Transducer design for high-efficient acoustic droplet ejection

Acoustic droplet ejection (ADE) has the advantage of mitigating cross-contamination and reducing cost for high-throughput liquid transfer. The ultrasound transducer design is important for the ADE systems. However, the commonly used systems with single-element focused transducer requires mechanical operation for focusing at different liquid surfaces positions, resulting into low liquid transfer efficiency. In this study, we designed a 15MHz annular array transducer enabling electronic focusing in axial direction, thereby allowing high efficient positioning of the liquid surfaces without mechanical operation. The proposed array element has a center frequency of 15.1MHz and a bandwidth of 88%. Transducer characterization results demonstrate the annular array has the ability of focusing at different depths, which enables high-efficient droplet ejection and liquid transfer.