Ultrasonic excitation and detection of capillary waves for the measurement of surface film properties

摘要

A 10 MHz focused ultrasonic transducer is used to excite capillary waves by placing its focus at the airhyphen;water interface and using a tone burst to excite the ultrasonic wave. The radiation pressure associated with the upward propagating ultrasonic pulse lifts the surface of the water which then relaxes by exciting a radially propagating capillary wave. An amplitude and phase measuring acoustic microscope operating at 10 MHz is used to detect the amplitude and slope of the capillary wave as it propagates over the focused transducer of the acoustic microscope. This arrangement allows us to make a noncontacting measurement of surface tension and surface viscosity which will be used for characterizing surface films, such as the marine microlayer.