Diversos pesquisadores vêm sugerindo o uso de glicerol e outros alcoóis como matéria-prima para produção de bens de maior valor agregado e para geração de energia elétrica, através de células a combustível. Contudo, o sucesso dessas tecnologias de conversão depende do desenvolvimento de catalisadores mais eficientes. Nesse aspecto, abordagens teóricas se apresentam como ferramentas auxiliares, capazes de fornecer informações difíceis de serem acessadas experimentalmente e que são fundamentais para o projeto de materiais mais eficientes. Nesta tese, foram investigados, via teoria do funcional da densidade (DFT), o papel de defeitos de superfície e efeitos de tensão na adsorção de alcoóis como metanol, etanol e glicerol, sobre superfícies Pt(111) contendo defeitos e ligas de Pt3Ni(111). Para melhorar a descrição dos sistemas de adsorção, foi adicionada a correção de dispersão DFT-D3 à abordagem da DFT. Através da dinâmica molecular empregando o potencial ReaxFF, foram estudados os efeitos de temperatura sobre glicerol, em diversos níveis de recobrimento de superfície, interagindo com os substratos Pt3Ni(111). Os resultados mostram que o glicerol se liga através do oxigênio dos grupos hidróxi aos sítios top de metais de transição (TM), orientando sua cadeia carbônica quase que totalmente paralela à superfície. Os cálculos de energia de adsorção indicam que o glicerol interage mais fortemente com sítios de baixa coordenação, presentes em superfícies com defeitos, o que pode ser compreendido por meio do modelo da banda d. Além disso, a presença de múltiplos sítios de baixa coordenação favorece configurações onde o glicerol se liga à superfície por dois grupos hidróxi, um central e um terminal. Entretanto, existe uma clara preferência de alcoóis se ligarem a sítios de adsorção catiônicos, indicando que a influência de interações Coulombianas é um fator preponderante no processo de adsorção de alcoóis sobre TM. Análises de densidade eletrônica dos sistemas adsorvidos sugerem que a adsorção promove perturbações na densidade eletrônica dos alcoóis, como o deslocamento de densidade eletrônica das ligações C-O e O-H para a região de interação entre a molécula e o substrato, que estão associadas ao estiramento/enfraquecimento das ligações C-O e O-H observados através de análises estruturais. Os resultados DFT também demonstraram que a adição da correção de dispersão DFT-D3 melhorou a descrição das energias de adsorção e se mostrou essencial para reproduzir a tendência do crescimento da energia de adsorção com o tamanho molecular dos alcoóis, enquanto sua natureza atrativa promoveu a diminuição das distâncias atômicas entre alcoóis e substratos. O estudo de dinâmica molecular mostrou que a configuração de adsorção DFT se mantém apenas em temperaturas próximas de 0 K e que outras configurações são favorecidas a temperaturas mais altas. A presença de outras moléculas de glicerol promove, mediante o aquecimento do sistema, a formação de aglomerados de moléculas ligadas através de interações de hidrogênio, o que estabiliza as moléculas e, provavelmente, retarda seu processo de dessorção. Nos sistemas com maior densidade de moléculas, observou-se, ao final da simulação, a formação de fragmentos CH3OH-CHOH-CH2O- e átomos de H adsorvidos na superfície, indicando a quebra de ligações O-H do grupo hidróxi terminal. / Several researchers have been suggesting the use of glycerol and other alcohols as a feedstock to produce higher value-added goods and electricity through fuel cells. However, the success of these conversion technologies depends on the development of efficient catalysts. In this context, theoretical approaches are useful tools that are able to yield important insights that could not be easily obtained from experiments and are fundamental for the future design of more efficient materials. Hence, in this thesis, we investigated via density functional theory (DFT) the role of surface defects and strain effects on the adsorption of methanol, ethanol and glycerol on defected Pt(111) and Pt3Ni-based surfaces. To improve the description of the adsorbed systems, we added the van der Waals (vdW) correction DFT-D3 to the DFT approach. We also studied through molecular dynamics, employing the ReaxFF potential, the effects of temperature on the glycerol, considering different levels of surface coverage, interacting with the Pt3Ni(111) substrates. Our results show that the glycerol binds through the oxygen from a terminal hidroxi group to top sites of transition-metals (TM) with the carbon chain almost parallel to the surface. The calculations of adsorption energy indicate that glycerol interacts strongly with low-coordinated sites, such as those of surface defects, which can be rationalized through the d-band model. Furthermore, the presence of multiple low-coordinated sites was related with configurations where the glycerol binds to the substrates by two hidroxi groups, the central and a terminal one. However, there is a clear preference of the alcohols to bind on cationic adsorption sites, which indicates that the Coulomb interactions play a major role on the adsorption process of alcohols on TM. Electron density analyzes suggest that the adsorption promotes perturbations in the electronic density of the alcohols, such as a partial displacement of electron density from the C-O and O-H bonds to the region between the molecule and the substrate, which are related with the stretching/weakening of the C-O e O-H, as found in the structural analyzes. The DFT results also show that the addition of the DFT-D3 dispersion correction enhanced the adsorption energies and was essential to reproduce correctly the dependence of the binding energy with the molecule size, while its attractive nature promoted the decrease of the atomic distances between alcohols and substrates. The molecular dynamics showed that the glycerol DFT lowest energy adsorption configuration is maintained for temperatures close to 0 K whereas different configurations are favored in higher temperatures. In the presence of multiple glycerol molecules, the heating of the system promotes the formation of molecular clusters bound through hydrogen interactions, which stabilize the molecules and, probably, delay the desorption process. In the systems with higher molecular density, we found that CH3OH-CHOH-CH2O- fragments and H atoms are formed in the end of the simulation, which indicates that the breaking of O-H bonds from the terminal hidroxi groups is promoted.

This thesis reports the analysis of the rectangular shaped defected ground structure (RS-DGS) and the application of the structure on some microwave devices. DGS is analyzed in terms of its superior properties, which enables the designers to easily realize many kind of microwave devices which are impossible to achieve with the standard applications. Within the scope of this thesis, the focus is on the rectangular shaped DGS and its characteristic properties. The basic slow wave and high impedance characteristics are utilized in the design of some microwave devices. The design is carried on at the two different frequency bands: X-band and Ka band, centering at 10 GHz and 35 GHz, respectively. Finally, using the high impedance property and the coupling between the defects, a wide band 1 : 4 beam forming network is designed and implemented at 10 GHz.

The main objective of this research is to design, model and implement several antenna geometries using electromagnetic band gap (EBG) material and a defected ground plane. Several antenna applications are addressed with the aim of improving performance, particularly the mutual coupling between the elements. The EBG structures have the unique capability to prevent or assist the propagation of electromagnetic waves in a specific band of frequencies, and have been incorporated here in antenna structures to improve patterns and reduce mutual coupling in multielement arrays. A neutralization technique and defected ground plane structures have also been investigated as alternative approaches, and may be more practical in real applications. A new Uni-planar Compact EBG (UC-EBG) formed from a compact unit cell was presented, giving a stop band in the 2.4 GHz WLAN range. Dual band forms of the neutralization and defected ground plane techniques have also been developed and measured. The recorded results for all antenna configurations show good improvement in terms of the mutual coupling effect. The MIMO antenna performance with EBG, neutralization and defected ground of several wireless communication applications were analysed and evaluated. The correlation coefficient, total active reflection coefficient (TARC), channel capacity and capacity loss of the array antenna were computed and the results compared to measurements with good agreement. In addition, a computational method combining Genetic Algorithm (GA) with surface meshing code for the analysis of a 2×2 antenna arrays on EBG was developed. Here the impedance matrix resulting from the meshing analysis is manipulated by the GA process in order to find the optimal antenna and EBG operated at 2.4 GHz with the goal of targeting a specific fitness function. Furthermore, an investigation of GA on 2×2 printed slot on DGS was also done.

Dielectric resonator antenna (DRA) technologies are applicable to a wide variety of mobile wireless communication systems. The principal energy loss mechanism for this type of antenna is the dielectric loss, and then using modern ceramic materials, this may be very low. These antennas are typically of small size, with a high radiation efficiency, often above 95%; they deliver wide bandwidths, and possess a high power handling capability. The principal objectives of this thesis are to investigate and design DRA for low profile personal and nomadic communications applications for a wide variety of spectrum requirements: including DCS, PCS, UMTS, WLAN, UWB applications. X-band and part of Ku band applications are also considered. General and specific techniques for bandwidth expansion, diversity performance and balanced operation have been investigated through detailed simulation models, and physical prototyping. The first major design to be realized is a new broadband DRA operating from 1.15GHz to 6GHz, which has the potential to cover most of the existing mobile service bands. This antenna design employs a printed crescent shaped monopole, and a defected cylindrical DRA. The broad impedance bandwidth of this antenna is achieved by loading the crescent shaped radiator of the monopole with a ceramic material with a permittivity of 81. The antenna volume is 57.0  37.5  5.8 mm3, which in conjunction with the general performance parameters makes this antenna a potential candidate for mobile handset applications. The next class of antenna to be discussed is a novel offset slot-fed broadband DRA assembly. The optimised structure consists of two asymmetrically located cylindrical DRA, with a rectangular slot feed mechanism. Initially, designed for the frequency range from 9GHz to 12GHz, it was found that further spectral improvements were possible, leading to coverage from 8.5GHz to 17GHz. Finally, a new low cost dual-segmented S-slot coupled dielectric resonator antenna design is proposed for wideband applications in the X-band region, covering 7.66GHz to 11.2GHz bandwidth. The effective antenna volume is 30.0 x 25.0 x 0.8 mm3. The DR segments may be located on the same side, or on opposite sides, of the substrate. The end of these configurations results in an improved diversity performance.

The main objective of this research is to design, model and implement several antenna geometries using electromagnetic band gap (EBG) material and a defected ground plane. Several antenna applications are addressed with the aim of improving performance, particularly the mutual coupling between the elements. The EBG structures have the unique capability to prevent or assist the propagation of electromagnetic waves in a specific band of frequencies, and have been incorporated here in antenna structures to improve patterns and reduce mutual coupling in multielement arrays. A neutralization technique and defected ground plane structures have also been investigated as alternative approaches, and may be more practical in real applications. A new Uni-planar Compact EBG (UC-EBG) formed from a compact unit cell was presented, giving a stop band in the 2.4 GHz WLAN range. Dual band forms of the neutralization and defected ground plane techniques have also been developed and measured. The recorded results for all antenna configurations show good improvement in terms of the mutual coupling effect. The MIMO antenna performance with EBG, neutralization and defected ground of several wireless communication applications were analysed and evaluated. The correlation coefficient, total active reflection coefficient (TARC), channel capacity and capacity loss of the array antenna were computed and the results compared to measurements with good agreement. In addition, a computational method combining Genetic Algorithm (GA) with surface meshing code for the analysis of a 2×2 antenna arrays on EBG was developed. Here the impedance matrix resulting from the meshing analysis is manipulated by the GA process in order to find the optimal antenna and EBG operated at 2.4 GHz with the goal of targeting a specific fitness function. Furthermore, an investigation of GA on 2×2 printed slot on DGS was also done. / Ministry of Higher Education Malaysia and Universiti Tun Hussein Onn Malaysia (UTHM)

Dielectric resonator antenna (DRA) technologies are applicable to a wide variety of mobile wireless communication systems. The principal energy loss mechanism for this type of antenna is the dielectric loss, and then using modern ceramic materials, this may be very low. These antennas are typically of small size, with a high radiation efficiency, often above 95%; they deliver wide bandwidths, and possess a high power handling capability. The principal objectives of this thesis are to investigate and design DRA for low profile personal and nomadic communications applications for a wide variety of spectrum requirements: including DCS, PCS, UMTS, WLAN, UWB applications. X-band and part of Ku band applications are also considered. General and specific techniques for bandwidth expansion, diversity performance and balanced operation have been investigated through detailed simulation models, and physical prototyping. The first major design to be realized is a new broadband DRA operating from 1.15GHz to 6GHz, which has the potential to cover most of the existing mobile service bands. This antenna design employs a printed crescent shaped monopole, and a defected cylindrical DRA. The broad impedance bandwidth of this antenna is achieved by loading the crescent shaped radiator of the monopole with a ceramic material with a permittivity of 81. The antenna volume is 57.0  37.5  5.8 mm3, which in conjunction with the general performance parameters makes this antenna a potential candidate for mobile handset applications. The next class of antenna to be discussed is a novel offset slot-fed broadband DRA assembly. The optimised structure consists of two asymmetrically located cylindrical DRA, with a rectangular slot feed mechanism. Initially, designed for the frequency range from 9GHz to 12GHz, it was found that further spectral improvements were possible, leading to coverage from 8.5GHz to 17GHz. Finally, a new low cost dual-segmented S-slot coupled dielectric resonator antenna design is proposed for wideband applications in the X-band region, covering 7.66GHz to 11.2GHz bandwidth. The effective antenna volume is 30.0 x 25.0 x 0.8 mm3. The DR segments may be located on the same side, or on opposite sides, of the substrate. The end of these configurations results in an improved diversity performance. / General Secretariat of Education and Scientific Research Libya

The main goals of this thesis are to design and examine heterogeneous antennas for different wireless applications of a wide variety of EM spectrum requirements: which includes WLAN 5.0 GHz, WLAN (2.45 GHz), UMTS (1.92-2.17 GHz), 2G, UMTS, LTE, ultra-wideband (UWB) applications, and MBAN applications (2.4 GHz). Various techniques for expanding bandwidth, enhancing performance, and balancing the operation have been examined through comprehensive simulated and physically fabricated models. Thereafter, a compact DRA, for UWB applications is examined. The combined resultant effects of asymmetric positioning of DRs (2, 3 and 4 Cylindrical elements), defected ground technique, dimensions, and profile of the aperture give RF designers detailed scope of the optimization process. More resonances are achieved, and the bandwidth is improved. The obtained results show that, an impedance bandwidth of 133.0%, which covers the Ultra­ Wideband band (3.6GHz - 18.0GHz), with a maximum power gain of 9dBi attained. In addition, a compact conformal wearable CPW antenna using EBG-FSS for MBAN applications at 2.4GHz is proposed. They are designed using fabric materials suitable for daily clothing. The performance of the antenna is investigated in free space, on a layered biological tissue model, and on a real human body to evaluate SAR. When the antenna is combined with an EBG-FSS structure, isolation between the antenna and the human body is introduced. The results show that the FBR is enhanced by 13 dB, the gain by 6.55dBi, and the SAR is lowered by more than 94%. The CPW antenna demonstrated here is appropriate for future MBAN wearable systems. The design, investigation, and application of water level monitoring utilizing subsurface wireless sensor are covered in this thesis. A wideband double inverted-F antenna is designed and examined to overcome signal attenuation issues. The obtained result is feasible, which has an operating bandwidth of 0.8 to 2.17GHz, with a reflection coefficient better than 10 dB. Moreover, a field trial is conducted to evaluate the robustness of the antenna under extreme conditions. A very good efficiency was also demonstrated, with losses of under 20%. Further, the results from the field experiment established that the antenna is a reliable contender for wireless communication in such challenging environments. / Libyan Ministry of Higher Education / The full text will be available at the end of the embargo: 19th June 2025

The thesis deals with the microstrip filter design using defected ground structure (DGS). The difference between standard asymmetric microstrip technique and DGS is in using the structures etched in the microwave substrate ground plane. The DGS resonant characteristics are then used in filter design. The thesis consists of three factual parts. The first one (chapter 4) introduces the use of the DGS resonators in the lowpass filter design. It involves experimental analysis of one type of the lowpass filter. The second part (chapter 5) deals with a novel microstrip lowpass filter design method using DGS. The proposed method is verified by simulations and several samples are realized and measured. Finally, the third part (chapters 7 and 8) deals with the bandpass filter design using specific defected ground structure as a resonator. The resonators are used in a coupled resonator structure. Filters of various orders and resonator configurations are designed and simulated. A combination of the DGS resonators and half-wavelength microstrip resonators is introduced as well. Selected samples are realized and measurement results are compared with simulations.