Up
to now, the brain’s magnetic field is measurable only under technical
laboratory conditions. This technique is therefore not feasible in terms
of the broader medical use, although it would be significant for
diagnosing numerous conditions such as epilepsy and dementia, or even
for improving therapies such as deep brain stimulation for treating
Parkinson’s disease.
Three
research teams at Kiel University, Germany, have now jointly developed a
new type of magnetoelectric sensor, which is intended to allow the use
of this important technology in the future. The scientific breakthrough:
As opposed to conventional magnetoelectric measuring techniques, the
new sensors operate at normal conditions. Neither cooling nor external
magnetic bias fields are required. A new article in Nature Materials describes the design and properties of these so-called exchange biased magnetoelectric composite materials.
“Our
composites with exchange biasing present an international milestone in
the research of magnetoelectric materials,” says Professor Eckhard
Quandt, senior author of the study and spokesperson of the Collaborative
Research Centre 855 Magnetoelectric Composites – Future Biomagnetic Interfaces
(CRC 855). “By eliminating the dependence on externally applied
magnetic bias fields, we have removed a significant obstacle for the
medical application of magnetoelectric sensors such as
magnetocardiography and magnetoencephalography.”
As
the sensors do not affect one another due to their particular design,
measuring arrays made up of hundreds of units are now conceivable. This
would enable the production of flow maps of heart currents or brain
waves.
The
new composites consist of a complex sequence of around a hundred layers
of material, each of which is only a few nanometres thick. The
magnetoelectric sensors contain both magnetostrictive and piezoelectric
layers which, on the one hand, deform due to a magnetic field to be
measured and, as a result of this, at the same time produce electrical
voltage which is used as the measuring signal. Enno Lage who has been
working on the study since 2010 explains its background: “With the
conventional magnetoelectric layer systems it is only possible to
perform such highly sensitive measurements if the sensor is subjected to
a bias magnetic field.
“What
makes our composites so extraordinary are antiferromagnetic supporting
layers made of manganese iridium, which act like magnetic fields inside
the material,” he adds. “This means that the bias field for the
measurement is produced directly in the sensor and no longer needs to be
provided externally.”
A
complete sensor is usually a few millimeters in size and contains a
multi-layer of this new material, which is approximately a thousandth of
a millimeter thick. The new composite materials have been produced in
the recently established Kiel Nano Laboratory’s cleanroom.
“These
types of sensor systems can only be produced successfully in this
particle-free environment,” says Dr. Dirk Meyners, who is scientifically
supervising Lage during the doctoral degree programme.
With
this step in the development towards removing the dependence of
magnetoelectric measurements on external magnetic bias fields, the
working groups led by Lorenz Kienle, Reinhard Knöchel and Eckhard Quandt
have achieved an important objective of the CRC 855, which has been
supported by the German Research Foundation since January 2010. The
CRC’s overall aim is to develop such new materials and to implement them
into a fully functional, biomagnetic interface between men and the
outside world. Quandt indicates future prospects: “Beyond the CRC’s
opportunities, in the Cluster of Excellence Materials for Life,
which is currently being reviewed, we could promote a range of further
applications on the basis of these composites, for example, as sensors
for non-invasive brain stimulation.”
Exchange biasing of magnetoelectric composites
Source: University of Kiel