Design, fabrication and characterization of electromagnetic resonators for medical and environmental applications

In this Ph.D. thesis, the feasibility investigation, design, and characterization of different resonant structures optimized to improve the performance of microwave devices for environmental monitoring and medical applications, such as cancer therapy, have been illustrated. In particular: ▪ A metamaterial lens based on a split ring resonator (SRR) has been designed to improve the focusing of an external applicator for superficial hyperthermia tumour therapy. A prototype has been fabricated by using the standard printed board circuits (PCB) technology and then characterized. The experimental results suggest that a metamaterial based on SRR is a potentially effective option for external microwave applicators in the field of dermatology [1]. ▪ An interstitial microwave applicator has been investigated for deep-seated tumours, a coaxial antenna working in the Industrial, Scientific, and Medical (ISM) frequency band at 𝑓=2.45 𝐺𝐻𝑧. Several simulations have been performed to explore various configurations, impedance matching techniques, and radiating sections. The insertion of a metamaterial lens based on Closed Loop Resonator (CLR) around the radiating section of the applicator has been numerically investigated for a further improvement of the performance. Two prototypes of mini-invasive needle applicators have been constructed and characterized [2-5]. ▪ Metamaterial lenses have been designed to improve the radiation performance of an antipodal Vivaldi antenna for wideband applications. Prototypes have been fabricated and characterized. The experimental results are in good agreement with simulations. The metalens allows the increase of the maximum gain, preserving the antenna bandwidth, and a more symmetrical radiation pattern [6-9]. ▪ A microwave sensor based on a substrate integrated waveguide (SIW) technology has been designed and characterized for the detection of water contamination in the fuel. A suitable radiating slot placed on the top of the SIW applicator allows the interaction between the microwave electromagnetic field and the fuel contaminated. The sensor is low-cost, low profile and ensures a good sensitivity for constant and real-time monitoring [10]. In addition, during the Ph.D. course, I have contributed to the following side research activities concerning optical electromagnetic field applications: ▪ The design, fabrication, and characterization of a 2×2 optical fiber coupler based on indium fluoride optical fibers [11]. In particular, I have contributed to the fabrication by means the glass processing system, Vytran® GPX2400, supplied by the “Electromagnetic Fields” laboratory led by Prof. Francesco Prudenzano, by developing preliminary silica glass samples and by searching the fabrication parameters used for obtaining fluoride glass combiners. ▪ The design of a gain-switched pulsed laser based on a commercial, heavily holmium-doped fluoroindate glass fiber, emitting in the middle-infrared range, at the wavelength λ = 3.92 μm [12]. In particular, I have contributed to run several cases and discuss the obtained results.