### ASA 125th Meeting Ottawa 1993 May

## 2aPA2. Experimental observation of bending wave localization.

**George Cody
**

**
Ling Ye
**

**
Minyai Zhou
**

**
Ping Sheng
**

**
**
*Exxon Res. & Eng. Co., Rte. 22 East, Annadale, NJ 08801
*

*
*
**Andrew N. Norris
**

**
**
*Rutgers University, Piscataway, NJ 08855
*

*
*
Localization of bending waves has been observed for the first time for
two-dimensional (2D) acoustic wave propagation in an inhomogeneous composite
system consisting of a steel plate decorated with two sets of randomly attached
Lucite blocks. A significant experimental feature of the localized modes is an
exponentially decay of the mode intensity from their peaked centers, with a
decay length that increases as (f[sub 0]-f)[sup -1] when the mode frequency f
approaches a quasimobility edge f[sub 0]. The minimum attenuation length is of
the order of a block diagonal and is about 40% of the banding wave's
wavelength. The experimental data, as well as results of finite-element
calculations, identify the source of the localization phenomenon as strong
scattering of the bending wave by shear and flexural resonances of the Lucite
blocks. This result supports theoretical predictions that resonant scattering
enhances localization [cf. Scattering and Localization of Classical Waves in
Random Media, edited by P. Sheng (World Scientific, Singapore, 1990)]. Recent
experiments on acoustic wave propagation in rough composite steel/refractory
walls also exhibit exponential localization at frequencies corresponding to 3-D
propagation. The experimental data suggest that a composite plate is a unique
vehicle for the study of classical localization: at low frequencies, in 2-D
and, at higher frequencies, in 3-D. The generic nature of the localization
phenomenon suggests its application as a tunable attenuation mechanism for
bending waves