人类牙齿的外貌结构对激光超声波传播影响的研究

发布时间：2018-04-20 23:25

本文选题：牙齿 + 激光超声　；参考：《南京理工大学》2012年硕士论文

【摘要】：本文主要研究人类牙齿的外貌结构对激光超声波传播的影响,因此建立了脉冲激光线源作用于不同曲率的牙齿材料表面上热弹激发超声波的理论模型。利用有限元方法对激光在牙齿材料中产生的温度场、激光在牙齿中激发超声波的机理、超声波的时域波形的特征、波的传播特性以及激光声表面波的相速度色散进行了数值计算和理论分析。本文主要对激光声表面波和纵波进行了研究：门牙的二维双层板状模型。先讨论了激光线源作用于牙齿表面时产生的瞬态温度场,得到了深度和光斑半径方向上的温升情况。接着研究了超声波的时域波形,由傅里叶变换得到激光声表面波的频谱图,用相位普法计算了激光声表面波的相速度色散曲线。二维管状双层模型。先分析了模型径向和周向的温度场,得到牙齿表面曲率越大,牙齿材料温升越高的结论。接着分析了不同曲率半径模型的不同探测点的激光超声的时域波形。数值结果表明：管中激光声表面波的脉冲极性发生由单极性向双极性的交替转变,由于模型是双层模型,分层对声表面波的频散产生影响,较单层模型而言使得频散复杂化,不同曲率模型中声表面波脉冲极性转换对应的角度不相同。最后对不同曲率模型距激光激发源相等距离的点的时域波形进行了分析,得到了传播距离相同,牙齿表面曲率越大,掠面纵波和声表面波的速度就越大的结论,并对声表面波进行了时频分析得到相速度色散曲线。在上两种模型的基础上对二维真实门牙模型进行模拟。在近唇面激发超声波,并在同侧接收声表面波信号,对声表面波进行了时频分析。建立大光斑激光作用于牙齿表面的二维门牙双层板状模型和真实门牙模型。通过分析一层珐琅质模型中和双层板状模型中超声波的时域波形,得到纵波在板状门牙中的传播路径,在此基础上又分析出了纵波在真实门牙模型中的传播路径。本文的研究成果将为激光超声对于牙齿的无损检测提供理论基础。
[Abstract]:In this paper, the influence of the appearance of human teeth on the propagation of laser ultrasonic wave is studied. Therefore, a theoretical model of ultrasonic wave excited by thermoelasticity on the surface of tooth materials with different curvature by pulsed laser line source is established. The finite element method is used to analyze the temperature field produced by laser in dental materials, the mechanism of laser excitation in teeth, and the characteristics of ultrasonic waves in time domain. The wave propagation characteristics and the phase velocity dispersion of the laser surface acoustic wave are numerically calculated and theoretically analyzed. In this paper, the laser surface acoustic wave and the longitudinal wave are studied. Two-dimensional double-layer plate model of incisors. The transient temperature field caused by the laser line source acting on the tooth surface is discussed, and the temperature rise in the direction of depth and spot radius is obtained. Then, the time domain waveform of ultrasonic wave is studied, and the spectrum of laser surface acoustic wave is obtained by Fourier transform. The phase velocity dispersion curve of laser surface acoustic wave is calculated by phase general method. Two dimensional tubular bilayer model. Firstly, the radial and circumferential temperature fields of the model are analyzed, and it is concluded that the higher the curvature of the tooth surface, the higher the temperature rise of the tooth material. Then the time domain waveforms of laser ultrasonic with different radii of curvature are analyzed. The numerical results show that the pulse polarity of laser saw changes alternately from unipolar to bipolarity in the tube. Because the model is a two-layer model, the delamination has an effect on the dispersion of saw, which makes the dispersion more complicated than the single-layer model. The angle corresponding to the polarity conversion of saw pulse in different curvature models is different. Finally, the time-domain waveforms of points with equal distance from the laser excitation source with different curvature models are analyzed. It is concluded that the same propagation distance, the greater the curvature of the tooth surface, the greater the velocity of the swept surface longitudinal wave and the surface acoustic wave. The phase velocity dispersion curve is obtained by time-frequency analysis of saw. Two-dimensional real incisor models are simulated on the basis of the above two models. The ultrasonic wave is excited on the near lip and the saw signal is received on the same side. The time frequency analysis of the saw is carried out. A two-dimensional double-layer plate model and a real incisor model of large spot laser applied on the surface of teeth were established. By analyzing the time domain waveforms of ultrasonic waves in a enamel model and a double-layer plate model, the propagation paths of longitudinal waves in plate incisors are obtained, and the propagation paths of longitudinal waves in real incisors are analyzed. The results of this paper will provide a theoretical basis for nondestructive testing of teeth by laser ultrasound.
【学位授予单位】：南京理工大学
【学位级别】：硕士
【学位授予年份】：2012
【分类号】：R318.51

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