Vibration mode and relevant ultrasonic applications of ferroelectric single crystals Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT)

Electromechanical coefficients of k_t, k₃₃´ and k₃₃ of (1-x)Pb(Mg_1/3Nb_2/3)O₃-xPbTiO₃ (PMN-PT) single crystals were mainly investigated for various medical ultrasonic applications. The [001] poled PMN-PT wafers exhibit relatively high k_t (62%), which is larger than that (49%) of conventional Pb(Zr_1-x, Ti_x)O₃ (PZT) ceramics. Accordingly, the pulse wave of 2MHz TCD probe manufactured with the PMN-PT wafers show high-quality performances compared with PZT probe. The bandwidth of the PMN-PT probe is 10% broader and its sensitivity is 4dB higher than the PZT probe. The coupling coefficient k₃₃´ is a key indicator for medical linear and phase array ultrasonic transducers. Different orientations and poling directions have benn invenstiaged to optimize the properties of PMN-PT. The optimized cut types of PMN-PT for array applications were obtained and its k₃₃´ ~93%, which is larger than that (70%) of conventional PZT ceramics. The simulations for the linear array transducer show the advancements of PMN-PT single crystals. 25% increased bandwidth is expected compared with PZT arrays. Based on the longitude extension mode (k₃₃), the PMN-PT/Epoxy 1-3 composites were modeled and fabricated. The holistic k_t (> 90%) of the composites far exceeds that of the PZT ceramics (only ~50%). The relatively low acoustic impedance makes the acoustic matching to human tissue much easier. The results would be favorable for single element ultrasonic transducers, especially in Doppler blood flow imaging applications.