Vector feedback homogeneity and inner layout influence on fluxgate sensor parameters

Vector feedback is a concept which can significantly improve linearity and stability of a magnetic field sensor. The feedback coils effectively cancel the measured magnetic field in the inner volume of the triaxial sensor. Thus, in case of fluxgates, it suppresses one possible source of nonlinearity—cross-field sensitivity error. The triaxial sensor axes orthogonality should be primarily defined by the orientation of the feedback coils, while the sensitivities are defined by feedback coil constants. The influence of the homogeneity of the feedback field and the influence of the sensor inner layout on calibration parameters of a vectorially compensated triaxial fluxgate magnetometer are presented.Peer ReviewedPostprint (author’s final draft

Magnetic sensors and gradiometers for detection of objects

Disertační práce popisuje vývoj nových detekčních zařízení s anizotropními magnetorezistoryThis thesis describes development of innovative sensor systems based on anisotropi

Radio frequency atomic magnetometer for applications in magnetic induction tomography

No abstract available.No abstract available

Magnetic calibration by using non-linear optimization method

Katedra měřen

Optically pumped Cs magnetometers enabling a high-sensitivity search for the neutron electric dipole moment

An array of 16 laser-pumped scalar Cs magnetometers was part of the neutron electric dipole moment (nEDM) experiment taking data at the Paul Scherrer Institute in 2015 and 2016. It was deployed to measure the gradients of the experiment's magnetic field and to monitor their temporal evolution. The originality of the array lies in its compact design, in which a single near-infrared diode laser drives all magnetometers that are located in a high-vacuum chamber, with a selection of the sensors mounted on a high-voltage electrode. We describe details of the Cs sensors' construction and modes of operation, emphasizing the accuracy and sensitivity of the magnetic-field readout. We present two applications of the magnetometer array directly beneficial to the nEDM experiment: (i) the implementation of a strategy to correct for the drift of the vertical magnetic-field gradient and (ii) a procedure to homogenize the magnetic field. The first reduces the uncertainty of the nEDM result. The second enables transverse neutron spin relaxation times exceeding 1500 s, improving the statistical sensitivity of the nEDM experiment by about 35% and effectively increasing the rate of nEDM data taking by a factor of 1.8

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

Fluxgate Impedanzanalysator für Empfindlichkeits- und Rauscheigenschaften

The fluxgate sensor is known as a precision, low noise, reliable magnetic field sensor, and has been developed for decades. The sensor has been used in measurement systems, which need high precision in magnetic field measurements such as in satellite systems, navigation, and geological exploration. Although there are lots of competitors to the fluxgate such as Hall, GMR, and AMR sensors, the development of fluxgate sensors is still continuing to get better performance. There are still many potential developments of fluxgate sensors, to make it better than what is nowadays commercially available. The main big potential is the development of sensitivity and noise properties. Many efforts have been done to obtain this such as treatment of the core material, tuning the coils, making a new model of output voltage involving the core permeability or coil inductance, and the electronics signal processing optimization. The new model is intended to obtain the good permeability, inductance, or any other parameters for the best sensitivity and noise performance by designing the geometry. This thesis describes the development of a novel fluxgate analyzer for fluxgate sensor characterization, which is used for modeling the fluxgate sensor output to study the parameters that affect fluxgate sensor output. The characterization is based on the impedance of fluxgate sensor coils, which contain high permeability material as fluxgate sensor core. The non-linearity of the core permeability becomes the crucial and important topic in designing the impedance analyzer. The instrument has been designed to comply with the fluxgate sensor characteristics, which has low impedance and high core permeability. For that reason, the fluxgate analyzer has been designed with low output impedance and to be able to provide a very low current for fluxgate impedance measurement. A model from the impedance measurement is used to calculate and predict the fluxgate output sensitivity. Together with other physical parameters such as winding number and length, the model is utilized to set-up an equation to calculate the fluxgate output voltage and sensitivity.Der Fluxgate-Sensor ist als präziser, rauscharmer, zuverlässiger Magnetfeldsensor bekannt, und wird seit Jahrzehnten entwickelt. Der Sensor wurde in Messsystemen verwendet, die eine hohe Präzision bei Magnetfeldmessungen erfordern, beispielsweise bei Satellitensystemen, bei der Navigation und bei der geologischen Erkundung. Obwohl für das Fluxgate viele Konkurrenten wie Hall-, GMR- und AMR-Sensoren vorhanden sind, wird die Entwicklung an Fluxgates für eine bessere Performance weiter geführt. Es gibt noch viele mögliche Entwicklungen an Fluxgate-Sensoren, um sie besser zu machen als die, die heutzutage kommerziell erhältlich sind. Das wichtigste und größte Potenzial ist die Verbesserung der Empfindlichkeits- und Rauscheigenschaften. Viele Anstrengungen wurden unternommen, um dies zu erreichen, wie eine Bearbeitung des Kernmaterials, ein Abstimmen der Spulen, ein neues Modell der Ausgangsspannung, die die Kernpermeabilität oder Spuleninduktivität beinhaltet, und die Optimierung der Elektroniksignalverarbeitung.Das neue Modell soll die gute Permeabilität, Induktivität oder andere Parameter für die beste Empfindlichkeit und Rauschleistung durch die Gestaltung der Geometrie enthalten. Diese Arbeit beschreibt die Entwicklung eines neuartigen Fluxgate-Analysators zur Fluxgate-Sensorcharakterisierung. Dieser wird zur Modellierung des Fluxgate-Sensorausgangs verwendet, um die Parameter zu untersuchen, die den Fluxgate-Sensorausgang beeinflussen. Die Charakterisierung basiert auf der Impedanz von Fluxgate-Sensorspulen, die als Fluxgate-Sensorkern hochpermeables Material enthalten. Die Nichtlinearität der Kernpermeabilität wird zum entscheidenden und wichtigen Thema beim Entwurf des Impedanzanalysators. Das Gerät wurde so entwickelt, dass es den Eigenschaften des Fluxgate-Sensors entspricht, der eine niedrige Impedanz und eine hohe Kernpermeabilität aufweist. Aus diesem Grund wurde der Fluxgate-Analysator mit einer niedrigen Ausgangsimpedanz entworfen und kann einen sehr niedrigen Strom für die Fluxgate-Impedanzmessung bereitstellen. Ein Modell aus der Impedanzmessung wird verwendet, um die Fluxgate-Ausgangsempfindlichkeit zu berechnen und vorherzusagen. Zusammen mit anderen physikalischen Parametern wie Wicklungszahlen und -länge wird das Modell verwendet, um eine Gleichung zur Berechnung der Fluxgate-Ausgangsspannung und -empfindlichkeit zu erstellen

Study of Orthogonal Fluxgate Sensor in Terms of Sensitivity and Noise

Ph.DDOCTOR OF PHILOSOPH

Pulsed Field Magnetometry for High-Speed Characterisation of Rare Earth Magnets

Pulsed Field Magnetometers (PFM) offer large advantages over conventional magnetic characterising equipment for high speed measurement of modern permanent magnet materials. A lack of systematic design procedure and many perceived problems has prevented adoption of the technique. This thesis examines in detail the system components of a PFM, the perceived problems and presents design methodology for critical system components and data processing methods to recover accurate and repeatable material characteristics. A method for the design of position insensitive gradient coils is presented and compared to a conventional design. By using an inverse Biot-Savat simulation, the coupling from each turn of the pickup coil to the point of interest is calculated and optimum winding positions calculated for homogenous pickup. Problems of thermal expansion due to differential temperatures are considered and a method developed to remove the problem using cooling. The possible origin of the zero signal is presented and a method for nulling of gradient coils to remove this zero signal using an external potentiometer is considered and results demonstrated. The design and construction of field generation coils are examined in detail and a complete method is developed for the determination of magnetic and electrical characteristics for a given geometry. The effect of skew due to conductor thickness is considered in the model to ensure optimum homogeneity of applied field and the size of the conductor wires are accounted for in a multifilament model. A software tool is created to implement these design methods and the results are compared to physical models with good agreement. The offline processing of PFM data is considered and methods for the removal of the effects of eddy currents are presented and results demonstrated. By measuring the sample at different rates of change of applied field, two measurements with different eddy current components are generated. This data can be then used to calculate and remove the eddy current component. Careful consideration is given to time aligning the data and insuring the stability of the differential equations. Possible methods for calibration of a PFM are examined in detail and compared. Methods include standard sample, calibration transfer coils, and the removal of eddy currents in calibration samples by using representative eddy currents in non-magnetic materials. Standard sample and transfer coils have proved successful and produced results with a high degree of agreement compared with conventional systems. A prototype industrial PFM was built, designed for the high speed characterisation of rare earth materials in an industrial environment. Details of the system are described. Extensive industrial trials were carried out and results from the trials are discussed in detail. Comparisons are made with conventional systems and the PFM is found to have better repeatability and comparable accuracy. Overall the PFM was highly successful and has proved the technology as viable for high speed characterisation of permanent magnet materials. Future work describes improvements to the measurement technique to achieve higher accuracy, such as accounting for distributed demagnetisation factors, and describes the next generation of PFM machines that are to be built due to this work.Hirst Magnetic Instruments Ltd