Wireless Power Link Design for Both High-Power Inductive Coupling and Smart Metasurfaces Exploitation

As future technologies are going to be autonomous under the umbrella of the Internet of things (IoT) we can expect WPT to be the solution for intelligent devices. WPT has many industrial and medical applications both in the near-field and far-field domains. Considering the impact of WPT, this thesis is an attempt to design and realize both near-field and far-field WPT solutions for different application scenarios. A 27 MHz high frequency inductive wireless power link has been designed together with the Class-E switching inverter to compensate for the efficiency loss because of the varying weak coupling between transmitter and receiver because of their mutual misalignment. Then a system of three coils was introduced for SWIPT. The outer coil for WPT and the inner two coils were designed to fulfil the purpose of communication and testing, operating at frequencies different from the WPT coil. In addition to that, a trapping filter technique has also been adopted to ensure the EM isolation of the coils. Moreover, a split ring resonator-based dual polarization converter has been designed with good efficiency over a wide frequency range. The gap or cuts have been introduced in the adjacent sides of the square ring to make it a dual-polarization converter. The converter is also stable over a wide range of incident angles. Furthermore, a meta-element based intelligent surface has been designed to work in the reflection mode at 5 GHz. In this research activity, interdigital capacitors (IDCs) instead of ICs are introduced and a thin layer of the HfZrO between substrate and meta elements is placed whose response can be tuned and controlled with the applied voltage to achieve IRS.

Characterization of first sorption cycle of white Portland cement by 1H NMR

The work carried out is focused on the exploration of processes occurring in cement materials during sorption cycles by using Nuclear Magnetic Resonance (NMR) relaxometry. Long (months) and short (days-weeks) sorption cycles of cement materials were explored. The long cycle consists of around 6 months of drying and re-wetting cement samples of different sizes and water-to-cement (w/c) ratios in a homemade relative humidity (RH) chamber. Short cycles were performed by drying samples of different sizes and w/c ratios in the oven at 60 ˚C and re-wetting underwater. Different NMR techniques, such as one- and two-dimensional relaxometry and solid-signal analyses, were used to study the samples. Firstly, by the interpretation of quasi-continuous distributions of T2 relaxation time, we demonstrated that some reversible and irreversible changes concerning smaller porosity happened during the first sorption cycle. Secondly, using 2D NMR and a new 2D NMR inversion algorithm we showed preliminary results on the cement T1-T2 maps. Data obtained during sorption processes indicated possible water exchange between different pore populations inside the cement samples. Thirdly, the solid structure of cement samples was qualitatively investigated with T1 measurements and, as far as we know, for the first time interpreted with the Pake-Doublet theory. Changes in the solid structure were observed. Precisely variations of the amount of Ettringite during drying/wetting were proposed to take place. Finally, a work on NMR single-sided equipment design for in situ cement investigation was shown. The multi-cubic-blocks magnet structure design was performed using different specific CAD software, and the magnetic fields generated by RF coils of different geometries were investigated using a customized Matlab script. The single-sided NMR instrument equipped with the designed single-sided magnet and coil was built by the ERICA partner company MR Solutions (Abingdon, UK), and the preliminary results resultsated the correctness of the developed design.

Analysis and design considerations of resonator arrays for inductive power transfer systems

In the frame of inductive power transfer (IPT) systems, arrays of magnetically coupled resonators have received increasing attention as they are cheap and versatile due to their simple structure. They consist of magnetically coupled coils, which resonate with their self-capacitance or lumped capacitive networks. Of great industrial interest are planar resonator arrays used to power a receiver that can be placed at any position above the array. A thorough circuit analysis has been carried out, first starting from traditional two-coil IPT devices. Then, resonator arrays have been introduced, with particular attention to the case of arrays with a receiver. To evaluate the system performance, a circuit model based on original analytical formulas has been developed and experimentally validated. The results of the analysis also led to the definition of a new doubly-fed array configuration with a receiver that can be placed above it at any position. A suitable control strategy aimed at maximising the transmitted power and the efficiency has been also proposed. The study of the array currents has been carried out resorting to the theory of magneto-inductive waves, allowing useful insight to be highlighted. The analysis has been completed with a numerical and experimental study on the magnetic field distribution originating from the array. Furthermore, an application of the resonator array as a position sensor has been investigated. The position of the receiver is estimated through the measurement of the array input impedance, for which an original analytical expression has been also obtained. The application of this sensing technique in an automotive dynamic IPT system has been discussed. The thesis concludes with an evaluation of the possible applications of two-dimensional resonator arrays in IPT systems. These devices can be used to improve system efficiency and transmitted power, as well as for magnetic field shielding.

Development of a hydrogel construct to prevent endoleaks occurrence following endovascular abdominal aortic aneurysm repair

Abdominal aortic aneurysm is the pathological dilation of the abdominal tract of the aorta and, if left untreated, could undergo rupture with a mortality rate of up to 90%. EVAR is the most common method for AAA treatment consisting in the internal coverage of the aorta with a metallic stent to isolate the aneurysmatic segment from the systemic circulation. Although EVAR technical success rate is high, reinterventions are common. Among the causes of reinterventions typeII endoleaks are the most frequent and consist in retrograde blood flow into the aneurysmal sac from collateral aortic branches. Continued perfusion of the aneurysm sac may lead to aneurysm rupture, therefore AAA sac embolization is performed using metallic coils. However, the presence of artifacts caused by the presence of metallic coils is a limitation because they are radiopaque and can hamper the endoleak during imaging follow-up. This study is aimed at developing a biocompatible hydrogel that could be injected into the aneurysmal sac and may allow a selective intraprocedural sac embolization to reduce post procedural typeII endoleak and eventual AAA rupture. P(BT75BSI25) was synthesized by polycondensation and its biocompatibility tested to assess whether the polymers had no toxic effects. HUVEC cell line was used to mimic the environment in which the polymer would be in contact with, PBS was used as a positive control and MTT assay was performed to evaluate cellular viability after being in contact with the hydrogel. MTT assay showed no significant difference between PBS and P(BT75BSI25), thus the polymer is biocompatible, as confirmed by the analysis of apoptosis by flow cytometry. An aromatic copolymer was obtained via polycondensation and was found to be biocompatible in contact with endothelial cells. This suggests that the hydrogel could be potentially used in the clinical setting for the treatment of type II endoleak after EVAR.

Analisi delle prestazioni energetiche di un impianto HVAC basato su un chiller con eiettore a geometria variabile mediante il software TRNSYS

Il lavoro svolto nella seguente Tesi ha avuto come obiettivo principale quello di modificare il precedente modello TRNSYS dell’impianto innovativo solare/biomassa studiato nell’ambito del progetto Hybrid-BioVGE, impianto che utilizza un gruppo chiller VGE con eiettore a geometria variabile, aggiungendo il circuito per la produzione di ACS, composto da un serbatoio di accumulo un campo di collettori solari dedicato ed una pompa di circolazione, modificando la circuitazione idraulica complessiva, modellando la configurazione finale. Sono state modificate e migliorate anche le logiche di controllo dei vari componenti dell’impianto, in particolare della caldaia a biomassa, del connettore tra accumulo caldo da un lato e circuito di riscaldamento ed accumulo per la produzione di ACS dall’altro lato, del gruppo chiller VGE e dell’accumulo di energia frigorifera con PCM. In ultima istanza, è stata implementata per la stagione estiva un’ulteriore logica di controllo che favorisce il funzionamento del gruppo chiller VGE quando è disponibile un alto contributo di energia solare ed in presenza di una temperatura ambiente in condizioni favorevoli. Attraverso il software TRNSYS 18 sono stati riprodotti in maniera fedele e accurata l'edificio, l'impianto innovativo ad esso associato e sono state svolte delle simulazioni in periodi temporali dell'anno precisi. Tali simulazioni hanno mostrato: un miglioramento nell’efficienza dell’impianto durante la stagione di riscaldamento per alimentare i pannelli radianti al servizio dell’edificio e la produzione di ACS, con valori di Solar Fraction pari al 70% e quota di energia rinnovabile del 90%; prestazioni migliori durante la stagione di raffrescamento con incremento dell'energia termica emessa dai fan-coils del 3%, della Solar Fraction pari al 50% e Seasonal Performance Factor di sistema migliori. Annualmente si è vista una quota di energia rinnovabile molto elevata (84.2%).