梯度型非均匀媒质及其声阻抗匹配应用

发布时间：2018-01-26 07:59

本文关键词： 阻抗匹配超声换能器梯度材料　出处：《南京大学》2015年硕士论文　论文类型：学位论文

【摘要】：声阻抗匹配是超声换能器的核心技术之一,可以提高换能器的性能。从上个世纪五十年代以来,人们深入研究了换能器阻抗匹配的问题,提出了诸多理论,其中最著名的是Mason等效电路理论和KLM等效电路理论,它们至今仍然用于指导换能器的设计。匹配层的设计经历了从单层到双层乃至多层的发展,单层匹配遵循四分之一波长匹配技术,双层或者多层利用耦合共振机制展宽带宽,其中每层厚度也设计在四分之一波长左右。目前最常见的中高端换能器采用双层匹配层设计。本文中,(1)我们建立了非均匀媒质的声阻抗率转移方程。该方程将阻抗率转移公式推广至更一般的结果,不仅可以方便计算非均匀材料的声透射性能,更可以将梯度变化材料匹配层纳入经典的换能器等效电路理论。利用阻抗率转移方程,我们研究了两端阻抗率分别等于入射介质和出射介质阻抗率的梯度型匹配层性能,并得出了声阻抗梯度匹配的一般规律。结果表明：(2)声学性质梯度变化的匹配层具有高频几乎全透射的性能,而低频截止频率随厚度增大而降低。(3)匹配层的透声性能依赖于层的几何和物理参数及其变化。固定厚度情况下,通常低截止频率和平坦的透射谱不能兼得,但是通过合理的材料参数分布设计,我们得到了理想的的阻抗匹配效果。(4)为了便于实际制备,我们研究了梯度离散化的多层结构的透声性能,结果表明透声性能与连续媒质的结果相似。(5)我们用复合材料和变截面管道等效的方式实现参数梯度变化材料并且得到了和理论一致的仿真效果。(6)我们也将变换声学的方案也用于解决阻抗匹配的问题。变换声学理论基于声波方程的共形变换,这种方式理论上可以达到实现全频带全透射,并且不存在共振透射的机制,波形可以无失真穿透两种媒质。本文设计了一种基于平面波的阻抗匹配的方案并做了仿真。本文研究的非均匀媒质中声传播问题及其在阻抗匹配中的应用,为研制新型超声换能器匹配层提供了新的理论方法。
[Abstract]:Acoustic impedance matching is one of the core technologies of ultrasonic transducers, which can improve the performance of transducers. Since -50s, the problem of impedance matching of transducers has been deeply studied and many theories have been put forward. The most famous are Mason equivalent circuit theory and KLM equivalent circuit theory, which are still used to guide the design of transducers. The design of matching layer has experienced the development from single layer to double layer and even multi-layer. The single-layer matching follows the 1/4 wavelength matching technique, and the bandwidth is widened by the coupling resonance mechanism between the bilayers and multi-layers. The thickness of each layer is also designed at about 1/4 wavelength. At present, the most common mid- and high-end transducers are designed with double-layer matching layer. 1) We have established the acoustic impedance rate transfer equation of inhomogeneous medium, which extends the impedance rate transfer formula to more general results, which can not only be convenient to calculate the acoustic transmission performance of non-uniform materials. Furthermore, the gradient material matching layer can be incorporated into the classical equivalent circuit theory of transducer, and the impedance rate transfer equation can be used. We study the performance of gradient matching layer with impedance ratio of two ends equal to that of incident medium and output medium respectively. The general law of acoustic impedance gradient matching is obtained. The results show that the matching layer with the gradient variation of acoustic properties has the property of almost full transmission at high frequency. The low frequency cutoff frequency decreases with the thickness increasing. The acoustic permeability of the matching layer depends on the geometric and physical parameters of the layer and its changes. Usually, the low cut-off frequency and flat transmission spectrum can not be obtained, but through the reasonable material parameter distribution design, we get the ideal impedance matching effect. 4) in order to facilitate the practical preparation. We study the sound transmission performance of gradient discretized multilayer structures. The results show that the acoustic permeability is similar to that of the continuous medium. (5) We use composite materials and pipes with variable cross-section equivalent to realize the gradient materials with parameters, and obtain the simulation results in accordance with the theory. We also use the scheme of transforming acoustics to solve the problem of impedance matching. The theory of transform acoustics is based on conformal transformation of acoustic equations. In this way, the full-band transmission can be achieved theoretically, and there is no resonant transmission mechanism. Waveforms can penetrate two kinds of media without distortion. In this paper, a scheme of impedance matching based on plane wave is designed and simulated. The problem of acoustic propagation in non-uniform media and its application in impedance matching are studied in this paper. It provides a new theoretical method for the development of a new type of ultrasonic transducer matching layer.
【学位授予单位】：南京大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB552

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