| High frequency ultrasound has been widely employed in various aspects including biomedical applications and high resolution NDT applications.High frequency ultrasonic transducers with good performance should have high working frequency,broad-6 dB frequency bandwidth,good sensitivity and excellent sound field distribution.Till now,Fabrication high frequency ultrasonic transducers with good performances still remain challenging.As the key component of ultrasonic transducer,piezoelectric materials especially lead free piezoelectric materials has drawn a lot of interest due to the increase of people's health and environment consciousness.At the same time,how to fabricate high frequency ultrasonic transducers based on lead free piezoelectric materials with good performances become a hot topic.In this thesis,we presented the design and fabrication and of high frequency ultrasonic transducers.The lead-free Na0.5Bi4.5Ti3.975Co0.025O15?NBT-Co?ceramics were fabricated through traditional solid-state reaction method.Microstructural morphology,phase transition,and electrical properties were investigated systematically.The NBT-Co ceramics have high Curie temperature,small dielectric constant,reasonable piezoelectric constant and electromechanical coupling coefficient,making them suitable for the fabrication of high frequency ultrasonic transducer.PiezoCAD simulation software based on the equivalent circuit model was used to simulate the performance of the NBT-Co transducer.Based on the simulation results,high frequency transducers were built based on NBT-Co ceramics.Characterization results demonstrated a center frequency of 70.4 MHz,and a-6 d B bandwidth of 52.7%,and an f number close to 1.A lateral resolution of 29.8?m was achieved by scanning a 10?m tungsten wire target,and an axial resolution of 20.8?m was calculated from the FWHM of the pulse length of the echo.Applications in high resolution biological and medical imaging could be possible with this lead-free ultrasonic transducer. |
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