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Focusing Wave Beyond the Diffraction Limitin Hyperthermia Application

Bilaki, Saeed | 2021

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  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 53951 (05)
  4. University: Sharif University of Technology
  5. Department: Electrical Engineering
  6. Advisor(s): Shishegar, Amir Ahmad
  7. Abstract:
  8. In this research, diffraction limit is introduced as the major challenge in wave focusing. Common wave focusing techniques have been reviewed and classified into two categories: far-field and near-field techniques. Through examples that illustrate its major inherent and practical challenges, super-oscillation has been presented as a specific idea of focusing waves using remote sources. By introducing subwavelength inhomogeneities in the region of interest, we have demonstrated sub-diffraction wave focusing in a near-field approach. Using the multipole method, the effect of injecting sub-wavelength cylindrical particles on focusing electromagnetic waves has been studied. Since when there are more aggregate particles, the multipole method requires solving a larger set of equations, we have created a small particle model that uses the long-wavelength approximation and requires assigning only one unknown to each particle. It has been shown that the behavior of random particles and those predicted by mixing formulas are compatible. Despite the fact that most homogenization approaches come from far-field computations, this research proves that they are true for the near-field case as well. Lastly, we have demonstrated that an absorber can have its power consumption increased if it is surrounded by a lossless dielectric particle aggregation during a hyperthermia case. With the Fourier modal method, we have demonstrated that the periodic array of disordered particles behaves as a homogeneous medium with an effective wavenumber, especially when the number of particles per period increases. Our analysis of periodic structures enabled us to propose a new homogenization method that agrees with the mixing formula while still utilizing a near-field approach. In the end, the proposed multipole method was introduced to analyze electromagnetic scattering from an aggregate of spheres. In dealing with these problems there are severe numerical challenges that differ from the cylindrical problems. All computations in this study were performed using MATLAB
  9. Keywords:
  10. Hyperthermia ; Homogenization ; Periodic Structure ; Wave Focusing ; Electromagnetic Scattering ; Multipole Method ; Random Media ; Diffraction Limit

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