Investigation of the Double-Y Balun for Feeding Pulsed Antennas Jaikrishna Venkatesan 232 Pages Directed by Dr. Waymond Scott, Jr. In this research, a double-y balun implemented with coplanar waveguide (CPW) and coplanar strip (CPS) was investigated for use with pulsed antennas. The balun was modeled using two commercial electromagnetic simulators: Momentum and HFSS. Using these numerical solvers, design information such as the design of CPW bridges, aspect ratio of the double-y balun, and stub lengths of the CPW and CPS open and short stubs were studied. A dipole, along with the outer conductor of a coaxial line was modeled in NEC. The model was used to study the currents along the arms and feedline of balanced and unbalanced dipoles. Normalized amplitude patterns were generated along the azimuth and elevation planes for balanced and unbalanced dipoles. These patterns were used later for comparison with measured patterns. Experimental work was conducted to measure the performance of a double-y balun designed to feed a resistively loaded V-dipole. The performance of the balun was investigated via VSWR, insertion loss, and antenna pattern measurements. Antenna pattern measurements along the azimuth plane were conducted for a 5 cm dipole fed without a balun, a 5 cm dipole fed with the double-y balun, a 5 cm dipole fed with the sleeve balun, a 12 cm dipole fed without a balun, and a 12 cm dipole fed with the double-y balun. The dipoles fed without a balun were fed directly with a 50 W coaxial line. An optical link, consisting of a laser modulator (LM) unit and a laser receiver (LR) unit, was constructed to measure the patterns along the elevation plane of the above dipoles. Resulting patterns agreed closely with patterns generated with NEC models. In addition, the patterns of a resistively loaded V-dipole were measured along the E-plane using the optical link. The measured patterns for the V-dipole were compared with numerical results obtained from literature. The experimental work conducted in this research illustrates the improvement obtained in the patterns of a dipole and a resistively loaded V-dipole with the use of the double-y balun.

Novel and low-cost antennas suitable for WLAN access points are presented. The operating bandwidths of the proposed antennas can cover the 2.4/5.2/5.8 GHz WLAN bands, and the antenna gain is larger than 2 and 4 dBi in the 2.4 and 5 GHz bands; respectively. Besides, they can also generate the good omnidirectional radiation patterns in the azimuthal plane. Dipole antenna, folded dipole antenna, monopole antenna and circularly polarized antenna has been applied in the proposed designs, and good antenna performance has been obtained.

Os métodos geoelétricos, principalmente a eletrorresistividade, estão sendo cada vez mais requisitados na área da mineração, indicando espessura de capeamento de solo, zonas fraturadas e heterogeneidades do material, viabilizando economicamente, ou não, um projeto minerário. Este trabalho, realizado no município do Cabo de Santo Agostinho -PE, apresenta e discute resultados de aplicações do método geofísico, da eletrorresistividade, como instrumento de auxílio na abertura de uma nova frente de lavra para extração de blocos graníticos de grande porte. Foi investigada a espessura do capeamento de solo, bem como as principais zonas locais de falhas e fraturas. Para isso foram realizadas 32 SEVs (03 SEVs por perfil, à exceção da Linha 11, com 02) com arranjo Schlumberger de AB/2 máximo de 60metros, e 11 caminhamentos elétricos com arranjo dipolo-dipolo de AB=MN=20 metros,com aproximadamente 1000m de extensão cada perfil. As SEVs foram dispostas nas linhas de modo a cobrir adequadamente a área do terreno, possibilitando a confecção de um mapa de contorno da profundidade do topo rochoso e a caracterização do perfil de alteração pedológico. Os caminhamentos elétricos foram dispostos paralelamente entre si e espaçados de 60 metros, podendo ser observadas as possíveis configurações do topo rochoso, como rocha não fraturada e zonas fraturadas. A partir dos dados dos caminhamentos elétricos foram elaboradas simulações 3D de resistividade e para a estimativa de volume de rocha não fraturada na área de estudo (com base nas resistividades mais elevadas).Os resultados obtidos mostraram a eficiência da eletrorresistividade na determinação do topo da rocha sã e detecção das zonas fraturadas no maciço granítico. / The geoeletric methods, especially electroresistivity, are being progressively more required on mining, for identifying soil thickness, fractured zones and geological heterogeneities, to check economical viability of mining projects. This work, held in Cabo de Santo Agostinho-PE city, presents and discusses geophysics application results of electroresistivity as a tool for helping the opening of a new granitic blocks exploitation front. The soil thickness was investigated, as well as the main local fault zones and fractures. A total of 32 VESs (03 VESs per section, exception made to line 11, with 02 VESs) using Schlumberger array with AB/2 maximum of 60 m, and 11 geoelectrical profilings using dipole-dipole array (AB=MN=20 m), with section lengths close to 1000 m. The VESs lines were organized in order to cover the studied area properly, allowing mapping the top of the rock massif and characterizing the soil profile. The geoelectrical profilings were disposed parallel with 60 m gap among each other, enabling the observation of the massif top configurations, such as fractured and non fractured zones. 3D resistivity simulations were performed using the geoelectrical profilings data in order to estimate the total volume of non fractured rock in the studied area (based on the highest resistivities). The obtained data showed the efficiency of electroresistivity for fractured zones detection and for mapping the top of the fresh rock massif.

A study of procedures and techniques of measuring dielectric constant and dipole moment of liquids.

No description available.

The pole-dipole (PD) electrical resistivity array is used as part of a geophysical technique, which can be used in exploration for mineral, geothermal and hydrological resources. Furthermore, it can be used in archaeological investigations. The PD array is useful in obtaining large depths of investigation, but the array requires one pole to be planted at a greater distance from the other electrodes. Placing the infinite pole is time consuming and costly, especially in rough terrains. It can also be a liability in populated areas. Previous data inversion software assumes the infinite pole to be planted at infinity. Therefore, the field data collected has to mimic the assumptions of the inversion software. Some recent inversion programs use all 4-electrode positions for data inversion. In this case, is a good approximation of infinity for the infinite pole still necessary? Is the depth of investigation still the same or relevant with a non-infinite, infinite pole? Is the resolution of the cross-sections retained? To answer the above questions a Generalized Electrode Array (GEA) 1 dimensional (1D) inversion program is used. Different sets of field data were collected with non-infinite pole (NIP) PD arrays; these arrays are set up as PD arrays with an infinite pole planted relatively close to or on the survey lines itself. A COMSOL finite element model were modelled with varying infinite pole distances to identify the distance required for the retention of the depth of investigation and resolution of the PD array. Modelling from GEA shows the NIP distances do not affect the 1D inversion accuracy of the resistivity nor the layer thickness. The field data indicates that it is necessary to have an infinite pole, but the distance to the infinite pole can be substantially less than 10 times the array length, which is the usual rule of thumb for infinite pole placement. With 3 dimensional (3D) COMSOL modelling results, it indicates a minimum pole distance to be 2.5-array length to retain the depth of investigation and precision of the inverted sections of the PD array.

La production des dipôles supraconducteurs de la machine LHC du CERN s'est terminée en automne 2006. Les aimants fonctionnent à la température cryogénique de 1.9 K et doivent produire un champ magnétique très uniforme permettant de conduire les protons dans la machine. Le champ magnétique a été contrôlé avec beaucoup de rigueur et différentes mesures ont été réalisées pendant les différentes phases de l'assemblage des dipôles. Le but a été la découverte de défauts de production et d'assemblage qui prouvent limiter les performances des aimants. Dans le travail de thèse les effets de la variation de la géométrie des composantes mécaniques comme les câbles supraconducteur, les cales et les colliers de soutien des bobines sur l'uniformité du champ magnétique ont été étudiés. Une méthode pratique pour identifier et corriger les problèmes d'usinage a été développée et utilisée dans la phase de production. La thèse consiste en trois parties principales :<br />-Analyse de la production des principales composantes mécaniques des dipôles et étude de l'influence de la géométrie et des procédures d'assemblage sur la qualité du champ magnétique.<br />-Utilisation pratique des mesures effectuées sur les dipôles dans l'atelier d'assemblage pour résoudre les problèmes de production et comprendre le comportement de la géométrie des bobines pendant les phases d'assemblage.<br />-Etude théorique des composantes aléatoires des harmoniques du champ magnétique pour qualifier la production des dipôles.

Two different time-resolved spectroscopic techniques are discussed theoretically and demonstrated experimentally in dilute gases. The first technique involves extending the advantages of Stark-effect based time-resolved spectroscopy to non-polar molecules. This involves the development of a stable, TEM₀₀ mode, cw, CO₂ laser capable of switching rapidly and controllably between two frequencies. Design problems and output characteristics are discussed. The frequency switchable laser is applied to the CO₂ 10.6 μm P(16) coincidence with the non-polar molecule SF₆. The population relaxation time, T₁, is measured using two-pulse delayed nutation. The decay of induced dipoles is studied using the phenomenon of photon echoes. It is found that the echoes decay in a manner characteristic of dephasing dominated by velocity-changing collisions. A fit of the data to a model for such decays gives values of γ(ab) ≡ 1/T₂ (the non-velocity-changing contribution to the dipole decay rate), Γ(VC) (the total probability of a velocity-changing collision per unit time), and Δu which is related to the mean velocity change of SF₆ upon a velocity changing collision. A comparison with the published results of the similar Stark experiments on C¹³ H₃F are made. The second technique involves the development of an alternative to the pulsed excitation typically used in time-resolved T₁ studies. This involves inversion of a portion of the velocity distribution by adiabatic rapid passage (ARP) techniques. The center of this portion is then probed in the manner of previous delayed nutation experiments. The system preparation is shown theoretically to be different and simpler than the pulse case. In addition, ARP preparation gives a larger signal than two-pulse delayed nutation experiments. ARP experiments on N¹⁴H₃ and N¹⁵H₃ are described and compared to two-pulse delayed notation experiments. The single exponential decay best fits to the data from the two methods are found to be in agreement. We would expect the N¹⁵H₃ results to be very similar to the N¹⁴H₃ results, though reduced rotational resonance effects in its upper state should give it an overall slower decay. It is indeed found that the decay appears to be a simple exponential as did the N¹⁴H₃ data over the time range studied. The pressure dependent single exponential decay rate for N¹⁵H₃ is however roughly 45% larger than the rate for N¹⁴H₃ in the pressure range from 0.5 to 9 mTorr.

This work has centered on the interface dipoles arising at heterojunctions between metals, semiconductor nanoparticles, self-assembled monolayers, and organic semiconductor materials. Alkanethiol self-assembled monolayers, CdSe nanocrystals, and the organic semiconductors zinc phthalocyanine (ZnPc) and Buckminster fullerene (C60) were the basis of these investigations. UV photoemission spectroscopy has proven to be an invaluable tool to observe the vacuum level shifts for these analyses while using XPS to corroborate surface structure. With a full evaluation of these surfaces, the shifts in the vacuum level, valence ionizations, and core ionizations, the impact of these interfaces, as well as their influence on the subsequent deposition of organic semiconductor layers is established.Alkanethiols possessing varying dipole moments were examined on gold and silver substrates. The viability of these alkanethiols was demonstrated to predictively adjust the work function of these metals as a function of their intrinsic dipole moments projected to surface normal, and established differences between Ag--S and Au--S bonds. The capability of the SAMs to modify the work function of gold provided an opportunity for mixed monolayers of the alkanethiols to produce a precise range of work functions by minimal adjustments of solution concentration, which were examined with a simple point dipole model.Photoemission spectroscopy offers a thorough analysis of CdSe nanoparticle films. Despite a plethora of research on these nanocrystals, there still is controversy on the magnitude of the shift in the valence band with diameter. In our research we found the majority of the valence band shift could be attributed to the interface dipole, ignored previously. Meanwhile, the valence band tethered films was obscured by the sulfur of the thiol tether.Finally, organic semiconductor layers deposited on SAMs on gold exhibited various interface dipole effects at these heterojunctions. Charge transfer states of ZnPc did not favor energy level alignment on the SAM/Au substrates used; C60 demonstrated vacuum level shifts on C15 and C12ph alkanethiol monolayers consistent with the interface charge transfer (ICT) model. These results provide credibility to models recently demonstrated in the literature for other passivated metal surfaces, and include the viability of SAMs in these discussions.

The existence of the matter in the universe is still an unsolved puzzle. After the Big Bang, both matter and antimatter should have been created in equal amounts, and subsequently annihilated. The leading theories to explain the existence of matter require an imbalance in the production of matter and antimatter in the early universe. This in turn requires CP violation, an asymmetry of the laws of physics between matter and antimatter. cryoEDM is designed to explore the total amount of CP violation and resolve this issue. cryoEDM is a next-generation neutron electric dipole moment search in a commissioning phase of development at the Institut Laue-Langevin, Grenoble. A critical requirement of EDM searches is knowledge of the magnetic environment. This work is concerned with the development, implementation, and performance of the currently operating magnetometry system based on SQUID magnetometers. An analysis scheme to provide magnetometry data over the volume occupied by the neutrons, from measurements using the available magnetometers, is developed. An updated method to calibrate the magnetometers using internal sources of magnetic fields is presented, and found to give good agreement with independent measurements. A new method of calibration using the neutrons as a reference is discussed, and tests on an example arrangement are shown to be promising. Algorithms for detecting and correcting for hardware induced artefacts in the data are produced, and demonstrated to reconstruct the field with good agreement in all but the noisiest environments. A software framework is developed to combine these into a real-time analysis that provides feedback and diagnostics to the experiment. Using this new system the resolution of the magnetometers installed in cryoEDM is found to be limited by the environmental noise, and would give a false EDM signal that is greater than the statistical uncertainty in neutron counting. However, the resolution has been somewhat artificially limited to reduce the susceptibility to the RF interference present. This still allows the magnetometry to act as a useful diagnostic tool on any issues in the current magnetic environment, even if in a sub-optimal configuration. For example, investigation of the magnetic shielding of the experiment finds a reduction in the shielding relative to the design, a situation which is being addressed with the design of additional shielding. Once this shielding is installed the resolution of the magnetometers will improve as well as the slew rate of the SQUIDs, which is found to be lower than the $47,mu extup{Ts}^{-1}$ required to measure AC fields applied during a measurement. The current system can also determine sources of magnetic perturbations created within the experiment, which will require addressing before a full EDM run can be performed. For example, cryogenic effects are observed to occur approximately hourly causing large shifts in the magnetic field. Also operation of valves controlling the flow of neutrons around the experiment are found to produce both AC magnetic fields from the driving motors, and shifts in the field from their movement. Situations which can be resolved by reexamination of installation and operational procedures.