Transition term method for the analysis of the reflected and the transmitted acoustic signals from water-saturated porous plates

Ultrasound reflection (R) and transmission (T) from an immersed porous plate of QF-20 (a registered trademark of Filtros((R)), 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 vertical bar R vertical bar and vertical bar T vertical bar. 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. (c) 2007 Acoustical Society of America.