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题名	固体波导中的时间反转法研究
作者	吴昊
学位类别	博士
答辩日期	2003
授予单位	中国科学院声学研究所
授予地点	中国科学院声学研究所
关键词	固体波导 时间反转法 射线近似 聚焦增益 主副瓣比值
中文摘要	本文是在固体板中开展的时间反转法自适应聚焦理论和实验研究，主要研究了时间反转法在多径效应下的自适应聚焦过程，通过聚焦增益和主副瓣比值等参数详细分析了时间反转聚焦声场特性。首先，在理论上对无穷长条形源在半无界固体中激发的声场进行了研究，采用远场射线近似法（鞍点法）求出条形源激发的柱面P波和S波的渐近解析表达式。当这种柱面波入射到固体自由界面上时，会发生反射和波型转换，本文根据边界条件，严格求解了柱面波在自由界面上的反射系数。当声源和接收器位置确定时，从声源到接收器存在无数条声波传播路径，我们根据声波在界面的反射次数和波型转换的类型，对固体板中的声波传播路径进行了分组，并讨论了同组内不同传播路径声波之间的关系。由于多径效应，当声源激励一个脉冲，接收器会收到很多个脉冲，它们分别对应于不同的传播路径，从而造成相位和波形畸变。研究结果表明，施与时间反转法处理后，即将第一次接收到的声波进行时间反转和归一化处理后，再加到原来阵元上进行重新发射，这时沿不同路径传播的声波将同时同相到达原接收器处，声场相干叠加形成自适应聚焦，自动补偿了这种由于多径效应造成的波形和相位畸变。实验上，利用我们研制的实验系统，分别开展了单阵元和多阵元的时间反转法研究，对于单阵元我们主要研究了不同水平距离下的波型演变规律，对于多阵元我们分别考察了阵元数目及阵列孔径等参数对时间反转聚焦声场的影响。实验结果和理论计算结果进行了对比，二者基本相符，从而得出：在固体波导中，时间反转法能够自适应补偿多径效应造成的声波畸变，实现时空聚焦。
英文摘要	Acoustic self-focusing in solid waveguide by Time Reversal Method (TRM) is studied theoretically and experimentally in this paper. It is mainly investigated TRM self-focusing considering multi-path phenomenon. The time reversal field is analyzed by focusing gain and ratio of principal to second lobes. At first, the acoustic field excited by an infinite long strip with finite width electro-mechanical transducer on the surface of a semi-infinite isotropic solid is studied. The ray approach method (saddle-point method) is adopted to study the far field of the acoustic field, and the asymptotic analytic expressions of the cylindrical compressional- and shear-waves are obtained. When such cylindrical waves are transmitted to a free surface, the reflection and conversion of waves are often happened. According to the boundary conditions on the free surface, different type reflection coefficient of cylindrical waves are obtained. When the transducer and receiver are fixed, there are many propagation paths from the source to the receiver. We divide all the propagation paths into different groups according to their reflection times and the types of wave conversion. The relationship of different propagation path of waves in a same group is studied too. Because of the multi-path effect in solid plant, that is to say, when the transducer transmits a pulse the receiver will receive a chain of pulses (every of these pulses represents different propagation path) with different travel time, the phases and shapes of waves will be distorted. However, after the TRM operation which using the first received time pulse chain, re-synthesized in a reversed temporal chain (last in, first out), re-transmitted the transducer again, the acoustic waves with different path will arrive at the receiver with the same time and phase. Therefore, the acoustic field is refocused at the receiver and high focusing gain and big ratio of principal to second lobes are obtained. The distorted phase and shape of waves are overcome automatically. Using the TRM system established in our laboratory, TRM experiments of single transducer and transducer array are carried out respectively. On single transducer we mainly investigate evolvement trend of the wave types. On transducer array the effects of the number of transducer array, the aperture of the transducer, and other parameters on the time reversal acoustical field are investigated. The quantitative comparisons about the experimental and theoretical results are analyzed. They are comparable in many aspects. It is showed that TRM is a powerful technology to compensate the time difference of different type of waves no matter the distribution of the transducer arrays and different propagation path.
语种	中文
公开日期	2011-05-07
页码	74
内容类型	学位论文
源URL	[http://159.226.59.140/handle/311008/1076]
专题	声学研究所_声学所博硕士学位论文_1981-2009博硕士学位论文
推荐引用方式 GB/T 7714	吴昊. 固体波导中的时间反转法研究[D]. 中国科学院声学研究所. 中国科学院声学研究所. 2003.

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