Study On Bismuth-layered Sodium Bismuth Titanate-based Piezoelectric Ceramic High-frequency Ultrasonic Transducer

Bismuth-layered structured ceramics Na0.5Bi4.5Ti4O15(NBT)has attracted much attention because of its characteristic advantages such as low dielectric constant,low dielectric loss,high mechanical quality factor,high Curie temperature,good fatigue resistance and temperature stability.However,low piezoelectric activity and poor electromechanical properties limit further practical applications of the material.The multi-doped Na0.5Bi4.5Ti4O15 piezoelectric ceramic developed by our group make up for the performance disadvantages of this ceramic to a certain extent.On this basis,an ultrasonic transducer for high-frequency ultrasound imaging was prepared for the advantages of low dielectric constant and low dielectric loss of materials.The main contents are as follows:(1)The multi-doped Na0.5Bi4.5Ti3.86Mn0.06Nb0.08O15.04 ceramics were prepared by solid-phase reaction method.The phase structures of the ceramic samples were found to be pure bismuth layered structure by XRD test.The surface morphology of the ceramic samples was observed as typical disc-shaped grains by SEM,which is the typical morphology feature of bismuth layered ceramics.The dielectric,piezoelectric and electromechanical properties of the ceramic samples were tested and the results showed enhanced piezoelectric activity(d33=33 p C/N)and electromechanical properties(kt=0.4)with high Curie temperature.The piezoelectric constant d33 is more than doubled compared to the pure NBT ceramic(16 p C/N).(2)Bismuth layered ceramic NBT are suitable for high frequency conditions due to their low dielectric constant and low dielectric loss advantages.On the basis of Krimholtz-LeadomMettaei model,focused ultrasonic transducers were designed for high frequency imaging based on Na0.5Bi4.5Ti3.86Nb0.08Mn0.06O15.04(NBT-Nb-Mn)ceramics.The transducer was simulated by Piezo CAD simulation software.The size of designed piezoelectric layer was2*2 mm2,the thickness was 48 μm,and theoretical center frequency of transducers was 40.1 MHz.The distribution of absolute acoustics pressure produced by the transducer in water was calculated by COMSOL software.(3)The electrical impedance test results of transducer show that the electrical impedance at highest point of phase reached 54.9 Ω,which meets electrical impedance matching requirement of 50 Ω and simulation results.The pulse-echo response test results show that the measured center frequency of transducer was 37.4 MHz,and the-6d B bandwidth was 47.2%.The insertion loss at center frequency was calculated to be-36.3d B.The results of 25 μm tungsten filament imaging also show its good focusing effect with a lateral resolution of 56 μm,which is consistent with COMSOL simulation results.Clear and accurate images were obtained in final imaging effect test.These results demonstrate that the high-frequency focused ultrasonic transducer based on NBT-Mn-Nb piezoelectric ceramics prepared has significant advantages for applications in the field of nondestructive testing and highresolution imaging.The bismuth layered ceramic material NBT has great potential in the area of high frequency ultrasound imaging.