热疗用聚焦超声换能器的研究

本文通过数值计算及实际测量,研究了凹球面声透镜聚焦换能器及凹球面自聚焦换能器产生的声场,证实此两种聚焦方式均可获得理想的聚焦效果,但自聚焦方式更适合高强度聚焦超声(HIFU)加热治疗。     

自聚焦换能器的声场研究

高强度聚焦超声（HIFU）治疗局部肿瘤是一项无创伤的新技术,有着很好的应用前景,因此对其声场的研究是有实际的价值的。对声场的研究不仅有利于换能器的设计,提高治疗的效果;而且有助声场测量方案的设计,提高对治疗超声剂量的安全保证。本文采用时域有限差分法研究了自聚焦换能器的声场,分别对简谐波,脉冲波进行了研究。比较清楚地看出在焦区的声场可以认为是平面波,这对光纤端面法声场测量提供了有力的支持。     

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。     

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.     

经颅超声聚焦方法和声场特性研究

针对井下前视成像问题, 设计了一种井下前视成像超声阵列换能器。换能器由平面圆环形阵列与凹面聚焦声学透镜组合而成, 通过相控阵发射聚焦声束并控制声束旋转扫描, 在阵元数相对较少的前提下实现了井孔前视方向的声束覆盖探测以及图像获取。推导了换能器的空间声场, 仿真分析了换能器的声场特性及相关参数对换能器聚焦性能的影响, 并据此确定了换能器的各项参数并试制出井下前视成像换能器。实验测试换能器的声场并进行了初步的成像实验, 结果表明, 换能器的实测声场与仿真结果基本符合, 所得前视图像可以反映障碍物的形状和位置信息。

     

高频聚焦换能器声场的激光测量法

本文描述了一种使用激光测振技术测量高频聚焦换能器声场布的方法，并给出了使用该方法对一种高频聚换能器进行测量的结果，通过理论计算对结果的正确性进行了验证。     

热疗用聚焦脉冲声场的时域和频域特性研究

本文用传递函数的概念导出了凹球面聚焦脉冲声扬的简洁表达式,从数值计算上和实验上研究了这种声场和中轴线上不同位置处声压信号的持续时间和频谱特征,分析了它们对热疗的影响。     

几类旋转圆弧式自聚焦换能器的声场特性分析

通过分析和比较几种有代表性的旋转圆弧式曲面聚焦换能器的声场特性,探索了不同类型聚焦曲面换能器用于加温的可行性。结果表明：旋转抛物面具有良好的聚焦效果,可以形成明显的聚焦点。圆锥面和旋转星形面具有较好的轴向线性聚焦效果,声束比较细,有较大的轴向加热范围。与圆锥面相比较,旋转星形面的声场受换能器参数影响小。在换能器设计中,设计者可根据不同加热对象,设计不同曲面换能器以达到最优加热效果。     

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     

共聚焦超声换能器的声场优化与粒子捕获

超声悬浮被广泛应用于多个领域,目前主要有驻波式和相控阵式悬浮系统.基于共焦点排列的聚焦换能器结构,本研究提出了一种单边式超声悬浮系统.其基本原理是利用反相激励成对聚焦换能器在空间构建具有势阱结构的特定声场,实现微粒的捕获与悬浮.针对4个共焦点排列的聚焦换能器,基于有限元仿真研究了换能器轴夹角及激励相位模式对声场分布的影响;利用实验演示了系统的粒子捕获效果,验证了其势阱分布情况.结果表明,换能器轴线与结构中轴线夹角为45°时,势阱强度最高;换能器的激励相位分别为0,0,π,π时,声场中存在1处主势阱、2处次级势阱,可以捕获3处粒子团;换能器的激励相位分别为0,π/2,π,3π/2时,声场中仅存在1处势阱,只可捕获1处粒子团.该系统具有成本低、自由度高、稳定性强、操作便捷的优点,且能够实现单个位置或多个位置粒子团的捕获与悬浮,可以用于流体中高密度物体操控.     

Simulation of sound field in a tissue medium generated by a concave spherically annular transducer

The concave spherically annular transducer is regarded as a negative and a positive concave spherical transducer, and the spheroidal beam equation is used to simulate the linear and nonlinear sound field in a tissue medium generated by this transducer. It is found that the acoustic focus of the ring does not coincide with the acoustic focus of its central part. If the width of the ring increases, its acoustic focus will move toward the geometric focus and the amplitudes of nonlinear harmonics will increase obviously. If there are several coaxial rings placed on the concave spherical surface, more than one peak will appear along the axial direction for the fundamental, and high harmonics focus better. The distribution of sound field will change with the number and the excited signals of rings, so it maybe is a potential approach to treat locally big tumors.     

矩形栅慢波系统的高频特性分析

对于矩形栅这一经典的慢波结构，采用场匹配法来分析其慢波特性，进而得到其耦合阻抗。其中对槽区内的场处理，保留其高次项，表示为一无限本征驻波之和的形式。然后通过数值实例具体分析了矩形栅的两种典型结构:浅槽栅和深槽栅。当增大槽深后，色散增强，系统通带变窄，同时耦合阻抗有明显增大，工作点移向前向波区，适合用在放大器的慢波结构上。     

Spatial distribution of sonoluminescence and sonochemiluminescence generated by cavitation bubbles in 1.2 MHz focused ultrasound field

An intensified charge coupled device (ICCD) camera was used to observe the spatial distribution of sonoluminescence (SL) and sonochemiluminescence (SCL) generated by cavitation bubbles in a 1.2 MHz focused ultrasound (FU) field in order to investigate the mechanisms of acoustic cavitation under different sonication conditions for FU therapeutic applications.It was found that SL emissions were located in the post-focal region. When the intensity of SL and SCL increased as the power rose, the growth of SCL was much higher than that of SL. In the post-focal region, the SCL emissions moved along specific paths and formed branch-like streamers. At the beginning of the ultrasound irradiation, cavitation bubbles generated SCL in both the pre-focal and the post-focal region. When the electrical power or the sonication time increased, the SCL in the post-focal region increased and became higher than that in the pre-focal region. The intensity of SCL in the focal region is usually the weakest because of “oversaturation”.The spatial distribution of SCL near a tissue boundary differed from that obtained in free fields. It organized into special structures under different acoustic amplitudes. When the electrical power was relatively low, the SCL emission was conical shape which suggested a standing wave formation at the tissue-fluid boundary. When the electrical power exceeded a certain threshold, only a bright spot could be captured in the focus. The cavitation bubbles which centralized in the focus concentrated energy and hindered the formation of standing waves. With rising electrical power at high levels, besides a bright spot in the focus, there were some irregular light spots in pre-focal region, which indicated some cavitation bubbles or small bubble clusters achieved the threshold of SCL and induced the reaction with the luminol solution.     

环形光束的聚焦性质研究

从理想的环形光束出发,理论上分析了环形聚焦光束在焦点附近的光强分布情况,以及光束内外径之比对聚焦性质的影响.然后利用数值模拟的手段,研究了带软化因子的环形光束的聚焦性质,在整体上给出了环形光束的聚焦性质.     

同轴放电环形增益区谐振腔镜面的场分布

 对几类环形增益区谐振腔进行了比较,得出利用谐振腔两镜之一的全工作面输出的新型环形增益区谐振腔是适合的谐振腔。提出了一种计算全工作面输出的同轴放电环形增益区谐振腔镜面场分布的方法,利用几何方法对腔镜镜面进行划分,得出了基于菲涅尔-基尔霍夫衍射积分定理的积分区域,并对该区域进行了有限元划分,应用计算机编程计算出了同轴放电环形增益区谐振腔镜面处的光场分布和相位分布。近场分布在环形区中央部分近似地呈高斯分布,且沿径向出现高阶模场分布特点,沿角向无差别。     

Extension of the crosstalk cancellation method in ultrasonic transducer arrays from the harmonic regime to the transient one

This paper describes a procedure to extend the crosstalk correction method presented in a previous paper [A. Bybi, S. Grondel, J. Assaad, A.–C. Hladky-Hennion, M. Rguiti, Reducing crosstalk in array structures by controlling the excitation voltage of individual elements: a feasibility study, Ultrasonics, 53 (6) (2013) 1135–1140] from the harmonic regime to the transient one. For this purpose a part of an ultrasonic transducer array radiating in water is modeled around the frequency 0.5 MHz using the finite element method. The study is carried out at low frequency in order to respect the same operating conditions than the previous paper. This choice facilitated the fabrication of the transducer arrays and the comparison of the numerical results with the experimental ones. The modeled array is composed of seventeen elements with the central element excited, while the others are grounded. The matching layers and the backing are not taken into account which limits the crosstalk only to the piezoelectric elements and fluid. This consideration reduces the structure density mesh and results in faster computation time (about 25 min for each configuration using a computer with a processor Intel Core i5-3210M, frequency 2.5 GHz and having 4 Go memory (RAM)).     

Acousto-optic interaction in a non-homogeneous acoustic field excited by a wedge-shaped transducer

The article is devoted to theoretical analysis of light diffraction in a non-homogeneous acoustic field created by a wedge-shaped piezoelectric transducer. Relationships describing electrical, acoustic and acousto-optic properties of the acousto-optic cell are derived in the approximation of a small thickness of the piezoelectric plate. Principal characteristics of acousto-optic interaction are examined such as dependences of the light diffraction efficiency on the phase mismatch and the acoustic wave amplitude. It is shown that the acoustic field has a complicated amplitude-phase structure changing with the acoustic frequency. It is demonstrated that the diffraction efficiency in the Bragg regime can approach 100% in spite of a noticeable phase mismatch. The appropriate optimal values of ultrasound power and incidence angles of light are found.     

医用梅花形超声探头声场的分析与计算

本文根据基尔霍失积分，推导了出民用于监护的梅花形超声多普勒探头声场的具体表达式。对中心大圆晶片发射，周围六个小圆片接收，以及七个相同晶片四发三收两种典型布局的换能器，其轴上声压分布，离辐射面不距离断面上的声压分布及不同定向平面上的这场指向性进行了数值计算。结果表明，采用四发三收式结构较一发六收式结构具有较大的优越性。计算结果与实际测试结果很好地吻合。     

医用梅花形超声探头声场的分析与计算

本文根据基尔霍夫积分．推导出了用于胎儿监护的梅花形超声多普勒探头声场的具体表达式．对中心大圆晶片发射、周围六个小圆片接收，以及七个相同晶片四发三收两种典型布局的换能器，其轴上声压分布，离辐射面不同距离断面上的声压分布及不同定向平面上的远场指向性进行了数值计算．结果表明，采用四发三收式结构较一发六收式结构具有较大的优越性．计算结果与实际测试结果很好地吻合．本项研究对此类探头的研制、使用及质量评价标准的制订，具有理论指导意义．     

压电晶体-液体-固体声波导中叉指换能器对导波的激发研究

本文对压电晶体－液体－各向同性固体结构的声波导中叉指换能器所激发的导波进行了理论研究和数值分析,给出了导波的相速度、叉指换能器激发导波的机电耦合系数与液体层归一化厚度、晶体取向之间的关系曲线,同时,还探讨了声波导中的位移场和电势场分布。