FEM Design And Fabrication Of Phased Array Ultrasonic Transducers With PMN-PT Single Crystals

Phased array ultrasonic transducer is a key component in cardiac ultrasound imaging.The quality of ultrasonic imaging is affected greatly by the electroacoustic performance of the array transducer.The PZT-based phased array transducer has low electroacoustic coupling efficiency,-6dB bandwidth and sensitivity,which indicate that the resolution,clarity and penetration depth of ultrasonic imaging can be limited.PMN-PT single crystal has obvious advantages in the application of ultrasonic transducers due to its excellent piezoelectric properties compared to PZT ceramics.However,for the design of high-performance array transducers,the overall design is relatively complex,which requires the demands of multiple disciplines such as acoustics,vibration mechanics,electronics,signal processing and material science.Therefore,the design and manufacture of high-end single crystal transducers are still the highest levels of trade secrets of most foreign manufacturers.At present,the design and optimization of single crystal array transducer have become the technical"bottleneck"of advanced ultrasonic equipment in China.In recent years,the national and local governments have issued relevant policies to encourage the autonomy and innovation of domestic high-end medical devices.Under the background of such emphasis on independent innovation,the development of high performance single crystal ultrasonic transducer is imminent.In this paper,the electroacoustic properties of array transducers with different acoustic structures were simulated by combining the one-dimensional equivalent circuit model and finite element modeling(FEM)simulation from the point of view of piezoelectric vibrator and acoustic matching optimization design.The structure and acoustic parameters of each acoustic layer of the transducer were extracted and the array transducer was fabricated and packaged under the condition of ideal performance.The design and fabrication of PMN-PT array transducer with large bandwidth,high sensitivity and narrow pulse are completed by comparing the measured and simulated results.The specific research results are summarized as follows:In terms of acoustic matching optimization,the design method of high sound velocity(HSV)matching is used to reduce the interference of transverse vibration of array elements.The results of finite element modeling(FEM)show that the crosstalk level of HSV-based arrays is reduced by 2.14dB compared with that of conventional low sound speed(LSV)based arrays.The pulse echo performance shows that the-6dB bandwidth of HSV-based arrays is 6.22%higher than that of the LSV array transducer,and the relative sensitivity is almost the same.Besides,HSV-based arrays maintain higher bandwidth and smaller crosstalk at the operating frequency from 2 MHz to5MHz,which indicates that the coupling effect of transverse vibration can be reduced effectively with the HSV matching layer.Applying the de-matching(DM)layer can effectively change the vibration mode and acoustic transmission mode of the array element,reduce the pulse width and clutter generation and optimize the electroacoustic performance of the transducer.The FEM results show that the crosstalk of DM arrays is 1.37dB less than that of LSV arrays.The echo performance shows that the-6dB bandwidth of DM arrays is 12.66%higher than that of LSV arrays,reaching 88.12%,and the sensitivity is 5.62dB higher.Also,the acoustic field characteristics show that the maximum sound beam focusing pressure of DM single crystal array is 1.63 times that of LSV arrays,which indicates that DM arrays have deeper detection depth and better image resolution.In terms of the optimization of the piezoelectric oscillator,compared with the direct current poling(DCP)method,the piezoelectric performance can be significantly improved(d₃₃ increases by 35.3%,the electromechanical coupling coefficient increases)by using the alternating current poling(ACP)method.FEM results show that the average crosstalk of ACP+HSV arrays is 0.68dB less than that of DCP+HSV arrays.The pulse echo results show that the-6dB bandwidth and the sensitivity of ACP+HSV arrays are increased by 6%and 1.03dB compared with DCP+HSV arrays,indicating that the electroacoustic performance of array transducer can be optimized with ACP single crystal.In addition,the pulse echo results showed that the-6dB bandwidth of ACP+DM arrays was the same as that of DCP+DM arrays,and the sensitivity was increased by 1.88dB,indicating that the sensitivity of the transducer was optimized only.The acoustic field characteristics show that the maximum focusing sound pressure of ACP+DM arrays is 24.5%higher than that of DCP+DM arrays.However,the acoustic beamwidth of ACP+DM arrays is increased,which means that the transverse resolution will be affected.Therefore,a suitable design scheme needs to be comprehensively considered and selected.In terms of the fabrication and testing of array transducer,the technological process was optimized and the measurement of array transducer under four design schemes was completed.The measured pulse echo results are consistent with the FEM simulation results.The-6dB bandwidth of the DCP+LSV arrays is 74.33%and the relative sensitivity is-53.97dB.The-6dB bandwidth of DCP+HSV arrays is 7%higher compared with the DCP+LSV arrays.The-6dB bandwidth of DCP+DM+LSV arrays is 12.85%higher,and the sensitivity is 5.79dB higher than those of DCP+LSV arrays,indicating that DCP+DM+LSV arrays will significantly improve the longitudinal resolution and detection depth of ultrasonic imaging.Subsequently,the package tuning test and ultrasonic imaging of DCP+DM+LSV single crystal phased arrays were completed.The consistency characterization of the array elements showed that the capacitance of the whole array elements fluctuated less(1.7%).The measured results of pulse echo show that the highest sensitivity and-6dB bandwidth can be obtained when the inductance value is 4?H.The imaging results show that the optimized phased array ultrasonic transducer has higher resolution,clarity,penetration depth and detection range of ultrasonic imaging.