Helmholtz Resonator Array With Absorptive Foam For Broadband Acoustic Damping
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Solution Overview
Problem
Existing acoustic metamaterials require significant thickness to achieve high sound absorption efficiency and often have limited frequency range, with complex structures and narrow frequency ranges of high absorption efficiency.
Innovation Solution
A periodic array of unit cells with Helmholtz resonators, each covered or partially filled with an acoustically absorptive medium, such as thermoplastic foam, to enhance resonant frequency bandwidth and achieve broadband acoustic absorption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If viscous materials are used to absorb airborne acoustic waves, then absorption efficiency is improved, but thickness increases significantly
Solution Approach 1:
The patent combines Helmholtz resonators (rigid cavity structures) with viscous absorbing materials (foam or fibrous media) to create a composite acoustic absorber. The resonators provide mass-spring resonance at specific frequencies while the viscous material provides broadband absorption, achieving high efficiency without requiring the large thickness of pure viscous absorbers.
Solution Approach 2:
The patent modifies the resonant frequency of the Helmholtz resonators by changing parameters such as cavity volume, neck area, and neck length to match and extend beyond the absorption peak frequency. This parameter tuning allows the resonant structure to broaden the effective absorption bandwidth when combined with the viscous material.
2Length of stationary object
If metasurfaces with resonant structures are used, then thickness is reduced, but frequency range of high efficiency absorption becomes narrow
Solution Approach 1:
The patent creates a composite structure where Helmholtz resonators (providing resonant enhancement) are combined with viscous absorbing materials (providing broadband damping). This combination allows the thin metasurface structure to achieve broadband absorption by merging the narrowband resonant peaks with the broadband viscous absorption characteristics.
Solution Approach 2:
The patent applies different materials and structures to different parts of the absorber: rigid Helmholtz resonator cavities provide localized resonant enhancement at specific frequencies, while the distributed viscous absorbing material provides broadband damping across the frequency spectrum, creating locally optimized zones that collectively achieve broadband performance.
3Reliability
If metamaterials combining viscous absorbers and resonant structures are used, then absorption performance is improved, but structural complexity increases
Solution Approach 1:
The patent divides the acoustic absorber into discrete unit cells, each containing a Helmholtz resonator and associated viscous absorbing material. These modular unit cells can be arranged in periodic arrays or quasi-random patterns, simplifying manufacturing and design while maintaining the combined resonant-viscous absorption mechanism at the unit cell level.
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 combination of Helmholtz resonators and acoustically absorptive media results in a structure that provides broad frequency range acoustic absorption with high efficiency, outperforming conventional materials by maintaining strong absorbance across a wider range with a thinner absorptive layer.
Implementation Method 1
each unit cell having a Helmholtz resonator having a resonant frequency. Each Helmholtz resonator includes a chamber portion bounded by at least one enclosure wall defining a chamber volume; and a neck, forming an aperture in the at least one enclosure wall
Implementation Method 2
an acoustically absorbing medium overlaying the neck, thereby increasing the resonant frequency bandwidth to achieve the absorption frequency range
Data Source
AI summary
Airborne acoustic absorbers include periodic arrays of Helmholtz resonators that are covered and/or partially filled with an acoustically absorptive material, such as a thermoplastic foam. The combined structures have much broader frequency ranges of high acoustic absorption than do structures having only Helmholtz resonators or acoustically absorbing foam.