Ultrasonic beam reflection from fluid-loaded cylindrical shells

The interaction of ultrasonic acoustic transducers with cylindrical shells in pitch-catch mode has been measured and predicted using a two-dimensional theoretical model. The measurements of the received voltage amplitude at selected frequencies and incidence angles are presented as a function of scanned angular position at fixed radius and beam launch angle. In the forward model, the received voltage is expressed in terms of a spectral integral whose integrand contains the spectral amplitudes of the transmitter and the receiver, and a spectral global reflection coefficient that accounts for the pressure wave interaction with the fluid-or air-loaded shell. The transmitter and receiver are modeled using the complex-transducer-point technique to simulate emitting and receiving electro-acoustic transducers with Gaussian profiles. The receiver voltage integral is reduced by uniform high-frequency saddle point asymptotics to closed form solutions for the dominant contributions from the specular reflected and (excited) leaky wave fields. We find generally good agreement between the model prediction and the experimental results, particularly near the voltage maximum. Experimental data are also shown for a solid cylinder, demonstrating in a time-angle plot the existence of whispering gallery modes, which is verified analytically. (C) 1998 American Institute of Physics.