Effect of alignment of phases in a 2-2 based dual layer high bandwidth transducer

The advent of harmonic imaging in medical diagnostic ultrasound has resulted in significantly increased demands on transducer bandwidth. One approach to satisfying this demand is to operate a dual layer transducer in a phased layer mode of operation. It has been shown in the literature that post alignment is critical to good response in stacked 1:3 composite transducer arrays. In order to easily facilitate electrical connection to the inner layer it is frequently preferable to use a 2-2 structure since then it is easier to assure electrode continuity in one dimension right through the internal portion of the transducer. Therefore, we have investigated the effect of ceramic strip alignment in stacked 2-2 transducers comprising 92% PZT-5H type ceramic. One transducer was made with perfect ceramic strip alignment and one with half pitch misalignment - ´perfect misalignment´. It was observed that the misalignment had no material impact on transducer performance. We hypothesize that if a high ceramic volume fraction 2-2 transducer is stacked then if the ceramic strips adequately ´bridge´ the kerf gaps (as they typically do at high ceramic volume fractions), and if a very. fine bond-layer is employed, then ceramic strip alignment is of secondary importance