Magnetic Field-Cured Lightweight Magnetic Nanocomposite Stealth Devices Based on Ferrofluid and Natural Rubber

Aqueous ferrofluids based on magnetite were incorporated in poly-isoprene (natural rubber) and crosslinked in the presence of a uniform magnetic field with different strength and orientation for various volume ratios. The obtained thin, flexible and magnetic elastomer in the form of sheets was subjected to structural, morphological and magnetic studies. The elastomers are further analyzed in the low frequency (100 kHz – 5 MHz) regime for determining their dielectric properties. The complex magnetic permeability and dielectric permittivity in the S-band was evaluated by employing cavity perturbation technique. The variation of reflection loss has been studied as a function of frequency and thickness using surface impedance modelling by assuming normal incidence of microwaves on a metal backed material. A maximum absorption of −30 dB (99%) with a broad band width which covers almost the entire S-band is achieved for an elastomer cured in the presence of an electromagnet with a matching thickness of 7.5 mm. The recorded minimum absorption among the magnetic field assisted cured samples is 90%, which itself explains the proper matching of the permittivity and permeability of the magnetic elastomers. • Magnetic field-assisted curing aligns ferrofluid nanoparticles in the natural rubber matrix. • The alignment leads to chain-like structures and improves the dielectric response. • Aligned samples show higher saturation magnetization and magnetic permeability than random ones. • A loading of 20 phr gives strong microwave absorption (≈ −38 dB) across the S-band. • Field-assisted curing helps achieve lightweight composites with good absorption at lower filler content.