Imperial is leading a new programme to manipulate metamaterials in the fourth dimension: time.

Metamaterials are synthetic materials that have been designed to have properties that are usually impossible to find in natural systems. They usually comprise of multiple materials that are structured and combined in 3D or planar assemble.

Their spatial structure and geometry give them their unique properties, such as the ability to control waves, and for example dramatically bend the direction of light.

Funded by the Engineering and Physics Sciences Research Council (EPSRC), researchers from Imperial, the University of Exeter and King’s College London will research the manipulation of waves, such as light waves or acoustic waves, using tailored metamaterials which vary in time instead of space.

The new consortium, Meta4D, will be led by the Dean of the Faculty of Natural Sciences, Professor Richard Craster from the Department of Mathematics.

Professor Craster said: "I am delighted by the opportunity this funding provides for us to explore the boundaries of what's possible, the chance to shape the future of wave physics, and excited to work with our partners and bring together experiments and theory to coherently tackle the research challenge.”

This is the new frontier of metamaterials – studying how we can control the temporal dimension of waves. Professor Riccardo Sapienza Department of Physics

Professor Riccardo Sapienza, the Director of Plasmonics and Metamaterials at the Department of Physics will be a Principal Investigator. He said: “This is the new frontier of metamaterials – studying how we can control the temporal dimension of waves.”

Professor Sir John Pendry, Chair of Theoretical Solid State Physics and co-investigator at Meta4D, said: “It is good to see Imperial carrying forward our tradition of metamaterials powered by this new grant. The time domain offers prospects of yet more discoveries and inventions particularly as it will demand our attention to the quantum consequences of violating energy conservation.”

Professor Alastair Hibbins, lead of the UK Metamaterials Network, and also part of the Meta4D leadership team, said: “Our 700-member strong Network has the ambition to drive the development of a well-funded, self-sustaining and world-class metamaterials-enabled UK ecosystem, to the benefit of the UK’s prosperity and security."

The early development of metamaterials

How a material responds to a wave, such as light, sound or water waves, is not only dependent on its chemical and mechanical properties, their microscopic structure can have also a large effect.

Some antique mirrors owe their high reflectivity to a thin pane of silver that lays on top of the glass. At the same time, the black pigment in old film photographs owe their darkness to silver particles in the film.

In one scenario, silver reflects light and in the other, it absorbs it – the difference lying in how the silver itself is structured and distributed in the material.

Metamaterials take this principle and expand it to the breadth of the electromagnetic spectrum, as well as other forms of waves such as acoustic or vibrational waves. The structures of metamaterials also take shape in much more complex forms than films or small particles.

Professor Sir John Pendry from the Department of Physics was an early pioneer of metamaterials. By manipulating the structure of materials, Professor Pendry laid the foundations of working invisibility cloaks and lenses that reconstruct images flawlessly, known as perfect lenses.

Now, Imperial is leading the next generation of metamaterials which are not only designed to have a specific spatial structure, but also properties that can be varied rapidly in time – faster than the speed of a wave’s oscillation.

For a sound wave carrying someone’s voice, that can be hundredths of a second. For a laser, that can be a millionth of a millionth of a second.

Time, the next frontier

When a material that a wave is travelling in abruptly changes it properties, a phenomenon known as a time reflection can occur. Spatial reflections occur when a wave hits a boundary in space, which is why you hear echoes as sound bounces off walls or see your own reflection as light bounces of a mirror.

A wave to ‘reflecting in time’ does not change its direction, but instead changes its frequency and energy. Though hypothesised for the past decades, scientists have only recently been able to change the properties of a material at the speeds needed.

If you control both spatial and temporal domains, you can transform all properties of a wave such as its direction, colour and energy. Professor Riccardo Sapienza Department of Physics

“The long-term goal is to have both space and time control of waves,” Professor Sapienza said, “If you control both spatial and temporal domains, you can transform all properties of a wave such as its direction, colour and energy.”

The EPSRC grant will fund both theoretical and experimental development of time-modulated metamaterials.

By collaborating closely with industrial partners, Professor Sapienza says that metamaterial research could revolutionise fields such as telecommunications and computing.

“We could unlock a new degree of freedom to control and process information,” he said.

Professor Hibbins said: "We’ve been working hard over the past few years to demystify metamaterials and grow the nation’s research collective efforts and investment in this area, so its fantastic to see this funded, not just for the immediate team, for the UK as a whole. It's certainly one of the biggest single investments in metamaterials the UK, and confirms the UK’s science superpower status in this area.”