超声磨粒监测传感器设计研究

针对用超声监测磨粒的难点和关键之一－－超声传感器设计的问题，从理论上分析了聚焦超声波声场特性，并进行了聚焦传感器声场的计算机模拟仿真，最后提出了一种聚焦超声传感器设计准则。     

1-3型压电复合材料壳式聚焦换能器的研究

为解决压电陶瓷聚焦换能器阻抗高、带宽窄,电声转换效率低等问题,采用新型的1-3型压电复合材料作为聚焦超声换能器材料,设计并制作了一种新型的1-3压电复合材料壳式聚焦换能器。通过对新型换能器的频率特性,电声转换效率研究后和当前应用的PZT壳式聚焦换能器进行对比,证明了1-3型压电复合材料壳式聚焦换能器的阻抗较低,相对带宽达61%,是PZT压电陶瓷壳式聚焦换能器的3.39倍,以及较高的电声转换效率η为54%,是PZT压电陶瓷壳式聚焦换能器的1.68倍。将换能器实际声场检测结果与Matlab声场仿真结果进行对比研究,得出换能器具有较好的声场特性及聚焦效果。为高性能的聚焦换能器的实现提供了理论及实验基础。     

基于扫描数据可视化的超声换能器参数测量

超声探头是超声无损检测中的关键部件,其参数直接影响到对超声检测系统性能的评价与校准。在自主建立的水浸超声声场自动扫查系统基础上,以标准ASTM E1065-99为依据,利用水听器法对聚焦超声换能器声场进行扫描,并将数据可视化。在数据可视化的基础上,对声场中若干重要参数进行了测量。实验结果表明,测量结果与理论计算结果吻合程度良好,所实现的声场自动扫查系统能够真实反应出换能器空间的声场分布,能够为超声换能器应用特性的准确评价提供可信的数据。     

声光偏折效应球壳型换能器聚焦焦点峰值声压的测量

利用声光偏折效应,设计了一种测量球壳型换能器辐射聚焦声场焦点峰值声压的简便实验方法.基于焦点峰值声压与最大光偏折量之间的理论关系,通过测定聚焦声场焦域的最大光偏折量,获得球壳型聚焦换能器的焦点峰值声压;采用有限元方法对聚焦换能器辐射声场进行数值分析.对比实验测量结果,发现二者相对误差为7.33%,符合较好.该实验方法在医疗超声快速校准方面具有广泛的应用前景.     

基于近场声全息的聚焦换能器声场测量方法研究

高强度聚焦超声(HIFU)被广泛应用于医疗领域,但聚焦换能器焦点处的声强比较大,直接测量容易造成水听器损坏。为了间接获得焦点处声压,将全息测量面近似等效为声源面,结合空间傅里叶变换算法,提出了一种高测量效率的聚焦换能器声场测量方法。以球面自聚焦换能器为对象,进行声场测量方法的仿真研究和实验验证。结果表明,该方法比积分法推算效率提高了1倍,测量误差保持在有效范围内,该方法可以有效用于聚焦换能器声场测量。     

聚焦超声清洗机的仿真设计与实验研究

目前,超声清洗机通常是将一组换能器排布于平面式清洗槽底部,但用此方法会形成驻波现象,不利于超声清洗。文章提出了一种球面式聚焦超声清洗的方法,与普通超声清洗相比,该方法提高了超声清洗的效率。文章采用有限元COMSOL Multiphysics软件对清洗机内声场进行分析,得到三维模型内声压的分布情况;研制了聚焦超声清洗机,并通过薄膜腐蚀实验验证了清洗机内的声压分布情况;通过对比试验发现,聚焦超声清洗油污的速度比普通超声清洗提高了77.27%。通过薄膜腐蚀实验和超声清洗实验可知,聚焦超声清洗机内声场分布均匀,且声场内存在能量聚焦区域,清洗速率高于普通超声清洗机。     

用锥面靶测量大口径聚焦换能器声功率的计算讨论

辐射压力法是超声功率测量中常采用的方法，用辐射压力法测量声动功率中对于不同反射靶面的功率与压力之间的换算关系是非常重要的。文章从能量守恒基础出发，推导了大口径聚焦换能器声场作用于锥面反射靶的功率与压力的换算关系，并将结果应用于凹锥面反射靶计算。     

多阵元合成孔径聚焦超声成像研究

对多阵元合成孔径聚焦超声成像进行了全面的研究.根据声场的辐射理论推导了多阵元孔径的声压分布,并分别对单阵元、多阵元聚焦和多阵元非聚焦的声场和缺陷响应进行了仿真,发现多阵元非聚焦的声场更适合于合成孔径聚焦超声成像,并根据这个原则进行了成像实验,结果表明在远场情况下,多阵元合成孔径聚焦超声成像可以获得比单阵元合成孔径聚焦成像更高的成像质量和分辨力.     

复合材料层压板分层缺陷相控阵超声检测参数优化方法EI北大核心CSCD

针对复合材料层压板分层缺陷的准确识别问题,通过仿真与实验提出相控阵超声检测激活孔径优化方法,研究并分析不同聚焦深度下激活孔径对声场特性和检测效果的影响。首先,针对相控阵超声接触式检测方法,推导出固固界面下的多点源三维声场模型;然后,对相控阵超声声场进行仿真,研究不同激活孔径下的声场特性;最后,采用热压工艺制备含分层缺陷的碳纤维增强树脂基复合材料(CFRP)层压板,并搭建相控阵超声检测系统对其进行检测。实验结果表明,通过对相控阵超声激活孔径进行优化选择,能够实现CFRP层压板分层缺陷的准确识别,有效提高缺陷检测精度。     

超声针灸相控阵声场及控制模式研究

超声“针灸”是利用二维相控阵实现声能在皮下不同深度的聚焦,刺激特定穴位,从而模拟传统针灸手法的治疗技术。对设计的超声针灸相控阵在不同聚焦深度下的垂直聚焦声场和偏转声场进行仿真,并对焦域进行统计分析,明确了所设计的相控阵探头延时聚焦声场可以满足超声“针灸”的“针形”声场要求。基于声场仿真,还对超声“针灸”声场控制模式进行了仿真研究,研究结果表明:控制超声相控阵聚焦声场聚焦位置的上下移动以及偏转聚焦,可以模拟传统针灸的提、插以及进针角度的变化,为超声“针灸”进一步模拟传统针灸手法提供了理论依据。     

基于经验模态分解的聚焦超声非线性声场检测

为精确检测聚焦超声声场中的谐波成分并得到谐波分布规律,开展了对聚焦超声非线性声场检测的研究,提出基于经验模态分解的聚焦超声谐波检测方法。首先对声场信号进行经验模态分解;然后利用噪声判断准则判断出固有模态函数（IMF）中的噪声分量,滤除噪声分量后将剩余的IMF分量予以重新组合;最后对新信号进行傅里叶变换,得到各次谐波的幅值。结果表明:它能较好地抑制噪声,相比于传统的检测方法可获得更平滑的谐波分布;该方法对开展谐波成像、医学超声检测具有重要意义。     

光纤布拉格传感器兰姆波检测的反射谱分析

传统的兰姆波多采用压电陶瓷换能器激发和接收。建立了新的超声兰姆波无损检测系统,其基本思想是采用布拉格光纤传感器作为兰姆波的接收器。光纤光栅传感的基本原理是通过检测光栅反射的中心波长移动实现对外界参量如超声的测量。超声作用下光纤光栅的反射谱发生变化,对超声作用下光纤光栅的反射谱变化进行了数值分析,结果表明,超声对光栅反射谱的影响与超声波长与光栅长度的比值是高度相关的。只有当这个比值相当大时,反射谱的形状才不会变化而中心波长发生偏移,此时光纤传感器可用来探测兰姆波。这个结论为利用新的兰姆波无损检测系统在布拉格光栅长度的设计和兰姆波波长的选择方面提供了有用的工具。     

A novel sensor for monitoring acoustic cavitation. Part I: Concept, theory, and prototype development

This paper describes a new concept for an ultrasonic cavitation sensor designed specifically for monitoring acoustic emissions generated by small microbubbles when driven by an applied acoustic field. Its novel features include a hollow, open-ended, cylindrical shape, with the sensor being a right circular cylinder of height 32 mm and external diameter 38 mm. The internal diameter of the sensor is 30 mm; its inner surface is fabricated from a 110 /spl mu/m layer of piezoelectrically active film whose measurement bandwidth is sufficient to enable acoustic emissions up to and beyond 10 MHz to be monitored. When in use, the sensor is immersed within the liquid test medium and high frequency (megahertz) acoustic emissions occurring within the hollow body of the sensor are monitored. In order to shield the sensor response from events occurring outside the cylinder, the outer surface of the sensor cylinder is encapsulated within a special 4 mm thick polyurethane-based cavitation shield with acoustic properties specifically developed to be minimally perturbing to the 40 kHz applied acoustic field but attenuating to ultrasound generated at megahertz frequencies (plane-wave transmission loss >30 dB at 1 MHz). This paper introduces the rationale behind the new sensor, describing details of its construction and the materials formulation program undertaken to develop the cavitation shield.     

Broadband ultrasound field mapping system using a wavelength tuned, optically scanned focused laser beam to address a Fabry Perot polymer film sensor

An optical system for rapidly mapping broad-band ultrasound fields with high spatial resolution has been developed. The transduction mechanism is based upon the detection of acoustically induced changes in the optical thickness of a thin polymer film acting as a Fabry Perot sensing interferometer (FPI). By using a PC-controlled galvanometer mirror to line-scan a focused laser beam over the surface of the FPI, and a wavelength-tuned phase bias control system to optimally set the FPI working point, a notional 1D ultrasound array was synthesized. This system enabled ultrasound fields to be mapped over an aperture of 40 mm, in 50-microm steps with an optically defined element size of 50 microm and an acquisition time of 50 ms per step. The sensor comprised a 38-microm polymer film FPI which was directly vacuum-deposited onto an impedance-matched polycarbonate backing stub. The -3 dB acoustic bandwidth of the sensor was 300 kHz to 28 MHz and the peak noise-equivalent-pressure was 10 kPa over a 20-MHz measurement bandwidth. To demonstrate the system, the outputs of various planar and focused pulsed ultrasound transducers with operating frequencies in the range 3.5 to 20 MHz were mapped. It is considered that this approach offers a practical and inexpensive alternative to piezoelectric-based arrays and scanning systems for rapid transducer field characterization and biomedical and industrial ultrasonic imaging applications.     

消声器气流再生噪声测试技术研究

摘 要：基于双传声器传递函数法,发展了一种采用传声器间距组合的消声器气流再生噪声测量方法。通过对三种取样管声场和流场分析,重点比较了其导流透声效果,分析表明选取的取样管能真实反映主管道内的声压,且导流透声结构对主管道内声场和流场的影响较小。在无气流条件下,试验验证了声场仿真计算的结果。在设计的试验台上对一穿孔管消声器测试表明：研究的测量方法以及研制的试验台能够较准确的测试消声器在不同气流速度下的气流再生噪声。     

基于图像处理的超声探头声场测量

在超声无损探测中,探头的性能好坏直接制约着整个检测系统的性能。论文以超声探头的声场特性为研究对象：首先建立探头的声场特性参数体系,然后采用球靶法进行C扫描成像,接着对声场图像进行预处理及二值化、边缘检测及特征提取,获得探头的近场长度、孔径大小和声束半扩散角等性能参数,根据实际检测的声场参数来指导超声无损检测。最后通过实验来验证了该方法的有效性。     

声成像技术及其在医学超声中的应用

由于声成像技术具有对材料内部力学特性进行成像检测的特点,它已成为医学超声中的重要研究领域。为了提高声成像的空间分辨力,近年来,又发展了光声成像,扫描电子声显微术和扫描探针声显微术等新的近场成像技术。结合同济大学声学研究所部分研究结果,对这些近场成像技术在医学超声中的应用作了简单介绍。     

Ultrasonic density sensor for liquids

This paper presents an ultrasonic density sensor for liquids that unifies high accuracy with high durability and is suitable for on-line measurements in a wide range of tube diameters. The sensor consists of a transducer with a piezoceramic disk mounted between two reference rods of quartz glass. Additionally, a second transducer is used as a sound receiver. The density is obtained from the reflection coefficient of ultrasound at the interface between the quartz glass rod and the liquid and the transit time of sound between this interface and the second transducer. Parameters, such as high long-term stability and accuracy of +/-0.1% of full scale, were obtained by an internal acoustic reference measurement. The reference signal is generated using the sound radiated from the rear side of the piezoceramic disk. Design aspects such as sensor materials and signal-to-noise ratio are discussed, and experimental results are given in this paper. Applications of the sensor include concentration measurement, and ultrasonic mass flow measurement.     

A concentric-ring equivalent phased array method to model fields of large axisymmetric ultrasound transducers

An equivalent concentric-ring ultrasound phased array method was developed to estimate ultrasonic continuous wave fields generated by axisymmetric single-source transducers. The method models a given source as a concentric-ring phased array by mathematically segmenting it into many rings and subsequently finding the amplitude and phase for each ring that produces an acoustic field similar to the field of the single-source transducer. The excitation source of each ring was calculated using an inverse technique based on complex pressure measurements along a radial line close to the source. The predicting abilities of the method are evaluated by comparing measured and estimated ultrasound fields for six different transducers. The results show that the concentric-ring equivalent phased array method (CREPAM) is able to estimate quantitatively the ultrasound fields generated by large axisymmetric planar and focused transducers.     

Assessment of anisotropic tissue elasticity of cortical bone from high-resolution, angular acoustic measurements

Assessment of anisotropic elastic properties at the tissue level is still one of the major challenges in bone research. In previous studies, bone sections were cut in different directions relative to a principle axis of symmetry. This causes a high preparation and measurement effort. We have developed a new acoustic scanning procedure that allows one to measure the angular dependence of the acoustic impedance of cylindrically shaped samples (diameter: 4.4 mm) with a single measurement. Our scanning acoustic microscope was equipped with a rotational stage, and a scanning procedure was developed that measures the surface reflection of the rotating cylinder. It was shown in a previous study that the acoustic impedance derived from the reflection coefficient is highly correlated with the elastic coefficient in the probing direction. From the angular reflection, the independent elastic coefficients were derived using assumptions of transverse isotropy and continuum micromechanical model constraints. This method was applied to the inspection of human femoral bone samples. Four cylinders were prepared from the anterior, posterior, medial, and lateral regions. The measurements were performed with a 50 MHz transducer, providing a lateral resolution of 23 microm. Remarkable structural and elastic variations were observed between the four samples. The means and standard deviations of the derived elastic coefficients were: c33 = 29.9 +/- 5.0 GPa, c11 = 21.9 +/- 2.1 GPa, c12 = 9.2 +/- 1.5 GPa, c13 = 9.7 +/- 1.6 GPa, and c44 = 6.7 +/- 1.2 GPa. The results demonstrate that microstructural and anisotropic elastic tissue parameters can be assessed by ultrasound in very small bone samples.