ASA 129th Meeting - Washington, DC - 1995 May 30 .. Jun 06

2pEA5. Axial shear wave transducer constructed of a piezoelectric continuously twisted structurally chiral medium.

Steven F. Nagle

Akhlesh Lakhtakia

Dept. of Eng. Sci. and Mech., Penn State Univ., University Park, PA 16802-1401

The material properties of a piezoelectric continuously twisted structurally chiral medium (PCTSCM) vary helicoidally along the axial direction. The quasielectrostatic approximation was implemented for axial propagation modes in PCTSCMs [S. F. Nagle and A. Lakhtakia, J. Acoust. Soc. Am. 96, 3226(A) (1994)]. The following conclusions were drawn: Axial propagation of shear modes is affected by piezoelectric stiffening. Axial propagation displays selective attenuation and the frequency response was classified into three zones: A zone of no attenuation and two handednesses (zone I); a zone of selective attenuation (zone II); and a zone of no attenuation and one handedness (zone III). Now, a boundary value problem is presented to model a future PCTSCM transducer. Linear excitation of a PCTSCM transducer is accomplished through the usual application of a potential difference across the two faces of a thin film realization. It is shown that such a transducer would launch linearly polarized shear waves with controlled polarization. Within the transducer, the polarization does not, in general, follow the material inhomogeneity. Shear wave characteristics are dependent on the specific frequency response zone (see above) in which the transducer is operated. [Work supported by NSF Graduate Fellowship.]