本文選題：牙齒 + 激光超聲�。� 參考：《南京理工大學(xué)》2012年碩士論文

【摘要】：本文主要研究人類牙齒的外貌結(jié)構(gòu)對(duì)激光超聲波傳播的影響,因此建立了脈沖激光線源作用于不同曲率的牙齒材料表面上熱彈激發(fā)超聲波的理論模型。利用有限元方法對(duì)激光在牙齒材料中產(chǎn)生的溫度場(chǎng)、激光在牙齒中激發(fā)超聲波的機(jī)理、超聲波的時(shí)域波形的特征、波的傳播特性以及激光聲表面波的相速度色散進(jìn)行了數(shù)值計(jì)算和理論分析。本文主要對(duì)激光聲表面波和縱波進(jìn)行了研究： 門牙的二維雙層板狀模型。先討論了激光線源作用于牙齒表面時(shí)產(chǎn)生的瞬態(tài)溫度場(chǎng),得到了深度和光斑半徑方向上的溫升情況。接著研究了超聲波的時(shí)域波形,由傅里葉變換得到激光聲表面波的頻譜圖,用相位普法計(jì)算了激光聲表面波的相速度色散曲線。 二維管狀雙層模型。先分析了模型徑向和周向的溫度場(chǎng),得到牙齒表面曲率越大,牙齒材料溫升越高的結(jié)論。接著分析了不同曲率半徑模型的不同探測(cè)點(diǎn)的激光超聲的時(shí)域波形。數(shù)值結(jié)果表明：管中激光聲表面波的脈沖極性發(fā)生由單極性向雙極性的交替轉(zhuǎn)變,由于模型是雙層模型,分層對(duì)聲表面波的頻散產(chǎn)生影響,較單層模型而言使得頻散復(fù)雜化,不同曲率模型中聲表面波脈沖極性轉(zhuǎn)換對(duì)應(yīng)的角度不相同。最后對(duì)不同曲率模型距激光激發(fā)源相等距離的點(diǎn)的時(shí)域波形進(jìn)行了分析,得到了傳播距離相同,牙齒表面曲率越大,掠面縱波和聲表面波的速度就越大的結(jié)論,并對(duì)聲表面波進(jìn)行了時(shí)頻分析得到相速度色散曲線。 在上兩種模型的基礎(chǔ)上對(duì)二維真實(shí)門牙模型進(jìn)行模擬。在近唇面激發(fā)超聲波,并在同側(cè)接收聲表面波信號(hào),對(duì)聲表面波進(jìn)行了時(shí)頻分析。 建立大光斑激光作用于牙齒表面的二維門牙雙層板狀模型和真實(shí)門牙模型。通過分析一層琺瑯質(zhì)模型中和雙層板狀模型中超聲波的時(shí)域波形,得到縱波在板狀門牙中的傳播路徑,在此基礎(chǔ)上又分析出了縱波在真實(shí)門牙模型中的傳播路徑。 本文的研究成果將為激光超聲對(duì)于牙齒的無(wú)損檢測(cè)提供理論基礎(chǔ)。
[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.
【學(xué)位授予單位】：南京理工大學(xué)
【學(xué)位級(jí)別】：碩士
【學(xué)位授予年份】：2012
【分類號(hào)】：R318.51

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