A simple method for generating the monopole ultrasonic pulse and its sound field

The cycloid function voltage having no resonant component is applied to the piezo-ceramic planar and concave circular transducers to generate the monopole ultrasonic pulse. On-axis pressure characteristics of two kinds of transducer are observed using monopole ultrasonic pulse. As the experimental results, 1) the sound field of monopole ultrasonic pulse is consisted of direct wave and edge wave, and these are separated in time near the transducer, 2) the monopole ultrasonic pulse from a planar transducer becomes bipolar pulse in the large distance from the transducer and 3) in case of the concave transducer, the monopole ultrasonic pulse is gradually changed to the bipolar pulse around the focus, are clearly observed. These experimental results can be explained by the interference between direct wave and edge wave using monopole ultrasonic pulse. A possibilities of the diffraction effect which dominated at the focus of concave transducer is also suggested.