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Ultrasound reflection (R) and transmission (T) from an immersed porous plate of QF-20 (a registered trademark of Filtros, Ferro Corporation) are investigated. Assuming open pores boundary conditions for the theoretical computations, values of the physical constants given by Johnson et al. [D. L. Johnson, D. L. Hemmick, and H. Kojima J. Appl. Phys. 76(1), 115-125 (1994)] are used at first. Comparisons of R and T with experimental results show a discrepancy. It is then assumed that visco-elastic losses exist inside the solid part. When a small imaginary constant part is considered for the bulk moduli, a better fit is obtained between theoretical and experimental values of /R/ and /T/. However, the numerous and very close peaks prevent easy measures of the resonance amplitudes and widths. The transition terms built up from the linear combinations R-T and R+T allow these peaks to be separated. Comparisons between theory and experiments are made. This work validates, in the frequency range where the agreement is good, a method for the location of the symmetrical and antisymmetrical modes of the plate. A discrimination is also possible between modes resulting from the fluid phase motions and from the solid phase motions.

We derive the Debye-series expansion of the normal transmitted plane wave through a water-saturated porous plate. By using relations from Biot's theory, the theoretical transmission coefficient of the plate is related to a limited number of unknown parameters ͑velocity, attenuation coefficient of the fast and slow wave, reflection coefficients at the interfaces of the plate͒. They are determined via a comparison with the experimental transmission coefficient. The measurements show that the attenuation of the dilatational waves scales as the second power of frequency.

Acoustics 08 ParisCalcium phosphate compounds have been studied for biomedical applications due to their chemical and structural similarity to the mineral phase of bone and tooth. The composition, physical and chemical properties, crystal size and morphology of synthetic apatite are extremely sensitive to preparation conditions and sometimes it resulted into non-stoichiometric calcium deficient hydroxyapathite (Hap) powders. The present paper refers to calcinations of calcium phosphate ceramics at 800 and 10000C. The effect of heat treatment were previously investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR), differential thermal analysis (DTA) and thermal gravimetric analysis (TGA). FTIR spectra showed the presence of various PO3_4 and OH-groups present in the powders. Powders compacted and sintered at 800 and 10000C showed an increasing density. The main objective of the paper is a comparison of results obtained by the previous methods to those obtained using the ultrasonic air-coupling technique. Modulated ultrasonic signals of 450 kHz central frequency have been transmitted through the calcium phosphate ceramics specimens. Correlation between signals allowed some conclusions concerning density, attenuation and preparation temperature influence on these specimens. These comparisons and correlation of methods, allow a better characterization of such important materials

A method for estimating the strength of the slow wave in the modes propagating in porous layers is presented. It is based upon expansions on transition terms which are linear combinations of the reflection and transmission coefficients. Suitable forms of these coefficients are needed and it is shown how they can be obtained. Both open pore and sealed pore boundary conditions are investigated. It is shown that the zeroth-order and the first-order terms of the expansions suffice to describe accurately the modes and to estimate the strength of the slow wave. Approximations of the absorption coefficient by the porous layer can be deduced. Angles of incidence above and below the critical angle of the shear wave are considered. Comparisons between theory and experiments for the two types of boundary conditions are presented at normal incidence for the transition terms.