【作者】 李威；

【导师】 王茁晨；

【作者基本信息】 天津大学 ， 仪器科学与技术， 2023， 硕士

【摘要】 超声聚焦效果是超声换能器,特别是高能超声探头设计的重要考虑因素,其中聚焦方式、聚焦位置、聚焦强度、焦斑大小以及旁瓣的强弱都是衡量超声换能器质量的重要指标。本文对超声传感器聚焦方式和聚焦效果进行了深入研究,针对现有聚焦超声传感器存在的非平面透镜易受到空化效应影响以及难以同时兼顾聚焦与声阻抗匹配问题,设计了一种能够完成高强度声学聚焦,同时实现压电层与传输介质间的声阻抗匹配的耦合匹配层的平面速度梯度透镜,并在此基础上进行了多层聚焦透镜组和拼接式声学透镜的研究。本文首先对超声换能器的基础理论、设计方法和声场计算进行介绍,之后结合声阻抗匹配理论提出了耦合匹配层的速度梯度透镜的超声透镜理论模型,并论断了其可行性。该透镜能够用于超声换能器的声阻抗匹配以及改变超声聚焦中焦点位置,提供了高能聚焦超声的声波聚焦效果、声波传输效率和易用性。其次,对所设计超声换能器进行了KLM模型仿真及实测,确定了超声换能器的几何参数,并根据实际声学材料以及该透镜理论制定了基于COMSOL的速度梯度透镜的制作和优化流程。该方案通过离散化的速度梯度拟合连续速度梯度,实现理论透镜模型的实际制作,并且对离散速度梯度透镜在聚焦效果以及声波传输效率进行了验证性实验测试。然后,在添加新声学材料的基础上,根据已经验证过的速度梯度透镜的设计流程,对离散速度梯度透镜拟合连续速度梯度透镜的方案进行了进一步优化,并将优化后的透镜与凹透镜结合组成多层聚焦透镜组,通过仿真和实验对比,验证了其进一步拉近聚焦位置、缩小焦斑、抑制近场声压的效应。最后,通过对速度梯度透镜拓扑结构的改进,实现了拼接型透镜的设计,能够通过改变该透镜拼接顺序实现聚焦位置的改变。本文中实际制作的拼接型透镜能够实现聚焦位置在65mm到81.2mm的范围内变化。更多还原

【Abstract】 Ultrasonic focusing effect is an important consideration in the design of ultrasonic transducers,especially high-energy ultrasonic probes,where the focusing method,focusing position,focusing intensity,focal spot size and the strength of the side flap are important indicators of the quality of ultrasonic transducers.In this paper,the focusing mode and focusing effect of ultrasound transducer have been studied intensively.Aiming at the drawback of traditional focusing ultrasound transducer,which has a non-planar lens susceptible to cavitation effect and its independent focusing and acoustic impedance matching layers,a planar velocity gradient lens with a coupled matching layer that can complete high-intensity acoustic focusing and realize acoustic impedance matching between piezoelectric layer and transmission medium is designed.The studies of multilayer focusing lens set and spliced acoustic lens are carried out in sequence.In this paper,the basic theory,design method and acoustic field calculation of ultrasonic transducer are firstly introduced.Followed with acoustic impedance matching theory,the ultrasonic lens theoretical model of velocity gradient lens with coupled matching layer is proposed and its feasibility is asserted.The lens can be used for acoustic impedance matching of the ultrasonic transducer and provides an acoustic focusing effect,which is good in acoustic transmission efficiency and easy of use.Secondly,the KLM model simulation and experimental measurements of the designed ultrasonic transducer are carried out to determine the geometric parameters of the ultrasonic transducer.The fabrication and optimization process of the COMSOL-based velocity gradient lens are developed based on the actual acoustic materials as well as the theory of this lens,by fitting the continuous velocity gradient with the discrete velocity gradient.The validation tests are conducted on the discrete velocity gradient lens in terms of focusing effect and acoustic wave transmission efficiency.Then,with more options in acoustic matching materials,the discrete velocity gradient lens is further optimized to fit the continuous velocity gradient lens according to the already verified velocity gradient lens design process.And the optimized lens is combined with a concave lens to form a multi-layer focusing lens set.The simulations and experimental results demonstrate that this design can further narrow the focus position,reduce the focal spot,and suppress the near-field effect.Finally,by studying the topology of the velocity gradient lens,a design of splicing lens is realized,which focusing position can be adjusted by changing the stitching order of the lens.The developed splicing lens can realize the gradual change of the focus position from 65mm to 81.2mm.更多还原