2aPAb4. Analysis and optimization of wedge transducers for Lamb wave excitation.

Session: Tuesday Morning, May 14

Time: 9:15

Author: F. Levent Degertekin
Author: Butrus T. Khuri-Yakub
Location: Stanford Univ., E. L. Ginzton Lab., Stanford, CA 94305


Wedge transducers are commonly used to excite and detect Lamb waves in solid plates for NDE purposes. In this paper, the analysis and design of wedge transducers for efficient, single mode Lamb wave excitation in general multilayered anisotropic plates is presented. The incident acoustic field distribution on the surface of the plate due to a wedge transducer with arbitrary apodization is calculated using the angular spectrum method. Then, the particle velocity and stress field distributions in the plate in response to this source is obtained by the surface impedance approach. This field distribution can be expressed as a sum of Lamb wave modes in the structure, since the Lamb waves form an orthogonal mode basis. Once the mode amplitudes are found, the excitation efficiency for the desired Lamb wave mode is calculated. The results indicate a trade-off between efficiency and multimode excitation, as expected. To achieve both high efficiency and single mode excitation, an optimization scheme is used where the parameters involve the frequency of operation, dimension of the wedge, and the apodization function. The results of this analysis are presented for various practical examples.

from ASA 131st Meeting, Indianapolis, May 1996