ASA 126th Meeting Denver 1993 October 4-8

2pPA3. High-frequency (10--25-MHz) wave propagation in argon at pressures up to 10 MPa.

C-H. Chiang L. J. Bond

Ctr. for Acoust., Mech. and Mater., Univ. of Colorado, Campus Box 427, Boulder, CO 80309-0427

Acoustic wave propagation in gaseous argon has been investigated using a high-power ultrasonic gated-tone-burst transmission system. Results of measurements of compression wave absorption and velocity in argon at frequencies 10 to 25 MHz, at static pressures up to 10 MPa, at temperatures of 21 to 23 (degrees)C, and at high power (above critical intensity 16.97 W/m[sup 2] at 10 MHz and 10 MPa) are presented. For small-amplitude waves at pressures up to 2 MPa, the resulting data are in good agreement with that predicted using ideal gas equations and fundamental thermophysical gas constants. At static pressures higher than 4 MPa and for higher-power settings, distortion of the waveform is observed. Excess attenuation, in addition to classical absorption, is also found at higher power settings. With a 10-MHz fundamental frequency, significant second harmonic generation is observed. The data are compared with existing theories for finite-amplitude waves in fluids. Current theories [F. Dunn et al., IEEE Ultrason. Symp., 527--532 (1981); A. L. Thuras et al., J. Acoust. Soc. Am. 6, 173--180 (1935)] for harmonic generation and attenuation are shown not to predict the observed experimental data for high-power, high-frequency waves in argon at high pressure.