scholarly journals Clamping Resonators for Low-Frequency S0 Lamb Wave Reflection

2019 ◽  
Vol 9 (2) ◽  
pp. 257 ◽  
Author(s):  
Christopher Hakoda ◽  
Cliff Lissenden ◽  
Parisa Shokouhi
Keyword(s):  
Band Gap ◽  
Lamb Wave ◽  
Wave Reflection ◽  
Stop Band ◽  
Low Frequency ◽  
Wave Mode ◽  
Design Concept ◽  
The Other ◽  
Transmitted Signal ◽  
Wave Modes

A recent elastic metamaterial study found that resonators that “clamp” a plate waveguide can be used to create a frequency stop-band gap. The result was that the resonator array can prohibit the propagation of an A0 Lamb wave mode. This study investigates whether the concept can be extended to S0 Lamb wave modes by designing resonators that can prohibit the propagation of S0 Lamb wave modes in a 1-mm aluminum plate waveguide at 50 kHz. The frequency-matched resonators did not reduce the transmitted signal, leading to the conclusion that the design concept of frequency-matched resonators is not always effective. On the other hand, the resonators designed to clamp the upper surface of the plate were very effective and reduced the transmitted signal by approximately 75%.

Dispersion curve analysis method for Lamb wave mode separation

2019 ◽  
Vol 19 (5) ◽  
pp. 1590-1601
Author(s):  
Yue Hu ◽  
Yanping Zhu ◽  
Xiaotong Tu ◽  
Jing Lu ◽  
Fucai Li
Keyword(s):  
Dispersion Curve ◽  
Lamb Wave ◽  
Hessian Matrix ◽  
Wave Mode ◽  
Curve Analysis ◽  
Energy Concentration ◽  
Time Frequency ◽  
Mode Separation ◽  
Multimodal Features ◽  
Wave Modes

The Lamb wave inspection has emerged as a promising method for structural health monitoring and nondestructive testing. However, because of the highly dispersive and multimodal features, the Lamb wave mode separation has become a challenging problem. Based on the dispersion curve analysis, a new signal processing method is proposed in this study to solve this problem. First, a novel function based on the Hessian matrix is constructed to enhance the energy concentration of the dispersion curve in the time–frequency representation to reduce the dispersion effect. Subsequently, the constrained penalty function algorithm is developed for detecting dispersion curves. Finally, a mode reconstruction algorithm is developed to recover Lamb wave modes. The proposed method can separate overlapping wave modes and detect the crack fault by enhancing the time–frequency feature of the Lamb wave signal. Two experiments are carried out to verify the effectiveness of the proposed method for Lamb wave mode separation.

WAVE PROPAGATION IN LIPOSOMES

2013 ◽  
Vol 13 (01) ◽  
pp. 1350015
Author(s):  
KE DONG ◽  
GUOXING LU
Keyword(s):  
Wave Propagation ◽  
Wave Speed ◽  
Critical Frequency ◽  
Low Frequency ◽  
Wave Mode ◽  
Frequency Region ◽  
Wave Number ◽  
Rotary Inertia ◽  
High Frequency Region ◽  
Wave Modes

The general behavior of wave propagation in liposomes, including the effect of rotary inertia, is examined in this paper, based on a continuum cylindrical shell model. The disperse curves are obtained by solving an eigenvalue problem. The characteristics of wave propagation in liposomes are described using numerical examples. The results show that wave propagation in liposomes has a threshold critical frequency beyond which the wave speed drops dramatically and also a cut-off critical frequency below which the corresponding wave mode does not appear. The torsional wave speed is obtained for the symmetrical circumferential mode n = 0. The cut-off or threshold critical frequency decreases with the increase of liposomal radius, but the effect of radius on wave speed is not significant in the frequency region higher than the critical frequency. On the other hand, the wave number n leads to an increase in the critical frequency. For the first and second wave modes, the wave speed is insensitive to the wave number when the frequency is greater than the critical frequency. For the third wave mode in the low frequency region, the wave number leads to an increase in the wave speed. The rotary inertia has little influence on those wave modes which contain cut-off frequencies. For other wave modes, the rotary inertia results in a decrease in the wave speed in the high frequency region. This investigation may provide a useful guide in the applications of liposomes in ultrasound-based drug delivery and release.

Lamb Wave Propagation Study Using Frequency-Wavenumber Analysis

2012 ◽  
Author(s):  
Zhenhua Tian ◽  
Lingyu Yu
Keyword(s):  
Wave Propagation ◽  
Lamb Wave ◽  
Experimental Testing ◽  
Wave Spectrum ◽  
Laser Doppler Vibrometer ◽  
Wave Mode ◽  
Wavenumber Domain ◽  
Time Space ◽  
Lamb Wave Propagation ◽  
Wave Modes

Lamb waves are dispersive and multi-modal. Various wave modes make the interpretation of Lamb wave signal very difficult. It is desired that different modes can be separated for individual analysis. In the this paper, we present our studies on the multimodal Lamb wave propagation and wave mode extraction using frequency-wavenumber analysis. Wave spectrum in the frequency-wavenumber domain shows clear distinction among Lamb wave modes being present. This allows separating them or extracting a desired Lamb wave mode through a novel filtering strategy. Thus a single mode Lamb can be identified and extracted for certain types of damage detection in structural health monitoring (SHM). These concepts are illustrated through experimental testing. A scanning laser Doppler vibrometer is used to acquiring the time-space wavefield regarding the multimodal Lamb wave propagation. Then the recorded wavefield was analyzed in frequency-wavenumber domain and decomposed into different wave modes.

scholarly journals Nonpenetrating Damage Identification Using Hybrid Lamb Wave Modes from Hilbert-Huang Spectrum in Thin-Walled Structures

2017 ◽  
Vol 2017 ◽  
pp. 1-11 ◽  
Author(s):  
Zijian Wang ◽  
Pizhong Qiao ◽  
Binkai Shi
Keyword(s):  
Lamb Wave ◽  
Damage Identification ◽  
Lamb Waves ◽  
Wave Mode ◽  
Thin Walled Structures ◽  
Damage Indices ◽  
Thin Walled ◽  
Experimental Validations ◽  
The One ◽  
Wave Modes

Lamb waves have shown promising advantages for damage identification in thin-walled structures. Multiple modes of Lamb wave provide diverse sensitivities to different types of damage. To sufficiently utilize damage-related wave features, damage indices were developed by using hybrid Lamb wave modes from Hilbert-Huang spectra. Damage indices were defined as surface integrals of Hilbert-Huang spectra on featured regions determined by time and frequency windowing. The time windowing was performed according to individual propagation velocity of different Lamb wave mode, while the frequency windowing was performed according to the frequency of excitation. By summing damage indices for all transmitter-receiver pairs, pixels were calculated to reconstruct a damage map to characterize the degree of damage at each location on structure. Both numerical and experimental validations were conducted to identify a nonpenetrating damage. The results demonstrated that the proposed damage indices using hybrid Lamb wave modes are more sensitive and robust than the one using single Lamb wave mode.

Excitation of Guided Waves in Oil Storage Tank Floor and Vertical Wall by Edge- and Wall-Mounted Transducers

2010 ◽  
Author(s):  
Weibin Wang ◽  
Zhanjun Feng ◽  
Choumin Zhao ◽  
Keyi Yuan ◽  
Zandong Han ◽  
...  
Keyword(s):  
Longitudinal Wave ◽  
Lamb Wave ◽  
Pulse Train ◽  
Guided Waves ◽  
Lamb Waves ◽  
Vertical Wall ◽  
Low Frequency ◽  
Longitudinal Waves ◽  
Oil Storage ◽  
Wave Modes

Oil storage tanks are crucial components in the petrochemical industry for transportation and storage. Corrosion of the tank floor and vertical walls is one of the most important safety concerns. In-situ inspection of the tank floor and walls with ultrasonic guided wave technique by edge- and wall-mounted transducers is still an active research area nowadays. A great deal of research has been conducted in detecting the defect of plate-like structures using Lamb waves. This application has been motivated by the fact that the Lamb wave velocity is the function of frequency and structural geometry (thickness), also the Lamb waves can propagate with low attenuation for long distance in plate structure. However, the complexity due to the existence of multiple Lamb wave modes weakens its applicability. Lamb waves are typically excited by transducers mounted on the surface of the inspected plates. Higher order modes are generated if the frequency-thickness product exceeds a certain threshold value that is dependent on the material of the plates. Low frequency guided waves can reduce this complication as only a small number of wave modes are generated. So operation with low frequency guided waves is usually recommended, but it encounters a problem that the resolution gets degraded hence small defects (compared to the wavelength) are difficult to detect. Our investigation considers the generation of guided waves in tank floor and vertical wall by edge excitation and wall-mounted excitation, respectively. Only when there is no access to the edge of the vertical wall, the wall-mounted excitation (surface excitation) is used. When the frequency-thickness product is small Lamb waves are generated, otherwise, longitudinal waves are generated. We investigate the intermediate frequency-thickness products where a pulse train of semi-longitudinal waves is excited. The pulse train is comprised of a leading pulse and some railing pulses, which have been predicted by the acoustic theory. The transition from Lamb wave to semi-longitudinal wave is investigated. In addition, energy transport from leading pulse to trailing pulses and the interaction of these trailing pulses with defects are studied. The results revealed that the semi-longitudinal wave is a viable option for tank floor and wall defect inspection.

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.

scholarly journals Nucleotide Variation at theCHALCONE ISOMERASELocus inArabidopsis thaliana

Genetics ◽  
2000 ◽  
Vol 155 (2) ◽  
pp. 863-872 ◽  
Author(s):  
Helmi Kuittinen ◽  
Montserrat Aguadé
Keyword(s):  
Nucleotide Diversity ◽  
Direct Relationship ◽  
Selective Sweep ◽  
Balancing Selection ◽  
Neutral Theory ◽  
Low Frequency ◽  
The Other ◽  
Nucleotide Variation ◽  
Rapid Population Growth ◽  
History Of

AbstractAn ~1.9-kb region encompassing the CHI gene, which encodes chalcone isomerase, was sequenced in 24 worldwide ecotypes of Arabidopsis thaliana (L.) Heynh. and in 1 ecotype of A. lyrata ssp. petraea. There was no evidence for dimorphism at the CHI region. A minimum of three recombination events was inferred in the history of the sampled ecotypes of the highly selfing A. thaliana. The estimated nucleotide diversity (θTOTAL = 0.004, θSIL = 0.005) was on the lower part of the range of the corresponding estimates for other gene regions. The skewness of the frequency spectrum toward an excess of low-frequency polymorphisms, together with the bell-shaped distribution of pairwise nucleotide differences at CHI, suggests that A. thaliana has recently experienced a rapid population growth. Although this pattern could also be explained by a recent selective sweep at the studied region, results from the other studied loci and from an AFLP survey seem to support the expansion hypothesis. Comparison of silent polymorphism and divergence at the CHI region and at the Adh1 and ChiA revealed in some cases a significant deviation of the direct relationship predicted by the neutral theory, which would be compatible with balancing selection acting at the latter regions.

Determining impact induced damage by lamb wave mode extracted by EMD method

Measurement ◽  
2015 ◽  
Vol 65 ◽  
pp. 120-128 ◽  
Author(s):  
Xu Baochun ◽  
Yuan Shenfang ◽  
Wang Mulan ◽  
Qiu Lei
Keyword(s):  
Lamb Wave ◽  
Wave Mode ◽  
Emd Method

Effect of Double Defects on Transmission Spectra of One-Dimensional Photonic Crystals

2010 ◽  
Vol 663-665 ◽  
pp. 725-728 ◽  
Author(s):  
Yuan Ming Huang ◽  
Qing Lan Ma ◽  
Bao Gai Zhai ◽  
Yun Gao Cai
Keyword(s):  
Photonic Crystals ◽  
Band Gap ◽  
Theoretical Calculations ◽  
Stop Band ◽  
Band Gaps ◽  
Characteristic Matrix ◽  
Frequency Range ◽  
Defect Band ◽  
One Dimensional ◽  
The One

Considered the model of the one-dimensional photonic crystals (1-D PCs) with double defects, the refractive indexes (n2’, n3’ and n2’’, n3’’) of the double defects were 2.0, 4.0 and 4.0, 2.0 respectively. With parameter n2=1.5, n3=2.5, by theoretical calculations with characteristic matrix method, the results shown that for a certain number (14 was taken) of layers of the 1-D PCs, when the double defects abutted, there was a defect band gap in the stop band gap, while when the double defects separated, there occurred two defect band gaps in the stop band gap; besides, with the separation of the two defects, the transmittance of the double defect band gaps decreased gradually. In addition, in this progress, the frequency range of the stop band gap has a little increase from 0.092 to 0.095.

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