Focused 20 MHz single-crystal piezocomposite ultrasound array

Lead-based piezoelectric single crystals such as PZN-PT and PMN-PT have been first developed for under water applications by the U.S. Navy. Their outstanding piezoelectric properties (d33 as high as 2000 pC/N and k33 > 90%) make them valuable for high-end ultrasound transducers. Thus, they have been successfully used and commercialized in medical field mainly for cardiac imaging (2-5 MHz) but manufacturing such a probe is critical since single crystal structures are more sensitive to thermal and mechanical stresses induced by standard micromachining process. We propose in this paper to manufacture a high frequency ultrasound probe (15-20 MHz) based on very thin 1-3 single crystal composite materials (<70 ¿m thick) using low-stressing machining process and exhibiting improved electroacoustical performances. This paper presents the acoustical design, fabrication and evaluation of an ultrasound array based on single crystal piezocomposite. The array specifications were a 3 mm elevation, 100 ¿m pitch, 20 MHz center frequency. We demonstrate the feasibility to produce a PMN-PT single crystal probe with suitable performances for high resolution imaging. A complete electro-acoustical characterization has been done: bandwidth, directivity and pressure performances are then discussed and compared to classical PZT probes with the same specifications. Performances are compared to those obtained with state-of-the-art piezocomposite transducers, achieving competitive bandwidth and an improvement of +6 dB in sensitivity.