Focusing of Rayleigh waves: simulation and experiments

Deutsch, W. A. K.; Cheng, A.; Achenbach, Jan Drewes

doi:10.1109/58.753021

Cited by 20 publications

(7 citation statements)

References 5 publications

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“…This work extends a number of recent investigations for elastic surface and interfacial waves. For time-harmonic disturbances, it was previously shown (Achenbach 1998;Deutsch et al 1999) that surface waves on a transversely isotropic half-space and waves in isotropic plates may have (complex) amplitude being any solution to the reduced-membrane (two-dimensional Helmholtz) equation (the disturbances at all depths are described as being 'carried by' the solution of the Helmholtz equation). In Kiselev (2004), elastic surface waves of Chadwick type yet having displacements varying linearly with the transverse coordinate have been constructed.…”

Section: Introductionmentioning

confidence: 99%

Omni-directional Rayleigh, Stoneley and Schölte waves with general time dependence

Kiselev

Parker

2010

Proc. R. Soc. A.

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Just as uni-directional Rayleigh waves at the traction-free surface of a transversely isotropic elastic half-space and Stoneley waves at the interface between two such media may have arbitrary waveform and may be represented in terms of a single function harmonic in a half-plane, it is shown that surface-guided waves travelling simultaneously in all directions parallel to the surface may be represented, at each instant, in terms of a single function satisfying Laplace's equation in a three-dimensional half-space. That harmonic function is determined so that its normal derivative at the surface equals the normal displacement of the surface (or interface). It is shown, moreover, that the time evolution of that normal displacement may be any solution to the membrane equation with wave speed being equal to that of classical, uni-directional, time-harmonic Rayleigh or Stoneley waves. A similar representation is also shown to exist for Schölte waves at a fluid-solid interface, in the non-evanescent case. Thus, every surface-or interfaceguided disturbance in media having rotational symmetry about the surface normal is governed by the membrane equation with appropriate wave speed, provided that the combination of materials allows uni-directional, time-harmonic waves that are nonevanescent. Conversely, each solution to the membrane equation may be used to construct a representation of either a Rayleigh wave, a Stoneley wave or a (non-evanescent) Schölte wave. In each case, the disturbance at all depths may be represented at each instant in terms of a single function harmonic in a half-space.

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Section: Introductionmentioning

confidence: 99%

Omni-directional Rayleigh, Stoneley and Schölte waves with general time dependence

Kiselev

Parker

2010

Proc. R. Soc. A.

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“…Fortunately, many attempts were made to concentrate the ultrasound waves launched by EMATs towards a focal line or point with sharp directivity in the existing literature [14][15][16][17][18][19][20][21][22]. In [20], Takishita et al presented a point focusing shear vertical electromagnetic ultrasonic transducer (PFSV-EMAT), which is a specially designed array of the meander-line elements.…”

Section: Introductionmentioning

confidence: 99%

Investigating the Influence of Design Frequency on the Ultrasonic Signal of PFSV-EMATs

et al. 2022

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The point-focusing shear vertical wave electromagnetic acoustic transducer (PFSV-EMAT) with a concentric meander line (CML) coil has been developed to detect and size micro defection concealed within a certain depth of materials. It is proved to be sensitive to the design frequency, which is associated with the spacing of CML coil. In this work, the relationship between the design frequency and characteristic of PFSV-EMATs, such as the particle displacement and focal offset, is studied quantitatively. First, the configuration and working principle of PFSV-EMATs are introduced comprehensively. Then, a finite element model is established to simulate the incentive and propagation process of ultrasonic waves. In addition, the relationship between magnet-to-coil radius ratio and the signal amplitude generated by the PFSV-EMATs is explored to ensure the consistency of transducer parameters at different frequencies. Furthermore, under the optimal magnet-to-coil radius ratio, the influence of design frequency on the characteristic of PFSV-EMATs is studied. Finally, the experimental results show good agreement with the simulation results and indicate that the signal amplitude and point-focusing performance of PFSV-EMATs employing CML coils could be improved by carefully choosing the design frequency.

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“…However, if a focused transducer is used, a narrower beam profile and increased signal strength at the focal point is achieved and this can be optimised for defect detection. Rayleigh wave focusing has previously been implemented using shaped piezoelectric elements [18] and with piezoelectric phased arrays [17,19]. The arrays allow for variable focusing, unlike the single shaped element which has a fixed focal point, but the arrays are costly and complex.…”

Section: Introductionmentioning

confidence: 99%

Focused Rayleigh wave EMAT for characterisation of surface-breaking defects

Thring

Yang

Edwards

2016

NDT & E International

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Developments towards higher resolution and the ability to detect small defects are bringing a step-change in non-destructive testing. This paper presents a new method for increasing resolution, using a focused electromagnetic acoustic transducer (EMAT) optimised to generate Rayleigh waves at 2 MHz. This high frequency allows detection of mm-depth defects, and the focusing allows sizing of much shorter defects than is possible when using standard EMATs. The focusing behaviour and the aperture angle effect are analysed using laser vibrometry and finite element modeling, showing that a reduced aperture shifts the focal point from the designed value and increases the focal depth. The dual-EMAT has excellent signal to noise ratio (up to 30 dB) and has been used in single shot mode to image a variety of surface-breaking defects, including detecting and positioning a pair of real defects in an aluminium billet sample, and a machined defect of 2 mm length, 0.2 mm width, and 1.5 mm depth, giving an upper limit on the defect length of 2.1±0.5 mm. The results can be used to design an EMAT with optimised focal behaviour for defect detection.

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Focusing of Rayleigh waves: simulation and experiments

Cited by 20 publications

References 5 publications

Omni-directional Rayleigh, Stoneley and Schölte waves with general time dependence

Omni-directional Rayleigh, Stoneley and Schölte waves with general time dependence

Investigating the Influence of Design Frequency on the Ultrasonic Signal of PFSV-EMATs

Focused Rayleigh wave EMAT for characterisation of surface-breaking defects

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