Acoustic far-field focusing effect for two-dimensional graded negative refractive-index sonic crystals

2010 ◽  
Vol 96 (26) ◽  
pp. 263502 ◽  
Author(s):  
Shasha Peng ◽  
Zhaojian He ◽  
Han Jia ◽  
Anqi Zhang ◽  
Chunyin Qiu ◽  
...  
Keyword(s):  
Refractive Index ◽  
Negative Refractive Index ◽  
Far Field ◽  
Two Dimensional ◽  
Focusing Effect ◽  
Sonic Crystals

Negative Refractive Index in a Two-Dimensional Nonlinear Rotator Lattice

2021 ◽  
Author(s):  
Lezheng Fang ◽  
Michael J. Leamy
Keyword(s):  
Numerical Simulation ◽  
Refractive Index ◽  
Direct Numerical Simulation ◽  
Incident Wave ◽  
Wave Amplitude ◽  
Multiple Scales ◽  
Negative Refractive Index ◽  
Index Of Refraction ◽  
Far Field ◽  
Negative Index

Abstract Acoustic metamaterials achieving negative index refraction usually operate linearly over a narrowband of frequency and consist of complex unit cell structures incorporating resonators. In this paper, we propose and analyze a simple, non-resonant, nonlinear rotator lattice structure which can be configured with either a positive or negative index of refraction over a broadband frequency range. The system’s frequency-dependent transmission is studied analytically via a reduced model along the interface of positive and negative refractive index lattices. Results for energy transmission are compared to those obtained using direct numerical simulation and close agreement is documented for small amplitude waves. For larger amplitude waves, a multiple scales analysis approach is used to show that the nonlinearity of the lattice shifts the system’s band structure, inducing amplitude-dependent transmission. For the studied system, the transmission decreases as we increase the incident wave amplitude, agreeing qualitatively with results from direct numerical simulation. At large-enough amplitudes, near the interface the wave amplitude decreases rapidly. As the wave travels further into the media, the amplitude drops, causing the nonlinear effect to decline as well. This decaying envelope does not result in a zero transmission in the far field, as expected from linear theory, and instead, the nonlinearity of the proposed rotator lattice prevents the far-field transmitted wave from surpassing a specific threshold amplitude, regardless of the incident wave. This finding may serve as an inspiration for designing nonlinear wave saturators.

Measurement of Effective Negative Refractive Index of Two-Dimensional Photonic Crystal Slabs

2017 ◽  
Vol 37 (6) ◽  
pp. 0616001
Author(s):  
蒋 强 Jiang Qiang ◽  
陈家璧 Chen Jiabi ◽  
梁斌明 Liang Binming ◽  
王 燕 Wang Yan ◽  
庄松林 Zhuang Songlin
Keyword(s):  
Refractive Index ◽  
Photonic Crystal ◽  
Negative Refractive Index ◽  
Two Dimensional ◽  
Dimensional Photonic Crystal ◽  
Photonic Crystal Slabs ◽  
Two Dimensional Photonic Crystal

Tunable far-field acoustic imaging by two-dimensional sonic crystal with concave incident surface

2017 ◽  
Vol 31 (02) ◽  
pp. 1650259 ◽  
Author(s):  
Feng-Fu Shen ◽  
Dan-Feng Lu ◽  
Hong-Wei Zhu ◽  
Chang-Ying Ji ◽  
Qing-Fan Shi
Keyword(s):  
Wave Beam ◽  
Acoustic Imaging ◽  
Concave Surface ◽  
Far Field ◽  
Two Dimensional ◽  
Acoustic Image ◽  
Tuning Mechanism ◽  
Sonic Crystal ◽  
Ray Trace ◽  
Sonic Crystals

An additional concave incident surface comprised of two-dimensional (2D) sonic crystals (SCs) is employed to tune the acoustic image in the far-field region. The tunability is realized through changing the curvature of the concave surface. To explain the tuning mechanism, a simple ray-trace analysis is demonstrated based on the wave-beam negative refractive law. Then, a numerical confirmation is carried out. Results show that both the position and the intensity of the image can be tuned by the introduced concave surface.

scholarly journals Analysis of the radar reflectivity of aircraft vortex wakes

2002 ◽  
Vol 463 ◽  
pp. 121-161 ◽  
Author(s):  
KARIM SHARIFF ◽  
ALAN WRAY
Keyword(s):  
Refractive Index ◽  
Vortex Pair ◽  
Normal Incidence ◽  
Radial Pressure ◽  
Far Field ◽  
Two Dimensional ◽  
Radar Echoes ◽  
Scattering Approximation ◽  
Weak Scattering ◽  
Reflected Power

Radar has been proposed as a way of tracking wake vortices to reduce aircraft spacing and tests have revealed radar echoes from aircraft wakes in clear air. The mechanism causing refractive index gradients in these tests is thought to be the same as that for homogeneous and isotropic atmospheric turbulence in the Kolmogorov inertial range, for which there is a scattering analysis due to Tatarski. In reality, however, the structure of aircraft wakes has a significant coherent part superimposed with turbulence, about whose structure very little is known. This work adopts a picture of a coherent (in fact two-dimensional) wake to perform a scattering analysis and calculate the reflected power. In particular, two simple mechanisms causing refractive index gradients are considered: (A) radial pressure (and therefore density) gradient in a columnar vortex arising from the rotational flow; (B) adiabatic transport of atmospheric fluid within a descending oval surrounding a vortex pair. In the scattering analysis, Tatarski's weak scattering approximation is kept but the usual assumptions of a far field and a uniform incident wave are dropped. Neither assumption is generally valid for a wake that is coherent across the radar beam. For analytical insight, an approximate analysis that invokes, in addition to weak scattering, the far-field and wide cylindrical beam assumptions, is also developed and compared with the more general analysis. Reflectivities calculated for the oval (mechanism B) are within 2–13 dB m2 of the measurements (≈−70 dB m2) of MIT Lincoln Laboratory at Kwajalein atoll. However, the present predictions have a cut-off away from normal incidence which is not present in the measurements. This implies that the two-dimensional picture is not entirely complete. Estimates suggest that the thin layer of vorticity which is baroclinically generated at the boundary of the oval is turbulent and this may account for reflectivity away from normal incidence. The reflectivity of a vortex (mechanism A) is comparable to that of the oval (mechanism B) but occurs at a frequency (about 50 MHz) that is lower than those considered in all the experiments to date. This result may be useful because: (i) existing atmospheric radars (known as ST radars) already operate at this frequency and so the present prediction could be verified; (ii) rain clutter is not a problem at this frequency; (iii) mechanism A is more robust because it is independent of atmospheric stratification.

scholarly journals Negative Index Metamaterial Lens for Subwavelength Microwave Detection

Sensors ◽  
2021 ◽  
Vol 21 (14) ◽  
pp. 4782
Author(s):  
Srijan Datta ◽  
Saptarshi Mukherjee ◽  
Xiaodong Shi ◽  
Mahmood Haq ◽  
Yiming Deng ◽  
...  
Keyword(s):  
Refractive Index ◽  
Periodic Structures ◽  
Negative Refractive Index ◽  
Far Field ◽  
Lens Design ◽  
Theoretical Formulation ◽  
System A ◽  
Numerical Studies ◽  
Naturally Occurring

Metamaterials are engineered periodic structures designed to have unique properties not encountered in naturally occurring materials. One such unusual property of metamaterials is the ability to exhibit negative refractive index over a prescribed range of frequencies. A lens made of negative refractive index metamaterials can achieve resolution beyond the diffraction limit. This paper presents the design of a metamaterial lens and its use in far-field microwave imaging for subwavelength defect detection in nondestructive evaluation (NDE). Theoretical formulation and numerical studies of the metamaterial lens design are presented followed by experimental demonstration and characterization of metamaterial behavior. Finally, a microwave homodyne receiver-based system is used in conjunction with the metamaterial lens to develop a far-field microwave NDE sensor system. A subwavelength focal spot of size 0.82λ was obtained. The system is shown to be sensitive to a defect of size 0.17λ × 0.06λ in a Teflon sample. Consecutive positions of the defect with a separation of 0.23λ was resolvable using the proposed system.

scholarly journals 2-D isotropic negative refractive index in a N-type four-level atomic system

Open Physics ◽  
2015 ◽  
Vol 13 (1) ◽  
Author(s):  
Shun-Cai Zhao ◽  
Qi-Xuan Wu ◽  
Kun Ma
Keyword(s):  
Refractive Index ◽  
Atomic System ◽  
Negative Refractive Index ◽  
Negative Permittivity ◽  
Two Dimensional ◽  
Orthogonal Signal ◽  
Wave Fields ◽  
Left Handedness ◽  
Permittivity And Permeability ◽  
Or Applications

Abstract2-D(Two-dimensional) isotropic negative refractive index (NRI) is explicitly realized via the orthogonal signal and coupling standing-wave fields coupling the Ntype four-level atomic system. Under some key parameters of the dense vapour media, the atomic system exhibits isotropic NRI with simultaneous negative permittivity and permeability (i.e. left-handedness) in the 2-D x-y plane. Compared with other 2-D NRI schemes, the coherent atomic vapour media in our scheme may be an ideal 2-D isotropic NRI candidate and has some potential advantages, significance or applications in the further investigation.

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