A Study On Performance Optimization Of Focused Ultrasonic Transducer Based On 1-3 Piezoelectric Composites

BackgroundThe High Intensity Focused Ultrasound?HIFU?is the core component of high intensity focused ultrasound tumor treatment system.Traditional transducers have the problems of narrow bandwidth,low electro-acoustic conversion efficiency,and poor energy output stability.The excellent performance of the transducer directly determines the therapeutic effect of HIFU.Therefore,it is very important to study the performance optimization of the transducer.The transducer is mainly composed of a piezoelectric vibrator,a matching layer,a backing layer,an electrode wire,and a housing.As an ultrasonic sound-generating element,the comprehensive performance of the 1-3 piezoelectric composite material directly determines the various performance indicators of the transducer.The excellent performance of the1-3 piezoelectric composite material enables the transducer to have a stable working output and High electro-acoustic conversion efficiency.When the piezoelectric material is determined,a well-designed matching layer can not only achieve acoustic matching between the transducer and the working medium,but also significantly improve the transmission efficiency of the acoustic energy of the transducer between human tissue and the transducer.,Significantly broaden the bandwidth of the transducer;and also protect the transducer surface and piezoelectric ceramics to avoid contamination or destruction in the working environment.This subject studies from two aspects of 1-3 piezoelectric composite material and matching layer,in order to find a method to optimize the performance of focused ultrasonic transducer based on 1-3 piezoelectric composite material.PurposeThe 1-3 piezoelectric composites were modified to make the transducer have stable output and high electroacoustic conversion efficiency;at the same time,the epoxy resin matching layer is modified by filling alumina to adjust the impedance value improves the efficiency and bandwidth of the electroacoustic conversion of the transducer through impedance matching and sound transmission coefficient matching.The influence of alumina on the acoustic characteristics of the matching layer was studied through theoretical model simulation and experiments,and the effect of the impedance value of the matching layer on the performance of the 1-3piezoelectric composite transducer was studied.Methods1.Polyether sulfone?PES?and hollow glass microbeads?HGB?are added as fillers to epoxy resins?EP?,PES is used to improve the mechanical properties of the material,the bonding force between the epoxy phase and the ceramic phase is increased,and the HGB is used to improve the thermal expansion coefficient of the epoxy polymerization phase,so that the epoxy phase and the ceramic phase are more matched.The optimal range of fillers and the influence of the filler loading on the acoustic,mechanical and thermal properties of the epoxy polymer phase are studied.2.In order to optimize the performance of 1-3 type piezoelectric composites,based on the best proportion of the fillers obtained above,a 1-3composite was prepared by cutting-filling method,and the modified 1-3composite was analyzed by impedance analyzer Measurement of impedance curve,analysis of its piezoelectric performance and temperature stability of performance.3.Theoretical model simulations and experiments were conducted to study the influence of different volume fractions?0%²0%?of alumina on the acoustic characteristics of the matching layer.4.A matching layer transducer with different acoustic impedance values was developed by using the modified 1-3 piezoelectric composites as the sound element.The conductivity curve was measured by an impedance analyzer.A platform was built to measure the electro-acoustic conversion efficiency within a certain frequency range.Result1.The compound addition of PES and HGB can better improve the acoustic,mechanical and thermal properties of epoxy polymer phase.The optimal ratio of PES and HGB is 10wt%PES+10wt%HGB.At this time,the sound velocity and sound attenuation of the epoxy phase are increased from 2506 m/s,1.53 dB/cm/MHz to 2567 m/s,1.62 dB/cm/MHz,which optimizes the acoustic characteristics of epoxy resin;the shear strength of the epoxy phase is increased by 33%,which improves the mechanical properties of the material;the thermal expansion coefficient is reduced from8.8×10^-5/K to 5.8×10^-5/K,reduced by 53.2%,effectively reduces the thermal expansion coefficient of the epoxy phase,can improve the thermal matching of the epoxy phase and the piezoelectric phase,and improve the thermal stability of the material.2.The filler is used to modify the 1-3 type piezoelectric composite with10wt%PES+10wt%HGB.The research results show that the electromechanical coupling coefficient kt of the modified 1-3 type piezoelectric composite is 0.65,the quality factor Qm is 12.2,under the condition that the piezoelectric phase and the epoxy polymerization phase are unchanged,the piezoelectric properties of the 1-3 piezoelectric composite material modified by the filler are basically unchanged;in the temperature range of 15°C⁵0°C,the fs and kt of the 1-3 composite material,the rate of change is?1%,and the rate of change of Qm is?10%.The temperature stability of the piezoelectric properties of the modified 1-3piezoelectric composite materials is greatly improved.3.Epoxy resin matching layer materials filled with alumina of different volume fractions?0%²0%?were prepared.The acoustic characteristics of the matching layer were studied using theoretical models and experimental verification methods.It was found that the density,sound velocity,The characteristic parameters of acoustic impedance and acoustic attenuation coefficient increase with the increase of alumina volume fraction,from 2453m/s,2.8Mrayl,2.40 dB/cm/MHz to 2647 m/s,4.3 Mrayl,3.37 dB/cm/MHz indicates that the acoustic characteristics of the matching layer can be changed by changing the alumina filling amount to obtain the optimal volume ratio suitable for acoustic matching of a focused ultrasound transducer.4.Using 10wt%PES+10wt%HGB filler modified 1-3 type piezoelectric composite material as the sounding element,the manufactured non-matching layer transducer,the test results show that its electroacoustic conversion efficiency has been greatly improved,In the resonance frequency range,the conversion efficiency is increased from 59%to 83%,and the transducer has good temperature stability.The research on the matching layer of the transducer found that as the impedance value of the matching layer continues to increase,the transducer The-3dB bandwidth is significantly wider,and the electro-acoustic conversion efficiency is improved.When the acoustic impedance value is 3.5 Mrayl,the-3dB bandwidth is 295 kHz,and the electro-acoustic conversion efficiency reaches90%.ConclusionThis subject is studied from two aspects:epoxy polymer phase modification of 1-3 piezoelectric composite materials and adjustment of the impedance value of acoustic matching layer materials,and through the research,we finally obtained a method to optimize the performance of the 1-3 piezoelectric composite focused ultrasonic transducer.