A kerfless dual-layer transducer combined with beamforming by spatial matched filtering for high frame rate ultrasound imaging

Dicing is typically required to create elements for array transducers made with piezoelectric ceramics. Kerfs, which are the cutting spaces generated during dicing, are introduced to prevent electrical and mechanical coupling, or cross-talk, between adjacent elements. Unfortunately, this dicing procedure can be very difficult and challenging, especially for high-frequency array transducers (> 30 MHz) because of the fine element spacing and small kerf requirements. In this work, we introduced the design, fabrication, and preliminary imaging using a transducer that does not require dicing of elements. The structure of this transducer is a dual-layer design, which has separate layers for transmit and receive respectively. A piece of un-diced PZT-5H ceramic was used as the transmitter that launched plane waves directly ahead. A sheet of P[VDF-TrFE] copolymer served as the receiver. In addition to simplifying the fabrication procedure, this kerfless dual-layer transducer also enables high frame rate imaging of the system because of the plane wave transmissions. However, the image quality of the transducer was intrinsically degraded due to the loss of transmit focusing capability. In order to compensate for the degradation, beamforming by spatial matched filtering (SMF), which is capable of dynamically focusing both the transmit and receive beams, was implemented to replace the conventional delay-and-sum (DAS) beamforming onto the kerfless transducer.