scholarly journals The influence of impedance mismatch of the medium with gradient change of impedance on acoustic characteristics

2019 ◽  
Vol 283 ◽  
pp. 09005
Author(s):  
Bo Hu ◽  
Moran Wang ◽  
Yimei Du
Keyword(s):  
Acoustic Impedance ◽  
Acoustic Waves ◽  
Propagation Mechanism ◽  
Acoustic Characteristics ◽  
Impedance Mismatch ◽  
Matching Layer ◽  
Composition And Structure ◽  
New Type ◽  
Boundary Impedance ◽  
Gradient Change

Medium with gradient change of acoustic impedance is a new type acoustic structure. It is composed of several materials and has a continuous gradient composition and structure whose specific acoustic impedance varies smoothly across the layer. It has been used in various practical situations such as acoustic rectifiers, medical devices, weakening vibration and reducing noise. The purpose of this paper is to investigate the effect of boundary impedance mismatch on acoustic characteristics of gradient impedance media. The propagation mechanism of acoustic waves in medium with gradient change of specific acoustic impedance was calculated by transfer matrix method. By setting the different ratios of the acoustic impedance at interfaces of matching layer, the relationship between specific acoustic impedance mismatch and acoustic characteristics are derived and the corresponding conclusions are drawn. These conclusions provide an idea for the preparation of relevant medium.

A New Type of Muffler Based on Microperforated Tubes

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
S. Allam ◽  
M. Åbom
Keyword(s):  
Acoustic Impedance ◽  
Noise Control ◽  
Wave Impedance ◽  
Sound Waves ◽  
Submillimeter Range ◽  
Perforated Plates ◽  
Characteristic Wave ◽  
Standard Temperature ◽  
New Type ◽  
Temperature And Pressure

Microperforated plate (MPP) absorbers are perforated plates with holes typically in the submillimeter range and perforation ratios around 1%. The values are typical for applications in air at standard temperature and pressure (STP). The underlying acoustic principle is simple: It is to create a surface with a built in damping, which effectively absorbs sound waves. To achieve this, the specific acoustic impedance of a MPP absorber is normally tuned to be of the order of the characteristic wave impedance in the medium (∼400 Pa s/m in air at STP). The traditional application for MPP absorbers has been building acoustics often combined with a so called panel absorber to create an absorption peak at a selected frequency. However, MPP absorbers made of metal could also be used for noise control close to or at the source for noise control in ducts. In this paper, the possibility to build dissipative silencers, e.g., for use in automotive exhaust or ventilation systems, is investigated.

scholarly journals Audibility within and Outside Deposited Snow

1985 ◽  
Vol 31 (108) ◽  
pp. 136-142 ◽  
Author(s):  
Jerome B. Johnson
Keyword(s):  
Acoustic Impedance ◽  
Acoustic Waves ◽  
Transmission Loss ◽  
Acoustic Noise ◽  
Acoustic Signals ◽  
Strong Absorption ◽  
Snow Surface ◽  
Subjective Awareness

AbstractFactors which control the audibility within and outside deposited snow are described and applied to explain the preferential detection of sound by persons buried under avalanche debris as compared to persons on the overlying snow surface. Strong attenuation of acoustic waves in snow and the small acoustic impedance differences between snow and air are responsible for the strong absorption and transmission-loss characteristics that are observed for snow. The absorption and transmission-loss characteristics are independent of the direction of propagation of acoustic signals through the snow. The preferential detection of sound by a person buried under snow can be explained by the relatively higher level of background acoustic noise that exists for persons above the snow surface as compared to an avalanche burial victim. This noise masks sound transmitted to persons on the snow surface, causing a reduction of hearing senstitivity as compared to the burial victim. Additionally, the listening concentration of a buried individual is generally greater than for persons working on the snow surface, increasing their subjective awareness of sound.

Axisymmetric waves in compressible Newtonian liquids contained in rigid tubes: steady-periodic mode shapes and dispersion by the method of eigenvalleys

1973 ◽  
Vol 58 (3) ◽  
pp. 595-621 ◽  
Author(s):  
H. A. Scarton ◽  
W. T. Rouleau
Keyword(s):  
Boundary Layer ◽  
Acoustic Waves ◽  
Mode Shapes ◽  
Periodic Mode ◽  
Rotational Mode ◽  
High Frequencies ◽  
Wide Range ◽  
Propagating Waves ◽  
New Type ◽  
Newtonian Liquids

In this paper the first thirty-two axisymmetric modes for steady-periodic waves in viscous compressible liquids contained in rigid, impermeable, circular tubes are calculated. These results end long speculation over the effects of viscosity on guided acoustic waves. Sixteen of the modes belong to a family of rotation-dominated modes whose existence was previously unknown. The thirty-two modes were computed for a wide range of frequencies, viscosities and wave-lengths.The modes were found through the use of the method of eigenvalleys, which also led to the discovery of backward-propagating waves, an exact analytical expression for the zeroth rotational mode eigenvalue, definitive boundaries between low and intermediate frequencies and between intermediate and high frequencies, and a new type of boundary layer, called a dilatational boundary layer.

scholarly journals The research of LWD acoustic isolator based on SAW spatial separation

2019 ◽  
Vol 283 ◽  
pp. 02004
Author(s):  
Peinian Yang ◽  
Dehua Chen ◽  
Wang Xiuming
Keyword(s):  
Acoustic Waves ◽  
Acoustic Analysis ◽  
Surface Acoustic Waves ◽  
Spatial Separation ◽  
P Wave ◽  
S Wave ◽  
Finite Element Software ◽  
Acoustic Insulation ◽  
New Type ◽  
Sufficient Strength

Acoustic logging while drilling (LWD) can extract P-wave and S-wave information from the formation. However, the transmission of the collar wave propagated directly from the emitter to the receiver may interfere with the P-wave and S-wave and affect the extraction of formation information. Therefore, it is necessary to design a suitable acoustic isolator between the transmitter and the receiver to attenuate the drill waves. The commonly used acoustic LWD isolator is that the outer surface of the drill collar is evenly grooved to attenuate the collar wave. However, there are still disadvantages such as the lack of mechanical strength of the evenly grooved acoustic insulators and the ability to extract clean longitudinal wave under certain circumstances. Therefore, there is an urgent requirement to design a new type of acoustic LWD isolator with sufficient strength and acoustic insulation requirements. In recent years, spoof surface acoustic waves (SSAWs) generated by periodic corrugated surface rigid plates have attracted the attention of many researchers, who can spatially separate the surface waves to attenuate acoustic waves. In this paper, a new type of acoustic LWD insulator based on SAW space separation structure is proposed. The finite element software ANSYS is used for acoustic analysis.

A Markov‐Gauss algorithm for blocking well logs

Geophysics ◽  
1988 ◽  
Vol 53 (8) ◽  
pp. 1118-1121 ◽  
Author(s):  
Paul N. Chouinard ◽  
Ken V. Paulson
Keyword(s):  
Electrical Resistivity ◽  
Markov Chain ◽  
Acoustic Impedance ◽  
High Probability ◽  
Rock Type ◽  
Well Logs ◽  
Physical Parameters ◽  
New Type

A characteristic common among petrophysical sections is “blockiness,” which results from the high probability that a given rock and the rocks above and below it are all of the same type. Furthermore, if a new rock type is encountered, the next rock’s type is dependent upon this new type and not on a previous type. This suggests that a Markov chain would be an appropriate basis for modeling such physical parameters as acoustic impedance, electrical resistivity, etc.

Microstructure Analysis of Soil Consolidation Material

2012 ◽  
Vol 557-559 ◽  
pp. 900-903
Author(s):  
Liang Yan ◽  
Xiang Yu
Keyword(s):  
Water Soluble ◽  
Soil Consolidation ◽  
Water Soluble Polymer ◽  
Industrial Solid Waste ◽  
Composition And Structure ◽  
The Matrix ◽  
New Type ◽  
Major Chemical ◽  
Consolidation Material ◽  
Scanning Electron

Polymer modified straw fiber-reinforced cementitious composition（PSFC） prepared by polyacrylamide, straw fiber, industrial solid waste and cement, was a new type of and soil consolidation material. Scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS) were used to identify major chemical composition and structure of the matrix-fiber interface. The results show that the polyacrylamide can efficiently improve the structure of matrix-fiber transition zone, and water-soluble polymer mixing amount acts significantly on its existing morphology.

A Combined Perfectly Matching Layer and Infinite Element Formulation for Unbounded Wave Problems in the Frequency Domain

2014 ◽  
Author(s):  
Joseph S. Pettigrew ◽  
Anthony J. Mulholland ◽  
Jeffrey L. Cipolla ◽  
John Mould ◽  
Robert Banks
Keyword(s):  
Frequency Domain ◽  
Marked Improvement ◽  
Test Problem ◽  
Near Field ◽  
Element Formulation ◽  
Infinite Element ◽  
Matching Layer ◽  
Modal Response ◽  
New Type ◽  
Wave Problems

In this paper, Berenger’s Perfectly Matching Layer (PML) and Bettess’ Infinite Element (IE) scheme are combined to create a new type of element for unbounded acoustic wave problems. An assessment of this new element formulation is made through its use in the calculation of the acoustic modal response of a spherical radiator in the frequency domain. The performance of the PML+IE approach is contrasted with the IE only methodology by comparing them to the exact solution of this test problem in terms of the surface inertia and resistance in the near field. The results are encouraging and the PML+IE approach shows a marked improvement in performance, particularly at lower frequencies.

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