Frequency tuning and sensitivity enhancement of surface acoustic wave sensors for magnetic field detection

This study investigates the center frequency-dependent performance of surface acoustic wave (SAW) magnetic field sensors based on 128° YX-cut LiNbO₃ with a SiO₂ guiding layer and exchange bias-coupled FeCoSiB multilayers. Two sensor designs are compared: one with an invariant geometry and one scaled with the center frequency. The frequencies range from 100 MHz to 750 MHz. In the invariant design, sensitivity increased with center frequency due to geometric effects, leading to a best limit of detection of 55 pT/Hz 1/2 at 10 Hz and 9 pT/Hz¹ᐟ² at 100 Hz. In contrast, the frequency scaled design showed relatively stable detection limits due to opposing trends in sensitivity and phase noise. Our analysis suggests that geometric factors alone do not fully explain the observed frequency dependence, pointing to additional contributions from structural and magnetic effects. These insights open the path for further optimization of SAW sensor design for high-sensitivity magnetic field detection. • SAW magnetic field sensors with center frequencies from 100 - 750 MHz are compared. • Higher center frequencies increase sensitivity and reduce limit of detection. • The best-performing sensor has a limit of detection of 55 pT/Hz 1/2 at 10 Hz. • Magnetic, geometrical, and structural contributions are elaborated.