scholarly journals Application of Air-Coupled Ultrasonic Arrays for Excitation of a Slow Antisymmetric Lamb Wave

Sensors ◽  
2018 ◽  
Vol 18 (8) ◽  
pp. 2636 ◽  
Author(s):  
Rymantas Kazys ◽  
Almantas Vilpisauskas ◽  
Justina Sestoke
Keyword(s):  
Lamb Wave ◽  
Guided Waves ◽  
Ultrasound Velocity ◽  
Optimization Procedure ◽  
Wave Mode ◽  
Zero Order ◽  
Air Gap ◽  
Thin Plates ◽  
Low Frequencies ◽  
Excitation Method

Air-coupled excitation and reception of ultrasonic guided waves is already used for non-destructive testing and evaluation (NDT & E). Usually for air-coupled NDT & E purposes the lowest zero-order antisymmetric Lamb wave mode A0 is used, because it is most sensitive to internal defects and thickness variations. The velocity of the A0 mode is reduced with a reducing frequency and at low frequencies may become slower than the ultrasound velocity in air. Such a wave is named a slow Lamb wave. The objective of this research was the development and investigation of an air-coupled excitation method of the slow zero-order antisymmetric Lamb wave based on application of a piezoceramic ultrasonic array. We have proposed to excite the A0 mode by a planar air-coupled phased array with rectangular elements. The array is matched to the wavelength of the A0 mode in the film. Performance of such an excitation method was investigated both theoretically and experimentally. Two excitation methods of the array were analysed: when all array elements were excited simultaneously or one by one with a proper delay. In order to reduce crosstalk between array elements via the air gap, we have proposed an optimization procedure based on additional shifts of electric excitation impulses of the array elements. For experimental verification of the proposed approach a prototype of the air-coupled eight element array made of Pz-29 piezoceramic strips was manufactured. Experimental validation confirmed the possibility of exciting the slow A0 Lamb wave mode through the air gap in thin plates and films.

scholarly journals Air-Coupled Excitation of a Slow A0 Mode Wave in Thin Plastic Films by an Ultrasonic PMN-32%PT Array

Sensors ◽  
2018 ◽  
Vol 18 (9) ◽  
pp. 3156 ◽  
Author(s):  
Rymantas Kazys ◽  
Liudas Mazeika ◽  
Reimondas Sliteris ◽  
Justina Sestoke
Keyword(s):  
Lamb Wave ◽  
Composite Structures ◽  
Guided Waves ◽  
Ultrasound Velocity ◽  
Processing Technique ◽  
Wave Mode ◽  
Destructive Testing ◽  
Plastic Films ◽  
Directivity Patterns ◽  
Thin Plastic

Ultrasonic non-destructive testing techniques (NDT) based on the application of guided waves are already used for inspection of plate-type structures made of various materials, including composite materials. Air-coupled ultrasonic techniques are used to test such structures by means of guided waves. The objective of this research was development and investigation of air-coupled excitation of a slow A0 Lamb wave mode in thin plastic films by a PMN-32%PT ultrasonic array. It is known that when the velocity of the A0 mode in the film is less than the ultrasound velocity in air no leaky wave is observed in a surrounding air. It opens new possibilities for NDT of composite structures. The influence of the airborne wave may be eliminated by 3D filtering in a wavenumbers-frequency domain. A special filter and corresponding signals processing technique were developed in order to obtain directivity patterns and velocity maps of the waves propagating in all directions. The measured ultrasound velocity values prove that, with the proposed method, it is possible to excite a slow A0 Lamb wave mode and to separate it from other parasitic waves propagating in air. Measurements of the parameters of the slow A0 mode, such as the propagation velocity in the plastic film, may be applied for the material characterization.

The effects of air gap reflections during air-coupled leaky Lamb wave inspection of thin plates

Ultrasonics ◽  
2016 ◽  
Vol 65 ◽  
pp. 282-295 ◽  
Author(s):  
Zichuan Fan ◽  
Wentao Jiang ◽  
Maolin Cai ◽  
William M.D. Wright
Keyword(s):  
Lamb Wave ◽  
Air Gap ◽  
Thin Plates ◽  
Leaky Lamb Wave

scholarly journals Attenuation of a Slow Subsonic A0 Mode Ultrasonic Guided Wave in Thin Plastic Films

Materials ◽  
2019 ◽  
Vol 12 (10) ◽  
pp. 1648 ◽  
Author(s):  
Rymantas Kažys ◽  
Reimondas Šliteris ◽  
Liudas Mažeika ◽  
Olgirdas Tumšys ◽  
Egidijus Žukauskas
Keyword(s):  
Guided Waves ◽  
High Efficiency ◽  
Lamb Waves ◽  
Ultrasonic Transducer ◽  
Plane Waves ◽  
Ultrasound Velocity ◽  
Guided Wave ◽  
Low Frequencies ◽  
Plastic Films ◽  
Thin Plastic

The ultrasonic testing technique using Lamb waves is widely used for the non-destructive testing and evaluation of various structures. For air-coupled excitation and the reception of A0 mode Lamb waves, leaky guided waves are usually exploited. However, at low frequencies (<100 kHz), the velocity of this mode in plastic and composite materials can become slower than the ultrasound velocity in air, and its propagation in films is accompanied only by an evanescent wave in air. To date, the information about the attenuation of the slow A0 mode is very contradictory. Therefore, the objective of this investigation was the measurement of the attenuation of the slow A0 mode in thin plastic films. The measurement of the attenuation of normal displacements of the film caused by a propagating slow A0 mode is discussed. The normal displacements of the film at different distances from the source were measured by a laser interferometer. In order to reduce diffraction errors, the measurement method based on the excitation of cylindrical but not plane waves was proposed. The slow A0 mode was excited in the polyvinylchloride film by a dry contact type ultrasonic transducer made of high-efficiency PMN-32%PT strip-like piezoelectric crystal. It was found that that the attenuation of the slow A0 mode in PVC film at the frequency of 44 kHz is 2 dB/cm. The obtained results can be useful for the development of quality control methods for plastic films.

Dispersion and Attenuation of Guided Waves in Tubular Section with Multi-Layered Viscoelastic Coating — Part II: Circumferential Wave Propagation

2017 ◽  
Vol 09 (02) ◽  
pp. 1750016 ◽  
Author(s):  
Chi-Wei Kuo ◽  
C. Steve Suh
Keyword(s):  
Guided Waves ◽  
Wave Mode ◽  
Guided Wave ◽  
Constitutive Law ◽  
Complex Frequency ◽  
Low Frequencies ◽  
Longitudinal Modes ◽  
Attenuation Characteristic ◽  
Viscoelastic Layers ◽  
Dispersion And Attenuation

In the second part of the study on guided wave motions in a hollow cylinder with epoxy layers, shear and longitudinal modes propagating in the circumferential direction are investigated. The corresponding dispersion and attenuation characteristic equations are derived by incorporating a complex, frequency-dependent constitutive law for the viscoelastic coating material. Continuous displacement boundary conditions are implemented to model perfect interfacial bonds between the tubular section and applied epoxy coatings. The presence of thin dissipative viscoelastic layers has profound impact on the propagation of both the circumferential shear and longitudinal waves. The number of admissible propagating modes increases with increasing number of viscoelastic layers and higher order modes dissipate significantly less at high frequencies than the lower order modes at low frequencies. Over the frequency range considered, all the circumferential propagating modes are significantly more attenuating than their axial propagating counterparts studied in Part 1 of the paper. Generation of the lowest shear wave mode is suppressed at approximately 0.2 MHz in the coated tubular. However, no such definitive cutoff frequencies are observed for the longitudinal modes regardless of how many viscoelastic layers are considered.

scholarly journals Selective Generation of Lamb Wave Modes in a Finite-Width Plate by Angle-Beam Excitation Method

Sensors ◽  
2020 ◽  
Vol 20 (14) ◽  
pp. 3868 ◽  
Author(s):  
Sang-Jin Park ◽  
Young-Sang Joo ◽  
Hoe-Woong Kim ◽  
Sung-Kyun Kim
Keyword(s):  
Lamb Wave ◽  
Laser Scanning ◽  
Wave Mode ◽  
Finite Width ◽  
Acoustic Insulation ◽  
Selective Generation ◽  
Lamb Wave Propagation ◽  
Different Characteristics ◽  
Beam Excitation ◽  
Excitation Method

A Lamb wave in a plate with a finite width has both thickness and width modes, whereas only thickness modes exist in an infinitely wide plate. The thickness and width modes are numerously formed in a finite-width plate, and they all have different cut-off frequencies, wave velocities, and wave structures. These different characteristics can be utilized in various applications, but a selective generation method for a particular Lamb wave mode in a finite-width plate has not been sufficiently studied, and only a method using multiple elements has been reported. This paper presents the selective generation of a certain Lamb wave mode in a finite-width plate by an angle-beam excitation method using single or dual wedges. In the proposed generation method, a specially designed wedge with grooves or a patch having insulation layers is employed for partial acoustic insulation of the ultrasonic energy incident into the plate. The feasibility of the proposed method was investigated through finite element method (FEM) simulations for Lamb wave excitation and propagation, and then experimentally demonstrated by the measurement of Lamb wave propagation using a laser scanning vibrometer.

Damage Detection in Thick Steel Beam Using Lamb Waves

2008 ◽  
Author(s):  
Kai Sun ◽  
Guang Meng ◽  
Fucai Li ◽  
Lin Ye ◽  
Ye Lu
Keyword(s):  
Damage Detection ◽  
Lamb Wave ◽  
Lamb Waves ◽  
Fem Simulation ◽  
Wave Mode ◽  
Thin Plates ◽  
Steel Beams ◽  
Thick Steel ◽  
Number Of Cycles ◽  
Detection And Localization

Different from the mostly concerned Lamb wave-based damage detection for thin plates, this paper presents a diagnosis procedure on thick steel beams with thickness of 34 mm. The diagnosis strategy and specimens were first described, and some parameters, such as the frequency and the number of cycles of the diagnostic waveform, were discussed. Based on finite element method (FEM) simulation, the experiment configuration was addressed, results from which show good similarity between the outcomes from the simulations and those from the experiments. Wavelet transform was further used to process the acquired Lamb wave signals for the purpose of damage detection and localization. Meanwhile, the velocity of the Lamb waves was calculated, illustrating that the fundamental anti-symmetric (A0) Lamb wave mode was excited in this case. The results demonstrate that Lamb waves can also be applied to some thick structures for the purpose of structural health monitoring.

scholarly journals Air-Coupled Reception of a Slow Ultrasonic A0 Mode Wave Propagating in Thin Plastic Film

Sensors ◽  
2020 ◽  
Vol 20 (2) ◽  
pp. 516 ◽  
Author(s):  
Rymantas J. Kazys ◽  
Almantas Vilpisauskas
Keyword(s):  
Evanescent Wave ◽  
Ultrasound Velocity ◽  
Thin Plates ◽  
Destructive Testing ◽  
Low Frequencies ◽  
Plastic Films ◽  
Additional Signal ◽  
Virtual Array ◽  
Thin Plastic ◽  
Coupled Technique

At low frequencies, in thin plates the phase velocity of the guided A0 mode can become slower than that of the ultrasound velocity in air. Such waves do not excite leaky waves in the surrounding air, and therefore, it is impossible to excite and receive them by conventional air-coupled methods. The objective of this research was the development of an air-coupled technique for the reception of slow A0 mode in thin plastic films. This study demonstrates the feasibility of picking up a subsonic A0 mode in plastic films by air-coupled ultrasonic arrays. The air-coupled reception was based on an evanescent wave in air accompanying the propagating A0 mode in a film. The efficiency of the reception was enhanced by using a virtual array which was arranged from the data collected by a single air-coupled receiver. The signals measured at the points corresponding to the positions of the phase-matched array were recorded and processed. The transmitting array excited not only the A0 mode in the film, but also a direct wave in air. This wave propagated at ultrasound velocity in air and was faster than the evanescent wave. For efficient reception of the A0 mode, the additional signal-processing procedure based on the application of the 2D Fourier transform in a spatial–temporal domain. The obtained results can be useful for the development of novel air-coupled ultrasonic non-destructive testing techniques.

Ultrasonic Guided Waves in Thin Orthotropic Layers: Exact and Approximate Analyses

2000 ◽  
Author(s):  
Subhendu K. Datta ◽  
Osama Mukdadi
Keyword(s):  
Wave Propagation ◽  
Exact Solutions ◽  
Elastic Constants ◽  
Guided Waves ◽  
Guided Wave ◽  
Thin Layers ◽  
Thin Plates ◽  
Low Frequencies ◽  
Ultrasonic Guided Wave ◽  
Guided Wave Propagation

Abstract Exact and approximate analyses of ultrasonic guided wave propagation in thin orthotropic layers are presented in this work. Exact solutions to the equations governing the dependence of guided wave propagation speeds on the elastic constants characterizing the anisotropic properties of the layers are presented and compared with the predictions of first order approximate theories for extensional and flexural waves in thin plates. Comparison with available experimental results for dispersion of these waves in thin sheets of different types of papers leads to the confirmation or modification of the elastic constants and density reported for these papers. A particular focus of this study is the coupling of three types of guided waves (extensional (S), flexural (A), and shear-horizontal (SH)) due to anisotropy of the material. It is shown that there are significant changes in the dispersion characteristics of these modes at certain frequencies, which can be exploited to measure the in-plane elastic properties of thin layers. Another focus is to study the limitations of approximate results when compared with exact solutions for wave propagation in different directions. In general good agreements are found at low frequencies.

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