Wideband Acoustic Luneburg Lens Based on Graded Index Phononic Crystal

2015 ◽  
Author(s):  
Chia-Fu Wang ◽  
Chia-Nien Tsai ◽  
I-Ling Chang ◽  
Lien-Wen Chen
Keyword(s):  
Refractive Index ◽  
Effective Refractive Index ◽  
Phononic Crystal ◽  
Homogeneous Medium ◽  
Phononic Crystals ◽  
Triangular Array ◽  
Filling Ratio ◽  
Acoustic Properties ◽  
Luneburg Lens ◽  
Operation Frequency

The present study proposes a wideband two-dimensional Luneburg lens using graded phononic crystals (GPCs). We present a method to broaden the range of operation frequency of the Luneburg lens based on GPCs. The GPCs is composed of circular cylindrical rods with triangular lattice air background. In long wavelength limit assumption, periodic structure behaves like a homogeneous medium since dispersion relations is almost linear. The effective refractive index can be tuned by adjusting the filling ratio. The plan wave expansion method is utilized to calculate the band structures of the locally GPCs and the effective refractive index of the locally GPCs with different filling ratio. Finite element simulations was employed to confirm the acoustic properties of designed device. Our numerical simulations demonstrate that the operation frequency range of GPCs of circular cylindrical rods arranged as triangular array is much wider than those of square array. A wideband acoustic Luneburg lens can be achieved by using graded phononic crystals of triangular array.

scholarly journals Tunable Low Frequency Band Gap and Waveguide of Phononic Crystal Plates with Different Filling Ratio

Crystals ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 828
Author(s):  
Shaobo Zhang ◽  
Jiang Liu ◽  
Hongbo Zhang ◽  
Shuliang Wang
Keyword(s):  
Band Gap ◽  
Composite Structure ◽  
Structural Parameters ◽  
Phononic Crystal ◽  
Low Frequency ◽  
Filling Ratio ◽  
Height Ratio ◽  
Road Vehicles ◽  
Aluminum Base ◽  
Gap Width

Aiming at solving the NVH problem in vehicles, a novel composite structure is proposed. The new structure uses a hollow-stub phononic-crystal with filled cylinders (HPFC) plate. Any unit in the plate consists of a lead head, a silicon rubber body, an aluminum base as outer column and an opposite arranged inner pole. The dispersion curves are investigated by numerical simulations and the influences of structural parameters are discussed, including traditional hollow radius, thickness, height ratio, and the new proposed filling ratio. Three new arrays are created and their spectrum maps are calculated. In the dispersion simulation results, new branches are observed. The new branches would move towards lower frequency zone and the band gap width enlarges as the filling ratio decreases. The transmission spectrum results show that the new design can realize three different multiplexing arrays for waveguides and also extend the locally resonant sonic band gap. In summary, the proposed HPFC structure could meet the requirement for noise guiding and filtering. Compared to a traditional phononic crystal plate, this new composite structure may be more suitable for noise reduction in rail or road vehicles.

Thermal Design of Highly-Efficient Thermoelectric Materials With Atomic-Scale Three-Dimensional Phononic Crystals

2007 ◽  
Author(s):  
Jean-Numa Gillet ◽  
Yann Chalopin ◽  
Sebastian Volz
Keyword(s):  
Thermal Conductivity ◽  
Bulk Material ◽  
Phononic Crystal ◽  
Three Dimensional ◽  
Mean Free Path ◽  
Dispersion Curves ◽  
Phononic Crystals ◽  
Thermal Design ◽  
Atomic Scale ◽  
Thermal Insulating

Owing to their thermal insulating properties, superlattices have been extensively studied. A breakthrough in the performance of thermoelectric devices was achieved by using superlattice materials. The problem of those nanostructured materials is that they mainly affect heat transfer in only one direction. In this paper, the concept of canceling heat conduction in the three spatial directions by using atomic-scale three-dimensional (3D) phononic crystals is explored. A period of our atomic-scale 3D phononic crystal is made up of a large number of diamond-like cells of silicon atoms, which form a square supercell. At the center of each supercell, we substitute a smaller number of Si diamond-like cells by other diamond-like cells, which are composed of germanium atoms. This elementary heterostructure is periodically repeated to form a Si/Ge 3D nanostructure. To obtain different atomic configurations of the phononic crystal, the number of Ge diamond-like cells at the center of each supercell can be varied by substitution of Si diamond-like cells. The dispersion curves of those atomic configurations can be computed by lattice dynamics. With a general equation, the thermal conductivity of our atomic-scale 3D phononic crystal can be derived from the dispersion curves. The thermal conductivity can be reduced by at least one order of magnitude in an atomic-scale 3D phononic crystal compared to a bulk material. This reduction is due to the decrease of the phonon group velocities without taking into account that of the phonon average mean free path.

scholarly journals NONLINEAR OPTICAL WAVEGUIDE STRUCTURE FOR SENSOR APPLICATION: TM CASE

2007 ◽  
Vol 21 (30) ◽  
pp. 5075-5089 ◽  
Author(s):  
HALA M. KHALIL ◽  
MOHAMMED M. SHABAT ◽  
SOFYAN A. TAYA ◽  
MAZEN M. ABADLA
Keyword(s):  
Refractive Index ◽  
Theoretical Analysis ◽  
Closed Form ◽  
Optical Waveguide ◽  
Effective Refractive Index ◽  
Nonlinear Optical ◽  
Waveguide Structure ◽  
Analytical Expressions ◽  
Evanescent Waveguide ◽  
Waveguide Sensor

In this work, we present an extensive theoretical analysis of nonlinear optical waveguide sensor. The waveguide under consideration consists of a thin dielectrica film surrounded by a self-focused nonlinear cladding and a linear substrate. The nonlinearity of the cladding is considered to be of Kerr-type. Both cases, when the effective refractive index is greater and when it is smaller than the index of the guiding layer, are discussed. The sensitivity of the effective refractive index to any change in the cladding index in evanescent optical waveguide sensor is derived for TM modes. Closed form analytical expressions and normalized charts are given to provide the conditions required for the sensor to exhibit its maximum sensitivity. The results are compared with those of the well-known linear evanescent waveguide sensors.

MCVM: MONTE CARLO MODELING OF PHOTON MIGRATION IN VOXELIZED MEDIA

2010 ◽  
Vol 03 (02) ◽  
pp. 91-102 ◽  
Author(s):  
TING LI ◽  
HUI GONG ◽  
QINGMING LUO
Keyword(s):  
Monte Carlo ◽  
Refractive Index ◽  
High Precision ◽  
Heterogeneous Media ◽  
Homogeneous Medium ◽  
Software Tool ◽  
Light Transport ◽  
Photon Migration ◽  
Monte Carlo Code ◽  
Monte Carlo Modeling

The Monte Carlo code MCML (Monte Carlo modeling of light transport in multi-layered tissue) has been the gold standard for simulations of light transport in multi-layer tissue, but it is ineffective in the presence of three-dimensional (3D) heterogeneity. New techniques have been attempted to resolve this problem, such as MCLS, which is derived from MCML, and tMCimg, which draws upon image datasets. Nevertheless, these approaches are insufficient because of their low precision or simplistic modeling. We report on the development of a novel model for photon migration in voxelized media (MCVM) with 3D heterogeneity. Voxel crossing detection and refractive-index-unmatched boundaries were considered to improve the precision and eliminate dependence on refractive-index-matched tissue. Using a semi-infinite homogeneous medium, steady-state and time-resolved simulations of MCVM agreed well with MCML, with high precision (~100%) for the total diffuse reflectance and total fractional absorption compared to those of tMCimg (< 70%). Based on a refractive-index-matched heterogeneous skin model, the results of MCVM were found to coincide with those of MCLS. Finally, MCVM was applied to a two-layered sphere with multi-inclusions, which is an example of a 3D heterogeneous media with refractive-index-unmatched boundaries. MCVM provided a reliable model for simulation of photon migration in voxelized 3D heterogeneous media, and it was developed to be a flexible and simple software tool that delivers high-precision results.

Acoustic wave frequency filtering in constant total length phononic crystals of Al/Pb multilayer

2021 ◽  
Author(s):  
Chittaranjan Nayak ◽  
Mehdi Solaimani ◽  
Alireza Aghajamali ◽  
Arafa H. Aly
Keyword(s):  
Acoustic Wave ◽  
Phononic Crystal ◽  
Phononic Crystals ◽  
Geometrical Parameters ◽  
One Dimensional ◽  
Internal Geometry ◽  
Total Length ◽  
Acoustic Filters ◽  
System Length ◽  
Phononic Band Gaps

In this study, we have scrutinized the frequency gap generation by changing the geometrical parameters of a one-dimensional phononic crystal. For this purpose, we have calculated the transmission coefficient of an incident acoustic wave by using the transfer matrix method. We have retained and fixed the total length of the system and changed the system internal geometry not to increase the system length too much. Another reason was to adjust the phononic band gaps and get the desired transmission properties by finding the optimum internal geometry without increasing or decreasing the total length of phononic crystals. In addition, we also propose few structures with the opportunity of applications in acoustical devices such as sonic reflectors. Our results can also be of high interest to design acoustic filters in the case that transmission of certain frequencies is necessary.

scholarly journals Titania Photonic Crystals with Precise Photonic Band Gap Position via Anodizing with Voltage versus Optical Path Length Modulation

Nanomaterials ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 651 ◽  
Author(s):  
Ermolaev ◽  
Kushnir ◽  
Sapoletova ◽  
Napolskii
Keyword(s):  
Refractive Index ◽  
Photonic Crystals ◽  
Band Gap ◽  
Titanium Oxide ◽  
Effective Refractive Index ◽  
Photonic Band Gap ◽  
Voltage Versus ◽  
Research Attention ◽  
Anodic Titanium Oxide ◽  
Photonic Band

Photonic crystals based on titanium oxide are promising for optoelectronic applications, for example as components of solar cells and photodetectors. These materials attract great research attention because of the high refractive index of TiO2. One of the promising routes to prepare photonic crystals based on titanium oxide is titanium anodizing at periodically changing voltage or current. However, precise control of the photonic band gap position in anodic titania films is a challenge. To solve this problem, systematic data on the effective refractive index of the porous anodic titanium oxide are required. In this research, we determine quantitatively the dependence of the effective refractive index of porous anodic titanium oxide on the anodizing regime and develop a model which allows one to predict and, therefore, control photonic band gap position in the visible spectrum range with an accuracy better than 98.5%. The prospects of anodic titania photonic crystals implementation as refractive index sensors are demonstrated.

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