Determination of nearfield-farfield boundary and ultrasonic wave propagation on cylindrical shells

Abstract

Determination of the nearfield-farfield boundary for a transducer of 1-MC and 1-inch diameter in water was performed from the measurement of the on-axis ultrasonic echo height using a finite size reflector. The boundary moved farther compared with the point field calculation. The last minimum position moved nearer. In contrast to the point field there was no real zero field. The result of our numerical simulation agreed well with the experiment in the farfield reasion. The ultrasonic wave propagation on the pyrex-glass cylindrical shells was investigated in water using the pulse-echo method. The shells were of 6 kinds with different inner radius b and outer radius a. There was a series of periodic echoes following the specular reflection echo. These echoes were direct verification of the existence of the "circumferential" or "Creeping" waves. For the available b/a-region, i.e., 0.84 b/a 0.95, the velocity was almost constant for 0.5<FH(frequency thickness)＜2.0, and decreased almost linearly for 2.0＜FH 4.5. There was no clear b/a-dependence. All the result agreed well with the numerical work of Breitenbach et al. The attenuation increased as FH increased for 2.0＜FH＜4.5 and stayed constant for 0.5＜FH＜2.0. The point FH=2.0 played a crucial reference in the above two set of results.