doc. Ing. Mattia Butta, Ph.D.

In order to improve the quality of fluxgate sensors a key point is the development of material with enhanced properties and low magnetic noise. The student will focus on electroplating of NiFe film studying the effect of different composition and plating techniques (e.g. stress reducing additives) on the properties of the film and finally on the noise of the film. Moreover he will be in charge to experiment new solutions for the structure of the electroplated cores to reduce the noise (e.g. multilayer stacks). The work will include a large part of experimental activity in developing the materials, as well as testing their properties, but also theoretical investigation to unveil the origin of the magnetic noise in the sensor and then find the best way to reduce it. http://measure.feld.cvut.cz/ripka

During the last decade a lot attention was attracted by orthogonal fluxgate sensors based on micro wires. This sensors are particularly suitable when high spatial resolution is required. In many cases, it is necessary to measure the gradient of magnetic field, rather than homogenous magnetic field. In this case it is more efficient to use a gradiometer configuration. While there is an extended literature about traditional fluxgate in gradiometer mode, there are simply a couple of works about gradiometer built with on orthogonal fluxgate sensors based on micro wires. Therefore it is an open field for investigation. The Ph.D. student will have to make simulation to study the response of magnetic wire on the gradient of magnetic field. Then, he will create a model which optimize the position of the coils to maximize the sensitivity. All this steps will be verified experimentally by assembling and testing gradiometer. After gaining experience, the students will be asked to propose himself new configuration for the gradiometer. Finally he will focus his attention on the noise developing a gradiometer with better performances in terms of noise when measuring gradient of magnetic field than a sensor of homogenous field. http://measure.feld.cvut.cz/ripka

So far, any model which describes the noise of fluxgate sensors has been based on macroscopical description of the properties of the magnetic core of the sensor, e.g. how the shape, anisotropy or magnetostriction of the core affect the noise. These quantities, however, can give only a general description of what happens in the magnetic core, thus the resulting model are not very precise and many mechanisms leading to the noise of fluxgate are still not understood. Our department has recently acquire a MOKE microscope, an instrument which allows to visualise the magnetic domains composing a ferromagnetic material. This is very useful because it allows to directly see the behaviour of the core at microscopic level, which give way more information than a macroscopic characterization of the core as a whole. The doctoral student will investigate these phenomena and eventually develop better model to describe the noise in both parallel and fluxgate sensors. The student will develop measurement set-ups for exposing the core to different excitation conditions. He will create methods to derive the behaviour of domains at larger frequency from their dynamic at lower frequency and will describe how these mechanisms lead to noise. The student will also investigate origin of the offset and how it is modified by annealing of the core.