frequency of the porous material, which will then work in the inertial regime
Implementation Method 2
Porous materials are used to absorb noise over wide ranges of acoustic frequencies in engines
Data Source
AI summary
An acoustic treatment coating includes a metamaterial, wherein the metamaterial includes a solid structure including at least one free space forming a folded cavity and at least one porous material placed in the free space of the solid structure.