抄録
Pulse-echo-overlap method has been applied to detect the phase advance due to diffraction. Two quartz transducers with electrodes 5mm in radius have been used for a transmitter-receiver system with one-way path length 62mm. Experiment has been made at 3MHz and 9MHz in methanol-water mixture as varying its concentration. Roundtrip travel time obtained at 3MHz is by 14.5ns shorter than the value at 9MHz when the velocity is 1497m/s. The difference in reciprocal of the travel time has been detected and plotted as a function of velocity. Outline of the results is described well by diffraction theory. The experimental curve has, however, small peaks occurring periodically, which can not be predicted with diffraction theory nor with wave-guide theory. Further experiment made using a cell with larger inner diameter suggests these peaks are some what related to the limited space of sound propagation, but clear explanation has not been given.
