Magic 'metamaterials' storm physics

Physicists are abuzz with possibilities for "metamaterials" that can be designed to have surprising properties, the BBC reports.

Tweaking the structure of materials to manipulate things like their appearance is already fairly well-known; the next phase is changing their mechanics.

A major conference is alive with ideas, designs and samples including springy ceramics, unfeelability cloaks and programmable rubber sponges.

They could help build spacecraft tiles or even terrain-sensitive shoe soles.

"I think this idea of metamaterials is slowly migrating into different areas," said Prof Martin Wegener, from the Karlsruhe Institute of Technology in Germany.

"Originally the excitement was all about electromagnetism - and then it went to totally different areas like thermodynamics and, lately, mechanics."

Prof Wegner also told the BBC that the term "metamaterial" has been applied to all sorts of weird and wonderful designs, without much consistency - but that it usually refers to a case where unusual properties jump out, which would not be expected from the original ingredients.

Prof Wegener works on cloaking, but his aim is not to make things invisible. He wants to hide them from physical forces, and last year his lab produced a honeycomb-like material that made an object beneath it unfeelable.

This particular metamaterial was a solid lattice that acts like a fluid in certain ways, deflecting pressure around its hidden cargo.

Now the tiny, hidden cylinder was very small in that case (less than 1mm) but related work by Prof Wegener's team was picked up by French physicists and engineers, who showed that a careful pattern of drilled holes could divert damaging earthquake vibrations.

Turning the ground itself into a sort of metamaterial, it seems, might go so far as to protect a power station from a tremor.

Here at the American Physical Society's March Meeting, Prof Wegener presented his latest work - which includes cloaking a hole at the centre of a flat sheet - saying: "It’s a design principle. You can apply it to anything you want."

Elsewhere at the meeting, Bastiaan Florijn, a final-year PhD student at Leiden University in the Netherlands, showed reporters what he calls the first ever mechanically "programmable" material.

It is a surprisingly low-tech looking slab of rubber, punched with an array of holes. But those holes, of two sizes, are specifically designed so that they can compress either vertically or sideways - and that switch is controlled by adding a small clamp.

The end result is a sort of oversized sponge that can be stiff, or soft, or flit between the two at a specific stage of the squeeze.

If it switches to become softer while still under pressure, this is known as "negative stiffness" - a property so weird that Mr Florijn said he still hasn't worked out an application for it.

But the slabs have another property that could be immensely, obviously useful: they absorb energy.

"Imagine a car bumper that you can program - for instance, if you drive in a neighbourhood with a lot of small kids, you want to have a very soft bumper," Mr Florign said.