@PhdThesis{diss_mods_00023562, author = {Salzer, Sebastian D.}, title = {Readout Methods for Magnetoelectric Sensors}, year = {2018}, publisher = {Christian-Albrechts-Universit{\"a}t zu Kiel}, address = {Kiel}, keywords = {magnetoelectric; noise; frequency conversion; Magnetoelektrisch; Rauschen; Frequenzumsetung}, abstract = {The detection of weak magnetic fields has the potential to provide additional, non-redundant information in scientific fields such as medical diagnostics, geomagnetic investigations, data storage, amongst others. Many substances feature a low permeability and magnetic fields can penetrate them nearly unhindered which yields the possibility to detect signals that originate from within a volume without contact. Thin-film magnetoelectric sensors are mm-sized magnetometers that transform magnetic fields into a measurable polarisation via a mechanical coupling of a magnetostrictive and a piezoelectric layer. They do not need to be cooled and their high dynamic range allows them to be operated in unshielded environments. The output signal of the cantilever-shaped sensors is enhanced at their resonance frequency which can be exploited to increase the signal-to-noise ratio. This dissertation treats the signal processing for thin-film magnetoelectric sensors from a system point of view. Four main readout methods are investigated, modelled, and evaluated with the aim to lower the limit of detection: The direct detection, magnetic frequency conversion, electric frequency conversion, and a completely novel method utilising the sensor as a microwave resonator. With the focus on the signal-to-noise ratio, the noise sources of the measurement systems are discussed in depth and the dominant noise sources identified. The ultimate noise limit is given by the thermal-mechanical noise of the sensors. Acoustic environmental interference can be reduced with a tuning fork assembly that discriminates magnetic and mechanical excitation of two cantilevers clamped face-to-face. The best limit of detection for thin-film magnetoelectric sensors at 10 Hz is 50 pT/Hz^1/2 achieved with the magnetic frequency conversion leading the way towards measurements of biomagnetic signals.}, url = {https://macau.uni-kiel.de/receive/diss_mods_00023562}, file = {:https://macau.uni-kiel.de/servlets/MCRFileNodeServlet/dissertation_derivate_00007813/Diss_Sebastian_Salzer.pdf:PDF}, language = {en} }