Today’s booming telecom technology and digital systems bring convenience to human life at the cost of a large amount of electromagnetic interference (EMI) and irradiation. This not only affects information security, but it is also emerging as the source of harmful electromagnetic radiation pollution.
To address these electromagnetic pollution problems, various EMI shielding materials have been developed. Among them, iron oxide, a typical magneto-dielectric material, is one of the most attractive microwave-absorbing materials. However, limitations on the direct application of magneto-dielectric materials or conventional metal-based materials in EMI shielding applications still exist due to high density, high material thickness, fabrication difficulty, and unsatisfactory shielding effectiveness.
To overcome the issues of current technology, Northeastern researchers have developed an inorganic mineralization method to endow native bioresourced wood with favorable magnetic and electromagnetic interference shielding properties along with an optical brown appearance.
The team uses hierarchical and porous structured wood as the directional lightweight 3D organic scaffold for the in situ incorporation of inorganic magnetic (brown iron oxide) nanoparticles. This is a two-step process that involves the removal of lignin from the natural wood via a cooking and bleaching process, followed by inorganic mineralization. The resultant magnetic wood retains the original micro and nanostructures, including the aligned cell walls. More importantly, the resultant magnetic wood composite displays an optical brown appearance, saturation magnetization of 4.5 emu/g and excellent EMI shielding effectiveness due to an enhanced magnetic loss tangent. The 3 mm-thick magnetic wood shows 5~10 dB (or 7~10X) enhanced electromagnetic wave attenuation across the X-band of 8~12 GHz compared to nonmagnetic wood with the same thickness.
Due to the use of low‑cost, readily available resources and scalable fabrication methods, the magnetic wood can meet the requirements for large scale production. For applications that require larger blocks, the researchers believe that assembling smaller magnetic wood blocks into a larger model is achievable.