Large-Scale Synthesis of Porous Inorganic Microspheres with Surface Assembly of Nanoscale Magnets for Electromagnetic Absorption

Herein, a scalable synthesis of core–shell structured spherical electromagnetic (EM) absorption resonant microcavity with lightweight and high EM shielding efficiency is reported. The microspheres are constructed by a spray drying method using halloysite nanotubes (HNTs) and carbon nanotubes (CNTs) as the core materials and hydrothermal assembly of ferrites or alloys on the surface layer. The optimized CoNi/HNT/CNT product has an effective absorption bandwidth of 6.64 GHz and a maximum attenuation capacity of −60.9 dB at a thickness of 2.2 mm. The phenomenon of magnetic coupling, the eddy spine effect, and the attenuation of magnetic field in the EM resonator were directly observed under a Lorentz transmission electron microscope. The product combines multiple shielding effects, including EM resonance absorption, eddy current loss, interface polarization, and conductivity loss. The ideal arrangement of an inorganic core and a magnetic shell composite structure provides an effective strategy for the design and large-scale synthesis of inexpensive, lightweight, and high-performance EM attenuation materials.