FEM Design And Fabrication Of Ultrasonic Transducer Based On Inverted-layer Structure

Medical ultrasound imaging technology is a comprehensive application technology that combines medicine and ultrasound.With the characteristics of high imaging speed,accurate and convenient detection,painless and non-invasive detection process,and low practical application cost,it has become the currently preferred method of medical testing during the human disease diagnosis and census.Ultrasonic transducers are the key component of the medical ultrasonic diagnostic systems,and its spatial resolution will significantly affect the final imaging effect.In order to detect different kind of organ diseases more accurately,ultrasonic transducer should have a wider bandwidth,a higher sensitivity and higher center frequency.Therefore,it’s one of the development trends of medical ultrasonic transducers.In order to further promote the development of ultrasonic technology,the performance of ultrasound probes must be improved.At present,the traditional single-piezoelectric-layer structure is used in most of the medical piezoelectric ultrasonic transducers.However,the center frequency of the transducer with a single-piezoelectric-layer structure is inversely proportional to the thickness of the piezoelectric layer.With the increase of center frequency,the manufacturing process of the transducer becomes more difficult.In this thesis,a dual-piezoelectric inversion layer technology is used to improve the piezoelectric layer structure and the PZFlex software is used as a tool of finite element analysis(FEA)simulation,aiming to adjust the center frequency and bandwidth of the transducer by changing the material combinations and thickness ratios of the dual-piezoelectric layer,so as to achieve the purpose of optimizing its spatial resolution.The main research contents and results are summarized as follows:First of all,the investigation on the single-element dual-piezoelectric-layer ultrasonic transducer was conducted.The PMNT single crystals and PZT-5H ceramics were used as the piezoelectric materials of the transducer in this work.The simulation results show that among the four connection methods of the dual-piezoelectric-layer structure,the performance of the connection methods based on the inversion layer technology is the best.Meanwhile,for a transducer with the dual-piezoelectric-layer structure,when the PMNT single crystal and the PZT-5H ceramic are used as the first and the second piezoelectric layer materials respectively,with a thickness ratio of PMNT:PZT=7.5:2.5,about 50% broader-6 d B bandwidth and 16% higher-6 d B center frequency can be obtained compared with the traditional transducer.Meanwhile,it has a shorter-6 d B lateral beam width.Based on the simulation results,four kinds of single-element ultrasonic transducers with different material combinations were fabricated,including a traditional single-piezoelectric-layer transducer #1,PMNT+PMNT dual-piezoelectric-layer transducer #2,PZT+PZT dual-piezoelectric-layer transducer #3 and PMNT+PZT dual-piezoelectric-layer transducer #4.The experimental results prove that the transducer #4 shows the optimal performance.Compared with the transducer #1,the center frequency of transducer #4 is increased by about 42% and the-6 d B bandwidth is increased by about 10.4%.At the same time,it has the shortest pulse length.Based on the study of single-element ultrasonic transducers,the design and fabrication of array ultrasonic transducers were conducted,including a traditional64-element single-piezoelectric-layer array transducer and a 64-element PMNT+PZT dual-piezoelectric-layer array transducer.The electrical impedance simulation results show that for the dual-piezoelectric-layer array transducer,its optimal thickness ratio is PMNT:PZT=7:3.The acoustic performance simulation results show that under the premise that the total thickness of the piezoelectric layer(0.4 mm)remains unchanged,the center frequency of the dual-piezoelectric-layer array transducer is about twice that of the single-piezoelectric-layer transducer,and its-6 d B bandwidth is increased by 10.29% at the same time.The two array transducers mentioned above were fabricated based on the simulation results.The experimental results also show that the center frequency of the dual-piezoelectric-layer array transducer was about twice that of the single-piezoelectric-layer array transducer,and its bandwidth increased by14.95%.The experimental results are consistent with the simulation results.The acoustic lens is another important part of the medical ultrasonic probe.On the one hand,the acoustic lens can protect the probe from water,oil,and dust.On the other hand,it can make the sound beam focus in the elevation direction.And it can improve the characteristics of the time-domain echo tailing and frequency bandwidth of the transducer at the same time..In this thesis,a systematic study of acoustic lens materials that can be applied to medical ultrasonic transducers was conducted.The effects of the type of silica gel and doped powder,the particle size and doping amount of the doped powder on the performance of the density,sound velocity,and acoustic attenuation of the acoustic lens were investigated.FEA was used to simulate and analyze the acoustic focusing performance and acoustic attenuation effect of the acoustic lens of different formulas in the meantime.