Magneto-mechanical Resonators (MMR)

Magneto-mechanical resonators (MMRs) are passive, battery-free sensors that are read out entirely wirelessly through magnetic fields. 

At their core, an MMR consists of two permanent magnets: a stator rigidly attached to the housing and a movably mounted rotator that can rotate about the main axis. The magnetic interaction between the two magnets provides a restoring torque, so that after a brief field excitation the rotator settles into a damped rotational oscillation. Because the resonance frequency depends on the distance between the magnets, a single, millimetre- to sub-millimetre-sized device can simultaneously provide position and full orientation (tracking) and a physical measurand (sensing) – for example temperature via thermal expansion or pressure via a compressible housing. MMRs require neither a power source nor an antenna, work without a line of sight, and can be manufactured at low cost. They thus address key limitations of established tracking and sensing methods, for instance in minimally invasive medicine, where instruments must be localised inside the body without radiation or cabling. Applications are also conceivable in industrial settings, such as pressure and temperature measurements in bioreactors.

At the Metrology Lab we work on advancing this still young sensor technology into a robust measurement method. We currently focus on four directions: 

• making the readout devices more sensitive through low-noise signal processing;
• modelling and characterising the sensors in order to understand their behaviour and to better determine its impact on measurement accuracy;
• solving the inverse problem of determining orientation and position more precisely and
• developing new approaches for the excitation of MMRs.

Our work is part of a growing research field. The overall goal are miniaturised, wireless markers and sensors for the radiation-free navigation of medical instruments, for ingestible and implantable sensors that capture physiological parameters, and for robust applications in engineering and industrial manufacturing.