In this conducted research, optical fiber sensors are used to measure low strength alternating magnetic fields. Various fiber sensor configurations are tested and investigated to demonstrate sensing capabilities at different field magnitudes and frequencies. Distributed acoustic sensing fibers (DAS) have been largely studied and documented across a variety of applications and sensing systems. This research uses the DAS technology in tandem with magnetostrictive materials to create a distributed multi-material optical fiber magnetic sensor. Magnetic sensing has high demand across different fields and often runs into challenges of extreme environments including high temperature, corrosion, and areas with poor accessibility. The robust and distributed nature of optical fiber sensors which can be cheaply produced for long lengths is an attractive option over other single point magnetic sensors. In down hole applications specifically, having a distributed sensor able to be deployed easily and over long distances for magnetic sensing would be a large improvement to bulkier traditional magnetometers. In the conducted study, different magnetostrictive materials are implemented in distributed optical fiber sensors to analyze and compare the effective sensitivity and potential commercial viability. Nickel, galfenol alloy, and MetGlas alloy inclusions are drawn into fused silica optical fibers with Bragg gratings inscribed later on for DAS capability. Each was investigated for its response to varying AC magnetic fields to determine relative sensitivity and resolution for distributed magnetic field sensing. / Master of Science / Magnetic sensing has high demand in biomedical applications as well as within the oil and energy industry. This research proposes a series of optical fiber-based sensors to overcome many of the challenges present amidst traditional magnetic sensors. Materials that respond to magnetic fields by either contracting or expanding are coined magnetostrictive. The proposed fiber-based sensors use magnetostrictive materials to create a change in the optical path length of the light being transmitted through the optical fiber. This path difference can be converted to a strain measurement and when compared with a standardized magnetometer, a calibration curve is established for the fiber sensor. Different magnetostrictive materials are studied for measuring various alternating magnetic field amplitude strengths to look at improved sensitivity and/or resolution. This includes nickel, galfenol alloy, which is made up of iron and gallium, and MetGlas, which is composed of primarily of iron. Small wires of the respective materials are drawn out inside the silica fiber while the optical fiber is made so that continuous lengths run the course of the fiber. Different sizes were experimented with. Another simplified tested setup used a ribbon of the MetGlas while a distributed acoustic fiber sensor was laid on top to pick up the strain response while exposed to an alternating magnetic field. All of the mentioned test setups showed success in measuring alternating magnetic field strengths with a clear positive correlation of strain response to magnetic field amplitude. A calibration curve was established for each sensing system and analyzed to show an effective sensitivity range.

Le centre coloré NV, constitué d’un atome d’azote et d’une lacune, est un défaut ponctuel du diamant qui se comporte comme un atome artificiel piégé dans cette matrice. Grâce aux propriétés de son spin électronique, qui peut être lu et manipulé comme un système quantique élémentaire, le centre NV as de nombreuses applications comme qubit pour l’information quantique ou comme sonde de champ magnétique. Cependant, ces applications nécessitent de contrôler les propriétés des centres NV ainsi que leur position dans le cristal. Cette thèse examine des méthodes pour atteindre ces objectifs en combinant des techniques d’implantation d’atomes et de croissance assistée par plasma (CVD) de diamant.Le mémoire est divisé en six chapitres. Le premier chapitre résume les propriétés des centres NV, ce qui permet de définir les objectifs principaux dans la fabrication des centres NV. Le chapitre deux montre qu’il est possible de créer un réseau de centres NV par implantation au moyen d’une colonne d’ions focalisés. Cette technique est adaptée à la création de centres NV dans des nanostructures comme des cristaux photoniques ou des pointes de type AFM. Cependant la faible énergie cinétique des ions, nécessaire pour atteindre une résolution meilleure que 10 nm en diamètre de spot, conduit à une implantation proche de la surface ce qui affecte fortement les propriétés des centres NV. Le troisième chapitre examine comment la recroissance d’une couche de diamant sur des centres NV implantés permet de réduire l’impact négatif de la surface. Les quatrième et cinquième chapitres décrivent des méthodes pour la fabrication des centres NV en contrôlant les paramètres de la croissance CVD. Des couches minces fortement dopées avec les centres NV peuvent être créées, et un contrôle quasi parfait de l’orientation de l’axe du centre NV peut être obtenu. Dans l’objectif d’optimiser les propriétés du temps de cohérence du spin, le sixième chapitre étudie comment le spin électronique du centre NV peut être protégé contre les effets de décohérence induits par les spins non-polarisés dans la matrice du diamant. / The Nitrogen-Vacancy (NV) color center is a defect of diamond which behaves as an artificial atom hosted in a solid-state matrix. Due to its electron spin properties which can be read-out and manipulated as an elementary quantum system, the NV center has found a wide panel of applications as a qubit for quantum information and as a magnetic field sensor. However these applications require to control the properties of the NV centers and their localization. This doctoral thesis investigates methods allowing us to tailor the properties of NV centers by combining techniques for the implantation of nitrogen atoms and the plasma-assisted (CVD) synthesis of diamond.The manuscript is divided into six chapters. The first chapter summarizes the properties of the NV center which will set our objectives for the NV engineering. The second chapter will describe how arrays of NV centers can be created using Focused Ion Beam implantation. The results open a wide range of applications for the targeted creation of NV centers in diamond structures such as photonic crystals and tips. However the low kinetic energy which is required for achieving implantation within a spot of 10-nm diameter leads to shallow defects which properties are strongly affected by the sample surface. The third chapter investigates how the overgrowth of a diamond layer over implanted NV centers can remove the detrimental influence of the surface. The fourth and fifth chapters describe effective methods for NV center fabrication through the control of the CVD growth conditions of the hosting crystal. Thin layers with high NV doping can be grown and almost perfect control of the orientation of the NV axis can be achieved. With the goal to optimize the spin coherence properties, the sixth chapter investigates how the electron spin of the NV center can be protected from decoherence effects induced by magnetic noise due to the unpolarized spins in the diamond lattice.

Kyoto University (京都大学) / 0048 / 新制・課程博士 / 博士(工学) / 甲第19002号 / 工博第4044号 / 新制||工||1622 / 31953 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 白川 昌宏, 教授 田中 庸裕, 教授 濵地 格 / 学位規則第4条第1項該当

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19002号 / 工博第4044号 / 新制||工||1622(附属図書館) / 31953 / 京都大学大学院工学研究科分子工学専攻 / (主査)教授 白川 昌宏, 教授 田中 庸裕, 教授 濵地 格 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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The aim of the thesis is to investigate the design of efficient wireless networks through practical as well as theoretical considerations. We constructed a wireless sensor network (WSN) testbed with battery operated nodes capable of RF communication. The system is a centralized tree-based WSN to study challenges of target modeling, detection, and localization. The testbed employed magnetic sensors, on which relatively few results have been reported in the literature. A ferrous test target is modeled as magnetic dipole by validating experimentally. The problem of sensor sensitivity variation is addressed by including sensitivity estimates in model validation. After reliably detecting the target, maximum-likelihood and least-squares techniques are applied for localization. Practical considerations of constructing a WSN utilizing magnetic sensors addressed. Maximum-lifetime operation of these networks requires joint consideration of sensing and communication. Energy harvesting is promising to overcome this major challenge for energy-constrained systems. In the second part of the thesis, we considered the minimization of transmission completion time for a given number of bits per user in an energy harvesting multiuser communication system, where the energy harvesting instants are known beforehand. The two-user case with achievable rate region having structural properties satisfied by the AWGN Broadcast Channel is studied. It is shown that the optimal scheduler ends transmission to both users at the same time while deferring a nonnegative amount of energy from each energy harvest for later use. The problem is formulated as an optimization problem and solved by exploiting its special structure.