【作者】 李向军；

【导师】 陈裕泉；

【作者基本信息】 浙江大学 ， 生物医学工程， 2011， 博士

【摘要】 太赫兹(Terahertz, THz)电磁波谱与有机及生物分子的转动和振动能量对应,非常适于鉴别和研究这些分子的动力学行为,尤其是基于飞秒超快激光技术的太赫兹时域光谱技术(THz-TDS),可以测量太赫兹波电场的幅度和相位,直接得到材料太赫兹波段的折射率和吸收系数,以及反应物质内部结构及微观运动状态的复介电谱。不仅如此,THz波对生物分子中的水非常敏感,可直接探测其它技术很难探测的生物分子-水分子界面的水分子网络动力学变化。本文研究了基于THz-TDS技术的液态物质光学材料参数的提取方法；比较了可以用于定量分析有机分子溶液THz吸收谱的回归校正建模方法；研究了有机分子水溶液THz介电谱产生的介电响应机理；以及可以用于测量溶液浓度的THz波段人工电磁材料传感器的特性。本文的主要研究工作包括：1)提出了一种基于THz脉冲时域波形重建技术的材料参数(如折射率和吸收系数)提取方法,该方法可以克服其它频域材料参数提取算法的固有缺陷,能够更为精确地测定材料的材料参数,特别是液体的材料参数。目前已有的材料参数频域提取算法在定义误差函数时必须把不同量纲的复数的幅度和相位一起考虑,而本文利用波形重建技术在时域定义的误差函数物理意义更为明确,结果更为准确可靠。该方法可以用于多层结构的透射测量以及反射测量方式,进一步提高了溶液材料参数的提取精度,并降低了测量难度,更适合现场测量。2)利用支持向量机回归模型定量分析了常温下食用植物油(液态)的THz吸收谱。采用THz时域谱技术和波形重建技术测得了30个食用油样本的THz吸收谱,随机分为训练集和预测集,利用支持向量回归算法和标准方法测得的参考含量在训练集上建立了植物油主要油酸成分含量、酸价和过氧化值的预测模型,并应用这些模型对测试集样本进行预测。结果表明支持向量回归算法所建模型对油酸含量、酸价和过氧化值预测的精度高于传统的偏最小二乘法(Partial Least Square, PLS)方法。3)利用基于动态Onsager有效电场的THz波段分子极化率模型估计了蔗糖和葡萄糖水溶液中结合水分子的数量、半径等重要参数。通过对蔗糖和葡萄糖水溶液的THz介电谱的研究,进一步印证了常温下水溶液中结合水分子的转动和平移等弛豫运动可从自由水的皮秒量级下降到纳秒和微秒量级,但相应的共振运动部分不变,并得到了结合水的宏观介电常数。结合水的这些性质可以用来估计生物有机分子水溶液中结合水分子的数量及大小等参数,并为将来动态监测生物分子的水合过程奠定基础。4)利用有限元方法仿真分析了THz人工电磁介质作为溶液浓度传感器的可行性,设计了基于PCB柔版工艺的双层人工电磁介质溶液浓度传感器,用于测量酒精溶液的浓度,并用THz-TDS系统进行了实验验证。研究发现双层人工电磁材料对有机分子水溶液进行反射测量时可形成明显的谐振峰,并随溶液浓度变化发生显著偏移。使用THz波段人工电磁材料作为溶液浓度传感器是可行的,灵敏度与单元的结构和层数有密切关系,值得进一步研究。更多还原

【Abstract】 Terahertz (THz) spectrum is corresponding to vibration and rotation of organic and biological molecules, which is suitable to identify and study those molecular dynamics. Especially, THz Time-domain spectroscopy(THz-TDS) can enable us to extract the material parameters or dielectric spectrum that show material micro-structure and dynamics by measuring amplitude and phase from coherent terahertz pulses. Furthermore, THz wave is very sensitive to water, through which we can directly detect the water dynamics in hydration layer between water and solute molecules. In this paper, material parameter extraction technology for THz-TDS is investigated. Different regressive calibration methods for THz spectrum quantitative analysis are compared. A THz metamaterial sensor is designed for the concentration measurement of the solution. Mechanism of dielectric response for glucose and sucrose in THz band is discussed. The details of the above research work are listed as follows:1) An innovative optical material parameter extraction algorithm based on waveform rebuilding technology for Terahertz time-domain spectroscopy (THz-TDS) is proposed. Unlike previously reported extraction algorithms in frequency domain, which have to be compromised between amplitude and phase, or the real part and imaginary part of the transfer function, we calculate material parameters by minimizing the difference between the measured sample waveform and the rebuilt one in time domain. Our cost function is more meaningful than those extraction methods in frequency domain, and thus the results are more accurate. The new method can also be used effectively in multilayer transmission mode or in reflection mode.2) THz Spectrum of edible oil is quantitatively analyzed by Support Vector Regression(SVR). The terahertz absorption spectrum of edible oil in 30 samples is measured by THz-TDS, and they are randomly divided into training set and testing set. Regression models for oil’s oleic acid concentration, acid number and peroxide value are built by SVR algorithm and reference values from standard methods with training set, then the values of acid concentration, acid number and peroxide value in testing set are predicted by those regressive models. The results show that the models by SVR have significant advantage compared with traditional Partial Least Square(PLS) method.3) Hydrated water parameters in glucose and sucrose solutions such as the number and the radius of the hydrated water molecule are estimated by Onsager’s molecular polarization theory for the case of a time-varying field in THz band. By THz dielectric spectrum of glucose and sucrose solutions it is confirmed that the relaxation responses of hydrated water is slowed down to GHz or MHz with its resonant response unchangeable, which enable us to calculate the number of hydrated water in solutions. At the same time, the dielectric spectrum of hydrated water is calculated. This is very important for monitoring the hydration dynamically.4) The feasibility of the solution’s concentration sensor by THz metamaterial is evaluated by Finite Element Method, and a sensor with a double golden finger structure on a flexible PCB is designed and tested by THz-TDS. It is shown that there are sharp resonant peaks in reflection coefficient which are shifted with solution concentration changing. The sensitivity is relative with cell structure and the number of layers in THz metamaterial, which is worth further research.更多还原