The development of a miniature, high efficiency transducer for use in ultrasonic flow meters is described. The transducer is based on coupling of energy between Plate Acoustic Waves (PAWs) and Bulk Acoustic Waves (BAWs). It consists of a thin plate of a suitable piezoelectric material on which Inter Digital Transducers (IDTs) are fabricated to generate and detect plate acoustic waves. It is shown that with proper design efficient conversion of energy from PAW to BAW and vice versa can be obtained. For example, using the fundamental anti symmetric plate wave mode (A0 mode) propagating in a lithium niobate substrate and water as the fluid, total conversion loss (PAW to BAW and back from BAW to PAW) of less than 6 dB has been obtained.