scholarly journals Shear-mediated contributions to the effective properties of soft acoustic metamaterials including negative index

2015 ◽  
Vol 5 (1) ◽  
Author(s):  
Derek Michael Forrester ◽  
Valerie J. Pinfield
Keyword(s):  
Effective Properties ◽  
Acoustic Properties ◽  
Double Negative ◽  
Acoustic Metamaterials ◽  
Viscous Losses ◽  
Backward Propagation ◽  
Phase Angles ◽  
Lossy Materials ◽  
Selection Of ◽  
Sub Wavelength

Abstract Here we show that, for sub-wavelength particles in a fluid, viscous losses due to shear waves and their influence on neighbouring particles significantly modify the effective acoustic properties and thereby the conditions at which negative acoustic refraction occurs. Building upon earlier single particle scattering work, we adopt a multiple scattering approach to derive the effective properties (density, bulk modulus, wavenumber). We show,through theoretical prediction, the implications for the design of “soft” (ultrasonic) metamaterials based on locally-resonant sub-wavelength porous rubber particles, through selection of particle size and concentration and demonstrate tunability of the negative speed zones by modifying the viscosity of the suspending medium. For these lossy materials with complex effective properties, we confirm the use of phase angles to define the backward propagation condition in preference to “single-” and “double-negative” designations.

Comparison of direct and acoustical area measurements in physical models of human central airways

1980 ◽  
Vol 48 (5) ◽  
pp. 896-902 ◽  
Author(s):  
A. C. Jackson ◽  
D. E. Olson
Keyword(s):  
Acoustic Pulse ◽  
Pulse Response ◽  
Physical Models ◽  
Acoustic Properties ◽  
Noninvasive Technique ◽  
Cross Sectional ◽  
Fifth Generation ◽  
Viscous Losses ◽  
Direct Measurements ◽  
Central Airway

Total cross-sectional areas were computed from direct measurements made on two human central airway casts. Acoustic pulse-response measurements were obtained on rigid-walled positive replicas of these casts. From the acoustic response data of each cast, we computed the area-distance function of the acoustically equivalent structure (i.e., the structure with regular branching and negligible viscous losses, but with similar acoustic properties). The acoustic data predicted equivalent areas that compared favorably to the total cross-sectional areas in the casts at all points from the beginning of the trachea to distances about 6 cm beyond the carina corresponding to airways of the third, fourth, or fifth generation. These results indicate that, at least in the central airways, branching asymmetry and internal energy losses introduced negligible errors in estimates of cross-sectional areas derived from acoustic pulse-response measurements. This rapid noninvasive technique thus shows promise as a method of detecting upper and central airway obstruction.

Acoustic manipulation of fractal metamaterials with negative properties and near-zero densities

2021 ◽  
Author(s):  
Guanghua Wu ◽  
Yibo Ke ◽  
Lin Zhang ◽  
Meng Tao
Keyword(s):  
High Potential ◽  
Experimental Results ◽  
Acoustic Properties ◽  
Sound Insulation ◽  
Sound Waves ◽  
Acoustic Metamaterials ◽  
Acoustic Device

Abstract Acoustic metamaterials have high potential in diverse applications, including acoustic cloaking, sound tunneling, wavefront reshaping, and sound insulation. In the present study, new metamaterials consisting of spatial coiled units are designed and fabricated to manipulate sound waves in the range 0-1600 Hz. The effective acoustic properties and band diagrams are studied. The simulation and experimental results demonstrate that the metamaterials provide an effective and feasible approach to design acoustic device such as sound cloaking and insulators.

scholarly journals Gradient index phononic crystals and metamaterials

Nanophotonics ◽  
2019 ◽  
Vol 8 (5) ◽  
pp. 685-701 ◽  
Author(s):  
Yabin Jin ◽  
Bahram Djafari-Rouhani ◽  
Daniel Torrent
Keyword(s):  
Refractive Index ◽  
Wave Propagation ◽  
Acoustic Waves ◽  
Effective Properties ◽  
Periodic Structures ◽  
Phononic Crystals ◽  
Ray Theory ◽  
Acoustic Metamaterials ◽  
Propagation Of Waves ◽  
At Will

AbstractPhononic crystals and acoustic metamaterials are periodic structures whose effective properties can be tailored at will to achieve extreme control on wave propagation. Their refractive index is obtained from the homogenization of the infinite periodic system, but it is possible to locally change the properties of a finite crystal in such a way that it results in an effective gradient of the refractive index. In such case the propagation of waves can be accurately described by means of ray theory, and different refractive devices can be designed in the framework of wave propagation in inhomogeneous media. In this paper we review the different devices that have been studied for the control of both bulk and guided acoustic waves based on graded phononic crystals.

scholarly journals Systematic design and realization of double-negative acoustic metamaterials by topology optimization

2019 ◽  
Vol 172 ◽  
pp. 102-120 ◽  
Author(s):  
Hao-Wen Dong ◽  
Sheng-Dong Zhao ◽  
Peijun Wei ◽  
Li Cheng ◽  
Yue-Sheng Wang ◽  
...  
Keyword(s):  
Topology Optimization ◽  
Double Negative ◽  
Systematic Design ◽  
Acoustic Metamaterials

Numerical models for evaluating the vibro‐acoustic properties of acoustic metamaterials

PAMM ◽  
2018 ◽  
Vol 18 (1) ◽  
Author(s):  
Quirin Aumann ◽  
Matthias Miksch ◽  
Gerhard Müller
Keyword(s):  
Numerical Models ◽  
Acoustic Properties ◽  
Acoustic Metamaterials

Effect of cementation on the small-strain parameters of sands

2001 ◽  
Vol 38 (1) ◽  
pp. 191-199 ◽  
Author(s):  
A L Fernandez ◽  
J C Santamarina
Keyword(s):  
Laboratory Test ◽  
Experimental Studies ◽  
Small Strain ◽  
Test Results ◽  
Loading History ◽  
Viscous Losses ◽  
Laboratory Test Results ◽  
Geotechnical Design ◽  
Selection Of

Natural cementation affects the properties of soils, the interpretation of in situ and laboratory test results, and the selection of criteria for geotechnical design. In this paper, published experimental studies are reviewed, a microscale analysis is presented of the effect of cementation on small-strain stiffness for distinct stress-cementation histories, and the effect of cementation on small-strain velocity and damping is experimentally studied. Observations include the prevailing effects of cementation over effective stress, the coexistence of frictional and viscous losses, and the effects of decementation when the medium is unloaded from the level of confinement prevailing during cementation.Key words: wave velocity, seismic response, stiffness, damping, sampling effects, loading history.

scholarly journals Predicting double negativity using transmitted phase in space coiling metamaterials

2018 ◽  
Vol 5 (5) ◽  
pp. 171042 ◽  
Author(s):  
Santosh K. Maurya ◽  
Abhishek Pandey ◽  
Shobha Shukla ◽  
Sumit Saxena
Keyword(s):  
Acoustic Waves ◽  
Negative Refraction ◽  
Acoustic Properties ◽  
Propagation Path ◽  
Elastic Response ◽  
Acoustic Metamaterials ◽  
Effective Response ◽  
Retrieval Method ◽  
S Parameter ◽  
Parameter Retrieval

Metamaterials are engineered materials that offer the flexibility to manipulate the incident waves leading to exotic applications such as cloaking, extraordinary transmission, sub-wavelength imaging and negative refraction. These concepts have largely been explored in the context of electromagnetic waves. Acoustic metamaterials, similar to their optical counterparts, demonstrate anomalous effective elastic properties. Recent developments have shown that coiling up the propagation path of acoustic wave results in effective elastic response of the metamaterial beyond the natural response of its constituent materials. The effective response of metamaterials is generally evaluated using the ‘S’ parameter retrieval method based on amplitude of the waves. The phase of acoustic waves contains information of wave pressure and particle velocity. Here, we show using finite-element methods that phase reversal of transmitted waves may be used to predict extreme acoustic properties in space coiling metamaterials. This change is the difference in the phase of the transmitted wave with respect to the incident wave. This method is simpler when compared with the more rigorous ‘S’ parameter retrieval method. The inferences drawn using this method have been verified experimentally for labyrinthine metamaterials by showing negative refraction for the predicted band of frequencies.

scholarly journals On the Selection of Optimal Propeller Diameter for a 120m Cargo Vessel

2018 ◽  
Author(s):  
Jennie Andersson ◽  
Robert Gustafsson ◽  
Arash Eslamdoost ◽  
Rickard E. Bensow
Keyword(s):  
Open Water ◽  
Operating Conditions ◽  
Series Data ◽  
Preliminary Design ◽  
Optimum Diameter ◽  
Viscous Losses ◽  
Computational Fluid Dynamics Cfd ◽  
Propulsion Unit ◽  
Hydrodynamic Effects ◽  
Selection Of

In the preliminary design of a propulsion unit the selection of propeller diameter is most commonly based on open water tests of systematic propeller series. The optimum diameter obtained from the propeller series data is however not considered to be representative for the operating conditions behind the ship, instead a slightly smaller diameter is often selected. We have used computational fluid dynamics (CFD) to study a 120m cargo vessel with an integrated rudder bulb-propeller hubcap system and a 4-bladed propeller series, to increase our understanding of the hydrodynamic effects influencing the optimum. The results indicate that a 3-4 % smaller diameter is optimal in behind conditions in relation to open water conditions at the same scale factor. The reason is that smaller, higher loaded propellers perform better together with a rudder system. This requires that the gain in transverse kinetic energy losses thanks to the rudder overcomes the increase in viscous losses in the complete propulsion system.

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