On propose une nouvelle methode de caracterisation tres precise des materiaux. On mesure les caracteristiques de propagation des ondes de fuite a la limite entre l'eau et l'echantillon; la vitesse de phase et l'attenuation sont determinees a travers des mesures de la courbe V(z). On presente une methode d'analyse spectrale pour obtenir les proprietes acoustiques a partir des courbes V(z). Description des mesures effectuees en utilisant des materiaux isotropes ou anisotropes pour lesquels les vitesses s'etendent de 2000 a 11000 m/s. On examine tous les modes d'ondes de fuite impliques dans les phenomenes d'interferences dans les courbes V(z). Resultats experimentaux confirmant les resultats theoriques. Application a l'analyse de la structure des materiaux polycristallins

Material Characterization by Line-Focus-Beam Acoustic Microscope

Characterization of Electronic Components by Acoustic Microscopy G. Pfannschmidt. Interaction of Acoustic Waves with Solid Surfaces Y. Tsukahara, et al. Scanning Acoustic Microscopy with Phase Contrast W. Grill, et al. Ultrasonic Focusing with Time Reversal Mirrors M. Fink, C. Prada.

Advances in acoustic microscopy

On utilise l'optique des rayons pour developper des expressions analytiques simples donnant la variation V(z) de la tension de sortie en fonction du deplacement z de la surface de l'objet par rapport au plan focal

Ray-Optical Evaluation of V(z) in the Reflection Acoustic Microscope

The design and fabrication of high frequency poly(vinylidene fluoride) transducers

Non-destructive, nanoscale characterization techniques are needed to understand both synthetic and biological materials. The atomic force microscope uses a force-sensing cantilever with a sharp tip to measure the topography and other properties of surfaces. As the tip is scanned over the surface it experiences attractive and repulsive forces that depend on the chemical and mechanical properties of the sample. Here we show that an atomic force microscope can obtain a range of surface and subsurface information by making use of the nonlinear nanomechanical coupling between the probe and the sample. This technique, which is called mode-synthesizing atomic force microscopy, relies on multi-harmonic forcing of the sample and the probe. A rich spectrum of first- and higher-order couplings is discovered, providing a multitude of new operational modes for force microscopy, and the capabilities of the technique are demonstrated by examining nanofabricated samples and plant cells.

New modes for subsurface atomic force microscopy through nanomechanical coupling

In the reflection-scanning acoustic microscope, interference fringes may be obtained from cracks and grain boundaries running at an angle to the surface. The periodicity of these fringes suggests that while sometimes they are caused by reflection of longitudinal waves within the specimen, when the feature is approximately normal to the surface, Rayleigh waves are responsible, and this confirms the dominant role played by Rayleigh waves in the contrast in acoustic microscopy. The variation of contrast with defocus may be expressed as a Fourier transform of the reflectance function of a specimen; oscillations in V(z) then arise as the transform of the change in phase around the Rayleigh angle. When Rayleigh waves strike a surface-breaking discontinuity, they may be strongly reflected even though the discontinuity is much less than a wavelength thick. This enables fine cracks and other features which would not be resolved according to conventional criteria to be revealed very clearly in acoustic micrographs.

Acoustic Microscopy of Elastic Discontinuities

The contrast obtained with polycrystalline specimens in the scanning acoustic microscope is computed by taking account of the anisotropic stiffness tensor. The resulting variation of signal with defocus is fundamentally different from that which could be obtained with an isotropic material regardless of the values of the elastic properties. In many cases this results largely from the excitation of pseudo-surface waves which effect the response of the microscope in a similar manner to ‘leaky’ Rayleigh waves. The reasons why some materials fail to give good acoustic images of grain structure are discussed.

The effect of elastic anisotropy on contrast in the scanning acoustic microscope

A range of reflection acoustic micrographs that demon- strate how different contrast mechanisms can lead to images useful in materials science are discussed. The most important class of mecha- mism affecting contrast involves disturbance of the leaky Rayleigh wave propagating along the surface of the specimen. Pictures of very fine cracks (considerably smaller than the acoustic wavelength) and regions of plastic deformation can be obtained using this mechanism. The abil- ity of the scanning acoustic microscope (SAM) to image plastic defor- mation is a particularly important application to materials science be- cause there are serious limitations to existing techniques. Useful images may also be obtained in situations where Rayleigh-wave excitation does not predominate; in such cases interference between hulk waves can be responsible for the contrast observed. The conditions necessary for the production of various types of image are discussed, in terms of the elastic properties of and the boundary conditions close to the feature of interest.

Applications of the Scanning Reflection Acoustic Microscope to the Study of Materials Science

Over the past two years transmission and reflection scanning acoustic microscopes have been built at Oxford in collaboration with AERE Harwell. The purpose of our work is to discover applications in materials studies for which acoustic microscopy is suitable, and then to exploit the technique in tackling problems in those areas. The microscopes have been operating for a little under one year now, and in these Proceedings we summarise our progress in that time.

C. Ilett

Papers

Acoustic Microscopy of Elastic Discontinuities

The effect of elastic anisotropy on contrast in the scanning acoustic microscope

Applications of the Scanning Reflection Acoustic Microscope to the Study of Materials Science

Acoustic Microscopy for Materials Studies

Acoustic microscopy of solid materials