scholarly journals Simultaneous Dirac-like Cones at Two Energy States in Tunable Phononic Crystals: An Analytical and Numerical Study

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1528
Author(s):  
Mustahseen M. Indaleeb ◽  
Sourav Banerjee

Simultaneous occurrence of Dirac-like cones at the center of the Brillouin zone (Г) at two different energy states is termed Dual-Dirac-like cones (DDC) in this article. The occurrence of DDC is a rare phenomenon. Thus, the generation of multiple Dirac-like cones at the center of the Brillouin zone is usually non-manipulative and poses a challenge to achieve through traditional accidental degeneracy. However, if predictively created, DDC will have multiple engineering applications with acoustics and vibration. Thus, the possibilities of creating DDC have been identified herein using a simple square periodic array of tunable square phononic crystals (PnCs) in air media. It was found that antisymmetric deaf bands may play critical roles in tracking the DDC. Hence, pivoting on the deaf bands at two different energy states, an optimized tuning parameter was found to achieve Dirac-like cones at two distinct frequency states, simultaneously. Orthogonal wave transport identified as key Dirac phenomena was achieved at two frequencies, herein. It was identified that beyond the Dirac-like cone, the Dirac phenomena remain dominant when a doubly degenerated state created by a top band with positive curvature and a near-flat deaf band are lifted from a bottom band with negative curvature. Utilizing a mechanism of rotating the PnCs near a fixed deaf band, frequencies are tracked to form the DDC, and orthogonal wave transport is demonstrated. Exploiting the dispersion behavior, unique acoustic phenomena, such as ballistic wave transmission, pseudo diffusion and acoustic cloaking are also demonstrated at the Dirac frequencies using numerical simulation. The proposed tunable acoustic PnCs will have important applications in acoustic and ultrasonic imaging, waveguiding and even acoustic computing.

2018 ◽  
Vol 382 (6) ◽  
pp. 423-427 ◽  
Author(s):  
Wen-Qiang Zhang ◽  
Xin Zhang ◽  
Fu-Gen Wu ◽  
Yuan-Wei Yao ◽  
Shui-Fang Lu ◽  
...  

Author(s):  
Zhongguo Sun ◽  
Guang Xi

The process of pressure wave transmission in liquid is simulated with the moving particle semi-implicit (MPS) method. The simulation is carried out in a tube full filled with an energy absorbing liquid. Here we studied the shapes and positions of pressure waves and investigated the behavior of the waves under different viscosities and densities of liquids. Some typical parameters of pressure wave, such as peak pressure value, wave length and transport speed are studied. Varying viscosity does not change the wave length and speed of the pressure wave evidently. The effect of interfaces which formed by viscosity difference or density difference is investigated. Reflection is found not always happened on such interfaces. Pressure wave transport to liquid-solid interface and free surface are also simulated. Pressure wave is vanished when closing to free surface. These results give useful qualitative suggestions on controlling the pressure wave in fluid engineering.


Author(s):  
Megan Hathcock ◽  
Bogdan-Ioan Popa ◽  
K. W. Wang

Abstract Recently the presence of a Dirac cone within the band structure of graphene has inspired research on phononic crystals with Dirac-like behaviors — including structures mimicking zero refractive index materials. The interesting phenomena produced by these structures occur at fixed frequencies and cannot be adaptive to needs and environmental changes. To address this constraint, researchers have designed tunable phononic structures; however, the tunable frequency ranges from the studies reported to date are limited by geometric constraints. Using a reconfigurable origami structure to modulate between different classes of phononic Bravais lattices, this research numerically investigates the effects of phononic lattice perturbation to produce drastic changes in the frequency of useful accidental degeneracies.


2013 ◽  
Vol 28 (02) ◽  
pp. 1441008 ◽  
Author(s):  
KAZUAKI SAKODA

The condition for the formation of Dirac cones at arbitrary points in the Brillouin zone by the accidental degeneracy of two photonic bands was examined by the degenerate perturbation theory and group theory based on the spatial symmetry of two modes. The analysis was applied to a two-dimensional square-lattice photonic crystal with C4v symmetry and the dispersion relation in the vicinity of the M point was examined. Exact agreement between the analytical and numerical calculation was obtained.


Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1577
Author(s):  
Luyun Chen ◽  
Yong Liu ◽  
Hui Kong

Acoustic tunneling is an essential property for phononic crystals in a Dirac-cone state. By analyzing the linear dispersion relations for the accidental degeneracy of Bloch eigenstates, the influence of geometric parameters on opening the Dirac-cone state and the directional band gaps’ widths are investigated. For two-dimensional hexachiral phononic crystals, for example, the four-fold accidental degenerate Dirac point emerges at the center of the irreducible Brillouin zone (IBZ). The Dirac cone properties and the band structure inversion problem are discussed. Finally, to verify acoustic transmission properties near the double-Dirac-cone frequency region, the numerical calculation of the finite-width phononic crystal structure is carried out, and the acoustic transmission tunneling effect is proved. The results enrich and expand the manipulating method in the topological insulator problem for hexachiral phononic crystals.


Author(s):  
Hossein Sadeghi ◽  
Joseph Magallanes ◽  
John Crawford

Phononic crystals are composites with architected microstructure that exhibit superior shock mitigation properties which cannot be achieved through natural materials. In this study, the capability provided by layered phononic crystals for protection of structures subjected to near-contact detonation is investigated. To evaluate the protective performance of the layered composite, finite element simulation of a reinforced concrete (RC) column, with a layered composite attached to its surface, subjected to near-contact detonation is performed. As a reference case, the same RC column under the same near-contact detonation, without the layered composite, is also studied. Contours of damage and residual load carrying capacity of the RC column are analyzed for both cases. It is observed that due to optimized band-gap in the composite, high frequency components of the shock wave are filtered, while the low frequency components of the shock front are highly scattered. Therefore, the intense shock front with large peak overpressure and short duration gets dispersed and transforms into a wave with a longer duration and lower peak overpressure. Comparing the damage pattern in the protected RC column with the bare column, high level of protection provided by the layered composite is demonstrated. This study provides insight on how stress waves can be controlled through microstructural design of phononic crystals through topology optimization to achieve a desired dynamic and structural response.


2005 ◽  
Vol 72 ◽  
pp. 177-188 ◽  
Author(s):  
Félix M. Goñi ◽  
F-Xabier Contreras ◽  
L-Ruth Montes ◽  
Jesús Sot ◽  
Alicia Alonso

In the past decade, the long-neglected ceramides (N-acylsphingosines) have become one of the most attractive lipid molecules in molecular cell biology, because of their involvement in essential structures (stratum corneum) and processes (cell signalling). Most natural ceramides have a long (16-24 C atoms) N-acyl chain, but short N-acyl chain ceramides (two to six C atoms) also exist in Nature, apart from being extensively used in experimentation, because they can be dispersed easily in water. Long-chain ceramides are among the most hydrophobic molecules in Nature, they are totally insoluble in water and they hardly mix with phospholipids in membranes, giving rise to ceramide-enriched domains. In situ enzymic generation, or external addition, of long-chain ceramides in membranes has at least three important effects: (i) the lipid monolayer tendency to adopt a negative curvature, e.g. through a transition to an inverted hexagonal structure, is increased, (ii) bilayer permeability to aqueous solutes is notoriously enhanced, and (iii) transbilayer (flip-flop) lipid motion is promoted. Short-chain ceramides mix much better with phospholipids, promote a positive curvature in lipid monolayers, and their capacities to increase bilayer permeability or transbilayer motion are very low or non-existent.


1998 ◽  
Vol 77 (2) ◽  
pp. 473-484 ◽  
Author(s):  
M. Sampoli, P. Benassi, R. Dell'Anna,

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