High Frequency Needle Ultrasonic Transducers Based on Lead-Free Co Doped Na(0.5)Bi(4.5)Ti(4)O(15) Piezo-Ceramics

This paper describes the design, fabrication, and characterization of tightly focused (ƒ-number close to 1) high frequency needle-type transducers based on lead-free Na(0.5)Bi(4.5)Ti(3.975)Co(0.025)O(15) (NBT-Co) piezo-ceramics. The NBT-Co ceramics, are fabricated through solid-state reactions, have a piezoelectric coefficient d(33) of 32 pC/N, and an electromechanical coupling factor k(t) 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.