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Posted: May 26, 2008
Metamaterials an emerging technology for printed electronics
(Nanowerk News) In metamaterials, the ultrafine patterning as well as the chemistry influences the properties. This is rather like the ancient Roman ruby glass containing gold chloride in very fine particles. It gave different optical effects at various angles thanks to both the chemistry and the physics.
Nowadays metamaterials are a hot topic because they can lead to unusually thin lenses and all sorts of previously impossible printed electronics. Here, both fine three dimensional patterning - much less than the wavelength of the electromagnetic radiation being emitted - and inherent material properties are used to modify several overall properties. An example is negative permeability and permittivity leading to negative refractive index.
These counterintuitive effects are sometimes achieved by flexographic printing, for instance of arrays of tiny split rings as resonators with microwires. One theoretician is asking engineers to print what he describes as nanoscale hedgehog shapes. Appropriately made, these materials with repeated three dimensional structures less than the wavelength of the radiation used will break the traditional laws of optics and magnetics because they employ quantum effects.
Following the original prediction of such effects by Russian physicist Victor Veselago in 1968, the practical demonstrations have now come from teams in the UK, USA and elsewhere. Negative refractive index has now been demonstrated for microwave and terahertz radiation which may lead to new types of beam steerers, modulators, band-pass filters, microwave couplers and antenna radomes.
There is even talk of making things invisible by so called masking with these patterned materials and limited demonstration of such effects has been made from microwave to optical frequencies. Indeed, in 2007, Ames Laboratory of the US Department of Energy and California Institute of Technology Pasadena, working with Karlsruhe University in Germany, demonstrated a metamaterial with a negative refractive index to both red and green visible light. It had very fine patterning on both sides of a thin dielectric.
Researchers now develop working metamaterials in Canada, the USA, Switzerland, the UK, Germany and East Asia. For example, the terahertz range is promising for automated inspection, zero-visibility navigation, biomedical imaging and security screening applications notably with solid-state sensors that can see through solid objects. At radio frequencies smaller antennas are in prospect, indeed a new European Commission program targets smaller RFID tags. In vehicle radar anti-collision systems may become more practicable, say some researchers. Metamaterials for acoustic, rather than electromagnetic waves are also being studied including making buildings invisible to earthquakes.
At the IDTechEx conference Printed Electronics Asia in Tokyo October 8-9 delegates will hear the latest on metamaterials from Dr Michael Wiltshire. He is a member of Professor Sir John Pendry's pioneering team at London's Imperial College in the UK which was one of the first to demonstrate working metamaterials. The team collaborates with Duke University in the USA and it is targeting the electromagnetic effects that can help to create the new electronics.