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February 29, 2012

Metamaterials Boosts Electromagnetism Safely

By using exotic man-made materials, scientists from Duke University and Boston College believe they can greatly enhance the forces of electromagnetism (EM), one of the four fundamental forces of nature, without harming living beings or damaging electrical equipment.

This theoretical finding could have broad implications for such applications as magnetic levitation trains, which ride inches above the surface without touching it and are propelled by magnets receiving electrical current.

Arxiv full 19 page paper - Magnetic levitation of metamaterial bodies enhanced with magnetostatic surface resonances

Physical Review B - Magnetic levitation of metamaterial bodies enhanced with magnetostatic surface resonances

We propose that macroscopic objects built from negative-permeability metamaterials may experience resonantly enhanced magnetic force in low-frequency magnetic fields. Resonant enhancement of the time-averaged force originates from magnetostatic surface resonances (MSRs), which are analogous to the electrostatic resonances of negative-permittivity particles, well known as surface plasmon resonances in optics. We generalize the classical problem of the MSR of a homogeneous object to include anisotropic metamaterials and consider the most extreme case of anisotropy, where the permeability is negative in one direction but positive in the others. It is shown that deeply subwavelength objects made of such indefinite (hyperbolic) media exhibit a pronounced magnetic dipole resonance that couples strongly to uniform or weakly inhomogeneous magnetic field and provides strong enhancement of the magnetic force, enabling applications such as enhanced magnetic levitation




“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,” Urzhumov said. “While we can’t suppress the electric field completely, a magnetically-active metamaterial could theoretically reduce the amount of current needed to generate a high enough magnetic field, thus reducing parasitic electric fields in the environment and making high-power EM systems safer. ”

The results of Urzhumov’s analysis were published online in the journal Physical Review B, and the team’s research was supported by the Air Force Office of Scientific Research.

The solution to this problem comes from the recent ability to fabricate exotic composite materials known as metamaterials, which are not so much a single substance, but an entire man-made structure that can be engineered to exhibit properties not readily found in nature. These metamaterials can be fabricated into a limitless array of sizes, shapes and properties depending on their intended use.

In the magnetic levitation train example, conventional electromagnets could be supplemented by a metamaterial, which would have been designed to produce significantly higher intensities of magnetic fields using the same amount of electricity.

The Duke scientists came up with the theoretical underpinning for the metamaterial, which is being fabricated by collaborators at Boston College, led by Willie Padilla, associate professor of physics.

“The metamaterial should be able to increase the magnetic force without increasing the electric current in the source coil,” Urzhumov said. “The phenomenon of magnetostatic surface resonance could allow magnetic levitation systems to increase the mass of objects being levitated by one order of magnitude while using the same amount of electricity.”

EM is currently being used in a host of devices and applications, ranging from subatomic “optical tweezers” scientists use to manipulate microscopic particles with laser beams, to potentially highly destructive weapons.

2011 (last year) research

Physical Review B - Metamaterial-enhanced coupling between magnetic dipoles for efficient wireless power transfer

Nonradiative coupling between conductive coils is a candidate mechanism for wireless energy transfer applications. In this paper we propose a power relay system based on a near-field metamaterial superlens and present a thorough theoretical analysis of this system. We use time-harmonic circuit formalism to describe all interactions between two coils attached to external circuits and a slab of anisotropic medium with homogeneous permittivity and permeability. The fields of the coils are found in the point-dipole approximation using Sommerfeld integrals which are reduced to standard special functions in the long-wavelength limit. We show that, even with a realistic magnetic loss tangent of order 0.1, the power transfer efficiency with the slab can be an order of magnitude greater than free-space efficiency when the load resistance exceeds a certain threshold value. We also find that the volume occupied by the metamaterial between the coils can be greatly compressed by employing magnetic permeability with a large anisotropy ratio.

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