The purpose of the School, the content of which is reflected in this book, is to bring together experiences and knowledge of those acousticians who are particularly sensible to materials and their properties, specifically to those materials that may be called inhomo geneous. The two things together: acoustics and inhomogeneity, define factually a dimension less parameter, AI a, which is the ratio between the sound wavelength and the spatial length of the material where its physical characteristics notably change. An implicit defmition is, therefore, at hand for an inhomogeneous medium, which has the characteristic of a condi tioned definition and sets a looser constraint to the otherwise strict statement of invariance under translations. Composite, biologicai, porous, stratified materials are in the list of inhomogeneous materials, whose technological or structural interest has grown greatly in recent times. Ul trasonic waves offer a means for their investigation, which is valuable for it can be non destructive, continuous in time, spatially localized, dependent on the size of inhomoge neities.

Proceedings of the NATO Advanced Study Institute, Erice, Italy, October 15-25, 1985

Inhalt
I. General.- Anisotropic material orientation with ultrasonics.- Thin film and layer characterization.- Determination of linear and nonlinear parameters of thin layers.- Measurement of the coherent and incoherent contributions of ultrasonic scattering in inhomogeneous media.- Amplitude and phase fluctuations in ultrasonic waves propagating in inhomogeneous materials.- Acoustooptical interaction in optically active media.- II. Methods.- Inhomogeneous materials studied with Brillouin scattering.- Characterisation through thermal waves: applications of optoacoustic and photothermal methods.- Cryogenic acoustic microscopy.- Composite material systems for surface wave integrated optic Bragg cells.- Quantum field theory methods in studies of ultrasonic waves propagation in random media.- Characterisation of microstructures using ultrasonics.- Study of the dislocation dynamics by ultrasonic cyclic bias stress experiments.- Analysis of signals generated by multiply reflected ultrasonic waves in plates.- Flaw classification in composites using ultrasonic echography.- Application of light diffraction by a system consisting of an ultrasonic wave and a phase optical diffraction grating.- III. Materials.- Three-dimensional composites.- Piezoelectric materials.- Physical and elastic characteristics of fiber reinforced composites.- Ultrasonic evaluation of elastic properties of directional fiber reinforced composites.- Characterisation of porous media with elastic waves.- Tissue characterisation by linear and non-linear ultrasound.- Wood characterisation through ultrasonic waves.- Measurement of the permeability of a porous plate by an ultrasonic test.- Laser generated ultrasonic waves for the investigation of porous solids.- Ultrasonic determination of texture and residual stress in polycrystalline metals.- Harmonic waves in three-directional carbon-carbon composites.- Ultrasonic quantum oscillations in semimetallic Bi1?x Sbx alloys.- List of participants.