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

Acoustic waves in liquids are known to have wavelengths comparable to that of visible light if the frequency is in the gigahertz range. The phenomena of Brillouin scattering in liquids is based on such waves. In helium near 2 K acoustic waves with a wavelength of 2000 A were studied some ten years ago at UCLA. It follows from these observations that an imaging system based on acoustic radiation with a resolving power competitive with the optical microscope is within reach if an ideal lens free from aberrations could be found. Such a lens, which was so elusive at the beginning, is now a simple device and it is the basic component in the acoustic microscope that forms the basis for this review. In this article we will establish the characteristic properties of this new instrument. We will review some of the simple properties of acoustic waves and show how a single spherical surface formed at a solid liquid interface can serve as this ideal lens free from aberrations and capable of producing diffraction limited beams. When this is incorporated into a mechanical scanning system and excited with acoustic frequencies in the microwave range images can be recorded with acoustic wavelengths equal to the wavelength of visible light. We will present images that show the elastic properties of specimens selected from the fields of material science, integrated circuits, and cell biology. The information content in these images will often exceed that of the optical micrographs. In the reflection mode we illuminate the smooth surface of a crystalline material with a highly convergent acoustic beam. The reflected field is perturbed in a unique way that is determined by the elastic properties of the reflecting surface and it shows up in the phase of the reflected acoustic field. There is a distinct and characteristic response at the output when the spacing between the object and the lens is varied. This behavior in the acoustic ieflection microscope provides a rather simple and direct means for monitoring the elastic parameters of a solid surface. It is easy to distinguish between different materials, to determine the layer thickness, and to display variations in the elastic constants on a microscopic scale. These features lead us to believe there is a promising future for the field of acoustic microscopy.

/pdf/acoustic-microscopy-with-mechanical-scanning-a-review-3zejr4iazf.pdf

Acoustic microscopy with mechanical scanning&#8212;A review

The scanning acoustic microscope in the reflection mode has proved to be a rather simple and direct means for monitoring the elastic properties of a solid surface. When smooth surfaces of crystalline material are examined in a liquid with a highly convergent sound beam they exhibit a distinct response. This characteristic response, which can be treated as a ’’signature’’, is obtained by recording the output of the microscope as the spacing between the acoustic lens and the object is varied. An angular‐spectrum approach is used to derive an expression for this output in terms of the reflectance function. This function has an angular dependence determined by the bulk constants of the material itself. The expression resulting from this treatment can be used to explain the source of contrast in acoustic images.

/pdf/an-angular-spectrum-approach-to-contrast-in-reflection-48dto03c67.pdf

An angular‐spectrum approach to contrast in reflection acoustic microscopy

We report the use of focused acoustic beams to eject discrete droplets of controlled diameter and velocity from a free‐liquid surface. No nozzles are involved. Droplet formation has been experimentally demonstrated over the frequency range of 5–300 MHz, with corresponding droplet diameters from 300 to 5 μm. The physics of droplet formation is essentially unchanged over this frequency range. For acoustic focusing elements having similar geometries, droplet diameter has been found to scale inversely with the acoustic frequency. A simple model is used to obtain analytical expressions for the key parameters of droplet formation and their scaling with acoustic frequency. Also reported is a more detailed theory which includes the linear propagation of the focused acoustic wave, the coupling of the acoustic fields to the initial surface velocity potential, and the subsequent dynamics of droplet formation. This latter phase is modeled numerically as an incompressible, irrotational process using a boundary integra...

Nozzleless droplet formation with focused acoustic beams

The output voltage of the reflection acoustic microscope depends on the location on the object surface in a way that is characteristic of its elastic properties. We present a ray model showing that this dependence is due to interference between a narrow bundle of axial rays and rays associated with the leaky Rayleigh wave excited on the surface.

Ray interpretation of the material signature in the acoustic microscope

When a polished surface of a single crystal is examined with a converging acoustic beam the reflected signal has a characteristic response that is dependent upon the elastic properties of the reflecting surface. This property can be used in the acoustic microscope to monitor the thickness of layers deposited on these surfaces and the small‐scale variations of the elastic parameters in these materials.

/pdf/phase-imaging-in-reflection-with-the-acoustic-microscope-4nezhm2xh3.pdf

H. K. Wickramasinghe

Papers

Acoustic microscopy with mechanical scanning—A review

Phase imaging in reflection with the acoustic microscope

H. K. Wickramasinghe

Papers

Acoustic microscopy with mechanical scanning&#8212;A review

Phase imaging in reflection with the acoustic microscope

Acoustic microscopy with mechanical scanning—A review