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。      

双层界面下非近轴近似多元高斯模型的相控阵声场模拟

非近轴近似多元高斯模型克服了近轴近似条件的限制,能保证较大偏转角度下模拟声场的精确度和效率。根据双层介质的瑞利积分模型和单层介质的非近轴近似多元高斯模型,推导出双层介质中基于非近轴近似多元高斯模型的单阵元辐射声场计算模型。并在得到各阵元声束偏转聚焦的延迟时间基础上,累加得到基于非近轴近似高斯模型的超声相控阵横波检测辐射声场计算模型。模拟计算带丙烯酸树脂楔块的超声相控阵探头在钢中横波检测的声束偏转与偏转聚焦辐射声场,并与近轴近似多元高斯模型的横波检测声束的偏转聚焦辐射声场进行比较分析。对比分析结果表明非近轴近似多元高斯模型计算速度更快,用时约为近轴近似多元高斯模型的1/13。此外,非近轴近似高斯模型方法横波检测的聚焦声束覆盖区域更大,能量更集中,更适于远场区域检测。      

Nonparaxial multi-Gaussian beam models and measurement models for phased array transducers

A nonparaxial multi-Gaussian beam model is proposed in order to overcome the limitation that paraxial Gaussian beam models lose accuracy in simulating the beam steering behavior of phased array transducers. Using this nonparaxial multi-Gaussian beam model, the focusing and steering sound fields generated by an ultrasonic linear phased array transducer are calculated and compared with the corresponding results obtained by paraxial multi-Gaussian beam model and more exact Rayleigh-Sommerfeld integral model. In addition, with help of this novel nonparaxial method, an ultrasonic measurement model is provided to investigate the sensitivity of linear phased array transducers versus steering angles. Also the comparisons of model predictions with experimental results are presented to certify the accuracy of this provided measurement model.     

多层奥氏体钢中超声相控阵辐射声场分析

针对一维线性超声相控阵透过楔块,在多层不同晶轴取向的奥氏体钢中的声场辐射问题,结合高斯声束等效点源模型以及基于时间最小原理的射线追踪法,给出了各层介质中透射声场的计算方法。将奥氏体钢近似为横向各向同性介质,计算了相控阵透过楔块,在晶轴取向为0°的奥氏体钢中的无延时纵波声场,计算结果与COMSOL仿真结果相吻合,从而验证了所用方法的正确性。通过加入不同的延迟法则,仿真计算了三层含有不同晶轴取向(0°,30°,100°)的奥氏体钢中的纵波声场,实现了相控阵声场的偏转与聚焦,分析了偏转声场与聚焦声场的传播特性。仿真结果表明,不同的晶轴取向将导致不同的声束偏转以及聚焦效果。通过延迟激励各阵元,虽然可以控制声束偏转或聚焦到预定位置,但是晶轴取向仍会对声束宽度以及幅值产生一定的影响。      

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     

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.     

楔块中脉冲声场及相控阵成像自检研究

相控阵横波检测必须在换能器前方加上楔块,对于楔块中的声场进行研究具有重要意义。本文通过数值计算和物理实验研究了超声相控阵楔块中的脉冲声场,分析并解释了超声相控阵系统自检成像过程中各种波形的产生机理和转换过程。首先从固体中超声传播理论出发,采用时域有限差分方法对相控阵楔块中各阵元独立发射条件下的脉冲声场进行仿真计算,给出了超声脉冲在楔块中的传播过程;然后开展了对应边界条件下相控阵楔块的B模式成像实验。数值模拟和物理实验的结果基本一致。本文的研究初步展示了楔块中的脉冲声场,其结果可为超声相控阵系统自检和楔块设计提供参考。     

超声数字式相控阵换能器动态聚焦系统研制

本文是研制超声相控阵换能器动态聚焦系统,它包括数字式多通道信号发射系统和两种超声相控阵换能器。用数字式多通道信号发射系统产生多路数字信号,通 过改变每路信号的时延(相位),控制相控阵换能器的各个阵元,使它们发出的声束在空间某点聚焦。我们对这两种相控阵进行了实验测量,结果表明,用数字控 制的相控阵换能器,可以实现精密的动态聚焦,并可取得良好的聚焦效果。     

瞬态波位移场计算方法在相控阵声场模拟中的实验验证

通过实验研究了声束偏转不同角度和声场半径变化时线性相控阵的声场特性,并与基于瞬态波位移解析解的相控阵声场计算方法得到的理论结果进行了对比。首先研究了基于半圆圆弧离面瞬态位移的声场计算方法,并进行了数值计算可靠性的优化。然后建立了一套相控阵瞬态波位移场的测量系统,以半圆形钢板为试件,纵波传感器为接收传感器,测量了偏转角度为-10°,-30°,-50°,-70°,及声场半径为50 mm,75 mm,100 mm和125 mm时线性超声相控阵的声束指向性;同时以基于瞬态波位移解析解的相控阵声场计算方法,计算了相同条件下该相控阵的声束指向性。最后将实验结果与理论结果进行了对比,取得了较好的一致。说明基于瞬态波位移的相控阵声场计算方法可以较好地计算线阵的声场,对于声束偏转较大角度和声场半径变化时也同样有效。      

C/Ku波段共口径宽角度扫描相控阵天线

设计了一款具有高功率容量与宽角度扫描特性的C/Ku双频段共口径平面相控阵天线。在同一辐射口径内,相控阵天线包含有基于平面偶极子单元的C波段4×4阵列,以及基于混合零阶谐振贴片单元的Ku波段8×9阵列。所设计的相控阵天线的宽角度扫描性能归功于双频段阵元天线的宽波束辐射特性。下层混合零阶谐振贴片天线既能作为Ku波段的宽波束辐射单元,又能够为C波段的偶极子天线提供零反射相位,进而基于镜像原理拓宽偶极子天线的波束宽度。并且,对天线进行了介质埋入式设计,避免了空气击穿以提高天线系统功率容量。全波仿真结果表明,所提出的共口径相控阵天线在C和Ku双频段均实现了±45°的波束扫描,增益波动小于3 dB,天线阵列在各单元输入功率之和为1 W时功率容量达18.9 MW。     

Development of phased array techniques to improve characterization of defect located in a component of complex geometry

Ultrasonic inspection of complex geometry components has to cope with different problems: limited access of the area assumed to be insonified, beam misorientation and distortions, loss of sensitivity. Those harmful effects can lead to inspection performance degradations, especially in terms of defect detection and characterization. Phased array techniques may be used to overcome such difficulties, as they can provide an optimal mastering of the ultrasonic beam radiated through the inspected component. This paper presents some applications of phased array inspections carried out by the French Atomic Energy Commission (CEA) and the French Company of Electricity (EDF) in the framework of R&D studies. Inspections of components with varying profile (of planar and cylindrical parts, misalignment and local depression), and containing artificial reflectors have been carried out with pulse echo immersion techniques, using standard and phased arrays transducers. Optimal delay laws have been applied to preserve the beam characteristics in spite of the varying profile geometry encountered as the phased array transducer was moved over the component. Those delay laws allow to efficiently compensate the beam distortions generated by the profile geometry. They were computed using a specific model and compared to experimental delays obtained using through transmission tests. Experimental and simulation results showed that the defect detection and characterization performances were greatly enhanced using phased array techniques. In the presented examples, with standard transducers, defects located below the irregular parts of the specimen were partially detected, in accurately located or even missed, whereas phased array inspections enabled to detect and locate all of these defects.     

Improving the air coupling of bulk piezoelectric transducers with wedges of power-law profiles: A numerical study

An air-coupled ultrasonic transducer is created by bonding a bulk piezoelectric element onto the surface of a thick plate with a wedge of power-law profile. The wedge is used to improve the ultrasonic radiation efficiency. The power-law profile provides a smooth, impedance-matching transition for the mechanical energy to be transferred from the thick plate to the air, through the large-amplitude flexural waves observed in the thinnest region of the wedge. The performance of the proposed transducer is examined numerically and compared to that of a design where the piezoelectric element is isolated and where it is affixed to a thin plate of uniform thickness. The numerical analysis is first focused on the free-field radiation of the transducers. Then, time-reversal experiments are simulated by placing the transducers inside a cavity of arbitrary shape with some perfectly reflecting boundaries. In addition to time-reversal mirrors, the proposed concept could be integrated in the design of phased arrays and parametric arrays.     

Calculation of radiation acoustical fields from phased arrays with nonparaxial multi-Gaussian beam model

A nonparaxial multi-Gaussian beam model based on the rectangular aperture is proposed in order to overcome the limitation of paraxial Gaussian beam model which losing accuracy in off-axis beam fields. With the method, acoustical field generated by an ultrasonic linear phased array transducer is calculated and compared with the corresponding field obtained by Rayleigh-Sommerfeld integral, paraxial multi-Gaussian beam model, and Fraunhoffer approximation method. Simulation examples show that nonparaxial multi-Gaussian beam model is not limited by the paraxial approximation condition and can predict efficiently and accurately the acoustical field radiated by a linear phased array transducer over a wide range of steering angles.     

多层介质中超声相控阵声场仿真*

由于良好的声束偏转与聚焦特性,超声相控阵已经广泛应用于多层固体介质的缺陷检测。当超声束经过多层介质时,由于反射、透射以及模式转换的存在,多种声束存在于这种结构中,使得声场分析变得复杂。为了提高多层介质检测的准确性,有必要对超声声场的分布规律进行深入地了解。该文结合高斯声束等效点源模型以及射线追踪法,给出了相控阵声源在多层固体介质中激发声场的仿真方法,并且模拟计算了一维线型相控阵在楔块-铝-黄铜-钢四层固体介质中的辐射声场。通过对不同延时法则的计算,实现了声波在这种复杂介质中的偏转与聚焦,进而研究了不同焦点处聚焦声场的分布。结果表明:相控阵方法能使聚焦点处的声场幅值增大,能量集中,提高了检测分辨率;不同聚焦点处声场聚焦效果不同,实际检测时应根据检测区域结构及位置特点,合理放置相控阵换能器。与瑞利积分法的比较表明,该文的仿真方法适用于多层介质相控阵声场的计算。     

The directivity pattern of an interferometer for measuring thermal acoustic radiation

The directivity patterns of a pair of piezoelectric transducers for measuring the spatial correlation function of sound pressures produced by sources of thermal acoustic radiation in the megahertz frequency range are calculated. Sources in the form of a heated plane or strip are considered. The signal detection by two circular or rectangular piezoelectric transducers and by focusing transducers is studied. It is demonstrated that, for measuring the correlation function, the piezoelectric transducers must partially overlap. To determine the directivity pattern with a strong dependence on the distance between the heated object and the pair of piezoelectric transducers, focusing piezoelectric transducers should be used. The results obtained offer possibilities for a noninvasive measurement of the absorption coefficient of a medium and also for the realization of the previously proposed [20] passive acoustic thermotomograph, which does not use a priori information on the absorption coefficient of the medium.     

Simulations of lesion detection using a combined phased array LHMI-technique

Ultrasound based elasticity imaging techniques have been developed during the past decades. Some of these techniques are based on an internal radiation force stimulation in which a transient or dynamic radiation force is produced by using a single or dual-frequency sonication. In addition, sonication and data acquisition can be implemented using combined or separate transducers. In this simulation study of lesion detection using localized harmonic motion imaging (LHMI), we used a combined phased array designed for simultaneous thermal ablation and lesion detection. In the sonication mode, a focused single-frequency amplitude-modulated sonication is used to induce harmonic motion and in the tracking mode, some of the array elements are used for pulse-echo tracking of the induced displacements. The results showed that the size of the lesion affected the induced displacement around the sonication point. The displacement tracking simulations demonstrated that these changes in the displacement distributions can be detected using only a few of the array elements in the tracking mode but the exact size of the lesion can not be detected accurately. The simulations also showed that two lesions having the radius of 2.5mm can be distinguished if distance between these lesions is at least 2.5mm.     

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。     

Optimal focusing by spatio-temporal inverse filter. II. Experiments. Application to focusing through absorbing and reverberating media

To focus ultrasonic waves in an unknown heterogeneous medium using a phased array, one has to calculate the optimal set of signals to be applied on the transducers of the array. (In most applications of ultrasound, medical imaging, medical therapy, nondestructive testing, the first step consists of focusing a broadband ultrasound beam deeply inside the medium to be investigated.) Focusing in a homogeneous medium simply requires to compensate for the varying focus-array elements geometrical distances. Nevertheless, heterogeneities in the medium, in terms of speed of sound, density, or absorption, may strongly degrade the focusing. Different techniques have been developed in order to correct such aberrations induced by heterogeneous media (time reversal, speckle brightness, for example). In the companion to this paper, a new broadband focusing technique was investigated: the spatio-temporal inverse filter. Experimental results obtained in various media, such as reverberating and absorbing media, are presented here. In particular, intraplate echoes suppression and high-quality focusing through a human skull, as well as hyper-resolution in a reverberating medium, will be shown. It is important to notice that all these experiments were performed with fully programmable multichannel electronics whose use is required to fully exploit the spatio-temporal technique.     

On the acoustic radiation modes of compact regular polyhedral arrays of independent loudspeakers

Compact spherical loudspeaker arrays can be used to provide control over their directivity pattern. Usually, this is made by adjusting the gains of preprogrammed spatial filters corresponding to a finite set of spherical harmonics, or to the acoustic radiation modes of the loudspeaker array. Unlike the former, the latter are closely related to the radiation efficiency of the source and span the subspace of the directivities it can produce. However, the radiation modes depend on frequency for arbitrary distributions of transducers on the sphere, which yields complex directivity filters. This work focuses on the most common loudspeaker array configurations, those following the regular shape of the Platonic solids. It is shown that the radiation modes of these sources are frequency independent, and simple algebraic expressions are derived for their radiation efficiencies. In addition, since such modes are vibration patterns driven by electrical signals, the transduction mechanism of compact multichannel sources is also investigated, which is an important issue, especially if the transducers interact inside a shared cabinet. For Platonic solid loudspeakers, it is shown that the common enclosure does not lead to directivity filters that depend on frequency.