Rayleigh wave suppression in reflection acoustic microscopy

Nikoonahad, M.; Sivaprakasapillai, P.; Ash, E.A.

doi:10.1049/el:19830619

Cited by 9 publications

(1 citation statement)

References 5 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The angular spectrum associated with such spherical lenses can extend out to ±50 • . However, some investigations have also been carried out using SAMs having other specific designs: spherical lenses driven by a shear-wave transducer to enhance image contrasts (Chou et al 1987), restricted-aperture lenses for Rayleighwave imaging (Davids et al 1989) planar lenses using Rayleigh-to-compressional waves (Farnell and Jen 1980), acoustic graded-index lenses (Jen et al 1991) and annular structures to suppress Rayleigh waves, to measure SAW attenuation and layer thicknesses or even to be used for dark-field imaging (Nikoonahad et al 1983, Smith and Wickramasinghe 1982, Saito et al 1992, Sinclair and Smith 1980. It should be noted that most of these proposed exceptions were concerned with qualitative investigations.…”

Section: Introductionmentioning

confidence: 99%

Theoretical and experimental investigations of acoustic signatures of materials using scanning microscopes with variable lens illumination

Doghmane

Hadjoub

1997

J. Phys. D: Appl. Phys.

View full text Add to dashboard Cite

The most important part of a scanning acoustic microscope system is the wide-opening-angle lens which could have many shapes and sizes. Such lenses include several interfering surface modes which may obscure the measured acoustic properties. In this paper, we investigate the conventional spherical wide-angle lens whose central part has been covered by a circular aperture stop of varying diameter, D, to absorb the energy of acoustic modes. The influence of increasing D of such absorbers on the acoustic signatures, V (z ), of plastic materials in which the speed of sound is slow (plexiglass) and materials in which the speed of sound is relatively fast (silica and stainless steel) is investigated theoretically and experimentally, leading to similar behaviours: a decrease in amplitude, a broadening of periodic spacings and the complete disappearance of the oscillatory form of V (z ) for large D, namely for large excluded angles. A novel formula for periods, z , is proposed for covered lenses, which explains the velocity shift associated with the period variation as the excluded angle increases.

show abstract

Section: Introductionmentioning

confidence: 99%

Theoretical and experimental investigations of acoustic signatures of materials using scanning microscopes with variable lens illumination

Doghmane

Hadjoub

1997

J. Phys. D: Appl. Phys.

View full text Add to dashboard Cite

show abstract

Acoustic Microscope Lens Optimization for Subsurface Imaging

Maslov¹

1993

Acoustical Imaging

View full text Add to dashboard Cite

Observation of a sub-surface defect in sapphire by Rayleigh wave reflection in the scanning acoustic microscope

Smith

Gee

1986

J Mater Sci Lett

View full text Add to dashboard Cite

Acoustic microscopy is a novel technique for nondestructive examination (NDE) that is rapidly finding increasing application in many areas of materials science. The principle of operation of the reflection scanning acoustic microscope (SAM) is well known and is described elsewhere [1,2]. Contrast in the images is a function of the elastic properties of the specimen.An important contribution to the contrast comes from the Rayleigh waves which are generated when an acoustic lens of sufficiently wide aperture is moved from the focus position towards the surface of the specimen. The Rayleigh waves propagate in the surface layers of the specimen, and re-radiate part of their energy back into the coupling medium. This is responsible, through the so-called V(z) effect [3], for the enhanced contrast seen in SAM images of cracks [4,5], grains and grain boundaries [6] and other material features.The Rayleigh waves may also be reflected from discontinuities such as cracks, edges, and similar features in the sample surface, giving rise to the characteristic fringes often seen in SAM images. In this letter we report the observation of a sub-surface feature detected in the SAM not by the production of a separate echo, or by its modification of V(z), but by its effect on the interference fringes produced by Rayleigh wave reflection.Single crystal sapphire was chosen for this study because it is transparent, therefore enabling subsurface features to be detected optically; it is acoustically and elastically well characterized, and the polycrystalline form, alumina, is in widespread use as an industrial material. The surface of the sample was oriented 15 ° off the (000 1) plane and was polished using diamond paste and silica suspension to a good optical finish. An impression was left in the surface of the sample by a Vickers pyramid indenter applied with a force of 4.9 N.The specimen was examined in a conventional reflection SAM operating at 0.8 GHz with a lens of half angle 57 °. Fig. 1 shows the SAM image obtained with the sample placed at the focus of the lens. The impression left by the indenting tool is clearly visible, as are the radial cracks, and a bifurcation near the end of the right-hand crack. The series of bright and dark fringes visible on the sides of the impression are due to interference and can be used to estimate the depth of the impression, given a knowledge of the wavelength. Although the faint contrast from around the indentation impression may possibly be attributed to the presence of lateral vents (a type of submerged crack) [7], there is little sub-surface information in the image of Fig. 1.An indication of the practical resolution of the SAM is given by Fig. 2 which shows a backscattered SEM image of the upper branch of the bifurcated crack. From Fig. 2 the crack width may be estimated to be ~ 75 mm. This crack branch is clearly visible in the SAM image. Thus the detection limit for surfacebreaking cracks in the SAM operating at 0.8 GHz is equal to or better than ~ 75 nm. The SEM image (Fig. 2) also reve...

show abstract

Rayleigh wave suppression in reflection acoustic microscopy

Cited by 9 publications

References 5 publications

Theoretical and experimental investigations of acoustic signatures of materials using scanning microscopes with variable lens illumination

Theoretical and experimental investigations of acoustic signatures of materials using scanning microscopes with variable lens illumination

Acoustic Microscope Lens Optimization for Subsurface Imaging

Observation of a sub-surface defect in sapphire by Rayleigh wave reflection in the scanning acoustic microscope

Contact Info

Product

Resources

About