PT Unknown
AU Salzer, SD
TI Readout Methods for Magnetoelectric Sensors
PY 2018
PU Christian-Albrechts-Universität zu Kiel
WP https://macau.uni-kiel.de/receive/diss_mods_00023562
LA en
DE magnetoelectric; noise; frequency conversion; Magnetoelektrisch; Rauschen; Frequenzumsetung
AB 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.
PI Kiel
ER