A Micromachined Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ Single Crystal Composite Circular Array for Intravascular Ultrasound Imaging

This paper describes the design, fabrication, and characterization of a micromachined high-frequency Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ (PMN-PT) single crystal/epoxy 1–3 composite ultrasound circular array. The 1–3 composites were fabricated by deep reactive ion etching (DRIE) of PMN-PT single crystal. The feature size of single crystal pillars was 18 μm in diameter. The kerf between pillars was less than 4 μm. A 50-element circular array transducer (radially outward) with the pitch of 100 μm was wrapped around a needle resulting in an outer diameter of 1.7 mm. The array test showed that the center frequency reached 39±2 MHz and −6-dB fractional bandwidth was 82±6%. The insertion loss was −41 dB, and crosstalk between adjacent elements was −24 dB. A radial outward imaging testing with phantom wires (D = 50 μm) was conducted. The image was in a dynamic range of 30 dB to show a penetration depth of 6 mm by using the synthetic aperture method. The −6-dB beam width was estimated to be 60 μm in the axial direction at 3.1 mm distance away from the probe. The results suggest that the 40 MHz micromachined 1–3 composite circular array is promising for intravascular ultrasound (IVUS) imaging applications.