Introducing the 'antimagnet'
Researchers in Spain have proposed a new type of invisibility cloak that could hide objects from magnetic fields. The cloak – which has not been built yet – is designed to have a dual effect. It ensures that a magnetic field generated inside the cloak does not leak outside, and it ensures that the cloak and its contents cannot be detected by an external magnetic field. If it can be realized as a practical device, the technology could prove useful in industrial applications that require specific magnetic environments.
When the Earth's magnetic field flips
A 7 minute in-depth audio interview.
French geophysicist Vincent Courtillot discusses why the Earth's magnetic field occasionally flips, explaining how the geological record reveals the planet's history of pole reversal. The Earth's magnetic field provides us with a vital shield from the Sun's deadly rays, as well as enabling compass bearers around the world to find their way. But the field is not as reliable as we first thought. There is strong evidence in the geological record to suggest that many times throughout the Earth's history the north and south magnetic poles have reversed, as the major dipole component of the field has flipped.
How do we know that the Earth's field has reversed direction in the past? Is another reversal likely to occur anytime soon? What processes deep within the Earth might cause these reversals to occur?
How to hide from a magnetic field
Researchers in Europe have built a magnetic cloak that, in theory, is reasonably practical to manufacture. An object concealed by the new cloak, the researchers claim, is magnetically undetectable, while the cloak itself is made from materials available in many physics labs the world over. This means that it is, in principle, the first cloak that should be reasonably practical to manufacture.
In 2011 Alvaro Sanchez and colleagues at Universitat Autònoma de Barcelona, Spain, developed a theory for a type of magnetic cloak they called an "antimagnet" that would have two crucial properties. One is that any magnetic field created within the cloak would not leak outside the cloaked region and the other is that the cloak and the cloaked region would be undetectable by an external magnetic field; that is, the field would not be distorted by the cloak. Now, Sanchez along with Fedor Gömöry and colleagues from the Slovak Academy of Sciences, has designed and demonstrated a modified version of the cloak proposed last year.
The new cloak is a simple bi-layer cloak made up of two common materials – an inner superconducting layer made up of a high-temperature superconducting tape and an outer ferromagnetic layer composed of a few turns of a thick FeNiCr commercial alloy sheet. "The cloak we proposed last year was more of an ideal cloak," explains Sanchez. "But it was complicated with 10 layers and included superconducting plates. This new cloak, while not perfect, is a much simpler design for achieving similar results using a static uniform magnetic field." He adds that it is fair to say that this is the first cloak that is an exact cloak that can be feasibly implemented in practice.
Vibrating molecule drives a motor
A single hydrogen molecule has been used to "push" an object much more massive than itself. So say researchers in Germany and Spain who have used a phenomenon called stochastic resonance to extract useful energy from "noise". Their experiments involve using an atomic force microscope tip mounted on a flexible, spring-like cantilever and the processes at play might be exploited to power up nanometre-sized machines – or even much larger devices.
How Earth's wandering poles return home
A number of times over the past one billion years, the Earth's surface has "wandered" relative to its rotational axis – before returning to its original position. Now, a team of geophysicists from the US and Canada says it has developed a theory that explains this curious phenomenon of "oscillatory true polar wander". Understanding the mechanics behind polar wander is crucial, as a shift could tip the Earth over by as far as 50° over a period of 10–100million years and this would cause profound global environmental and geological changes.