Elevation focusing of a phased array using variable ultrasound propagation speed in inter-mediate layer

1.5D arrays have the advantage in dynamically focusing the array in elevation. However, they have the drawback that they require many more beamforming channels and connections than 1D arrays. A transducer with lens having electrorheological fluid has been proposed as another method of dynamic elevation focusing. To the author´s knowledge, however, few publications on this method have appeared in the literature. We have therefore experimentally investigated the elevation focusing of a phased array by using variable ultrasound propagation speed in inter-mediate layer. Piezoelectric material whose elastic stiffness is dependent on loaded electrical impedance was used as inter-mediate layer for controlling the ultrasound propagation speed. We have fabricated a 3.0MHz phased array with 8 inter-mediate layer rows in elevation. The ultrasound propagation speed in each row can be independently controlled. We have verified that these inter-mediate layer rows function as effective elevation focusing. In this paper, the theory and the method of using variable ultrasound propagation speed in inter-mediate layer are presented. Measurements from this phased array are compared with those from a 3.0 MHz phased array with conventional lens.