Design,Fabrication And Evaluation Of Medical Piezoelectric Ultrasonic Transducer With Magnesium Alloy Matching Layer

For an ultrasonic image system,the ultrasonic transducer plays a critical role,which determines the quality of ultimate images.The basic structure of a transducer includes the piezoelectric material,backing and matching layers.For the first time,this paper attempts to apply magnesium alloys as the matching layer material of medical piezoelectric ultrasonic transducer.Firstly,the acoustic performance of magnesium alloy was systematically tested.Then,the planar piezoelectric ultrasonic transducers with magnesium alloy as the matching layer were designed and prepared.The influence of the matching layer of magnesium alloy on the performance of the transducer;finally,the multi-physics coupled finite element simulation calculation was used to optimize the design of the focused piezoelectric ultrasonic transducer,which provides support for the preparation of higher performance medical piezoelectric ultrasonic transducers.The AZ31 B,GW83 and ZK60 wrought magnesium alloys in different states were selected and their sound velocity in different directions were measured by ultrasonic method.The results show that the sound speeds of magnesium alloys with different compositions and states are isotropy and similar,about 5800 m/s.The elastic matrixes of three magnesium alloys were established.The acoustic impedance values of the three magnesium alloys were all about 10 MRayl,and the acoustic attenuation coefficient at 7.5 MHz was about 0.02 dB/mm,much smaller than that of conventional composite material,showing superiority as matching layer materials in ultrasonic transducer application.Based on the Krimholtz-Leedom-Matthae(KLM)model,planar PZT-5H medical piezoelectric ultrasonic transducers with AZ31 B magnesium alloy as the first matching layer were designed and fabricated.The center frequency,bandwidth,and insertion loss of the 5 MHz transducer are 4.60 MHz,79%,and-11.11 dB,respectively.The center frequency,bandwidth,and insertion loss of the 10 MHz transducer are 9.25 MHz,71% and-14.43 dB,respectively.Compared with transducers using conventional composite matching layers,transducers with AZ31 B magnesium alloy as the matching layer have a wider bandwidth,a much smaller insertion loss,showing better performance.Coupled finite element software COMSOL Multiphysics was used to simulate the focused PZT-5H piezoelectric ultrasonic transducers with a frequency of 5 MHz and the diameter of the piezoelectric element is 4 mm.The simulation results show that as the radius of curvature increases,the focal length of the focused ultrasonic transducer increases,and depth range of focused cylinder increases;the density of the acoustic energy at the focus decreases,the width of the acoustic beam increases,and the lateral resolution gradually decreases.The focusing transducer with a radius of curvature of 4.5 mm shows the best overall performance with a focal length of 10.45 mm and an acoustic energy density of 337% higher than that of the planar transducer at the focus;the beam width is 0.91 mm,48.7% of the planar transducer;the maximum sidelobe level is 6.38 dB lower than that of the planar type,which is expected to greatly improve the sensitivity and lateral resolution of the ultrasonic transducer.