| The process of transmitting and receiving ultrasonic wave by ultrasonic transducer is realized by piezoelectric effect of piezoelectric element and external hardware circuit.In the field of medical ultrasound imaging,the matching layer,as the matching part of acoustic impedance between the transducer and the external medium,plays a key role in improving the bandwidth and pulse amplitude of the transducer.At the same time,the parameters of the backing material are also one of the key factors affecting the sensitivity and bandwidth of the ultrasonic transducer.The matching layer and the backing act together on the transducer,and optimize the output efficiency of the transducer by using the excellent acoustic properties of the material.Aiming at the acoustic matching problem of 12 MHz ultrasonic transducer,this paper used epoxy resin and alumina powder to adjust the characteristic parameters of the composite material and combined with the acoustic properties of the backing material to explore its influence on the performance of the transducer.In theoretical basis part,firstly,the equivalent circuit of each part of the transducer is analized and the loss is considered.Secondly,the acoustic characteristics of the matching layer and backing are analyzed theoretically.Finally,in order to verify that the epoxy-alumina matching layer material can meet the matching requirements of the transducer,the transducer is simulated by COMSOL software.Aiming at the matching layer of epoxy-alumina composite,this paper uses alumina powder as filler,epoxy and curing agent as matrix,and uses casting process to prepare matching layer samples of alumina powder with different mass fraction.The variation law of density,sound velocity,acoustic impedance and acoustic attenuation coefficient of different component matching layer samples was studied by pulse echo method.As the component of alumina powder increases,the density,sound velocity and acoustic impedance of the sample increase gradually.The matching layer sample of aluminum oxide powder 60wt% has high sound velocity and acoustic impedance,and the sound attenuation is within a reasonable range.In the study of backing materials,silver rubber backing,epoxy-tungsten powder backing and epoxy-hollow glass microsphere light backing materials with good acoustic impedance and acoustic attenuation properties were fabricated.The acoustic properties of the latter two materials were tested by pulse insertion method.The test results show that the two backing materials have the characteristics of high sound impedance.With the increase of packing mass fraction,the maximum acoustic impedance of the material exists.Epoxy-tungsten powder backing with high impedance and high attenuation is a good traditional backing material.The density and acoustic impedance of epoxy hollow glass microspheres are low and can be used as light backing materials.Finally,according to the influence of different component matching layer on the performance of transducer,the epoxy-alumina material of different components is used as the matching layer of transducer,and the epoxy-silver glue is used as the backing material to test the acoustic characteristics of different transducers by echo method.Based on the principle of quarter wavelength matching layer,the matching layer thickness optimization experiment is carried out to solve the problem of trailing the matching layer transducer waveform of 60wt% components.According to the test results of the transducer,the epoxyalumina matching layer with 60wt% alumina has the best improvement on the transducer.The echo pulse duration is reduced,the amplitude is increased to 1136 m V(+104%),and the-6d B bandwidth can reach 49.679%(+107%).At the same time,the thickness optimization experiment of 1/4 wavelength thickness matching layer transducer waveform trailing phenomenon shows that the matching layer with slightly less than 1/4 wavelength thickness can improve the phenomenon of transducer waveform trailing.Epoxy-alumina composite material can improve the performance of the transducer,and has a great application potential in the design of high frequency ultrasonic transducer. |
PDF Full Text Request