scholarly journals Study on the Dynamic Performance of Locally Resonant Plates with Elastic Unit Cell Edges

2021 ◽  
Vol 2021 ◽  
pp. 1-7
Author(s):  
Yonggan Sun
Keyword(s):  
Band Gap ◽  
Elastic Waves ◽  
Noise Control ◽  
Dynamic Performance ◽  
Unit Cell ◽  
Band Gaps ◽  
Transition Stage ◽  
Unit Cells ◽  
Elastic Unit ◽  
Application Scope

A Floquet–Bloch approach is employed to demonstrate the stop bands for an infinite locally resonant plate. In addition, the effects of the connection stiffness of the unit cells on the band gap and dynamic performance of a locally resonant plate are analysed. The results show that the degree of inhibition of elastic waves in the band gaps increases rapidly when the connection stiffness of the unit cells increases within the scope of the transition stage stiffness. However, outside of the range of transition stage stiffness, the degree of inhibition of elastic waves in the band gaps basically remains unchanged. This discovery widens the application scope for vibration and noise control using locally resonant plates.

Band Gap Control in an Active Elastic Metamaterial With Negative Capacitance Piezoelectric Shunting

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Y. Y. Chen ◽  
G. L. Huang ◽  
C. T. Sun
Keyword(s):  
Band Gap ◽  
Elastic Waves ◽  
Low Frequency ◽  
Lattice System ◽  
Band Gaps ◽  
Negative Capacitance ◽  
Bending Waves ◽  
Stiffness Constant ◽  
Elastic Metamaterials ◽  
Gap Control

Elastic metamaterials have been extensively investigated due to their significant effects on controlling propagation of elastic waves. One of the most interesting properties is the generation of band gaps, in which subwavelength elastic waves cannot propagate through. In the study, a new class of active elastic metamaterials with negative capacitance piezoelectric shunting is presented. We first investigated dispersion curves and band gap control of an active mass-in-mass lattice system. The unit cell of the mass-in-mass lattice system consists of the inner masses connected by active linear springs to represent negative capacitance piezoelectric shunting. It was demonstrated that the band gaps can be actively controlled and tuned by varying effective stiffness constant of the linear spring through appropriately selecting the value of negative capacitance. The promising application was then demonstrated in the active elastic metamaterial plate integrated with the negative capacitance shunted piezoelectric patches for band gap control of both the longitudinal and bending waves. It can be found that the location and the extent of the induced band gap of the elastic metamaterial can be effectively tuned by using shunted piezoelectric patch with different values of negative capacitance, especially for extremely low-frequency cases.

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.

Tailoring of Two-Dimensional Band-Gap Materials for Broadband Frequency Isolation

2007 ◽  
Author(s):  
Mahmoud I. Hussein ◽  
Karim Hamza ◽  
Gregory M. Hulbert ◽  
Kazuhiro Saitou
Keyword(s):  
Band Gap ◽  
Vibration Isolation ◽  
Optimization Techniques ◽  
Band Gaps ◽  
Two Dimensional ◽  
Frequency Bandwidth ◽  
Periodic Composite ◽  
Unit Cells ◽  
Periodic Materials ◽  
Broadband Frequency

The spatial distribution of material phases within a periodic composite can be engineered to produce band gaps in its frequency spectrum. Applications for such composite materials include vibration and sound isolation. Previous research focused on utilizing topology optimization techniques to design two-dimensional periodic materials with a maximized band gap around a particular frequency or between two particular dispersion branches. While sizable band gaps can be realized, the possibility remains that the frequency bandwidth of the load that is to be isolated might significantly exceed the size of the band gap. In this paper, genetic algorithms are used to design squared bi-material unit cells with a maximized sum of relative band-gap widths over a prescribed frequency range of interest. The optimized unit cells therefore exhibit broadband frequency isolation characteristics. The effects of the ratios of contrasting material properties are also studied. The designed cells are subsequently used, with varying levels of material damping, to form a finite vibration isolation structure, which is subjected to broadband loading conditions. Excellent isolation properties of the synthesized material are demonstrated for this structure.

scholarly journals Minimization of Mutual Coupling in Arrays using Cross-shape EBG

2019 ◽  
Vol 8 (11) ◽  
pp. 2599-2603
Keyword(s):  
Band Gap ◽  
Mutual Coupling ◽  
Unit Cell ◽  
Operating Frequency ◽  
Design Parameters ◽  
Substrate Thickness ◽  
Electromagnetic Band Gap ◽  
Area Reduction ◽  
Unit Cells ◽  
Current Scenario

In current scenario, the utilization of Electromagnetic Band Gap (EBG) has increased tremendously in microwave engineering. Mutual Coupling (MC) is a significant constraint to be measured in antennas specialization when used with arrays. Electromagnetic Band-Gap (EBG) is a well-known procedure applied in microwave and RF region due to its inherent bandgap feature at predefined frequency. MC arises due to surface currents excited on printed arrays whenever the substrate thickness ℇr > 1. By incorporating EBG in between array elements, various parameters like bandwidth, gain, radiation pattern, directivity, and current distribution can be improved based on the design parameters. Compactness and patch area reduction can be achieved through suitable unit cells of EBG structures. A patch performance is effective with better radiation characteristics and good return loss provided the operating frequency fall within the operating frequency of the unit-cell of the EBG. The unit cell can be constructed depending on the reflection phase, dispersion diagram. In this, a cross-EBG is used to enhance the MC between the arrays. The Cross EBG size is 6.3mm x 6.3mm. The antenna resonates at 5.8GHz WLAN range.

Design of Disordered Periodic Structures for Mode Localization

2017 ◽  
Author(s):  
Gabriele Cazzulani ◽  
Emanuele Riva ◽  
Edoardo Belloni ◽  
Francesco Braghin
Keyword(s):  
Wave Propagation ◽  
Periodic Structures ◽  
Unit Cell ◽  
Band Gaps ◽  
Mode Shapes ◽  
Mode Localization ◽  
Geometrical Properties ◽  
Unit Cells ◽  
The Mean ◽  
Propagation Properties

Periodic structures are the repetition of unit cells in space, that provide a filtering behavior for wave propagation. In particular, it is possible to tailor the geometrical, physical and elastic properties of the unit cells, in order to attenuate certain frequency bands, called band-gaps or stop-bands. Having each element characterized with the same parameters, the filtering behavior of the system can be described through the wave propagation properties of the unit cell. This is technologically impossible to obtain, therefore the Lyapunov factor is used, in order to define the mean attenuation of a quasi-periodic structure. Tailoring Gaussian unit cell properties potentially allows to extend the stop-bands width in the frequency domain. A drawback is that some unexpected resonance peaks may lie in the neighborhood of the extended regions. However, the correspondent mode-shapes are localized in a particular region of the structure, and they partially decrease the global attenuating behavior. In this paper, the aperiodicity introduced in the otherwise perfect repetition is investigated, providing an explanation for the mode-localization problem and for the stop-bands extension. Then, the proposed approach is applied to a passive quasi-periodic beam, characterized from a localized peak within a designed band-gap. The geometrical properties of its aperiodic parts are changed in order to deterministically move the localization peak in the frequency response. Numerical and experimental results are compared.

scholarly journals Optimal Designs of Phononic Crystal Microstructures Considering Point and Line Defects

Symmetry ◽  
2021 ◽  
Vol 13 (11) ◽  
pp. 1993
Author(s):  
Jingjie He ◽  
Jiamei Sun ◽  
Juncheng Fan ◽  
Zhiyuan Jia ◽  
Xiaopeng Zhang
Keyword(s):  
Finite Element ◽  
Band Gap ◽  
Phononic Crystal ◽  
Hyperelliptic Curves ◽  
Unit Cell ◽  
Optimal Designs ◽  
Finite Element Models ◽  
Optimization Strategy ◽  
Unit Cells ◽  
Line Defects

In this paper, a two-stage optimization strategy for designing defective unit cells of phononic crystal (PnC) to explore the localization and waveguide states for target frequencies is proposed. In the optimization model, the PnC microstructures are parametrically described by a series of hyperelliptic curves, and the optimal designs can be obtained by systematically changing the designable parameters of hyperellipse. The optimization contains two individual processes. We obtain the configurations of a perfect unit cell for different orders of band gap maximization. Subsequently, by taking advantage of the supercell technique, the defective unit cells are designed based on the unit cell configuration for different orders of band gap maximization. The finite element models show the localization and waveguide phenomenon for target frequencies and validate the effectiveness of the optimal designs numerically.

Vibration isolation characteristics of finite periodic tetra-chiral lattice coating filled with internal resonators

2016 ◽  
Vol 230 (16) ◽  
pp. 2840-2850 ◽  
Author(s):  
Dawei Zhu ◽  
Xiuchang Huang ◽  
Hongxing Hua ◽  
Hui Zheng
Keyword(s):  
Band Gap ◽  
Vibration Isolation ◽  
Periodic Structures ◽  
Low Frequency ◽  
Band Gaps ◽  
Stiffened Plate ◽  
Frequency Range ◽  
Vibration Attenuation ◽  
Unit Cells ◽  
Internal Resonators

Owing to their locally resonant mechanism, internal resonators are usually used to provide band gaps in low-frequency region for many types of periodic structures. In this study, internal resonators are used to improve the vibration attenuation ability of finite periodic tetra-chiral coating, enabling high reduction of the radiated sound power by a vibrating stiffened plate. Based on the Bloch theorem and finite element method, the band gap characteristics of tetra-chiral unit cells filled with and without internal resonators are analysed and compared to reveal the relationship between band gaps and vibration modes of such tetra-chiral unit cells. The rotational vibration of internal resonators can effectively strengthen the vibration attenuation ability of tetra-chiral lattice and extend the effective frequency range of vibration attenuation. Two tetra-chiral lattices with and without internal resonators are respectively designed and their vibration transmissibilities are measured using the hammering method. The experimental results confirm the vibration isolation effect of the internal resonators on the finite periodic tetra-chiral lattice. The tetra-chiral lattice as an acoustic coating is applied to a stiffened plate, and analysis results indicate that the internal resonators can obviously enhance the vibration attenuation ability of tetra-chiral lattice coating in the frequency range of the band gap corresponding to the rotating vibration mode of internal resonators. When the soft rubber with the internal resonators in tetra-chiral layers has gradient elastic modulus, the vibration attenuation ability and noise reduction of the tetra-chiral lattice coating are basically enhanced in the frequency range of the corresponding band gaps of tetra-chiral unit cells.

Photonic Band-Gaps in Porous Silicon Based Mirrors with a Ellipse Profile Refractive Index

2011 ◽  
Vol 236-238 ◽  
pp. 1811-1813
Author(s):  
Shuan Ming Li ◽  
Fu Ru Zhong ◽  
Zhen Hong Jia ◽  
Min Tian
Keyword(s):  
Refractive Index ◽  
Porous Silicon ◽  
Band Gap ◽  
Photonic Band Gap ◽  
Unit Cell ◽  
Band Gaps ◽  
Index Structure ◽  
Photonic Band Gaps ◽  
Silicon Based ◽  
Photonic Band

We investigate the use of ellipse refractive index structure to enlarge photonic band-gap (PBG). The PBG structure was prepared on porous silicon with 10 unit cell. Each unit cell is consisting of 21 layers with the refractive index varying according to the envelope of the ellipse function. The width of this photonic band-gap is high to 451nm.

Analysis of Periodicity Termination in Phononic Crystals

2011 ◽  
Author(s):  
Bruce L. Davis ◽  
Andrew S. Tomchek ◽  
Edgar A. Flores ◽  
Liao Liu ◽  
Mahmoud I. Hussein
Keyword(s):  
Band Gap ◽  
Timoshenko Beam ◽  
Periodic Structures ◽  
Beam Theory ◽  
Phononic Crystals ◽  
Timoshenko Beam Theory ◽  
Band Gaps ◽  
Pass Band ◽  
Unit Cells

While resonant propagation modes are non-existent within band gaps in infinite periodic structures, it is possible for anomalous band-gap resonances to appear in finite periodic structures. We establish two criteria for the characterization of band-gap resonances and propose approaches for their elimination. By considering flexural periodic beams, we show that as the number of unit-cells is increased the vibration response corresponding to band-gap resonances (1) does not shift in frequency, and (2) drops in amplitude. Both these outcomes are not exhibited by regular pass-band resonances, nor by resonances in finite homogenous beams when the length is changed. Our conclusions stem from predictions based on Timoshenko beam theory coupled with matching experimental observations.

Bayesian removal of noise for increased sensitivity in vector pattern recognition lattice imaging of interfaces

1993 ◽  
Vol 51 ◽  
pp. 994-995
Author(s):  
L. Fei ◽  
P. Fraundorf
Keyword(s):  
Pattern Recognition ◽  
Perfect Crystal ◽  
Unit Cell ◽  
Ion Milling ◽  
Beam Radiation ◽  
Major Interest ◽  
Unit Cells ◽  
Mapping Process ◽  
Increased Sensitivity ◽  
Electron Microscopes

Interface structure is of major interest in microscopy. With high resolution transmission electron microscopes (TEMs) and scanning probe microscopes, it is possible to reveal structure of interfaces in unit cells, in some cases with atomic resolution. A. Ourmazd et al. proposed quantifying such observations by using vector pattern recognition to map chemical composition changes across the interface in TEM images with unit cell resolution. The sensitivity of the mapping process, however, is limited by the repeatability of unit cell images of perfect crystal, and hence by the amount of delocalized noise, e.g. due to ion milling or beam radiation damage. Bayesian removal of noise, based on statistical inference, can be used to reduce the amount of non-periodic noise in images after acquisition. The basic principle of Bayesian phase-model background subtraction, according to our previous study, is that the optimum (rms error minimizing strategy) Fourier phases of the noise can be obtained provided the amplitudes of the noise is given, while the noise amplitude can often be estimated from the image itself.

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