Science News

Ron-Marco Friedrich recently reported on great progress the project project B7. Here, the aim is the detection of magnetically labeled cells for biomaterial scaffold characterization and first measurements of the magnetic field and localization of magnetic nanoparticles were successful. For the measurement, an ME sensor samples space over a surface with magnetic nanoparticles (Fig. 1). The magnetic field is measured and the inverse problem is solved to localize the sources of that magnetic field (Fig. 2).

Fig. 1: Sampling of the surface with magnetic nanoparticles using an ME sensor. The magnetic moment is aligned with the AC magnetic field.

 

   
Fig. 2: a) Reference sample with magnetic nanoparticles (red), b) Measured magnetic field (red – positive, blue - negative), c) Reconstructed sources of the magnetic field.

Good news from our central project Z2. Alexander Teplyuk (project Z2) has finished a new scheme for mounting and characterization of our cantilever-based ME sensors. Instead of of permanenty fixing the cantilevers on a mouning plate (as we did it so far), we can contact the cantilevers now in a non-permanent manner. This allows to adjust the resonance frequency of our sensors in an easy way. Consequently, sensor characterisation with a predetermined center frequency is possible now.

The video above shows how easy it is to install and contact the ME cantilevers with the new measurement setup. By using a simple torque wrench, it is possible to ajust the claming force which dircetly influcenes the resonance frequency. This allows to characterize a large set of sensors with exactly the same resonance behaviour.

Alexander Teplyuk (project Z2) had improved the head scanner with respect to scanning speed, robustness, and saftety means. It is ready now to be used for patient measurements. First evaluations have been performed in close cooperation with our medical project B5.

The scanner has reached the next level ...

 

Furthermore, a head phantom for emulation of a network of connected sources in the brain has been designed in close cooperation with the rearchers from project B3. Small coils can be arbitrarily placed at designated postions. This allows us to generate a variety of source configurations and we are able now to create the corresponding magentic fields on the surface of our artifical head.

 
  Schematic of an magnetoelectric cantilever sensor the magnified region represents the layer stacking of piezolectric (AlN), and the self biased magnetostrictive stack (Ta, Cu, MnIr, FeCoSiB). The arrow represents the bias field orientation.

For his work about magnetoelectric sensors in medical engineering Dr. Enno Lage, post doc at Kiel University, received an award for young researchers from the German Society for Materials Science (DGM, Deutsche Gesellschaft für Materialkunde). The prize was awarded at the annual conference of the DGM in Darmstadt on September 26th 2016. It honors outstanding achievements of young researchers in material science.

During his PhD, Enno Lage conducted his research on highly sensitive magnetoelectric sensors within the collaborative research center “Magnetoelectric Composites” at the Faculty of Engineering.

Those sensors show their highest sensitivity in presence of well-defined magnetic bias fields. For vector sensors and in densely arranged sensor-arrays each component needs an individually oriented bias field. Thus, the sources of bias fields, either generated with electromagnetic coils or with permanent magnets, are detrimental in terms of miniaturization.

In order to overcome these limitations, the researchers utilized the exchange bias effect which is well established in magneto-resistive sensing. The challenge in their approach was the precise adjustment of the bias field. The orientation of the internal bias field is crucial for the sensitivity. If one would simply substitute the external bias field by an internal field with same orientation and strength, the sensors would show a vanishingly small response and hence an alternative orientation had to be considered. Additionally, if the field is too large the sensitivity decreases, if it is too small the sensor behaves partially unbiased.

The followed approach led to the successful realization of self-biased magnetoelectric sensors and was suitable to combine sensor elements for vector sensing.

Corresponding publication:

Lage, E., Kirchhof, C., Hrkac, V., Kienle, L., Jahns, R., Knöchel, R., Quandt, E. and Meyners, D., 2012. Exchange biasing of magnetoelectric composites. Nature materials, 11(6), pp.523-529.

Lage, E., Woltering, F., Quandt, E. and Meyners, D., 2013. Exchange biased magnetoelectric composites for vector field magnetometers. Journal of Applied Physics, 113(17), p.17C725.

Lage, E., Urs, N.O., Röbisch, V., Teliban, I., Knöchel, R., Meyners, D., McCord, J. and Quandt, E., 2014. Magnetic domain control and voltage response of exchange biased magnetoelectric composites. Applied Physics Letters, 104(13), p.132405.

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Kiel University
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