High-Frequency Ultrasonic Imaging with Lead-free (Na,K)(Nb,Ta)O3 Single Crystal

Lead-free (Na,K)(Nb,Ta)O-3 (KNNT) piezoelectric single crystal has been successfully grown using the top-seeded solution growth technique. The electromechanical coupling factors are very high (k(33) = 0.827, k(t) = 0.646), and the dielectric loss tangent is as low as 0.004. Acoustic impedance was calculated to be 26.5 MRayl. From the single crystal, a single element transducer was fabricated. The transducer achieved a 57.6% -6 dB bandwidth and 32.3 mu m axial resolution at the center frequency of 45.4 MHz, which can identify the cornea of porcine eyeball with high resolution. Comparison between KNNT single crystal and lead-based single crystal was discussed. The results suggest that this single crystal transducer is an excellent candidate to replace lead-containing transducer for high-frequency ultrasonic imaging applications.