The wedged transducer - A transducer design for broad band characteristics

A method of increasing the bandwidth of transducers feeding low acoustic impedance loads such as fluids and of electrically matching them over the full bandwidth is presented. The method consists of interposing a wedge made of material with the desired acoustic impedance between the transducer and the actual load. The wedge angle is so chosen that no reflected wave from the wedge-load interface can return to the transducer. Thus, the effective load seen by the transducer is that of the wedge itself, regardless of the actual load. The electrical matching is achieved by means of a hybrid band pass filter containing electrical and mechanical components, with the transducer as an integral part. Experimental results on a 4-in. diameter transducer, coupled to water through a brass wedge, demonstrated a bandwidth of 75% and an insertion loss of 8.5 dB in accordance with theory.