Enhanced SAW magnetic sensing via acoustic energy confinement of high-order harmonics

Abstract

Surface acoustic wave (SAW) magnetic sensors offer an attractive platform for weak magnetic field detection, benefiting from compact form factor and wireless operation. However, intrinsic acoustic energy leakage into the substrate fundamentally limits the achievable sensitivity. Here, we present a compact SAW magnetic sensor based on high-order shear horizontal modes to enhance magnetoelastic coupling via acoustic energy confinement. We show that the magnetic-induced phase response is governed by harmonic-dependent acoustic energy confinement within the magnetostrictive layer. The reduced wavelength of higher-order harmonics strengthens acoustic energy confinement, increasing the fraction of acoustic energy participating in magnetoelastic coupling and thereby significantly amplifying the ΔG-induced phase modulation. As a result, the proposed device achieves a superior phase sensitivity of 3486°/mT under seventh-order harmonic excitation, corresponding to an approximately 770-fold enhancement over the fundamental mode, together with a limit of detection of 17 pT/Hz1/2 at 100 Hz. Offset frequency-dependent characterization under AC magnetic field modulation further reveals stable and high-performance detection of low-frequency weak magnetic signals. These results establish acoustic energy confinement as an effective mechanism for enhancing ΔG-based SAW magnetic sensing and provide a viable pathway toward high-density and on-chip integrated weak-field magnetic sensor arrays.