Formation and tunable microwave reflection loss of ferromagnetic solitons in the presence of dynamic magnetic field

Abstract

This study investigates the spatiotemporal evolution and dynamic microwave absorption properties of ferrofluid interfaces under lateral confinement and vertical magnetic excitation. We examine the morphological transition of a magnetite-based ferrofluid in a confined cylindrical domain (D = 2 cm) subjected to oscillating magnetic fields (B_max = 40.5 mT, f = 0–105 Hz). Electromagnetic characterization in the Ku-band (12–18 GHz) was conducted using a metal-backed configuration to explicitly isolate Reflection Loss (RL). Results reveal that microwave absorption is governed by a synergy between bulk dissipation and surface geometry. While static layers exhibit thickness-dependent absorption, dynamic excitation enables an active “geometric enhancement” mechanism. We demonstrate an optimal operational window at low frequencies (f = 15–35 Hz) for thick layers (d≥7 mm), where the stable ferromagnetic soliton functions as a gradient-index impedance matcher. Although the absolute peak RL of −9.46 dB at 17.8 GHz is numerically modest compared to traditional solid-state absorbers, its significance lies in its in-situ, reversible spatial tunability. This dynamic topology minimizes surface reflection and maximizes energy coupling, establishing a design strategy for adaptive electromagnetic absorbers capable of switching their reflection characteristics through precise fluid control.