An airborne ultrasonic transducer is generally required to generate high sound pressure in order to realize precise detection and long-range measurement. The purpose of this study is to analyze the vibration mechanism of a piezoceramic transducer and to indicate guidelines for the optimum structure in order to increase the pressure amplitude. We focus our attention on the peak appearance in the pressure response of the transducer. We then clarify, experimentally and numerically, the sound radiation mechanism from vibrational and acoustical points of view. In this report, we present newly observed vibration modes with two peaks and promising schemes for efficiently increasing the sound pressure amplitude.