John Pendry: so much more than invisibility

What are metamaterials?

An ordinary material responds to an electric field, say, according to how the atoms and molecules polarize. But in a metamaterial, the atoms and molecules are replaced by slightly larger elements, such as tiny metallic rings. By designing their structure, you can design into these materials electric and magnetic properties that have never been seen in natural materials.

What are people working on now in basic metamaterials research?

What people are still doing is they’re having fun, and just seeing what you can do with this technology. There’s also a related technique called transformation optics, which teaches you what sort of metamaterial you need to put the electric and magnetic fields where you want them.

So nothing about invisibility cloaks then?

The cloak, of course, was wonderful for the public because it rang so many bells, but that was just the extreme of how far can you go with these technologies.

So what could be the first application of metamaterials?

The most advanced one is by a US company called Kymeta, which is a spin-out from the patent firm Intellectual Ventures, in Seattle. Kymeta uses metamaterials to build satellite-communications receivers.

Satellite receivers are one of the things where metamaterials are making things cheaper, better

How is this different from a normal receiver?

A usual receiver is a 30 cm steerable dish. It’s heavy and takes quite a bit of power to run the electric motor. There is a more sophisticated version of a receiver called a phased array and that’s in the form of a flat plate that is full of little dipole antennas that you can steer the direction of electronically – nothing moves mechanically.

What’s wrong with using a phased array receiver?

It’s expensive – many tens of thousands of dollars! You’ve got hundreds of thousands of transistors, making the phased array an order of magnitude more expensive than a dish.

So how can metamaterials help?

Metamaterials are cheap and can do this job of making a phased array, as you can make them tuneable by putting a little nonlinear device there.

How close is this device to market?

Kymeta has a product ready to go, which it will license to satellite-communications companies. The firm has capital of around $50m – half of which came from Microsoft founder Bill Gates.

How much will this receiver cost?

Kymeta hopes to market it for under a thousand dollars. So that’s one success story. It is one of the things where metamaterials are helping make things cheaper, better. The receiver can also plug into a USB port in your laptop, which is nice.

Are there any other applications for metamaterials?

My colleague Richard Syms in electrical engineering at Imperial is using hundreds of little metamaterial elements called split-ring resonators and stacking them together to make a wire. Instead of conducting electrical current, this wire conducts magnetic flux down the centre of these little resonators. It only works at one frequency but that’s fine if you’re dealing with magnetic resonance imaging (MRI).

How are such scans currently done?

With heart scans, for example, doctors usually cut a nearby vein and then they push this little coil of wire up near the heart so it can pick up the weak magnetic signals that are produced when hydrogen nuclei in the body are excited using an external RF field.

Why does the technique need improving?

When you turn the magnetic signal into an electrical one it travels down the wire, but the wire is about the right length to resonate with the exciting signal, which is usually quite powerful. If that wire gets hot it then sticks to the side of the vein – not a good experience.

What properties do metamaterials have to solve this problem?

While the body responds dramatically to an electrical current, it hardly responds to a magnetic one. Syms’ wire takes the magnetic signal and keeps it as a magnetic signal that travels safely out of the body.

Why are defence agencies so interested in metamaterials research?

There’s a whole lot of stuff happening that I never hear about because a lot of it has gone confidential because it’s useful. The US defence agency DARPA, for example, allows you to publish everything while you’re in the “what if?” stage, but once you get devices, you then find that the wraps go over it and it goes into patents and what-not.

Any defence research you can tell us about?

There is something called compressive sensing, which is a way of taking a very limited amount of data from a scene and using that data to construct a very accurate image with less information than you’d use for a whole scene capture.

How does that work?

The way they do that is a version of this satellite-communications receiver, only instead of receiving a signal, using terahertz or low-frequency radiation you actually throw out a signal around the room and “sense” the room.