Influence of fineness, length and hollow section of fibers on acoustic absorption

2021 ◽  
pp. 004051752110362
Author(s):  
Roberto Atiénzar-Navarro ◽  
M Bonet-Aracil ◽  
J Gisbert-Payá ◽  
Romina del Rey ◽  
Rubén Picó
Keyword(s):  
Cross Section ◽  
Fibrous Material ◽  
Sound Absorption ◽  
Normal Incidence ◽  
Hollow Fibers ◽  
Acoustic Behavior ◽  
Hollow Section ◽  
Polyester Fibers ◽  
Acrylic Fibers ◽  
High Length

A fibrous material is characterized by its fineness, flexibility and high length/fineness ratio and it is used to reduce noise in indoor rooms due to their porous structure. The aim of this work is focused on investigating the structure of two different fibers (acrylic and polyester) from the analysis of the macrostructural parameters, such as fineness, length and cross-section (solid or hollow). Furthermore, the degree of influence of these parameters on the average sound absorption has been investigated. The sound absorption coefficient of fibers is measured at normal incidence in the impedance tube. In acrylic fibers, results showed that the fineness of the fiber has a significant influence on the sound absorption compared to the length of the fiber. In polyester fibers, hollow fibers have a better acoustic behavior compared to solid fibers.

scholarly journals Non-Circula Cross Section Acrylic Fibers

1998 ◽  
Vol 54 (2) ◽  
pp. P48-P53
Author(s):  
HIROSHI HOSOKAWA
Keyword(s):  
Cross Section ◽  
Acrylic Fibers

scholarly journals Excess sound absorption at normal incidence by two microperforated panel absorbers with different impedance

2011 ◽  
Vol 32 (5) ◽  
pp. 194-200 ◽  
Author(s):  
Motoki Yairi ◽  
Kimihiro Sakagami ◽  
Kenichi Takebayashi ◽  
Masayuki Morimoto
Keyword(s):  
Sound Absorption ◽  
Normal Incidence

Sheaths of the Motor Axons of the Crab Carcinus

1964 ◽  
Vol s3-105 (70) ◽  
pp. 175-181
Author(s):  
G. A. HORRIDGE ◽  
R. A. CHAPMAN
Keyword(s):  
Cell Membrane ◽  
Glial Cell ◽  
Cross Section ◽  
Glial Cells ◽  
Fibrous Material ◽  
Motor Axons ◽  
Cell Cytoplasm ◽  
Fibrous Sheath ◽  
Outer Sheath ◽  
Sheath Structure

In crab leg nerves, the largest axons, which are the motor axons usually isolated for physiological experiments, have a sheath structure which is different from that in medium sized and smaller axons of the same nerve or of any other described nerves. Axons with a diameter over 20 µ have (a) an outer sheath, about 5µ thick, of wellspaced layers of alternating glial cell cytoplasm and extracellular fibrous material, formed from fewer cells than there are layers, and (b) an inner sheath of elongated cells which creep along the axon longitudinally and interdigitate where they meet, as seen 2 or 3 times round the outside of the membranes of axons in cross-section. Therefore, possible channels between inner glial cells are elongated and few. On these structural grounds, together with physiological evidence, they seem unlikely to be preferred pathways of diffusion of ions in crab axons. Smaller axons have simple sheaths; some occur in groups within a fibrous sheath; the thinnest axons frequently occur in bundles and have no glial cell membrane in contact with them.

Sound absorption of a finite flexible micro-perforated panel absorber back by a rigid air cavity filled with a fibrous porous material

2021 ◽  
Vol 263 (3) ◽  
pp. 3625-3632
Author(s):  
Ho Yong Kim ◽  
Yeon June Kang
Keyword(s):  
Energy Dissipation ◽  
Porous Material ◽  
Fibrous Material ◽  
Alternative Energy ◽  
Sound Absorption ◽  
Sound Pressure ◽  
Absorption Coefficients ◽  
Air Cavity ◽  
Acoustic Cavity ◽  
Absorption Performance

Back by a rigid cavity filled with a layer of porous layer, the sound absorption performance of a micro-perforated panel (MPP) can be enhanced in comparison with other resonance based sound absorbers. In this paper, a theoretical model of a finite flexible MPP back by a rigid air cavity filled with a fibrous porous material is developed to predict normal sound absorption coefficients. Displacements of MPP and sound pressure field in fibrous porous material and acoustic cavity are expressed using a series of modal functions, and the sound absorption coefficients of MPP system are obtained. Additionally, comparison of energy dissipation by MPP and fibrous material is performed to identify effects of a fibrous material on the sound absorption of a MPP. As expected, at anti-resonance frequency of an MPP, the fibrous material provide an alternative energy dissipation mechanism.

scholarly journals Simulation of Normal Incidence Sound Absorption Coefficients of Perforated Panels With/Without Glass Wool by Transmission Line Parameters in a Two-Port Network

2016 ◽  
Vol 44 ◽  
pp. 123-130
Author(s):  
Takayoshi Nakai
Keyword(s):  
Transmission Line ◽  
Input Impedance ◽  
Thermal Conduction ◽  
Sound Absorption ◽  
Sound Propagation ◽  
Viscous Friction ◽  
Normal Incidence ◽  
Glass Wool ◽  
Absorption Coefficients ◽  
Transfer Function Method

This paper describes simulation of normal incidence sound absorption coefficients of perforated panels by transmission line parameters in a two-port network. Maa and Sakagami have investigated micro perforated panels, MPP. But their theories can treat only near 1 % perforation rates of perforated panels with back cavities. If sound propagates as a plane wave, sound propagation can be represented as transmission line parameters in a two-port network. Perforated panels, back cavities, and glass wool absorption materials are represented as matrix of transmission line parameters, respectively. Transmission line parameters of a perforated panel with a back cavity are calculated as multiplication of their matrices. An input impedance can be calculated from the transmission line parameters. A normal incident absorption coefficient is calculated from the input impedance. Holes of the perforated panels have losses of viscous friction and thermal conduction at their walls. Simulations are done in the condition of 0.25 mm to 5 mm diameters of holes, 0.25 % to 25 % perforation rates, 0.5 mm to 5 mm thickness of the perforated panels with back cavities in which there are or are not glass wool absorption materials. The results of these simulations are good agreements with the results of our measurements by transfer function method except in the condition of more than 1 mm diameter of holes.

scholarly journals An UWB Physical Optics Approach for Fresnel-Zone RCS Measurements on a Complex Target at Non-Normal Incidence

Sensors ◽  
2019 ◽  
Vol 19 (24) ◽  
pp. 5454
Author(s):  
Ilie Valentin Mihai ◽  
Razvan Tamas ◽  
Ala Sharaiha
Keyword(s):  
Cross Section ◽  
Fresnel Zone ◽  
Normal Incidence ◽  
Radar Cross Section ◽  
Physical Optics ◽  
Fast Method ◽  
Field Zone ◽  
Fresnel Region ◽  
Receiving Antenna ◽  
Complex Target

In this paper, we propose a fast method for measuring the radar cross section of a complex target at non-normal incidences and Fresnel region antenna-to-target distances. The proposed method relies both on the physical optics approach and on averaging the field distribution over the transmitting and receiving antenna apertures. The ratio between the analytical expression of the radar cross section at far-field and Fresnel region results in a field-zone extrapolation factor. The RCS resulting from the scattering parameters measured at Fresnel region distances is then corrected with that field-zone extrapolation factor. The method is suitable to be used in a perturbed, multipath environment by applying the distance averaging technique, coupling subtraction or time gating. Our technique requires a very simple measuring configuration consisting of two horn antennas and a vector network analyzer. The experimental validation of the proposed technique demonstrates reasonable agreement with simulated radar cross section at non-normal incidence.

Investigation of a Compound Perforated Panel Absorber With Backing Cavities Partially Filled With Polymer Materials

2015 ◽  
Vol 137 (4) ◽  
Author(s):  
C. Q. Wang ◽  
Y. S. Choy
Keyword(s):  
Sound Absorption ◽  
Normal Incidence ◽  
Polyester Fiber ◽  
Polymer Materials ◽  
Element Simulation ◽  
Parallel Arrangement ◽  
Cavity Configuration ◽  
Absorption Performance ◽  
Good Agreement ◽  
Panel Absorber

The paper concerns the sound absorption performance of a compound absorber which consists of a parallel arrangement of multiple perforated panel absorbers of different backing cavity depths partially filled with poroelastic polymer materials. Three polymer materials are considered: expandable polystyrene (EPS) foam, polymethacrylimide (PMI) foam, and polyester fiber. The normal incidence sound absorption coefficients of the compound panel absorber are tested experimentally. Results show that the former two foams can achieve similar absorption performance to the rigid cavity configuration, while the resonances shift to lower frequencies due to the changes of effective cavity depths. It is also found that the additional attenuation by polymer foams may improve sound absorption, but the effect is marginal. For polyester fiber, results show that it performs more like a single perforated panel absorber. Finite element simulation of the compound panel absorber is also discussed, and good agreement is observed between simulated and experimental results.

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