层状多孔介质中声反射和透射

本文根据流体饱和多孔介质中声传播的Biot理论和多孔介质界面上的六个边界条件研究了平面声波斜入射于多层水平板状多孔介质时的反射和透射。数值计算了快纵波为入射波时声波频率、入射角等量的变化对能量的反射系数、透射系数的影响。数值计算结果表明,当声波波长与中间介质厚度呈一定比例时,反射系数、透射系数取得极值,入射角、多孔介质的性质对反射系数、透射系数的影响很大。     

π相移光纤光栅水听器的超声波传感指向特性

π相移光纤光栅因具有较短的有效光栅传感长度,近年来成为了超声传感领域的研究热点.本研究旨在探究π相移光纤光栅作为水听器应用时对超声波的指向性特性.选取π相移光纤光栅作为超声传感单元,先基于分层介质的声传播理论计算出水中超声波入射时光纤纤芯的应变,再运用基于光学耦合模方程的传递矩阵法计算反射光谱得到光波长偏移.将角度-频率空间分为三个区域,计算了声波频率在1—10 MHz时不同角度下的应变结果和光波长偏移响应特性,并开展了实验研究.结果表明,理论和实验结果具有较高的一致性,π相移光纤光栅在超声波垂直光纤入射时响应最大,随声波入射方向与光纤法向间夹角的增加,π相移光纤光栅的声响应先急剧下降,后在水中直达声波和光纤中导波叠加时出现极大值.此外,π相移光纤光栅的声响应随声波频率增加而降低.本研究对π相移光纤光栅在超声传感中的实际应用具有重要意义.     

基于衍射波的孔类缺陷超声相控阵定量方法研究

针对常规超声检测方法对小孔型缺陷难以准确定量的问题,利用超声相控阵的声束偏转聚焦和成像技术,基于声波在体积缺陷处的衍射特性,提出采用一次反射回波和衍射回波来确定体积缺陷的直径尺寸。以横孔模拟孔型缺陷,利用动态光弹技术对声波入射横孔的传播规律进行研究,并采用超声相控阵对孔径为Φ1-Φ4mm不同埋深以及相同埋深下Φ0.8-Φ4.8mm的等差横孔进行了试验。研究结果表明利用本文提出的定量方法能快速有效的确定孔型缺陷直径尺寸,实际计算值与理论值误差较小,对相控阵的定量问题研究具有一定的参考价值。     

钢-铅粘接结构的粘接强度对超声体波反射与 透射特性的影响*

针对多层异种金属粘接结构中粘接强度的超声检测与表征困难的问题,采用线性弹簧模型和等效弹性模量模型来分别表征界面粘附强度和内聚强度,推导了超声体波斜入射N层粘接结构的反射与透射系数表达式。通过在不同入射面和入射声波模式等条件下,同时连续改变两种参数来系统研究粘接层界面粘附强度与内聚强度变化对超声波反射与透射特性的影响关系,确定了能够敏感表征粘接强度的超声参量,为粘接强度的无损检测与评价提供理论依据。     

超声法测量高浓度矿浆两相流粒径分布和浓度

研究了超声衰减谱法和超声多次回波反射法测量高浓度矿浆两相体系粒径分布和浓度。实验测量了多个浓度下硫矿浆在3～6 MHz频率下的声衰减谱,结合反演算法由实验数据计算得到矿浆两相流粒径分布。同时测量了不同浓度下硫矿的声阻抗值,由超声多次回波反射法计算得到浓度。粒径分布与浓度测量得到的结果与标准配置值较为吻合,表明超声法适用于高浓度矿浆两相流粒径分布和浓度的在线检测。     

“多通道数字成像超声探伤设备”项目简介

高波阻介质下面多层低波阻抗介质的界面脱粘检测是长期以来国内外一直没有解决的世界性难题，称为“二界面问题”。困难主要有两点：其一、高波阻介质与低波阻介质之间的界面两侧波阻抗相差较大，前一介质表面上接收到的界面脱粘反射信号相对入射信号而言是经过了4次镜面屏蔽作用之后的十分微弱的信号；其二、声波在高波阻介质内的多次反射强信号淹没了低波阻介质表面反射的信号。对于高低波阻介质界面间脱粘的超声检测，犹如光学中兽看到一个双面镜子后面的物体一样。     

周期镶嵌亥姆霍兹共鸣腔平板的声全背向反射

研究斜入射声波在周期镶嵌亥姆霍兹共鸣器的刚性界面上的反射行为.共鸣器间的空间周期间隔d和入射声波的波长入相当,且大于共振腔尺寸,因此可被视为具有集总参数的声学元件.理论分析和数值计算均表明,当入射波频率和方向既满足布拉格共振条件又同时满足亥姆霍兹共振条件时,在通常的反射方向上反射声波消失,反射波逆入射方向传播,引起与常规反射全然不同的全背向反射.     

固体滑移界面的超声评价

为评价固体滑移界面的特性,根据QSM界面模型和粘滞流体的本构方程导出了滑移界面的界面劲度系数及垂直入射到固体滑移界面的超声纵波和SH波的反射系数公式,其中纵波的反射系数与滑移界面层的绝热体积弹性模量、粘滞系数和入射声波的频率有关,而SH波的反射系数与界面层的绝热体积弹性模量和入射波的频率无关。因此,可以用SH波直接评价界面的不同粘滞状态,且不受检测频率的限制。要评价界面的绝热体积弹性模量,则必须增加纵波检测。利用蜂蜜和水模拟不同滑移界面层的声波反射实验验证了上述理论结果。     

海面冰层对声波的反射和散射特性

北极海面冰层复杂多变,其对声波的反射和散射严重影响冰下水声信道的传输特性,建立海面冰层的声波反射和散射模型对冰下水声通信研究具有重要意义.假设海面冰层为多层固体弹性介质且冰-水界面粗糙,满足微扰边界条件,导出声波从海水介质入射到海面冰层时相干反射系数满足的线性方程组.对相干反射系数随声波频率、掠射角、冰层厚度的变化进行数值分析.进一步引入根据散射声场功率谱密度计算散射系数的方法,改变掠射角,对冰层厚度、散射掠角对散射系数的影响进行研究.     

超声波易被空气“吸收”吗?

全国中等卫生学校《物理学》教材在超声波一节中,讲到“作超声诊断前,必须在被检查部位上涂上液体石蜡油,其原因是超声波易被空气吸收”．而蝙蝠恰恰是通过向空间发射超声波来获得反射超声信息的．这就提出了一个问题：超声波究竟是不是易被空气吸收？超声波和声波一样在传播到不同物质的分界面时发生反射和折射．而反射超声能量的大小与两种介质的声阻抗有关．设超声波垂直从介质１入射到介质２,入射声强为Ｉｉ,反射声强Ｉｒ,折射声强为Ｉｔ,介质１声阻抗为Ｚ１,介质２声阻抗为Ｚ２,则声强的反射因数ａＩｒ＝ＩｒＩｉ＝（Ｚ２－Ｚ…     

通过滤波检测水泥胶结质量的超声反射法

为防止流体沿井轴向窜槽,水泥与套管和地层的胶结必须是良好的。在固井质量检测中,超声反射法因具有较强的方位指向性而被广泛使用。但套管的高声阻抗导致了套管后的反射波信号比较微弱,使得水泥胶结质量的判别变得困难。为提高超声反射法的识别能力,我们以套管的共振频率为中心频率对反射全波进行滤波,降低套管的前表面反射波幅度,凸显套管后面携带水泥胶结信息的反射波。滤波后的波形呈现出数个波包,不同胶结情况下这些波包的幅度存在明显差异,通过这些差异可以判断水泥胶结质量。我们还利用有限声束模型计算了斜入射时的反射全波,探讨了入射角对超声反射波的影响。      

Evaluation of the cement bond quality through filtering the reflected ultrasonic waves

High cement bond quality is required to keep an oil well from hydraulic communication between zones.In the cement bond evaluation,the ultrasonic echo method is widely used for its capability of channeling azimuth detection.Full waveforms reflected from the cased hole are simulated for different bonding conditions by the generalized transfer matrix method.Because of the high acoustic impedance of casing,the amplitudes of the reflected waves from the cement and the formation are small and cannot easily be used to evaluate the cementing condition.The wave that can propagate into the cement and the formation through the casing concentrates closely on the casing resonant frequency.To reduce the amplitude of the reflected wave from the casing inner surface and highlight the part of the reflected wave which carries the cementing quality information,the reflected full wave is filtered according to the casing resonant frequency.There are several wave packets in the filtered waveform.When the amplitude of the second wave packet is low,the cement bonds well with the casing,otherwise poorly.A low amplitude third wave packet is an indication of a good bond of the cement with the formation,otherwise poor.To reveal the sensitivity of the reflection wave amplitudes to the incident angle,reflected full waveform is modeled when an acoustic beam with finite width is incident on the casing.It is shown that the bond evaluation method based on filtered wave packets is valid for incident angle less than 5 degrees.     

Reconstruction of a complex-shaped defect from the known arrival time of the reflected ultrasonic wave

The problem of reconstructing the boundary of an arbitrarily shaped defect formed inside an elastic body from the measured time of arrival of the reflected ultrasonic wave in the echo method is considered. The characteristic size of the defect is assumed to be greater than the wavelength, and the defect is irradiated from the far-field zone, which means that the incident wave can be considered as plane. An algorithm is developed for reconstructing the convex envelope of a nonconvex defect from the arrival times of echo signals measured at different angles with the use of circular scanning.     

声表面波检测铝板表面微缺陷深度实验研究

为了探究声表面波与不同深度微裂纹缺陷相互作用的关系,将脉冲激光作用于一系列不同缺陷的试件铝板上进行线光源激励,激发激光超声波。用超声传感器接收在铝板中传播的激光超声信号,通过数字荧光示波器采集激光超声在铝板中的传播数据。对采集到的反射波数据进行分离谱分离过程得到的铝板中激光超声的时域分布和透射波数据进行频域分析。实验发现:缺陷深度影响着反射回波两峰值特征点到达时间差,两者之间近似线性关系,也影响着透射波的截止频率且二者呈现递减关系。     

Radiation reflection from inhomogeneities moving in a medium with a plasma dispersion law

The dependence of the complex frequency of radiation reflected from an inhomogeneity moving in a medium on the frequency of the incident radiation is found for inhomogeneous wave regimes. Explicit expressions for the plasma dispersion law of the medium are presented. The complex Doppler effect, where one (real) frequency of the incident radiation corresponds to two complex frequencies of the reflected radiation, is demonstrated.     

Resonant excitation of intense acoustic waves in crystals

The resonant excitation of an intense elastic wave through nonspecular reflection of a special pump wave in a crystal is described. The choice of the plane and angle of incidence is dictated by the requirement that the excited reflected wave be close to the bulk eigenmode with its energy flow along a free boundary. The resonance parameters have been found for a medium with an arbitrary anisotropy. General relations are concretized for monoclinic, rhombic, and hexagonal systems. A criterion is formulated for an optimal selection of crystals in which the resonant reflection is close to the conversion one, when almost all of the energy from the incident beam of the pump wave falls into the near-surface narrow high-intensity reflected beam. Estimates and illustrations are given for such crystals as an example. The intensity of the reflected beam increases with its narrowing, but its diffraction divergence also increases with this narrowing. Nevertheless, the intensity of the beam can be increased by a factor of 5–10 at sufficiently high frequencies while keeping its divergence at an acceptable level. Amplification by two orders of magnitude can be achieved by compressing the beam in two dimensions through its double reflection.     

平面电磁波在任意方向运动的介质-介质界面上的反射和透射

研究平面电磁波从一种介质入射到另一种以任意方向运动的介质时,在介质界面上发生的反射和透射现象,从Maxwell方程组、运动界面的边值关系和运动介质的本构关系出发,得到了反射波和透射波电磁场矢量与入射波电磁场矢量的关系的表达式、反射和透射系数,讨论了反射波、透射波与入射波之间的能量关系,电磁波对运动介质作用力的性质,并得出一些新的结论． 关键词：     

Acousto-optic study of the unusual cases of reflection of bulk elastic waves in a paratellurite crystal

The propagation and reflection of bulk ultrasonic waves in a paratellurite crystal have been investigated by the acousto-optic method. Simultaneous excitation of two acoustic waves by one piezoelectric transducer has been observed in a cell of complex, specially chosen configuration. Maximally efficient conversion of the energy of a quasi-longitudinal wave into a single reflected quasi-shear wave with a walkoff angle 72° is implemented for the reflection from a free crystal boundary. The wave beam compression by a factor of 7 is observed for this reflection. A reflection (close to backward) of waves with an angle of spatial separation of the incident and reflected beams equal to 8° is also implemented. The acousto-optic figure of merit values of the medium are calculated for arbitrary propagation and polarization directions of the interacting light and ultrasonic waves. Possible applications of the effects studied in acousto-optics and acoustoelectronics are indicated.     

The parametric Doppler effect upon oblique incidence of probe radiation

Transformation of frequency and intensity of probe radiation obliquely incident on a moving inhomogeneity induced by an intense laser radiation in a nonlinear medium is analyzed. The dependences of frequency and intensity of radiation reflected from the inhomogeneity have been found for a variant of frequency dispersion corresponding to collision-free plasma. These dependences possess singularities under conditions corresponding to the Vavilov-Cherenkov effect. The initially weak noise components of probe radiation increase in the reflected radiation up to a considerable value.     

Ultrasonic characterization of liquids using resonance antireflection

This paper presents an ultrasonic method for measuring the density of liquids with a solid layer separating a reference fluid and a test fluid. By adjusting the frequency of the exciting signal according to the thickness of the layer, it is possible to generate destructive interference of the waves reflected at the first and at the second boundary of the layer. Thus, the layer appears to vanish for the incident waves. The resulting echo signal depends only on the acoustic impedances of the reference fluid and the test fluid and the density which is of interest can be extracted. Short and long-term drifts of the electronics and the ultrasonic transducer implied are eliminated by using the well-known pulse-echo technique with additional frontwave detection.