相控阵高强度聚焦超声高阵元驱动效率相位独立控制方法

针对如何简化上百阵元高强度聚焦超声相控阵控制模块的问题,本文提出高阵元驱动效率的相位独立控制方法。利用该方法计算了一种256阵元中心开孔球面相控阵的聚焦声场,并与传统的幅度相位综合控制方法进行了分析和比较。计算和实验结果表明该方法在简化相控阵驱动控制模块、提高阵元驱动效率的同时,可以有效实现相控阵的空间三维单焦点聚焦。由于阵元驱动控制的简化而引起的焦域能量偏差,可以通过适当调整相控阵输入总声功率进行有效的补偿。      

被控点声压直接加权的相控声场合成模式

为快速高效地对相控阵声场进行优化,对伪逆算法进行了简化.通过对被控点声压进行幅值和相位补偿,得到了一个近似的声压加权公式.应用该公式预设被控点声压值,然后运用改进的伪逆矩阵算法确定相控阵各阵元的振幅和相位,从而得到一个直接的多焦点声场合成模式.基于该合成模式设计了一16×16个正方形阵元构成的平面相控阵,并对多焦点声场的合成进行了数值仿真.结果表明,该方法可提高声能在目标点的沉积能力,具有较高的声场合成效率,为超声热疗中声聚焦控制提供了一条有效的途径.     

基于时间反演电磁波的稀疏阵列单频信号空间功率合成

基于时间反演技术, 建立了稀疏阵列单频信号相干合成的数学模型, 定义了合成效率函数概念, 推导出合成信号幅度最大时刻目标点合成效率值的统计特征与相位误差及阵元数的关系表达式, 并通过理论分析与仿真计算研究了相位误差对时间反演单频信号合成效果的影响. 分析表明, 当其他参数确定时, 假设相位误差服从一定范围的均匀分布, 且相互独立, 则峰值功率时刻的合成效率均值与阵元数无关, 仅与误差分布范围有关; 峰值功率时刻的合成效率方差与两者均相关, 且误差分布范围确定时, 阵元数越大, 峰值功率时刻的合成效率方差越小. 仿真计算结果表明, 即使存在一定的相位误差, 利用时间反演技术, 仍可实现单频信号在目标点邻域的相干合成及能量聚焦; 对相位误差的控制精度应结合需求与实现条件折中考虑. 本文的方法与结论可为研究稀疏阵列功率合成在高功率微波武器等技术中的应用提供理论依据.     

凹面线性相控阵聚焦与扫描成像

研究了凹面线性相控阵聚焦声场的聚焦特性与扫描成像处理,首先对凹面线性相控阵聚焦声场进行了深入的分析,对凹面线阵聚焦中变迹处理、阵元间距及f数等参数对相控阵瞬态声场聚焦特性的影响进行了分析和讨论;然后,分析了相控阵聚焦声场在散射物体上产生的散射声场特性,得到了利用凹面线性相控阵进行线性查扫的B扫图像,在此基础上,利用凹面线性相控阵辐射声场在非均匀体上的散射声场进行了扫描成像研究和处理,针对实际管材质量的相控阵检测问题,得到了管材纵波扫描整个区域的检测图像.     

环形相控阵换能器辐射和反射声场

研究了超声环形相控阵辐射声场和反射声场的基本特性。理论上详细分析了环形相控阵的阵元数目、环形阵半径、阵元间距、中心频率、焦点位置等因素对辐射声场的影响。实验上设计并制作了具有8个环的等面积环形相控阵列并进行了实验测量。通过理论和实验分析,研究了环形相控阵的辐射声场及在液固界面上的反射声场特性,取得了理论和实验相吻合的结果。     

多通道超声相控阵驱动控制系统设计

低强度经颅聚焦超声是一种利用脉冲聚焦超声调控脑神经元的治疗技术。为抑制人颅骨的非均质性和个体结构差异影响,须对多阵元相控阵聚焦换能器的各阵元进行参数调控实现经颅精准定位聚焦,各阵元参数调控需通过相位控制和驱动电路系统来实现。该文设计并搭建了一种基于直接数字式频率合成技术的多通道相位、幅值独立可调的相控驱动系统。实测结果表明,可实现正弦波和方波高精度相控输出,输出信号电压峰峰值在0~37.5 V可调,相位分辨率为0.1°,延时误差小于1 ns,可满足多阵元相控阵聚焦换能器驱动及其所需相位分辨率的需要。     

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。      

光纤延迟线噪音对相控阵波束指向的影响

基于相位噪音和相控阵理论,运用线阵天线原始方向图函数和光纤链路噪音系数公式,根据天线波束指向实际误差进行合理近似,推导了光延迟线链路噪音系数、天线阵元数与波束指向误差的理论公式.采用常规光纤链路参量进行了仿真研究,结果表明:相控阵天线波束指向误差均方差随光纤链路噪音系数增大而增加,随天线阵元数增加而减小,指向误差与光纤延迟线链路噪音系数的1/2次方成正比,与阵元数的3/2次方成反比.在相控阵天线工作频段内,低频波段受噪音系数影响更加明显.     

光纤放大器阵列的远场特性研究

从光纤激光器阵列相干合成远场光强分布的解析表达式出发，详细研究了阵列占空比、阵元个数以及阵元的相位误差对相干合成远场图样分布、中心主瓣的角宽度及所占能量的影响. 给出了占空比为12.5%时，三路保偏光纤放大器相干合成的实验结果. 关键词： 光纤激光器阵列 相干合成 相位     

基于相位差实时计算法实现相控式高强度超声聚焦

利用时间反转法对相控阵高强聚焦超声系统进行自适应聚焦,需要计算出各阵元的初始发射相位。锁相环电路初始工作时频率有震荡,用常规计算相位差的方法当截取数据的时间段不同时计算出的相位差不相同。提出一种计算相位差的方法,可以实时显示相位差的变化,将稳定后的相位差作为相控阵聚焦系统各发射阵元的初始相位。实验结果表明,用此方法计算的相位差进行聚焦可以在一定空间范围内得到较好的声场分布。      

A synthesis pattern of acoustic field produced by phased array based on the direct weighting of the controlled acoustic pressure

To optimize the acoustic field produced by phased array effectively and quickly, the pseudo-inverse method proposed previously is simplified.An approximate weight formula of sound pressure using a method of compensation to the amplitude and phase of the controlled sound pressure was presented.A multiple-focus field patterns based on the pseudo-inverse matrix algorithm can be obtained by presetting the value of the controlled sound pressure.A phased array comprised of 16×16 square elements is used for numerical simulation.The results show that the acoustic energy can be effectively deposited at the desired points,and the acoustic field can be synthesized quickly using the direct weight formula of the sound pressure.This study may offer an effective way for controlling the distribution of acoustic field in ultrasound hyperthermia.     

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。     

Analytical method for evaluating the quality of acoustic fields radiated by a multielement therapeutic array with electronic focus steering

The paper presents an analytical method for calculating and analyzing the quality of 3-D acoustic fields of multielement phased arrays used in noninvasive ultrasound surgical devices. An analytical solution for the far field of each of its elements is used when calculating the array field. This method significantly accelerates calculations while preserving the high accuracy of results as compared to conventional direct numerical integration. Radiation from typical phased arrays is calculated using this approach, and the quality of their dynamic focusing is analyzed. Undesired diffraction effects caused by electronic focus steering are considered: an amplitude decrease in the main maximum and the appearance of grating lobes. The quality of dynamic focusing of the acoustic fields of two practically interesting arrays with a quasi-random element distribution (256 and 1024 elements, respectively), as well as of the regular array consisting of 256 elements is compared. In addition as well, a study is made of how the dimensions of the array elements and their spatial distributions affect the dimensions of the areas in which dynamic focusing is possible without occurrence of strong grating lobes and significant decrease in pressure amplitude at the main focus.

     

Field characterization of therapeutic ultrasound phased arrays through forward and backward planar projection

Spatial planar projection techniques propagate field measurements from a single plane in front of a transmitter to arbitrary new planes closer to or further away from the source. A linear wave vector frequency-domain projection algorithm is applied to the acoustic fields measured from several focused transducer arrays designed for ultrasound therapy. A polyvinylidene difluoride hydrophone is first scanned in a water tank over a plane using a three-dimensional positioning system to measure the complex pressure field as a function of position. The field is then projected to a series of new planes using the algorithm. Results of the projected fields are compared with direct measurements taken at corresponding distances. Excellent correlation is found between the projected and measured data. The method is shown to be accurate for use with phase-controlled field patterns, providing a rapid and accurate method for obtaining field information over a large spatial volume. This method can significantly simplify the characterization procedure required for phased-array application used for therapy. Most significantly, the wavefront propagated back to a phased array can be used to predict the field produced by different phase and amplitude settings of the array elements. A field back-projected to the source could be used as an improved source function in acoustic modeling.     

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。      

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.     

Two-dimensional phased arrays for surgery: Movement of a single focus

Numerical simulation and comparative analysis of acoustic fields generated by two-dimensional phased arrays designed for ultrasonic surgery is conducted. The case of movement of a single focus by an array with the surface shaped as a part of a spherical shell with the curvature radius 120 mm is considered. The influence of the number of elements (varying from 64 to 1024), their diameter (from 2.5 to 10 mm), frequency (from 1 to 2 MHz), and the degree of sparseness of the elements at the array surface on the field characteristics is studied. The calculations are performed for arrays with elements positioned at the surface both regularly (in square, annular, or hexagonal patterns) and randomly. Criteria for the evaluation of the “quality” of intensity distributions in the field generated by an array in the case of movement of a single focus are suggested. Of all arrays studied, the best quality of distributions is obtained for an array containing 256 elements of diameter 5 mm randomly positioned at the array surface. The quality of the intensity distributions for arrays consisting of 255, 256, and 1024 elements positioned regularly (in square, annular, and hexagonal patterns) is inferior to the corresponding quality for arrays with randomly positioned elements. The irregularity in elements’ positioning considerably improves the distribution quality by suppressing the secondary intensity peaks in the field generated by the array; or, alternatively, it provides an opportunity to obtain the same distribution quality with a fraction of the number of elements in the array. The effects of the number and shape of elements, errors in phase setting, frequency modulation of signals, and non-uniform distribution of amplitudes over the array surface on the distribution quality are analyzed.     

Numerical study on scanning radiation acoustic field in formations generated from a borehole

The directivity of acoustic transducers used in conventional acoustic logging tools is uncontrollable[1,2], which inevitably affects investigation depth and resolution. At present, deep and wide range of investigation in petroleum exploration is urgently re- quired. It is important to improve the exploration capability to find more complex and fine reservoirs[3], for which the direction of the radiated acoustic energy is a direct factor. Acoustic field in the formations generated by the source…