Subwavelength electromagnetic wave absorption with ferroelectric particles that enhance the magnetic permeability in magnetodielectric composites

The need to block specific frequencies of electromagnetic (EM) waves in complex communication systems such as in wireless autonomous vehicles with EM absorption films is becoming increasingly important. Increasing safety requirements necessitate that the films operate with highly precise and accurate frequency selectivity, while commercial specifications demand extremely small thicknesses. Herein, we demonstrate that the mixing of ferroelectric BaTiO₃ particles into a soft magnetic FeSiAl flake composite, followed by heat-pressing, not only enhances the electric permittivity, ϵ, which can be further tuned by oxygen vacancy engineering, but also increases the effective magnetic permeability, μ, by geometrically-induced suppression of eddy current losses and stressed-induced enhancements in the saturation magnetization. The enhanced refractive index (√ϵμ) in conjunction with the dielectric and magnetic loss leads to perfect absorption at a unique thickness that is ~15–44% thinner than its magnetic counterpart and an order of magnitude less than a quarter wavelength. These results pave the way for developing highly precise frequency selective absorption films with subwavelength thicknesses, and also provide strategies for reducing the soft magnetic material content in high-frequency ferromagnetic applications for decreased materials cost and weight.