scholarly journals Trapped Modes and Negative Refraction in a Locally Resonant Metamaterial: Transient Insights into Manufacturing Bounds for Ultrasonic Applications

2021 ◽  
Vol 11 (16) ◽  
pp. 7576
Author(s):  
Domenico Tallarico ◽  
Stewart G. Haslinger
Keyword(s):  
Negative Refraction ◽  
Square Lattice ◽  
Ultrasonic Frequency ◽  
Statistical Parameters ◽  
Wave Trapping ◽  
Practical Applications ◽  
Modelling Framework ◽  
Wave Effects ◽  
Frequency Regime ◽  
Transient Scattering

The transient scattering of in-plane elastic waves from a finite-sized periodic structure, comprising a regular grid of Swiss-cross holes arranged according to a square lattice, is considered. The theoretical and numerical modelling focuses on the unexplored ultrasonic frequency regime, well beyond the first, wide, locally resonant band-gap of the structure. Dispersive properties of the periodic array, determined by Bloch–Floquet analysis, are used to identify candidates for high-fidelity GPU-accelerated transient scattering simulations. Several unusual wave phenomena are identified from the simulations, including negative refraction, focusing, partial cloaking, and wave trapping. The transient finite element modelling framework offers insights on the lifetimes of such phenomena for potential practical applications. In addition, nonideal counterparts with rough edges are modelled using characteristic statistical parameters commonly observed in additive manufacturing. The analysis shows that the identified wave effects appear likely to be robust with respect to potential manufacturing uncertainties in future studies.

Negative Refractive Index Materials

2006 ◽  
Vol 3 (2) ◽  
pp. 189-218 ◽  
Author(s):  
Victor Veselago ◽  
Leonid Braginsky ◽  
Valery Shklover ◽  
Christian Hafner
Keyword(s):  
Photonic Crystals ◽  
Negative Refraction ◽  
Negative Refractive Index ◽  
Index Of Refraction ◽  
Negative Index ◽  
Practical Applications ◽  
The Third ◽  
Left Handed ◽  
Negative Index Of Refraction ◽  
History Of

The main directions of studies of materials with negative index of refraction, also called left-handed or metamaterials, are reviewed. First, the physics of the phenomenon of negative refraction and the history of this scientific branch are outlined. Then recent results of studies of photonic crystals that exhibit negative refraction are discussed. In the third part numerical methods for the simulation of negative index material configurations and of metamaterials that exhibit negative index properties are presented. The advantages and the shortages of existing computer packages are analyzed. Finally, details of the fabrication of different kinds of metamaterials are given. This includes composite metamaterials, photonic crystals, and transmission line metamaterials for different wavelengths namely radio frequencies, microwaves, terahertz, infrared, and visible light. Furthermore, some examples of practical applications of metamaterials are presented.

scholarly journals Health Monitoring on the Spacecraft Bearings in High-Speed Rotating Systems by Using the Clustering Fusion of Normal Acoustic Parameters

2019 ◽  
Vol 9 (16) ◽  
pp. 3246 ◽  
Author(s):  
Wu ◽  
Wang ◽  
Liu ◽  
He ◽  
Xie
Keyword(s):  
High Speed ◽  
High Reliability ◽  
Quality Parameters ◽  
Normal Operation ◽  
Acoustic Parameters ◽  
Statistical Parameters ◽  
Monitoring Method ◽  
Practical Applications ◽  
Rotating Systems ◽  
Long Life

The rolling bearings in moment wheel assemblies (MWAs) or control moment gyros (CMGs) are not only the core components in spacecrafts but also prone to failure. Therefore, a high reliability is the critical characteristic for spacecraft bearings, and long-life testing on the ground is one of the main means for bearing reliability assessment. In practical applications, a convenient and reliable method is required for monitoring the health status of abnormal bearings in MWAs during the long-life test. In this paper, a monitoring method based on the clustering fusion of normal operation acoustic parameters is proposed for the identification of abnormal bearings. Firstly, the characteristics of MWA’s acoustic signal and its feasibility as a monitoring medium are clarified based on tests and modal analysis. Then statistical parameters and sound quality parameters are introduced to characterize the changes caused by bearing faults, and the root mean square (RMS), kurtosis, and sharpness parameters are selected to construct the feature vectors. The K-medoids clustering technology is used to fuse the characteristic parameters, and the safety distance for normal bearing operation can be obtained by a suitable method. Finally, the abnormal index is presented based on the excess rate and excess distance to judge the abnormal states of several types of bearings through tests. The research results indicate that the presented monitoring method based on the clustering of the normal operation acoustic parameters can not only identify various faults of the spacecraft bearing (ball defects, outer ring defects, cage instability, etc.) effectively but also give a quantitative evaluation of the severity of the abnormality.

Design of a Coaxial Positioning System Based on Flexible Decoupling Beams

2012 ◽  
Vol 490-495 ◽  
pp. 2141-2145
Author(s):  
Tao Chen ◽  
Li Guo Chen ◽  
Ming Qiang Pan ◽  
Li Ning Sun
Keyword(s):  
Finite Element Method ◽  
Finite Element ◽  
Vision System ◽  
Square Lattice ◽  
Positioning System ◽  
Flexible Beams ◽  
Positioning Accuracy ◽  
Practical Applications ◽  
Positioning Device ◽  
Better Than

To overcome the shortcomings of existing technology and achieve a type of shaft and sleeve assembly in navigate with high coaxial requirements, a novel coaxial positioning system is presented based on the flexible decoupling beams and micro-vision system. In order to meet the adjustments online and maintain posture of the shaft and sleeve, a flexible beams structure with pattern of “square lattice” is designed. Combined with micro motorized X-Y stage and clamps, the structure achieves exact coaxial positioning precision and station keeping function. The mechanics theory and finite element method are used to analysis and simulate the beams. The Hough algorithm is applied in the micro-vision system to realize the precise coaxial positioning of real-time detection and calculation. Experiments show that the coaxial positioning accuracy is better than 8μm, and the positioning device could guarantee the realization of positioning assembly in practical applications.

Negative Refraction and Partition in Acoustic Valley Materials of a Square Lattice

2019 ◽  
Vol 12 (2) ◽  
Author(s):  
Zhenxiao Zhu ◽  
Xueqin Huang ◽  
Jiuyang Lu ◽  
Mou Yan ◽  
Feng Li ◽  
...  
Keyword(s):  
Negative Refraction ◽  
Square Lattice

Applicability of Dynamic Homogenization for Acoustic Metamaterials

2014 ◽  
Author(s):  
Ankit Srivastava ◽  
Sia Nemat-Nasser
Keyword(s):  
Negative Refraction ◽  
Effective Properties ◽  
Dynamic Properties ◽  
Low Frequency ◽  
Bloch Wave ◽  
Acoustic Metamaterials ◽  
Infinite Domain ◽  
True Negative ◽  
Periodic Composite ◽  
Frequency Regime

Dynamic homogenization seeks to define frequency dependent effective properties for heterogeneous composites for the purpose of studying wave propagation in them. These properties can be used to predict and design for metamaterial behavior. However, there is an approximation involved in replacing a heterogeneous composite with its homogenized equivalent. In this paper we propose a quantification to this approximation. By way of explicit examples we show that a comprehensive homogenization scheme proposed in earlier papers is applicable in a finite composite setting and in the low frequency regime. We also show that there exist good arguments for considering the second branch of a locally resonant composite a true negative branch. Furthermore, we note that infinite-domain homogenization is more applicable to finite cases of locally resonant metamaterial composites than it is to 2-phase composites. We also study the effect of the interface location on the applicability of homogenization. The results open intriguing questions regarding the effects of replacing a semi-infinite periodic composite with its Bloch-wave (infinite domain) dynamic properties on such phenomenon as negative refraction.

An evaluation technique for high-frequency dynamic behavior of a sandwich microcantilever beam

2017 ◽  
Vol 21 (3) ◽  
pp. 1133-1149
Author(s):  
Yun Young Kim
Keyword(s):  
High Frequency ◽  
High Speed ◽  
Beam Theory ◽  
Tone Burst ◽  
Ultrasonic Frequency ◽  
Vibration Modes ◽  
High Frequency Response ◽  
Frequency Regime ◽  
Contact Transducer ◽  
Microcantilever Beam

A method was developed to measure the first- and second-order vibration modes in a sandwich microcantilever beam oscillating in the megahertz frequency regime in the present study. Taking advantage of the ultrasonic frequency, a test platform was developed to induce free vibration of the microcantilever using a high-power radio frequency pulser that transmits tone burst signals to a contact transducer, and the resonant frequencies of the microcantilever were measured using a laser-optic interferometer. Results show that the microcantilever’s vibration above 8 MHz can be successfully detected, and its vibration modes were identified through a theoretical study based on the Euler–Bernoulli beam theory and a numerical analysis using the finite element method. The present study proposes a facile and effective way to actuate a high-speed sandwich microcantilever and detect its high-frequency response so that the technique can be employed to study the characteristics of micro- and nanomechanical sandwich structures and their properties.

Deterministic interface modes in two-dimensional acoustic systems

2020 ◽  
pp. 2150010
Author(s):  
Shao-Yong huo ◽  
Hong-Bo Huang ◽  
Lin-Jun Wang ◽  
Jiu-Jiu Chen
Keyword(s):  
Phase Transitions ◽  
Acoustic Waves ◽  
Tight Binding ◽  
Interface State ◽  
Interface States ◽  
Square Lattice ◽  
Two Dimensional ◽  
Practical Applications ◽  
Acoustic Interface ◽  
Sonic Crystals

The interface state in two-dimensional (2D) sonic crystals (SCs) was obtained based on trying or cutting approach, which greatly limits its practical applications. In this paper, we theoretically demonstrate that one category of interface states can deterministically exist at the boundary of two square-lattice SCs due to the geometric phase transitions of bulk bands. First, we derive a tight-binding formalism for acoustic waves and introduce it into the 2D case. Furthermore, the extended 2D Zak phase is employed to characterize the topological phase transitions of bulk bands. Moreover, the topological interface states can be deterministically found in the nontrivial bandgap. Finally, two kinds of SCs with the [Formula: see text] symmetry closely resembling the 2D Su–Schrieffer–Heeger (SSH) model are proposed to realize the deterministic interface states. We find that tuning the strength of intermolecular coupling by contacting or expanding the scatterers can effectively induce the bulk band inversion between the trivial and nontrivial crystals. The presence of acoustic interface states for both cases is further demonstrated. These deterministic interface states in 2D acoustic systems will be a great candidate for future waveguide applications.

Development of a Novel Deterministic-Statistical Approach for Vibro-Acoustic Problems in Mid-Frequency based on Modified Integration Rule

2019 ◽  
Vol 17 (03) ◽  
pp. 1850142
Author(s):  
Fu Wu ◽  
Lingyun Yao ◽  
Zhicheng He ◽  
Mu Hu
Keyword(s):  
Statistical Approach ◽  
Energy Analysis ◽  
Mass Matrix ◽  
Response Prediction ◽  
Fem Model ◽  
Integration Rule ◽  
Practical Applications ◽  
Modal Density ◽  
Different Types ◽  
Frequency Regime

Recently, FE-SEA was proposed especially for the analysis of vibro-acoustic problems in mid-frequency regime. In practical applications, the use of conventional FEM in this hybrid FE-SEA method entails some inherent drawbacks, which is closely associated with well-known “overly-stiff” feature of FEM and the balance of mass matrix and stiffness matrix. In this work, a modified integration rule (MIR) is applied in the acoustic FEM model to readjust the mass matrix. Then, the MIR-FEM is embedded to achieve a hybrid MIR-FE-SEA framework, aiming to further improve the accuracy of mid-frequency response prediction. In the proposed MIR-FE-SEA model, the plate structure which often has a higher modal density is considered as a statistical subsystem and modeled statistically using statistical energy analysis (SEA). The acoustical cavity with a relative lower modal density is modeled deterministically using MIR-FEM. The coupling between these two different types of subsystems is achieved through the diffuse field reciprocity relation. The proposed MIR-FE-SEA is verified by various numerical examples.

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