指導教授：曾雪峰臺灣大學：光電工程學研究所和佑Clares, Sergio CanteroSergio CanteroClares2014-11-262018-07-052014-11-262018-07-052014http://ntur.lib.ntu.edu.tw//handle/246246/261883在大多數生物組織中，散射會限制光學成像技術的適用性。近年來，利用有限差分時域法（FDTD）在巨觀散射模擬中解出準確電磁場的分佈成為一種常見的方法。在這個研究中，我們提出光學靶，應用在有限差分時域法光學散射模擬中。為了建構出光傳遞通過巨觀混濁介質到目標位置，必須設置具有消掉任何入射光性質的光學吸收體，摺積式完美匹配層(CPML)吸收邊界條件被用來產生局部的圓形結構的光學吸收體，此光學吸收體可以吸收來自所有方向的光。為了驗證此方法的可行性，我們利用二維FDTD演算法來產生一個柱狀的光學吸收體，並且探討在全方向入射的光條件下的情況。藉由改變CPML相關變因，我們計算其吸收效率在不同應用中的可行性，並且分析數值光學靶在光的巨觀散射模擬中表現的影響因素。High scattering in most biological tissues limits the applicability of optical imaging techniques: Focusing depth and resolution depend not only on the absorption loss, but also on the successive scattering through the medium. Due to the complexity of the light propagation in tissue, accurate and robust simulations are necessary. In recent years, computations use the finite-difference time-domain (FDTD) method to exactly solve the electromagnetic field distribution in scattering through macroscopic media. In this research, we propose implementing an optical target for FDTD light scattering simulations. To model light propagation through a macroscopic turbid medium to a target position, an absorber is required to eliminate impinging light. To construct a tool that absorbs incident light from all incident directions, we modify the convolutional perfectly matched layers (CPML) absorbing boundary condition into a localized, round-shaped optical target. The cylindrical target is then validated using two-dimensional FDTD simulations under omnidirectional light incidence. Varying the different CPML parameters, we compute the absorption efficiency for its characterization in a wide range of applications, and we analyze the factors affecting its performance as a numerical optical target in macroscopic light scattering simulations. To demonstrate the applicability of the presented model, three examples are given in which we report: 1) Effective light elimination and isolation of electromagnetic fields within the problem region. 2) Detection of an ideal absorber within random media. And, 3) shaping the CPML absorbing boundary condition for reduction in computational time and memory resources of an FDTD simulation.CONTENTS ACKNOWLEDGMENTS v 中文摘要 vii ABSTRACT ix CONTENTS xi LIST OF FIGURES xv LIST OF TABLES xxi Chapter 1 Introduction 1 1.1 An Optical Target for Light Scattering Simulations 1 1.2 FDTD Simulations of Optical Imaging Techniques 2 1.3 Modeling of Perfectly Absorbing Media 4 1.4 Chapter Outline 5 Chapter 2 Finite-Difference Time-Domain Method 7 2.1 Finite Difference Scheme 7 2.2 Yee Algorithm 9 2.3 Central Difference Approximation of Maxwell Equations 11 2.4 Stability and Dispersion 17 2.5 Alternative Schemes and Improvements 23 Chapter 3 Absorbing Boundary Conditions 25 3.1 Mur ABC 26 3.2 Berenger Perfectly Matched Layers 28 3.3 Modifications to Berenger PML 32 3.4 Validation and Performance of Berenger PML 34 3.4.1 Comparison between Mur ABC and Berenger PML 34 3.4.2 Conductivity Discretization and Constitutive Parameters 39 3.4.3 Performance and Optimal Parameters 40 Chapter 4 Electromagnetic Wave Source Conditions and Time Domain Analysis 45 4.1 Source Implementation in Yee Grid 45 4.1.1 Hard Source 46 4.1.2 Soft Source 47 4.1.3 Total-Field/Scattered-Field Formulation 48 4.2 Fourier Analysis 51 4.3 Gaussian Beam 56 4.4 Complex Field Calculation via Hilbert Transform 61 4.5 Summary 65 Chapter 5 CPML Optical Target 67 5.1 Implementation of the Convolutional PML 67 5.2 Cylindrical versus Planar Geometry 71 5.3 Omnidirectional Light Absorption 73 5.3.1 Simulation Setup 73 5.3.2 Performance Evaluation 77 5.3.3 Optimal Conductivity Stepping 81 5.3.4 Limitations 83 5.4 Absorption of Gaussian Beams 85 5.4.1 Simulation Setup 85 5.4.2 Performance of the circular target 88 5.4.3 Comparison with a Planar Absorber 91 5.5 Summary 94 Chapter 6 Applications of the CPML Optical Target 95 6.1 Extracting and Isolating Portion of the Scattered Field 95 6.2 Detection of an Ideal Absorber inside Biological Tissue 99 6.2.1 Placement of the Optical Target in Turbid Media 99 6.2.2 Variation of the Target’s Depth 103 6.2.3 Variation of the Position in the Transversal Axis 107 6.2.4 Placement under Different Incident Wavelength 108 6.2.5 Conclusion 111 6.3 Shaping Absorbing Boundary Conditions 112 6.4 Summary 114 Chapter 7 Conclusion and Future Prospect 115 7.1 Conclusion 115 7.2 Future Prospect 116 REFERENCES 11910468418 bytesapplication/pdf論文公開時間：2014/08/08論文使用權限：同意有償授權(權利金給回饋學校)光散射時域有限差分法光學模擬光學靶thesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/261883/1/ntu-103-R00941105-1.pdf