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This paper describes development of a novel, high efficiency transducer for use in ultrasonic flow meters. It is based on conversion of energy between surface acoustic waves (SAWs) and bulk acoustic wave (BAWs). The transducer consists of thin plate of a suitable piezoelectric material whose SAW velocity is greater than velocity of BAW in the fluid. Under these conditions a surface wave traveling on the substrate radiates a bulk acoustic wave in the fluid. We show that with proper design efficient conversion of energy from SAW to BAW and vice versa can be obtained. For example. using lead zirconate titanate (PZT) as the piezoelectric material and water as the fluid, total conversion loss (SAW to BAW and back from BAW to SAW) of less than 3 dB has been obtained.