A 2.5 MHz phased linear array made from stacked piezoelectric composite

Piezoelectric composites have been shown to yield transducers with gain-bandwidth products substantially higher than transducers made from piezoelectric ceramic. The application of composite technology to medical ultrasound arrays has been limited by the low effective dielectric constant of the composite, which results in elements with high electrical impedance. The high electrical impedance leads to a requirement for high transmit voltages and a loss in receiving sensitivity when the element must drive a cable. One solution to this limitation is to stack layers of composite and connect the layers electrically in parallel.. This paper reports on both single layer and stacked composite and arrays made from them. It is shown that the use of single layer composite can yield an array with a well-shaped spectrum and fractional bandwidth between 80% and 90% but the sensitivity is reduced due to electrical mismatch. Results from one and two layer stacked composites are given that show coupling factors over 90% of that achievable with an unstacked composite and an effective dielectric constant consistent with the n/sup 2/ increase predicted. Results from a 2.5 MHz phased linear array built using a novel construction technique in which a 2-2 composite is stacked and diced into a 1-3-like form during the array fabrication process are presented.