We found experimentally that short monopole ultrasonic pulses can be radiat
ed from a piezoelectric polymer film transducer driven by a step-function v
oltage with a fast rising time and low output impedance. We clarified that
the pulse width of the received ultrasonic monopole pulse depends on the ri
sing time of step-function driving voltage, and is limited by transmission
time (T-h) in the thickness direction of the film.