宽带相控线阵声源在套管井外地层辐射声场的指向性

套管井中的声传播涉及到波在柱状多层介质中的传播问题。通过数值计算对比了宽带相控线阵声源在套管井外均匀地层中产生的纵横波声场的指向性。结果表明,在任意胶结状况下,均可实现向套管井外地层定向辐射纵横波的技术;与地层中纵波的传播特征不同的是在主瓣偏转角方向横波幅度随着偏转角的增大逐渐增加,且在主瓣辐射方向的横波幅度受套管井胶结状况的影响较纵波小;采用玻璃钢套管代替钢套管,会进一步减弱地层声场受胶结状况的影响,这有利于实现在套管井外地层较大范围内的精确定向辐射声波的技术。     

相控圆弧阵声源在TI地层井孔中产生的声场

研究了相控圆弧阵声源在各向异性地层井孔中产生的声场的特征,重点分析了该声源对于地层横波各向异性的方位敏感性,旨在探索一种新的地层声学各向异性测量方法。结果显示:相控圆弧阵声源在地层中可激发多种方位阶数的声场,主要成分为单极子波场和偶极子波场;在HTI地层竖直井中,方位角不同的圆弧阵声源激发的波动的速度不同,相控圆弧阵声源对于地层横波速度的方位各向异性的敏感性主要是它所激发的弯曲波的贡献。相比于传统的正交偶极子声波测井而言,采用相控圆弧阵声源可以评价井附近地层的周向非均质性,可以提高井周测量覆盖次数,提高反演结果的可靠性。另外,相控圆弧阵声源兼具备多极子声源的功能,优化的相位控制方式可以实现方位各向异性的最佳测量。      

经颅超声聚焦方法和声场特性研究

基于高分辨的CT数据建立了非均匀颅骨仿真模型,该模型引入了颅骨的声衰减系数,深入研究和分析了声波时间反转法和超声相控阵法在颅脑中的聚焦方法及效果。颅骨具有较强的声波衰减特性,使用时间反转聚焦时需要进行幅度补偿,对于0.7MHz的频率信号,幅度补偿后的时间反转聚焦声场主瓣宽度窄、旁瓣低,焦点处声场比无幅度补偿的时间反转法提高8.86dB,比超声相控阵聚焦法提高7.89dB,具有很好的空间聚焦精度和聚焦效率。研究了颅骨衰减系数、声场焦点位置、声波频率、换能器阵列位置和方位等参数对聚焦声场的影响,结果表明,幅度补偿时间反转法比相控阵法具有更低的旁瓣,且高频时的聚焦效果比相控阵好,相控阵聚焦对换能器阵列的位置和方位比较敏感,而时间反转经颅超声聚焦对声传播路径和入射角具有更高的鲁棒性。      

Radiation Acoustic Field of a Linear Phased Array on a Cylindrical Surface

A new linear ultrasonic phased array fixed on a cylindrical surface is designed. This kind of the cylindrical phased array can meet the specific requirements of the application in testing pipe quality inside pipes. Using the transducer, we can not only avoid mechanical rotating but also test the quality of any point in a pipe by ultrasonic phase array technology. The focused acoustic field distributions in the axial, radial and tangential directions of the transducer are investigated theoretically by numerical simulation. The energy flux density, the width of the main lobe, the imaging resolution, the grating lobe elimination and other characteristics are analysed. The effect of the focal distance, effective aperture, transducer radius, number of total element, and steering angle on the acoustic field distribution is also studied.thoroughly. Many important results are obtained.     

FPGA-based implementation of steerable parametric loudspeaker using fractional delay filter

Parametric loudspeaker enables high directivity sound along the radiation direction to be generated by the nonlinear effects of ultrasonic waves in air. Based on the theory of phased array, the beams of parametric loudspeakers can be steered to other directions. In this paper, the Fractional Delay (FD) filter is introduced to generate any arbitrary delay to accurately control the steering angle of the beam. Field Programmable Gate Array (FPGA) is a better choice for the system of steerable parametric loudspeaker due to its strong capability of parallel and real-time processing. The algorithms have been realized easily and quickly by combining the tools of Matlab simulink and DSP Builder. Finally, the validity of the system is verified through comparing the theoretical simulations with the experimental results.     

圆弧片状声源向地层中辐射声场的有限差分模拟

提出了一种可用于随钻声波测井的非对称的圆弧片状声源,旨在发展一种能够在钻井过程中精确确定反射体位置的三维反射声波远探测方法。研究了在复杂的井孔条件(钻铤偏心、各向异性和不规则井孔形状)下,该声源向地层中辐射的声场的特征,进一步分析了不同井况条件对三维随钻远探测声波测井的影响。数值模拟结果表明,在圆形井孔、钻铤居中条件下,无论快速地层还是慢速地层,圆弧片状声源均能够向地层中定向辐射声波信号,其辐射指向性图主瓣3 dB角宽窄,旁瓣级低,方位分辨率较高,适用于随钻三维反射成像测井;井壁粗糙程度、地层各向异性等因素对声场特征影响不大,说明该方法适用于粗糙井壁和各向异性地层情况;钻铤偏心和井壁一侧的破坏对辐射声场的影响较大。对本文的模型而言,在破坏深度小于3 cm或者偏心距离小于2 cm时,声场仍有较好的方位特征,该方法仍然适用。而当破坏深度大于6 cm,声场指向性图出现多个幅值较大的角瓣,可能无法利用其确定反射体的方位。本文的研究结果为三维随钻反射声波仪的设计和研发提供了必备的理论基础。      

Fringed sound fields and their interaction with liquid-solid interfaces

On the one hand, it is well known that Gaussian beams possess the ability to stimulate Rayleigh waves, resulting in the Schoch effect, a lateral beam displacement. This effect, often characterized by a reflected sound pattern consisting of two anti-phase beams, is due to the re-radiation of sound because of the stimulation of leaky Rayleigh waves. On the other hand, fringed sound beams are characterized by the fact that they consist of a number of neighboring anti-phase narrow beams. They are a first approximation of a sound field originating from a phased array of harmonic vibrating crystals in which each crystal vibrates in anti-phase compared to its neighbor. The individual lobes within the fringed sound pattern diverge much less than standard Gaussian beams of the same size. The current study investigates the interaction of fringed beams with a liquid-solid interface. It is found that under certain conditions, a fringed beam, incident at the Rayleigh angle, produces a reflected sound pattern that contains a wide lobe that is not fringed. It is also shown that under other conditions, contrary to the famous forward displacement of the reflected sound for incident Gaussian beams, a strong backward displacement occurs for fringed beams.     

界面条件下线型超声相控阵声场特性研究

开展了界面条件下线型超声相控阵声场特性的研究.将带有楔块的超声相控阵问题合理简化为液固界面的情况进行讨论.根据射线声学理论,计算了单阵元在液固界面存在时的辐射声场,进而推导了聚焦法则,得到了超声线型阵在液固界面存在时的声场、位移场表达式.对安装在楔块上的相控阵换能器的辐射声场进行了仿真,并讨论了聚焦对换能器轴向和横向声场的影响,结果表明利用聚焦能提高分辨率和灵敏度,但聚焦区域之外声束性能更差,在实际检测中要合理利用聚焦. 关键词： 超声相控阵 界面 声场 聚焦     

圆环形聚焦声场的构建与调控

提出了一种由径向振动模式的圆环形压电换能器晶片组成的圆柱形阵列换能器结构, 依据阵元激励信号的相位调控机理, 推导了圆环形聚焦声场的调控公式, 在三维空间中构建了圆环形聚焦声场, 实现了对其聚焦区域大小、聚焦圆环半径以及轴向位置移动的调控. 理论分析和仿真研究表明, 所提出的圆柱形阵列换能器实现了对圆环形聚焦声场的调控. 为检测超声、功率超声、医学超声等应用领域提供了一种可实现的新型圆环形可调控聚焦声场.     

反射声波成像测井的有限元模拟

应用有限元法对新兴的反射声波成像测井进行了数值模拟研究，计算了井旁附近存在不同倾角声阻抗不连续界面对声波的反射，使用的井内激励源为幅度加权相控线阵声波辐射器。从计算出的声全波波形上可以清楚地看到沿井壁传播的折射波和来自井旁界面的反射纵波。应用偏移叠加等数据处理技术对数值模拟波形进行了处理，从偏移剖面上反演出的反射界面的尺寸、位置和倾角等几何特性与数值模拟输入参数基本一致。     

微纳相控线阵超声换能器参数的理论分析*

微纳相控线阵超声换能器参数(阵元数目、阵元宽度及阵元间距)直接影响其横向声场分布,而其横向声场分布是能否实现高成像分辨率、大探测深度的决定性因素,也是制备换能器的主要依据。该文利用数值模拟研究微纳相控线阵超声换能器阵元参数对其横向声场中主瓣强度、-3 dB主瓣宽度、第一级旁瓣及栅瓣的影响。结果表明,主瓣强度随着阵元数目增加而增大,随阵元间距减小而增大,随着阵元宽度的增大呈现先增大后减小的趋势;-3 dB主瓣宽度随着阵元数目和阵元间距的增大而减小,随着阵元宽度的减小而减小;此外,减小阵元数目、减小阵元间距或增大阵元宽度均可以抑制旁瓣;栅瓣在阵元间距满足一定条件时可以完全消除。通过这些研究为微纳相控线阵超声换能器的优化设计与制备提供理论参考。     

带楔块二维面阵列超声相控阵声场特性分析

开展了带楔块二维面阵脉冲超声相控阵辐射声场特性的研究。将安装在一定角度斜楔块上二维面阵相控阵换能器声场问题简化为液固界面情况进行讨论。以单阵元在液固平界面条件下的辐射声场为基础,推导了聚焦偏转法则,给出了带楔块二维面阵超声相控阵声场计算方法。以检测材料为钢板,安装在倾斜角为36°有机玻璃楔块上的频率为5 MHz、8×8二维面阵相控阵的辐射声场计算为例,分析了在不同偏转角和不同聚焦深度下检测材料中的辐射声场特性。计算结果表明该方法可有效的分析带楔块二维面阵超声相控阵声场特性并用于指导二维超声面阵角束探头的设计。      

激光激发超声波的新方法研究

介绍了激光激发超声波的原理，分别给出了热弹机制和烧蚀机制下的纵波和剪切波理论波形；基于排列因子作用，提出了一种新型激光激发超声波的方法——激光定相位排列激发超声波，激光源经过定相位排列后，在某一方向上产生的超声波幅度比传统单一源产生的超声波幅度要强很多，采用此种方法，可实现对超声信号方向和强度的有效激发控制，对下一步的超声无损检测有非常重要的意义；结合实际给出了该方法的实现方式.     

An acoustic imaging system of migration technique used in borehole

In order to detect the damage of casing boreholes, an acoustic imaging method with a two-dimensional ultrasonic array was presented. Each element of the array independently emits down ultrasonic waves, the echoes received by all elements are sampled and transmitted to a computer on ground surface, where the dynamic migration method is used to form a 2 or 3-dimensional image of the situation in the borehole. The numerical simulation and experiment are conducted that demonstrate a high imaging accuracy with a small number of elements used in array. Since the delay circuits used in the traditional phased array imaging system is not needed in this system, and all data process could be completed in a ground system. the complexity and the volume of system in borehole may be significantly simplified, which is critical to the borehole instrument.     

Phased Array Beam Fields of Nonlinear Rayleigh Surface Waves

This study concerns calculation of phased array beam fields of the nonlinear Rayleigh surface waves based on the integral solutions for a nonparaxial wave equation.Since the parabolic approximation model for describing the nonlinear Rayleigh waves has certain limitations in modeling the sound beam fields of phased arrays,a more general model equation and integral forms of quasilinear solutions are introduced.Some features of steered and focused beam Gelds radiated from a linear phased array of the second harmonic Rayleigh wave are presented.     

Borehole guided waves in a non-Newtonian (Maxwell) fluid-saturated porous medium

<正>The property of acoustic guided waves generated in a fluid-filled borehole surrounded by a non-Newtonian (Maxwell) fluid-saturated porous formation with a permeable wall is investigated.The influence of non-Newtonian effects on acoustic guided waves such as Stoneley waves,pseudo-Rayleigh waves,flexural waves,and screw waves propagations in a fluid-filled borehole is demonstrated based on the generalized Biot-Tsiklauri model by calculating their velocity dispersion and attenuation coefficients.The corresponding acoustic waveforms illustrate their properties in time domain.The results are also compared with those based on generalized Biot's theory.The results show that the influence of non-Newtonian effect on acoustic guided wave,especially on the attenuation coefficient of guided wave propagation in borehole is noticeable.     

Precise micro-particle and bubble manipulation by tunable ultrasonic bottle beams

This paper reports a method to generate tunable bottle beams using an ultrasonic lens, by which the bottle position can be precisely adjusted with the change of the acoustic frequency. Therefore, the position of a single particle or bubble in liquid can be manipulated without using phased array which is costly and huge with complex circuits. Furthermore, we introduced this method to multiple bubble manipulation using acoustic holography. The bottle properties against frequency are theoretically and experimentally analyzed. It is shown that the bottle position depends almost linearly on the operating frequency, which provides a basis for the precise manipulation of bubbles and particles. In addition, the relationship between the acoustic radiation force and the drag force under different incident acoustic pressures is considered, establishing a limit on the moving velocity of the trapped particles. The ultrasonic field observation is further demonstrated by Schlieren imaging system. The proposed method has potential biomedical applications, such as more flexible cell manipulation and targeted drug delivery in vivo, as well as potential applications in the study of chemical reactions between micro objects.     

高斯叠代法研究相控阵非线性声场

相控阵在聚焦超声治疗应用中不可避免地受到非线性影响,提出了采用高斯叠代法计算相控阵的非线性声场。在该方法中,利用预设焦点参数并应用伪逆矩阵算法得到阵元的激励参数;然后将阵元近似拟合成一组高斯声束的叠加,通过高斯声束叠代计算非线性声场。数值计算中以64阵元一维相控阵为研究对象;线性条件下,高斯叠代法结果与菲涅耳积分结果的误差低于0.5%,验证了该方法的可行性;单焦点及双焦点模式的相控阵非线性声场结果表明非线性效应能提高焦点聚焦性能,并且非线性效应与激励声压及激励频率成正比。      

Peculiarities of the Self-Action of Inclined Wave Beams Incident on a Discrete System of Optical Fibers

Based on a discrete nonlinear Schrödinger equation (DNSE), we studied analytically and numerically the peculiarities of the self-action of one-dimensional quasi-optic wave beams injected into a spatially inhomogeneous medium consisting of a set of equidistant mutually coupled optical fibers. A variational approach allowing the prediction of the global evolution of localized fields with the initially plane phase front was developed. The self-consistent equations are obtained for the main parameters of such beams (the position of the center of mass, the effective width, and linear and quadratic phase-front corrections) in the aberrationless approximation. The case of radiation incident on a periodic system of nonlinear optical fibers at an angle to the axis oriented along them is analyzed in detail. It is shown that for the radiation power exceeding a critical value, the self-focusing of the wave field is observed, which is accompanied by the shift of the intensity maximum followed by the concentration of the main part of radiation only in one of the structural elements of the array under study. In this case, the beams propagate along paths considerably different from linear and the direction of their propagation changes compared to the initial direction. Asymptotic expressions are found that allow us to estimate the self-focusing length and to determine quite accurately the final position of a point with the maximum field amplitude after radiation trapping a channel. The results of the qualitative study of the possible self-channeling regimes for wave beams in a system of weakly coupled optical fibers in the aberrationless approximation are compared with the results of direct numerical simulations within the DNSE framework.     

光学相控阵光束电扫描技术及仿真

光学相控阵技术是一种新型光束偏转及扫描技术,介绍了光学相控阵技术光束电扫描的原理,分析了光学相控阵主要参数及高斯光束替代平行光束入射对偏转效果的影响,研究了三种利用光学相控阵实现多光束扫描的方法。研究结果表明,为了提高光束质量应尽量减小单元周期,增大光学相控阵尺寸和填充率,但减小周期并不能完全抑制栅瓣,而高斯光束取代平行光束入射仅影响偏转光束的角宽度,所研究的三种多光束扫描方法均有效,三种方法各有优缺点。