Effect of Instability of Ferrofluid for Enhanced EMI Shielding in Ku-Band

Ferrofluid is a type of smart material consisting of stable colloidal suspensions of magnetic nanoscale particles dispersed in a nonmagnetic carrier liquid. It is known that ferromagnetic nanoparticles may improve the magnetic and dielectric properties of host materials, which exhibit novel functionality to provide better microwave absorption properties. A ferrofluid layer subjected to an external magnetic field resulting in cone-shaped structures may further enhance the reflection loss of the incident electromagnetic wave (EMW). This study investigates the effect of the ferrofluid crests on the enhancement of the EMW shielding effectiveness (SE) in the frequency range of 13-18 GHz. It is noted that such a ferrofluid has significant shield effectiveness at the frequency of 16 GHz. When the magnetic field is applied to create the ferrofluid crests, the value of SE initially increases, then decreases as the field strength is further increased, which causes more area of trough without ferrofluid. The variation of the electromagnetic interference (EMI) shield effectiveness is dominated by the arrangement of the ferrofluid crests array, which is closely related to the thickness, composition of the ferrofluid, and external magnetic field condition. The experimental results show that a ferrofluid layer with a thickness of 6 mm subjected to a magnetic flux density of B-max = 100 mT obtains an SE value higher than 21 dB throughout almost all the testing frequency range of 13-18 GHz, and the highest SEmax is 29.3 dB located at 16 GHz.