The structure of the CRC 1261 relies on the two project areas A “Sensor Technology” and B “Magnetoelectric Sensor Systems for Medical Applications” with a total of 14 research projects supported by two service projects, the Integrated Research Training Group and the public relations project. Although the projects follow five different sensor approaches for obtaining sufficient limits of detection at biomagnetic frequencies and four different application areas, there are a number of overarching scientific questions that will be addressed by three focus groups F1, F2 and F3. The focus groups are action groups across projects that foster exchange between projects on particular aspects. Each focus group will has regular meetings on a monthly basis for presentations and comparison of achieved results. The participating projects are committed to send at least one representative to the focus group meetings and to address overarching aspects. The following figure shows a schematic of the involvement of the different projects in the three focus groups.
Focus group "F1 Modeling"
This focus group unites all activities on device and system modeling within the CRC 1261. All projects of project area A and projects B1, B2 and B3 participate in this focus group. All these projects include the modeling of particular aspects, e.g. material and domain modeling, modeling of non-linear effects, simulation of mechanical and electromagnetic characteristics, simulation of signal strengths and noise contributions as a function of frequency, and models for digital signal processing as well as for solving the inverse problem. A wide selection of simulation methods is employed within the CRC 1261, ranging from self-implemented equation-based models to numerical techniques (in particular the finite-element method, FEM) to iterative methods combining different software tools. Within the focus group, simulation approaches and algorithms will be compared, exchanged and combined. The validity of specific assumptions will be discussed and parameter ranges of particular interest will be identified. A particular focus is on the transfer of models and simulation results to other projects. This is in the form of software or tables of results. Complex algorithms are reduced to simpler models for specific ranges of values. Order reduction techniques are employed to provide modeling results to the projects on the next level of complexity. The joint work within the focus group F1 guarantees the coherent evaluation of approaches within the broad topic of the CRC. It is expected to gain a detailed knowledge of the behavior of the ME sensor systems by joining forces. The activities of focus group F1 are coordinated by Martina Gerken.
Focus group "F2 Sensor Concepts"
This focus group encompasses all projects of project area A and projects B1, B2, Z1 and Z2. It is mainly concerned with aspects of ME sensors that are of general interest for the different sensor concepts and is coordinated by Eckhard Quandt. One important subject is material-related issues such as deposition conditions and post deposition treatment, domain engineering for reduction of magnetic losses, stress control, alternative magnetostrictive and piezoelectric materials as well as exchange coupling for self-biased magnetostrictive materials. Resonator geometries, improvements of electromechanical coupling, and an increase in the quality factor of the resonators are other points, which are highly relevant for all sensor concepts. Since the sensors should in the end be incorporated into sensor arrays, integration into MEMS devices is of particular interest. Here, substantial synergy effects are expected with respect to process development via participation of the central project Z1 in the focus group. The investigation of all sensor concepts also requires extensive characterization in terms of micro and nanostructure, magnetic and piezoelectric properties as well as of the resulting magnetoelectric properties and in particular the limit of detection. Therefore central project Z2 is also an integral part of the focus group. This also holds for projects B1 and B2, which cover all aspects related to operation as well as readout of the sensors and also deal with noise reduction, which is crucial for further improvement of the signal to noise ratio and requires joint efforts from analog and digital signal processing.
Focus group "F3 Biomagnetic Signal Analysis"
In this focus group signal processing related aspects are bundled to minimize redundancy among the projects and allow for common research on overlapping topics. Such topics start with very basic preprocessing steps such as offset removal (high pass filtering) for the recorded ME signals. Several of the medical projects need 3-dB cut-off frequencies of about 0.1 to 1 Hz at sample rates of 100 kHz and more. This results in sophisticated filter structures even for hardware components with 32-bit floating-point precision. The same is true for notch filters (removal of 50 Hz distortions and multitudes of this basis frequency). Furthermore, the removal of artifacts and noise, either in terms of temporal exclusion or attenuation as well as subtraction (using adaptive filters), is necessary in a variety of B projects. The same is true for multi-channel localization approaches such as beamforming or correlation-based approaches. After such preprocessing steps, a multitude of signal analyses, either of single ME signals or of a whole set of simultaneously recorded ME signals, are performed. This includes, for example, coherence estimations with electrical counterparts of the ME signals or visualization of the data in different domains (time-domain analyses, frequency-domain conversion with different resolutions, mixed-time-frequency-plots, short-term auto- and cross-correlation analyses, inverse solutions, Kalman filtering, beamformer techniques, to name just a few).
The participating projects are B2, B3, B5, B6, B7 and Z2. The activities of the focus group are coordinated by Gerhard Schmidt. During the meetings, current measurement and research results are presented. Data are shared among the projects and the strengths of the data analysis competence in the different projects are capitalized on. The focus group is the place to exchange data, new ideas on data analysis and results. Furthermore, signal analyses that are important for more than one project will be presented and reference implementation are generated using, for example, the simulation tool Matlab.