Simulation study of acoustic refraction wave manipulation based on sub-wavelength artificial periodic structure

2020 ◽  
pp. 2150082
Author(s):  
Shuai Tang ◽  
Jianning Han
Keyword(s):  
Acoustic Wave ◽  
Steel Plate ◽  
Three Dimensional ◽  
Unit Cell ◽  
Asymmetric Transmission ◽  
Plate Structures ◽  
Coding Method ◽  
Acoustic Focusing ◽  
Unit Cells ◽  
Sub Wavelength

We proposed a kind of unit cell composed of simple steel plate structures in this work. A variety of acoustic phenomena including anomalous refraction, asymmetric transmission, acoustic splitting and acoustic focusing were realized by coding the unit cells with different splicing modes. The transformation from plane acoustic wave to vortex acoustic wave was also realized by using the coding method of three-dimensional rotation. This work increased the functionality of the unit cell and provided a method for the design of sub-wavelength acoustic devices.

scholarly journals MEMS mirrors using sub-wavelength High- Contrast-Gratings with asymmetric unit cells

2016 ◽  
Vol 19 (2) ◽  
pp. 52
Author(s):  
Milan Maksimović
Keyword(s):  
Spectral Response ◽  
Practical Interest ◽  
Optimization Procedure ◽  
Material Design ◽  
Unit Cell ◽  
High Contrast ◽  
Asymmetric Unit ◽  
Unit Cells ◽  
Thin Elements ◽  
Sub Wavelength

High-contrast gratings (HCG) are ultra-thin elements operating in sub-wavelength regime with the period of the grating smaller than the wavelength and with the high-index grating material fully surrounded by low-index material. Design of MEMS mirrors made from HCG with specific reflectivity response is of great practical interest in integrated optoelectronics. We theoretically investigate design of the spectral response for HCGs with the complex unit cells. We show that the spectral response can be tailored via the unit cell perturbations and with the asymmetric unit cell perturbations may introduce completely new spectral response. Our results can serve as guidance for the design of the complex HCGs and help with the choice of the efficient initial grating topology prior to global optimization procedure.

scholarly journals Acoustic Focusing with Intensity Modulation Based on Sub-Wavelength Waveguide Array

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1461
Author(s):  
Mingran Zhang ◽  
Guangrui Gu
Keyword(s):  
Focal Length ◽  
Intensity Modulation ◽  
Waveguide Array ◽  
Refractive Index Modulation ◽  
Destructive Testing ◽  
Equivalent Impedance ◽  
Coding Method ◽  
Acoustic Focusing ◽  
Arbitrary Amplitude ◽  
Sub Wavelength

Acoustic focusing with intensity modulation plays an important role in biomedical and life sciences. In this work, we propose a new approach for simultaneous phase and amplitude manipulation in sub-wavelength coupled resonant units, which has not been reported so far. Based on the equivalent impedance and refractive index modulation induced by the change of geometry, arbitrary amplitude response from 0 to 1 and phase shift from 0 to 2π is realized. Thus, the acoustic focusing with intensity modulation can be achieved via waveguide array. Herein, the focal length can be adjusted by alternating the length of supercell, and the whole system can work in a broadband of 0.872f0–1.075f0. By introducing the coding method, the thermal viscosity loss is reduced, and the wavefront modulation can be more accurate. Compared with previous works, our approach has the advantages of simple design and broadband response, which may have promising applications in acoustic communication, non-destructive testing, and acoustic holography.

Design of Three-Dimensional, Triply Periodic Unit Cell Scaffold Structures for Additive Manufacturing

2018 ◽  
Vol 140 (7) ◽  
Author(s):  
Mazher Iqbal Mohammed ◽  
Ian Gibson
Keyword(s):  
Additive Manufacturing ◽  
Periodic Structures ◽  
Three Dimensional ◽  
Unit Cell ◽  
Final Size ◽  
Fused Filament Fabrication ◽  
Cell Structures ◽  
Triply Periodic ◽  
Unit Cells ◽  
Scaffold Structure

Highly organized, porous architectures leverage the true potential of additive manufacturing (AM) as they can simply not be manufactured by any other means. However, their mainstream usage is being hindered by the traditional methodologies of design which are heavily mathematically orientated and do not allow ease of controlling geometrical attributes. In this study, we aim to address these limitations through a more design-driven approach and demonstrate how complex mathematical surfaces, such as triply periodic structures, can be used to generate unit cells and be applied to design scaffold structures in both regular and irregular volumes in addition to hybrid formats. We examine the conversion of several triply periodic mathematical surfaces into unit cell structures and use these to design scaffolds, which are subsequently manufactured using fused filament fabrication (FFF) additive manufacturing. We present techniques to convert these functions from a two-dimensional surface to three-dimensional (3D) unit cell, fine tune the porosity and surface area, and examine the nuances behind conversion into a scaffold structure suitable for 3D printing. It was found that there are constraints in the final size of unit cell that can be suitably translated through a wider structure while still allowing for repeatable printing, which ultimately restricts the attainable porosities and smallest printed feature size. We found this limit to be approximately three times the stated precision of the 3D printer used this study. Ultimately, this work provides guidance to designers/engineers creating porous structures, and findings could be useful in applications such as tissue engineering and product light-weighting.

scholarly journals Two-Dimensional Composite Acoustic Metamaterials of Rectangular Unit Cell from Pentamode to Band Gap

Crystals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1457
Author(s):  
Qi Li ◽  
Ke Wu ◽  
Mingquan Zhang
Keyword(s):  
Wave Propagation ◽  
Acoustic Wave ◽  
Band Gap ◽  
Unit Cell ◽  
The Other ◽  
Two Dimensional ◽  
Acoustic Metamaterials ◽  
Acoustic Wave Propagation ◽  
Theoretical Support ◽  
Unit Cells

Pentamode metamaterials have been receiving an increasing amount of interest due to their water-like properties. In this paper, a two-dimensional composite pentamode metamaterial of rectangular unit cell is proposed. The unit cells can be classified into two groups, one with uniform arms and the other with non-uniform arms. Phononic band structures of the unit cells were calculated to derive their properties. The unit cells can be pentamode metamaterials that permit acoustic wave travelling or have a total band gap that impedes acoustic wave propagation by varying the structures. The influences of geometric parameters and materials of the composed elements on the effective velocities and anisotropy were analyzed. The metamaterials can be used for acoustic wave control under water. Simulations of materials with different unit cells were conducted to verify the calculated properties of the unit cells. The research provides theoretical support for applications of the pentamode metamaterials.

Experimental Electron Microscopy of Determining B. subtilis Alpha-Amylase Crystals

1990 ◽  
Vol 48 (1) ◽  
pp. 104-105
Author(s):  
Jingqiang Zhang ◽  
Ye Qiaozhen ◽  
Lu Xinying ◽  
Zhou Suiwen ◽  
Luo Jinxian
Keyword(s):  
Electron Microscopy ◽  
Low Dose ◽  
High Vacuum ◽  
Three Dimensional ◽  
High Sensitivity ◽  
Unit Cell ◽  
Alpha Amylase ◽  
Aqueous Environment ◽  
Information Need ◽  
Unit Cells

The structure determination of unstained biological molecules by electron microscopy would be straightforward but for two factors: One is their high sensitivity to electron damage and the other is the loss of three-dimensional order that generally takes place when the specimen's natural aqueous environment is replaced by the high vacuum of the electron microscope. In order to surmounting these difficulties, following methods would be used: (i) Phase contrast; (ii) For vacuum preservation the aqueous medium is replaced by glucose; (iii) Low dose (le/Å2.S) electron microscopy is used to prevent specimen from electron damage. However, a low dose image will not display the projected structure of a molecule or unit cell directly, because contrast and S/N are very low. Nenertheless, provided that the object is comprised of a large enough number of unit cells and that the periodicities are precisely maintained, all the information need to reconstruct the “average” molecule or unit cell will be available by computer. In order to recontrast the object, one needs to determine the Fourier amplitude and phase for each reflection. Fourier analysis of the micrograph data provide the phase and the measurement of the electron diffraction pattern provide the amplitudes. In this paper an experimental method of determining molecular structure of B. subtilis alpha-amylase crystal is discussed.

scholarly journals Regularly configured structures with polygonal prisms for three-dimensional auxetic behaviour

2017 ◽  
Vol 473 (2202) ◽  
pp. 20160926 ◽  
Author(s):  
Junhyun Kim ◽  
Dongheok Shin ◽  
Do-Sik Yoo ◽  
Kyoungsik Kim
Keyword(s):  
Poisson’S Ratio ◽  
Three Dimensional ◽  
Unit Cell ◽  
Poisson's Ratio ◽  
Numerical Verification ◽  
Geometric Conditions ◽  
Unit Cells ◽  
Negative Poisson's Ratio ◽  
Poisson's Ratios ◽  
Poisson’S Ratios

We report here structures, constructed with regular polygonal prisms, that exhibit negative Poisson’s ratios. In particular, we show how we can construct such a structure with regular n -gonal prism-shaped unit cells that are again built with regular n -gonal component prisms. First, we show that the only three possible values for n are 3, 4 and 6 and then discuss how we construct the unit cell again with regular n -gonal component prisms. Then, we derive Poisson’s ratio formula for each of the three structures and show, by analysis and numerical verification, that the structures possess negative Poisson’s ratio under certain geometric conditions.

scholarly journals Harnessing the anisotropic multistability of stacked-origami mechanical metamaterials for effective modulus programming

2018 ◽  
Vol 29 (14) ◽  
pp. 2933-2945 ◽  
Author(s):  
Sattam Sengupta ◽  
Suyi Li
Keyword(s):  
Adaptive Systems ◽  
Three Dimensional ◽  
Unit Cell ◽  
Effective Modulus ◽  
Stable States ◽  
Mechanical Metamaterials ◽  
Principal Axes ◽  
Unit Cells ◽  
Multiple Unit ◽  
Parametric Analyses

This study examines a three-dimensional, anisotropic multistability of a mechanical meta material based on a stacked Miura-ori architecture, and investigates how such a unique stability property can impart stiffness and effective modulus programming functions. The unit cell of this metamaterial can be bistable due to the nonlinear relationship between rigid-folding and crease material bending. Such bistability possesses an unorthodox property: the arrangement of elastically stable and unstable equilibria are different along different principal axes of the unit cell, so that along certain axes the unit cell exhibits two force–deformation relationships concurrently within the same range of deformation. Therefore, one can achieve a notable stiffness adaptation via switching between the two stable states. As multiple unit cells are assembled into a metamaterial, the stiffness adaptation can be aggregated into an on-demand modulus programming capability. That is, via strategically switching different unit cells between stable states, one can control the overall effective modulus. This research examines the underlying principles of anisotropic multistability, experimentally validates the feasibility of stiffness adaptation, and conducts parametric analyses to reveal the correlations between the effective modulus programming and Miura-ori designs. The results can advance many adaptive systems such as morphing structures and soft robotics.

Quasicrystals Perspectives and Potential Applications

MRS Bulletin ◽  
1997 ◽  
Vol 22 (11) ◽  
pp. 34-39 ◽  
Author(s):  
Daniel J. Sordelet ◽  
Jean Marie Dubois
Keyword(s):  
Window Glass ◽  
Dimensional Space ◽  
Three Dimensional ◽  
Unit Cell ◽  
Translational Symmetry ◽  
Integer Number ◽  
Unit Cells ◽  
Potential Applications ◽  
Incommensurate Structures ◽  
Three Dimensional Space

For decades scientists have accepted the premise that solid matter can only order in two ways: amorphous (or glassy) like window glass or crystalline with atoms arranged according to translational symmetry. The science of crystallography, now two centuries old, was able to relate in a simple and efficient way all atomic positions within a crystal to a frame of reference in which a single unit cell was defined. Positions within the crystal could all be deduced from the restricted number of positions in the unit cell by translations along vectors formed by a combination of integer numbers of unit vectors of the reference frame. Of course disorder, which is always present in solids, could be understood as some form of disturbance with respect to this rule of construction. Also amorphous solids were naturally referred to as a full breakdown of translational symmetry yet preserving most of the short-range order around atoms. Incommensurate structures, or more simply modulated crystals, could be understood as the overlap of various ordering potentials not necessarily with commensurate periodicities.For so many years, no exception to the canonical rule of crystallography was discovered. Any crystal could be completely described using one unit cell and its set of three basis vectors. In 1848 the French crystallographer Bravais demonstrated that only 14 different ways of arranging atoms exist in three-dimensional space according to translational symmetry. This led to the well-known cubic, hexagonal, tetragonal, and associated structures. Furthermore the dihedral angle between pairs of faces of the unit cell cannot assume just any number since an integer number of unit cells must completely fill space around an edge.

scholarly journals Modulation of out-of-plane reflected waves by using acoustic metasurfaces with tapered corrugated holes

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Xiao-Shuang Li ◽  
Yan-Feng Wang ◽  
A-Li Chen ◽  
Yue-Sheng Wang
Keyword(s):  
Dimensional Space ◽  
Three Dimensional ◽  
Wide Frequency Range ◽  
Square Lattice ◽  
Reflected Waves ◽  
Incident Plane ◽  
Acoustic Focusing ◽  
Out Of Plane ◽  
Unit Cells ◽  
Circular Holes

Abstract In this paper, modulation of reflected wavefront out of the incident plane by a tunable acoustic metasurface is investigated based on the fully generalized Snell’s law in the three-dimensional space. The metasurface is constructed by a square lattice of circular holes with gradient annular bumps. The phase shift is tuned by changing the volume of water filled in the holes. The acoustic wave steering out of the incident plane and the out-of-plane acoustic focusing with the oblique incidence at the subwavelength scale are demonstrated numerically by selecting suitable distributions of water depth. The numerical results show that the wavefront of the reflected wave can be manipulated over a wide frequency range; and the gradient design of the unit cells can suppress the parasitic reflection. The present work is relevant to the practical design of novel acoustic devices.

A New Geometric Model for Three-Dimensional Braided Composites

2014 ◽  
Vol 662 ◽  
pp. 15-19 ◽  
Author(s):  
Chen Bing Ni ◽  
Gao Feng Wei
Keyword(s):  
Cross Section ◽  
Geometric Model ◽  
Geometric Analysis ◽  
Three Dimensional ◽  
Structural Features ◽  
Unit Cell ◽  
Braided Composites ◽  
Unit Cells ◽  
Analysis Models ◽  
Surface Unit Cell

According to the structural features of 3-D braided composites, the whole structure is divided into three types of sub-unit cells, these are the interior unit cell, the surface unit cell and the corner unit cell. Considering the bending of fiber bundle and the deformation of cross-section which are caused by the space fiber extrusion and twist together, the corresponding geometric analysis models for every type of sub-unit cell are established, and the engineering elastic constants of the 3-D braided composites are predicted. The results show that the calculated results well agree with the experimental results, and the effectiveness of the model is verified.

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