Fabrication And Acoustic Field Characteristics Of High Performance Single Element Piezoelectric Ultrasonic Transducer

Ultrasound imaging diagnosis technology is an important non-destructive testing technology,which has the advantages of safety and high efficiency.In the medical field,it is known as the four major medical imaging diagnosis technologies together with X-ray imaging,nuclear magnetic resonance imaging and computerized tomography.Single element piezoelectric ultrasonic transducer plays an important role in medical ultrasonic system,whose development trend is high performance,high application temperature and high frequency.The development of single-element ultrasonic transducer puts forward urgent needs for piezoelectric materials with high electrical constant,high electromechanical coupling performance and high Curie temperature.Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃（PMN-PT）single crystal is one of the most excellent piezoelectric materials with piezoelectric constant d₃₃ of 2500 pC/N and electromechanical coupling coefficient k₃₃ of 94%.PMN-PH-PT piezoelectric ceramics have high Curie temperature and piezoelectric properties.In this paper,the piezoelectric properties of PMN-PT single crystal and PMN-PH-PT piezoelectric ceramics are studied,and a new type of single element ultrasonic transducer with high performance,high frequency and high application temperature is prepared.PMN-0.3PT relaxor ferroelectric single crystal and Epoxy were used to fabricate1-3 composite piezoelectric materials.The finite element model and performance simulation method of PMN-PT single crystal/Epoxy 1-3 piezoelectric composites were established by using COMSOL multi physical field coupling software.The PMN-PT single crystal/Epoxy 1-3 piezoelectric composites with high performance and high frequency were prepared by dice and fill method The resonant frequency of thickness stretching vibration mode is 47.53 MHz,and the electromechanical coupling coefficient k_t is higher than 67.3%.The model of high performance and high frequency PMN-PT single crystal/Epoxy1-3 piezoelectric composite ultrasonic transducer was established.The acoustic impedance and matching thickness parameters of backing layer,piezoelectric composite element and front matching layer were designed and optimized by using KLM equivalent circuit model and acoustic transmission line theory.The fabrication process of matching layer,backing layer and matching layer thinning was optimized.A single element piezoelectric ultrasonic transducer with high performance,high working frequency and wide bandwidth for nondestructive testing and medical high-frequency ultrasound applications was fabricated by using E-solder 3022 as the backing layer and parylene as the front matching layer.The center frequency of the transducer is 42.5 MHz,the bandwidth of-6 dB is 90.6%,the insertion loss is only16 dB,and the emission sensitivity is 314m V/V.The acoustic distribution of the ultrasonic transducer in the water is analyzed by the ultrasonic field test instrument.The focal length of the ultrasonic transducer is 2.3mm,the acoustic beam width of-3 dB is 0.38 mm×0.42 mm,and the acoustic radiation power is 4.4×10^-3m W.The high sensitivity,wide bandwidth,high working frequency and excellent acoustic characteristics of the single element ultrasonic transducer indicate that the PMN-PT single crystal/Epoxy 1-3 piezoelectric composite ultrasonic transducer prepared by the dice and fill method has important application value in the fields of nondestructive testing,high frequency ultrasonic electronics and biomedicine.The dielectric constant,piezoelectric constant d₃₃ and Curie temperature T_c of0.15PMN-0.38PH-0.47PT piezoelectric ceramics are 1968,447 p C/N and 297℃,respectively It is found that the electromechanical coupling coefficient of the thickness stretching vibration mode of the piezoelectric ceramic at room temperature is as high as 56.9%,The stability of PMN-PH-PT ceramics is maintained from room temperature to 200℃.PiezoCAD software is used to design another single element ultrasonic transducer based on PMN-PH-PT piezoelectric ceramics.The working frequency,bandwidth and sensitivity characteristics are simulated and analyzed.The high Curie temperature PMN-PH-PT piezoelectric ceramics act as piezoelectric vibrator,the matching layer and backing layer are optimized,and the thickness stretching vibration mode single element piezoelectric ultrasonic transducer is prepared.The center frequency of the transducer is 2.15 MHz,the bandwidth of-6 dB is 79.07%,and the insertion loss is-31.75 dB.The focal length of the transducer is about 47 mm,the beam width of-3dB is 3.5 mm×3.6 mm,the beam area is 9.83 mm²,and the acoustic radiation power is17.98 m W.The high piezoelectric properties of PMN-PH-PT piezoelectric ceramics are expected to fabricate novel ultrasonic transducer with high performance and high service temperature.