Impact of Structural Design on Magneto-Mechanical Resonators: The Case of a Jewel Bearing Variant

Abstract

Magneto-mechanical resonators (MMRs) are passive, wirelessly read sensors whose small size, miniaturizability, and low cost make them attractive for tracking and for sensing physical and chemical quantities. Their operation is based on a permanent-magnet rotor whose mechanical resonance encodes the sensing and tracking information. The bearing that suspends this rotor is therefore decisive both for the in-operation performance and for the manufacturability of the device. The original design suspends the rotor on a thin thread, which is nontrivial to assemble. This work investigates the impact of that structural design choice by introducing an alternative bearing in which the spherical rotor magnet rests in a cup-shaped industrial jewel. A dynamic model of this Jewel-MMR is derived, including the angle-dependent dry friction torque at the jewel contact. From it, a geometric trade-off between friction torque and resilience against unwanted oscillation modes is identified and quantified. Since the conventional quality factor loses its meaning under dominant dry friction, a two-tiered framework is proposed that compares MMR variants by estimation precision at equal magnet size and natural frequency. Both variants are characterized at a fixed pose on a Helmholtz-coil detection platform. The Jewel-MMR is self-aligning and assembled in less than half the time from fewer parts. Its response signal decays faster, so that under laboratory noise conditions the natural frequency and the orientation are recovered more precisely from the thread variant. The jewel bearing, however, tolerates a considerably larger deflection angle and thus a stronger signal, which reverses this relation above an experimentally determined noise level and indicates an advantage wherever the signal-to-noise ratio is reduced.