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

Lead-free (Na,K)(Nb,Ta)O₃ (KNNT) piezoelectric single crystal has been successfully grown using the top-seeded solution growth technique. The electromechanical coupling factors are very high ( k₃₃ = 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 µm 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.