Molecular structure dependence of acoustic nonlinearity parameter B/A for silicone oils

Exploring new acoustic parameters is essential to develop a noninvasive imaging technique for the surgery of silicone oil tamponades. In this study, the acoustic nonlinearity parameters B/A of varied silicone oil samples （e.g., linear or hyper-branched） are experimentally measured by using a modified thermodynamic method. The results show that： （i） when the concentration of the silicone oil with a molecular weight of 5 × 10^4 increases from 0.5 g/100 ml to 8 g/100 ml, the corresponding B/A value increases by about 18%, but the acoustic velocity only increases by about 0.1%; （ii） when the molecular weight of the hyper-branched silicone oil is enhanced from 2 × 10^5 to 1 × 10^6, the B/A value increases by about 22%, while the acoustic velocity is only raised by about 0.2%. This study suggests that the B/A parameter of the silicone oil is more sensitive to the change in its molecular structure than that of the acoustic velocity. Thus, the B/A parameter might be utilized as an effective index for the development and optimization of the noninvasive imaging of the surgery of silicone oil tamponades.

A semi-analytical method to compute acoustic nonlinearity parameter of Cu,Ag and Au

In this paper,a semi-analytical method was proposed to evaluate the acoustic nonlinearity parameter for single crystals of Cu,Ag and Au.The acoustic nonlinearity parameter can be derived analytically by general expressions in terms of the interatomic potentials with the distances between each pair of atoms in these transition metals.To evaluate the acoustic nonlinearity parameter,one needs to conduct one step molecular static simulation and obtain the equilibrium positions of all the atoms.Further,based on this method,numerical experiments with molecular dynamic code LAMMPS were given to compute the acoustic nonlinearity parameter of Cu,Ag and Au.To illustrate the validity of these expressions,comparison was made between calculation results and data in the literature.Reasonable agreement is observed.Because of the analytical nature of this method,it provides a fundamental understanding of the nonlinear elastic behavior of these transition metals.

Computation of the acoustic nonlinearity parameter in organic liquid binary mixtures

Based on Jacobson’s molecular free length theory in liquids and the relationship between the ultrasonic velocity and the molecular free length in organic liquids, the equation of the acoustic nonlinearity parameter in organic liquid binary mixtures is derived. The calculated values from the equation are in good agreement both with those from Apfel’s and from Sehgal’s mixture laws.

Relationship between the temperature and the acoustic nonlinearity parameter in biological tissues

Recently with the rapid development of the high-intensity focused ultrasound (HIFU) in biomedical ul- trasound, much attention has been paid to the noninvasive temperature estimation in biological tissue in order to de- termine the region and degree of the ultrasound-induced lesions. In ultrasound hyperthermal therapy it is highly de- sirable to study the real-time noninvasive monitoring of temperature distribution in biological tissue. In this paper, the relationship between the nonlinearity parameter B/A and the temperature in biological tissue is studied and compared with the theoretical model as well as the experimental results from the thermocouple. Results indicated that B/A could be used as an effective tool to monitor the temperature distribu- tion in biological media.

Nonlinearity acoustic parameter B/A in organic liquids

Based on Jacobson's free length theory and the dependence of ultrasonic velocity on the free length in organic liquids, the equation of nonlinearity acoustic parameter B/A was given, and the calculated nonlinearity acoustic parameter B/A in some organic liquids are in good agreement with the measured results.

Measurement of the acoustic nonlinearity parameter BIA of lossy medium in a focused field

An analytical description for the linear and nonlinear acoustic fields in lossy medium of a focusing source is derived. The relationship of pressure amplitudes at focus for fundamental and the second harmonic waves is discussed. At high linear focusing gain G, a new method using the insert substitution method for measuring the acoustic nonlinear parameter BIA of biological tissues is presented. Results for some biological tissues are experimentally obtained.

INVESTIGATION OF ACOUSTIC NONLINEARITY PARAMETER B/A IN BIOLOGICAL MEDIA USING PHASE SHIFT METHOD

I. INTRODUCTION It has become a very important subject to investigate the acoustic nonlinearity parameter B/A in biological media since 1980. Experimental evidence indicates that there are nonlinear phenomena under biological frequencies and intensities. B/A is one of the ba-

STUDY OF THE ACOUSTIC NONLINEARITY PARAMETER B/A IN BINARY BIOLOGICAL MIXTURE

I. INSTRUCTIONThe study of the acoustic nonlinearity parameter B/A in the biological medium has been of the basic importance and has been treated as the frontier in the field of biomedical acoustics since 1980 when the nonlinear acoustic effects were found in that area. In those years, the measurement of B/A shows that B/A value varies with the physical,

Acoustic Nonlinearity Parameters Due to Microstructural Defects

This study presents a general approach to derive the acoustic nonlinearity parameters induced by various types of dislocation configurations including dislocation strings （monopoles）, dislocation dipoles, dislocation pileups and extended dislocations. It is found that expressions of the acoustic nonlinearity parameter induced by such a variety of dislocation con- figurations share a common mathematical form. They are all scaled with （Lch/b）n, where Lch is a characteristic length of the dislocation configuration, b is the magnitude of the Burgers vector, and n is either 3 or 4. Semiquantitative analysis is presented to compare the magnitudes of the acoustic nonlinearity parameters among different types of dislocation configurations.

The influence of molecular structure of protein on the acoustic nonlinearity parameter B/A

In this paper, the influence of molecular structure of proteins on the acoustic non-linearity parameter B/A has been studied. By using biochemical technique, three proteins such as bovine serum albumin, bovine hemoglobin and pepsin were employed and their quarternary,tertiary and secondary protein structures were perturbed by the denaturing agent sodium do-decyl sulfate (SDS) solution, while their primary structures of protein were not changed. This means that only the structural features were altered and the chemical composition maintained unchanged. B/A has been measured by using improved thermodynamic method. The experi-mental results show that when the concentration of SDS solution increases, the alterations of the protein structure increase, and the contribution of protein to the B/A value decreases. Re-sults indicate that the B/A values can display the destruction of molecular structure of protein.Some explanation of these phenomena has also been made in this paper.

高频聚焦超声声场和温度场的仿真研究

为探究临床常用的7 MHz高频聚焦超声在多层生物组织中的声传播以及毫秒级时间内的生物传热规律问题,基于Westervelt方程和Pennes传热方程,使用有限元方法建立高频聚焦超声辐照多层组织的非线性热黏性声传播及传热模型。首先分析了线性模型和非线性模型之间的差异,然后在非线性模型下探究换能器的参数对声场和温度场的影响。仿真结果显示:在7 MHz频率下,当换能器输出声功率超过5 W时,声波传播的非线性效应不可忽视(p<0.05);当声功率从5 W增大到15 W时,非线性模型与线性模型预测的温度偏差从20%增加到34.703%;高频聚焦超声波的非线性行为比低频更加显著,基频能量向高次谐波转移的程度增大,声功率为10 W和15 W时4次谐波与基波之比分别达到7.33%和12.12%;高频换能器参数的改变对组织中声场和温度场分布的影响较大,换能器焦距从12 mm减小到11.2 mm,焦点处最高温度增加了77%。结果表明,7 MHz聚焦超声的非线性声传播需要考虑到4次谐波的影响。该文提出的多层组织非线性仿真模型可为高频聚焦超声换能器参数优化及制定安全、有效的术前治疗方案提供理论参考。

STUDY ON THE MAGNITUDE OF THE NONLINEARITY PARAMETER B/A IN ORGANIC LIQUIDS

Ⅰ. INTRODUCTION It was discovered that the nonlinearity parameters of biological media differed strikingly from each other according to their molecular structure. And so we can think that B/A will give some information of the molecular structure of a medium. But we know very little about the relation between them. Since the acoustic pro-

CFRP板倾斜冲击损伤的非线性超声评价

针对碳纤维增强聚合物(CFRP)板的倾斜冲击损伤检测问题,提出用非线性Lamb波响应进行评估,并应用ABAQUS软件中的Explicit模块,通过有限元法建立了CFRP板受到低速冲击以及损伤后的非线性超声检测的全过程仿真模型,通过低速冲击试验和非线性检测试验验证了模型的正确性。利用此模型进一步研究了冲击角度与检测距离对相对非线性系数(RANP)的影响。研究结果表明:在一定冲击角度区间中,冲击角度的增加会导致CFRP板吸收能量及分层损伤的减小,并进一步导致了RANP的降低,而RANP与检测距离的变化趋势相一致。

基于非线性超声技术的球墨铸铁石墨大小及表层硬度的表征

球墨铸铁具有优良的力学性能被广泛应用在各工业领域,其内部的石墨形态和分布情况会影响其各项力学性能。相比于石墨球化率,石墨大小的表征研究相对较少,对球墨铸铁的石墨大小及表层硬度进行无损评定具有重要的工程意义。浇注了具有不同石墨大小和基体组织的球墨铸铁试件,对试件进行了金相观察及硬度试验。基于临界折射纵(longitudinal critical refraction, LCR)波和Rayleigh波模型,利用超声波声速及超声非线性系数表征球墨铸铁石墨大小及表层硬度。结果表明:LCR波的超声非线性系数随着表面硬度的增大而增大,随着石墨平均直径的增大而减少,并且相比超声波声速具有更高的灵敏度;LCR波的超声非线性系数的增加与微观组织中的晶界数量和碳化物的增加有关。因此,可以利用LCR波的超声非线性系数表征球墨铸铁的石墨大小和表面硬度,建立微观组织、超声非线性系数及机械性能之间的关系。

铝合金拉伸塑性变形的非线性电磁超声检测

针对金属构件早期塑性损伤检测的难点问题,建立非线性电磁超声表面波弹塑性模型,通过改变材料内部塑性应变大小模拟不同程度的塑性损伤,研究应力应变、塑性损伤、超声非线性系数三者之间的关系,并利用非线性电磁超声实验方法,对拉伸变形的试件进行塑性损伤评估。搭建了非线性电磁超声表面波检测系统,对导入不同塑性变形的试件进行相对非线性系数的检测。实验结果表明,在材料屈服硬化阶段早期(ε≤5%),随着被测试件中导入塑性应变量的增加,相对非线性系数迅速增大;在材料屈服硬化阶段后期(5%<ε≤7%),随塑性损伤程度的增加,相对非线性系数增幅逐渐趋于平缓;在材料出现颈缩时(ε>7%),材料内部应力的降低导致相对非线性系数出现明显下降。据此,可以对塑性损伤的变化情况进行有效监测,并进一步评估材料的力学寿命。

金属材料表面涂层损伤的非线性超声评价

提出了一种金属材料表面涂层损伤的非线性超声评价方法。表面涂层的损伤以及涂层与基体材料间的界面粘接状况与超声信号的非线性效应密切相关。将存在表面涂层的AZ31镁铝合金试件加载到不同的拉伸载荷后,利用RitecSNAP-0.25-7-G2非线性超声测试系统激发和接收Rayleigh表面波,通过实验测试在不同载荷作用后涂层试件的声学非线性系数。研究结果表明,在应力不超过某一极限值的情况下,虽然不能观察到试件表面涂层外观的明显变化,但通过非线性超声实验测试得到的声学非线性系数随着加载应力的增加而不断增加。因此,对具有表面涂层的结构来说,可利用声学非线性系数对其表面涂层的损伤进行非线性超声无损评价。

地震、测井联合预测地层压力的方法研究

通过提取井旁地震道的特征参数 ,利用神经网络建立其与测井声波时差的非线性映射 ,进而外推井底以下声波曲线 ,从而实现地震、测井联合预测井底以下的地层压力。该方法克服了单纯地震层速度或单纯声波时差预测地层压力的局限性。经 NH地区实际资料模拟预测 。

超声造影剂的声学特性(英文)

研究了一种新型超声造影剂SDA的声学特性 .SDA即声振葡萄糖白蛋白溶液 ,是一种含有稳定包膜气泡的悬浮液 ,微气泡的平均直径为 2 .0 μm .测量了SDA(浓度从 1.0× 10 7到 2 .0 5× 10 8个 /mL)的线性和非线性超声参量 ,包括声速、声衰减、非线性声参量及它们随气泡浓度的变化关系 .在 2～ 6MHz频率范围内 ,SDA的衰减系数随气泡浓度和频率线性增长 .值得指出的是 ,SDA的非线性声参量B/A值非常惊人 。

非线性声参量对病变生物组织的超声定征

非线性声参量Ｂ／Ａ是描述生物媒质非线性超声效应的重要参量。本文用有限振幅插入取代法研究了猪的病变肝脏组织的非线性声参量，用显微摄影分析了相应组织的病理状态，研究结果表明非线性声参量作为病变组织定征的新参量具有令人鼓舞的前景。

利用超声二次谐波测试水泥试样的非线性系数

使用RITEC公司的RAM5000非线性测试仪器构建稳定、高可重复性的非线性系数相对观测及数据处理系统。为水泥制品损伤演化的非线性特征研究提供可靠的观测平台。测量三种不同颗粒直径的水泥试样的名义非线性系数。使用三组高频换能器对试验样品在40组电压激励下产生的高次谐波幅值进行观测。获取减少三次谐波的影响并突出二次谐波的合理的电压激励参数和数据处理方法。采用线性相关系数作为名义非线性系数稳定性的判断依据。通过86.5 h,173次观测验证了系统的稳定性和可重复性。并获取水泥试样水饱和过程中非线性系数变化和波速变化。