Magnetostatic Surface Resonances Increase Levitation Forces
Duke University and Boston College
Researchers led by Yaroslav Urzhumov at Duke University and Willie Padilla at Boston College have discovered the theoretical framework for increasing the magnetic levitation of metamaterials enhanced with magnetostatic surface resonances. The finding could increase the mass of objects that can be magnetically levitated by an order of magnitude without a concurrent increase in the electromotive force of the drive coil, the researchers note in Physical Review B. This could make high-power electromagnetic systems safer.
“For any EM applications dealing with things on the human scale, high-intensity electromagnetic fields needed for the generation of strong forces interfere with other devices and may be harmful to biological tissues, including humans," says Urzhumov, an assistant research professor in electrical and computer engineering at Duke's Pratt School of Engineering. "The severity of this problem is substantially reduced if the fields are predominantly magnetic, since virtually all biological substances and the majority of conventional materials are transparent to magnetic fields.”
The key, the researchers discovered, is to create a magnetic version of surface plasmon resonances, which occur by collective oscillation of valence electrons in a solid stimulated by incident light. Magnetostatic surface resonances are possible with negative magnetic permeability materials which enable resonant enhancement of magnetic polarizability. The magnetic dipole resonance couples strongly to the magnetic field and enhances the magnetic force. Additionally, due to the resonant nature of the phenomenon, a levitation system based on magnetostatic metamaterial resonances can confine all electromagnetic energy to a narrow band of the frequency spectrum, which reduces electromagnetic interference and further improves the safety of the system.
While naturally occurring negative permeability materials are rare and are subject to large loss tangents, artificial metamaterials can be made with negative permeability and low loss tangents. Magnetic metamaterials are relatively easy to fabricate in the radio frequency range of 10 to 100 MHz, according to Urzhumov. Padilla and his colleague Wenchen Chen at Boston College are working on such a metamaterial structure with cells made of copper to show the practical application of this theoretical discovery. [Physical Review B]