Rapid, Precise, and High-Sensitivity Acquisition of Paleomagnetic and Rock-Magnetic Data: Development of a Low-Noise Automatic Sample Changing System for Superconducting Rock Magnetometers

Among Earth sciences, paleomagnetism is particularly linked to the statistics of large sample sets as a matter of historical development and logistical necessity. Because the geomagnetic field varies over timescales relevant to sedimentary deposition and igneous intrusion, while the fidelity of recorded magnetization is modulated by original properties of rock units and by alteration histories, "ideal" paleomagnetic results measure remanent magnetizations of hundreds of samples at dozens of progressive demagnetization levels, accompanied by tests of magnetic composition on representative sister specimens. We present an inexpensive, open source system for automating paleomagnetic and rock magnetic measurements. Using vacuum pick-and-place technology and a quartz-glass sample holder, the system can in one hour measure remanent magnetizations, as weak as a few pAm2, of ~30 specimens in two vertical orientations with measurement errors comparable to those of the best manual systems. The system reduces the number of manual manipulations required per specimen ~8 fold

A Novel Variable Geometry based Planar Inductor Design for Wireless Charging Application

In this thesis, the performance, modelling and application of a planar electromagnetic coil are discussed. Due to the small size profiles and their non‐contact nature, planar coils are widely used due to their simple and basic design. The uncertain parameters have been identified and simulated using ANSYS that has been run utilising a newly developed MATLAB code. This code has made it possible to run thousands of trials without the need to manually input the various parameters for each run. This has facilitated the process of obtaining all the probable solutions within the defined range of properties. The optimum and robust design properties were then determined. The thesis discusses the experimentation and the finite element modelling (FEM) performed for developing the design of planar coils and used in wireless chargers. In addition, the thesis investigates the performance of various topologies of planar coils when they are used in wireless chargers. The ANSYS Maxwell FEM package has been used to analyse the models while varying the topologies of the coils. For this purpose, different models in FEM were constructed and then tested with topologies such as circular, square and hexagon coil configurations. The described methodology is considered as an effective way for obtaining maximum Power transfer efficiency (PTE) with a certain distance on planar coils with better performance. The explored designs studies are, namely: (1) Optimization of Planar Coil Using Multi-core, (2) planar coil with an Orthogonal Flux Guide, (3) Using the Variable Geometry in a Planar coil for an Optimised Performance by using the robust design method, (4) Design and Integration of Planar coil on wireless charger. In the first design study, the aim is to present the behaviour of a newly developed planar coil, built from a Mu-metal, via simulation. The structure consists of an excitation coil, sensing coils and three ferromagnetic cores 2 located on the top, middle and bottom sections of the coil in order to concentrate the field using the iterative optimisation technique. Magnetic materials have characteristics which allows them to influence the magnetic field in its environment. The second design study presents the optimal geometry and material selection for the planar with an Orthogonal Flux Guide. The study demonstrates the optimising of the materials and geometry of the coil that provides savings in terms of material usage as well as the employed electric current to produce an equivalent magnetic field. The third design study presents the variable geometry in a planar inductor to obtain the optimised performance. The study has provided the optimum and robust design parameters in terms of different topologies such as circular, square and hexagon coil configurations and then tested, Once the best topology is chosen based on performance. The originality of the work is evident through the randomisation of the parameters using the developed MATLAB code and the optimisation of the joint performance under defined conditions. Finally, the fourth design study presents the development of the planar coil applications. Three shapes of coils are designed and experimented to calculate the inductance and the maximum power transfer efficiency (PTW) over various spacing distances and frequency

Using electromagnetic methods to map and delineate high-grade harzburgite pods within the Ni-Cu mineralised Jacomynspan ultramafic sill, Northen Cape, South Africa

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2016.The Jacomynspan Ni-Cu sulphide mineralisation is hosted within a 100m thick steeply dipping tabular, differentiated, sill of mafic to ultramafic composition intruded into country gneissic rocks of the Namaqualand Metamorphic complex. This sill is predominantly composed of tremolite schist (metamorphosed pyroxenite) containing lenticular bodies of harzburgite. The harzburgite generally hosts net-textured mineralisation with up to 50% by volume of the rock. Massive sulphide veins and stringers are occasionally present within the harzburgite. The sulphide minerals are a typical magmatic assemblage of pyrrhotite, chalcopyrite and pentlandite. The sill covers an approximate strike length of about 5km but only a small portion covering 1km x 1km was selected for this study. Physical property studies carried out on the drill core (magnetic susceptibility and conductivity) indicate that the country gneissic rocks are not conductive and neither are they magnetically susceptible. However, the mineralized sill has elevated values of both magnetic susceptibility and relative conductivity compared to its host making it a suitable target for both magnetic and electromagnetic inversion. Drilling done so far on the study area has shown that the well-mineralised harzburgite (hosted within the poorly mineralised ultramafic sill) is not a continuous body but occurs in ‘pockets’. There is therefore need to use the available geophysical and geological datasets to derive a model of these well mineralised pods. This study is therefore intended to assess the feasibility of using electromagnetic (EM) methods together with other geophysical methods and geology in obtaining a model of the harzburgite pods hosted within the less conductive poorly mineralised ultramafic sill in order to guide further drilling. Geosoft’s VOXI Earth Modelling software was used to model the high resolution airborne magnetic data for this study. Cooper’s Mag2dc (www.wits.ac.za) and Stettler’s Magmodintrp software (personal communication, 2015) was also used during modelling of the magnetic data to compliment the modelling from VOXI. The mineralised ultramafic sill was clearly mapped in both the 3D model representation from Mag2dc modelling and VOXI’s 3D unconstrained smooth model inversion for the study area. Based on the physical properties studies carried out on the study area, EM data (both ground and downhole EM) were modelled using Maxwell software. The poorly mineralised tremolite schist was clearly modelled. In order to better constrain the targets, an assumption was made that at late decay times the currents would be focused in the centre of the large EM plate probably giving an indication of the most conductive part of the intrusion. Smaller ‘Resultant EM plates’ of dimensions, 300mx300m that coincide with the centre of the large EM plates (with a conductance above 100S) were constructed in iv Maxwell software and integrated with the DXF file of the Micromine geology model of the well mineralised harzburgite clearly mapping the well-mineralised harzburgite and showing its possible extensions. 2D inversion modelling was conducted on all audio-frequency magnetotelluric (AMT) data for this study area. The modelling results clearly mapped the mineralised intrusion

Using Magnetostratigraphy to Find the Cretaceous-Paleogene Boundary in La Colonia Formation, Patagonia, Argentina

The Cretaceous-Paleogene (K-Pg) boundary is a geologic record that marks the occurrence of one of the most important events in Earth’s history. At this time, approximately 66 million years ago, a mass extinction occurred, caused primarily by a meteorite impact. This also caused a change in global climate and widespread deposition of material ejected from the impact crater. Studying the K-Pg boundary can help us understand how Earth responds to catastrophic events. Currently, there are few continental records of the K-Pg boundary in South America, resulting in poor understanding of its effects there. One method for finding the boundary uses magnetostratigraphy (measuring the magnetic polarity of a rock, preserved from when it formed). Earth’s magnetic field has reversed through time, and these reversals are recorded in rock formations. Chron C29r is an interval of reversed magnetic polarity that encompasses the K-Pg boundary. Samples taken from strata in La Colonia Formation in Patagonia, Argentina, were analyzed to find their magnetic polarity, resulting in the magnetostratigraphy for that formation. I successfully identified Chron C29r in samples taken from La Colonia. This information will help us better understand the mass extinction, especially how prevalent it was in South America and the extent to which biodiversity in that area suffered

Prototyping the next generation of versatile paleomagnetic laboratory

Investigating the Earth’s magnetic field provides a unique window into the history of Earth’s outer core, where the field is generated. Rocks gain a magnetization that is in the direction of and proportional to the Earth’s magnetic field at the time of their formation, such as when magma erupts from a volcano and cools below its Curie temperature. The gained magnetization has a relaxation time that is frequently longer than the age of the universe, but unfortunately, rocks are subject to the whims of the Earth over geologic time. Given the ages of rocks commonly studied (millions to billions of years old), some paleomagnetic data is noisy and complex. Paleomagnetic intensity data in particular have long been plagued by large and poorly quantified uncertainties. Extracting accurate magnetic measurements relies on having the most advanced equipment and best experimental techniques. This thesis approaches these goals from two directions: prototyping new equipment, which also introduces novel methodology, and fine-tuning existing methods. Contained herein is the development of the world’s first automated high-temperature SQUID (Superconducting Quantum Interference Device) thermomagnetometer. This system can automatically measure the remanent magnetic field of a specimen at an elevated temperature without needing to cool the specimen to ambient temperature. Without repeated heating/cooling cycles, thermochemical alteration is minimized, and the rate of data collection is greatly increased. SQUID sensors improve the sensitivity of the magnetometer system, avoid low blocking temperature components, and provide precise temperature control and minimal alteration. While the original design called for an instrument that could provide continuous magnetization measurements, this proved to be untenable due to technical constraints with the SQUID sensors. Thus, a stepwise version was produced that measures each specimen in (up to) 10 °C increments, instead of continuously. Introducing new equipment by itself is futile if the experiments performed on them are not well calibrated and optimized. To address this problem, this thesis investigates differences in paleomagnetic intensity results produced by different variants of Thellier-style paleointensity protocols using established instruments. The most modern protocol, the IZZI protocol, was found to be broadly accurate but sometimes imprecise. This thesis further attempts to ascertain the cause of differences observed in paleointensity data when the demagnetization mechanism or paleointensity protocol is changed, as nearly a dozen methods are in use throughout the world. Finally, a series of tests evaluates whether the addition of alternating field or liquid nitrogen demagnetization cleansing steps can improve data fidelity. The additional cleansing steps can, in some cases, improve the linearity of paleointensity data sufficiently to pass selection criteria, but cannot affect, for example, other complications like thermochemical alteration. With the ever-growing pressure to provide tangible impacts to the broader scientific community, expanding the versatility of magnetic techniques to new applications is paramount. This thesis broadly applies magnetic techniques to the energy sector, through Magnetic Flux Leakage experiments on Coiled Tubing, in conjunction with Schlumberger as an industrial partner. The future paleomagnetic laboratory is a versatile one, capable of running large batches of specimens (both paleomagnetic and metallic) quickly and accurately, through a combination of improved methods and equipment. This thesis has successfully introduced a new prototype magnetometer design and found that for non-ideal (i.e. real) rocks, the interactions between the rocks and methods are complex. Going forward, the new magnetometer brings high temperature remanence measurements to more rock types and potentially further partnerships with external, industrial partners, like Schlumberger

MEMS Components for NMR Atomic Sensors

This dissertation introduces a batch fabrication method to manufacture Micro-Electro-Mechanical System (MEMS) components for NMR atomic sensors, such as NMR gyroscope (NMRG) and NMR magnetometer (NMRM). The introduced method utilized a glassblowing process, origami-like folding, and a more traditional MEMS fabrication. We developed an analytical model of imperfections, including errors associated with micro-fabrication of MEMS components. In light of the developed error model and experimental evaluation of components, we predicted the effect of errors on performance of NMRG and NMRM. We concluded that with a realistic design, a 5mrad angular misalignment between coils and folded mirrors and a 100um linear misalignment between folded coils, it would be feasible to achieve an NMRG with ARW 0.1deg/rt-hr and an NMRM with sensitivity on the order of 10fT/rt-hz using MEMS technology. A design process for miniaturized atomic vapor cells using the micro-glassblowing process was presented in this dissertation. Multiple design considerations were discussed, including cell geometry, optical properties, materials, and surface coating. The geometry and the optical properties were studied using experimentally verified analytical and Finite Element Models (FEM). The cell construction material and surface coating were the focus of our experimental study on factors that affect the transverse relaxation time (T2) of nuclear spins. We showed that the developed wafer-level coating process with Atomic Layer Deposition (ALD) of Al2O3 increased the relaxation time (T2), which is projected to reduce the ARW of NMR gyroscopes and the sensitivity of NMR magnetometers by four times. Complementary to the developed atomic sensors components, an analog emulator for NMR atomic sensors was developed. The emulator represents the spin dynamics of atoms in an applied magnetic field that are governed by Bloch equations. Characterization of atomic sensors' components using the emulator was achieved by including one or more of those components with the emulator in a hardware-in-the-loop (HIL) configuration. Finally, we presented a comparison of the response between the NMR emulator and an actual NMR system, showing similarities of responses of the two systems and feasibility of using HIL configuration in development of micro-scale NMR sensors