Australasian Science: Australia's authority on science since 1938

New Views with Metamaterial Lens

By Stephen Luntz

A lens made from metamaterials – a mixture of metal and plastic – would have properties different from anything in nature and increase our capacity to observe objects like small melanomas with greater clarity.

Such a lens could bend terahertz waves, which lie between microwaves and infra-red light on the electromagnetic spectrum, in a way that is radically different to how glass bends optical light.

“An X-ray allows us to see inside objects at a high resolution but with associated danger from radiation,” says Dr Alessandro Tuniz of the University of Sydney’s School of Physics. “By contrast our metamaterial lens allows us not only to see through some opaque materials, but also to gather information on their chemical composition, and even information on interactions between certain molecules – without the danger of X-rays.

“Creating metamaterials is a cutting-edge area of science with a massive range of potential uses from aerospace to solar power, telecommunications to defence,” says A/Prof. Boris Kuhlmey, co-author of the Nature Communications paper that announced the lens’ creation.

So far the potential has largely been unrealised. “We know of only two or three other cases worldwide, including for wireless internet and MRI applications, where metamaterials could also be put into practice in the next couple of years.”

Tuniz says lenses made from metamaterials have been around for a while, but were orders of magnitude too large to be useful for terahertz waves. “The difficulty was making large quantities of matter structured on a micrometric scale.” The research team has overcome this difficulty by using the same techniques that produce optical fibres.

“As you move to lower frequencies you get lower resolution with conventional materials,” says Tuniz, “but with metamaterials that limit no longer applies. Terahertz frequencies are a very information-rich part of the spectrum that has been underutilised.”

Terahertz microscopes would “allow earlier skin cancer diagnosis because smaller melanomas can be recognised,” Tuniz says. “For breast cancer it can also be used to more accurately check that all traces of a tumour have been cut out during surgery.”

The lens is made of metal wires 10 µm across and spaced 50 µm apart. With wavelengths around 3 mm long, the wires prevent diffraction, allowing the radiation to be focused.

Spotting a melanoma on a body will remain a challenge, Tuniz acknowledges, but if a possible site is identified “the image will be ten times sharper,” enabling the detection of much smaller cancers.