by Dr. Tilmann Sander-Thömmes, Physikalisch-Technische Bundesanstalt, Berlin, Germany
23.04.2018, 17:15 h, TF, Aquarium
Biomagnetische Sensor- und Auswertesysteme - Fortschritt durch einen modularen Ansatz
In the field of biomagnetism the application of mathematical algorithms has been as important as the hardware itself. Traditionally, the hardware (the sensor Array) was based on superconducting quantum interference devices (SQUIDs) and operated for decades without large modifications. In contrast to that the range of relevant mathematical algorithms increased at a steady pace. This was driven by factors such as an ever increasing PC based computing power, new physiological insights motivating the application of existing algorithms, and the development of new algorithms to test biophysical models among others.
After around three decades of SQUID based Hardware, now new magnetic field sensors with the potential to replace or complement SQUIDs are available or under development. The opportunity for new sensors is the consequence of clinical challenges unsolved by state-of-the art SQUID based systems and due to new technology allowing alternative quantum physics based sensors in a small sized housing. These new sensors often have extra capabilities compared with SQUIDs and naturally some disadvantages. I will illustrate the modular approach using the example of optically pumped magnetometers and the signal processing toolbox FieldTrip.
Tilmann Sander-Thömmes studied Physics at University of Freiburg and ETH Zürich and graduated there in 1992. He continued to obtain a PhD in solid-state physics at Imperial College in London. Following two post-docs in Berlin he has been working at Physikalisch-Technische Bundesanstalt since 2000 in the laboratory for Biosignals. Since 1998 he is involved with measuring and analysing magnetic brain signals. He is an expert in magnetoencephalography using both SQUIDs and more recently optically pumped magnetometers.
by Prof. Dr. Jörg Wrachtrup, Institute for Quantum Science and Technology, University of Stuttgart, Germany
08.03.2018, 17:00 h, TF, Aquarium
The accuracy of measurements is limited by quantum mechanics. Ingenious demonstrations, like measuring gravitational fields or time have explored accuracy limits and reached fundamental obstructions. Yet, precision measurements so far are restricted to dedicated environmental conditions essentially excluding “every day” applications. In the talk I will discuss spin quantum sensors comprising a single or multiple electron spins. With such a system we measure a variety of quantities including electric and magnetic fields, temperature, and force under ambient conditions. We use nuclear spins to enhance the measurement accuracy of the electron spin e.g. via quantum error correction or as ancillary quantum bits as memory or for quantum Fourier transformation [1-3]. I will present a variety of applications ranging from quantum simulations to imaging of cellular structures. I will emphasize the engineering challenges of these sensors and discuss their use to e.g. measure biomagnetic fields.
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by Prof. Dr. Oskar Paris
08.02.2018, 17:00 h, TF, Aquarium
Advanced functional materials for sensing, actuation, or energy storage are often based on highly porous materials with large surface area. They are typically organized at several length scales and their functionality critically depends on the pore geometry at the nanometre and sub-nanometre scale. The quantification of the interaction of the internal solid surface with guest atoms, -molecules, or -ions calls for non-destructive, bulk-sensitive in-situ techniques. The lecture will discuss the potential of small-angle X-ray (SAXS) and neutron scattering (SANS) in this respect. My first example will deal with the interaction of fluid guest phases with the solid pore walls of nanoporous silica, leading to a fluid-pressure dependent, non-monotonous deformation of the material. By using tailor made materials with ordered mesopores, this deformation can be monitored via the pore lattice strain from in-situ SAXS or in-situ SANS. The structural origin for the macroscopic adsorption-induced mechanical deformation of complex systems such as macroscopic monoliths with hierarchical porosity , or nanoporous thin films on non-porous substrates  will be discussed, both systems being promising model systems for actuation devices. The second example deals with structural studies of aqueous electrolytes in nanoporous carbons as a function of an applied voltage. The results from such model supercapacitors demonstrate that in-situ SAXS from disordered carbon electrodes together with new ways of data analysis allow far-reaching interpretation of ion storage mechanisms and related predictions about optimum pore geometry . Moreover, electrodes based on ordered mesoporous carbons allow assessing electrosorption induced deformation of the carbon electrodes in-situ as a function of applied voltage .
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by Prof. Dr. Sebastiaan van Dijken
11.01.2018, 17:00 h, TF, Aquarium
Spintronic devices currently rely on magnetic switching or controlled motion of magnetic domain walls by an external magnetic field or electric current. Achieving the same degree of magnetic controllability using an electric field has potential advantages including low power consumption. Here, an approach to electrically control local magnetic properties will be discussed [1-5]. The method is based on recurrent strain transfer from regular ferroelastic stripe domains in a ferroelectric BaTiO3 substrate to magnetostrictive films (e.g. CoFe, CoFeB, and Fe). Dominance of the strain-induced magnetoelastic anisotropy in these heterostructures causes full imprinting of ferroelectric domain patterns into ferromagnetic films and strong pinning of magnetic domain walls onto ferroelectric boundaries [6,7]. Optical polarization microscopy measurements of the ferromagnetic and ferroelectric domain structures indicate that domain correlations and strong inter-ferroic domain wall pinning are maintained in an applied electric field. As a result, deterministic electric-field control over the formation and erasure of ferromagnetic domains [1-3] and reversible motion of magnetic domain walls [4,5] are obtained. In addition, regular modulations of magnetic anisotropy in strain-coupled multiferroic heterostructures provide a versatile platform for the excitation and manipulation of spin waves [8,9]. These findings open up new routes towards electric-field driven spintronics and magnonics.
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