Several weeks ago, BBC Science and Technology Reporter Jason Palmer reported that “Researchers have apparently designed a ‘cloak’ that is invisible to magnetic fields both coming in and coming out”. Did I read this correctly — folks have developed a Harry Potter-like invisibility cloak that guides magnetic waves around a cloak's wearer? (In Harry’s case, you couldn’t see him or the cloak, so the cloak somehow deflected light… and light and magnetism are essentially two facets of the same force)
The idea of blocking magnetic fields has been proposed before, but the recent technical developments reported by Spain’s Autonomous University of Barcelona (AUB) in September’s issue of the New Journal of Physics, seem to have advanced the concept. (Note: New Journal of Physics is an open-access, peer-reviewed journal of physics. It covers physics in general, as well asinterdiscipliary topics where physics forms the central theme. The journal was established in 1998).
AUB’s Alvaro Sanchez, the report’s lead author, noted "Magnetism has been very important in technology for the last 150 years. We know very well how to create magnetic fields, but we don't know how to cancel them in a given space region." As such, Sanchez and his Team set about to find a design for the elusive ‘antimagnetic’. Their idea is to essentially use an inner cloak of superconducting material, surrounded by layers of metamaterials whose response to the magnetic field varies in a prescribed way through the thickness of the cloak
Metamaterials are artificially designed materials designed to guide electromagnetic waves – like light or magnetic fields – in a way that natural materials do not. These metamaterials are engineered to have properties that may not be found in nature, usually gaining their properties from structure rather than composition, using small inhomogeneities to create effective macroscopic behavior (I apologize if this has gotten a bit too ‘tech-heavy’)
The AUB team is now working to produce a working model of such an antimagnet, which they believe may ultimately find application in allowing pacemaker or implant wearers to undergo MRI scans, or in a number of energy generation scenarios in which magnetic fields play a large part. The technology could apparently also be put to use in hiding the magnetic signatures of submarines to evade detection or underwater mines, or even to trick metal detectors.
In a ‘light’ context, metamaterial cloaking is essentially accomplished by manipulating the paths traversed by light through novel optical materials. Metamaterials direct and control the propagation and transmission of specified parts of the light spectrum, and demonstrate the potential to render an object seemingly invisible. More simply put (I hope), the technique bends light well beyond its natural tendencies. It has been used for years in lenses used ultra-high-resolution imaging and has also been applied to real visible-light cloaking devices. Ultimately, a cloaked object in a specific location is still present, but incident waves are guided around them without being affected by the object itself (… sounds Harry Potter-ish to me!).
Researchers have also been able to refocus sound around certain objects and effectively render them sonically invisible to sonar. Metamaterials essentially bend sound back on itself, essentially making a sort of acoustic lens like the light lenses.
The primary research in metamaterials investigates materials with negative refractive index. Negative refractive index materials appear to permit the creation of superlenses which can have a spatial resolution below that of the wavelength. Some folks suggest that metamaterials are able to achieve negative refractive index, zero refractive index, and fractional values in between zero and one, however, it is probably more accurate to say that gradations of refractive index, when combined, create invisibility-cloaking.
Potential applications of metamaterials are diverse and could include remote aerospace applications, sensor detection and infrastructure monitoring, smart solar power management, public safety, radomes, high-frequency battlefield communication and lenses for high-gain antennas, improving ultrasonic sensors, and even shielding structures from earthquakes.
It is interesting to be reminded that the research in metamaterials is interdisciplinary and involves such fields as electrical engineering, electromagnetics, solid state physics, microwave and antennae engineering, optoelectronics, classic optics, material sciences, semiconductor engineering, nanoscience and others.
If you would like to read more about this latest development in a fascinating world, just click on http://www.bbc.co.uk/news/science-environment-15017479 and http://www.nature.com/nmat/journal/v7/n4/abs/nmat2126.html
Until soon… Ian