Near point-source longitudinal and transverse mode ultrasonic arrays for material characterization.

Specially constructed near point-source ultrasonic transducers (0.75 MHz) were designed to preferentially stimulate and receive the one longitudinal (P) and two transverse (S) propagation modes. Arrays of these transducers were placed on a rectangular prism of common sodalime glass, which served as an ideal homogeneous, isotropic medium, to evaluate the uncertainty of a newly developed phase velocity measurement method. Through the use of the Radon transform, the data were transformed from the offset-time (x-t) domain to the intercept time--horizontal slowness (tau-p) domain. From the shape of the curves in the tau-p domain, the phase velocity of the propagating waves may be determined for a range of directions. The phase velocities determined using this method were accurate for incidence angles up to 76 degrees, 64 degrees, and 77 degrees for the P, SV, and SH wave modes, respectively. Phase velocities of 5724 +/- 64, 3411 +/- 30, and 3467 +/- 15 m/s were determined for the P-wave, SV-wave, and SH-wave modes, respectively. This agrees with the direct transmission P-wave and S-wave velocities of 5690 +/- 60 and 3440 +/- 26 m/s, respectively, to better than 1%.