A bending-mode asymmetric bilayer magnetoelectric antenna for very-low-frequency communication

Objective Very-low-frequency (VLF, 3–30 kHz) links are useful for underwater and lossy-media communication, but conventional electrically small antennas have serious size and radiation-efficiency limitations. Methods This study proposes an asymmetric bilayer magnetoelectric antenna using a piezoelectric layer and a magnetostrictive layer operated in bending resonance. The proposed design exploits strain-mediated magnetization modulation rather than current-driven electromagnetic resonance. A bending-resonance model, equivalent circuit model, and equivalent magnetic-dipole radiation model are established to describe electromechanical conversion and magnetic-field radiation. A 30 mm × 10 mm × 3 mm prototype was fabricated and tested. Results The measured first- and second-order bending resonance frequencies are 7388 Hz and 12,410 Hz, both in the VLF band. The measured magnetic field exhibits an approximately inverse-cube dependence on propagation distance in the near-field region, consistent with the equivalent magnetic-dipole model. A proof-of-concept 2FSK transmission experiment using the two bending resonances demonstrates frequency switching at a symbol rate of 100 Baud. Within the adopted theoretical efficiency model, the estimated radiation efficiency of the proposed antenna is approximately seven orders of magnitude higher than that of a copper loop antenna with the same lateral dimensions. Conclusion The results demonstrate that bending-mode asymmetric bilayer magnetoelectric antennas can provide a potential compact transmitting approach for VLF applications.