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1.
滕旭东  郭霞生  章东 《声学学报》2019,44(6):1053-1059
弹性体材料在早期退化阶段会出现一些长度不同,且分布不均匀的介观尺度微裂纹,声波在这些裂纹聚集区(或裂纹群)传播会激发较强的非经典非线性。文中以缓变截面的锥棒为研究对象,在Preisach-Mayergoyz (PM)空间模型下研究了声波通过微裂纹聚集区激发的非经典非线性谐波传播特性,实验验证了三次谐波位移幅度与缺陷位置、宽度的反演关系。理论计算和实验结果表明:微裂纹群激发了较强的奇次谐波,引起非经典非线性传播;其谐波幅度与微裂纹聚集区域位置、宽度及非经典非线性参数紧密相关,利用三次或五次谐波位移幅度能够准确定位缺陷的区域。   相似文献   
2.
Due to the unique magnetic, mechanical and thermal properties, magnetic nanoparticles(MNPs) have comprehensive applications as the contrast and therapeutic agents in biomedical imaging and magnetic hyperthermia. The linear and nonlinear magnetoacoustic responses determined by the magnetic properties of MNPs have attracted more and more attention in biomedical engineering. By considering the relaxation time of MNPs, we derive the formulae of second harmonic magnetoacoustic responses(2H-MARs) for a cylindrical MNP solution model based on the mechanical oscillations of MNPs in magnetoacoustic tomography with magnetic induction(MAT-MI). It is proved that only the second harmonic magnetoacoustic oscillations can be generated by MNPs under an alternating magnetic excitation. The acoustic pressure of the 2H-MAR is proportional to the square of the magnetic field intensity and exhibits a linear increase with the concentration of MNPs. Numerical simulations of the 2H-MAR are confirmed by the experimental measurements for various magnetic field intensities and solution concentrations using a laser vibrometer. The favorable results demonstrate the feasibility of the harmonic measurements without the fundamental interference of the electromagnetic excitation, and suggest a new harmonic imaging strategy of MAT-MI for MNPs with enhanced spatial resolution and improved signal-to-noise ratio in biomedical applications.  相似文献   
3.
李宜令  马青玉  章东  夏荣民 《中国物理 B》2011,20(8):84302-084302
An acoustic dipole radiation model for magnetoacoustic tomography with magnetic induction (MAT-MI) is pro-posed,based on the analyses of one-dimensional tissue vibration,three-dimensional acoustic dipole radiation and acoustic waveform detection with a planar piston transducer.The collected waveforms provide information about the conductiv-ity boundaries in various vibration intensities and phases due to the acoustic dipole radiation pattern.Combined with the simplified back projection algorithm,the conductivity configuration of the measured layer in terms of shape and size can be reconstructed with obvious border stripes.The numerical simulation is performed for a two-layer cylindrical phantom model and it is also verified by the experimental results of MAT-MI for a tissue-like sample phantom.The proposed model suggests a potential application of conductivity differentiation and provides a universal basis for the further study of conductivity reconstruction for MAT-MI.  相似文献   
4.
马致遥  单锋  章东 《声学学报》2018,43(2):217-223
高强度聚焦超声(HIFU)是一种新型的无创治疗肿瘤新技术,其中换能器声场数值计算能够为HIFU治疗提供重要的依据。传统非线性KZK和SBE模型广泛应用于换能器声场数值计算,但依然存在某些不足。我们采用一种介观尺度的新型流体力学方法,即格子Boltzmann方法(LBM),基于2维9离散速度(D2Q9)格子构建了轴对称多弛豫参数LBM模型,并通过调节弛豫参数分析其对模型的影响;利用该模型对两个具有不同张角的球面聚焦换能器的声场进行数值模拟,并与KZK和SBE模型的计算结果进行比较。结果表明LBM模型能够很好地描述超声波的激发和传播机制,从流体力学的角度描述聚焦声场的分布,具有清晰的物理意义,且计算过程不受换能器张角的限制,在换能器声场的理论分析和模拟计算及其在HIFU治疗中的应用有着积极的意义。   相似文献   
5.
马青玉  邱媛媛  黄蓓  章东  龚秀芬 《中国物理 B》2010,19(9):94302-094302
The difference-frequency (DF) ultrasound generated by using parametric effect promises to improve detection depth owing to its low attenuation, which is beneficial for deep tissue imaging. With ultrasound contrast agents infusion, the harmonic components scattered from the microbubbles, including DF, can be generated due to the nonlinear vibration. A theoretical study on the DF generation from microbubbles under the dual-frequency excitation is proposed in formula based on the solution of the RPNNP equation. The optimisation of the DF generation is discussed associated with the applied acoustic pressure, frequency, and the microbubble size. Experiments are performed to validate the theoretical predictions by using a dual-frequency signal to excite microbubbles. Both the numerical and experimental results demonstrate that the optimised DF ultrasound can be achieved as the difference frequency is close to the resonance frequency of the microbubble and improve the contrast-to-tissue ratio in imaging.  相似文献   
6.
黄蓓  张艳丽  章东  龚秀芬 《中国物理 B》2010,19(5):54302-054302
This article proposes a finite element model(FEM) for predicting the acoustic scattering from an encapsulated microbubble near rigid boundary.The validity of the model is first examined by comparing the acoustic nonlinear response of a free microbubble with that obtained by the Church model.Then this model is used to investigate the effect of the rigid boundary on acoustic scattering signals from microbubble.The results indicate that the resonance frequency decreases while the oscillation amplitude increases as the microbubble approaches the rigid boundary.In addition,the fundamental component of the acoustic scattering signal is enhanced compared with that of the free microbubble.  相似文献   
7.
孙健明  于洁  郭霞生  章东 《物理学报》2013,62(5):54301-054301
在高强度聚焦超声(high intensity focused ultrasound, HIFU) 的研究中, 生物组织的衰减和色散性质会对声能量的空间分布产生影响. 本文提出应用分数导数修正非线性Khokhlov-Zabolotskaya-Kuznetsov (KZK)方程, 研究生物组织中非线性HIFU声场. 对三种生物仿体的衰减和声速色散的理论实验研究表明分数导数应用的可行性, 在此基础上通过数值仿真分析研究了衰减及声速随频率的变化对HIFU焦域分布的影响. 研究结果表明, 在计算强非线性聚焦超声时, 由于高次谐波的强色散作用, 引入分数导数来解决生物组织特殊的衰减以及色散问题可进一步提高HIFU治疗的安全性. 关键词: 分数导数 声衰减 色散 高强度聚焦超声  相似文献   
8.
The influence of the inhomogeneous tissue layer on the generation of acoustic vortices(AV) is studied theoretically and experimentally based on the phase screen model. By considering the time-shift of a random phase screen, the formula of acoustic pressure for the AV beam generated by a circular array of eight planar piston sources is derived. With the actual correlation length of the abdominal wall, numerical simulations before and after the insertion of the inhomogeneous tissue layer are conducted, and also demonstrated by experimental measurements. It is proved that, when the thickness variation of the phase screen is less than one wavelength, no significant influence on the generation of AVs can be produced. The variations of vortex nodes and antinodes in terms of the location, shape, and size of AVs are not obvious. Although the circular pressure distribution might be deformed by the phase interference with a larger thickness variation, AVs can still be generated around the center axis with perfect phase spirals in a reduced effective radius. The favorable results provide the feasibility of AV generation inside the human body and suggest the application potential of AVs in object manipulation for biomedical engineering.  相似文献   
9.
朱晓峰  周琳  章东  龚秀芬 《中国物理》2005,14(8):1594-1599
应用角谱方法理论研究了聚焦声束在层状生物组织中的非线性传播特性,将声波分解为角谱,可计算垂直于声轴的任意平面的非线性声场。在圆形平面活塞聚焦换能器的焦区中插入多种生物组织样品,数值计算了样品内部及外部的二次谐波声场,并通过实验测量验证了理论方法的有效性。基于快速傅氏变换的角谱方法可直观地描述非线性声传播,对非线性声成像有指导作用。  相似文献   
10.
反射式非线性声参量层析成像的研究   总被引:6,自引:1,他引:5  
非线性声参量B/A描述了有限振幅波在媒质中传播的非线性特性,有可能成为生物组织定征的新参量。本文提出了利用复合式换能器进行反射式的非线性参量B/A层析成像的新方法。利用反射二次谐波的传播理论及有限振幅波插入取代法给出了计算机重建B/A层析像的理论方法。对部分流体及生物组织进行了计算机模拟成像及实验研究,取得了较为满意的结果。  相似文献   
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