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.