IMMS conducted research in cooperation with Ilmenau TU on MEMS sensors for detecting weakest magnetic fields. Such fields occur, for example, in the human body, where they must be measured very precisely, without contact or destruction.

For this purpose, sensors based on superconductive quantum interference devices (SQUIDs) are used in medical technology as well as in geology, archaeology or materials science. However, these sensors have to be cooled to at least –196 °C with a very high cryotechnical effort in order to be operated at all.

As an alternative to this, magnetoelectric MEMS, which are comparatively easy to manufacture and are operated at room temperature, were investigated in the MagSens group led by Ilmenau TU. Corresponding test structures of the sensors have been produced at Ilmenau TU and measured at IMMS.

The researched sensor principle is based on magnetostrictive-piezoelectric multilayer systems. A resonator consisting of these layers is made to vibrate piezoelectrically by applying a voltage. The magnetostrictive layer changes the oscillation behaviour, or more precisely the resonator’s natural frequency, under the influence of a magnetic field. The change in the natural frequency can be used to infer the strength of the acting magnetic field.

IMMS has taken over the modelling of the sensor principle and has analytically described the so-called Delta-E effect. This effect was identified as the decisive magnetostrictive effect. It describes the change of the Young’s modulus of the magnetostrictive layer under the effect of a magnetic field. Further, the vibration behaviour of the sensor was simulated at IMMS in the FEM software ANSYS.

This was used to investigate the influence of material and geometry data on the sensitivity of the sensor. The aim was to find structures that react with a maximum frequency shift to the effect of the smallest magnetic fields. On the one hand, this required the optimisation of the magnetostrictive layer with regard to a Delta-E effect that is as pronounced as possible. This involves material data that are dependent on the manufacturing process of the layer. Together with the colleagues from the TU, possibilities were discussed to influence these data and initial steps were taken to design the magnetostrictive layer accordingly. 

On the other hand, it was a matter of dimensioning the entire multilayer system in order to maximise the influence of the change in Young’s modulus on the frequency shift. For this purpose, various fundamental geometries with variable aspect ratios were simulated and evaluated.

The test structures developed by the TU are cantilevers and double-clamped beams of different dimensions. These structures could be successfully simulated at IMMS. The simulation data coincided with the measurement results and were used for parameter identification of unknown material data. Based on this, design rules and guidelines for the development of variable magnetoelectric sensor systems were derived.