Tuning of Surface-Acoustic-Wave Dispersion via Magnetically Modulated Contact Resonances

In this work, we propose the use of contact resonances, controlled via an external magnetic field, as a tunable platform to manipulate the dispersion of surface acoustic waves (SAWs). We exploit the analogy between surface acoustic waves in a semi-infinite medium and edge waves in a plate, to realize a compact experimental setup and to demonstrate our tuning strategy. The setup consists of a set of ferromagnetic bead resonators in contact with thin, permanent magnets and positioned at the free edge of an elastic plate. An additional set of magnets, placed at a controlled and variable distance from the beads, is used to alter the contact stiffness and natural frequencies of the bead resonators. We exploit resonances to open large-frequency band gaps via edge-wave hybridization and implement our tuning strategy to shift their frequency ranges. We predict the tuned dispersive properties of hybridized edge waves via numerical models and experimentally reconstruct them via laser vibrometry, finding excellent agreement. The use of magnetic interaction and contact mechanics as a tuning strategy for SAW systems could pave the way toward programmable devices for sensing and electronic components.