### ASA 128th Meeting - Austin, Texas - 1994 Nov 28 .. Dec 02

## 5aPA11. An asymptotic model for compressional and shear wave excitation in
plates by ultrasonic transducers.

**Smaine Zeroug
**

**
Fred E. Stanke
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*Schlumberger-Doll Res., Old Quarry Rd., Ridgefield, CT 06877
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Pulsed beams excited and detected by ultrasonic transducers are routinely
used to characterize elastic structures. An efficient model for
transducer--structure interactions is presented and applied to transmission
through a fluid-loaded plate with a transmitter--receiver pair. Each transducer
is modeled as several complex-transducer points (CTPs) [Zeroug et al., Review
of Progress in QNDE, edited by Thompson and Chimenti (Plenum, New York, 1994),
Vol. 13], which behave as reciprocal, electroacoustic quasi-Gaussian
transducers. The interaction of each CTP transmitter--receiver pair with the
plate is solved by wave-number spectral decomposition and ray expansions,
resulting in a sum of multiply reflected beams propagating within the plate.
The resulting time-harmonic beam integrals are approximated asymptotically and
transformed to the time domain to yield the received voltage as a finite sum of
multiply reflected compressional (P), shear (S), and coupled (P--S) arrivals.
Comparison with experiments shows that (a) three CTPs accurately model the flat
circular transducers, (b) the efficient asymptotic solution is accurate when
the observed arrivals are distinct in time, and (c) at normal incidence, the S
and P--S arrivals which are excited by the transducers' finite spectrum
necessitate higher-order asymptotic expansions. This approach can be
generalized to transducers' arbitrary orientation, multilayered and cylindrical
configurations.