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Mikrodalga görüntüleme ve tedavi sistemleri için anten tasarımı

Antenna design for microwave imaging and therapy systems

  1. Tez No: 1010929
  2. Yazar: ANIL ARSLAN
  3. Danışmanlar: DOÇ. DR. TUBA YILMAZ ABDOLSAHEB
  4. Tez Türü: Yüksek Lisans
  5. Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2026
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Lisansüstü Eğitim Enstitüsü
  11. Ana Bilim Dalı: Elektronik ve Haberleşme Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Telekomünikasyon Mühendisliği Bilim Dalı
  13. Sayfa Sayısı: Belirtilmemiş.

Özet

Bu tez çalışmasında, mikrodalga tabanlı meme görüntüleme ve mikrodalga hipertermi uygulamalarında kullanılmak üzere geniş bantlı bir anten tasarımı ve bu antenlerle oluşturulan çok elemanlı bir sistem kurgusu geliştirilmiştir. Tasarım hedefi; 2-3 GHz bandını kapsayan, doku ile etkileşime uygun, üretilebilir ve ölçümlerle doğrulanabilir bir anten elde etmektir. Bu amaçla Quasi-Yagi anten yapısı temel alınmış; mikroşerit besleme, mikroşerit–CPS geçişi (balun), sürücü eleman, yönlendirici elemanlar ve kırpılmış toprak düzlemi birlikte tasarlanmıştır. Bant genişliğini artırmak için ayrık halka rezonatör (AHR)(split ring resonatör,SRR) yapısı anten geometrisine eklenmiş, ardından boyutlar ve kritik parametreler elektromanyetik simülasyonlar ile adım adım optimize edilmiştir. Optimizasyon sonucunda anten, -10 dB geri dönüş kaybı şartına göre 1.99-3.33 GHz aralığında çalışarak yaklaşık 1.34 GHz bant genişliği sağlamıştır. S11 minimum değeri yaklaşık 2.464 GHz civarında -32.32 dB seviyesine kadar düşmüştür. Tasarımın pratikte uygulanabilirliğini göstermek için anten FR4 altlık üzerinde üretilmiş; VNA ölçümleriyle alınan S-parametre sonuçları simülasyon verileriyle karşılaştırılarak genel uyum doğrulanmıştır. Antenin doku benzetimlerinde ve dizi yapısında performansını incelemek amacıyla 8 elemanlı dairesel bir dizilim oluşturulmuş, elemanlar fantom etrafına 45° açısal aralıklarla yerleştirilmiştir. Yağlı meme ve yoğun meme fantom senaryolarında anten–fantom mesafesinin (d) S11 davranışı üzerindeki etkisi değerlendirilmiş; aynı mesafe koşullarında doku tipinden kaynaklanan farklılıkların sınırlı kaldığı, baskın etkinin anten–fantom mesafesi olduğu görülmüştür. Örneğin d = 10 mm durumunda dizinin yaklaşık 2.01-3.27 GHz aralığında -10 dB altında kaldığı ve empedans bant genişliğinin yaklaşık 1.26 GHz olduğu belirlenmiştir. Hipertermi uygulaması için EM–termal birleştirilmiş analiz akışı kurulmuş ve Pennes biyo-ısı modeli kullanılarak sıcaklık dağılımları hesaplanmıştır. Hedef bölgede ısıl odaklanmayı artırmak için anten uyarımları Parçacık Sürü Optimizasyonu (PSO) ile önce yalnız faz, ardından genlik+faz birlikte optimize edilmiştir. Tümörlü/tümörsüz ve d = 10 mm ile d = 35 mm senaryolarında yapılan karşılaştırmalar, hedef bölgede ana maksimumun oluşturulabildiğini ve genlik+faz optimizasyonunun hedef dışı ikincil birikimleri daha iyi kontrol edebildiğini göstermiştir. Örnek senaryolarda hedef bölge çevresinde maksimum sıcaklığın yaklaşık 44-45°C bandına ulaştığı gözlenmiştir.

Özet (Çeviri)

In this thesis, a printed antenna element and an array-based application setup are developed for microwave imaging and microwave hyperthermia studies. The design target is to obtain an antenna that provides reliable impedance matching over a wide portion of the 2-3 GHz region and remains functional under tissue-loading conditions when used in a circular multi-antenna configuration. The study covers the antenna design process, resonator-based bandwidth enhancement, fabrication considerations, and system-level evaluations with breast phantom scenarios. In addition, an electromagnetic–thermal coupled workflow is established in CST Studio Suite to investigate hyperthermia focusing performance using an eight-element array. A planar Quasi-Yagi antenna topology is selected as the main structure. The antenna is designed with a microstrip feed and a microstrip-to-CPS transition (balun) to excite the radiating section. The radiating region includes a driver element and a director arrangement, while a truncated ground plane is employed to support the intended matching and radiation characteristics. The full-wave electromagnetic design is carried out in CST with a staged approach: first, the baseline geometry is optimized by parametric sweeps; then resonator-based structures are integrated to improve matching continuity and to expand the -10 dB bandwidth; finally, critical antenna parameters are re-optimized to meet the target frequency coverage more effectively. To improve impedance matching over a wider frequency range, resonator-based structures are introduced into the design. A square split-ring resonator (SSRR) unit cell is defined with two nested square rings having opposite splits. For a consistent description, the unit cell is parameterized by the outer square side length LSRR, ring trace width WSRR, inter-ring gap G1, and split length S1. In the initial sizing, WSRR, G1, and S1 are each selected as 1 mm, and LSRR is chosen as 12 mm to correspond to the intended resonance region. After the unit-cell behavior is verified, a three-cell SSRR array is positioned in front of the director element to exploit coupling with the end-fire field distribution of the Quasi-Yagi structure. The coupling is controlled through parametric sweeps of two key parameters: (i) the spacing between split ring resonator (SRR) cells and (ii) the distance between the SRR array and the director element. The goal of this integration is to obtain a more continuous impedance matching behavior within the target band by leveraging the additional resonance/coupling mechanism. In addition to the SSRR-based consideration, the antenna is also evaluated with an SRR array integration and its placement is optimized. After SRR integration, the reflection response shows a deep minimum around 2.476 GHz, where the S11 value reaches approximately -43.75 dB, indicating stronger matching around the target center region. When evaluated with the -10 dB criterion, the SRR-integrated design provides an impedance bandwidth of approximately 2.12-3.11 GHz (about 990 MHz). For comparison, in the optimized case before SRR integration, the -10 dB region remains around 2.19-2.94 GHz (about 750 MHz). Therefore, integrating the square SRR array and tuning placement/spacing parameters increases the impedance bandwidth by approximately 240 MHz and yields a response that is more suitable for covering the intended 2-3 GHz region. Following resonator integration, further improvement is achieved by re-optimizing the driver element dimensions. Since the driver geometry directly affects the electrical length and the resulting input impedance character, it is treated as one of the most effective tuning mechanisms for bandwidth expansion. Parametric sweeps on the driver dimensions lead to a final response where the -10 dB impedance bandwidth expands to 1.99-3.33 GHz, corresponding to an overall bandwidth of approximately 1.34 GHz. The final design also exhibits a deep reflection minimum around 2.464 GHz with an S11 value of approximately -32.32 dB. These results demonstrate that the combination of resonator-based enhancement and driver re-optimization provides broad and continuous matching rather than isolated resonance points. The antenna is realized on an FR4 epoxy substrate, and reflection behavior is validated through measurement using a vector network analyzer. The measurement step is used to confirm the feasibility of the printed structure and to compare the overall reflection behavior with the simulation-based design expectations. After single-element evaluation, the antenna is investigated within an array configuration and under phantom loading conditions. An eight-element circular arrangement is constructed with antennas placed around the phantom at 45° angular spacing. Two phantom classes are considered: a fatty phantom and a dense phantom. In this setup, the antenna–phantom distance (d) is treated as a key parameter and its effect on the reflection response is analyzed. For example, for the fatty phantom at d = 25 mm, the -10 dB region is observed approximately from 2.016 GHz to 3.220 GHz, corresponding to an impedance bandwidth of about 1.204 GHz. For the dense phantom at d = 10 mm, the -10 dB condition is satisfied approximately from 2.008 GHz to 3.272 GHz, yielding an impedance bandwidth of about 1.264 GHz. Across comparative evaluations, it is concluded that the dominant factor that determines S11 behavior is the antenna–phantom distance rather than phantom type. In other words, while the general matching character is largely preserved between fatty and dense phantoms, changing the distance produces more pronounced differences in the S11 curves. This finding highlights the importance of controlling and repeating the antenna placement distance in practical system implementations. The hyperthermia part of the thesis is conducted using the designed eight-element array in CST Studio Suite with an electromagnetic–thermal coupled workflow. In the electromagnetic stage, the field distribution and power loss are obtained for the array placed around the phantom. The computed power loss is then transferred to the thermal solver as a volumetric heat source term. Temperature evolution is calculated based on the Pennes bio-heat equation framework, enabling hyperthermia evaluation through temperature rise rather than only electromagnetic indicators such as field magnitude or SAR. Before thermal simulation, thermal material parameters are defined for the phantom tissue and tumor region. In the thermal setup, the initial/ambient temperature is taken as 25°C, and a convection boundary condition is applied at the outer surface of the phantom to represent heat exchange with the environment. The convection heat transfer coefficient is assigned as h = 200 W/(m²·K), so that heat loss from the surface to the environment is included in the thermal model. To focus energy at a predefined target location, antenna excitations are optimized using particle swarm optimization (PSO). The target point is defined at the coordinate (0, -25) in the phantom model. The optimization is implemented in MATLAB by using complex electric field contributions obtained from CST at the target point, and the resulting excitation sets are then assigned back to the CST model under a simultaneous solution. Two optimization strategies are examined: phase-only optimization (with equal amplitudes) and joint amplitude-and-phase optimization. Hyperthermia simulations are performed for tumor-free and tumor-included scenarios, and for different antenna–phantom distances, specifically d = 10 mm and d = 35 mm. In tumor-free cases, the results show that the maximum temperature region overlaps with the intended focus region around y ≈ -25 mm, and the maximum temperature reaches approximately 45°C in the presented examples. In tumor-included cases where the tumor is defined at (0, -25), the normalized power loss and SAR distributions indicate that the highest values concentrate in and around the tumor region, and the corresponding thermal results show maximum temperature values reaching approximately the 44-45°C band. The temperature distribution is observed to be spatially more spread compared to power loss/SAR maps due to thermal conduction and perfusion effects; however, the main maximum location is preserved. Comparative evaluations of phase-only versus joint amplitude-and-phase strategies indicate that both approaches can produce a main concentration near the target, while allowing amplitude to vary provides an additional control dimension to suppress off-target secondary accumulations more effectively. Overall, the developed antenna and array setup support the intended operating conditions in terms of impedance matching and focusing behavior, and the thesis presents a complete numerical workflow from electromagnetic modeling to thermal response evaluation for microwave hyperthermia planning.

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