Normal incidence acoustic absorption characteristics of a carbon nanotube forest

Electromagnetic absorbing materials with broadband, lightweight, wide-angle, and polarization-insensitive characteristics attracts extensive research interest recently, due to rapid advancement in radar detection techniques and communication devices. Three-dimensional printing is being employed to realize cost-effective structured electromagnetic absorbers that has lately become a common practice of improving radar stealth performance and shielding effectiveness. Structured absorbers permit realization of desired absorption characteristics by careful design of their geometrical structures. In this study, a two-layer structured microwave absorber using conductive ABS polymer is simulated. COMSOL Multiphysics environment is used to investigate the absorption characteristics of the designed structure. Under normal incidence, simulation results revealed at least 90% of absorption from 7.2 GHz to 18.0 GHz for both Transverse Electric (TE) and Transverse Magnetic (TM) polarizations. Oblique incidence results for TE polarization indicate that the absorption rate is more than 90% in the whole range of 7.2–18 GHz frequency band up to 450 while the absorption rate is more than 80% for 600 incident waves. The absorption rate is more than 90% in the 7.2-18 GHz range for oblique incidences of up to 300 only for TM polarization, but greater than 70% at 450 incident angles. Additionally, the designed absorber is independent of the polarization of the incident wave. As a result of the exhibited favourable absorption characteristics, the studied absorber provides great potentials for its experimentation and practicability using the low-cost 3D printing manufacturing process

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Basic Study for Acoustic Absorption Characteristics of Soft and Light Granular Material (Basic Characteristics for Expanded Polystyrene Beads)

Journal of Advanced Mechanical Design Systems and Manufacturing ◽

10.1299/jamdsm.7.677 ◽

2013 ◽

Vol 7 (4) ◽

pp. 677-689 ◽

Cited By ~ 1

Author(s):

Shuichi SAKAMOTO ◽

Masaru SASAKI ◽

Itaru KOURAKATA ◽

Kensaku YANAGIMOTO ◽

Seiji WATANABE

Keyword(s):

Granular Material ◽

Expanded Polystyrene ◽

Acoustic Absorption ◽

Basic Study ◽

Polystyrene Beads ◽

Basic Characteristics ◽

Absorption Characteristics

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Low Frequency Absorption of Additively Manufactured Cylinders

Volume 11: Acoustics, Vibration, and Phononics ◽

10.1115/imece2019-11338 ◽

2019 ◽

Author(s):

Sophie R. Kaye ◽

Ethan D. Casavant ◽

Paul E. Slaboch

Keyword(s):

Low Frequency ◽

Normal Incidence ◽

Frequency Noise ◽

Outer Diameter ◽

Acoustic Absorption ◽

Frequency Range ◽

Large Space ◽

Low Frequencies ◽

Cylinder Length ◽

Hollow Cylinders

Abstract Attenuating low frequencies is often problematic, due to the large space required for common absorptive materials to mitigate such noise. However, natural hollow reeds are known to effectively attenuate low frequencies while occupying relatively little space compared to traditional absorptive materials. This paper discusses the effect of varied outer diameter, and outer spacing on the 200–1600 Hz acoustic absorption of additively manufactured arrays of hollow cylinders. Samples were tested in a 10 cm diameter normal incidence impedance tube such that cylinder length was oriented perpendicular to the incoming plane wave. By varying only one geometric element of each array, the absorption due to any particular parameter can be assessed individually. The tests confirmed the hypothesis that minimizing cylinder spacing and maximizing cylinder diameter resulted in increased overall absorption and produced more focused absorption peaks at specific low frequencies. Wider cylinder spacing produced a broader absorptive frequency range, despite shifting upward in frequency. Thus, manipulating these variables can specifically target absorption for low frequency noise that would otherwise disturb listeners.

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Microwave-absorption characteristics of polyaniline-coated multi-walled carbon nanotube composites

Plastics Rubber and Composites ◽

10.1080/14658011.2020.1860669 ◽

2020 ◽

pp. 1-9

Author(s):

T. Haritha ◽

K. Ramji ◽

Ch Subrahmanyam ◽

K. Krushnamurthy ◽

P. S. Nagasree

Keyword(s):

Carbon Nanotube ◽

Microwave Absorption ◽

Multi Walled Carbon Nanotube ◽

Nanotube Composites ◽

Carbon Nanotube Composites ◽

Absorption Characteristics

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Sound Absorption Characteristics of Porous Steel Manufactured by Lost Carbonate Sintering

MRS Proceedings ◽

10.1557/proc-1188-ll07-04 ◽

2009 ◽

Vol 1188 ◽

Cited By ~ 1

Author(s):

Miao Lu ◽

Carl Hopkins ◽

Yuyuan Zhao ◽

Gary Seiffert

Keyword(s):

Absorption Coefficient ◽

Pore Size ◽

Sound Absorption ◽

Single Layer ◽

Normal Incidence ◽

Sound Absorption Coefficient ◽

Absorption Coefficients ◽

Impedance Tube ◽

Absorption Characteristics

AbstractThis paper investigates the sound absorption characteristics of porous steel samples manufactured by Lost Carbonate Sintering. Measurements of the normal incidence sound absorption coefficient were made using an impedance tube for single-layer porous steel discs and assemblies comprising four layers of porous steel discs. The sound absorption coefficient was found not to vary significantly with pore size in the range of 250-1500 μm. In general, the absorption coefficient increases with increasing frequency and increasing thickness, and peaks at specific frequencies depending on the porosity. An increase in porosity tends to increase the frequency at which the sound absorption coefficient reaches this peak. An advantage was found in using an assembly of samples with gradient porosities of 75%-70%-65%-60% as it gave higher and more uniform sound absorption coefficients than an assembly with porosities of 75%.

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