With the Collaborative Research Center CRC 1261, Project A2,  we develop novel ME sensors that are not fabricated from conventional magnetostrictive and piezoelectric materials. In cooperation with the Chair for Functional Nanomaterials (Prof. Dr. Rainer Adelung), new material concepts are dpursued to achieve a particularly effective conversion of the magnetic field into an electrical signal. To achieve this goal, passive materials and components are reduced. Special attention is paid to the complete omission or drastic reduction of the substrate and its effects. Furthermore, the energy for bond stretching is minimized by the use of extremely soft materials, e.g. magnetoactive elastomers instead of ceramic magnetostrictive materials. They are combined in a special electret generator/transducer principle, as shown in Fig. 1 (left), to completely avoid the piezoelectric material

Fig 1. Left: Electret generator/transducer concept. Magnetoactive polymer (blue); Electret (red). Right: A unique property of the electret generator/transducer concept is the softening of the cantilever. With decreasing gap size between cantilever and electret, the resonance is shifted to lower values and the bandwidth increases

The magnetoactive material (blue) oscillates over a permanently charged electret film (red). They are separated by an air gap (d0). The induced charges in the counter electrode, positioned on the magnetoactive material facing the electret, change with time and thereby creates a detectable signal. At the same time a new approach to soften the oscillating cantilever was introduced, as shown in Fig. 1 (right). The electret reduces the restoring force of the cantilever and increases oscillation amplitude as well as the bandwidth. The sensors enable thus direct detection with large bandwidths. This is especially interesting for magnetocardiography applications in the frequency range of 10-40Hz. Our part is focused on the fabrication of polymer electrets for these sensors. We use the iCVD process, which enables us to deposit high-quality PTFE films. After charging in a corona discharge these films show an excellent charge stability. Currently we are working on new materials in close cooperation with the Chair for Functional Nanomaterials (Prof. Dr. Rainer Adelung) to further increase the sensitivity of the sensors. Further details on project A2 can be found on the official website of the CRC 1261.

Selected publication

Mona Mintken, Marleen Schweichel, Stefan Schröder, Sören Kaps, Jürgen Carstensen, Yogendra Kumar Mishra, Thomas Strunskus, Franz Faupel and Rainer Adelung. Nanogenerator and piezotronic inspired concepts for energy efficient magnetic field sensors, Nano Energy 56 , 420-425 (2019)