Boosting wireless transmission of power with magnetic metamaterials

Metamaterials have introduced many relevant new possibilities in the manipulation of light, microwaves, sound waves, and other systems. In many cases, the design and optimization of metamaterials has been achieved in conjunction with the mathematical technique of transformation optics, which allows one to guide rays of light or electromagnetic fields along desired directions. This is achieved by tailoring the electromagnetic properties of materials, the recipe of which is provided by the transformation optics technique. A particularly active application of metamaterials has been in the magnetostatic case, where magnetic fields have been cloaked, concentrated in a spatial region or transferred at a distance. Here we use magnetic metamaterials, specially designed with transformation optics technique, to demonstrate two new important effects. First, on a general basis, we analytically demonstrate that the magnetic mutual inductance between two coils is greatly enhanced when surrounding them with our magnetic metamaterials, without increasing their self-inductances. Second, this property is further exploited to boost the wireless transmission of power between distant circuits, because such a transmission depends on the magnetic coupling between emitter and receiver. We experimentally demonstrate that the efficiency of the wireless power transmission is largely increased when using the magnetic metamaterials. Different from previous proposals, in our case the enhancement is produced while keeping the gap of air between emitter and receiver free. Also, the metamaterials are constructed from widely available conventional materials, using alternating layers of soft ferromagnets and conductors, not requiring any special property such as low temperature (unlike previous proposals that involved the use of superconducting materials). This combination of feasibility and power indicates the relevance that magnetic metamaterials can have in future technologies.