Phase Relation of Harmonics in Nonlinear Focused Ultrasound

The phase relation of harmonics in high-intensity focused ultrasound is investigated numerically and experimen- tally. The nonlinear Westervelt equation is solved to model nonlinear focused sound field by using the finite difference time domain method. Experimental waveforms are measured by a robust needle hydrophone. Then the relative phase quantity is introduced and obtained by using the zero-phase filter. The results show that the nth harmonic relative phase quantity is approximately （n - 1） π/3 at geometric center and increases along the axial direction. Moreover, the relative phase quantity decreases with the increase of source amplitude. This phase relation gives an explanation of some nonlinear phenomena such as the discrepancy of positive and negative pressure.

Broadband acoustic focusing by symmetric Airy beams with phased arrays comprised of different numbers of cavity structures

We realize broadband acoustic focusing effect by employing two symmetric Airy beams generated from phased arrays,in which the units of the phased arrays consist of different numbers of cavity structures, each of which is composed of a square cavity and two inclined channels in air. The exotic phenomenon arises from the energy overlapping of the two symmetric Airy beams. Besides, we demonstrate the focusing performance with high self-healing property, and discuss the effects of structure parameters on focusing performance, and present the characteristics of the cavity structure with straight channels. Compared with other acoustic lenses, the proposed acoustic lens has advantages of broad bandwidth（about 1.4 kHz）, high self-healing property of focusing performance, and free adjustment of focal length. Our finding should have great potential applications in ultrasound imaging and medical diagnosis.

Direct MALDI-MS Analysis of Proteins Isolated by Liquid-phase Isoelectric Focusing Electrophoresis

A liquid-phase isoelectric focusing electrophoresis system(Rotofor) was used as the prefractionation tool for the sample preparation in the MALDI-MS analysis of a protein mixture. Each fraction collected was then directly subjected to MALDI-TOF-MS analysis. By this approach, we are able to resolve two types of hemoglobins, A and C, which cannot be successfully separated by means of the traditional SDS-PAGE method.

Tight Focusing Properties of Phase Modulated Radially Polarized Laguerre Bessel Gaussian Beam

We propose a new approach for generating a multiple focal spot segment of subwavelength size, by tight focusing of a phase modulated radially polarized Laguerre Bessel Gaussian beam. The focusing properties are investigated theoretically by .vector diffraction theory. We observe that the focal segment with multiple focal structures is separated with different axial distances and a super long dark channel can be generated by properly tuning the phase of the incident radially polarized Laguerre Bessel Gaussian beam. We presume that such multiple focal patterns and high intense beam may find applications in atom optics, optical manipulations and multiple optical trapping.

Thermoacoustic-reflected focusing lens based on acoustic Bessel-like beam with phase manipulation

We report the realization of broadband reflected acoustic focusing lenses based on thermoacoustic phased arrays of Bessel-like beams, in which the units of phase manipulation are composed of three rigid insulated boundaries and a thermal insulation film in air with different temperatures. Based on these units, we realize a reflected focusing lens which can focus reflected acoustic energy on a line, and its fractional bandwidth can reach about 0.29. In addition, we discuss the influences of the base angle of Bessel-like beam, the number of basic unit, and the variation of unit temperature on focusing performances in details. Furthermore, the reflected focusing lens for the cylindrical acoustic wave based on the Bessel-like beam is also demonstrated. The proposed focusing lens has the advantages of a broad working bandwidth, large focus size,and high robustness, which may provide possibilities for the design and application of acoustic lenses.

Ultrasonic beam focusing characteristics of shear-vertical waves for contact-type linear phased array in solid

We investigate the beam focusing technology of shear-vertical(SV) waves for a contact-type linear phased array to overcome the shortcomings of conventional wedge transducer arrays. The numerical simulation reveals the transient excitation and propagation characteristics of SV waves. It is found that the element size plays an important role in determining the transient radiation directivity of SV waves. The transient beam focusing characteristics of SV waves for various array parameters are deeply studied. It is particularly interesting to see that smaller element width will provide the focused beam of SV waves with higher quality, while larger element width may result in erratic fluctuation of focusing energy around the focal point. There exists a specific range of inter-element spacing for optimum focusing performance. Moreover, good beam focusing performance of SV waves can be achieved only at high steering angles.

在役螺栓超声三维成像监测数据的智能化分析方法

螺栓是一种常见的机械连接件,一旦失效,可能会导致设备损坏、结构崩塌,甚至危及人身安全。因此,在役螺栓的监测一直受到广泛关注。将相控阵超声全聚焦技术应用于螺栓在役监测,开发了专用系统和阵列探头,实现了三维成像可视化监测,改变了螺栓监测数据单一的现状。针对大量三维图像化数据处理的关键问题,提出了智能化分析方法,对比分析了决策树、支持向量机和神经网络算法的适用性,最终开发了基于决策树算法的智能分析评价软件模块并取得了较好的检测效果。

基于相控阵合成孔径的颅骨轮廓快速测量算法研究

作为一项新兴的神经调控技术,经颅聚焦超声技术目前广泛应用于脑深部的神经调控与治疗中。颅骨的异形和声参数的极大差异性是导致聚焦超声穿透颅骨后实际焦点的偏移和焦域散焦的主要原因。本研究以合成孔径技术为基础,由相控阵发射超声信号并接收于颅骨内外轮廓反射的回波信号,同时计算得到颅骨轮廓点坐标,实现对颅骨轮廓的快速测量。建立仿真模型,并利用颅骨仿体对算法进行仿真与实验验证。仿真结果表明,颅骨模型外轮廓中心区域的最大探测误差为0.15 mm,边缘区域为0.4 mm;内轮廓中心区域最大探测误差为0.3 mm,边缘区域为0.5 mm。实验结果表明:颅骨仿体外轮廓中心区域的最大探测误差为0.4 mm,边缘区域为0.8 mm;内轮廓中心区域最大探测误差为0.6 mm,边缘区域为0.9 mm。所设计的颅骨轮廓快速测量算法能够实现在2 min内完成颅骨内外轮廓的精确测量,并控制最大测量误差在1 mm以内。与核磁共振扫描(MRI)以及电子计算机断层成像(CT)相比,降低了治疗成本和治疗时间,同时为下一步调整相控阵阵元发射延时,实现在颅内的实时精确聚焦,提供了新的方法和思路。

圆柱类构件超声相控阵聚焦模型

在利用平面相控阵超声换能器对圆柱类构件检测时,受曲界面结构引起的入射波和回波时延的影响,扫描声束的波阵面产生弯曲,在利用传统迭代遍历算法计算延迟时间时效率低,无法发挥相控阵换能器检测优势。针对上述问题,建立了一种基于圆柱类构件特征和耦合介质特性的超声相控阵扫描成像的聚焦模型。该模型基于换能器、耦合介质、圆柱类构件材料特性和几何关系以及声线模型和折射定律,建立了耦合介质及被检构件的声速、曲面曲率半径、阵列与曲面间的距离等关联的延迟时间聚焦控制模型。利用该模型计算出的延时时间,对各阵元发射时间进行控制,从而实现扫描声束的聚焦。该文以液体和有机玻璃制介质楔块为例,对圆柱钢曲面的相控阵声束聚焦进行了仿真实验,结果表明该文方法计算效率显著提升,同时声束可以在预设位置实现聚焦,验证了该模型在计算效率上的优势与有效性。

基于人工电磁超表面的葡萄糖溶液检测装置

提出了一种基于人工电磁超表面结构的葡萄糖浓度检测装置。基于经人工超表面反射的电磁波近场聚焦特性对介电常数具有的高敏感性,实现了对葡萄糖溶液浓度的高精度检测。该人工超表面结构尺寸为400×400×1 mm^(3),由20×20个具有不同电磁波反射相位差的异构人工电磁超表面单元组成。为验证设计的可行性,对不同浓度值的葡萄糖溶液进行了实验测试,结果表明葡萄糖浓度值的改变将导致溶液相对介电常数的改变,进而对聚焦特性产生显著的影响,葡萄糖溶液的最大检测误差低于3.8%,检测线性度优于0.96。

应用于斜楔块的子孔径虚拟源全聚焦成像

楔块斜入射检测工艺下,楔块会进一步降低全聚焦成像的缺陷检测能力。尤其是在检测大深度缺陷和粗晶材料时,全聚焦图像会因为缺陷回波幅值下降,导致缺陷图像的信噪比较低。为了提高入射能量,提出了应用于斜楔块的子孔径虚拟源全聚焦成像技术。研究结果表明:该技术通过延时控制子孔径阵元激励形成虚拟源发射,显著增加了射入到被检构件中的声能。在横向L值为20∼40 mm探头移动区间内,17∼38 mm深度范围内Φ3边钻孔幅值较黄铜全聚焦图像提高4.58∼7.12 dB;当钢制试块为被检对象时,在横向L值为30∼40 mm探头移动区间内,40∼65 mm深度范围内Φ1边钻孔幅值较全聚焦图像提高0.63∼2.35 dB。因此在该技术应用于楔块斜入射检测工艺下的粗晶材料检测,具有较好的检测效果。

多种相控阵超声后处理聚焦算法的仿真对比

相控阵超声检测是1种新型、高级的工件内部缺陷无损超声检测技术,其可使用多个不同晶片独立发射超声波,并按照设定的时序和要求通过电子信息控制系统激发各晶片阵源,从而实现声场的偏转、多角度和聚焦。随着该技术的快速发展,出现了多种相控阵超声后处理聚焦算法。文章通过对几种常见相控阵超声后处理聚焦算法的原理简介与仿真,对比各种算法在分辨率设置、成像质量和运算数据量等的差异,分析各种算法的优缺点和适用范围,为合理的选择相控阵超声后处理聚焦算法提供参考依据。

钛焊缝的对置串列PCI与脉冲回波TFM组合检测

随着近年来PCI技术及TFM技术的发展与应用,与FMC及PWI所对应的数据处理方式已日渐丰富,从原先优化定性的辅助工具逐步转变为可用于实际检测的整套先进技术。针对钛焊缝检测中PCI技术与TFM技术的组合使用开展了相关分析,进行了二者与FMC和PWI配合使用的不同结合方式的对比试验。结果表明,采用PWI-TFM与对置串列PWI/FMC-PCI组合检测方式,能够优化钛焊缝检测效率与成像质量。

储氢钢瓶的在线水浸聚焦相控阵自动超声检测

传统的储氢钢瓶在线自动检测通常采用水浸点聚焦或线聚焦的超声检测方法,但点聚焦检测速度受到一定限制,线聚焦的检测灵敏度和分辨力比点聚焦的差。提出了带凹面声透镜的相控阵检测技术,通过凹面声透镜水浸耦合实现超声波在钢瓶截面方向的聚焦。利用CIVA软件对带凹面声透镜的相控阵探头辐射声场进行仿真分析,并根据仿真结果设计了相控阵探头参数,在此基础上开发了一套针对储氢钢瓶的五轴联动相控阵超声水浸C扫描自动检测系统,利用相控阵电子扫描技术快速规划超声检测路径和重构曲面。利用该检测系统,对带有人工缺陷的试件进行检测试验。试验结果表明:该方法融合了水浸点聚焦和线聚焦两种方法的优点,能够实现储氢钢瓶轴向和周向缺陷的自动在线超声检测。

Study on Energy Spectrum Instability in the Processes of Propagating and Breaking of Focusing Waves

Based on phase focusing theory, focusing waves with different spectral types and breaking severities were generated in a wave flume. The time series of surface elevation fluctuation along the flume were obtained by utilizing 22 wave probes mounted along the mid-stream of the flume. Based on the wave spectrum obtained using fast Fourier transform(FFT), the instability characteristics of the energy spectrum were reported in this paper. By analyzing the variation of total spectral energy, the total spectral energy after wave breaking was found to clearly decrease, and the loss value and ratio gradually increased and tended to stabilize with the enhancement of breaking severity for different spectral types. When wave breaking occurred, the energy loss was primarily in a high-frequency range of f/fp>1.0, and energy gain was primarily in a low-frequency range of f/fp<1.0. As the breaking severity increased, the energy gain-loss ratio decreased gradually, which demonstrates that the energy was mostly dissipated. For plunging waves, the energy gain-loss ratio reached 24% for the constant wave steepness(CWS) spectrum, and was slightly larger at approximately 30% for the constant wave amplitude(CWA) spectrum, and was the largest at approximately 42% for the Pierson-Moskowitz(PM) spectrum.

Influence of the abdominal wall on the nonlinear propagation of focused therapeutic ultrasound

This article theoretically studies the influence of inhomogeneous abdominal walls on focused therapeutic ultrasound based on the phase screen model. An inhomogeneous tissue is considered as a combination of a homogeneous medium and a phase aberration screen. Variations of acoustic parameters such as peak positive pressure, peak negative pressure, and acoustic intensity are discussed with respect to the phase screen statistics of human abdominal walls. Results indicate that the abdominal wall can result in energy loss of the sound in the focal plane. For a typical human abdominal wall with correlation length of 7.9 mm and variance of 0.36, the peak acoustic intensity radiated from a 1MHz transmitter with a radius of 30 mm can be reduced by about 14% at the focal plane.

Efficient Focusing Models for Generation of Freak Waves

Four focusing models for generation of freak waves are presented. An extreme wave focusing model is presented on the basis of the enhanced High-Order Spectral （HOS） method and the importance of the nonlinear wave-wave interaction is evaluated by comparison of the calculated results with experimental and theoretical data. Based on the modification of the Longuet-Higgins model, four wave models for generation of freak waves （a. extreme wave model ＋ random wave model; b. extreme wave model ＋ regular wave model; e. phase interval modulation wave focusing model; d. number modulation wave focusing model with the same phase） are proposed. By use of different energy distribution techniques in the four models, freak wave events are obtained with different Hmax/Hs in finite space and time.

An efficient focusing model for generation of freak waves

Based on the Longuet-Higgins wave model theory, the previews studies have shown that freak waves can be generated in finite space and time successfully. However, as to generating high nonlinear freak waves, the simulation results will be unrealistic. Therefore, a modified phase modulation method for simulating high nonlinear freak waves was developed. The surface elevations of some wave components at certain time and place are positive by modulating the corresponding random initial phases, then the total surface elevation at the focused point is enhanced and furthermore a freak wave event is generated. The new method can not only make the freak wave occur at certain time and place, but also make the simulated wave surface time series satisfy statistical properties of the realistic sea state and keep identical with the target wave spectrum. This numerical approach is of good precision and high efficiency by the comparisons of the simulated freak waves and the recorded freak waves.

Bidirectional asymmetric acoustic focusing with two flat acoustic metasurfaces

We design an asymmetric transmission system(ATS)with two flat acoustic metasurfaces(AMs)to yield bidirectional asymmetric acoustic focusing(BAAF).The acoustic waves could be focused on both sides of the ATS with different focal lengths and intensities.To achieve high intensity energy concentration,the accelerating acoustic beams are selected to realize the BAAF.The working bandwidth of the BAAF based on our ATS could reach ～0.4 k Hz.It is found that by adjusting the distance between two flat AMs,the focal length and intensity of the bidirectional focusing could easily be modulated.Because the distance between two flat AMs is large enough,the BAAF even could be converted into a unidirectional acoustic focusing.The proposed BAAF may find applications in non-destructive evaluation,biomedical imaging and medical diagnosis.

Phase-shifting digital holography in image reconstruction

A phase-shifting digital holography scheme developed to investigate internal defects in artworks is described. Phase-shifting is utilized to obtain a clear reconstructed object wave from a rough surface texture. A reverse-transform algorithm is employed to reconstruct the object wave on its original position of unknown distance or the imaging position from the object wave information on the holographic plane. To get the clearest reconstruction the exact registration of the unknown distance is determined by applying the intensity sum as the auto-focusing function, The spatial resolution of the reconstruction image is also investigated for a variety of affecting factors. Laboratory results of reconstruction images under deformation are presented.