Design and Characterization of Microwave and Optical Resonators for Biomedical Applications

In this Ph.D. dissertation, the feasibility investigation, design and characterization of different microwave and optical resonator devices with applications in the fields of medicine, such as cancer radiotherapy, and diagnostic, such as chemical/biological fluid sensing, is detailed. Different microwave and optical resonant structures have been considered, the common thread among them is related to the electromagnetic field theory and the exploitation of the resonance effect to improve their performance. Ad-hoc homemade computer codes have been developed, for accurate investigations, and validated via experimental data. Finally, the design and optimization of side-coupled proton linear accelerator microwave cavities via a novel hybrid numerical/analytical approach is reported. Such microwave cavities are typically used in proton linear accelerators devoted to hadron therapy applications. The design hybrid approach has been validated through measurements. An excellent agreement between simulation and experiment has been found in terms of accelerator frequency and accelerating field nonuniformity. By exploiting the same foregoing hybrid approach, the design and optimization of a novel proton linear accelerator based on on-axis coupled electromagnetic band-gap (EBG) cavities for hadron therapy applications is also reported. The use of EBG cavities allows a very strong reduction (by about 65%) of the peak surface electric field, paving the way to the design and fabrication of very high gradient proton linear accelerators. The design of optical whispering gallery mode (WGM) microresonators efficiently and selectively excited via tapered optical fibers and long period gratings is illustrated. The design has been well validated via experimental data. A microbubble-based set-up for chemical and biomedical fluid sensing has been also investigated. By proper coupling the WGMs with the tapered fiber modes, resonance shifts higher than i) −40 GHz/wt.% at 1550 nm and ii) −3 GHz/wt.% at 589 nm, have been calculated for a sodium chloride (NaCl) and glucose (C6H12O6) fluid sensing set-ups, respectively.