A small Antenna Design for Tomography Based on Sensing the Difference between Dielectrics

다국어 초록 (Multilingual Abstract)

Meningiomas represent a significant category of primary intracranial neoplasms, and timely detection is crucial for optimal clinical outcomes. Conventional imaging modalities, such as magnetic resonance imaging (MRI) and computed tomography (CT), offer superior spatial resolution. However, these modalities are characterized by substantial installation and operational expenses, considerable system footprints, and limited accessibility. CT is a medical procedure that also exposes patients to ionizing radiation. This thesis proposes a low-cost, portable microwave tomography system designed to detect meningiomas by leveraging the dielectric contrasts between pathological and healthy brain tissues. A miniaturized planar antenna operating in the 433 MHz ISM band has been designed using a meandered patch combined with a defected ground structure, achieving a footprint of 28 mm (0.040 λ) while maintaining good impedance matching. These elements are integrated into a linear receive array, which serves as a compact alternative to conventional converging arrays employing 8–16 fixed sensor positions. This integration simplifies the mechanics and reduces the overall system volume. A multilayer head phantom reproducing major intracranial tissues was modeled by applying frequency-dependent dielectric properties. Synthetic S-parameter data were processed using an enhanced inverse scattering solver combining iterative field updates and normalized inversion to reconstruct the complex permittivity distribution. Numerical experiments demonstrate the ability to localize tissue interfaces and meningioma-like lesions with an effective resolution of approximately These results demonstrate the feasibility of a miniaturized linear‑array microwave tomography framework for meningioma localization and provide a foundation for future experimental validation and clinical translation.

국문 초록 (Abstract)

수막종은 제1기 두개내 종양 중 중요한 범주를 차지하며, 최적의 임상 결과를 위해서는 시기적절한 검출이 필수적이다. 자기공명영상(MRI) 및 컴퓨터 단층 촬영(CT)과 같은 기존 영상 기법은 우수한 공간 분해능을 제공하지만, 상당한 설치 및 운영 비용, 큰 시스템 설치 공간, 제한된 접근성 등의 특징이 있다. 또한 CT는 환자를 이온화 방사선에 노출시키는 의료 절차이다. 본 논문에서는 병리학적 뇌 조직과 정상 뇌 조직 간의 유전율 대비를 활용하여 수막종을 검출할 수 있는 저비용 휴대용 마이크로파 단층 촬영 시스템을 제안한다. 433MHz ISM 대역에서 작동하는 소형 평면 안테나는 미엔더 패치와 결함 접지 구조를 결합하여 설계되었으며, 우수한 임피던스 매칭을 유지하면서 28mm(0.040λ)의 설치 공간을 차지한다. 이러한 요소들은 선형 수신 배열로 통합되어 8~16개의 고정 센서 위치를 사용하는 기존 수렴형 배열에 대한 소형 대안을 제시한다. 이를 통해 기계적 구조가 단순화되고 전체 시스템의 부피가 감소한다. 주요 두개 내 조직을 재현하는 다층 두개골 팬텀은 주파수 의존적 유전 특성을 적용하여 모델링 되었다. 합성 S-파라미터 데이터는 반복적인 전계 업데이트와 정규화 된 역산 과정을 결합한 향상된 역산 솔버를 사용하여 처리되었으며, 이를 통해 복소 유전율 분포를 재구성할 수 있었다. 수치 실험을 통해 약 5mm의 유효 분해능으로 조직 경계면과 수막종 유사 병변을 국소화 할 수 있음을 입증했다. 이러한 결과는 수막종 국소화를 위한 소형 선형 배열 마이크로파 단층 촬영 체계의 실현 가능성을 입증하며, 향후 실험적 검증과 임상 적용을 위한 기반을 마련한다.

목차 (Table of Contents)

• Abstact i
• Table of Contents ii
• List of Tables vi
• List of Figures vii
• Chapter 1. Introduction 1
• 1.1. Research Background 1
• 1.1.1.Meningioma and Early Detection Importance 1
• 1.1.2.Limitations of Conventional Imaging Modalities 2
• 1.1.3.Advantages of Microwave Imaging 4
• 1.2. Research Objectives 6
• 1.3. Thesis Organization 7
• Chapter 2. Theoretical Background 9
• 2.1. Fundamentals of Microwave Imaging 9
• 2.1.1.Electromagnetic Wave Interaction with Biological Tissues 10
• 2.1.2.Scattering and Absorption Phenomena 12
• 2.2. ISM Band and Frequency Allocation 13
• 2.2.1.ITU Radio Regulation 13
• 2.2.2.UHF Band Characteristics 15
• 2.3. Literature Review 15
• 2.3.1.Microwave Imaging for Tumor Detection 15
• 2.3.2.Previous Tomography Applications 17
• Chapter 3. Electromagnetic Properties of Human Tissues and Phantom Design . 20
• 3.1. Dielectric Properties of Biological Tissues 20
• 3.1.1.Complex Permittivity and Conductivity 20
• 3.1.2.Frequency Dependence of Biological Tissues 21
• 3.1.3.Cole-Cole Dispersion Model 22
• 3.2. Head Tissue Characterization 24
• 3.2.1.Outer Head Tissues 24
• 3.2.2.Cerebrospinal Fluid (CSF) 28
• 3.2.3.Brain Properties 28
• 3.3. Meningioma Dielectric Properties 30
• 3.3.1.Liteature Review 30
• 3.3.2.Permittivity Contrast with other Tissues 31
• 3.4. Multilayer Head Phantom Design 32
• 3.4.1.Anatomical Structure and Dimensions 32
• 3.4.2.Electrical Parameter Assignment 34
• Chapter 4. Inverse Scattering Problem and Image Reconstruction Algorithms 38
• 4.1. Inverse Scattering Problem Formulation 38
• 4.1.1.Forward Problem: Scattered Signals 38
• 4.1.2.Inverse Problem: Dielectric Profile 41
• 4.1.3.Discretization of Electric Field Integral Equation 42
• 4.2. Distorted Born Iterative Method 44
• 4.2.1.DBIM Principles 44
• 4.2.2.Total Field Update Mechanism 46
• 4.3. Extended Born Iterative Method 47
• 4.3.1. EBIM formulation 48
• 4.3.2. Localized Non‑Linear Approximation and EBIM Iteration 50
• 4.4. Hybrid LSQR Algorithm 53
• 4.4.1.LSQR Fundamentals 53
• 4.4.2. Tikhonov Regularization in Projected Space 56
• Chapter 5. Antenna Design and Linear Array Configuration 58
• 5.1. Miniaturized Planar Antenna Design 58
• 5.1.1.Basic Structure 58
• 5.1.2.Miniaturization Techniques 59
• 5.1.3.Design Parameters and Optimization 63
• 5.2. Antenna Simulation Analysis 69
• 5.2.1.S-parameter Characteristics 69
• 5.2.2.Radiation Pattern and Gain 71
• 5.3. Linear Array Configuration 73
• 5.3.1. Linear Array Geometry and Clinical Coverage 73
• 5.3.2.Spatial Resolution Enhancement Strategy 75
• 5.3.3.Comparison with Converging Array 77
• Chapter 6. Results and Discussion 80
• 6.1. Free-Space Validation 80
• 6.1.1.Baseline Signal Characteristics 80
• 6.1.2.System Calibration 82
• 6.2. Phantom Imaging Results 83
• 6.2.1.Comparison with Free-Space Condition 83
• 6.2.2.Dielectric Distribution Reconstruction 85
• 6.2.3.Numerical Validation 90
• Chapter 7. Conclusion 94
• Reference 96
• 국문초록 101
• Appendix 102
• Acknowledgement 105