scholarly journals Anomalous Reflection of Acoustic Waves in Air with Metasurfaces at Low Frequency

2018 ◽  
Vol 2018 ◽  
pp. 1-7 ◽  
Author(s):  
Huaijun Chen
Keyword(s):  
Acoustic Waves ◽  
Design Method ◽  
Low Frequency ◽  
New Approach ◽  
Reflected Waves ◽  
Acoustic Lens ◽  
Anomalous Reflection ◽  
Unit Cells ◽  
Frequency Regime ◽  
At Will

An acoustic metasurface made of a composite structure of cavity and membrane is proposed and numerically investigated. The target frequency is in the low frequency regime (570 Hz). The unit cells, which provide precise local phase modulation, are rather thin with thickness in the order around 1/5 of the working wavelength. The numerical simulations show that the designed metasurface can steer the reflected waves at will. By taking the advantage of this metasurface, an ultrathin planar acoustic axicon, acoustic lens, and acoustic nondiffracting Airy beam generator are realized. Our design method provides a new approach for the revolution of future acoustic devices.

A reconfigurable membrane-type acoustic metasurface for low-frequency and broadband wave front modulation

2019 ◽  
Vol 33 (19) ◽  
pp. 1950208
Author(s):  
Xinpei Song ◽  
Tianning Chen ◽  
Jian Zhu ◽  
Yanbin He
Keyword(s):  
Wave Front ◽  
High Speed ◽  
Power Transmission ◽  
Design Method ◽  
Real Life ◽  
Low Frequency ◽  
Pumping System ◽  
Unit Cells ◽  
Membrane Type ◽  
Structure Complexity

Low-frequency and broadband are the critical challenges in real-life applications. Here, we try to tackle the challenges by proposing a reconfigurable acoustic metasurface (AM) composed of the membrane-type metamaterial (MAM) structure of deep sub-wavelength scale. By employing the external air pumping system into each individual unit cell of the AM, the tension of the membrane can be readily tailored by the system with little interference from other unit cells. Two strategies of the constant pressure method (CPM) and constant volume method (CVM) are reported to design the MAM. And the CVM is adopted as the ultimate design strategy by comparing both methods from aspects of the dimension, operating frequency, and structure complexity. In order to validate the low-frequency and broadband performances of the AM, the Airy-like beams and the acoustic converging based on two identical Airy-like beams are introduced and proof-of-concept simulations are performed with the finite element method. The simulated results agree well with the theoretical predictions. Our design provides the little-interference active design method for the low-frequency and broadband AM to manipulate the wave front, and may have practical engineering applications in areas of the aerospace, high-speed train, marine vessel, and power transmission and transformation project.

scholarly journals Sub-wavelength focusing of acoustic waves in bubbly media

2017 ◽  
Vol 473 (2208) ◽  
pp. 20170469 ◽  
Author(s):  
Habib Ammari ◽  
Brian Fitzpatrick ◽  
David Gontier ◽  
Hyundae Lee ◽  
Hai Zhang
Keyword(s):  
Acoustic Waves ◽  
Wave Scattering ◽  
Low Frequency ◽  
Scattering Function ◽  
Point Scatterer ◽  
Layer Potential ◽  
Spherical Bubble ◽  
Acoustic Wave Scattering ◽  
Frequency Regime ◽  
Sub Wavelength

The purpose of this paper is to investigate acoustic wave scattering by a large number of bubbles in a liquid at frequencies near the Minnaert resonance frequency. This bubbly media has been exploited in practice to obtain super-focusing of acoustic waves. Using layer potential techniques, we derive the scattering function for a single spherical bubble excited by an incident wave in the low frequency regime. We then propose a point scatterer approximation for N bubbles, and describe several numerical simulations based on this approximation, that demonstrate the possibility of achieving super-focusing using bubbly media.

scholarly journals Power flow–conformal metamirrors for engineering wave reflections

2019 ◽  
Vol 5 (2) ◽  
pp. eaau7288 ◽  
Author(s):  
Ana Díaz-Rubio ◽  
Junfei Li ◽  
Chen Shen ◽  
Steven A. Cummer ◽  
Sergei A. Tretyakov
Keyword(s):  
Power Distribution ◽  
Electromagnetic Waves ◽  
Power Flow ◽  
Flow Distribution ◽  
Physical Nature ◽  
Wave Reflections ◽  
Reflected Waves ◽  
Anomalous Reflection ◽  
Unit Cells ◽  
Reflecting Surfaces

Recently, the complexity behind manipulations of reflected fields by metasurfaces has been addressed, showing that, even in the simplest scenarios, nonlocal response and excitation of auxiliary evanescent fields are required for perfect field control. In this work, we introduce purely local reflective metasurfaces for arbitrary manipulations of the power distribution of reflected waves without excitation of any auxiliary evanescent field. The method is based on the analysis of the power flow distribution and the adaptation of the reflector shape to the desired distribution of incident and reflected fields. As a result, we find that these power-conformal metamirrors can be easily implemented with conventional passive unit cells. The results can be used for the design of reflecting surfaces with multiple functionalities and for waves of different physical nature. In this work, we present the cases of anomalous reflection and beam splitting for both acoustic and electromagnetic waves.

Diffraction in phase gradient acoustic metagratings: multiple reflection and integer parity design

2021 ◽  
Vol 263 (3) ◽  
pp. 3167-3175
Author(s):  
Mohammad Uzair ◽  
Xiao Li ◽  
Yangyang Fu ◽  
Chen Shen
Keyword(s):  
Acoustic Waves ◽  
High Efficiency ◽  
Periodic Structures ◽  
Dominant Role ◽  
Underlying Mechanism ◽  
Multiple Reflections ◽  
Phase Gradient ◽  
Anomalous Reflection ◽  
Unit Cells ◽  
Diffraction Patterns

Diffraction occurs when acoustic waves are incident on periodic structures such as graded metasurfaces. While numerous interesting diffraction phenomena have been observed and demonstrated, the underlying mechanism of diffraction in these structures is often overlooked. Here we provide a generic explanation of diffraction in phase gradient acoustic metagratings and relate high-order diffractions to multiple reflections in the unit cells. As such, we reveal that the number of unit cells within the metagrating plays a dominant role in determining the diffraction patterns. It is also found that the integer parity of the metagrating leads to anomalous reflection and refraction with high efficiency. The theory is verified by numerical simulations and experiments on planar metagratings and provides a powerful mechanism to manipulate acoustic waves. We further extend the theory to cylindrical waveguides for the control of sound vortices via topological charge in azimuthal metagratings. The relevance of the theory in achieving asymmetric wave control and high absorption is also discussed and verified both numerically and experimentally.

scholarly journals Influence of Li2CO3 addition on electrical and magnetic properties of Ni0.6Mg0.4Fe2O4

2020 ◽  
Vol 10 (03) ◽  
pp. 2050003
Author(s):  
M. R. Hassan ◽  
M. T. Islam ◽  
M. N. I. Khan
Keyword(s):  
Magnetic Properties ◽  
Single Phase ◽  
Low Frequency ◽  
Solid State Reaction Method ◽  
Charge Carriers ◽  
X Ray Diffraction ◽  
X Ray ◽  
Electrical And Magnetic Properties ◽  
Frequency Regime ◽  
Xrd Patterns

In this research, influence of adding Li2CO3 (at 0%, 2%, 4%, 6%) on electrical and magnetic properties of [Formula: see text][Formula: see text]Fe2O4 (with 60% Ni and 40% Mg) ferrite has been studied. The samples are prepared by solid state reaction method and sintered at 1300∘C for 6[Formula: see text]h. X-ray diffraction (XRD) patterns show the samples belong to single-phase cubic structure without any impurity phase. The magnetic properties (saturation magnetization and coercivity) of the samples have been investigated by VSM and found that the higher concentration of Li2CO3 reduces the hysteresis loss. DC resistivity increases with Li2CO3 contents whereas it decreases initially and then becomes constant at lower value with temperature which indicates that the studied samples are semiconductor. The dielectric dispersion occurs at a low-frequency regime and the loss peaks are formed in a higher frequency regime, which are due to the presence of resonance between applied frequency and hopping frequency of charge carriers. Notably, the loss peaks are shifted to the lower frequency with Li2CO3 additions.

Topological crystallography of gas hydrates

2015 ◽  
Vol 71 (4) ◽  
pp. 444-450 ◽  
Author(s):  
Sergey V. Gudkovskikh ◽  
Mikhail V. Kirov
Keyword(s):  
Hydrogen Bonding ◽  
Gas Hydrates ◽  
Periodic Boundary ◽  
Periodic Boundary Conditions ◽  
Hexagonal Structure ◽  
New Approach ◽  
Quotient Graphs ◽  
Disordered Structure ◽  
Unit Cells ◽  
Cubic Structure

A new approach to the investigation of the proton-disordered structure of clathrate hydrates is presented. This approach is based on topological crystallography. The quotient graphs were built for the unit cells of the cubic structure I and the hexagonal structure H. This is a very convenient way to represent the topology of a hydrogen-bonding network under periodic boundary conditions. The exact proton configuration statistics for the unit cells of structure I and structure H were obtained using the quotient graphs. In addition, the statistical analysis of the proton transfer along hydrogen-bonded chains was carried out.

An inverse design method of the acoustic lens

2021 ◽  
Vol 119 (15) ◽  
pp. 153503
Author(s):  
Chengfu Gu ◽  
Zengtao Yang ◽  
Hua Wang
Keyword(s):  
Design Method ◽  
Inverse Design ◽  
Acoustic Lens ◽  
Inverse Design Method

Design and optimization of acoustic liners with a shear grazing flow: OPAL software platform applications

2021 ◽  
Vol 263 (6) ◽  
pp. 152-163
Author(s):  
Remi Roncen ◽  
Pierre Vuillemin ◽  
Patricia Klotz ◽  
Frank Simon ◽  
Fabien Méry ◽  
...  
Keyword(s):  
Noise Reduction ◽  
Low Frequency ◽  
Small Scale ◽  
Software Platform ◽  
Total Size ◽  
Linearized Euler Equations ◽  
Design And Optimization ◽  
Acoustic Liners ◽  
Frequency Regime ◽  
Grazing Flow

In the context of noise reduction in diverse applications where a shear grazing flow is present (i.e., engine nacelle, jet pump, landing gear), improved acoustic liner solutions are being sought. This is particularly true in the low-frequency regime, where space constraints currently limit the efficiency of classic liner technology. To perform the required multi-objective optimization of complex meta-surface liner candidates, a software platform called OPAL was developed. Its first goal is to allow the user to assemble a large panel of parallel/serial assembly of unit acoustic elements, including the recent concept of LEONAR materials. Then, the physical properties of this liner can be optimized, relatively to given weighted objectives (noise reduction, total size of the sample, weight), for a given configuration. Alternatively, properties such as the different impedances of liner unit surfaces can be optimized. To accelerate the process, different nested levels of optimization are considered, from 0D analytical coarse designs in order to reduce the parameter space, up to 2D plan or axisymmetric high-order Discontinuous Galerkin resolution of the Linearized Euler Equations. The presentation will focus on the different aspects of liner design considered in OPAL, and present an application on different samples made for a small scale aeroacoustic bench.

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