Broadband Sparse Acoustic Absorber Using Helmholtz Resonators
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Solution Overview
Problem
Conventional acoustic metamaterials are impermeable to ambient fluid and have limited frequency absorption ranges, making them ineffective for broad frequency absorption and fluid flow applications.
Innovation Solution
A periodic array of laterally spaced-apart, two-sided Helmholtz resonators with unit cells designed to allow fluid communication, creating a sparse structure that enables broadband acoustic absorption by stacking layers with different resonance frequencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If conventional acoustic metamaterials are used, then acoustic absorption is achieved, but the material is impermeable to ambient fluid and has narrow frequency absorption range
Solution Approach 1:
The patent employs porous acoustic absorbing material filling the cavities of the resonator structures, creating a material that is inherently permeable to fluid while maintaining acoustic absorption capabilities. The porous nature allows ambient fluid to pass through the material freely.
Solution Approach 2:
The acoustic metamaterial is segmented into discrete resonator units with specific geometric configurations (cylindrical, conical, or frustoconical shapes) that are spaced apart from each other. This segmentation creates channels for fluid flow while the resonator structures provide broadband acoustic absorption through their geometric resonance characteristics.
2Ease of operation
If conventional solid surface metamaterials are used, then acoustic absorption is achieved, but fluid flow is blocked
Solution Approach 1:
The use of porous acoustic absorbing material throughout the resonator structures creates a uniformly permeable structure that allows fluid flow in all directions while maintaining acoustic absorption functionality. The material's porous structure eliminates the need for complex channel designs.
Solution Approach 2:
The resonator structures serve multiple functions simultaneously: they provide acoustic absorption through their geometric resonance, allow fluid flow through their porous construction, and can be configured in various shapes (cylindrical, conical, frustoconical) to optimize performance for different applications.
3Adaptability or versatility
If narrow frequency absorption range is accepted, then simpler structure is used, but broadband absorption is not achieved
Solution Approach 1:
Different resonator units within the array have different geometric parameters (radii, heights, neck dimensions) that are optimized for specific frequency ranges. This local variation in geometric quality across the array enables broadband absorption as each resonator targets specific frequencies while collectively covering a wide spectrum.
Solution Approach 2:
The acoustic metamaterial combines multiple resonator geometries (cylindrical, conical, frustoconical) with different dimensional ratios arranged in a periodic array. This composite structure leverages the complementary absorption characteristics of each resonator type to achieve broadband performance that no single resonator design could provide alone.
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 structure achieves tunable, very broadband acoustic absorption, allowing for efficient sound dampening while allowing air or fluid to pass through, as demonstrated by increased absorption breadth and applicability in sound suppression systems like vehicle engines.
Implementation Method 1
The acoustic absorber includes a periodic array of laterally spaced-apart, two-sided Helmholtz resonators
Implementation Method 2
The structure achieves tunable, very broadband acoustic absorption, allowing for efficient sound dampening
Data Source
AI summary
A broadband sparse acoustic absorber includes a periodic array of spaced apart unit cells, generally having a lateral fill factor less than 0.5. Each unit cell includes a pair of joined, and inverted, Helmholtz resonators, having longitudinal and lateral neck portions that are perpendicular to one another. The longitudinal neck portions are typically covered and/or filled with acoustic absorbing material. Sound suppression systems include sound emitting devices that are at least partially surround by one or more such arrays.