Spring-integrated low-frequency ME resonator with strong coupling capability and low equivalent magnetic noise

Resonant magnetoelectric (ME) sensors offer the advantages of high sensitivity and inherent narrow-band filtering capability. However, the development of ultra-low-frequency (ULF) ME resonators combining high mechanical quality factor (Q_m), low noise performance, and stable near-ideal boundary conditions remains a significant challenge. In this study, a spring-integrated ULF ME resonator is proposed and systematically investigated. The device consists of an elastic support layer, a piezoelectric layer, and a piezomagnetic layer. The elastic support layer incorporates two meander springs at both ends, creating quasi-free boundary conditions for the central sandwich-structured ME composite and enabling excitation of a high-order bending mode with a substantially reduced resonant frequency. Experimental results confirm the excitation of the third-order bending mode at a low frequency of 1266 Hz, with a calculated Q_m of 144.8. In addition, the resonant ME coefficient reaches as high as 1633.5 V/(cm Oe), and the equivalent magnetic noise decreases to 300 fT/√Hz around the resonance frequency, demonstrating great potential for specific-frequency magnetic field detection applications, including signature current identification and underground cable tracing. More importantly, the spring-integrated resonant structure provides fixed boundary conditions and maintains a stable operating frequency during long-term operation.