Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

‘T-ray’ devices with perfect imaging abilities move a step closer

04.03.2004


A team of American and British scientists has demonstrated an artificially made material that can provide a magnetic response to Terahertz frequency radiation, bringing the realisation and development of novel ‘T-ray’ devices a step closer.



The advance, reported in the journal Science (5 March), suggests many applications in biological and security imaging, biomolecular fingerprinting, remote sensing and guidance in zero visibility weather conditions, say the authors.

Theorist John Pendry of Imperial College London, also co-author of the paper, hailed the making of the material as a feat of technological virtuosity, and looked forward to some incredible applications.


“This was terra incognita, but we just pushed on to higher frequencies,” said Professor Pendry. “This is the first material to show a Terahertz frequency magnetic response; it’s the proof of concept experiment. We’ve shown we can do it, and that sends a powerful message out to the community of researchers.”

Terahertz frequencies sit in a largely unexplored region of the electromagnetic spectrum between infra-red and microwaves, known as far infra-red radiation. The frequency of a terahertz is 1 trillion cycles per second and Terahertz radiation has a wavelength between 0.1 and 1 millimetre. It is thought to be safe, as it is non-ionising and does not have DNA-damaging effects.

The authors from the University of California Los Angeles, University of California San Diego and Imperial College London, are collectively looking to build materials that respond magnetically to THz, infra-red, and visible radiation as there is an almost total absence of naturally occurring materials with magnetic responses to these frequencies.

Their quest to build such artificial materials, or metamaterials, is motivated by their desire to explore a strange and intriguing property, named ‘negative refractive index’, which is found only in this new class of materials.

Conventional optical devices are limited in resolution by the wavelength of radiation employed (eg light or X-rays), but in a series of papers building on forgotten work by Russian physicist Victor Veselago from 1968, Professor Pendry in 2000* predicted the existence of devices capable of focusing features smaller than the wavelength of light.

Referred to as ‘perfect lenses’, these revolutionary lenses break the wavelength barrier and achieve resolution limited only by the quality of the materials from which they are constructed.

Perfect lenses rely on a phenomenon theorised by Veselago who made a theoretical investigation of novel electromagnetic materials in which the normal response to both electric and magnetic fields is reversed. He referred to these materials as ‘left handed’ because the inverted response reverses the energy flow associated with a ray of light.

Amongst many strange properties of left handed materials, he found that when light is refracted from air into a left handed medium, it bends the opposite way to light entering a normal medium such as water or glass, making a chevron shape at the surface as it bends back on itself inside the left handed medium. This strange effect has subsequently been interpreted as a negative refractive index. Left handed materials are triply negative: in response to electric and magnetic fields, and also in response to a ray of light. The problem Veselago faced was that there are no such materials found in nature and this field of research was abandoned for almost thirty years.

In 1999, Professor Pendry’s Condensed Matter Theory group at Imperial College were collaborating with scientists from the Marconi Company on the new class of metamaterial. In normal materials the constituent atoms and molecules determine electrical and magnetic properties; they are much smaller than the wavelength of light so only the average response of the atoms matters. In the new materials an intermediate or meta-structure is engineered on a scale somewhere between atomic dimensions and the wavelength of radiation. The properties of Metamaterials are not limited by the periodic table and scientists can now engineer a huge range of electromagnetic responses that can be tailored to anything allowed by the laws of electromagnetism, says Professor Pendry.

The Imperial/Marconi team proposed the first design for a magnetic metamaterial, known as a ‘Split Ring’ structure. “A simple, plain ring of metal gives a magnetic response, but in the wrong direction,” says Professor Pendry, “By cutting the ring the flow of current is interrupted by capacitance across the gap which, together with the inductance of the ring, makes a tuned circuit whose resonant frequency is determined by the inductance and capacitance. It is well known that a resonant structure responds with opposite signs on either side of the resonant frequency. Hence by tuning through the resonance the desired negative magnetic response is obtained: positive or negative.”

A Split Ring viewed from above looks like a small letter ‘C’ inside a larger letter ‘C’, with the smaller C turned to face the opposite direction. A single Split Ring is the metamaterial equivalent of a magnetic atom; many Split Rings brought together in organised 2D or 3D grids form a magnetic metamaterial.

The original Split Rings were designed to operate at Gigahertz, or microwave, frequencies: orders of magnitude or hundreds or thousands of times below the Terahertz range. To get a magnetic response at Terahertz frequencies, the resonant frequency of the rings has to be raised, requiring researchers to build metamaterials with a much smaller size and spacing of the elements. The microstructure must always be much smaller than the wavelength so that radiation sees only average properties of the structure.

The key technical achievement by the authors at UCLA and UCSD was to fabricate the Terahertz-responding Split Rings using a special ‘photo-proliferated process’ that deposited the 3 micrometer-wide (0.003 mm) copper rings on a quartz base.

“This is a technological advance by the virtuosi of their craft,” said Professor Pendry of the work by his colleagues at UCLA and UCSD.

“Looking to higher frequencies, in the optical region of the spectrum, magnetism just does not at present figure in our thinking because almost all materials are magnetically inert at these frequencies.

Optical properties are almost entirely due to the electrical response of materials to one of the two available fields - the electric field. Professor Pendry likens controlling light in this way to driving a motorbike with one hand - it’s possible, but gives you only a fraction of the possible control and subtlety of resolution available in imaging. By bringing the magnetic field into play, he suggests, we may be able to harness a vastly more powerful imaging technology. “Now we are all on notice to include the possibility of optical magnetism when discussing new devices,” he adds.

“We want to push the limits of frequency and produce structures that work in the infra red and ultimately in the visible. The march of magnetism towards the visible will enhance our power to control and use electromagnetic radiation in these frequency ranges.” he said.

“So far we have only seen negative refraction at microwave or GHz frequencies but some of the most exciting applications in sensing, communication, and data storage would be at higher frequencies,” he said. “But I believe that the really valuable applications have yet to be dreamt of. Think back to when the first lasers were made, the reaction was that they were just incredible, but what the hell would we do with them?” said Professor Pendry.

The Multidisciplinary University Research Initiative (MURI) of the US Office of Naval Research (ONR Grant # N00014-01-1-0803), funded the research.


*John Pendry’s 2000 paper is Phys. Rev. Lett. 85, 3966-9 (2000)

Tom Miller | alfa
Further information:
http://www.imperial.ac.uk

More articles from Materials Sciences:

nachricht Nanomaterial makes laser light more applicable
28.03.2017 | Christian-Albrechts-Universität zu Kiel

nachricht New value added to the ICSD (Inorganic Crystal Structure Database)
27.03.2017 | FIZ Karlsruhe – Leibniz-Institut für Informationsinfrastruktur GmbH

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: A Challenging European Research Project to Develop New Tiny Microscopes

The Institute of Semiconductor Technology and the Institute of Physical and Theoretical Chemistry, both members of the Laboratory for Emerging Nanometrology (LENA), at Technische Universität Braunschweig are partners in a new European research project entitled ChipScope, which aims to develop a completely new and extremely small optical microscope capable of observing the interior of living cells in real time. A consortium of 7 partners from 5 countries will tackle this issue with very ambitious objectives during a four-year research program.

To demonstrate the usefulness of this new scientific tool, at the end of the project the developed chip-sized microscope will be used to observe in real-time...

Im Focus: Giant Magnetic Fields in the Universe

Astronomers from Bonn and Tautenburg in Thuringia (Germany) used the 100-m radio telescope at Effelsberg to observe several galaxy clusters. At the edges of these large accumulations of dark matter, stellar systems (galaxies), hot gas, and charged particles, they found magnetic fields that are exceptionally ordered over distances of many million light years. This makes them the most extended magnetic fields in the universe known so far.

The results will be published on March 22 in the journal „Astronomy & Astrophysics“.

Galaxy clusters are the largest gravitationally bound structures in the universe. With a typical extent of about 10 million light years, i.e. 100 times the...

Im Focus: Tracing down linear ubiquitination

Researchers at the Goethe University Frankfurt, together with partners from the University of Tübingen in Germany and Queen Mary University as well as Francis Crick Institute from London (UK) have developed a novel technology to decipher the secret ubiquitin code.

Ubiquitin is a small protein that can be linked to other cellular proteins, thereby controlling and modulating their functions. The attachment occurs in many...

Im Focus: Perovskite edges can be tuned for optoelectronic performance

Layered 2D material improves efficiency for solar cells and LEDs

In the eternal search for next generation high-efficiency solar cells and LEDs, scientists at Los Alamos National Laboratory and their partners are creating...

Im Focus: Polymer-coated silicon nanosheets as alternative to graphene: A perfect team for nanoelectronics

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are less stable. Now researchers at the Technical University of Munich (TUM) have, for the first time ever, produced a composite material combining silicon nanosheets and a polymer that is both UV-resistant and easy to process. This brings the scientists a significant step closer to industrial applications like flexible displays and photosensors.

Silicon nanosheets are thin, two-dimensional layers with exceptional optoelectronic properties very similar to those of graphene. Albeit, the nanosheets are...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

International Land Use Symposium ILUS 2017: Call for Abstracts and Registration open

20.03.2017 | Event News

CONNECT 2017: International congress on connective tissue

14.03.2017 | Event News

ICTM Conference: Turbine Construction between Big Data and Additive Manufacturing

07.03.2017 | Event News

 
Latest News

Periodic ventilation keeps more pollen out than tilted-open windows

29.03.2017 | Health and Medicine

Researchers discover dust plays prominent role in nutrients of mountain forest ecoystems

29.03.2017 | Earth Sciences

OLED production facility from a single source

29.03.2017 | Trade Fair News

VideoLinks
B2B-VideoLinks
More VideoLinks >>>