On-axis ultrasonic field characteristics of monopole pulse radiated from planar and concave transducers

Monopole ultrasonic pulses having different pulse widths are generated from the piezo-ceramic planar and concave circular transducers using the cycloid function voltages with different rise time as an exciting voltage. The on-axis pressure characteristics of the monopole ultrasonic pulse are observed. As the experimental results, the monopole ultrasonic pulse radiated from a planar transducer is changed to the bipolar pulse by the interference between direct wave and edge wave. The limit of distance for near field of the monopole ultrasonic pulse varies with the pulse width. In case of the concave transducer, the main cause of the change from monopole ultrasonic pulse to bipolar one around the focus is estimated by the diffraction effect of direct wave. The position of the maximum amplitude of the on-axis pressure moved from the center of the curvature with the difference of the pulse widths is also observed.