<i>Acoustic Absorbers and Diffusers, Theory, design and application</i>

Cox, Trevor J.; D’Antonio, Peter; Schroeder, Manfred R.

doi:10.1121/1.1861060

Cited by 159 publications

(226 citation statements)

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“…The inherent viscothermal losses of an acoustic system combined with wave interference can give rise to perfect absorption, a phenomenon which is of great applied interest in many fields like room acoustics [1,2], duct mufflers [3], aeroacoustic liners [3] and environmental acoustics [4]. In the particular case of a two-port, resonator/waveguide system, it has been shown that Coherent Perfect Absorption (CPA) can be obtained under a so-called critical coupling condition when the two-sided incident waves correspond to an eigenmode of the scattering matrix of the system.…”

Section: Introductionmentioning

confidence: 99%

Coherent perfect absorption induced by the nonlinearity of a Helmholtz resonator

Achilleos¹,

Richoux²,

Theocharis³

2016

The Journal of the Acoustical Society of America

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In this work, coherent perfect absorption of sound waves induced by the nonlinear response of a Helmholtz Resonator side loaded to a waveguide, is reported. It is shown that this two-port system can perfectly absorb two high amplitude symmetric incident waves under a certain condition. For the one-sided incidence configuration, this condition leads to an absorption equal to 0.5. Experiments verify these results and are in agreement with an analytical nonlinear impedance model for the resonator. The nonlinear control of perfect absorption opens new possibilities in the design of high amplitude sound attenuators for aero-engine applications.

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Section: Introductionmentioning

confidence: 99%

Coherent perfect absorption induced by the nonlinearity of a Helmholtz resonator

Achilleos¹,

Richoux²,

Theocharis³

2016

The Journal of the Acoustical Society of America

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“…This BC models a resonating sound absorber such as of a membrane type, characterized by its complex impedance [37] z…”

Section: Resonance Absorbermentioning

confidence: 99%

Ray-tracing semiclassical (RTS) low frequency acoustic modeling validated for local and extended reaction boundaries

Prislan¹,

Svenšek²

2018

Journal of Sound and Vibration

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The recently introduced acoustic ray-tracing semiclassical (RTS) method is validated for a set of practically relevant boundary conditions. RTS is a frequency domain geometrical method which directly reproduces the acoustic Green's function. As previously demonstrated for a rectangular room and weakly absorbing boundaries with a real and frequency-independent impedance, RTS is capable of modeling also the lowest modes of such a room, which makes it a useful method for low frequency sound field modeling in enclosures. In practice, rooms are furnished with diverse types of materials and acoustic elements, resulting in a frequency-dependent, phase-modifying absorption/reflection. In a realistic setting, we test the RTS method with two additional boundary conditions: a local reaction boundary simulating a resonating membrane absorber and an extended reaction boundary representing a porous layer backed by a rigid boundary described within the Delany-Bazley-Miki model, as well as a combination thereof. The RTS-modeled spatially dependent pressure response and octave band decay curves with the corresponding reverberation times are compared to those obtained by the finite element method.

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“…25,26 The reason thicker foams have better sound absorption comes from the particle velocity theory described by Cox. 27 The theory states that significant sound absorption COMPRESSION-MOLDED OPEN-CELL PP FOAMS only occurs where particle velocity is high. High particle velocity will occur in foam farthest away from the rigid wall boundary; hence, thicker samples should have better sound absorption.…”

Section: Effect Of Cell Morphology On Sound Absorptionmentioning

confidence: 99%

Mechanical and Acoustic Performance of Compression Molded Open Cell Polypropylene Foams

McRae

Naguib

Atalla

2008

Smart Materials, Adaptive Structures and Intelligent Systems, Volume 1

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Open-cell materials are lightweight and multifunctional capable of absorbing acoustic energy and supporting mechanical load. The acoustic and mechanical performance of open-cell materials can be optimized through processing. In this article, the relationships between processing parameters and acoustic and mechanical performance are shown for polypropylene (PP) foams. PP foam samples are fabricated using a combined compression molding and particulate leaching process. The results from a parametric study showed that both salt size and salt to polymer ratio affect the acoustic and mechanical performance of open-cell PP foams. As salt size increases, cell size increased and cell density decreased. The salt to polymer ratio had opposite affect on cell density, and increasing the salt to polymer mass ratio increased the open-cell content. The airflow resistivity decreased significantly by increasing the cell size, which means that foam samples with smaller cell size have better sound absorption. When foam samples were thin, smaller cell sizes produced better sound absorption; however, as thickness of the sample increases, medium cell size offered the best acoustic performance. The compressive strength of the foams was increased by increasing the relative density. Acoustic performance results from the parametric study were compared to the Johnson-Allard model with good agreement. Finally, optimal cellular morphologies for acoustic absorption and mechanical performance were identified.

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Acoustic Absorbers and Diffusers, Theory, design and application

Cited by 159 publications

References 0 publications

Coherent perfect absorption induced by the nonlinearity of a Helmholtz resonator

Coherent perfect absorption induced by the nonlinearity of a Helmholtz resonator

Ray-tracing semiclassical (RTS) low frequency acoustic modeling validated for local and extended reaction boundaries

Mechanical and Acoustic Performance of Compression Molded Open Cell Polypropylene Foams

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