scholarly journals Multiresonant Layered Acoustic Metamaterial (MLAM) solution for broadband low-frequency noise attenuation through double-peak sound transmission loss response

2021 ◽  
pp. 101368
Author(s):  
D. Roca ◽  
J. Cante ◽  
O. Lloberas-Valls ◽  
T. Pàmies ◽  
J. Oliver
Keyword(s):  
Transmission Loss ◽  
Low Frequency ◽  
Sound Transmission ◽  
Frequency Noise ◽  
Noise Attenuation ◽  
Sound Transmission Loss ◽  
Low Frequency Noise ◽  
Double Peak ◽  
Acoustic Metamaterial

Broadband low-frequency noise reduction using Helmholtz resonator-based metamaterial

2021 ◽  
Vol 69 (4) ◽  
pp. 351-363
Author(s):  
Jhalu Gorain ◽  
Chandramouli Padmanabhan
Keyword(s):  
Transmission Loss ◽  
Low Frequency ◽  
Helmholtz Resonator ◽  
Broadband Noise ◽  
Unit Cell ◽  
Frequency Noise ◽  
Noise Attenuation ◽  
Low Frequency Noise ◽  
Low Frequencies ◽  
Pu Foam

Achieving broadband noise attenuation at low frequencies is still a significant challenge. Helmholtz resonators offer good low-frequency noise attenuation but are effective only over a narrow band; the cavity volume required at these frequencies is also larger. This article proposes a new broadband acoustic metamaterial (AMM) absorber, which uses polyurethane (PU) foam embedded with small-size resonators tuned to different frequencies. The AMM design is achieved in three phases: (1) develop a transfer-matrix-based one-dimensionalmodel for a resonator with intruded neck; (2) use this model to develop a novel band broadeningmethod, to select appropriate resonators tuned to different frequencies; and (3) construct a unit cell metamaterial embedded with an array of resonators into PU foam. A small-size resonator tuned to 415 Hz is modified, by varying the intrusion lengths of the neck, to achieve natural frequencies ranging from 210 to 415 Hz. Using the band broadening methodology, 1 unit cell metamaterial is constructed; its effectiveness is demonstrated by testing in an acoustic impedance tube. The broadband attenuation characteristics of the constructed unit cell metamaterial are shown to match well with the predicted results. To demonstrate further the effectiveness of the idea, a metamaterial is formed using 4 periodic unit cells and is tested in a twin room reverberation chamber. The transmission loss is shown to improve significantly, at low frequencies, due to the inclusion of the resonators.

Excellent low-frequency sound absorption of radial membrane acoustic metamaterial

2017 ◽  
Vol 31 (03) ◽  
pp. 1750011 ◽  
Author(s):  
Nansha Gao ◽  
Jiu Hui Wu ◽  
Hong Hou ◽  
Lie Yu
Keyword(s):  
Transmission Loss ◽  
Low Frequency ◽  
Sound Transmission ◽  
Ring Structure ◽  
Circular Ring ◽  
Effective Density ◽  
Geometrical Parameters ◽  
Membrane Thickness ◽  
Sound Transmission Loss ◽  
Acoustic Metamaterial

This paper proposes a new radial membrane acoustic metamaterial (RMAM) structure, wherein a layer membrane substrate is covered with a rigid ring (polymethyl methacrylate frame and aluminum lump). The dispersion relationships, transmission spectra and displacement fields of the eigenmodes of this radial membrane acoustic metamaterial are studied with FEM. In contrast to the traditional radial phononic crystals (RPCs), the proposed structures can open bandgaps (BGs) in lower frequency range (0–300 Hz). Simulation results show that the physical mechanism behind the bandgaps is the coupling effects between the rotational vibration of aluminum lump and the transverse vibration of membrane. Geometrical parameters which can adjust the bandgaps’ widths or positions are analyzed. Finally, we investigate the axial sound transmission loss of this acoustic metamaterial structure, and discuss the effects of factor loss, membrane thickness and the number of layers of unit cell on the axial sound transmission loss. Dynamic effective density proves the accuracy of the FEM results. This kind of structure has potential application in pipe or circular ring structure for damping/noise reduction.

scholarly journals Low-Frequency Broadband Sound Transmission Loss of Infinite Orthogonally Rib-Stiffened Sandwich Structure with Periodic Subwavelength Arrays of Shunted Piezoelectric Patches

2017 ◽  
Vol 2017 ◽  
pp. 1-17 ◽  
Author(s):  
Zhifu Zhang ◽  
Weiguang Zheng ◽  
Qibai Huang
Keyword(s):  
Sandwich Structure ◽  
Transmission Loss ◽  
Virtual Work ◽  
Low Frequency ◽  
Sound Transmission ◽  
Sound Insulation ◽  
Convergence Criterion ◽  
Sound Transmission Loss ◽  
Space Harmonic ◽  
Broadband Sound

This paper studies low-frequency sound transmission loss (STL) of an infinite orthogonally rib-stiffened sandwich structure flexibly connected with periodic subwavelength arrays of finite shunted piezoelectric patches. A complete theoretical model is proposed by three steps. First, the panels and piezoelectric patches on both sides are equivalent to two homogeneous facesheets by effective medium method. Second, we take into account all inertia terms of the rib-stiffeners to establish the governing equations by space harmonic method, separating the amplitude coefficients of the equivalent facesheets through virtual work principle. Third, the expression of STL is reduced. Based on the two prerequisites of subwavelength assumption and convergence criterion, the accuracy and validity of the model are verified by finite element simulations, cited experiments, and theoretical values. In the end, parameters affecting the STL performance of the structure are studied. All of these results show that the sandwich structure can improve the low-frequency STL effectively and broaden the sound insulation bandwidth.

Reply by the authors to the Discussion by B. Biswas

Geophysics ◽  
1989 ◽  
Vol 54 (3) ◽  
pp. 406-407
Author(s):  
T. L. Davis ◽  
G. M. Jackson
Keyword(s):  
Noise Reduction ◽  
Low Frequency ◽  
Phase Response ◽  
Frequency Noise ◽  
Noise Attenuation ◽  
Low Frequency Noise ◽  
Seismic Wavelet

28 Hz geophones without a low‐cut filter provided a very similar amplitude (and phase) response to the 10 Hz geophones combined with a 25 Hz low‐cut filter. Combining 28 Hz geophones with a 15 or 20 Hz low‐cut filter would produce a record intermediate between Figure 4b and c. There is, however, a tradeoff between low‐frequency noise attenuation and the bandwidth of the seismic wavelet. Before stacking and deconvolution, the more severe low‐cut filtering produces dramatic noise reduction (Figure 4). After deconvolution and stacking, this improvement is much less dramatic. It was decided not to attenuate frequencies in the 10 to 25 Hz range too severely as this could decrease the signal bandwidth and provide a more “ringy,” if marginally cleaner, section.

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