Relaxor Ferroelectric Single Crystals PMNT And Their Applications In Medical Phased Array Ultrasonic Transducers

PMNT(Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃)relaxor ferroelectric single crystal as a representative of the high performance of piezoelectric materials,can considerably increase the sensitivity and bandwidth of the ultrasonic transducer and thus improve the quality of the ultrasonic imaging.However,the uneven performance of piezoelectric properties of single crystals which grow along[111]direction restrict the applications of the array ultrasonic transducers for a long time.More recently,the large size,high uniformity of[001]-oriented single crystals laid a solid foundation for the construction of the array ultrasonic transducer.However,there are many scientific problems such as characterization and optimization of the properties of single crystals,electrical matching and acoustic matching between acoustic materials etc.,indicating that the fabrication of the array ultrasonic transducer has become the"bottleneck"of the development of the medical ultrasonic imaging equipment in our country.The main works of this paper are the characterization and application of relaxor ferroelectric single crystals in medical phased array ultrasonic transducers,the specific research results summarized as follows:The field-induced phase transition behavior and the dielectric,piezoelectric,and ferroelectric properties of the poled PIMNT-Mn single crystals were investigated.The poled single crystals exhibit three apparent ferroelectric phase transitions around120?(T_R-M)?145?(T_M-T)?170?(T_T-C),respectively.And the path of phase transition was R-M-T-C.In addition,the evolution of the phase transition is a continuous process rather than a mutation process,which suggests the coexistence of multiphase.The performance parameters of the PIMNT-Mn single crystals,including the longitudinal electrostrictive coefficient?Q?,the converse piezoelectric constant(d₃₃),and the maximum strain value(S_max%)have changed abnormally around the phase transition temperatures(T_R-M and T_M-T).For the application of[001]-oriented single crystal in phased array ultrasonic transducer,the size effect and the modes of vibration of the single crystal were investigated.The mode of vibration of the piezoelectric vibrator is the height-extensional mode,and the electromechanical coupling coefficient k₃'₃ keeps at0.86⁰.87 when the aspect ratio G<0.7.However,when the aspect ratio further increased,k'₃₃ has decreased obviously and the lateral-tensional mode increased significantly.The 3MHz phased array ultrasonic transducers which used single crystal show higher-6dB bandwidth?27.7%?,relative sensitivity?5.2dB?,and lower pulse length?0.19?s?compared to the PZT-based ultrasonic transducer.In addition,PMNT-based array ultrasonic transducers possess good performance of consistency,indicating that PMNT-based ultrasonic transducers are the promising application in the medical ultrasonic imaging.The-6d B bandwidth and the relative sensitivity of the 2.7MHz PMNT-based phased array ultrasonic transducers are 83.5%,-27dB,respectively.The 2.7MHz PMNT-based array transducers possess better-6dB bandwidth?10%?and relative sensitivity?4.5dB?compared to commercial domestic phased array transducers.In addition,the properties of the PMNT-based array transducers is consistent with the single crystal array transducers which developed by Philips company.