Microporous Sound Absorber with Compact Quarter-Wave Resonators
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Solution Overview
Problem
Existing sound absorbers for aircraft engines, such as honeycomb sandwich panels and porous materials, are either too bulky, heavy, or mechanically weak, and fail to effectively absorb noise at low frequencies, especially in engines with high bypass ratios, while additive manufacturing solutions offer limited frequency ranges and mechanical fragility.
Innovation Solution
A sound absorber comprising quarter-wave acoustic resonators and a microporous element with periodically repeating unit cells, where the resonators are inclined or bent to minimize size and the microporous element is reinforced with superposed layers, allowing for broad frequency absorption and mechanical strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If porous materials are used to absorb low frequency noise, then sound absorption effectiveness is improved, but the thickness required becomes excessively large (approximately quarter of acoustic wavelength)
Solution Approach 1:
The sound absorber is divided into multiple functional layers: a porous core layer for broadband absorption, quarter-wave resonator layers for enhanced low-frequency absorption, and a micro-perforated panel for additional resonance control. Each layer segments the absorption function to achieve comprehensive performance without excessive thickness
Solution Approach 2:
The invention uses a composite structure combining porous materials (foam or fibrous), rigid frame structures (quarter-wave resonators), and micro-perforated panels. This composite approach integrates the advantages of each material type to achieve effective low-frequency absorption in a compact thickness
2Object-affected harmful factors
If honeycomb sandwich panels are used for sound absorption, then low frequency noise absorption is improved, but the device becomes particularly bulky
Solution Approach 1:
The invention employs porous materials as the core absorption layer, which provide broadband noise reduction in a much thinner profile compared to honeycomb structures. The porous structure allows acoustic energy dissipation through viscous losses and thermal conduction without requiring large cell dimensions
Solution Approach 2:
Instead of using large-dimensional honeycomb cells that occupy significant volume, the invention transitions to a thin-panel structure with sub-wavelength resonators and micro-perforations that achieve similar low-frequency absorption in a dimensionally compact form factor
3Strength
If metal porous materials with high mechanical strength are used, then mechanical strength is improved, but the weight becomes excessively high
Solution Approach 1:
The invention uses a composite construction with a lightweight porous core (foam or fibrous material) supported by rigid frame structures and micro-perforated panels. This composite approach provides the necessary mechanical strength through the rigid frameworks while keeping the overall weight low by using lightweight porous infill
Solution Approach 2:
Mechanical strength is localized to specific structural elements (the rigid frame of quarter-wave resonators and micro-perforated panel) rather than requiring the entire absorber volume to be structurally strong. The porous core provides absorption while the rigid frameworks provide localized strength support
4Object-affected harmful factors
If interconnected pore structures are used in porous materials, then sound absorption is improved, but air flow disturbance in engine increases, degrading engine efficiency
Solution Approach 1:
The invention uses controlled porous materials with specific pore size distributions that allow smooth air flow through the structure. The porous architecture is designed to minimize flow separation and turbulence while maintaining effective acoustic absorption, thus preserving engine efficiency
Solution Approach 2:
The pore size, porosity, and flow resistance parameters of the porous material are optimized to balance acoustic absorption performance with minimal impact on air flow. By adjusting these parameters, the material absorbs sound effectively while allowing engine air flow to pass with minimal disturbance
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 proposed sound absorber achieves high sound absorption across a wide frequency range with compact size and mechanical durability, suitable for environments with mechanical stress, such as aviation engine nacelles.
Implementation Method 1
each cell of the honeycomb can function as a Helmholtz resonator, in order to attenuate the noise
Implementation Method 2
one or more first quarter-wave acoustic resonators each having a first length
Implementation Method 3
it has therefore been proposed to use porous materials, the individual pores of which act as Helmholtz resonators
Implementation Method 4
the individual pores of which act as Helmholtz resonators
Implementation Method 5
The use of additive manufacturing has been proposed by Z. Liu, J. Zhan, M. Fard, and J. L. Davy in 'Acoustic properties of a porous polycarbonate material produced by additive manufacturing'
Data Source
AI summary
A sound absorber extending between two opposite surfaces, and combining one or more quarter-wave acoustic resonators, with a microporous element. Each acoustic resonator, has a length L, which is substantially greater than a thickness t of the sound absorber, between a first open end on a first surface of the two opposite surfaces, of the sound absorber and a second closed end. The microporous element is made up of a plurality of periodically repeating unit cells adjacent to the acoustic resonators. A method for producing this sound absorber, which method includes at least one additive manufacturing step.