High frequency needle ultrasonic transducers based on lead-free Co doped Na0.5Bi4.5Ti4O15 Piezo-Ceramics

Abstract

This paper describes the design, fabrication, and characterization of tightly focused (f-number close to 1) high frequency needle-type transducers based on lead-free Na0.5Bi4.5Ti3.975Co0.025O15 (NBT-Co) piezo-ceramics. The NBT-Co ceramics, are fabricated through solid-state reactions, have a piezoelectric coefficient d33 of 32 pC/N, and an electromechanical coupling factor kt of 35.3%. The high Curie temperature (670 °C) indicates a wide working temperature range. Characterization results show a center frequency of 70.4 MHz and a -6 dB bandwidth of 52.7%. Lateral resolution of 29.8 μm was achieved by scanning a 10 μm tungsten wire target, and axial resolution of 20.8 μm was calculated from the full width at half maximum (FWHM) of the pulse length of the echo. This lead-free ultrasonic transducer has potential applications in high resolution biological imaging.